Systems and processes for capturing carbon dioxide and producing carbonate material

Abstract

Provided herein are systems and processes for capturing / sequestering carbon dioxide and converting the carbon dioxide to produce carbonate materials.

Description

[0001] SYSTEMSAND PROCESSES FOR CAPTURING CARBON DIOXIDE AND PRODUCING CARBONATE MATERIAL

[0002] This application claims priority from Australian provisional patent application no. 2025900474, filed on 19 February 2025, the entire contents of which is incorporated herein by this reference.

[0003] Field

[0004] The present disclosure relates to systems and processes for capturing / sequestering carbon dioxide and converting the carbon dioxide to produce carbonate materials.

[0005] Background

[0006] Carbon dioxide (CO2) is a greenhouse gas that has a significant impact on global warming. In this regard, carbon dioxide absorbs heat radiating from the surface of the Earth and re-releases said heat in all directions including back towards the surface of the Earth. As more carbon dioxide is created and retained in the atmosphere, there has been significant heating occurring in the atmosphere and this has caused significant environmental concerns. Carbon dioxide contributes to radiative forcing and global warming when present in elevated atmospheric concentrations.

[0007] Over the past several decades, global concern regarding atmospheric carbon dioxide (CO2) emissions has intensified. Excess greenhouse gases are associated with rising mean land and sea temperatures, ocean acidification, increased storm frequency, and sea-level rise. Industrial activity, including mining, energy production, agriculture, wastewater treatment, municipal management, and manufacturing, continues to emit significant point-source CO2 that must be mitigated.

[0008] Carbon dioxide is produced naturally and through industrial processes. Sequestering carbon dioxide from industrial processes and removal of carbon dioxide from the atmosphere will assist in preventing carbon dioxide exacerbating the effects of global warming.

[0009] Many conventional carbon capture and storage (CCS) approaches, face economic and environmental constraints including high regeneration energy, amine degradation, and long-term storage liability. Carbon capture and utilisation (CCU) pathways convert CO2 into valuable products but often lack permanence; most products are short-lived and re-release CO2 during use or disposal.

[0010] A key bottleneck in both direct air capture and point-source capture is the availability of scalable alkaline absorbents and permanent mineralisation pathways. Traditional capture agents such as monoethanolamine (MEA) are energy-intensive and environmentally burdensome.

[0011] Alkali metal hydroxides have also been proposed. These alkalis are industrially abundant, produced globally via the chlor-alkali process, which electrolyses brine (NaCl or KCl) to yield chlorine gas (Cl2), hydrogen (H2), and sodium hydroxide (NaOH). However, since the chlor-alkali process generates chlorine gas and chlorine-containing or halogen-bearing byproducts there are the associated environmental and safety challenges.

[0012] To date, neutralisation of excess chlorine has relied on reagents such as soda ash, activated carbon, and sulfur-based reducing agents (sodium metabisulfite, potassium metabisulfite, sodium sulfite). Theseapproaches consume additional chemicals and generate secondary CO2 emissions through the manufacture and oxidation of precursor materials.

[0013] It would be desirable to provide systems and methods for efficient and effective carbon dioxide capture and storage, for example which could be used in a variety of contexts, for example retrofitted to existing processes during which carbon dioxide is generated or released. It would further be desirable to provide systems and processes for carbon dioxide capture which are not environmentally burdensome, and which do not consume large amounts of reagents such as soda ash, activated carbon or sulfur-based reducing agents. It would also be advantageous if captured carbon dioxide could be provided in a long-lived stable form. It would also be advantageous if the sequestered carbon dioxide could be utilized to produce useful materials or components. It would further be advantageous to address one or more of the above issues and / or to provide the consumer with a commercial alternative to the presently available solutions.

[0014] Summary

[0015] The present inventor has identified processes and systems for capturing carbon dioxide, and storing it in stable forms such that it can be effectively removed from the atmosphere or from CO2-rich waste streams. In some forms, the processes and systems provide a way for maintaining ionic and charge balance via a closed electrochemical and / or electromineral loop, wherein carbon dioxide is converted to carbonate species under thermodynamically favoured conditions while alkaline reagents may be regenerated, ionic species may be substantially conserved on an equivalent basis, and the system may remain substantially closed with respect to halides, reducing or avoiding exit of waste ionic streams from the system boundary. In particular, in various embodiments, the process or system is substantially closed loop with respect to chloride, reducing chloride waste streams.

[0016] Further, the systems and processes can be readily integrated into existing plants and treatment centres, for example at mine sites, power stations or CCh-producing plants. Similarly, the systems and processes can be readily integrated into water treatment facilities, in some embodiments utilising brine and / or magnesium sources from seawater as feedstocks for example. Still further, in various embodiments, species generated at one step of the process can be used for reaction with mineral feedstocks in the process generating further useful species that are themselves utilised at a different part of the process. Yet further, various outputs from the processes can be used in applications such as cementitious materials, e.g. carbonate species and / or silicate species.

[0017] Some aspects of the present disclosure provide a closed or substantially closed electrochemical system for the capture and permanent conversion of carbon dioxide (CO2) into stable carbonate materials through coupled electrochemical, chemical equilibrium, and mineralisation reactions. The system for example employs saline brines, such as reverse-osmosis reject, seawater, or solar salt, together with e.g. calcium- and magnesium-bearing silicate minerals or oxides, including brucite, basaltic and ultramafic feedstocks, to generate alkaline and acidic reagents within a closed chemical loop.

[0018] In some embodiments, an electrochemical cell electrolyses a halide-containing brine to generate an alkaline catholyte and an acidic or halogen-rich anolyte. The alkaline stream reacts with gaseous ordissolved CO2 to form carbonate and bicarbonate ions, while the acidic stream, preferably comprising hydrochloric acid, dissolves calcium- and magnesium-bearing silicate minerals, releasing divalent metal cations (Ca2+, Mg2+) and producing a silica residue. The acidic stream may for example comprise hydrochloric acid, carbonic acid, or other regenerated acidity suitable for mineral activation and cation mobilisation. The liberated cations subsequently react with the carbonate ions to precipitate solid carbonates, thereby mineralising CO2, regenerating neutral brine, and retaining halogens within a closed electrochemical loop.

[0019] In some embodiments, the disclosure provides a modular system comprising: an electrochemical cell for brine electrolysis; a mineral -dissolution reactor for acid leaching or silicate activation; a carbonation reactor for precipitation of carbonate solids; a halogen-management module for capture, conversion, or valorisation of chlorine -bearing gases; a silica-handling or dehydration unit for co-product formation; and a brine-recirculation loop maintaining ionic and water balance.

[0020] In some embodiments, the disclosure relates to processes and / or systems that include: an electrochemical unit that produces alkaline stream + acid / halogen stream; an alkaline stream that contacts CO2 to form carbonate / bicarb (speciation controlled by pH / CCh pp); an acid stream that activates mineral to produce MCI2 (or equivalent cation source); a reaction between a carbonate stream + MCI2 which precipitates MCO3 and regenerates NaCl; recycling of NaCl to the electrochemical unit; halogen management to close oxidant / acid balance; and optional purge / makeup handling to manage impurities.

[0021] Such integrated operations establish a self-sustaining closed or substantially closed electrochemical loop that achieves durable CO2 sequestration with minimal halogen losses and negligible discharge to the environment. The process may for example be powered by renewable or waste electricity, operate under ambient to moderate conditions, and be deployed in containerised or distributed units at emission sources such as power generators, biogas facilities, or desalination plants. Carbonate products exhibit long-term geochemical stability and are suitable for use as cementitious materials, aggregates, or mineral fillers.

[0022] In some embodiments, an alkaline phase generated by electrolysis or derived from mineral sources, such as sodium hydroxide, participates in neutralisation or secondary mineralisation reactions with silicate minerals and CO2 to yield carbonate solids and insoluble silicate co-products, thereby operating as a complementary pathway within the same closed-loop electro-mineral framework.

[0023] In some embodiments the system is employed as a mechanism for halogen management. In further embodiments, the carbonation column and hydroxide contacting component can be deployed at distributed sites with the spent solution collected and taken back for central processing.

[0024] In some embodiments, the processes and systems allow for retention of ionic species while creating the necessary operating conditions to produce solid carbonates which are exported from the process with brine inventory recycled for use as a continuous supply of alkalinity and conductivity as the working electrolyte allowing for continuous operation of the electrochemical unit and the pH gradient to be maintained.Accordingly, at least in part, the present disclosure can be considered as being directed to a closed electrochemical loop that regenerates alkalinity and acidity within a conserved ionic inventory to convert carbon dioxide into solid carbonate while recycling electrolyte.

[0025] At least in part, the present disclosure is associated with the concept of maintaining a conserved circulating electrolyte inventory in which alkalinity and acidity are generated from minerals, brines, and / or electrochemical processes and regenerated within the system, enabling continuous conversion of carbon dioxide into solid carbonate while substantially preventing discharge of halide -containing waste stream.

[0026] In a first aspect, there is provided a process for capturing carbon dioxide, comprising: a) electrochemically treating an alkali metal halide (e.g. chloride) and water to produce aqueous alkali metal hydroxide and a hydrohalic acid (e.g. HC1); b) contacting a carbon dioxide-containing feed with aqueous alkali metal hydroxide from a), to produce an alkali metal carbonate and / or bicarbonate; c) reacting hydrohalic acid (e.g. HC1) from a), with an alkaline earth metal -containing mineral feedstock to produce alkaline earth metal chloride; and d) reacting alkali metal carbonate and / or bicarbonate from b) with alkaline earth metal chloride from c) in the presence of water to produce solid alkaline earth metal carbonate and alkali metal chloride; wherein alkali metal chloride produced in d) is recycled to a), and wherein the process is substantially closed-loop with respect to halide (e.g. chloride).

[0027] In another aspect, there is provided a process for producing an alkaline earth metal carbonate, comprising: a’) electrochemically treating an alkali metal halide (e.g. chloride) and water to produce aqueous alkali metal hydroxide and hydrohalic acid (e.g. HC1); b’) reacting hydrohalic acid (e.g. HC1) from a’), with an alkaline earth metal-containing mineral feedstock to produce alkaline earth metal halide (e.g. chloride); and reacting the alkaline earth metal halide (e.g. chloride) with alkali metal hydroxide from a’), to produce alkaline earth metal hydroxide and alkali metal halide (e.g. chloride); or reacting alkali metal hydroxide from a’) with an alkaline earth metal-containing mineral feedstock, wherein the alkaline earth metal-containing mineral feedstock is a silicate-containing alkaline earth metal-containing mineral feedstock, to produce alkaline earth metal hydroxide and an alkali metal silicate; and reacting the alkali metal silicate with hydrohalic acid (e.g. HC1) from a’) to produce a silicic acid and alkali metal halide (e.g. chloride); and c’) contacting a carbon dioxide-containing feed with aqueous alkaline earth metal hydroxide from b’), to produce solid alkaline earth metal carbonate; wherein alkali metal halide (e.g. chloride) produced in b’) is recycled to a’), and wherein the process is substantially closed-loop with respect to halide (e.g. chloride).

[0028] In another aspect, there is provided a process for producing magnesium carbonate, comprising: a”) electrochemically treating an alkali metal halide (e.g. chloride) and water to produce aqueous alkali metal hydroxide; b”) contacting a carbon dioxide-containing feed with aqueous alkali metal hydroxide from a”), to produce an alkali metal carbonate and / or bicarbonate; and c”) reacting alkali metal carbonate and / or bicarbonate from b”) with a magnesium species in the presence of water to produce solid magnesium carbonate.In another aspect, there is provided a process for producing an alkali metal or alkaline earth metal carbonate, comprising: contacting a carbon dioxide-containing feed with aqueous alkali metal hydroxide or with alkaline earth metal hydroxide, wherein one or more of pH, temperature, pressure, CO2 partial pressure, and contact time, is controlled, thereby producing a stable solid alkali metal carbonate or alkaline earth metal carbonate.

[0029] In another aspect, there is provided a system for capturing carbon dioxide, comprising: A) an electrochemical unit configured to electrochemically treat an alkali metal halide (e.g. chloride) and water to produce aqueous alkali metal hydroxide, wherein the electrochemical unit is configured to i) produce hydrohalic acid (e.g. HC1), or ii) produce hydrogen and halogen (e.g. chlorine), and wherein, when configured to produce hydrogen and halogen (e.g. chlorine), the system also comprises a hydrohalic acid (e.g. HC1) generation unit configured to produce hydrohalic acid (e.g. HC1) from the hydrogen and halogen (e.g. chlorine); B) a carbon dioxide capture unit configured to contact a carbon dioxide-containing feed with the aqueous alkali metal hydroxide, to produce an alkali metal carbonate and / or bicarbonate; C) a mineral feedstock activation unit configured to react the hydrohalic acid (e.g. HC1) with an alkaline earth metal-containing mineral feedstock to produce alkaline earth metal halide (e.g. chloride); D) an alkaline earth metal carbonate formation unit configured to react the alkali metal carbonate and / or bicarbonate with alkaline earth metal halide (e.g. chloride) in the presence of water to produce solid alkaline earth metal carbonate and alkali metal halide (e.g. chloride); and E) a recycle pathway configured to recycle alkali metal halide (e.g. chloride) produced in D), to A), and wherein the system is configured to be substantially closed-loop with respect to halide (e.g. chloride).

[0030] In another aspect, there is provided a system for producing an alkaline earth metal carbonate, comprising: A’) an electrochemical unit configured to electrochemically treat an alkali metal halide (e.g. chloride) and water, to produce aqueous alkali metal hydroxide, wherein the electrochemical unit is configured to i) produce hydrohalic acid (e.g. HC1), or ii) produce hydrogen and halogen (e.g. chlorine), and wherein, when configured to produce hydrogen and halogen (e.g. chlorine), the system also comprises a hydrohalic acid (e.g. HC1) generation unit configured to produce hydrohalic acid (e.g. HC1) from the hydrogen and halogen (e.g. chlorine); B’) an alkaline earth metal hydroxide production unit comprising either a mineral feedstock activation unit configured to react the hydrohalic acid (e.g. HC1) with an alkaline earth metal -containing mineral feedstock to produce alkaline earth metal halide (e.g. chloride), and a halide (e.g. chloride) exchange unit configured to react the alkaline earth metal halide (e.g. chloride) with the alkali metal hydroxide to produce alkaline earth metal hydroxide and alkali metal halide (e.g. chloride); or an alkaline mineral feedstock activation unit configured to react the alkali metal hydroxide with a silicon-containing alkaline earth metal-containing mineral feedstock to produce alkaline earth metal hydroxide and an alkali metal silicate, and a silicic acid production unit configured to react the alkali metal silicate with the hydrohalic acid (e.g. HC1) to produce a silicic acid and alkali metal halide (e.g. chloride); and C’) a carbon dioxide capture unit configured to contact a carbon dioxide-containing feed with the aqueous alkaline earth metal hydroxide, to produce an alkaline earth metal carbonate; and D’) a recycle pathwayconfigured to recycle alkali metal halide (e.g. chloride) produced in B’), to A’), and wherein the system is configured to be substantially closed-loop with respect to halide (e.g. chloride).

[0031] In another aspect, there is provided a system for producing magnesium carbonate, comprising: A”) an electrochemical unit configured to electrochemically treat an alkali metal halide (e.g. chloride) and water, to produce aqueous alkali metal hydroxide, wherein the electrochemical unit is configured to i) produce hydrohalic acid (e.g. HC1), or ii) produce hydrogen and halogen (e.g. chlorine), and wherein, when configured to produce hydrogen and halogen (e.g. chlorine), the system also comprises a hydrohalic acid (e.g. HC1) generation unit configured to produce hydrohalic acid (e.g. HC1) from the hydrogen and halogen (e.g. chlorine); B”) a carbon dioxide capture unit configured to contact a carbon dioxide -containing feed with the aqueous alkali metal hydroxide, to produce an alkali metal carbonate and / or bicarbonate; and C”) a magnesium carbonate formation unit configured to react the alkali metal carbonate and / or bicarbonate with a magnesium species in the presence of water to produce solid magnesium carbonate.

[0032] In another aspect, there is provided a magnesium carbonate material produced by a process as defined herein, wherein the magnesium carbonate material is or comprises one or more of magnesite, nesquehonite, hydromagnesite, dypingite, and amorphous magnesium carbonate.

[0033] In another aspect, there is provided a crystalline form of magnesium carbonate, wherein the crystalline form is produced or producible by a process as defined herein.

[0034] In another aspect, there is provided an aluminosilicate material, comprising: an aluminosilicate; and an alkaline earth metal carbonate; wherein the alkaline earth metal carbonate is obtained by a process as defined herein.

[0035] In another aspect, there is provided a method of producing solid carbonates including steps of: providing a hydroxide solution to a column having a first end and an opposing second end; injecting carbon dioxide through a gas injection portion connected at or adjacent the first end; recirculating carbon dioxide gas through a recirculation assembly into the column at or adjacent the first end; to thereby produce solid carbonates.

[0036] In another aspect, there is provided a method of producing solid carbonates including steps of: providing a hydroxide solution to a column having a first end and an opposing second end; and injecting carbon dioxide through a gas injection portion connected at or adjacent the first end; to thereby produce solid carbonates.

[0037] In another aspect, there is provided a system for preparing carbonates comprising: a column having a first end and an opposing second end; a gas injection port connected to the column at or adjacent the first end and configured to introduce a carbon dioxide -containing gas stream into the column; a gas outlet connected to the column at or adjacent the second end and configured to discharge gas from the column; a liquid outlet connected to the column at or adjacent the first end and configured to withdraw liquid from the column; and a solids collection chamber connected to the column at or adjacent the first end and configured to collect precipitated carbonate solids or a carbonate-containing slurry comprising precipitated carbonate solids; wherein the column is configured to receive a hydroxide reactant for reaction with thecarbon dioxide-containing gas stream to form carbonate species, bicarbonate species, precipitated carbonate solids, or combinations thereof.

[0038] In another aspect, there is provided a system for preparing carbonates comprising: a column having a first end and an opposing second end; a gas injection portion connected at or adjacent the first end; a gas outlet connected at or adjacent the second end, wherein the gas outlet comprises a valve connection adapted to control fluid flow between a recirculation assembly and an expended gas outlet, wherein the recirculation assembly is connected at or adjacent the first end; a liquid outlet connected at or adjacent the first end; and a solid carbonate collection chamber connected at or adjacent the first end.

[0039] In another aspect, there is provided a process for capturing carbon dioxide in a closed electrochemical loop, comprising: electrochemically generating an alkaline stream and an acidic or halogen-containing stream from an alkali metal halide electrolyte; contacting carbon dioxide with the alkaline stream to produce carbonate species; removing carbonate as a solid or dissolved export stream; and recycling halide-containing electrolyte to the electrochemical step, wherein alkali metal and halide ions are substantially retained within a circulating electrolyte inventory.

[0040] In another aspect, there is provided a system configured to operate a closed electrochemical loop for carbon dioxide mineralisation, comprising: (i) an electrochemical unit configured to generate acidity and alkalinity from a halide electrolyte; (ii) a carbonate formation unit configured to convert carbon dioxide to carbonate species using the alkalinity; (iii) a mineral activation or cation source module; and (iv) a recycle pathway configured to return halide-containing electrolyte to the electrochemical unit while exporting carbonate solids.

[0041] Brief Description of the Drawings

[0042] To assist in understanding the invention and to enable a person skilled in the art to put the invention into practical effect, embodiments of the invention will be described by way of example only with reference to the accompanying drawings, in which:

[0043] Figure 1 shows an embodiment of the present system for producing carbonate material;

[0044] Figure 2 shows a perspective view of an embodiment of the present system for producing carbonate material.

[0045] Figure 3 shows a schematic embodiment of the present system being utilized with saline water; Figure 4 shows a schematic embodiment of the present system being utilized with salt crystallization; and sodium chloride regenerated during carbonate precipitation is recycled to a chlor-alkali electrolysis step to establish a closed brine loop.

[0046] Figure 5 shows a schematic embodiment of a system in accordance with aspects of the present disclosure including electrolysis, carbonate precipitation, mineral dissolution and cation exchange.

[0047] Figure 6 shows a schematic embodiment of a system in accordance with aspects of the present disclosure including a brine feed, electrolysis, carbonate precipitation, mineral dissolution and cation exchange.

[0048] Figure 7 shows a schematic embodiment of the present system for producing carbonate material.Figure 8 shows a schematic embodiment of the present system for producing carbonate material. Figure 9 shows titration curves for samples generated in example 1 produced by contacting of an alkaline NaOH solution with CO2 and with flue gas from a generator, to confirm that carbonate is the dominant species.

[0049] Figure 10 shows a schematic embodiment of a system in accordance with aspects of the present disclosure which was used in carrying out the experiment of Example 2.

[0050] Figure 11 shows overlaid XRD patterns of samples of magnesium carbonate produced in Example 3.

[0051] Figures 12 to 14 show results of TGA analysis of samples of magnesium carbonate produced in Example 3.

[0052] Figure 15 shows the XRD pattern of a sample obtained from Trial 3 in Example 2, which confirmed the formation of crystalline carbonite phases, with hydromagnesite and magnesite identified as dominant phases.

[0053] Detailed Description

[0054] Definitions

[0055] Unless specifically defined otherwise, all technical and scientific terms used herein shall be taken to have the same meaning as commonly understood by one of ordinary skill in the art.

[0056] Any reference to background art herein is not to be construed as an admission that such art constitutes common general knowledge in Australia or elsewhere.

[0057] In this specification, adjectives such as first and second, upper and lower, and the like may be used solely to distinguish one element or action from another element or action without necessarily requiring or implying any actual such relationship or order.

[0058] Words such as “comprises” or “includes” are intended to define a non-exclusive inclusion, such that a device, system or method that comprises a list of elements does not include only those elements but may include other elements not expressly listed, including elements that are inherent to such a composition, formulation or method.

[0059] As used herein, the term ‘about’ means the amount is nominally the number following the term ‘about’, but the actual amount may vary from this precise number to an unimportant degree. For example it may refer to + / - 10%, of the designated value.

[0060] As used herein, the term “and / or”, e.g., “X and / or Y” shall be understood to mean either " X and Y" or " X or Y" and shall be taken to provide explicit support for both meanings or for either meaning.

[0061] As used herein, the phrase “at least one of’, when used with a list of items, means different combinations of one or more of the listed items may be used and only one of the items in the list may be needed. The item may be a particular object, thing, or category. In other words, “at least one of’ means any combination of items or number of items may be used from the list, but not all of the items in the list may be required. For example, “at least one of item A, item B, and item C” may mean item A; item A and item B; item B; item A, item B, and item C; or item B and item C. In some cases, “at least one of item A, itemB, and item C” may mean, for example and without limitation, two of item A, one of item B, and ten of item C; four of item B and seven of item C; or some other suitable combination.

[0062] Table of Reference Numerals

[0063] Reference Feature

[0064] Numeral

[0065] 10 Water feed

[0066] 11 Alkali metal halide feed

[0067] 12 Feed treatment

[0068] 13 Treated brine solution

[0069] 14 Feed treatment

[0070] 15 Optional brine bittern

[0071] 16 Purified brine solution

[0072] 17 Electrolysis

[0073] 18 NaOH stream

[0074] 19 HC1 stream

[0075] 20 Mineral dissolution

[0076] 21 Carbonate production

[0077] 22 Carbonate / soda ash

[0078] 23 Cation exchange

[0079] 24 Silicate mineral feed

[0080] 100 System for preparing carbonates

[0081] 100a Carbon dioxide capture unit

[0082] 110, 110a, 110b Column

[0083] 111 First end of column

[0084] 112 Second end of column

[0085] 120 Gas injection portion

[0086] 130 Gas outlet

[0087] 131 Valve arrangement

[0088] 135 Recirculation assembly

[0089] 136 Pump

[0090] 140 Liquid outlet

[0091] 150 Solids collection chamber

[0092] 210 Feed treatment unit

[0093] 210a Chloralkali feed treatment unit

[0094] 211, 211a Electrochemical unit

[0095] 212 Hydrohalic acid generation unit

[0096] 213 NaOH purification unit

[0097] 214 Carbonate filtration unit

[0098] 215 NaCl crystallisation unit

[0099] 216, 216a, 216b Heat exchanger

[0100] 217 Inlet / outlet fan / blower

[0101] 218, 218a, 218b Transfer pump

[0102] 219 Feed tank

[0103] 220 Discharge tank

[0104] 221 Gas inlet pipe

[0105] 222 Gas inlet tee

[0106] 223 Packing / Wet contacting region

[0107] 224 Packing

[0108] 225 Top assembly

[0109] 226 Gas outlet assembly

[0110]

[0111] 227 Liquid holding vessel228 Liquid inlet

[0112] 229 Liquid recirculation pump

[0113] 230 Liquid line heater assembly

[0114] 231 Liquid line heater valve

[0115] 232 Butterfly valve

[0116] 233 Liquid feed funnel

[0117] 234 Brine feed tank

[0118] 235 Pump

[0119] 236 Hydrohalic acid generation unit

[0120] 237 Alkaline liquid solution tank

[0121] 238 Recirculation pump

[0122] 239 Liquid solution feed pump

[0123] 240 Cation exchange column

[0124] 241 Heat exchanger

[0125] 242, 242a Filter

[0126] 243 Recirculation tank

[0127] 244 HP Pump

[0128] 245 Disposals tank

[0129] 246 Pump

[0130] 247 Nanofiltration membrane unit

[0131] 248 Filtrate tank

[0132] 249 Pump

[0133] 250 Low pressure reverse osmosis membrane

[0134] unit

[0135]

[0136] 251 Impurity removal unit

[0137] Processes and Systems for Capturing Carbon Dioxide

[0138] As discussed above, processes and systems have been identified for capturing carbon dioxide, and storing it in stable forms such that it can be effectively removed from the atmosphere or from CO2-rich waste streams. Conventional carbon capture and storage (CCS) approaches, while technically feasible, face economic and environmental constraints, including high regeneration energy requirements, solvent degradation (for example amine degradation), and long-term storage liability. Carbon capture and utilisation (CCU) pathways convert CO2 into valuable products but often lack permanence; many products are shortlived and may re-release CO2 during use, degradation, or disposal. It would be advantageous if end users had practical alternatives to presently available carbon-management solutions, particularly where such alternatives reduce reliance on long-term subsurface storage, complex transport and injection logistics, and associated long-term monitoring and liability. In this regard, systems that convert captured CO2 into stable carbonate materials and / or carbonate / carbon-bearing intermediates can provide a distinct advantage over geological sequestration by producing useful products and co-products that may be utilised in existing supply chains, including without limitation, construction materials (for example cementitious additives, aggregates, and fillers), soil amendments, remediation reagents and water-treatment media, while providing durable storage of CO2 in mineral form. Accordingly, there remains a need for carbon-capture systems that not only remove CO2 but also provide pathways for conversion into useful carbonate materials, thereby improving adoption economics, enabling distributed deployment at point sources and reducing dependence on geological storage infrastructure.A key bottleneck in both direct air capture and point-source capture is the availability of scalable alkaline absorbents and durable mineralisation pathways. Traditional capture agents such as monoethanolamine (MEA) can be energy-intensive and environmentally burdensome. In contrast, alkali metal hydroxides such as sodium hydroxide (NaOH) and potassium hydroxide (KOH) are highly reactive with CO2 and can enable absorption under both flue-gas and ambient conditions. Such alkalis are produced globally at industrial scale, commonly via chlor-alkali electrolysis, which electrolyses brine (NaCl and / or KCl) to yield chlorine gas (Ch), hydrogen (EL), and aqueous alkali metal hydroxide (NaOH and / or KOH). However, co-production of chlorine and other halogen-bearing streams introduces associated safety, handling, environmental, and regulatory challenges. In practice, neutralisation or treatment of chlorine and related oxidants may rely on reagents such as soda ash, activated carbon, and sulphur-based reducing agents (including sodium metabisulfite, potassium metabisulfite, and sodium sulfite). These approaches consume additional chemicals and may generate secondary emissions associated with reagent manufacture, transport, and downstream treatment. Existing industrial practices typically address halogen management and CO2 mineralisation as separate operations, often requiring additional reagents, transport logistics, and / or waste handling. This separation represents a gap in industrial decarbonisation and halogen management. In parallel with large-scale alkali production, reverse osmosis (RO) operations generate significant volumes of concentrate (reject brine), representing an abundant and underutilised feedstock for electrochemical alkali generation and mineralisation pathways. Disposal of RO concentrate, including ocean discharge, remains a dominant management approach and may contribute to marine ecosystem stress and local salinity increases. Valorisation of RO reject brine for alkali generation and CO2 mineralisation could convert this waste stream into a useful input for carbon-management processes. While desalination reject brine is a promising feedstock, seawater remains the dominant and widely distributed saline resource. Seawater typically contains salt on the order of about 30–40 g·L⁻¹ and serves as a base material for existing solar-salt and chlor-alkali industries. Integration of seawater-derived brines, including solar-salt brines, into an electrochemical mineralisation process can support scalability independent of desalination infrastructure. Simultaneously, ultramafic and other silicate minerals, comprising a considerable portion of the Earth’s crust, represent large resources rich in divalent cations (Mg2+, Ca2+) suitable for carbonate formation. Mining and industrial residues such as steel slag, red mud, and tailings may also contain reactive mineral phases suitable for carbonation. These saline and mineral resources provide a broad chemical and industrial context in which future carbon-management systems may operate. While electrochemical alkali generation and mineral carbonation have each been investigated independently, practical integration of such processes in industrial settings remains challenging due to reagent losses, waste streams, and operational complexity. Further, electrochemical processing of saline feeds, including chlor-alkali electrolysis, salt splitting, and brine treatment associated with desalination, inherently generates alkaline and halogenbearing ionic streams in fixed or constrained stoichiometric relationships. In practice, downstream utilisation of these streams is frequently unbalanced due to site-specific safety, regulatory, logistical, and / or economic constraints, resulting in partial neutralisation, discharge, or under-utilisation of alkaline, acidic,and / or halogen-containing species. Concurrently, large volumes of saline brine and mineral-bearing residues are discharged or stockpiled without effective valorisation. Existing carbon-capture and mineralisation approaches typically address CO2 removal, reagent regeneration, brine management, and mineral utilisation as separate operations and do not provide an integrated framework for resolving these coupled ionic imbalances. There remains a need for systems capable of sequestering carbon dioxide as stable carbonates while regenerating alkaline capture capacity and reducing net discharge of halogencontaining and saline waste streams. Such a system should preferably also meet operability requirements in hard-to-abate sectors by functioning as a retrofit and / or drop-in solution for emissions mitigation, thereby enabling reduction of emissions associated with anthropogenic activities including agriculture, wastewater treatment, municipal waste management, mining and metals processing, cement and concrete production, chemical manufacturing, and bioprocessing operations. To support scalability and cost-effectiveness, the system should preferably utilise abundant resources and existing waste streams and be operable on industrial brines and on calcium- or magnesium-bearing oxide and silicate minerals. Examples of suitable oxide-bearing feeds include naturally occurring brucite and tailings from nickel laterite operations, where magnesium oxide phases may convert to hydroxides during comminution and flotation. Additional suitable mineral sources include tailings from mafic and ultramafic deposits, nickel deposits, and rare-earth deposits, and minerals such as serpentine, olivine, pyroxene, scawtite, spurrite, and volcaniclastic rocks. Such minerals and tailings may be used for ex-situ mineralisation either (i) at large-scale mining or industrial hubs, including for alkalinity control within tailings systems, or (ii) as mineral-enabled reagents for distributed emissions sites such as water-treatment facilities, agricultural waste-to-energy plants, and municipal waste-processing facilities. Precipitated magnesium hydroxide (brucite) may also be produced by dosing magnesium chloride solutions, derived from bitterns, seawater concentration, and / or magnesium-bearing minerals, with alkaline reagents. Given that seawater contains about 1.26 g·L-1magnesium, and comparable concentrations occur in many bore waters, this approach enables large-scale production of precipitated brucite suitable for durable carbon removal through formation of magnesium carbonate phases.

[0139] Similar approaches can be applied to magnesium / calcium bearing oxide and silicate minerals available in abundance in mine sites, natural mineral deposits and industrial residues. Systems and methods disclosed herein are configured to utilise such mineral feedstocks, optionally in combination with brine or other saline streams, within an integrated process for producing stable carbonate materials. This process provides advantages in waste management and resource valorisation while also enabling sequestration of carbon dioxide from point sources and ambient air.

[0140] In various aspects and embodiments, the present disclosure accordingly provides continuous, ionically closed carbonate production processes with internal alkalinity regeneration, and systems configured to run such processes.

[0141] The present disclosure provides a new class of industrial process that uses electrochemistry to maintain an internally closed ionic loop that converts CO2 into stable mineral carbonates while preventing halide discharge.Closed and Partially Closed Electrochemical Systems For Sequestering Carbon Dioxide In some aspects, the present disclosure provides systems and methods for producing solid carbonates from carbon dioxide via an electrochemically driven mineralisation process. For example, an electrochemical cell can electrolyse a halide-containing brine to generate acidic and alkaline phases. The acidic phase can liberate divalent cations such as calcium and magnesium from mineral feedstocks, forming soluble salts and a silica residue, while the alkaline phase can react with gaseous or dissolved carbon dioxide to form carbonate and bicarbonate ions. The liberated cations can combine with these ions to precipitate solid carbonates, regenerating neutral brine and retaining halogens within a closed electro-mineral loop.

[0142] Such a process enables continuous or batch operation for durable carbon dioxide sequestration and brine valorisation under ambient or near-ambient conditions, providing a regenerable pathway for mineral conversion and halogen management with minimal reagent consumption.

[0143] Put another way, various aspects and embodiments of the present disclosure provides processes and systems which achieve: electrochemical generation of acidity + alkalinity from a halide electrolyte, CO2 conversion to carbonate species under controlled alkalinity, mineral activation producing soluble divalent cations, carbonate precipitation regenerating alkali metal halide, recycle of halide electrolyte to electrochemical unit, export of carbonate as an electrically neutral solid, and conservation of ionic charge carriers inside the loop.

[0144] The present disclosure further provides an integrated electro-mineral system for the capture and permanent conversion of carbon dioxide (CO2) into stable carbonate materials through coupled electrochemical, chemical equilibrium, and mineralisation reactions. The system can employ saline brines, such as reverse-osmosis reject, seawater, or solar salt, together with metal -bearing (e.g. calcium- and / or magnesium-bearing) silicate minerals, including basaltic and ultramafic feedstocks, to generate alkaline and acidic reagents within a closed chemical loop.

[0145] In some embodiments, an electrochemical cell electrolyses a halide-containing brine to generate an alkaline catholyte and an acidic or halogen-rich anolyte. The alkaline stream reacts with gaseous or dissolved CO2 to form carbonate and bicarbonate ions, while the acidic stream, preferably comprising hydrochloric acid, dissolves calcium- and magnesium-bearing silicate minerals, releasing divalent metal cations (Ca2+, Mg2+) and producing a silica residue. The liberated cations subsequently react with the carbonate ions to precipitate solid carbonates, thereby mineralising CO2, regenerating neutral brine, and retaining halogens within a closed electrochemical loop.

[0146] In some embodiments, the system may also utilise alkali-derived hydroxide species, such as sodium hydroxide (NaOH), to partially react with silicate minerals or dissolved metal salts, thereby enhancing cation liberation and promoting complete conversion of residual magnesium and calcium species to carbonates. This secondary alkalinity pathway complements the primary acid-mediated mineral dissolution, enabling flexible operation under variable mineral compositions or brine chemistries while maintaining overall halogen retention and carbon mineralisation efficiency.Such an integrated electro-mineral loop operates by coupling electrochemically generated acid and base with mineral dissolution and carbonate precipitation in a closed circuit. The acidic and alkaline streams are neutralised through reaction with silicate minerals, carbon dioxide, and the resulting metal carbonates, thereby regenerating a near-neutral halide brine suitable for reuse in the electrochemical cell. This configuration enables sustained halogen retention, minimises reagent loss, and achieves continuous conversion of carbon dioxide into stable carbonate solids derived from naturally abundant minerals and recycled process fluids.

[0147] Such embodiments of the process typically yield three principal outputs: a solid carbonate product, a silica-rich residue, and a regenerated halide brine. The carbonate product, comprising predominantly calcium and / or magnesium carbonates, provides a durable form of carbon storage suitable for use as a construction material, mineral filler, or feedstock for subsequent processing. The silica residue may be recovered as an inert by-product or utilised as a supplementary pozzolanic or adsorptive material. The regenerated brine can be recirculated to the electrochemical cell, maintaining halogen balance and enabling sustained operation without significant net consumption of acids, bases, or salts.

[0148] In certain embodiments, the system may incorporate multiple electrochemical or mineral reaction stages to optimise pH control, ion transport, and carbonate precipitation kinetics. Carbon dioxide may for example be introduced from direct air capture units, flue gas streams, or dissolved inorganic carbon in aqueous media.

[0149] Operating conditions including temperature, residence time, and electrolyte composition may be adjusted to control carbonate polymorph formation, particle size distribution, and precipitation efficiency.

[0150] The process may further include gas-liquid contactors, ion-selective membranes, or crystallisation modules configured to enhance mineralisation yield and system energy efficiency.

[0151] Various aspects of the present systems and processes provide a durable and energy-efficient approach to carbon dioxide removal, by coupling electrochemical acid-base generation with mineral carbonation in a closed halogen cycle. Unlike conventional mineralisation or electrolysis processes, the electro-mineral loop eliminates reagent loss through continuous brine regeneration and internal halogen recycling. The process achieves net carbon sequestration in stable solid form without external chemical inputs, enabling scalable, modular deployment at distributed emission sources. Through integrated electrochemical and mineral pathways, the system simultaneously manages halogens, valorises brines, and produces carbon-negative mineral products suitable for long-term storage or utilisation.

[0152] Illustrative reaction framework for Closed Electrochemical / Electromineral Loop (CEL)

[0153] This summary provides an illustrative reaction framework for a closed electrochemical / electromineral Loop (CEL). The CEL is characterised by (i) electrochemical generation of alkalinity and acidity within a working electrolyte, (ii) capture of CO2 into carbonate / bicarbonate species, (iii) liberation of divalent cations (e.g., Ca2+, Mg2+) from mineral feedstocks, and (iv) precipitation of solid carbonateproducts with regeneration of the working electrolyte inventory. Unless explicitly stated, reactions are illustrative and may proceed via equilibria and intermediate species depending on operating conditions.

[0154] A. Stepwise Description

[0155] Step 1. Electrochemical generation of alkalinity and acidity (working electrolyte)

[0156] • (R-1) Electrolysis (NaCl example): 2 NaCl + 2 H₂O → 2 NaOH + H₂(g) + Cl₂(g)

[0157] • (R-1c) Cathode (alkalinity generation): 2 H₂O + 2 e⁻ → H₂(g) + 2 OH⁻

[0158] • (R-1a) Anode (halide oxidation): 2 Cl⁻ → Cl₂(g) + 2 e⁻

[0159] • (R-1r, optional) Halogen–hydrogen recombination / acid formation: H₂(g) + Cl₂(g) → 2 HCl(aq)

[0160] Step 2. CO₂ capture and carbonate speciation in the alkaline stream

[0161] Carbonic equilibria (electroneutral, spectator-ion balanced):

[0162] • (E-1) CO₂ hydration: CO₂ + H₂O ⇌ H₂CO₃

[0163] • (E-2) First dissociation: H₂CO₃ ⇌ HCO₃⁻ + H⁺

[0164] • (E-3) Second dissociation: HCO₃⁻ ⇌ CO₃²⁻ + H⁺

[0165] Representative capture reactions (alkali example):

[0166] • (R-2) Carbonate formation: 2 NaOH + CO₂ → Na₂CO₃ + H₂O

[0167] • (R-2b) Bicarbonate formation: NaOH + CO₂ → NaHCO₃

[0168] • (R-2c, optional) Carbonate bicarbonate (excess CO2):

[0169] Na₂CO₃ + CO₂ + H₂O → 2 NaHCO₃

[0170] Step 3. Mineral dissolution / liberation of M2+into the working electrolyte (acid branch) Representative acid leach reactions:

[0171] • (R-3) Ca metasilicate: CaSiO₃ + 2 HCl → CaCl₂ + H₄SiO₄

[0172] • (R-4) Mg orthosilicate: Mg₂SiO₄ + 4 HCl → 2 MgCl₂ + H₄SiO₄

[0173] • (R-5) Ca oxide: CaO + 2 HCl → CaCl₂ + H₂O

[0174] • (R-6) Mg hydroxide: Mg(OH)₂ + 2 HCl → MgCl₂ + 2 H₂O

[0175] Step 4. Carbonate precipitation + regeneration of the alkali -metal halide working electrolyte Double-displacement precipitation (representative):

[0176] • (R-7Ca): Na₂CO₃ + CaCl₂ → CaCO₃(s)↓ + 2 NaCl

[0177] • (R-7Mg): Na₂CO₃ + MgCl₂ → MgCO₃(s)↓ + 2 NaCl

[0178] Step 5. Silica formation (silicate embodiments)

[0179] • (R-8) Silicic acid dehydration (optional endpoint selection):

[0180] H₄SiO₄ → SiO₂(s) + 2 H₂O

[0181] B. Overall Net Reactions (Na7Cl“ Cancelled)

[0182] Let M²⁺ ∈ {Ca²⁺, Mg²⁺}.Silicate feedstocks

[0183] 1) Metasilicate basis (MSiCh)

[0184] • Silicic -acid endpoint:

[0185] MSiO₃ + CO₂ + 2 H₂O → MCO₃(s)↓ + H₄SiO₄

[0186] • Solid-silica endpoint:

[0187] MSiO₃ + CO₂ → MCO₃(s)↓ + SiO₂(s)

[0188] 2) Orthosilicate basis (M2SiO4)

[0189] • Silicic -acid endpoint:

[0190] M₂SiO₄ + 2 CO₂ + 2 H₂O → 2 MCO₃(s)↓ + H₄SiO₄

[0191] • Solid-silica endpoint:

[0192] M₂SiO₄ + 2 CO₂ → 2 MCO₃(s)↓ + SiO₂(s)

[0193] Oxide and hydroxide feedstocks

[0194] 3) Oxide basis (MO)

[0195] • Net: MO + CO₂ → MCO₃(s)↓

[0196] 4) Hydroxide basis (M(0H)2)

[0197] • Net: M(OH)₂ + CO₂ → MCO₃(s)↓ + H₂O

[0198] Endpoint definition

[0199] • Silicic acid dehydration: H₄SiO₄ → SiO₂ + 2 H₂O

[0200] Notes (non-limiting)

[0201] • Hydrated / basic magnesium carbonates may form depending on conditions (e.g., MgCOrxELO, hydromagnesite). Idealised MgCO₃ stoichiometry is shown to illustrate CEL loop logic.

[0202] • Mixed cation feedstocks (Ca / Mg with Al / Fe / Si / trace metals) are common; the net logic generalises.

[0203] C. Worked Embodiments (Minimal)

[0204] Cl. Common CEL header (applies unless stated otherwise)

[0205] • (H-1) Electrolysis: 2 NaCl + 2 H₂O → 2 NaOH + H₂ + Cl₂

[0206] • (H-2, optional) Recombination / acid formation: H₂ + Cl₂ → 2 HCl

[0207] • (H-3) Carbonation (NaOH branch): CO₂ + 2 NaOH → Na₂CO₃ + H₂O

[0208] C2. Orthosilicate loop (illustrative): Ca2SiO4

[0209] Primary path (acid leach + precipitation):

[0210] • Leach: Ca₂SiO₄ + 4 HCl → 2 CaCl₂ + H₄SiO₄

[0211] • Precipitation: Na₂CO₃ + CaCl₂ → CaCO₃↓ + 2 NaCl

[0212] • Net (silicic acid): Ca₂SiO₄ + 2 CO₂ + 2 H₂O → 2 CaCO₃↓ + H₄SiO₄

[0213] • Optional dehydration: H₄SiO₄ → SiO₂ + 2 H₂O• Net (solid silica): Ca₂SiO₄ + 2 CO₂ → 2 CaCO₃↓ + SiO₂

[0214] C3. Orthosilicate loop (illustrative): Mg2SiO4

[0215] Primary path (acid leach + precipitation):

[0216] • Leach: Mg₂SiO₄ + 4 HCl → 2 MgCl₂ + H₄SiO₄

[0217] • Precipitation: Na₂CO₃ + MgCl₂ → MgCO₃↓ + 2 NaCl

[0218] • Net (silicic acid): Mg₂SiO₄ + 2 CO₂ + 2 H₂O → 2 MgCO₃↓ + H₄SiO₄

[0219] • Optional dehydration: H₄SiO₄ → SiO₂ + 2 H₂O

[0220] • Net (solid silica): Mg₂SiO₄ + 2 CO₂ → 2 MgCO₃↓ + SiO₂

[0221] C4. Hydroxide routing (worked embodiment): Mg(0H)2

[0222] Acid leach + precipitation route:

[0223] • Leach: Mg(OH)₂ + 2 HCl → MgCl₂ + 2 H₂O

[0224] • Precipitation: Na₂CO₃ + MgCl₂ → MgCO₃↓ + 2 NaCl

[0225] • Net: Mg(OH)₂ + CO₂ → MgCO₃ + H₂O

[0226] Equivalent precipitation forms (illustrative, electroneutral):

[0227] • Mg²⁺ + CO₃²⁻ → MgCO₃(s)↓

[0228] • Mg(OH)₂(s) + H₂CO₃(aq) → MgCO₃(s)↓ + 2 H₂O(l)

[0229] D. Optional “Brine I Seawater” Variant (MCE direct feed; acid exported)

[0230] This branch is optional, but illustrates direct use of chloride brines.

[0231] • Hydroxide precipitation (optional intermediate): MCl₂ + 2 NaOH → M(OH)₂↓ + 2 NaCl • Carbonation: M(OH)₂ + CO₂ → MCO₃↓ + H₂O

[0232] • Direct net (acid exported): MCl₂ + CO₂ + H₂O → MCO₃↓ + 2 HCl where M²⁺ ∈ {Ca²⁺, Mg²⁺}.

[0233] E. Supporting Notes

[0234] 1. Spectator-ion I electroneutrality:

[0235] References to H⁺ and OH⁻ denote acidity / alkalinity equivalents in aqueous solution (e.g., hydronium / hydroxide) that are charge-balanced by the working electrolyte (e.g., Na⁺ / Cl⁻ or other alkali-metal / halide ions). They do not imply isolated accumulation of free protons or hydroxide.

[0236] 2. Closed-loop accounting:

[0237] In the idealised closed CEL reaction accounting, Na⁺ / Cl⁻ species cancel, and the external material inputs are CO2 and the mineral feedstock (and water where required by stoichiometry). Electrical energy is supplied to drive electrolysis.

[0238] 3. Equilibrium I operating controls:

[0239] The equilibria above may be driven toward desired products by controlling pH, temperature, pressure, ionic strength / conductivity, residence time, and gas-liquid mass transfer.

[0240] 4. Optional industrial embodiments:Hydrogen utilisation (e.g., fuel cell), hypochlorite / oxidant generation, or other chlor-alkali oxidation pathways may be included in certain embodiments and are not required for carbonate formation.

[0241] CEL Stepwise Description

[0242] A stepwise description of key operations employed by the CEL is provided to illustrate how the modular components can be deployed.

[0243] Electrochemical Generation of Alkalinity and Acid

[0244] In one embodiment, an aqueous alkali-metal halide brine (for example, NaCl or KCl is subjected to electrolysis using a membrane, diaphragm, bipolar, or multichamber electrolysis cell. A representative overall reaction for sodium chloride is:

[0245] (R-1) 2 NaCl + 2 H₂O → 2 NaOH + H₂ + Cl₂

[0246] At the cathode, water is reduced to form hydroxide ions and hydrogen gas, yielding an alkaline catholyte:

[0247] 2 H₂O + 2 e⁻ → H₂(g) + 2 OH⁻

[0248] At the anode, halide ions evolve to halogen gas:

[0249] 2 Cl⁻ → Cl₂(g) + 2 e⁻ The halogen gas is absorbed into water or brine to form hydrochloric acid, hypochlorous acid, or related halide acids, depending on pH and cell configuration.

[0250] The electrolysis step converts electrical energy into chemically separated acid and base streams that drive the mineral dissolution and carbonation sub-processes. In preferred embodiments, membrane or bipolar-membrane cells operate at approximately 2.2-3.0 V at industrially relevant current densities, with caustic current efficiencies typically in the range of about 70-95%.

[0251] The electrochemical generator of alkaline and acidic reagents may be implemented as an alkaline water or brine electrolyser. At 25 °C, the thermodynamic decomposition potential for water is approximately 1.23 V. In practice, alkaline electrolyser cells operate at about 1.6-2.0 V at industrial current densities and deliver hydrogen and oxygen (or halogens in brine) with Faradaic efficiencies typically above 95%. When the anolyte and catholyte contain sodium or other alkali cations, the same cell architecture can be operated as a chlor-alkali or salt-splitting unit, generating sodium hydroxide at electrical energy inputs comparable to conventional membrane chlor-alkali technology (approximately 2-3 kWh kg1NaOH). CO2 Capture and Carbonate Formation

[0252] In some embodiments, a sodium hydroxide-containing catholyte generated in the electrochemical stage is contacted with a CO2-containing gas stream derived from flue gas, biogas, direct-air capture (DAC), engine exhaust, or other process gases. Contacting promotes CO2 dissolution, hydration, and subsequent neutralisation under operating ranges of approximately 0-20 bar and 0-150 °C, with typical pH control between about 10 and 14 to favour formation of carbonate species (CO32).

[0253] Carbonic equilibria and base neutralisation proceed according to the following reactions:CO₂ + H₂O ↔ H₂CO₃ (1)

[0254] H₂CO₃ ↔ HCO₃⁻ + H⁺ (2)

[0255] HCO₃⁻ ↔ CO₃²⁻ + H⁺ (3)

[0256] 2 NaOH + CO₂ → Na₂CO₃ + H₂O (4)

[0257] Na₂CO₃ + CO₂ + H₂O → 2 NaHCO₃ (5)

[0258] In some embodiments, the neutralisation may be represented more generally as:

[0259] (R-2) 2 NaOH + CO₂ → Na₂CO₃ + H₂O

[0260] (R-2b) NaOH + CO₂ → NaHCO₃

[0261] At pH values above about 10, carbonate (CO₃²⁻) dominates the dissolved inorganic carbon pool, enabling subsequent precipitation of alkaline-earth carbonates. The NaOH scrubber thus converts electrical work into a carbonate-rich alkaline solution without thermal regeneration or CO₂ compression. The resulting sodium carbonate or bicarbonate liquor can be directed either to:

[0262] (a) a mineral-dissolution unit where divalent cations are liberated from silicates, oxides, hydroxides, brines, or residues; or

[0263] (b) a carbonation reactor where solid carbonates are precipitated with magnesium hydroxide or calcium hydroxide.

[0264] Acid-Driven Mineral Dissolution (Primary Embodiment)

[0265] In some embodiments, the acid stream produced in the electrochemical stage is reacted with alkaline earth-bearing (e.g. calcium- or magnesium -bearing) minerals and / or industrial residues. Suitable solids include, without limitation, wollastonite (CaSiO3), forsterite (Mg2SiO4), serpentine, olivine, basalt, mafic or ultramafic rocks, cement kiln dust, steel slag, red mud, and other alkaline solids containing Ca2+and / or Mg2+.

[0266] Representative reactions for silicate leaching with hydrochloric acid are:

[0267] (R-3) CaSiO3+ 2 HC1 CaCl2+ H4SiO4

[0268] (R-4) Mg2SiO4+ 4 HC1 2 MgCb + H4SiO4

[0269] For oxide and hydroxide feedstocks, leaching proceeds similarly, for example:

[0270] (R-3C) CaO + 2 HCl → CaCl₂ + H₂O

[0271] (R-4C) Mg(OH)₂ + 2 HCl → MgCl₂ + 2 H₂O

[0272] This step:

[0273] • liberates Ca2+and / or Mg2+as soluble halide salts;

[0274] • produces orthosilicic acid (H4SiO4) and / or hydrated silica; and

[0275] • neutralises and valorises the halogen-derived acidity from electrolysis.

[0276] The acid-leach pathway operates under mild conditions (for example, 20-120 °C and 0.1-5 bar) and allows rapid mineral activation without high-temperature calcination. This embodiment allows accesses to both Ca2+and Mg2+from abundant, low-cost minerals with favourable kinetics and produces chloride liquors that can be directly combined with sodium carbonate solutions in the subsequent carbonation step.

[0277] Double-Displacement Carbonation and Sodium Loop ClosureThe acid-leach pathway can operate under mild conditions (for example, 20-120 °C and 0.1-5 bar) and allow the carbonate or bicarbonate solution from the CO2 capture stage to be contacted with the divalent metal chloride liquor from the mineral dissolution stage. Representative double-displacement reactions include:

[0278] (R-5) Na₂CO₃ + CaCl₂ → CaCO₃↓ + 2 NaCl

[0279] (R-6) Na₂CO₃ + MgCl₂ → MgCO₃↓ + 2 NaCl

[0280] These reactions proceed spontaneously due to the low solubility of alkaline-earth carbonates. The regenerated NaCl can be recycled to the electrolysis unit, forming a closed sodium / halide loop. The precipitated CaCO3and MgCO3constitute stable, permanent CO2mineralisation products. The carbonate solids may be recovered by settling, thickening, filtration, or centrifugation and used as fillers, supplementary cementitious materials, aggregates, or other carbonate products.

[0281] Combining the electrolysis, mineral dissolution, carbonation, and silica dehydration stages gives, at the mineral / CO2level, an overall net transformation such as:

[0282] CO₂ + CaSiO₃ + H₂O → CaCO₃ + SiO₂ + H₂O

[0283] with Na⁺, Cl⁻, H₂, and water circulating internally and not consumed in the net reaction. This is chemically equivalent to accelerated natural silicate weathering, driven by electrical energy instead of geological timescales and thermal calcination.

[0284] Silica Formation and Water Regeneration

[0285] The orthosilicic acid (H₄SiO₄) formed during mineral dissolution undergoes condensation and dehydration at moderate temperature to produce solid silica and water. A schematic reaction is:

[0286] (R-7) H₄SiO₄ → SiO₂(s) + 2 H₂O

[0287] The explicit polymerisation / condensation step is:

[0288] H₄SiO₄ → SiO₂·nH₂O → SiO₂ + water

[0289] This dehydration typically occurs at temperatures of about 120-180 °C and may be driven by low-grade or waste heat. The resulting amorphous or finely divided Si02can be used as a supplementary cementitious material, pozzolanic additive, filler, or inert by-product. The water released in this step is of high purity, and may be recycled to the brine preparation or electrolysis stage, thereby improving the overall water balance of the loop.

[0290] Halogen Recovery and Acid Recycling

[0291] Halogen gas (for example, Cl2) and hydrogen gas (H2) generated during electrolysis may for example be:

[0292] (a) recombined directly to produce hydrochloric acid, or

[0293] (b) converted electrochemically in a fuel cell to recover part of the input electrical energy.

[0294] A representative direct recombination is:

[0295] (R-8) H₂ + Cl₂ → 2 HCl

[0296] Reaction (R-8) is strongly exothermic and regenerates acid that can be used for the mineral leaching step. In some embodiments, a hydrogen-chlorine fuel cell is employed so that chemical recombinationsimultaneously produces HC1 and electrical power. Alternatively, part of the halogen stream may be diverted into hypochlorite or chlorate production (for example, Ch + 2 NaOH NaCl + NaClO + H2O) while maintaining the overall chloride inventory in the loop.

[0297] Ionic and Mass Balances

[0298] In preferred embodiments, major ionic species circulate internally as follows:

[0299] • Na+ / Cl: fully recycled via NaCl NaOH Na2CO3 / NaHCO3 NaCl;

[0300] • H2O: recycled through neutralisation and silicic-acid dehydration;

[0301] • CO2: fixed as solid CaCCh and / or MgCOs; and

[0302] • H2 / CI2 (or H2 / O2 in water-splitting variants): recombined or valorised as acid or energy.

[0303] Loop summary (ideal stoichiometry, Ca-silicate example):

[0304] CO2 + CaSiO3+ H2O CaCO3+ Si02+ H2O

[0305] with NaCl, H2, and CI2 regenerated internally.

[0306] Secondary Pathway: Alkaline Dissolution

[0307] In some other embodiments, the divalent metal source can be obtained not by acid leaching but via alkaline dissolution of calcium- and magnesium-bearing silicate minerals. In this configuration, the electrochemically generated hydroxide stream is contacted directly with a silicate feedstock such as wollastonite, forsterite, serpentine, olivine, basaltic glass, volcanic ash, or industrial silicate residues. Under high-pH conditions (typically pH > 12), silicate frameworks undergo nucleophilic attack by hydroxide ions, releasing divalent metal species that precipitate as solid hydroxides and forming soluble sodium silicate species. Representative reactions include:

[0308] (R-3A) CaSiO3+ 2 NaOH Ca(0H)2+ Na2SiO3

[0309] (R-4A) Mg2SiO4+ 4 NaOH 2 Mg(0H)2+ Na4SiO4

[0310] (R-4B) Mg3Si205(0H)4+ 8 NaOH 3 Mg(0H)2+ 2 Na^iCL + 3 H2O The resulting Ca(0H>2 and Mg(0H)2 solids can be carbonated directly using C02-rich gas or carbonate -bearing solution from the carbonation stage:

[0311] (R-6A) Ca(OH)2+ CO2→ CaCO3+ H2O

[0312] (R-6B) Mg(OH)2+ CO2→ MgCO3+ H2O

[0313] In such embodiments, sodium remains predominantly in solution as sodium carbonate and sodium silicate species, and hydroxide is regenerated electrochemically rather than by thermal calcination. The alkaline-loop configuration thus provides a fully low-temperature route for mineral activation and carbonation, avoids kiln-based regeneration, and maintains the electro-mineral loop entirely within a sodium / hydroxide / carbonate / silicate domain. This alkaline variant is interchangeable with, or may be operated in parallel to, the acid-leach variant, with both configurations sharing the same electrochemical alkalinity generation and CO2 carbonation infrastructure.

[0314] CEL Worked Chemistry ExamplesThe following worked examples are provided to demonstrate the core CEL chemistry. The purpose of this section is to demonstrate stoichiometric loop closure and the key reaction equations for the species of interest which can be implemented in the CEL.

[0315] Calcium Silicate: (Ca Silicate Loop)

[0316] In one embodiment, the worked chemistry for calcium reforming occurs according to the following reaction sequence:

[0317] Electrolysis: 2 NaCl + 2 H2O 2 NaOH + H2 + Ch

[0318] Halogen recombination: H2 + Ch 2 HC1

[0319] Carbonation (NaOH branch): CO2 + 2 NaOH Na2COs + H2O

[0320] Primary acid-leach path (silicate):

[0321] Leach (Ca, primary): Ca2SiO4 + 4 HC1 2 CaCL + H4SiO4

[0322] Precipitation (Ca, primary): Na2COs + CaCL —> CaCO + 2 NaCl

[0323] Primary net, silicic-acid form:

[0324] Ca2SiO4+ 2 CO2 + 2 H2O 2 CaCO3+ H4SiO4

[0325] Primary net, solid-silica summary (after dehydration of H4SiO4):

[0326] Silica dehydration (primary): H4SiO4 Si02 + 2 H2O

[0327] Net (primary, solid-silica): Ca2SiO4 + 2 CO2 2 CaCO3+ Si02 Secondary NaOH-attack path (base dissolution + CEL regeneration):

[0328] Secondary base attack: Ca2SiO4 + 4 NaOH 2 Ca(0H)2 + Na4SiO4 Secondary Ca carbonation: Ca(0H)2 + CO2 —> CaC0 + H2O Secondary silicate neutralisation: Na4SiO4 + 4 HC1 —> H4SiO4 + 4 NaCl Secondary silica dehydration: H4SiO4 Si02 + 2 H2O

[0329] Secondary net, silicic-acid form (after cancelling NaCl / Na0H / HCl / Na2C03 / Na4Si04 intermediates):

[0330] Ca2SiO4+ 2 CO2 + 2 H2O 2 CaCO3+ H4SiO4

[0331] Secondary net, solid-silica summary (after dehydration):

[0332] Ca2SiO4+ 2 CO2 2 CaCO3+ Si02

[0333] In both the primary (acid-leach) and secondary (NaOH-attack) paths, the closed electrochemical loop implements the same overall calcium-silicate weathering reaction, with NaCl brine and associated sodium species internally recycled and Si02 (or H4SiO4 prior to dehydration) representing the silica coproduct. Note, similar logic can be applied to all Ca silicate species.

[0334] Magnesium Silicate: (Mg Silicate Loop)

[0335] In one embodiment, the worked chemistry for magnesium reforming occurs according to the following reaction sequence:

[0336] Electrolysis: 2 NaCl + 2 H2O 2 NaOH + H2 + CL

[0337] Halogen recombination: H2 + CI2 2 HC1

[0338] Carbonation (NaOH branch): CO2 + 2 NaOH Na2CO3+ H2OPrimary acid-leach path (silicate):

[0339] Leach (Mg, primary): Mg2SiC>4 + 4 HC1 2 MgCL + PLSiCL Precipitation (Mg, primary): Na2CO3+ MgCL —> MgCOsj, + 2 NaCl

[0340] Primary net, silicic-acid form:

[0341] Mg2SiO4 + 2 CO2+ 2 H2O 2 MgCO3+ H4SiO4

[0342] Primary net, solid-silica summary (after dehydration of PLSiCL):

[0343] Silica dehydration (primary): PLSiCL SiCL + 2 H2O

[0344] Net (primary, solid-silica): Mg2SiC>4 + 2 CO2 2 MgCCL + SiCL Secondary NaOH-attack path (base dissolution + CEL regeneration):

[0345] Secondary base attack: Mg2SiC>4 + 4 NaOH 2 Mg(0H)2 + NaiSiCL Secondary Mg carbonation: Mg(0H)2 + CO2 MgCO + H2O Secondary silicate neutralisation: NaiSiCL + 4 HC1 ELSiCL + 4 NaCl Secondary silica dehydration: ELSiCL SiCL + 2 H2O

[0346] Secondary net, silicic-acid form (after cancelling NaCl / Na0EI / HCl / Na2C03 / Na4Si04 intermediates):

[0347] Mg2SiO4 + 2 CO2 + 2 H2O 2 MgCO3+ H4SiO4

[0348] Secondary net, solid-silica summary (after dehydration):

[0349] Mg2SiO4 + 2 CO2 2 MgCO3+ Si02

[0350] In both the primary (acid-leach) and secondary (NaOH-attack) paths, the closed electrochemical loop implements the same overall magnesium-silicate weathering reaction, with NaCl brine and associated sodium species internally recycled and Si02 (or H4SiO4 prior to dehydration) representing the silica coproduct. Note, similar logic can be applied to all Mg silicate species.

[0351] Worked Chemistry Summary (Magnesium Oxide / Hydroxide Branch)

[0352] In one embodiment, the worked chemistry for magnesium reforming occurs according to the following reaction sequence:

[0353] Electrolysis: 2 NaCl + 2 H2O 2 NaOH + H2 + CL

[0354] Halogen recombination: H2 + CI2 2 HC1

[0355] Carbonation (NaOH branch): CO2 + 2 NaOH Na2CO3+ H2O

[0356] Primary acid-leach path (oxide / hydroxide feedstocks)

[0357] For magnesium oxide and magnesium hydroxide feedstocks, the electrochemically generated HC1 converts the solid base into soluble MgCL. which is then carbonated via cation exchange with Na2CO3.

[0358] Leach (MgO, primary):

[0359] MgO + 2 HC1 MgCb + H2O

[0360] Leach (Mg(0H)2, primary):

[0361] Mg(0H)2+ 2 HC1 MgCb + 2 H2O

[0362] Precipitation (Mg, primary):

[0363] Na2CO3+ MgCb MgC0 + 2 NaClPrimary net, oxide feed (after cancelling NaCl / NaOH / HC1 / Na2CO3 / MgCft intermediates):

[0364] MgO + CO2MgCO3

[0365] Primary net, hydroxide feed (after cancelling intermediates):

[0366] Mg(OH)2+ CO2→ MgCO3+ H2O

[0367] In both cases, NaCl, NaOH, HC1, Na2CO3and MgCL function as internal loop reagents, while MgO or Mg(OH)2and CO2 are the net reactants and MgCO3is withdrawn as the solid carbonate product.

[0368] Secondary hydration / direct-carbonation path

[0369] In another embodiment, magnesium oxide is first hydrated to magnesium hydroxide, which is then carbonated directly. This represents a degenerate case of the loop in which the electrochemically generated acid is not required for Mg(OH)2formation (for example, where hydration or upstream processing has already produced Mg(OH)2).

[0370] Secondary hydration:

[0371] MgO + H2O Mg(0H)2

[0372] Secondary Mg carbonation:

[0373] Mg(0H)2+ CO2 MgC0 + H2O

[0374] Secondary net (oxide feed, via hydration):

[0375] MgO + CO2 MgC0

[0376] Secondary net (hydroxide feed, direct):

[0377] Mg(0H)2+ CO2 MgC0 + H2O

[0378] In this secondary embodiment, Mg(OH)2may be provided directly as a feedstock, or generated from MgO by process water, while the electrochemical loop provides additional CO2 capture capacity (via NaOH / Na2CO3) and can be used to condition other streams in an integrated CEL deployment.

[0379] In both the primary (acid-leach) and secondary (hydration / direct-carbonation) paths, the closed electrochemical loop implements the same overall magnesium-oxide / hydroxide weathering reaction, with NaCl brine and associated sodium species internally recycled, and MgCO3representing the durable carbonate product.

[0380] Additional pathways include the following:

[0381] MgCh + 2 NaOH Mg(OH)2( + 2 NaCl

[0382] Mg0-V2) Carbonation (CO2): Mg(0H)2+ CO2 MgC0 + H2O Mg(0H)2(s) + CO32(aq) MgCO3(s) + 2 OH (aq)

[0383] Mg(0H)2(s) + H2CO3(aq) MgCO3(sH + 2 ILO(l)

[0384] Mg(0H)2(s) + Na2CO3(aq) MgCO3(sH + 2 NaOH(aq)

[0385] (Mg-Hyd-1) Mg(0H)2(s) + CO2(aq) + 21^0(1) MgC033H2O(sH

[0386] 5 Mg(0H)2(s) + 4 CO2(aq) + 3 ILOQ) Mg5(C03)4(0H)24H2O(sH 5 MgO(s) + 4 CO2(aq) + 5 ILOQ) Mg5(C03)4(0H)24H2O(s) (Mg-Hyd-gen) Mg2++ CO32+ x H2O MgC03xtLT sH (or) a Mg2++ b CO32+ c OH + d H2O Mga(C03)P(0H)c dH20(sHMg(0H)2 + CO2 MgCOs + H2O (fine as a simplified net)

[0387] Mg(0H)2 + H2CO3 MgCCfi + 2 H2O (fine as simplified net) Mg(0H)2 + Na2CC>3 —> MgCCfi + 2NaOH (metathesis in aqueous, it’s typically represented as Mg2++ CO32MgCC>3(s) with Na+spectator; or via Mg(0H)2(s) + CO32MgCC>3(s) + 2 OH ) Worked Chemistry Summary (Calcium Oxide / Hydroxide Branch)

[0388] In one embodiment, the worked chemistry for calcium reforming occurs according to the following reaction sequence:

[0389] Electrolysis: 2 NaCl + 2 H2O 2 NaOH + H2 + CL

[0390] Halogen recombination: EL + CL 2 HC1

[0391] Carbonation (NaOH branch): CO2 + 2 NaOH Na₂CO₃ + H2O

[0392] Primary acid-leach path (oxide / hydroxide feedstocks)

[0393] For calcium oxide and calcium hydroxide feedstocks, the electrochemically generated HC1 converts the solid base into soluble CaCL, which is then carbonated via cation exchange with Na2CO3.

[0394] Leach (CaO, primary):

[0395] CaO + 2 HC1 CaCL + H2O

[0396] Leach (Ca(0H)2, primary):

[0397] Ca(0H)2+ 2 HC1 CaCL + 2 H2O

[0398] Precipitation (Ca, primary):

[0399] Na2CO3+ CaCL CaCO3+ 2 NaCl

[0400] Primary net, oxide feed (after cancelling NaCl / NaOH / HC1 / Na₂CO₃ / CaCL intermediates):

[0401] CaO + CO2 CaCO3

[0402] Primary net, hydroxide feed (after cancelling intermediates):

[0403] Ca(OH)2+ CO2→ CaCO3+ H2O

[0404] In both cases, NaCl, NaOH, HC1, Na₂CO₃ and CaCL function as internal loop reagents, while CaO or Ca(0H)2 and CO2 are the net reactants and CaCO is withdrawn as the solid carbonate product.

[0405] Secondary hydration / direct-carbonation path

[0406] In another embodiment, calcium oxide is first hydrated to calcium hydroxide, which is then carbonated directly. This represents a degenerate case of the loop in which the electrochemically generated acid is not required for Ca(0H>2 formation (for example, where hydration or upstream processing has already produced Ca(0H)2).

[0407] Secondary hydration:

[0408] CaO + H2O Ca(0H)2

[0409] Secondary Ca carbonation:

[0410] Ca(OH)2+ CO2→ CaCO3+ H2O

[0411] Secondary net (oxide feed, via hydration):

[0412] CaO + CO2 CaCO3Secondary net (hydroxide feed, direct):

[0413] Ca(0H)2+ CO2CaCO3+ H2O

[0414] In this secondary embodiment, Ca(OH)2may be provided directly as a feedstock, or generated from CaO by process water, while the electrochemical loop provides additional CO2 capture capacity (via NaOH / Na2CO3) and can be used to condition other streams in an integrated CEL deployment.

[0415] In both the primary (acid-leach) and secondary (hydration / direct-carbonation) paths, the closed electrochemical loop implements the same overall calcium-oxide / hydroxide weathering reaction, with NaCl brine and associated sodium species internally recycled, and CaCO3representing the durable carbonate product.

[0416] Seawater (MgCL Loop)

[0417] Worked Chemistry Summary (Magnesium Chloride Branch)

[0418] In one embodiment, the worked chemistry for magnesium reforming occurs according to the following reaction sequence:

[0419] Electrolysis: 2 NaCl + 2 H2O 2 NaOH + H2 + CL

[0420] Halogen recombination (optional — not used for leaching here):

[0421] H2 + Ch 2 HC1

[0422] In this embodiment, HC1 is not consumed in the loop and may be treated, stored, or valorised externally (for example, sold, neutralised, or used in an unrelated process).

[0423] Carbonation (NaOH branch):

[0424] CO2 + 2 NaOH Na2CO3+ H2O

[0425] Primary path (direct cation-exchange carbonation)

[0426] Here, MgCL is supplied directly (for example, from seawater RO brine, desal reject, bitterns, process brines, or purchased salts).

[0427] No acid leaching step is required.

[0428] Cation-exchange precipitation:

[0429] Na2CO3+ MgCb MgC0 + 2 NaCl

[0430] Primary net (after cancelling NaCl / NaOH / Na2CO3intermediates):

[0431] MgCb + CO2 + ILO MgC0 + 2 HC1

[0432] But operationally:

[0433] • MgCO3is the captured CO2 product

[0434] • HC1 is generated and leaves the CEL

[0435] The sodium chloride formed in the precipitation reaction is recycled to electrolysis:

[0436] NaCl (regen) back to electrolysis (R-l)

[0437] The loop remains closed on sodium, but open with respect to chloride acidity.

[0438] Secondary pathway (carbonate recycle + external HCl fate)

[0439] In one embodiment, a second variant explicitly recognises that the carbon capture step may run continuously, while HCl is removed from the system.Carbonation:

[0440] CO2+ 2 NaOH Na2CO3+ H2O

[0441] Cation exchange (as above):

[0442] Na2CO3+ MgCb MgC0 + 2 NaCl

[0443] Electrolysis regenerates NaOH and Cl2, creating HC1 that is not used internally:

[0444] Electrolysis:

[0445] 2 NaCl + 2 EO - 2 NaOH + H2+ CL

[0446] Halogen recombination / off-loop use:

[0447] EE + Cl2— 2 HC1 (—> exits system)

[0448] Secondary net (after cancelling sodium species):

[0449] MgCb + CO2+ H20 MgC0 + 2 HC1

[0450] Again:

[0451] • CO2is mineralised as MgCO3

[0452] • HC1 exits the system (off-loop utilisation, storage, or neutralisation)

[0453] • NaCl remains the recyclable working electrolyte

[0454] In both the primary and secondary embodiments of the MgCL loop:

[0455] • Magnesium is supplied directly as MgCE, without the need for mineral or oxide leaching.

[0456] • CO2is absorbed using electrochemically generated NaOH to form Na2CO3.

[0457] • Na2CO3reacts with MgCl2to form solid magnesium carbonate and regenerate NaCl.

[0458] • Electrolysis maintains NaOH production, while HC1 generated in the halogen branch is not consumed in the loop and leaves the system.

[0459] This branch therefore represents a partially open CEL architecture, closed with respect to NaCl but open with respect to HC1, while still implementing durable magnesium-carbonate formation as the carbon-removal step.

[0460] Seawater (CaCE Loop)

[0461] Worked Chemistry Summary (Calcium Chloride Branch)

[0462] In one embodiment, the worked chemistry for calcium reforming occurs according to the following reaction sequence:

[0463] Electrolysis: 2 NaCl + 2 H2O 2 NaOH + H2+ Cl2

[0464] Halogen recombination (optional, not used for leaching here):

[0465] H2+ Ch 2 HC1

[0466] In this embodiment, HC1 is not used to leach calcium feedstocks. It is generated as a coproduct and leaves the system (for example, stored, neutralised, or valorised externally).

[0467] Carbonation (NaOH branch):

[0468] CO2+ 2 NaOH Na2CO3+ ILO

[0469] Primary path (direct cation-exchange carbonation of CaCC)Here, CaCE is supplied directly (for example, from industrial brines, process liquors, or purchased calcium chloride). No HC1 leaching step is applied.

[0470] Cation-exchange precipitation:

[0471] Na2CO3+ CaCE CaCO3+ 2 NaCl

[0472] NaCl formed in this step is recycled to electrolysis as the working electrolyte.

[0473] If electrolysis and NaOH-based CO2 capture are included, and then NaCl / NaOH / Na2CO3intermediates are cancelled, the net transformation of the CaCE branch is:

[0474] Primary net (CaCE loop):

[0475] CaCE + CO2 + H2O CaCO3+ 2 HC1

[0476] Operationally:

[0477] • CaCO3is the solid carbonate product (durable CO2 store).

[0478] • HC1 is generated and exits the loop, not re-used for calcium leaching.

[0479] • NaCl is internally recycled via electrolysis.

[0480] Secondary pathway (continuous carbonate cycle + external HCl fate)

[0481] In some embodiments, a secondary description makes explicit that the carbon capture cycle can run continuously while HCl is removed from the system.

[0482] Electrolysis:

[0483] 2 NaCl + 2 H2O 2 NaOH + H2 + CE

[0484] Carbonation (NaOH branch):

[0485] CO2 + 2 NaOH Na2CO3+ H2O

[0486] Cation exchange (as above):

[0487] Na2CO3+ CaCE CaC0 + 2 NaCl

[0488] Halogen recombination (off-loop acid):

[0489] H2 + CI2 2 HCl (— > exits system; no Ca-leach step)

[0490] After cancelling NaCl, NaOH and Na2CO3, the same net result is obtained:

[0491] Secondary net (CaCE loop, after cancelling sodium species):

[0492] CaCE + CO2 + H2O CaCO3+ 2 HCl

[0493] Again:

[0494] • CO2 is mineralised as CaCO3.

[0495] • HCl is produced as an export acid stream, not consumed in the CEL loop.

[0496] • NaCl is regenerated and fed back to electrolysis, closing the sodium cycle.

[0497] In both the primary and secondary embodiments of the CaCE loop:

[0498] • Calcium is supplied directly as CaCE (for example, from brines or industrial sources), so no HCl leaching of Ca-silicates or Ca-oxides is required.

[0499] • CO2 is captured using electrochemically generated NaOH to form Na2CO3.

[0500] • Na2CO3reacts with CaCE to produce solid CaCO3and regenerate NaCl.• Electrolysis maintains NaOH supply, while the associated halogen branch forms HC1 that is not consumed internally and leaves the system.

[0501] In some embodiments, this defines a partially open CEL configuration: closed with respect to NaCl (NaOH / Na₂CO₃ / NaCl cycle), but open with respect to HC1, while still implementing durable calcium carbonate formation as the carbon-removal step.

[0502] Primary and secondary pathway reaction loop summaries:

[0503] In one embodiment, the worked chemistry for both primary and secondary pathways, by loop, including both silicic-acid and Si02 end-states where applicable are as follows:

[0504] 1. Magnesium Silicate Loop (Mg2SiO4)

[0505] Primary path (acid-leach cation exchange)

[0506] • Primary net, silicic-acid form:

[0507] Mg2SiO4 + 2 CO2 + 2 H2O 2 MgCO3+ H4SiO4

[0508] • Primary net, solid-silica form (after dehydration):

[0509] Mg2SiO4 + 2 CO2 2 MgCO3+ Si02

[0510] Secondary path (NaOH attack Mg(0H)2 CEL regeneration)

[0511] • Secondary net, silicic-acid form:

[0512] Mg2SiO4+ 2 CO2 + 2 H2O 2 MgCO3+ H4SiO4

[0513] • Secondary net, solid-silica form (after dehydration):

[0514] Mg2SiO4+ 2 CO2 2 MgCO3+ Si02

[0515] 2. Calcium Silicate Loop (Ca2SiO4)

[0516] Primary path (acid-leach cation exchange)

[0517] • Primary net, silicic-acid form:

[0518] Ca2SiO4+ 2 CO2 + 2 H2O 2 CaCO3+ H4SiO4

[0519] • Primary net, solid-silica form (after dehydration):

[0520] Ca2SiO4+ 2 CO2 2 CaCO3+ Si02

[0521] Secondary path (NaOH attack Ca(0H)2 CEL regeneration)

[0522] • Secondary net, silicic-acid form:

[0523] Ca2SiO4+ 2 CO2 + 2 H2O 2 CaCO3+ H4SiO4

[0524] • Secondary net, solid-silica form (after dehydration):

[0525] Ca2SiO4+ 2 CO2 2 CaCO3+ Si02

[0526] 3. Magnesium Oxide / Hydroxide Loop (MgO / Mg(0H>2)

[0527] Primary path (acid dissolution MgCL cation exchange)

[0528] • Primary net, oxide feed:

[0529] MgO + CO2 MgCO3• Primary net, hydroxide feed:

[0530] Mg(0H)2+ CO2MgCO3+ H2O

[0531] Secondary path (hydration + direct carbonation)

[0532] • Secondary net, via MgO hydration:

[0533] MgO + CO2 MgCO3

[0534] • Secondary net, direct Mg(OH)2carbonation:

[0535] Mg(OH)2+ CO2→ MgCO3+ H2O

[0536] 4. Calcium Oxide / Hydroxide Loop (CaO / Ca(0H)2) Primary path (acid dissolution CaCL cation exchange) • Primary net, oxide feed:

[0537] CaO + CO2 CaCO3

[0538] • Primary net, hydroxide feed:

[0539] Ca(OH)2+ CO2→ CaCO3+ H2O

[0540] Secondary path (hydration + direct carbonation)

[0541] • Secondary net, via CaO hydration:

[0542] CaO + CO2 CaCO3

[0543] • Secondary net, direct Ca(0H)2carbonation:

[0544] Ca(OH)2+ CO2→ CaCO3+ H2O

[0545] 5. Magnesium Chloride Loop (MgCL)

[0546] (Direct MgCL feed; no HC1 leaching, HC1 exits the system.) Primary path (Na2C03-MgC12 cation exchange)

[0547] • Primary / loop net:

[0548] MgCb + CO2 + H2O MgCO3+ 2 HC1 Secondary path (same chemistry, different operational framing) • Secondary net (after cancelling sodium species):

[0549] MgCb + CO2 + H2O MgCO3+ 2 HC1

[0550] 6. Calcium Chloride Loop (CaCL)

[0551] (Direct CaCL feed; no HC1 leaching, HC1 exits the system.) Primary path (Na2CO3-CaC12 cation exchange)

[0552] • Primary / loop net:

[0553] CaCL + CO2 + H2O CaCO3+ 2 HC1 Secondary path (same chemistry, different operational framing) • Secondary net (after cancelling sodium species):

[0554] CaCL + CO2 + H2O CaCO3+ 2 HC1The above provides a compact catalogue of net reactions for different branches, with both H₄SiO₄ and SiO₂ end-states explicitly captured where silicates are involved, and clean oxide / chloride nets where they are not.

[0555] In some embodiments, both primary and secondary pathways can be combined as necessary to balance the system and minimize ions leaving the system boundary (e.g. the objective of the loop is to minimize volatile ions leaving with most ion species conserved within the loop).

[0556] Operating Environment Embodiments

[0557] In some embodiments, operating conditions and examples of implementation of the CEL are as follows:

[0558] In practice, the electrochemical / electromineral loop can be operated over a range of temperatures, pressures, and gas compositions, which influence both reaction rate and the identity of the resulting carbonate polymorphs.

[0559] In various embodiments, the carbonation and cation-exchange steps are conducted at:

[0560] • temperatures from about 0 °C to about 200 °C, preferably from about 20 °C to about 150 °C, more preferably from about 40 °C to about 120 °C;

[0561] • total pressures from about 0.000001 bar to about 100 bar and at the upper limit approximately 300bar, preferably from about 0.1 bar to about 80 bar; and

[0562] • carbon dioxide partial pressures from about 0.0-1 bar to about 30 bar, preferably from about 0.1 bar to about 74 bar.

[0563] The aqueous phase pH in the carbonation zone is typically maintained between 8 and 14, and in many embodiments between 10 and 12 to favour CO32−over HCO3−, while the leach and acid neutralisation zones may be operated at lower pH, for example pH < 4, to keep chloride salts of Ca, Mg, Fe, or Al in solution prior to cation-exchange.

[0564] The foregoing CEL chemistry permits formation of different carbonate polymorphs depending on temperature, supersaturation, and residence time. For calcium, the precipitated CaCO3may be one or more of calcite, aragonite, vaterite, amorphous calcium carbonate, or mixtures thereof. For magnesium, the precipitated MgCO3phase may be magnesite and / or hydrated polymorphs such as nesquehonite, hydromagnesite, dypingite, artinite, or related basic magnesium carbonates. In some embodiments, the process conditions (including but not limited to temperature, CO2 partial pressure, seed mineralogy, ionic strength and additives) are selected to favour formation of low-solubility, thermodynamically stable phases such as magnesite; in other embodiments, the process is operated to deliberately produce hydrated or amorphous phases that are more reactive or better suited to downstream product applications (for example, fillers or binders).

[0565] Similarly, in some embodiments the carbonation step is carried out under elevated pCO2(for example in a pressurised gas–liquid contactor) to accelerate CO2uptake and promote denser polymorphs, whereas in other embodiments the carbonation is performed at or near atmospheric pressure using flue gas, directair capture gas, or biogas as the CO2 source, with longer residence time compensating for the lower driving force.

[0566] Separation and conditioning operations (for example, solid-liquid separation, washing, ageing, and thermal or hydrothermal treatment) may be used to transform metastable carbonate phases into more stable polymorphs. For instance, hydrated magnesium carbonates formed at lower temperature can be aged, heated, or recarbonated to increase magnesite content, and amorphous or vateritic CaCO3can be converted to calcite.

[0567] CEL Process Architecture

[0568] In various embodiments, the process of the present disclosure is configured such that the principal intentional mass export is stable solid carbonate, while halide ions are substantially retained and recycled within the loop as a circulating electrolyte.

[0569] In preferred embodiments, the defining boundary condition of the system is that reactive ionic species, including alkali metal cations and halide anions, are substantially retained and recycled within a circulating electrolyte inventory, while exported products comprise predominantly electrically neutral, geochemically stable carbonate solids and benign co-products. The system is configured such that reactive ionic species are substantially retained within a recirculating electrolyte inventory, while exported outputs are primarily electrically neutral and stable products, thereby maintaining ionic balance across the system boundary.

[0570] Conventional alkaline scrubbing systems based on sodium hydroxide operate by consumptive use of alkali, requiring continuous external chemical supply and lacking any integrated electrochemical regeneration loop to restore reagent capacity. Chlor-alkali processes, while electrochemical in nature, are fundamentally directed toward the production and export of commodity chemicals such as chlorine, hydrogen, and sodium hydroxide, and are not configured as closed-loop systems for the mineralisation and permanent fixation of carbon dioxide. Traditional mineral carbonation approaches typically rely on singlepass consumption of alkaline minerals or industrial residues, without regeneration of reactive equivalents or maintenance of a recirculating electrolyte framework. Likewise, solvent-based direct air capture systems employ organic sorbents or aqueous amine solutions in which carbon dioxide is reversibly bound and subsequently released, rather than being converted into stable solid carbonate. In contrast, the systems and methods described herein integrate electrochemical regeneration of acidity and alkalinity with mineral dissolution, carbonate formation, and electrolyte recycle within a mass-balanced loop in which carbon dioxide is permanently exported as solid carbonate while halide electrolyte species are substantially retained and reused.

[0571] In contrast, various aspects and embodiments of the present disclosure involve a continuously operating, electrochemically driven mineral carbonation system configured as an integrated, mass- and charge-balanced process loop. Electrical energy is supplied to an electrochemical unit that regenerates reactive acidity and alkalinity from a circulating aqueous halide electrolyte, such as a sodium chloride brine, with these reactive equivalents being internally consumed within the process rather than exported asprimary products. The regenerated alkaline stream is contacted with a carbon dioxide-containing gas to absorb CO2 and convert it into dissolved carbonate and / or bicarbonate species under controlled pH conditions. In parallel, the regenerated acidic stream is directed to a mineral reaction zone where it dissolves alkaline earth-bearing minerals to release divalent cations into solution. Dissolved carbonate species and divalent cations are subsequently combined in a precipitation zone to form solid carbonate material, which constitutes the principal intentional mass export of carbon dioxide from the system. Following separation of the carbonate solids, the remaining aqueous phase is subjected to electrolyte purification and conditioning steps that remove accumulated impurities while retaining the halide salt. The conditioned electrolyte is then recycled to the electrochemical unit, such that halide ions function primarily as internal ionic carriers and are substantially retained within the loop, thereby maintaining continuous operation with electrolyte recycle and minimal net halide loss.

[0572] In some embodiments, the system is implemented as an integrated, modular process plant comprising interconnected fluid-processing units arranged to form a substantially closed electrochemicalmineral loop. The plant may for example include an electrochemical unit configured to regenerate acidic and alkaline streams from a circulating halide electrolyte; a carbon dioxide capture unit configured as a gas-liquid contactor for absorbing CO2 into an alkaline liquor; a mineral reaction section comprising one or more mineral feedstock activation reactors, and precipitation vessels for producing alkaline earth metal hydroxides and / or carbonates; a solids separation and finishing section for recovering stable carbonate solids; an electrolyte conditioning and recycle section for removing impurities while retaining halide salts; and a halogen-management module configured to absorb, convert, and redox-condition halogen species prior to electrolyte return.

[0573] Fluid transfer between these units can for example be achieved using corrosion-resistant pumps, pipelines, and manifolds arranged in closed-loop recirculation circuits. Gas streams may be routed through blowers or induced-draft fans to scrubbers and absorbers, while liquid streams are directed through heat exchangers, filters, membrane units, and mixing vessels as required. Each major unit operation may be housed within a skid-mounted or containerised module to allow transportable or distributed deployment, with inter-module connections provided by flexible hoses or flanged piping. The system may include instrumentation and control hardware comprising pH, conductivity, temperature, pressure, flow, and oxidation-reduction potential sensors, which are connected to an automated control system configured to regulate dosing, recycle rates, and electrochemical operating conditions to maintain ionic balance and halide retention within the loop. In this architecture, the principal intentional mass export of the plant is stable solid carbonate product, while the aqueous halide electrolyte is continuously conditioned and recycled as an internal ionic working fluid.

[0574] Closed Electrochemical Loop and Mineral Carbonation Process

[0575] As used herein, “Closed Electrochemical / Electromineral Loop (CEL)” refers to a process architecture in which electrochemically generated acidity and alkalinity are regenerated within a circulatingelectrolyte inventory and used to convert carbon dioxide into stable carbonate solids while substantially retaining reactive ionic species within the system boundary.

[0576] In preferred embodiments, the present disclosure comprises a continuously operating, electrochemically driven mineral carbonation system configured as a mass-balanced, ionically closed process loop with halide retention.

[0577] Electrical energy is supplied to an electrochemical unit that regenerates reactive acidity and alkalinity from a circulating aqueous halide electrolyte, such as sodium chloride brine. The halide electrolyte functions primarily as an internal ionic carrier and charge -balancing medium rather than being consumed as a net reagent.

[0578] The regenerated alkaline stream is directed to a gas-liquid contactor, where carbon dioxide is absorbed and converted into dissolved carbonate and / or bicarbonate species under controlled pH conditions. In parallel, the regenerated acidic stream is delivered to a mineral reaction zone, where it dissolves alkaline earth-bearing mineral feedstocks to release divalent cations into solution.

[0579] Dissolved carbonate species and divalent cations are subsequently combined in a precipitation zone to form solid carbonate material, which constitutes the principal form in which carbon dioxide is permanently exported from the system.

[0580] Following carbonate separation, the remaining aqueous phase, comprising predominantly monovalent ions such as sodium and chloride, is routed through electrolyte conditioning and purification steps that remove accumulated impurities while retaining the halide salt. The conditioned electrolyte is then recycled to the electrochemical unit as regenerated brine feed, forming a continuous circulation loop.

[0581] Reactive acid and base equivalents generated electrochemically are predominantly consumed internally in carbon dioxide absorption, mineral dissolution, carbonate formation, and electrolyte conditioning reactions, rather than being withdrawn as external chemical products.

[0582] The system boundary is defined such that the principal intentional mass export is stable solid carbonate formed from captured carbon dioxide, while halide ions remain substantially within the process and are continuously recycled, with only minor purge streams permitted for impurity management. Monovalent ions such as sodium and chloride therefore function primarily as internal charge-balancing and transport species.

[0583] Electrical energy supplied to the electrochemical unit is effectively stored in chemical form as acid and base equivalents which are used to generate stable, mineralised carbonate carbon through continuous cyclic loop operation.

[0584] The present disclosure is not directed to a reagent supply system in which externally produced chemicals are consumed in a single pass, nor to a process in which alkalinity or mineral reactivity is irreversibly depleted. Instead, it provides a regenerating electrochemical-mineral process architecture in which acidity and alkalinity are continuously regenerated from a circulating electrolyte and used predominantly within the system to drive carbon dioxide conversion and mineral reactions.The present system integrates electrochemical regeneration, mineral reaction, carbonation, and electrolyte recycle into a single ionically closed loop in which reagents are regenerated internally, halides are retained and recycled, and carbon dioxide is permanently converted into stable inorganic carbonate solids.

[0585] Disclosed herein in certain aspects and embodiments is a continuously operating, electrochemically driven, ionically closed mineral carbonation loop where halides are retained and recycled and CO2 is permanently exported as solid carbonate. Such a system provides a continuously operating, regenerating electrochemical-mineral process architecture configured to convert carbon dioxide into stable solid carbonate materials while maintaining an ionically closed internal loop. Electrical energy is supplied to an electrochemical unit that regenerates reactive acidity and alkalinity from a circulating halide electrolyte. These regenerated species are predominantly consumed within the system: alkalinity is used to absorb carbon dioxide and form dissolved carbonate species, while acidity is used to dissolve alkaline earthbearing mineral feedstocks and liberate divalent cations. The dissolved carbonate species and divalent cations are then combined under controlled conditions to precipitate stable carbonate solids, which constitute the principal form in which carbon dioxide is permanently exported from the process. The remaining aqueous phase, comprising primarily monovalent halide salts, is subjected to conditioning and purification steps and is recycled to the electrochemical unit, such that halide ions function as internal charge-balancing carriers and are substantially retained within the system boundary. Through this integration of electrochemical regeneration, carbon dioxide absorption, mineral reaction, carbonate precipitation, and electrolyte recycle, the invention establishes a continuous, cyclic carbon conversion loop in which electrical energy is stored in mineralised carbon while ionic species are maintained in circulation, distinguishing the process from consumptive scrubbing systems, single-pass mineral carbonation, and electrochemical plants designed for export of chemical reagents.

[0586] The electrochemical regeneration architecture and the carbonation reactor may be deployed either together at a single site or separately at distributed locations while maintaining a conserved circulating electrolyte inventory. In some embodiments, the carbonation unit is deployed independently and supplied with alkaline or divalent feeds, including hydroxide-bearing materials (e.g., brucite), divalent alkaline solutions, or anion absorbents (e.g., sodium hydroxide), for local CO2 absorption prior to downstream processing. In certain configurations, absorption and / or mineral-activation units operate at distributed emission sites and carbonate -bearing liquor is transported to a centralised facility for precipitation, mineral regeneration, and brine recirculation, whereas in other configurations the electrochemical cell, absorber, mineral-activation unit, carbonation reactor, halogen-management module, and brine loop are co-located at a single industrial site. The system may also be coupled to direct air capture units and optionally to in-situ mineralisation via introduction of carbonate-bearing intermediates into subsurface formations containing reactive minerals, thereby enabling combined ex-situ and in-situ mineralisation pathways while preserving the closed electrochemical / electromineral loop. In some embodiments, magnesium hydroxide produced by the process is supplied to a stirred reactor configured to contact a carbon dioxide-containing gas stream,such as emissions from a water treatment facility via a brucite spear, to produce magnesium carbonate. In further embodiments, sodium hydroxide produced by the process is supplied to distributed emission sources, such as generator sets, or DAC modules for carbon dioxide capture, with recovered carbonate optionally collected in an anhydrous form for use in cementitious or geopolymer materials and / or returned for centralised processing.

[0587] In some embodiments, carbonate or bicarbonate species formed by contacting carbon dioxide with the electrochemically generated alkaline stream, wherein the carbon dioxide is derived from a point source gas stream (e.g., flue gas, process exhaust, or biogas) and / or from atmospheric air in a direct air capture (DAC) configuration may be subjected to acidification within the process boundary, including reaction with hydrochloric acid or other acidity generated from the halide electrolyte, thereby lowering pH and releasing carbon dioxide gas while regenerating a halide-containing brine suitable for recycle to the electrochemical unit; in this manner, acidity produced during electrochemical operation is consumed to convert carbonate species back to carbon dioxide while restoring the circulating electrolyte inventory for continued loop operation and maintaining the substantially closed-loop condition with respect to alkali metal and halide ions, and the released carbon dioxide may be recovered as a compressed gas stream, utilised in downstream industrial processes, or transported for injection into subsurface geological formations (including saline aquifers, depleted hydrocarbon reservoirs, basaltic formations, or other storage sites beneath an impermeable cap rock), enabling durable carbon storage while reactive ions remain substantially retained within the circulating electrolyte inventory of the closed electrochemical loop, and in some embodiments, the carbon dioxide may remain present as dissolved carbonic species in solution and be injected into subsurface formations and / or used in further processing.

[0588] Closed Electrochemical-Mineral Carbonation Process

[0589] Various aspects described herein share a common inventive architecture: an electrochemically regenerated, internally conserved ionic loop that continuously converts carbon dioxide and mineral feedstocks into stable carbonate solids while retaining halide electrolyte species within the process boundary.

[0590] In various embodiments, the systems and processes described herein operate according to a closed electrochemical / electromineral loop (CEL) architecture. In this architecture, an electrochemical unit regenerates alkalinity and acidity within a circulating electrolyte inventory; carbon dioxide is converted using the regenerated alkalinity into carbonate and / or bicarbonate species; divalent cations are supplied from a mineral feedstock, brine, or other cation source; carbonate species are converted into solid carbonate materials; and the working electrolyte is regenerated and recirculated while carbonate is withdrawn as a substantially electrically neutral export stream.

[0591] In this manner, alkali metal ions and halide ions are substantially retained within the circulating electrolyte inventory on an equivalent basis, while carbon is removed from the system primarily in the form of solid carbonate. The electrochemical unit maintains a pH gradient and regenerates reactive equivalentsthat drive carbonate formation and mineral activation, while downstream precipitation and separation steps restore the electrolyte composition for reuse.

[0592] The CEL therefore couples electrochemical regeneration, CO2 speciation control, mineral activation, carbonate precipitation, and electrolyte recycle into a coordinated sequence. These steps are not independent but are operated in a mass- and charge -balanced manner such that the system can function continuously or semi -continuously with reduced or avoided discharge of halide -containing waste streams.

[0593] In certain embodiments of the Closed Electrochemical / Electromineral Loop (CEL), processing of concentrated brines or bittern streams may introduce a temporary imbalance in halide inventory due to the high chloride content of the feed. In such cases, the loop may operate in a condition that is transiently open with respect to halides during the brine-processing step, while remaining substantially closed over the full operating cycle through coordinated mineral reactions that restore ionic balance.

[0594] Halogen management is achieved by coupling brine electrolysis with mineral-based neutralisation and precipitation reactions that convert reactive halogen-bearing species into recycled electrolyte or inert products while preserving the CEL boundary condition that reactive ions are retained and recycled and only stable carbonate solids leave the system.

[0595] In some embodiments, magnesium-rich brine bitterns are processed with electrochemically generated alkali metal hydroxide to precipitate magnesium hydroxide (brucite) according to:

[0596] MgCl2+ 2NaOH → Mg(OH)2(s) + 2NaCl

[0597] The resulting alkali metal chloride is returned to the electrochemical unit for regeneration, thereby maintaining the circulating electrolyte inventory. The precipitated magnesium hydroxide may subsequently react with carbon dioxide to form stable magnesium carbonate materials for export from the system.

[0598] Hydrochloric acid generated in the electrochemical step is preferentially neutralised using alkaline earth metal-bearing minerals, including magnesium- or calcium -containing silicates, oxides, or hydroxides. Suitable materials include naturally occurring brucite, serpentine -group minerals, magnesium oxide residues, or brucite-bearing tailings such as those produced during nickel laterite processing. Neutralisation of excess hydrochloric acid using such minerals converts reactive halogen species into metal chlorides that are recycled within the loop while simultaneously activating divalent cations for downstream carbonation. Where seawater is used as a magnesium source, the relatively low magnesium concentration (approximately 1.26 g / L) may limit process efficiency; therefore, higher-concentration sources such as brine bitterns or magnesium-rich tailings are preferred. These feedstocks enable reduced reagent consumption, improved operating economics, and more effective halogen management due to their higher divalent metal content. In certain embodiments, mineral addition is controlled to offset any deficit in divalent cations created during brine processing, thereby restoring ionic balance and maintaining the substantially closed-loop condition with respect to halides and alkali metals. Magnesium carbonate formation may therefore derive both from magnesium recovered from brine and from supplemental mineral feedstock, enabling continuous operation without net accumulation of reactive halogen species.Accordingly, halogen management within the CEL may be accomplished through coordinated electrochemical regeneration, mineral neutralisation, and carbonate precipitation reactions that maintain ionic closure while producing stable carbonate solids as the primary exported product.

[0599] Closed Electrochemical Loop (CEL) Integrated Process Architecture

[0600] In various embodiments, the systems described herein operate as a closed electrochemical-mineral conversion loop (CEL) in which electrochemical regeneration of alkalinity and acidity is continuously coupled to carbon dioxide capture, mineral conversion, carbonate precipitation, and electrolyte recycle within a single mass- and charge-balanced process boundary.

[0601] Within this architecture:

[0602] 1. An electrochemical unit regenerates reactive equivalents

[0603] A circulating electrolyte containing alkali metal halide (e.g., NaCl) is supplied to an electrochemical unit. Electrical energy drives separation of ionic species, producing:

[0604] o an alkaline stream containing hydroxide equivalents, and

[0605] o an acidic stream containing acidity equivalents.

[0606] These streams are not exported as final products but are internally consumed to drive downstream carbonation and mineral conversion reactions.

[0607] 2. Carbon dioxide is converted to dissolved carbonate species

[0608] The regenerated alkaline stream is contacted with a CO2-containing gas stream. Under controlled pH and contacting conditions, CO2 is absorbed and converted to dissolved carbonate and / or bicarbonate species.

[0609] Electrical work supplied to the electrochemical unit is stored chemically as alkalinity that is subsequently converted into bound carbonate.

[0610] 3. Divalent cations are liberated from mineral or brine sources

[0611] The regenerated acidic stream is reacted with a magnesium- and / or calcium-containing feedstock (e.g., hydroxides, oxides, silicates, residues, brines, or concentrates), dissolving divalent cations into solution.

[0612] This step converts solid or sparingly soluble mineral phases into soluble cation species suitable for carbonate precipitation.

[0613] 4. Carbonate is transferred from the electrolyte into solid mineral form

[0614] Dissolved divalent cations react with dissolved carbonate species to form sparingly soluble carbonate solids.

[0615] During this reaction, alkali metal and halide ions are returned to solution, thereby regenerating the working electrolyte.

[0616] 5. Carbonate solids are removed as the primary material export

[0617] The precipitated carbonate is separated from the electrolyte as a solid product. This solid constitutes the principal pathway by which carbon leaves the system boundary.6. Electrolyte is conditioned and recycled to the electrochemical unit

[0618] The remaining liquor, now enriched in regenerated alkali metal halide, is clarified and conditioned to remove suspended solids and excess multivalent ions. The conditioned brine is returned to the electrochemical unit, completing the loop.

[0619] Closed Electrochemical Loop Architecture and Operational Invariants

[0620] Functional Invariants of the CEL

[0621] Across these steps, the CEL maintains the following system-level invariants:

[0622] • Electrochemical regeneration replaces thermal regeneration

[0623] Alkalinity and acidity required for carbonation and mineral activation are regenerated electrically rather than by high-temperature calcination.

[0624] • Internal carrier species are conserved

[0625] Alkali metal ions and halide ions circulate within the loop as electrolyte carriers. These species are not consumed in net and are substantially retained within the system boundary.

[0626] • Carbon is exported in electrically neutral solid form

[0627] Carbon dioxide entering the system is converted to stable carbonate solids that are removed from the loop, while charge-bearing electrolyte species remain in circulation.

[0628] • The process operates as a coupled ionic loop, not independent unit operations

[0629] The electrochemical unit, carbonation reactor, mineral dissolution reactor, precipitation system, and brine conditioning train operate in coordinated balance. Flows of alkalinity, acidity, cations, and carbonate are interdependent and regulated to maintain ionic closure.

[0630] Operational Process Description of a Closed Electrochemical Carbonate Production Loop

[0631] The following describes a canonical CEL operational sequence for a brucite embodiment. Variants for other mineral feedstocks (including silicates) are provided as described above. Although unit operations may be modified for different feeds, the CEL architecture and ionic-closure logic remain the same.

[0632] Step 1. Electrochemical Splitting of Brine

[0633] Step 1 generates alkalinity and acidity equivalents for internal use within the CEL and may be implemented using multiple electrochemical architectures. In addition to chlor-alkali electrolysis, acidity and alkalinity suitable for CO2 capture and mineralisation may be generated using other electrochemical and mineral activation architectures including, without limitation, bipolar membrane electrodialysis (BMED / EDBM), electrodialysis, electro-deionisation, membrane electrolysis, and electrochemical water splitting configurations that generate hydroxide at a cathode and acid at an anode. These approaches may reduce or avoid the handling of chlorine gas, enable operation with mixed-salt brines (e.g., seawater, RO reject, or industrial brines), and support closed-loop recycling of ionic species.

[0634] In one embodiment, the electrochemical unit comprises a chlor-alkali membrane electrolyser configured to generate separate acid and base product streams for use within the closed electrochemical loop (CEL). A purified brine solution comprising an aqueous sodium chloride feed is introduced into an anode compartment of the electrochemical cell. When a direct current is applied across the electrodes,electrolysis of the brine occurs, resulting in separation of ionic species and evolution of gaseous products according to established electrochemical half-reactions.

[0635] At the anode, chloride ions in the brine are oxidised to produce chlorine gas according to the halfreaction:

[0636] 2Cl~ -> Cl2(g) + 2e~

[0637] (Rla)Chlorine gas evolved at the anode is collected separately from other products of the cell. At the cathode, water is reduced to produce hydrogen gas and hydroxide ions according to the halfreaction:

[0638] 2H2O + 2e~ -> H2(g) + 2OH~ (Rib) Hydrogen gas evolved at the cathode is similarly collected.

[0639] A cation-exchange membrane disposed between the anode and cathode compartments permits selective transport of sodium cations (Na+) from the anolyte to the catholyte while substantially restricting the transport of chloride (Cl−) and hydroxide (OH ) ions. Suitable membranes include perfluorinated sulfonic acid membranes such as Nafion® or equivalent ion-permeable polymers that tolerate high current densities, elevated temperatures, and corrosive environments typical of membrane chlor-alkali cells. In the cathode compartment, sodium cations that migrate through the membrane combine with the generated hydroxide ions to form aqueous sodium hydroxide (NaOH). The sodium hydroxide solution may be withdrawn from the cathode compartment as a product stream for use in downstream unit operations of the CEL.

[0640] The overall stoichiometric reaction for membrane electrolysis of aqueous sodium chloride brine is: 2NaCl(aq') + 2H2O(l) -> 2NaOH aq) + Cl2(g) + H2(g) (Rl) This net transformation represents production of sodium hydroxide, chlorine gas, and hydrogen gas in a membrane cell configuration, which is the current industrial standard for chlor-alkali electrolysis due to energy efficiency and improved product purity relative to diaphragm or mercury processes.

[0641] Electrode materials in such electrochemical cells are selected for corrosion resistance and catalytic activity in the respective half-reactions. In industrial membrane electrolysers, anodes typically comprise a titanium substrate coated with mixed metal oxide (MMO) catalysts configured for the chlorine evolution reaction, while cathodes typically comprise corrosion-resistant metals that are compatible with alkaline environments that facilitate the hydrogen evolution reaction. A plurality of anode and cathode pairs may be arranged within a stack to achieve desired production capacity and distribution of current density.

[0642] In preferred embodiments, the electrolyser is operated at average cell voltages of 3.0-3.6 V and current densities of 3-5 kA / m2, consistent with commercial practice and achieving high Faradaic efficiency (>90%) for conversion of brine to sodium hydroxide, chlorine gas, and hydrogen gas.

[0643] In embodiments in which the evolved chlorine gas and hydrogen gas are captured and reacted, the gases may be forwarded to an integrated synthesis reactor, where they are combined under controlled catalytic, thermal, or photocatalytic conditions to form hydrogen chloride (HC1). The resulting hydrogen chloride gas is absorbed into water to produce aqueous hydrochloric acid. Alternatively, in embodimentsemploying bipolar membrane electrodialysis (BMED), acid and base streams may be generated directly in situ without requiring external gas recombination reactors. The resulting HC1 solution is collected and stored in a stock tank for subsequent utilisation in downstream processing steps of the CEL.

[0644] Step 2. Carbonation of Process Derived Alkalinity.

[0645] In one embodiment, a sodium hydroxide-rich alkaline stream generated in Step 1 is contacted with a CCE-containing gas stream derived from flue gas, biogas, direct-air capture (DAC), engine exhaust, or other process gas streams. Contacting occurs in a carbonation reactor configured to promote dissolution of carbon dioxide into the alkaline liquid phase, hydration to acid dissociation species, and neutralisation with hydroxide ions under elevated pH conditions selected to favour formation of dissolved carbonate and / or bicarbonate species. Typical operating conditions include gas-liquid contacting at pressures up to about 20 bar and temperatures up to about 150 °C, with pH control above about pH 10 to bias speciation toward carbonate (CO? ) in the aqueous phase.

[0646] Dissolved CO2 participates in aqueous carbonate equilibria according to the following reactions: CO2+ H2O H2CO3(El)

[0647] H2CO3HC03~ + H+(E2)

[0648] HCO3-↔ CO32-+ H+(E3)

[0649] Under alkaline conditions, the hydroxide species react with dissolved CO2 to form carbonate species and / or bicarbonate species:

[0650] 2NaOH + CO2→ Na2CO3+ H2O (R2)

[0651] NaOH + CO2→ NaHCO3(R2a)

[0652] Formation of carbonate (CO? ) is favoured at high pH (e.g., >10), whereas bicarbonate (HCOs ) formation predominates under more moderate alkaline conditions.

[0653] In embodiments directed to direct carbonation of divalent-cation hydroxides, basic magnesium hydroxide (Mg(OH)₂) and / or calcium hydroxide (Ca(OH)₂) may be contacted directly with a CO2-containing gas stream to produce respective solid carbonate products. In such embodiments, the reactions proceed according to well-recognised mineral carbonation chemistry:

[0654] Mg(OH)2+ CO2→ MgCO3+ H2O

[0655] Ca(OH)2+ CO2→ CaCO3+ H2O

[0656] Direct carbonation of Mg(OH)₂ or Ca(OH)₂ thus converts gaseous CO₂ into sparingly soluble carbonate solids while consuming hydroxide equivalents provided by the electrolyte or by external sources. Mineral carbonation of Mg(OH)₂ and Ca(OH)₂ is a known pathway in engineered sequestration and materials synthesis contexts.

[0657] In representative alkaline capture embodiments where NaOH is the primary anionic counter-ion, the alkaline sodium carbonate or sodium bicarbonate liquor produced in the carbonation reactor may be directed to a mineral dissolution unit or to further carbonation stages. Specifically, the carbonate -rich liquor may be routed to (a) a mineral dissolution unit configured to liberate divalent cations by contacting silicates,oxides, hydroxides, brines, residues, or other feedstocks with an acidic stream, or (b) a carbonation reactor configured to combine dissolved divalent cations with carbonate species to form sparingly soluble solid carbonate products.

[0658] Carbonation Process Control and Operating Logic

[0659] In some embodiments, the carbonate-rich liquor produced by these reactions effectively converts electrical work invested in hydroxide generation into carbonate formation without requiring thermal regeneration or high-pressure CO2 compression and permits downstream valorisation of carbonate species as captured carbon products.

[0660] In certain embodiments, control of carbonate versus bicarbonate formation is implemented by selecting and modulating (i) CO2 partial pressure in the feed gas, (ii) gas-liquid contacting intensity and residence time, and (iii) liquid alkalinity and pH. In some embodiments, operation at relatively low CO2 partial pressures, including low CO2 partial pressures (e.g., ambient air) and intermediate concentrations (e.g., several vol% CO2, may be preferred to promote conversion under strongly alkaline conditions in a manner that favours carbonate formation. Higher CO2 concentrations may also be employed; in such embodiments, the system may be operated at reduced effective contact time and / or reduced liquid alkalinity to maintain a selected carbonate / bicarbonate speciation. A mixed carbonate and bicarbonate liquor is acceptable and, in some embodiments, is preferred depending on downstream precipitation, transport, or product requirements.

[0661] In a non-limiting control scheme, the carbonation reactor comprises an alkaline wet contactor (e.g., a packed column, spray column, structured packing contactor, or wetted-wall contactor) configured to provide high gas-liquid interfacial area using fouling-resistant packing or equivalent contacting internals. Process monitoring may include measurement of CO2 concentration in the treated gas outlet (e.g., via NDIR or other CO2 sensor) and measurement of liquid pH in the circulating alkaline liquor.

[0662] In some embodiments, the carbonation reactor is operated such that the CCh-containing gas stream is contacted with the alkaline solution until a high degree of CO2 removal is achieved, for example a reduction of the CO2 concentration in the outlet gas corresponding to an overall conversion on the order of about 90% to about 99%, subject to gas composition, flow rate, and contacting conditions. During operation, the outlet CO2 concentration may remain low or substantially stable until the available alkalinity in the circulating liquor becomes depleted, at which point the outlet CO2 concentration rises.

[0663] Accordingly, in one illustrative control logic, when the outlet CO2 concentration rises above a selected threshold (optionally sustained for an averaging period of approximately 1 to 5 minutes to avoid false triggering due to flow perturbations), the carbonation liquor is partially or fully discharged from the contactor sump or holding tank and replaced with fresh alkaline feed (or supplemented by make-up hydroxide), thereby restoring capture capacity. In parallel or alternatively, pH is used as a state variable for alkalinity depletion, wherein fresh feed may exhibit pH values in the range of approximately 12.5 to 14, and spent or partially spent liquors may exhibit pH values in the range of approximately 8 to 12.5, depending on carbonate / bicarbonate speciation and ionic strength. In some embodiments, when the pH fallsinto a selected lower band and / or the outlet CO2 concentration rises above threshold, the liquor is discharged and replenished.

[0664] In alternative embodiments, rather than full discharge, the reactor is operated in a semi -continuous or continuous mode by periodic bleed-and-feed or continuous top-up of alkaline feed, wherein outlet CO2 concentration and pH act as feedback control variables to adjust one or more of: (i) alkaline feed rate or concentration, (ii) recycle flow rate, (iii) gas flow rate, (iv) contacting intensity, and / or (v) discharge / bleed rate, thereby maintaining a selected CO2 removal performance and a selected carbonate / bicarbonate composition of the produced liquor.

[0665] In preferred embodiments, the contacting column is temperature-controlled (e.g., about 35 °C when using NaOH) to reduce precipitation and fouling within the packing and associated internals and may include heat exchange to maintain selected operating temperature.

[0666] Antifouling geometries for both random packing and trayed column configurations are employed.

[0667] Step 3. Mineral Dissolution and Cation Exchange Reactions

[0668] The third step of the closed electrochemical loop (CEL) process comprises liberation of divalent cations from a mineral feedstock and subsequent carbonate formation, thereby regenerating the working electrolyte. Brucite (magnesium hydroxide, Mg(0H)2) is used herein as an illustrative embodiment; however, other oxide, hydroxide, or silicate minerals may be used.

[0669] Primary and secondary reactions may occur in tandem within the mineral dissolution / cation exchange reactor, depending on local pH, reagent distribution, residence time, and gas-liquid-solid contacting.

[0670] In representative embodiments, magnesium hydroxide derived from mineral processing residues, flotation concentrates, tailings, or synthetic sources is introduced as a powder or slurry into the reactor. Streams comprising hydrochloric acid from Step 1 and carbonate -containing liquor and / or dissolved CO2 from Step 2 are also introduced.

[0671] Acid Dissolution of Mineral Feedstock

[0672] An acidic stream generated in Step 1 (for example aqueous hydrochloric acid formed via recombination of electrolytically produced hydrogen and chlorine, or produced via BMED) is introduced into the mineral dissolution reactor. The acid reacts with magnesium hydroxide to liberate soluble magnesium cations:

[0673] Mg(OH)2+ 2HCI -> MgCl2+ 2H2O (8)

[0674] This step converts solid-phase magnesium hydroxide into a soluble magnesium salt, enabling subsequent carbonate formation.

[0675] Carbonate Formation via Cation Exchange

[0676] A carbonate-containing stream produced in Step 2 (for example an aqueous sodium carbonate and / or sodium bicarbonate solution formed by reaction of NaOH with CO2) is also introduced into the reactor. Dissolved magnesium ions react with carbonate ions to form solid magnesium carbonate while regenerating sodium chloride:MgCl2+ Na2CO3→ MgCO3(s) + 2NaCl (9)

[0677] This reaction transfers carbonate from the sodium phase to a solid divalent carbonate product, while returning sodium chloride to solution. The regenerated NaCl solution constitutes working electrolyte that can be recycled to the electrochemical unit of Step 1.

[0678] Secondary Alkalinity-Driven Pathway

[0679] In addition to, or in place of, acid dissolution, a secondary alkalinity-driven pathway may occur under strongly alkaline conditions within the mineral dissolution and carbonate precipitation environment. In such embodiments, dissolved alkali hydroxide present in the working electrolyte (for example NaOH) may interact with solid magnesium hydroxide to generate soluble and / or colloidal magnesium hydroxo species. These species may include, in some embodiments, sodium-magnesium hydroxo complexes, while in other embodiments they may exist as dispersed or partially solvated magnesium hydroxide species. Alkali metal ions function primarily as counter-ions that maintain electroneutrality within the solution phase.

[0680] Without being bound to any particular speciation model, such interactions may be represented illustratively by equilibria of the following general form:

[0681] Mg(OH)2(s) + 2Na++ 2OH-⇌ Na2[Mg(OH)4] (8a)

[0682] This representation is provided as one possible depiction of soluble hydroxo species formation and is not intended to limit the invention to any specific coordination chemistry, solvation structure, or intermediate complex.

[0683] The resulting soluble and / or colloidal magnesium hydroxo species may subsequently react with carbonate species and / or dissolved CO2to form solid magnesium carbonate. In some embodiments, this reaction may regenerate hydroxide equivalents in the circulating electrolyte:

[0684] Na2[Mg(OH)4] + CO2→ MgCO3(s) + 2NaOH(aq) + H2O(l) (8b)

[0685] Through this alkalinity-mediated pathway, magnesium may be transferred from a hydroxide or mineral phase into a stable carbonate solid without requiring complete prior dissolution by strong acid, while alkali metal species remain available within the electrolyte for continued circulation within the closed electrochemical loop (CEL).

[0686] In other embodiments, carbonate may form via reaction of such hydroxo species with dissolved carbonate ions and / or bicarbonate species.

[0687] Optional Direct Carbonation Pathway

[0688] In embodiments where hydrochloric acid and carbonate species coexist in the reactor, acid-carbonate neutralisation may liberate carbon dioxide, which can locally react with magnesium hydroxide to promote direct carbonation.

[0689] Na2CO3(aq) + 2HCl(aq) → 2NaCl(aq) + CO2(g) + H2O(l) (10a)

[0690] Mg(OH)2+ CO2→ MgCO3(s) + H2O (10b)Cation Exchange Overall Net Reactions for Parallel Pathways (Non-Limiting)

[0691] Multiple reaction pathways may occur in parallel and / or sequentially depending on local pH, reagent distribution, residence time, mixing, CO2 availability, and solids loading.

[0692] Pathway A. Acid Dissolution + Cation Exchange

[0693] Mg(OH)2+ 2HCl → MgCl2+ 2H2O (A1)

[0694] MgCl2+ Na2CO3→ MgCO3(s) + 2NaCl (A2)

[0695] Overall Net: Mg(OH)2+ Na2CO3+ 2HCl → MgCO3(s) + 2NaCl + 2H2O (A net) Pathway B. Acid-Carb onate Neutralisation + Direct Carbonation

[0696] Na2CO3+ 2HCl → 2NaCl + CO2+ H2O (B1)

[0697] Mg(OH)2+ CO2→ MgCO3(s) + H2O (B2)

[0698] Overall Net:

[0699] Mg(OH)2+ Na2CO3+ 2HCl → MgCO3(s) + 2NaCl + 2H2O (B Net)

[0700] Pathway C. Alkalinity-Driven Metathesis

[0701] Mg(OH)2+ Na2CO3→ MgCO3(s) + 2NaOH (C1)

[0702] If acid is present:

[0703] 2NaOH(aq) + 2HCl(aq) → 2NaCl(aq) + 2H2O(l) (C2)Overall Net (with HCl):

[0704] Mg(OH)2+ Na2CO3+ 2HCl → MgCO3(s) + 2NaCl + 2H2O (C Net)

[0705] Process Outcome

[0706] Regardless of the specific pathway, the reactor outcome of the combined reactions in the mineral dissolution and carbonate precipitation reactor can often be represented in an aggregate form as:

[0707] Mg(OH)2+ Na2CO3+ 2HCl → MgCO3(s) + 2NaCl + 2H2O

[0708] This overall expression reflects the consumption of brucite, carbonate species and acid to yield a solid magnesium carbonate product, regeneration of sodium chloride, and retention of water.

[0709] In embodiments in which magnesium hydroxide, carbonate species, and hydrochloric acid are simultaneously present within the mineral dissolution / cation exchange reactor, the reactor conditions may be selected such that the net process outcome is:

[0710] 1. Conversion of magnesium hydroxide to a solid magnesium carbonate product

[0711] 2. Conversion of sodium carbonate / bicarbonate and hydrochloric acid to sodium chloride in the aqueous phase (thereby regenerating the working electrolyte)

[0712] 3. Retention of water as the process solvent

[0713] Stated differently, in a non-limiting sense, the unit operation is configured such that carbonate is transferred into a magnesium carbonate solid phase while chloride is conserved as sodium chloride in solution, with carbon dioxide potentially being generated and consumed locally as an intermediate, and with the overall reactor effluent comprising

[0714] (a) a magnesium carbonate -containing solids stream and

[0715] (b) a sodium chloride-containing liquor suitable for recycle.

[0716] Through the combined action of acid dissolution and carbonate precipitation:• Magnesium is transferred from a hydroxide or mineral phase into a stable solid carbonate

[0717] • Sodium chloride is regenerated in solution

[0718] • The ionic working electrolyte is conserved and recycled

[0719] • Carbon is exported from the system as a solid carbonate product

[0720] Operating conditions (pH, temperature, residence time, carbonate concentration, solids loading, and mixing intensity) are selected such that magnesium carbonate precipitation is favoured while sodium chloride remains in solution, enabling downstream solid-liquid separation and electrolyte recycle.

[0721] Step 4. Solid / Liquid Separation

[0722] Following carbonate formation in the mineral dissolution and precipitation reactors, the resulting slurry comprises a suspension of solid carbonate particles in an aqueous electrolyte phase containing predominantly sodium chloride and residual dissolved carbonate species. Step 4 separates the solid carbonate product from the recyclable electrolyte liquor.

[0723] In some embodiments, the slurry is first directed to a conditioning vessel, such as a continuously stirred tank reactor (CSTR) or holding tank, in which temperature is adjusted to optimise phase behaviour. Heating or cooling may be employed to:

[0724] • Maximise solubility of sodium chloride and other dissolved salts

[0725] • Promote additional conversion of residual dissolved CO2 or bicarbonate into solid carbonate • Improve crystal growth and settling characteristics of the carbonate solids

[0726] Temperature adjustment may also reduce solution viscosity and enhance downstream separation efficiency. After conditioning, the slurry is subjected to one or more solid-liquid separation operations.

[0727] Suitable separation technologies include, without limitation:

[0728] • Gravity settlers or clarifiers

[0729] • Lamella or inclined-plate settlers

[0730] • Hydrocyclones for density-based classification

[0731] • Thickeners or high-rate thickeners

[0732] • Filtration systems such as pressure filters, membrane filters, belt filters, or filter presses

[0733] • Centrifuges, including decanter or disc-stack centrifuges

[0734] In certain embodiments, a primary thickening or clarification step produces an underflow enriched in carbonate solids and an overflow comprising clarified sodium chloride-rich liquor. The clarified liquor is returned to the electrolyte recycle loop for reuse in the electrochemical unit, optionally after polishing treatment to remove residual suspended solids or multivalent cations.

[0735] The solids-rich underflow may be washed with water or dilute electrolyte to displace entrained salts and reduce chloride content associated with the carbonate product. Washing may be performed in one or more counter-current stages integrated with filtration or centrifugation equipment.

[0736] In this manner, Step 4 produces (i) a concentrated carbonate solids stream suitable for downstream purification, drying, or further conversion, and (ii) a clarified electrolyte stream suitable for recycle, therebymaintaining ionic closure of the Closed Electrochemical Loop while exporting carbon primarily in the form of solid carbonate.

[0737] Step 5. Carbonate Purification and Washing

[0738] Following primary solid-liquid separation, the recovered carbonate solids may contain entrained electrolyte solution, including sodium chloride and trace halide species. Step 5 provides purification of the carbonate product to reduce soluble salt content and tailor material properties for downstream applications. In various embodiments, the carbonate solids are transferred to one or more dewatering and washing units. Suitable equipment includes, without limitation:

[0739] • Filter presses (plate-and-frame, recessed plate, or membrane-assisted)

[0740] • Membrane filter presses

[0741] • Vacuum or pressure belt filters

[0742] • Centrifuges, including decanter or basket centrifuges

[0743] These units separate residual liquid from the carbonate solids to produce a filter cake or centrifuge cake.

[0744] The separated filtrate or centrate, which may contain dissolved sodium chloride and minor carbonate species, is recycled to the electrolyte management or brine conditioning stages of the Closed Electrochemical Loop (CEL).

[0745] To further reduce soluble salt and halide content in the solid product, one or more washing stages may be employed. Washing may be conducted using water, dilute electrolyte, or low-salinity process condensate. In some embodiments, counter-current washing is used to maximise removal of soluble species while minimising wash water consumption. Wash effluent is returned to the process for salt recovery or reuse, maintaining overall ionic closure.

[0746] After washing, the purified carbonate solids may be dried, milled, classified, or otherwise conditioned to achieve desired particle size distribution, morphology, and surface properties. Depending on the mineral system employed, the product may comprise magnesium carbonate, calcium carbonate, mixed alkaline-earth carbonates, or hydrated carbonate phases. These materials may be suitable, in non-limiting examples, for use as specialty mineral fillers, supplementary cementitious materials (SCM), cosmetic-grade powders, adsorbents, or magnesium carbonate products such as gym chalk.

[0747] Optional Conversion to More Stable Carbonate Phases

[0748] In some embodiments, the purified carbonate product serves as a precursor or seed material for conversion into more thermodynamically stable or higher-density carbonate phases.

[0749] For example, where the initial product comprises hydrated magnesium carbonates or basic magnesium carbonates, further reaction with carbon dioxide under elevated temperature and pressure may be conducted in a sealed reactor, such as an autoclave, to promote formation of anhydrous magnesium carbonate (magnesite, MgCCE). This secondary carbonation step may utilise CO2 derived from the process gas stream or other available CO2 sources.

[0750] In alternative embodiments, the carbonate solids may be exposed to a controlled CCE-rich atmosphere at ambient or moderately elevated pressures and temperatures to drive further carbonation orphase transformation without the need for high-pressure autoclave operation. In such cases, the initially formed carbonate acts as a seed surface that promotes nucleation and growth of more crystalline or durable carbonate phases.

[0751] Through these optional post-treatment steps, the CEL process can produce carbonate materials with tunable phase composition, crystallinity, density, and durability, while maintaining compatibility with the upstream electrochemical and electrolyte recycle architecture.

[0752] Step 6. Brine Recycle and Feed Conditioning

[0753] The salt-containing liquor remaining after carbonate separation (including press filtrate and wash liquors) is treated in a brine conditioning train configured to reduce multivalent ions (e.g., Mg2+and Ca2+) while retaining the primary electrolyte species (Na+and CL) for recycle to the electrochemical unit, thereby maintaining ionic closure within the Closed Electrochemical Loop (CEL). In non -limiting embodiments, the conditioning train includes clarification and microfiltration to remove suspended solids, and one or more separations such as nanofiltration (NF) and / or low-pressure reverse osmosis (LPRO) configured to reduce Mg2+ / Ca2+relative to Na / CI with appropriate recycle routing. Cleaning -in-place (CIP), antiscalant / softening, and chemical dosing may be supported using reagents generated within the CEL (e.g., HC1 and sodium carbonate), thereby reducing external reagent consumption. In further embodiments, the conditioned brine is concentrated to a target NaCl strength suitable for the electrochemical unit using one or more of: closed-circuit reverse osmosis (CCRO), thermal evaporation or vacuum boiling, densimetric separation, and / or salt crystallisation, optionally with recovery and recycle of condensate and / or mother liquor to maintain ionic closure. In representative embodiments, the target NaCl concentration for feed to a membrane chlor-alkali electrolyser is in the range of approximately 100 g / L to 280 g / L, depending on plant design and operating efficiency. The process may proceed as follows in representative embodiments.

[0754] Collection of Recycle Electrolyte

[0755] Liquors recovered from solid-liquid separation and carbonate washing are combined into a recycle brine stream. This stream typically contains sodium chloride as the dominant dissolved species, along with residual carbonate / bicarbonate and dissolved calcium and magnesium ions.

[0756] Suspended Solids Removal

[0757] The recycle brine is first clarified to remove fine suspended solids that could foul membranes or electrodes in the electrochemical unit. Clarification may be performed using one or more of:

[0758] • Microfiltration or ultrafiltration membranes

[0759] • Cartridge, sand, or media filters

[0760] • Clarifiers or polishing filters

[0761] This step produces a clarified brine suitable for further ionic conditioning.

[0762] Reduction of Multivalent Cations

[0763] The clarified brine may then be treated to reduce concentrations of calcium and magnesium ions that may cause scaling or membrane degradation. One or more of the following unit operations may be employed:• Nanofiltration (NF) to preferentially reject divalent ions while allowing sodium and chloride to pass

[0764] • Low-pressure reverse osmosis (LPRO) configured to fractionate ionic species

[0765] • Ion exchange resins selective for Ca2+and Mg2+

[0766] • Chemical softening via precipitation using carbonate or hydroxide dosing

[0767] Streams enriched in multivalent cations may be directed to mineral processing units, used in secondary carbonation reactions, or otherwise managed to minimise waste discharge.

[0768] Brine Concentration and Salinity Adjustment

[0769] After removal of suspended solids and multivalent ions, the brine may be concentrated to a target sodium chloride concentration suitable for electrolysis.

[0770] In various embodiments:

[0771] • Closed-circuit reverse osmosis may be used to remove water and increase salt concentration • Further concentration may be achieved by thermal evaporation, vacuum boiling, or densimetric separation

[0772] • Salt crystallisation may be used where additional concentration or purification is required Typical sodium chloride concentrations for feed to a membrane chlor-alkali electrolyser may range from approximately 100 g / L to 280 g / L, depending on plant design and operating efficiency. Conductivity and salinity of the conditioned brine are monitored to ensure compatibility with electrochemical operating requirements.

[0773] Chemical Conditioning and Cleaning Support

[0774] Chemical dosing may be applied as needed to maintain electrolyte quality and prevent fouling. In some embodiments, reagents generated within the CEL, including hydrochloric acid and sodium carbonate, are used for:

[0775] • Cleaning-in-place (CIP) of membranes, piping, and reactors

[0776] • pH adjustment

[0777] • Dissolution of scale-forming deposits

[0778] Use of internally generated reagents reduces external chemical demand and supports closed-loop operation.

[0779] Return to Electrochemical Unit

[0780] The conditioned brine, now substantially free of suspended solids and with reduced levels of scaling ions, is returned to the electrochemical unit. Continuous monitoring of conductivity, salinity, and impurity levels ensures that electrolyte composition remains within design limits for stable membrane electrolysis.

[0781] Zero Liquid Discharge and Byproduct Handling (Optional)

[0782] In some embodiments, additional treatment is applied to minimise or eliminate liquid waste streams. Concentrated reject brines containing calcium and magnesium chlorides may be:

[0783] • Further concentrated and crystallised to recover solid salts

[0784] • Reintroduced into upstream mineral processing or carbonation pathways

[0785] • Stored as brine bitterns for later reuse within the processThrough these measures, sodium and chloride ions are substantially conserved within the circulating electrolyte inventory, carbonate is exported as solid product, and overall brine losses are minimised. Outcome

[0786] Salt is recycled to the electrochemical unit following purification and conditioning. Continuous monitoring of conductivity and salt concentration supports stable electrolysis and preserves ionic closure, enabling the CEL to function as a closed electrochemical process that converts CO2 and mineral feedstocks into carbonate solids while retaining halides within the loop.

[0787] Summary of CEL Process Description (Brucite Embodiment)

[0788] The Closed Electrochemical Loop (CEL) integrates electrochemical regeneration of alkalinity and acidity with carbonation and mineral conversion to produce stable carbonate solids while conserving the working electrolyte.

[0789] The principal stepwise reactions for the brucite embodiment are as follows:

[0790] Step 1. Chlor-alkali electrolysis

[0791] 2NaCl(aq) + 2H2O(l) → 2NaOH(aq) + Cl2(g) + H2(g)Optional gas recombination

[0792] H2(g) + CIM “► 2HCl aq)

[0793] Step 2. Carbonation of electrochemically generated alkalinity

[0794] 2NaOH(aq) + CO2(g) → Na2CO3(aq) + H2O(l)

[0795] Step 3. Mineral conversion and electrolyte regeneration

[0796] Mg(OH)2(s) + Na2CO3(aq) + 2HCl(aq) → MgCO3(s) + 2NaCl(aq) + 2H2O(l)

[0797] Within the CEL boundary, sodium chloride, sodium hydroxide, sodium carbonate, and hydrochloric acid function as internally regenerated electrolyte carrier species. When these internal species are cancelled, the net overall reaction for the brucite embodiment is:

[0798] Mg(OH)2(s) + CO2(g) → MgCO3(s) + H2O(l)

[0799] Thus, the CEL uses electrical energy to mediate conversion of carbon dioxide and brucite into stable magnesium carbonate while substantially conserving alkali metal and halide ions within the circulating electrolyte inventory.

[0800] Control Logic and Control Variables

[0801] Key control variables include:

[0802] • pH windows for carbonation

[0803] • Conductivity control of brine

[0804] • Ion concentration ranges

[0805] • Carbonate solids bleed rate

[0806] • Electrolyser current density ranges

[0807] • Mineral feed rate vs CO2 and CL loadIn various embodiments, the Closed Electrochemical Loop (CEL) is operated using coordinated process control to maintain ionic balance, sustain carbonate production, and stabilise electrochemical performance. The system is therefore engineered as a continuously regulated process architecture rather than a batch or laboratory chemistry sequence. Control may be implemented using conventional industrial instrumentation, distributed control systems (DCS), programmable logic controllers (PLC), or equivalent supervisory control platforms.

[0808] The following control variables and operating windows are illustrative and non-limiting.

[0809] 1. pH Control in the Carbonation Reactor

[0810] Liquid pH in the carbonation unit is a primary state variable governing carbonate versus bicarbonate speciation and overall CO2 capture efficiency.

[0811] In representative embodiments:

[0812] • fresh alkaline feed from the electrochemical unit may exhibit pH values in the range of approximately 12.5-14

[0813] • Carbonation is typically operated at pH values above approximately pH 10 to favour carbonate (CO32−) formation

[0814] • Spent or partially depleted liquors may fall within a pH range of approximately 8-12, depending on carbonate loading and CO2 partial pressure

[0815] pH may be monitored continuously using corrosion-resistant probes. When pH decreases below a selected threshold band, one or more corrective actions may be triggered, including:

[0816] • Increased alkaline feed rate

[0817] • Partial or full discharge of spent carbonate liquor

[0818] • Adjustment of gas flow rate or contact time

[0819] In embodiments generating chlorine, chlorine handling rate and recombination / absorption capacity are monitored as additional process constraints.

[0820] 2. Brine Conductivity and Electrolyte Strength

[0821] Electrical conductivity of the circulating brine is monitored to maintain stable electrochemical operation and ionic closure.

[0822] Illustrative conductivity control ranges include:

[0823] • Brine feed to the electrolyser: selected to maintain sodium chloride concentration within approximately 2-6 mol / L, or equivalent ionic strength

[0824] • Post-carbonation electrolyte: monitored to ensure sodium and chloride ions remain within operating tolerances that sustain membrane transport efficiency and limit scaling

[0825] If conductivity falls below a selected setpoint, brine make-up or salt recycle streams may be increased. If conductivity rises excessively, dilution, bleed, or purification steps may be initiated.

[0826] 3. Ionic Concentration Control

[0827] Ion concentrations within the loop are monitored to preserve electrolyte composition and prevent accumulation of multivalent cations or impurities.In some embodiments, the following ranges are controlled:

[0828] • Na+and Cl−: maintained at levels consistent with membrane electrolysis performance and ionic closure

[0829] • Mg2+ / Ca2+in recycle streams: maintained below selected thresholds to prevent scaling within the electrochemical unit

[0830] • Carbonate / bicarbonate concentration: controlled to balance precipitation kinetics and slurry handling properties

[0831] Ion monitoring may be performed via inline conductivity, density, titration, ion-selective electrodes, or periodic analytical sampling.

[0832] 4. Carbonate Solids Bleed Rate

[0833] Solid carbonate is continuously or intermittently removed to maintain steady-state solids inventory in precipitation and slurry handling units.

[0834] Control variables may include:

[0835] • Slurry density or solids weight percent

[0836] • Turbidity or optical backscatter

[0837] • Settling or filtration rate

[0838] When solids concentration exceeds a selected operating window, a controlled bleed of carbonate slurry may be withdrawn to downstream solid-liquid separation. This prevents over-accumulation of solids and maintains effective gas-liquid contacting and mixing performance.

[0839] 5. Electrolyser Current Density and Power Input

[0840] Electrochemical performance is regulated through control of current density, voltage, and brine flow.

[0841] Illustrative operating ranges include:

[0842] • Current density: approximately 2-6 kA / m2

[0843] • Cell voltage: selected to maintain high Faradaic efficiency while limiting membrane degradation • Brine temperature and flow: adjusted to maintain stable membrane hydration and ionic transport Increased CO2 loading downstream may be matched by increasing current density to generate additional alkalinity, while reduced load may allow current to be lowered to conserve energy.

[0844] 6. Mineral Feed Rate Relative to CO2 Load

[0845] The rate of mineral feed (e.g., brucite or other magnesium / calcium sources) is coordinated with carbonate production capacity and CO2 absorption rate.

[0846] In some embodiments:

[0847] • Mineral feed rate is increased when carbonate concentration or precipitation rate rises

[0848] • Mineral feed rate is reduced when acid availability, carbonate supply, or reactor residence time becomes limiting

[0849] • Feedback variables may include pH in the mineral dissolution reactor, magnesium ion concentration, or carbonate solids formation rateThis coupling ensures that divalent cation supply remains matched to carbonate availability, preserving ionic balance and steady carbonate production.

[0850] Integrated Control Concept

[0851] Control schemes described herein are illustrative and non-limiting; stable operation may be achieved using any suitable combination of measurement, feedback, and operating setpoints known to those skilled in the art. Taken together, these control variables enable the CEL to operate as a self-balancing, continuously regulated ionic loop in which:

[0852] • Electrochemical generation of acid and base is matched to downstream mineral dissolution and carbonation

[0853] • Ionic species are conserved within the electrolyte inventory

[0854] • Carbon dioxide uptake is dynamically linked to electrochemical and mineral processing capacity • Carbonate solids are removed as the principal material export stream

[0855] This coordinated control architecture distinguishes the CEL as an engineered chemical process system rather than a sequence of independent reactions, and supports continuous, semi-continuous, or loadfollowing operation across a range of industrial CO2 sources.

[0856] System States

[0857] System States and Operational Modes (Non-Limiting)

[0858] In various embodiments, the Closed Electrochemical Loop (CEL) operates through defined system states that describe how the integrated electrochemical, carbonation, mineral processing, and electrolyte recycle units behave under different operating conditions. These states demonstrate that the CEL functions as an engineered, continuously operable process architecture rather than a single-pass reaction sequence. The following system states are illustrative and non-limiting.

[0859] 1. Start-Up State

[0860] During start-up, the system is brought from an idle or uncharged condition to an operational ionic and hydraulic steady state.

[0861] In representative embodiments:

[0862] • The electrolyte inventory is initially charged with a sodium chloride brine of selected concentration.

[0863] • Circulation pumps are activated to establish flow through the electrochemical unit, carbonation reactor, mineral dissolution unit, and recycle loops.

[0864] • The electrochemical unit is energised at a reduced initial current density to begin generation of alkalinity (NaOH) and acidity (e.g., HC1 or equivalent acidic stream).

[0865] • An initial alkaline charge is directed to the carbonation reactor to establish elevated pH conditions.

[0866] • Mineral feed (e.g., brucite slurry) is gradually introduced into the mineral dissolution / cation exchange reactor once sufficient acidic and carbonate -bearing streams are available.

[0867] • Gas handling systems are brought online to begin controlled introduction of CO2-containing gas to the carbonation reactor.During this phase, pH, conductivity, temperature, and flow rates are ramped toward their target operating windows. Carbonate solids formation may begin at low rates and increase as ionic balance and reagent inventories approach steady-state conditions.

[0868] 2. Steady-State Operation

[0869] In steady state, the CEL operates as a continuous or semi-continuous loop with balanced ionic flows and sustained carbonate production.

[0870] Under steady-state conditions:

[0871] • The electrochemical unit continuously regenerates alkalinity and acidity from the circulating brine.

[0872] • The carbonation reactor continuously absorbs CO2 and converts it into dissolved carbonate and / or bicarbonate species.

[0873] • The mineral dissolution / cation exchange reactor continuously converts divalent cation feedstock into solid carbonate while regenerating sodium chloride.

[0874] • Carbonate solids are continuously or periodically removed via controlled solids bleed and downstream separation.

[0875] • Regenerated sodium chloride solution is recycled to the electrochemical unit, maintaining ionic closure.

[0876] During this state, system control maintains target bands for pH, conductivity, ion concentration, and solids inventory. CO2 capture, carbonate precipitation, and electrolyte regeneration occur in coordinated balance, enabling sustained carbon removal with conserved halide and alkali metal ions.

[0877] 3. Load Change / Dynamic Response State

[0878] The CEL is capable of responding to changes in CO2 feed concentration, gas flow rate, or mineral feed availability.

[0879] In embodiments where CO2 loading increases:

[0880] • The electrochemical unit current density may be increased to generate additional alkalinity.

[0881] • Alkaline flow to the carbonation reactor may be increased.

[0882] • Mineral feed rate may be increased to match higher carbonate availability.

[0883] • Carbonate solids removal rate may be increased to prevent solids accumulation.

[0884] In embodiments where CO2 loading decreases:

[0885] • Electrolyser current density may be reduced to conserve energy.

[0886] • Alkaline feed and mineral feed rates may be proportionally reduced.

[0887] • Solids bleed rate may be decreased.

[0888] This load-following behaviour allows the CEL to operate with variable industrial CO2 sources while maintaining ionic balance and stable internal chemistry.

[0889] 4. Shutdown State

[0890] During shutdown, the CEL is transitioned to a safe, preserved condition while maintaining containment of halide-containing electrolyte.

[0891] In representative embodiments:• CO2feed is halted and the carbonation reactor is allowed to complete reaction of residual alkalinity.

[0892] • Mineral feed is stopped while allowing ongoing reactions in the dissolution / precipitation unit to reach completion.

[0893] • Electrolyser current is gradually reduced and then switched off.

[0894] • Circulation may continue for a defined period to equalise concentrations and prevent localised precipitation.

[0895] • Electrolyte is retained within the closed loop, with valves and containment systems configured to prevent discharge of halide-containing streams.

[0896] • Upon shutdown the electrolyser is flushed with water and the water purification trains undergo clean in place (CIP) maintenance.

[0897] Carbonate solids may be removed prior to full shutdown or left in slurry form for removal during subsequent restart procedures.

[0898] Industrial Enablement Significance

[0899] Definition of these system states demonstrates that the CEL is operable as a managed industrial process with predictable behaviour during start-up, steady production, dynamic load variation, and shutdown. The coordinated transitions between these states further support continuous or semi-continuous operation while maintaining ionic closure, halide retention, and sustained conversion of CO2 and mineral feedstocks into stable carbonate solids.

[0900] Processes Involving Reaction of Alkali Metal Hydroxide With Carbon Dioxide

[0901] One aspect of the present disclosure relates to processes for capturing carbon dioxide which involve contacting of a CO2-containing feed with aqueous alkali metal hydroxide (e.g. NaOH) to produce the corresponding bicarbonate and / or carbonate, and subsequent cation exchange with an alkaline earth metal halide (e.g. chloride) to produce the alkaline earth metal carbonate (e.g. MgCOs). The processes are substantially closed loop with respect to halide, in that the alkali metal halide is produced by electrochemically treating an alkali metal halide (e.g. chloride) and water to produce alkali metal hydroxide (which can be used for contacting with the C Ch-containing feed) and hydrohalic acid (e.g. HC1). The hydrohalic acid is used to react with an alkaline earth metal-containing mineral feedstock (e.g. a magnesium-containing mineral feedstock) to produce the corresponding metal halide, which can then be used for cation exchange. Further, alkali metal halide produced in the cation exchange can be recycled to the process.

[0902] Accordingly, there is provided a process for capturing carbon dioxide, comprising: a) electrochemically treating an alkali metal halide and water to produce aqueous alkali metal hydroxide and hydrohalic acid; b) contacting a carbon dioxide-containing feed with aqueous alkali metal hydroxide from a), to produce an alkali metal carbonate and / or bicarbonate; c) reacting hydrohalic acid from a), with an alkaline earth metal-containing mineral feedstock to produce alkaline earth metal halide; and d) reacting alkali metal carbonate and / or bicarbonate from b) with alkaline earth metal halide from c) in the presenceof water to produce solid alkaline earth metal carbonate and alkali metal halide; wherein alkali metal halide produced in d) is recycled to a), and wherein the process is substantially closed-loop with respect to halide.

[0903] The process is for capturing carbon dioxide. Any suitable carbon dioxide -containing feed may be used, such as for example air. Direct air capture may be carried out, for example. Further examples of carbon dioxide -containing feeds include a power station exhaust stream, a biogas CO2-containing stream, a diesel, petrol, LPG, natural gas or biogas generator exhaust stream, a pyrolysis exhaust stream, an industrial furnace exhaust stream, a methane pyrolysis exhaust stream, a cement kiln exhaust stream, and a metallurgical smelter exhaust stream. In some embodiments, the carbon dioxide feed is air, and direct air capture is carried out.

[0904] In step a), an alkali metal halide and water are electrochemically treated to produce aqueous alkali metal hydroxide and hydrohalic acid. In some embodiments the halide is chloride, and HC1 is produced. Examples of alkali metal chlorides include lithium chloride, sodium chloride and potassium chloride. In some embodiments, the alkali metal chloride is sodium chloride (i.e. sodium is the akali metal used in the process).

[0905] Any suitable form of alkali metal halide (e.g. sodium chloride) may be used. For example, sodium chloride may be obtained from seawater.

[0906] Step a) may produce the alkali metal hydroxide and hydrohalic acid directly or indirectly. For example, in some embodiments, a halogen gas may initially be produced (e.g. chlorine) which may then be converted to hydrohalic acid (e.g. through reaction with hydrogen gas). In other words, a halogencontaining stream may be produced, optionally hydrogen and chlorine, which can be converted to HC1.

[0907] Any suitable form of electrochemical treatment may be carried out. The electrochemical unit may be implemented using chlor-alkali electrolysis, bipolar membrane electrodialysis, electrodialysis, electrodeionisation, membrane electrolysis, electrochemical water splitting, electropurification, HER (hydrogen evolution reaction) / OER (oxygen evolution reaction), or other electrochemical configurations capable of generating acidity and alkalinity equivalents from a circulating electrolyte. Regardless of configuration, the electrochemical unit performs the same functional role within the CEL architecture: regeneration of alkalinity and acidity while maintaining ionic closure and enabling carbonate export as the principal net reaction product. Examples include the chloralkali process, and bipolar membrane electrodialysis (EDBM). Chloralkali electrolysis is a process used to make chlorine, hydrogen and sodium hydroxide by passing electricity through brine. Chloralkali processes can be carried out for example using a diaphragm cell (e.g. using a porous asbestos or polymer diaphragm to keep the anode and cathode apart), a membrane cell (e.g. using an ion exchange membrane such as Nafion that allows sodium to pass but blocks chloride and hydroxide ions), or using a mercury cell (e.g. where the cathode is liquid mercury that forms an amalgam with sodium). In some embodiments, a membrane cell chloralkali electrolysis step is used. Membrane cell processes can have lower energy demand, for example.

[0908] In some embodiments, salt splitting / electrodialysis-based systems are used for the electrochemical step. Electrodialysis uses alternating cation exchange membranes and anion exchange membranes underan electrical field. This creates concentrated and depleted streams of, for example, NaCl, and can be used to concentrate NaCl to optimal levels for electrolysis, for example. It can also be useful for removing impurities. The streams can be directed to a chloralkali cell for example and converted to Cl2and NaOH.

[0909] Electrodialysis with bipolar membranes (EBDM) can also be used. This involves electrodialysis stacks containing alternating cation exchange membranes, anion exchange membranes, and bipolar membranes, forming a salt compartment from where NaCl is depleted, an acid compartment where HC1 forms, and a base compartment where NaOH forms.

[0910] Other forms of electrochemical treatment and variants can also be used, including membrane-free electrochemical systems that generate acid and base via paired electrolytic half-reactions using separators, and other membrane electrochemical systems, such as other membrane electrolysis configurations (MEC), and electrodialysis reversal (EDR).

[0911] In various embodiments, the electrochemical unit comprises one or more of: chlor-alkali electrolysis; bipolar membrane electrodialysis (BMED / EDBM) configured to generate acid and base streams from a circulating electrolyte; electrodialysis or electro-deionisation configured to separate and concentrate ionic species; and / or electrochemical water-splitting configurations (including HER / OER) configured to generate hydroxide and acidity without net consumption of the circulating halide inventory.

[0912] In some embodiments, the electrochemical unit is configured to operate with mixed-ion brines including seawater, reverse-osmosis reject, produced water, or industrial brines, while maintaining a closed or substantially closed loop with respect to halides and / or alkali metal ions. In some embodiments, the system operates in a halogen-free or halogen-minimised mode in which chlorine evolution is substantially suppressed, captured, or converted within the process boundary, while the principal function of the electrochemical unit is generation of a controlled pH gradient and regeneration of alkalinity for carbonate formation within the closed electrochemical loop.

[0913] The electricity used for the electrochemical treatment may originate from any suitable source. In some embodiments, the electrochemical treatment is carried out using electricity generated from a renewable source.

[0914] Step b) involves contacting a carbon dioxide-containing feed with aqueous alkali metal hydroxide from a), to produce an alkali metal carbonate and / or bicarbonate. For example, where the alkali metal is sodium, the carbon dioxide-containing feed is contacted with aqueous sodium hydroxide.

[0915] Any suitable reactor or vessel may be used for carrying out step b). Examples include a column, tower or scrubber, such as a packed column, trayed column, fluidised bed reactor, spray tower, bubble column, venturi scrubber, membrane contactor, CTSR (continuous stirred tank reactor), or mechanically agitated reactor.

[0916] In some embodiments, a system as defined herein comprising a column, gas injection portion, gas outlet, liquid outlet, and solid carbonate collection chamber, is used for step b).If desired, multiple reactors, vessels, or systems may be utilised for carrying out step b). For example, a set-up containing 2 or more columns may be used. In some embodiments, a system comprising 2 or more columns in series is used.

[0917] The contacting in step b) is carried out under suitable conditions, e.g. temperature, time, pressure, to produce alkali metal carbonate and / or bicarbonate.

[0918] In some embodiments, one or more of pH, temperature, pressure, contact time, and CO2partial pressure is set so as to control production of carbonate and / or bicarbonate species. In some embodiments, one or more parameters is monitored (e.g. pH, pressure, CO2 partial pressure, temperature) and depending on the value of the one or more parameters, the reaction conditions may be adjusted (e.g. rate of introduction of carbon dioxide -containing feed, rate of introduction of aqueous alkali metal hydroxide, pH, temperature) to control production of carbonate and / or bicarbonate. For example initially step b) may in some cases be hydroxide-dominant but as more carbon dioxide-containing feed is introduced, carbonate may be the dominant species.

[0919] In some embodiments, the pH is a pH sufficient to promote conversion of dissolved CO2 to carbonate species, for example in the range of from 8 to 14, or 9 to 13, or 10 to 12.5.

[0920] In some embodiments, additional alkali metal hydroxide is added when CO2 content (e.g. CO2 content in a flue) rises above a desired level. For example, carbon dioxide partial pressure may be measured and used to determine dosing / addition of alkali metal hydroxide. For example, in some embodiments the liquid contents may be discharged and fresh alkali metal hydroxide and water added. In some embodiments, aqueous alkali metal hydroxide is added continuously, maintaining pH at a desired level.

[0921] In some embodiments, the temperature is in the range of from 0 °C to 90 °C, for example in the range of from 5 °C to 60 °C, or from 10 °C to 35 °C. In some embodiments step b) is carried out at ambient temperature. In some embodiments, step b) is carried out at elevated temperature.

[0922] In some embodiments, the pressure is in the range of from 0.01 bar to 20 bar, or from 0.9 bar to 10 bar. In some embodiments, pressure is near atmospheric pressure. In some embodiments, the CO2 partial pressure is in the range of from 0.0004 bar to 10 bar, or from 0.001 bar to 5 bar, or from 0.004-1 bar.

[0923] In some embodiments, the contact time is in the range of from 10 seconds to 48 hours, or from 1 minute to 12 hours, or up to 1 month.

[0924] In some embodiments, alkali metal carbonate or bicarbonate, or alkaline earth metal carbonate, is precipitated. In some embodiments, solid alkali metal carbonate or bicarbonate, or alkaline earth metal carbonate, is separated, for example by filtration, decanting or siphoning.

[0925] In some embodiments, a flow of carbon dioxide-containing feed is passed through aqueous alkali metal hydroxide, for example the carbon dioxide-containing feed may be introduced at or near the bottom of a vertically oriented column or tower reactor containing aqueous alkali metal hydroxide.

[0926] In certain embodiments, dissolved carbonate and / or bicarbonate species generated in one stage may be transferred to another stage in which CO2 is selectively released by pH adjustment, pressure reduction, temperature change, electrochemical pH swing, or combinations thereof, and the released CO2 may be re-absorbed into regenerated alkalinity. Such reversible release and re-absorption may be used to increase overall conversion efficiency, enable operation with dilute CO2 feeds such as ambient air, or decouple capture and mineralisation steps, while maintaining retention of the circulating ionic inventory.

[0927] If desired, a carbon dioxide feed may be contacted multiple times, for example by passing through a series of reactors, or by recirculation / reintroduction into the reactor.

[0928] In some embodiments, CO2 released during processing within the process is recycled and contacted with the alkali metal hydroxide.

[0929] Step c) involves reacting hydrohalic acid (e.g. HC1) from a), with an alkaline earth metal-containing mineral feedstock to produce alkaline earth metal halide. The alkaline earth metal may for example be calcium or magnesium. In some embodiments, the alkaline earth metal is magnesium. Any suitable alkaline earth metal-containing mineral feedstock may be used. For example, it may be a mineral, or a treated mineral, that contains an alkaline earth metal (e.g. in cationic form). For example, treatment may involve contacting with a suitable agent that facilitates obtaining the alkaline earth metal from the mineral. Treatment may also include carrying out a suitable particle size reduction step, e.g. mechanical treatment, grinding and the like. Examples of alkaline earth metal -containing mineral feedstock include nickel laterite tailings, brucite, serpentine, olivine, pyroxene, hydrotalcite, basaltic materials, ultramafic rocks, industrial tailings, and oxide / hydroxide phases occurring in mining residues. In some embodiments, a mineral feedstock selected from basalt, peridotite, dunite, harzburgite, serpentinised ultramafic rock, and mixtures thereof, and / or industrial residues comprising steel slag, red mud, mine tailings, fly ash, cement kiln dust, may be used, including partially altered or weathered forms of the foregoing. Feedstocks may include mixtures of minerals or treated minerals. In some embodiments, the alkaline earth metal -containing mineral feedstock is a magnesium-containing mineral feedstock. In some embodiments, the alkaline earth metalcontaining mineral feedstock is a calcium-containing mineral feedstock. In some embodiments, the alkaline earth metal-containing mineral feedstock is a silicon-containing magnesium feedstock, for example it may be a silicon-containing magnesium-containing mineral feedstock. Examples of silicon and magnesium-containing minerals include olivine, pyroxene, and serpentine.

[0930] The reaction with hydrohalic acid (e.g. HC1) is carried out under conditions suitable to produce an alkaline earth metal halide (e.g., magnesium chloride or calcium chloride) in solution. Suitable reaction times may include reacting with hydrohalic acid for a period in the range of from about 10 seconds to about 48 hours, such as from about 1 hour to about 24 hours. Exemplary temperature conditions may include reacting at ambient or elevated temperature, for example at a temperature in the range of from about 20 °C to about 95 °C, such as from about 40 °C to about 80 °C. These conditions may be selected based on mineral reactivity, particle size, and acid concentration, and to achieve a desired dissolved divalent cation concentration compatible with downstream carbonate formation and electrolyte recycle within the process loop. In the case of hydrochloric acid leaching, residence times depend on mineralogy, particle size, acid concentration, and temperature. In the present system, the mineral feedstocks are typically alkaline earth hydroxides, oxides, carbonates, or partially weathered silicates, which react rapidly with hydrochloric acidcompared to refractory oxide or sulfide ores. Accordingly, dissolution residence times are generally much shorter than those used in heap leaching or high-temperature metal extraction processes.

[0931] In agitated slurry reactors, suitable residence times for dissolution of reactive magnesium or calcium-bearing phases may range from about 10 seconds to about 24 hours, such as from about 5 minutes to about 6 hours, or from about 15 minutes to about 2 hours. In many continuous embodiments using finely divided feedstocks (for example d50 below 200 pm) and acid concentrations in the range of about 0.5-4 M HC1, effective cation release may be achieved with average residence times on the order of 10-90 minutes.

[0932] Elevated temperature can accelerate dissolution kinetics. For example, operation at temperatures of about 40-95 °C, such as 50-80 °C, may reduce required residence time relative to ambient conditions. Higher acid concentrations may similarly shorten dissolution time, while lower concentrations may be used where longer residence time or staged acid addition is employed to manage pH and downstream carbonate precipitation.

[0933] In contrast to heap or dump leaching processes, which may require weeks to months, the mineral dissolution step in the present process is preferably conducted in a controlled, agitated reactor system configured for continuous or semi-continuous operation, with residence time selected to achieve a target dissolved divalent cation concentration suitable for downstream carbonate formation while maintaining ionic balance and electrolyte recycle within the closed electrochemical loop.

[0934] In some embodiments, the alkaline earth metal-containing mineral feedstock is an alkaline earth metal silicate and step c) produces alkaline earth metal halide and a silicic acid. For example, it may be a magnesium silicate, with step c) producing magnesium halide and a silicic acid.

[0935] Step d) involves reacting alkali metal carbonate and / or bicarbonate from b) with alkaline earth metal halide from c) in the presence of water to produce solid alkaline earth metal carbonate and alkali metal halide. The reaction is carried out under conditions suitable to produce solid alkaline earth metal carbonate. For example, one or more of pH, concentration, water volume, temperature, pressure, and contact time, is set so as to control production of carbonate species. Suitable time conditions may for example include reacting for a period of time in the range of from 1 hour to 48 hours, or from 2 hours to 24 hours. Exemplary temperature conditions may for example include reacting at ambient or elevated temperature, e.g. at a temperature in the range of from 40 to 95 °C. If desired, the step may be carried out at low temperature, e.g. in the range of from 5 to 15 °C.

[0936] In some embodiments, the pressure is in the range of from 0.01 bar to 20 bar, or from 0.9 bar to 10 bar. In some embodiments, pressure is near atmospheric pressure.

[0937] In some embodiments, substantially all of the alkaline earth metal carbonate produced is in solid form (e.g. it precipitates), and most or all of the alkali metal halide (e.g. chloride) produced is dissolved in water.

[0938] In some embodiments, alkaline earth metal carbonate is precipitated. In some embodiments, substantially all of the alkaline earth metal carbonate produced is in solid form (e.g. it precipitates), and most or all of the alkali metal halide (e.g. chloride) produced is dissolved in water.In some embodiments, solid alkaline earth metal carbonate, is separated, for example by filtration, decanting or siphoning.

[0939] Carbonate that is produced may for example be exported as an electrically-neutral solid. By this is meant that exported solids do not contain significant amounts of net electrolyte charge, and the halide ions and, in some embodiments, the alkali metal ions remain predominantly within the system, e.g. in the circulating liquid phase.

[0940] Alkali metal halide produced in d) is recycled to a), and the process is substantially closed loop with respect to halide (e.g. chloride). In other words, no or low amounts of halide exit the process. The alkali metal halide may for example be returned to a) via a return loop. If desired, the alkali metal halide may undergo one or more treatment steps, e.g. to adjust concentration, or to remove impurities, prior to being recycled to a). By recycling alkali metal halide, losses of halide (e.g. chloride) from the system are reduced, providing a relatively environmentally benign process.

[0941] As used herein, “substantially closed-loop” refers to a system in which one or more ionic species are retained and recycled within a circulating electrolyte inventory, with export primarily limited to electrically neutral products such as stable carbonate solids.

[0942] As used herein, the term ‘substantially closed with respect to halide’ means that, with each iteration of the process steps, no or low amounts of halide are lost from the system. In some embodiments the term refers to a process or system configuration in which halide ions function predominantly as circulating electrolyte carrier species that remain within the internal liquid phase of the process and are recycled between unit operations rather than being consumed or exported as a primary product. In such embodiments:

[0943] • halide ions generated, released, or regenerated during process reactions are returned to the electrochemical or electrolyte regeneration stage in the form of dissolved alkali metal halide. • halide does not constitute a principal exported material stream, and net halide loss occurs only through minor, controlled purge, bleed, entrainment, or product washing streams necessary for impurity management or solids purification.

[0944] • the process is configured so that carbonate solids represent the primary carbon-containing export, while halide ions, such as chloride, are retained within the circulating electrolyte inventory to maintain ionic balance and support continued electrochemical operation.

[0945] In some embodiments, any net loss of halide from the system is limited to minor purge or bleed streams used for impurity control, concentration management, or electrolyte conditioning, and does not constitute a principal or intended mass flow of the process.

[0946] The halide species can for example be considered to function primarily as internal charge-balancing and ionic transport carriers within a regenerating electrochemical-mineral loop, while the principal intentional mass export of the process is stable solid carbonate formed from captured carbon dioxide.

[0947] In some embodiments, with each cycle, not more than 20% by weight of the halide (e.g. chloride) from the alkaline earth metal halide used in step d) is lost from the system, or not more than 15%, or notmore than 10%, or not more than 5%, or not more than 3%, or not more than 2%, or not more than 1% is lost.

[0948] In some embodiments, the process is also substantially closed-loop with respect to alkali metal ions, such as sodium ions, which are predominantly retained and recycled within the electrolyte.

[0949] In some embodiments, with each cycle, not more than 20% by weight of the alkali metal from the alkaline earth metal halide used in step d) is lost from the system, or not more than 15%, or not more than 10%, or not more than 5%, or not more than 3%, or not more than 2%, or not more than 1% is lost.

[0950] In some embodiments, ionic species are substantially conserved within the process, whilst carbonate is exported from the process.

[0951] In some embodiments, small amounts of halide-containing feed, for example an alkali metal halide solution such as aqueous sodium chloride brine, may be introduced as make-up to maintain halide and / or alkali metal levels within the circulating electrolyte. Such make-up addition may be used to compensate for minor operational losses associated with purge streams, entrainment, solids moisture carryover, sampling, or maintenance. The amount of halide added as make-up may correspond to not more than about 20% by weight of the circulating chloride inventory over a defined operating period, such as not more than about 15%, 10%, 5%, 2%, or 1%.

[0952] In some preferred continuous embodiments, average steady-state halide make-up is below about 5% of the circulating halide inventory over the same operating period.

[0953] In some embodiments, ionic species are substantially conserved within the process boundary, while carbonate is intentionally exported from the process as a solid product.

[0954] If desired, the level of alkali metal halide (e.g. sodium chloride) may be monitored, for example using conductivity, density, ion-selective electrodes, or chemical analysis, and make-up halide and / or alkali metal may be added when the measured value falls outside a predetermined operating range. For example, where alkali metal halide is recycled to step a), the process or system may be configured to allow measurement of conductivity, using a conductivity meter, and additional alkali metal halide may be added when the conductivity is outside required levels (e.g. too low).

[0955] In some embodiments, the products exported from the process are substantially electrically neutral, and net ionic species (e.g. such as halide and alkali metal ions) are substantially retained within the process loop.

[0956] Depending on the conditions employed, following initial contacting of the carbon dioxide -containing feed with aqueous alkali metal hydroxide or alkaline earth metal hydroxide, the post-contact gas may still contain higher than desired concentrations of carbon dioxide. Accordingly the post-contact gas may be recirculated and further contacted with aqueous alkali metal hydroxide or alkaline earth metal hydroxide if desired. Accordingly, in some embodiments, following contacting of the carbon dioxidecontaining feed with aqueous alkali metal hydroxide or alkaline earth metal hydroxide, at least a portion of the remaining carbon dioxide is recirculated and re-contacted with the aqueous alkali metal hydroxide or alkaline earth metal hydroxide.It will be appreciated that impurities may build up within the system over time. Accordingly, in some embodiments, a controlled purge is carried out to manage impurity accumulation. This can be performed as needed to assist in maintaining normal operating conditions and process efficiency, for example.

[0957] In some embodiments, the process is continuous or semi-continuous.

[0958] In certain embodiments, carbonate and / or bicarbonate species generated in a first contacting stage are transferred as a dissolved inorganic carbon-bearing liquor to a second stage in which CO2may be selectively released by pH adjustment, pressure reduction, temperature adjustment, electrochemical pH swing, or combinations thereof. The released CO2may then be re-contacted with regenerated alkalinity to increase overall conversion efficiency or to enable operation with dilute CO2feeds such as ambient air. Such release and re-absorption steps may be carried out while retaining halide and alkali metal ions within the circulating electrolyte inventory. In some embodiments, once sufficient carbon dioxide and related variant forms has been contacted with the alkali earth metal.

[0959] The solid alkaline earth metal carbonate can be recovered, and used in any of a variety of different ways if desired. For example, it can be used as a store for carbon dioxide. Advantageously, in some embodiments, the process produces a stable form of solid alkaline earth metal carbonate, e.g. magnesium carbonate. In some embodiments, the solid alkaline earth metal carbonate is or comprises magnesite and / or hydromagnesite.

[0960] The carbonate may for example be stockpiled, or it may be used for soil amendment. If desired it may be used for mine backfill. Carbonates can be used in fillers, for example in cosmetics and toothpastes. Carbonates such as magnesium carbonate may be used in gym chalk. The solid alkaline earth carbonate can also be used as a source for releasing carbon dioxide, e.g. on treatment with a suitable acid.

[0961] The solid alkaline earth metal carbonate can also be used to make further products. For example, it may be incorporated in construction material, for example in a cementitious material such as a concrete. It may be incorporated into a geopolymer. Alkaline earth metal carbonates can be used as fillers or additives, for example for particle packing adjustment, or to adjust density, rheology or thermal behaviour.

[0962] In some embodiments, at least a portion of the alkali metal carbonate and / or bicarbonate produced in b) is used to produce a cementitious material, optionally wherein the cementitious material is a geopolymer.

[0963] As discussed above, in some embodiments, a silicon-containing alkaline earth metal-containing mineral feedstock may be used. In such embodiments, silicon-containing byproducts may be produced. In some embodiments, a silicon-containing byproduct is exported from the process, optionally wherein the silicon containing byproduct is a silicic acid or silicon oxide. In some embodiments, a silicic acid is produced. In some embodiments, the silicic acid is dehydrated to produce silicon oxide. Such products can for example be used in cementitious materials, e.g. in Portland cement, Wagners EFC, or a geopolymer. For example, silicon oxide may be used as a filler, contributing to properties such as particle packing and strength. Silicic acid may be used in the form of dissolved silica species that form binding gels. In someembodiments, at least a portion of the silicon-containing byproduct is used to produce a cementitious material, optionally wherein the cementitious material is a geopolymer or Portland cement.

[0964] An example of a process for producing a carbonate in accordance with the present disclosure is provided in figure 1. The process shown in figure 1 includes steps including electrolysis, reaction of a carbon-dioxide feed with sodium hydroxide and precipitation of sodium carbonate and / or bicarbonate, mineral dissolution using HC1, and cation exchange. As shown in the figure, a water feed (10), which may be for example pure water, deionized water, or town water, and an alkali metal halide feed (11) (e.g., saline water, sea water, underground water, solar salt, pan evaporated salt, or lab grade (e.g. 99.99%) salt) undergo feed treatment (12). If required, an HC1 stream resulting from electrolysis may also be introduced into this stage of the process. A treated brine solution (13) is produced which then undergoes further feed treatment (14). Additional feeds may be introduced, such as for example a sodium chloride recycle stream from the cation exchange stage, water, and / or an optional brine bittern (15). Following feed treatment, an aqueous NaCl feed of appropriate purity and concentration for subsequent stages is produced as purified brine solution (16). The aqueous alkali metal chloride stream (15) is then subjected to electrolysis (17), for example in the form of BDEM, or a chloralkali process followed by reaction of hydrogen and chlorine, resulting in production of a sodium hydroxide stream (18), and an HC1 stream (19). The HC1 stream can, as mentioned above, be used for treatment of further feed if needed, or can be used for mineral dissolution (20). The sodium hydroxide stream (18) can then be used in a carbonate production and precipitation step (21), in which it is contacted with a carbon dioxide -containing feed, resulting in production of sodium carbonate and / or bicarbonate, which precipitates. The carbonate / soda ash and / or sodium bicarbonate, if produced (22), is then subject to cation exchange (23) by reaction with an alkaline earth metal chloride (e.g. magnesium chloride) in the presence of water. This produces sodium chloride and magnesium carbonate. Due to the significantly different solubilities of the products, the sodium chloride predominantly remains in solution, whilst the magnesium carbonate is obtained as a solid. The products can be separated and, as discussed above, the sodium chloride can be recycled to the process e.g. by reintroduction into feed treatment step (14), forming a substantially closed loop. If needed, small additional amounts of brine feed (13) can be introduced into the loop to account for any minor losses that may occur, e.g. due to purges. As discussed above, HC1 resulting from the electrolysis step may be used in a mineral dissolution step, e.g. being used to react with an alkaline earth-containing mineral feedstock, such as a suitable silicate mineral feed (e.g. basalt, ultramafic deposits and mafic minerals), a suitable oxide / hydroxide mineral feed e.g. precipitated magnesium hydroxide), mine residues such as laterite processing comminution and flotation tailings, or CaO / MgO-containing feed minerals. This results in generation of an alkaline earth metal chloride (e.g. magnesium chloride) containing stream which can be used for the cation exchange step.

[0965] As an alternative to the above, sodium hydroxide (e.g. a portion of the stream resulting from electrolysis) can be used for reaction with a silicate mineral feedstock, producing alkaline earth metal hydroxide and a sodium silicate. The sodium silicate can then be reacted with HC1 (e.g. produced via electrolysis) to regenerate sodium chloride and a silicic acid.Thus, inputs to the system include the carbon dioxide-containing stream, the mineral feedstock, and electricity / energy inputs for the electrolysis and other steps. Brine feed is used initially to generate the circulating electrolyte, and then to top up the system as needed to accommodate for any minor losses.

[0966] Figure 6 provides a schematic of a further embodiment of a process for producing a carbonate according to the present disclosure. The process shown in figure 6 is similar to that shown in figure 5, with the exception that the first feed treatment step (12) is omitted, with a brine feed being directly introduced to feed treatment (14) and a purified brine solution being produced and then subjected to electrolysis. Again, the process includes a mineral dissolution step, whereby a mineral feedstock (24) such as a silicate or oxide / hydroxide mineral feed (e.g. basalt ultramafics, magnesium hydroxide) and / or calcium or magnesium-rich mine tailings are treated.

[0967] Systems Configured to Run Processes Involving Reaction of Alkali Metal Hydroxide With Carbon Dioxide

[0968] There is also provided a system or apparatus adapted for carrying out the above-described process. More particularly, there is provided a system for capturing carbon dioxide, comprising: A) an electrochemical unit configured to electrochemically treat an alkali metal halide and water to produce aqueous alkali metal hydroxide, wherein the electrochemical unit is configured to i) produce hydrohalic acid (e.g. HC1), or ii) produce hydrogen and halogen, and wherein, when configured to produce hydrogen and halogen, the system also comprises a hydrohalic acid generation unit configured to produce hydrohalic acid (e.g. HC1) from the hydrogen and halogen (e.g. chlorine); B) a carbon dioxide capture unit configured to contact a carbon dioxide-containing feed with the aqueous alkali metal hydroxide, to produce an alkali metal carbonate and / or bicarbonate; C) a mineral feedstock activation unit configured to react the hydrohalic acid with an alkaline earth metal-containing mineral feedstock to produce alkaline earth metal halide; D) an alkaline earth metal carbonate formation unit configured to react the alkali metal carbonate and / or bicarbonate with alkaline earth metal halide in the presence of water to produce solid alkaline earth metal carbonate and alkali metal halide; and E) a recycle pathway configured to recycle alkali metal halide produced in D), to A), and wherein the system is configured to be substantially closed-loop with respect to halide.

[0969] Any suitable configuration of apparatus may be used for the system. The electrochemical unit A) may for example include an apparatus for carrying out the chloralkali process, such as a diaphragm cell or a membrane cell. It may for example include an apparatus for carrying out EDBM. Where hydrogen and chlorine are used, the electrochemical unit may for example also contain a suitable apparatus for producing HC1, such as a direct combustion burner, or a graphite or PTFE-lined HC1 synthesis unit.

[0970] In some embodiments, the system comprises a halogen-management module including a hydrohalic acid (e.g. HC1) generation unit which comprises a recombination reactor and / or an electrochemical cell configured to react hydrogen and halogen to produce hydrohalic acid for recycle to the mineral activation unit. In some embodiments, the halogen-management module comprises an absorber configured to convert halogen species, for example chlorine species, into one or more of hydrochloric acid, hypochlorite, chlorate,and regenerated halide salts, and optionally wherein an oxidant residual of a recycled brine stream is controlled using oxidation-reduction potential (ORP) measurement and / or free-halogen measurement.

[0971] The carbon dioxide capture unit may for example be a reactor or vessel such as a column, tower or scrubber, such as a packed column, trayed column, fluidised bed reactor, spray tower, bubble column, venturi scrubber, membrane contactor, CTSR (continuous stirred tank reactor), or mechanically agitated reactor. In some embodiments, a system as defined herein comprising a column, gas injection portion, gas outlet, liquid outlet, and solid carbonate collection chamber, is used for step b). In some embodiments, the carbon dioxide capture unit comprises a packed column, spray tower, bubble column, venturi scrubber, membrane contactor, or mechanically agitated reactor, optionally which is configured to enhance gas-liquid mass transfer and to control carbonate / bicarbonate speciation by pH and alkalinity.

[0972] If desired, multiple reactors, vessels, or systems may be utilised for carrying out step b). For example, a set-up containing 2 or more columns may be used. In some embodiments, a system comprising 2 or more columns in series is used.

[0973] The mineral feedstock activation unit may comprise any reactor system suitable for contacting an alkaline earth-bearing mineral feedstock with an acidic solution, such as hydrochloric acid, under conditions effective to dissolve the mineral and produce soluble alkaline earth metal halides. In various embodiments, the activation unit may comprise an agitated leach reactor, such as a continuously stirred tank reactor (CSTR), configured to operate as a slurry reactor with controlled solids loading and residence time. One or more such reactors may be arranged in series to increase overall conversion while allowing staged acid addition and pH control. In other embodiments, the activation unit may comprise a pressurised reactor or autoclave, particularly where elevated temperature is used to accelerate dissolution of less reactive mineral phases. Suitable reactor constructions include corrosion-resistant lined vessels, polymer-lined steel, glass-lined reactors, or reactors constructed from acid-resistant alloys or composites. The reactor system may further include solids handling equipment such as slurry feed hoppers, metering pumps, agitation systems, and overflow or underflow arrangements for continuous solids and liquid removal. In some embodiments, the mineral feedstock activation unit is or comprises a venturi, fluidized bed reactor, a CSTR, a column reactor with a long contacting column.

[0974] Following dissolution, the slurry or liquor containing dissolved divalent cations may be transferred, optionally after primary solids separation, to a carbonate formation unit. The alkaline earth metal carbonate formation unit may comprise a precipitation reactor configured to contact the cation-containing solution with dissolved carbonate species generated elsewhere in the process. In some embodiments, this unit is a stirred tank precipitator, such as a CSTR-type reactor, allowing controlled mixing, pH regulation, and supersaturation management. Multiple precipitation reactors may be arranged in series to allow staged crystal growth and improved control over particle size distribution. Alternative reactor configurations include fluidised-bed crystallisers, which promote growth of larger, denser carbonate particles on seed material, or mixed suspension mixed product removal (MSMPR) crystallisers for continuous operation with controlled residence time and solids withdrawal. In all cases, the reactor may be equipped with agitation,pH monitoring, temperature control, and controlled addition points for carbonate -bearing streams and recycle liquors.

[0975] The mineral activation unit and the carbonate formation unit may be hydraulically connected as part of a continuous loop, with intermediate clarification, filtration, or membrane separation units positioned between them where needed to remove undissolved solids or manage impurities. These reactor units may be arranged in modular form, for example as skid-mounted or containerised process modules, allowing distributed deployment and integration with the upstream electrochemical unit and downstream electrolyte recycle system.

[0976] In some embodiments, the mineral feedstock activation unit is configured to receive a mineral feedstock selected from basalt, peridotite, dunite, harzburgite, serpentinised ultramafic rock, and mixtures thereof, and / or industrial residues comprising steel slag, red mud, mine tailings, fly ash, cement kiln dust, including partially altered or weathered forms of the foregoing, and including mixtures thereof, optionally wherein the mineral feedstock activation unit is configured to receive a weathered form of the foregoing which has undergone particle size reduction.

[0977] As discussed above, one or more parameters such as temperature, pH, pressure, pressure, CO2partial pressure, and conductivity may be monitored. The system may for example include appropriate monitoring and / or sampling sites. For example, where alkali metal chloride is recycled to A), the system may contain a conductivity meter arranged to sample the conductivity of the recycled stream.

[0978] In some embodiments, the system is incorporated into a power station, a wastewater treatment facility, a municipal waste processing facility, a mine site, a chemical or biotechnological plant, a gasification and / or pyrolysis system, or a cement and / or concrete manufacturing facility.

[0979] In some embodiments, the system is configured to receive a carbon dioxide-containing feed selected from the group consisting of air, a power station exhaust stream, a biogas CO2-containing stream, a diesel, petrol, LPG, natural gas or biogas generator exhaust stream, a pyrolysis exhaust stream, an industrial furnace exhaust stream, a methane pyrolysis exhaust stream, a cement kiln exhaust stream, and a metallurgical smelter exhaust stream.

[0980] In some embodiments, the system is configured as a retrofit module for direct mineralisation of flue gas from a generator set or combined heat-and-power (CHP) unit, wherein the carbon dioxide capture unit is arranged as an exhaust scrubber receiving flue gas and discharging a CO2-depleted exhaust stream.

[0981] In some embodiments, the retrofit module is operable without substantial modification of the host generator’s combustion system. If required, slight modifications may be made, for example an exhaust fan may be used with the scrubber to maintain pressure at the exhaust. As further examples, depending on the unit’s sensitivity to backpressure, include 1) a direct bolt on option, and 2) a bolt on plus fan and ancillary equipment option. In some embodiments, a heat exchanger maty be used for example to control the temperature in the column. In some embodiments, the retrofit module is transportable and comprises an exhaust connection interface, a recirculating alkaline loop, and a neutralised discharge mode in which an aqueous effluent is discharged or reused when pH and oxidant residual meet predetermined thresholds.In some embodiments, the system is configured for biogas upgrading, wherein in use a raw biogas stream is contacted with the aqueous alkali metal hydroxide or alkaline earth metal hydroxide to remove CO2and produce an upgraded methane stream, and wherein removed CO2is mineralised to carbonate in the carbonate formation unit.

[0982] In some embodiments, the system comprises a central processing facility configured to receive a carbonate -bearing and / or bicarbonate-bearing liquor generated by one or more distributed retrofit modules and to perform precipitation, solids finishing, and / or brine regeneration at a centralised scale.

[0983] Processes Involving Reaction of Alkaline Earth Metal Hydroxide With Carbon Dioxide Another aspect of the present disclosure relates to processes for producing an alkaline earth metal carbonate which involve contacting of a CO2-containing feed with aqueous alkaline earth metal hydroxide (e.g. Mg(OH)2) to produce the corresponding carbonate.

[0984] Accordingly, there is provided a process for producing an alkaline earth metal carbonate, comprising: a’) electrochemically treating an alkali metal halide and water to produce aqueous alkali metal hydroxide and hydrohalic acid; b’) reacting hydrohalic acid from a’), with an alkaline earth metalcontaining mineral feedstock to produce alkaline earth metal halide; and reacting the alkaline earth metal halide with alkali metal hydroxide from a’), to produce alkaline earth metal hydroxide and alkali metal halide; or reacting alkali metal hydroxide from a’) with an alkaline earth metal-containing mineral feedstock, wherein the alkaline earth metal-containing mineral feedstock is a silicate-containing alkaline earth metal-containing mineral feedstock, to produce alkaline earth metal hydroxide and an alkali metal silicate; and reacting the alkali metal silicate with hydrohalic acid from a’) to produce a silicic acid and alkali metal halide; and c’) contacting a carbon dioxide-containing feed with aqueous alkaline earth metal hydroxide from b’), to produce solid alkaline earth metal carbonate; wherein alkali metal halide produced in b’) is recycled to a’), and wherein the process is substantially closed-loop with respect to halide.

[0985] The processes are substantially closed loop with respect to halide, in that the alkali metal halide is produced by electrochemically treating an alkali metal halide and water to produce hydrohalic acid and alkali metal hydroxide. Either the hydrohalic acid is used to react with an alkaline earth metal-containing mineral feedstock (e.g. a magnesium-containing mineral feedstock) to produce the corresponding metal halide, which is then reacted with alkali metal hydroxide to produce alkaline earth metal hydroxide (which can then be used for contacting with the carbon dioxide-containing feed), or if the mineral is a silicate-containing mineral, the alkali metal hydroxide can be reacted with that mineral to produce alkaline earth metal hydroxide (e.g. Mg(OH)2) and an alkali metal silicate which is reacted with hydrohalic acid to produce a silicic acid and alkali metal halide. Further, alkali metal halide produced in the cation exchange can be recycled to the process.

[0986] The discussion above in preceding aspects in relation to features such as carbon dioxide-containing feeds, electrochemical treatment of alkali metal halides, applies equally to this aspect. For example, in some embodiments, the halide is chloride. In some embodiments, the alkali metal is sodium. In some embodiments, the alkali metal chloride is sodium chloride which is obtained from seawater.Step b’) in some embodiments requires reacting hydrohalic acid from a’), with an alkaline earth metal-containing mineral feedstock to produce alkaline earth metal halide; and reacting the alkaline earth metal halide with alkali metal hydroxide from a’), to produce alkaline earth metal hydroxide and alkali metal halide.

[0987] The discussion above in preceding aspects in relation to features such as reaction of hydrohalic acid with alkaline earth metal -containing mineral feedstock, applies equally to this aspect. For example, in some embodiments, the alkaline earth metal is magnesium or calcium, optionally magnesium. In some embodiments, the alkaline earth metal-containing mineral feedstock is selected from the group consisting of nickel laterite tailings, brucite, serpentine, olivine, pyroxene, hydrotalcite, basaltic materials, ultramafic rocks, industrial tailings, and oxide / hydroxide phases occurring in mining residues, including partially altered or weathered forms of the foregoing, and including mixtures thereof, optionally wherein the alkaline earth metal -containing mineral feedstock is a weathered form of the foregoing which has undergone particle size reduction. In some embodiments, the alkaline earth metal-containing mineral feedstock is a silicon-containing alkaline earth metal -containing mineral feedstock.

[0988] The reaction of the alkaline earth metal halide (e.g. magnesium chloride, calcium hydroxide) with alkali metal hydroxide (e.g sodium hydroxide) from a’), to produce alkaline earth metal hydroxide and alkali metal halide, may be carried out under any suitable conditions. A suitable reactor may be used, for example a continuous stirred-tank reactor or CSTR-type precipitator may be used.

[0989] The reaction is carried out under conditions suitable to produce solid alkaline earth metal hydroxide. Suitable time conditions may for example include reacting for a period of time in the range of from 1 hour to 48 hours, or from 2 hours to 24 hours. Exemplary temperature conditions may for example include reacting at ambient or elevated temperature, e.g. at a temperature in the range of from 40 to 95 °C. If desired, the step may be carried out at low temperature, e.g. in the range of from 5 to 15 °C.

[0990] The alkaline earth metal hydroxide is typically significantly less water soluble than the alkali metal halide (e.g. chloride). In some embodiments, substantially all of the alkaline earth metal hydroxide produced is in solid form (e.g. it precipitates), and most or all of the alkali metal halide (e.g. chloride) produced is dissolved in water. In some embodiments, alkaline earth metal hydroxide is precipitated.

[0991] In some embodiments, substantially all of the alkaline earth metal hydroxide produced is in solid form (e.g. it precipitates), and most or all of the alkali metal halide produced is dissolved in water. In some embodiments, solid alkaline earth metal hydroxide is separated, for example by filtration, decanting or siphoning.

[0992] In some embodiments, step b’) involves reacting an alkali metal hydroxide stream from step a) with a silicon-containing alkaline earth metal mineral feedstock, to produce an alkaline earth metal hydroxide (e.g., magnesium hydroxide or calcium hydroxide) and an alkali metal silicate. The silicon-containing magnesium-containing mineral feedstock may for example be selected from minerals such as olivine, pyroxene, and serpentine. The reaction with alkali metal hydroxide is carried out under conditions suitable to convert the silicate mineral to a dissolved or partially dissolved alkaline earth metal-bearing liquor andalkali metal silicate species. Suitable residence times for the alkaline hydroxide contact may range from about 10 minutes to about 24 hours, such as from about 30 minutes to about 6 hours, depending on mineral reactivity, particle size, alkali concentration, and temperature. Exemplary temperature conditions for silicate dissolution may include ambient to elevated temperatures, such as from about 20 °C to about 95 °C, and in some embodiments from about 40 °C to about 80 °C, with higher temperatures generally accelerating the dissolution rate. The reaction may also be carried out at lower temperatures, for example in the range of from about 5 °C to about 15 °C, where slower dissolution rates are acceptable or other process constraints apply.

[0993] Similarly, the reaction of the alkali metal silicate with hydrohalic acid from step a’) to produce a silicic acid species and alkali metal halide may be carried out under conditions effective for acidification and silicate conversion. Suitable residence times for the acidification step may also range from about 10 minutes to about 24 hours, such as from about 30 minutes to about 6 hours, depending on the composition of the silicate solution and the desired degree of silicate hydrolysis or silicic acid release. Exemplary temperature conditions for acidification may include ambient to elevated temperatures, for example in the range of about 20 °C to about 95 °C, or from about 40 °C to about 80 °C, with process conditions selected to balance reaction kinetics and downstream process integration.

[0994] In some embodiments, a silicon-containing byproduct is exported from the process. For example, the silicon-containing byproduct may comprise silicic acid, which may be further processed, dehydrated, or converted to silicon oxide, silica gel, or other silicon oxide materials depending on process conditions and desired product specifications.

[0995] Step c’) requires contacting a carbon dioxide-containing feed with aqueous alkaline earth metal hydroxide from b’), to produce solid alkaline earth metal carbonate; For example, where the alkaline earth metal is magnesium, the carbon dioxide-containing feed is contacted with aqueous magnesium hydroxide.

[0996] Any suitable reactor or vessel may be used for carrying out step c’). Examples include a column, tower or scrubber, such as a packed column, trayed column, fluidised bed reactor, spray tower, bubble column, venturi scrubber, membrane contactor, CTSR (continuous stirred tank reactor), or mechanically agitated reactor.

[0997] In some embodiments, a system as defined herein comprising a column, gas injection portion, gas outlet, liquid outlet, and solid carbonate collection chamber, is used for step c’).

[0998] If desired, multiple reactors, vessels, or systems may be utilised for carrying out step c’). For example, a set-up containing 2 or more columns may be used. In some embodiments, a system comprising 2 or more columns in series is used.

[0999] The contacting in step c’) is carried out under suitable conditions, e.g. temperature, time, pressure, to produce alkali metal carbonate and / or bicarbonate. In some embodiments, one or more of pH, temperature, pressure, contact time, and CO2partial pressure is set so as to control production of carbonate species. In some embodiments, one or more parameters is monitored (e.g. pH, pressure, CO2partial pressure, temperature) and depending on the value of the one or more parameters, the reaction conditionsmay be adjusted (e.g. rate of introduction of carbon dioxide -containing feed, rate of introduction of aqueous alkaline earth metal hydroxide, pH, temperature) to control production of carbonate. For example initially step c’) may in some cases be hydroxide -dominant but as more carbon dioxide -containing feed is introduced, carbonate may be the dominant species. In some embodiments, the pH is a pH sufficient to promote conversion of dissolved CO2 to carbonate species, for example in the range of from 8 to 14, or 9 to 13, or 10 to 12.5.

[1000] In some embodiments, additional alkaline earth metal hydroxide is added when CO2 content (e.g. CO2 content in a flue) rises above a desired level. For example, carbon dioxide partial pressure may be measured and used to determine dosing / addition of alkaline earth metal hydroxide. For example, in some embodiments the liquid contents may be discharged and fresh alkaline earth metal hydroxide and water added. In some embodiments, aqueous alkaline earth metal hydroxide is added continuously, maintaining pH at a desired level.

[1001] In some embodiments, the temperature is in the range of from 0 °C to 90 °C, for example in the range of from 5 °C to 60 °C, or from 10 °C to 35 °C. In some embodiments step c’) is carried out at ambient temperature. In some embodiments, step c’) is carried out at elevated temperature.

[1002] In some embodiments, the pressure is in the range of from 0.01 bar to 20 bar, or from 0.9 bar to 10 bar. In some embodiments, pressure is near atmospheric pressure. In some embodiments, the CO2 partial pressure is in the range of from 0.0004 bar to 10 bar, or from 0.001 bar to 5 bar, or from 0.004-1 bar.

[1003] In some embodiments, the contact time is in the range of from 10 seconds to 48 hours, or from 1 minute to 12 hours, or up to 1 month.

[1004] In some embodiments, alkaline earth metal carbonate is precipitated. In some embodiments, solid alkaline earth metal carbonate, is separated, for example by filtration, decanting or siphoning.

[1005] In some embodiments, a flow of carbon dioxide-containing feed is passed through aqueous alkaline earth metal hydroxide, for example the carbon dioxide-containing feed may be introduced at or near the bottom of a vertically oriented column or tower reactor containing aqueous alkaline earth metal hydroxide.

[1006] If desired, a carbon dioxide feed may be contacted multiple times, for example by passing through a series of reactors, or by recirculation / reintroduction into the reactor.

[1007] As discussed above, advantageously in some embodiments, the process produces a stable form of solid alkaline earth metal carbonate, e.g. magnesium carbonate. In some embodiments, the solid alkaline earth metal carbonate is or comprises magnesite and / or hydromagnesite.

[1008] Alkali metal halide produced in b’) is recycled to a’), and the process is substantially closed-loop with respect to halide. In other words, no or low amounts of chloride exit the process.

[1009] The alkali metal halide may for example be returned to a’) via a return loop. If desired, the alkali metal halide may undergo one or more treatment steps, e.g. to adjust concentration, or to remove impurities, prior to being recycled to a’).

[1010] In some embodiments, the process is substantially closed-loop with respect to alkali metal. In some embodiments, ionic species are substantially conserved within the process, whilst carbonate is exportedfrom the process. In some embodiments, the products exported from the process are substantially electrically neutral, and net ionic species are substantially retained within the process.

[1011] In some embodiments, small amounts of halide-containing feed, e.g. an alkali metal halide-containing feed such as an aqueous sodium chloride feed, is introduced as needed to maintain halide levels and / or to maintain alkali metal levels. For example an amount of up to 20% by weight, or up to 15%, or up to 10%, or up to 5%, or up to 2%, or up to 1% of the circulating amount of halide (e.g. chloride) may be added periodically.

[1012] If desired, the level of alkali metal halide (e.g. sodium chloride) may be monitored, e.g. using a conductivity meter, and the conductivity reading used to determine whether additional halide and / or alkali metal should be added. For example, where alkali metal halide is recycled to step a’), the process or system may be configured to allow measurement of conductivity, using a conductivity meter, and additional alkali metal halide (e.g. chloride) may be added when the conductivity is outside required levels (e.g. too low).

[1013] In some embodiments, the products exported from the process are substantially electrically neutral, and net ionic species are substantially retained within the process.

[1014] In some embodiments, the process is continuous or semi-continuous.

[1015] The solid alkaline earth metal carbonate can be recovered, and used as discussed above for previous aspects.

[1016] As discussed above, in some embodiments, a silicon-containing alkaline earth metal-containing mineral feedstock may be used. In such embodiments, silicon-containing byproducts may be produced. For example these may be treated or used as set out above for other aspects

[1017] Systems Configured to Run Processes Involving Reaction of Alkaline Earth Metal Hydroxide With Carbon Dioxide

[1018] There is also provided a system or apparatus adapted for carrying out the above-described process. Accordingly, in another aspect, there is provided a system for producing an alkaline earth metal carbonate, comprising: A’) an electrochemical unit configured to electrochemically treat an alkali metal halide and water, to produce aqueous alkali metal hydroxide, wherein the electrochemical unit is configured to i) produce hydrohalic acid, or ii) produce hydrogen and halogen, and wherein, when configured to produce hydrogen and halogen, the system also comprises a hydrohalic acid generation unit configured to produce hydrohalic acid from the hydrogen and halogen; B’) an alkaline earth metal hydroxide production unit comprising either a mineral feedstock activation unit configured to react the hydrohalic acid with an alkaline earth metal-containing mineral feedstock to produce alkaline earth metal halide, and a halide exchange unit configured to react the alkaline earth metal halide with the alkali metal hydroxide to produce alkaline earth metal hydroxide and alkali metal halide; or an alkaline mineral feedstock activation unit configured to react the alkali metal hydroxide with a silicon-containing alkaline earth metal-containing mineral feedstock to produce alkaline earth metal hydroxide and an alkali metal silicate, and a silicic acid production unit configured to react the alkali metal silicate with the hydrohalic acid to produce a silicic acid and alkali metal halide; and C’) a carbon dioxide capture unit configured to contact a carbon dioxide-containing feed with the aqueous alkaline earth metal hydroxide, to produce an alkaline earth metal carbonate; and D’) a recycle pathway configured to recycle alkali metal halide produced in B’), to A’), and wherein the system is configured to be substantially closed-loop with respect to halide.

[1019] The discussion above in preceding aspects in relation to features such as electrochemical units, carbon dioxide capture units, and recycle pathways, applies equally to this aspect.

[1020] In some embodiments, the system comprises a halogen-management module including a hydrohalic acid generation unit which comprises a recombination reactor and / or an electrochemical cell configured to react hydrogen and halogen (e.g. chlorine) to produce hydrohalic acid (e.g. HC1) for recycle to the mineral activation unit.

[1021] In some embodiments, the halogen-management module comprises an absorber configured to convert halogen species, such as chloride species, into one or more of hydrochloric acid, hypochlorite, chlorate, and regenerated halide salts, and optionally wherein an oxidant residual of a recycled brine stream is controlled using oxidation-reduction potential (ORP) measurement and / or free-halogen measurement.

[1022] In some embodiments, the halogen-management module comprises one or more gas-liquid contacting and redox-conditioning units configured to convert halogen species into reusable or neutralised forms while maintaining halide closure within the process loop.

[1023] Where an absorber is used, it may for example comprise one or more of the following: a packed column scrubber (countercurrent gas-liquid contact), a spray tower, a venturi scrubber, a bubble column absorber, and a plate or tray column. The absorber may for example be constructed from corrosion-resistant materials such as FRP, PVC, CPVC, PTFE-lined steel, rubber-lined steel, titanium, or high-nickel alloys. The absorber may for example be configured to contact a halogen-containing gas stream (e.g., Ch, HOC! vapor, mixed oxidants) with an aqueous absorbent comprising recycled brine, alkaline liquor, or conditioned electrolyte. Within the absorber, halogen species are converted into one or more of: hydrochloric acid (HC1), hypochlorite (OCF), chlorate (CIOs ) and regenerated chloride salts (e.g., NaCl, MgCh). The choice of operating pH, temperature, and redox conditions determines product distribution.

[1024] Downstream of the absorber, the system may for example include a redox conditioning vessel or in-line reaction zone configured to reduce or stabilise oxidant residuals prior to electrolyte recycle. This zone may comprise one or more of: a stirred tank reactor (CSTR), a static mixer section, a pipe reactor with injection ports. Optional reductants include: hydrogen gas, sulfite / bisulfite salts, thiosulfate, ferrous salts, electrochemical reduction cells. Control of oxidant residual may be achieved using, for example: oxidation-reduction potential (ORP) probes, free chlorine / total chlorine analyzers, pH sensors, conductivity meters.

[1025] If desired, instrumentation may be arranged in feedback loops controlling one or more of: reductant dosing pumps, electrochemical reduction current, recycle flow rates. This ensures the recycled brine remains compatible with upstream electrochemical and mineral processing units.

[1026] The system includes B’) an alkaline earth metal hydroxide production unit comprising either a mineral feedstock activation unit configured to react the hydrohalic acid with an alkaline earth metal-containing mineral feedstock to produce alkaline earth metal halide, and a halide exchange unit configured to react the alkaline earth metal halide with the alkali metal hydroxide to produce alkaline earth metal hydroxide and alkali metal halide; or an alkaline mineral feedstock activation unit configured to react the alkali metal hydroxide with a silicon-containing alkaline earth metal-containing mineral feedstock to produce alkaline earth metal hydroxide and an alkali metal silicate, and a silicic acid production unit configured to react the alkali metal silicate with the hydrohalic acid to produce a silicic acid and alkali metal halide.

[1027] Any suitable reactor(s) or vessel(s) may be used for the mineral feedstock activation unit, halide exchange unit, alkaline mineral feedstock activation unit, and silicic acid production unit.

[1028] For example the mineral feedstock activation unit may comprise one or more of: agitated leach tanks (CSTR cascade), Pachuca tanks (air-lift reactors), pressure leach autoclaves and attrition scrubbers for slurry activation. Features may for example include: slurry density control, acid dosing ports, steam or heat-exchange jackets, and / or solid-liquid separation (thickeners, filters, hydrocyclones).

[1029] In some embodiments, the mineral feedstock activation unit is configured to receive a mineral feedstock selected from basalt, peridotite, dunite, harzburgite, serpentinised ultramafic rock, and mixtures thereof, and / or industrial residues comprising steel slag, red mud, mine tailings, fly ash, cement kiln dust, including partially altered or weathered forms of the foregoing, and including mixtures thereof, optionally wherein the mineral feedstock activation unit is configured to receive a weathered form of the foregoing which has undergone particle size reduction.

[1030] The halide exchange unit may for example comprise one or more of: a stirred tank precipitator (MSMPR crystallizer), draft-tube baffle crystallizer, fluidised-bed crystallizer, and / or a continuous mixed suspension mixed product removal (MSMPR) reactor. The unit may for example include one or more of a pH control system, a seeding loop for particle size control, and classified overflow / underflow solids handling.

[1031] The alkaline mineral feedstock activation unit may for example comprise one or more of: a heated stirred reactor, a slurry loop reactor, an attrition mill with alkaline dosing, and / or a pressurised digester.

[1032] The silicic acid production unit may for example comprise one or more of: a neutralisation reactor (CSTR), a static mixer with acid injection, a gel precipitation vessel, a filtration and washing system.

[1033] The carbon dioxide capture unit may for example comprise a packed column absorber, a spray tower, a bubble column, a Venturi scrubber, a membrane contactor, and / or a mechanically agitated gasliquid reactor. The unit may if desired be configured to enhance gas-liquid mass transfer, for example via: structured packing, fine bubble diffusers, high-shear impellers, and / or recirculation loops. It may for example be configured to control carbonate / bicarbonate speciation by pH and alkalinity.

[1034] As discussed above, one or more parameters such as temperature, pH, pressure, pressure, CO2partial pressure, and conductivity may be monitored. The system may for example include appropriate monitoring and / or sampling sites. The system may if desired include one or more of: pH probes, ORP probes, conductivity sensors, NDIR CO2 gas analyzers, flow meters (magnetic, coriolis, ultrasonic),pressure transmiters, temperature probes, turbidity and / or suspended solids sensors Sensors may feed into, for example, PLC or DCS control systems, automated dosing skids, and / or variable-speed pump controls. For example, where alkali metal chloride is recycled to A’), the system may contain a conductivity meter arranged to sample the conductivity of the recycled stream.

[1035] The system may be implemented as, for example: containerised skid modules, trailer-mounted process units, retrofit exhaust scrubber skids, and centralised processing hubs receiving liquor from distributed units. Modules may include one or more of: exhaust interface ducting, recirculation pumps, heat exchangers, chemical storage tanks, CIP systems, and / or spill containment and bunding.

[1036] In some embodiments, the system is incorporated into a power station, a wastewater treatment facility, a municipal waste processing facility, a mine site, a chemical or biotechnological plant, a gasification and / or pyrolysis system, or a cement and / or concrete manufacturing facility.

[1037] In some embodiments, the system is configured to receive a carbon dioxide-containing feed selected from the group consisting of air, a power station exhaust stream, a biogas CO2-containing stream, a diesel, petrol, LPG, natural gas or biogas generator exhaust stream, a pyrolysis exhaust stream, an industrial furnace exhaust stream, a methane pyrolysis exhaust stream, a cement kiln exhaust stream, and a metallurgical smelter exhaust stream.

[1038] In some embodiments, the system is configured as a retrofit module for direct mineralisation of flue gas from a generator set or combined heat-and-power (CHP) unit, wherein the carbon dioxide capture unit is arranged as an exhaust scrubber receiving flue gas and discharging a C Ch-depleted exhaust stream.

[1039] In some embodiments, the retrofit module is transportable and comprises an exhaust connection interface, a recirculating alkaline loop, and a neutralised discharge mode in which an aqueous effluent is discharged or reused when pH and oxidant residual meet predetermined thresholds.

[1040] In some embodiments, the system is configured for biogas upgrading, wherein in use a raw biogas stream is contacted with the aqueous alkali metal hydroxide or alkaline earth metal hydroxide to remove CO2and produce an upgraded methane stream, and wherein removed CO2is mineralised to carbonate in the carbonate formation unit.

[1041] In some embodiments, the system comprises a central processing facility configured to receive a carbonate -bearing and / or bicarbonate-bearing liquor generated by one or more distributed retrofit modules and to perform precipitation, solids finishing, and / or brine regeneration at a centralised scale.

[1042] Processes For Producing Magnesium Carbonate

[1043] Another aspect of the present disclosure relates to processes for producing magnesium carbonate. The processes include electrochemical treatment of an alkali metal chloride and water to produce alkali metal hydroxide, contacting of a CCf-containing feed with the alkali metal hydroxide (e.g. NaOH) to produce the corresponding bicarbonate and / or carbonate, and subsequent cation exchange with a magnesium species (e.g. magnesium chloride) to produce magnesium carbonate.

[1044] Accordingly, there is provided a process for producing magnesium carbonate, comprising: a”) electrochemically treating an alkali metal chloride and water to produce aqueous alkali metal hydroxide;b”) contacting a carbon dioxide-containing feed with aqueous alkali metal hydroxide from a”), to produce an alkali metal carbonate and / or bicarbonate; and c”) reacting alkali metal carbonate and / or bicarbonate from b”) with a magnesium species in the presence of water to produce solid magnesium carbonate.

[1045] The discussion above in preceding aspects in relation to features such as electrochemical treatment, contacting a carbon dioxide-containing feed with aqueous alkali metal hydroxide, reacting alkali metal carbonate and / or bicarbonate to produce solid magnesium carbonate, and uses of the products obtained, applies equally to this aspect.

[1046] In some embodiments, c”) produces alkali metal halide (e.g. chloride), and wherein alkali metal halide (e.g. chloride) produced in c”) is recycled to a”). In other words, no or low amounts of alkali metal halide exit the process. The alkali metal halide may for example be returned to a”) via a return loop. If desired, the alkali metal halide may undergo one or more treatment steps, e.g. to adjust concentration, or to remove impurities, prior to being recycled to a”).

[1047] In some embodiments, the process is substantially closed-loop with respect to halide. In some embodiments, the process is substantially closed-loop with respect to alkali metal. In some embodiments, ionic species are substantially conserved within the process, whilst carbonate is exported from the process.

[1048] In some embodiments, the products exported from the process are substantially electrically neutral, and net ionic species are substantially retained within the process. In some embodiments, small amounts of halide -containing feed, e.g. an alkali metal chloride-containing feed such as an aqueous sodium chloride feed, is introduced as needed to maintain halide levels and / or to maintain alkali metal levels. For example an amount of up to 20% by weight, or up to 15%, or up to 10%, or up to 5%, or up to 2%, or up to 1% of the circulating amount of halide may be added periodically.

[1049] If desired, the level of alkali metal halide (e.g. sodium halide) may be monitored, e.g. using a conductivity meter, and the conductivity reading used to determine whether additional halide and / or alkali metal should be added. For example, where alkali metal halide is recycled to step a), the process or system may be configured to allow measurement of conductivity, using a conductivity meter, and additional alkali metal halide may be added when the conductivity is outside required levels (e.g. too low).

[1050] In some embodiments, the process comprises: reacting hydrohalic acid (e.g. HC1) produced in a”) with a magnesium -containing mineral feedstock to produce magnesium halide (e.g. chloride), which is used in c”). Any suitable magnesium-containing mineral feedstock may be used. For example, treatment may involve contacting with a suitable agent that facilitates obtaining the magnesium from the mineral. Treatment may also include carrying out a suitable particle size reduction step, e.g. mechanical treatment, grinding and the like. Examples include nickel laterite tailings, brucite, serpentine, olivine, pyroxene, hydrotalcite, basaltic materials, ultramafic rocks, industrial tailings, and oxide / hydroxide phases occurring in mining residues. In some embodiments, a mineral feedstock selected from basalt, peridotite, dunite, harzburgite, serpentinised ultramafic rock, and mixtures thereof, and / or industrial residues comprising steel slag, red mud, mine tailings, fly ash, cement kiln dust, may be used, including partially altered or weathered forms of the foregoing. Feedstocks may include mixtures of minerals or treated minerals. In someembodiments, the magnesium-containing mineral feedstock is a silicon-containing magnesium feedstock, for example it may be a silicon-containing magnesium-containing mineral feedstock. Examples of silicon and magnesium-containing minerals include olivine, pyroxene, and serpentine.

[1051] The reaction with hydrohalic acid is carried out under conditions suitable to produce magnesium chloride. Suitable time conditions may for example include reacting with hydrohalic acid for a period of time in the range of from 1 hour to 48 hours, or from 2 hours to 24 hours. Exemplary temperature conditions may for example include reacting at ambient or elevated temperature, e.g. at a temperature in the range of from 40 to 95 °C.

[1052] In some embodiments, the magnesium-containing mineral feedstock is a magnesium silicate and magnesium halide and a silicic acid is produced.

[1053] In some embodiments, the magnesium species is magnesium hydroxide.

[1054] In some embodiments, the process is continuous or semi-continuous.

[1055] In some embodiments, at least a portion of the alkali metal carbonate and / or bicarbonate produced in b”) is used to produce a cementitious material. For example it may be used in a geopolymer, for example as an alkali activator. Further uses for alkali metal carbonate (e.g. sodium carbonate), include as an activator for blast furnace slag or fly ash.

[1056] Systems Configured to Run Processes For Producing Magnesium Carbonate

[1057] There is also provided a system or apparatus adapted for carrying out the above-described process. In another aspect, there is provided a system for producing magnesium carbonate, comprising: A”) an electrochemical unit configured to electrochemically treat an alkali metal halide and water, to produce aqueous alkali metal hydroxide, wherein the electrochemical unit is configured to i) produce hydrohalic acid, or ii) produce hydrogen and halogen, and wherein, when configured to produce hydrogen and halogen, the system also comprises a hydrohalic acid generation unit configured to produce hydrohalic acid from the hydrogen and halogen; B”) a carbon dioxide capture unit configured to contact a carbon dioxide-containing feed with the aqueous alkali metal hydroxide, to produce an alkali metal carbonate and / or bicarbonate; and C”) a magnesium carbonate formation unit configured to react the alkali metal carbonate and / or bicarbonate with a magnesium species in the presence of water to produce solid magnesium carbonate.

[1058] Any suitable configuration of apparatus may be used for the system.

[1059] The discussion above in preceding aspects in relation to features such as electrochemical units, and carbon dioxide capture units, applies equally to this aspect.

[1060] In some embodiments, the system comprises a halogen-management module including a hydrohalic acid generation unit which comprises a recombination reactor and / or an electrochemical cell configured to react hydrogen and halogen (e.g. chlorine) to produce hydrohalic acid (e.g. HC1) for recycle to the mineral activation unit.

[1061] In some embodiments, the halogen-management module comprises an absorber configured to convert halogen species such as chlorine species into one or more of hydrochloric acid, hypochlorite,chlorate, and regenerated halide salts, and optionally wherein an oxidant residual of a recycled brine stream is controlled using oxidation-reduction potential (ORP) measurement and / or free-halogen measurement.

[1062] In some embodiments, the carbon dioxide capture unit comprises a packed column, spray tower, bubble column, venturi scrubber, membrane contactor, or mechanically agitated reactor, optionally which is configured to enhance gas-liquid mass transfer and to control carbonate / bicarbonate speciation by pH and alkalinity.

[1063] The system includes C”) a magnesium carbonate formation unit configured to react the alkali metal carbonate and / or bicarbonate with a magnesium species in the presence of water to produce solid magnesium carbonate.

[1064] The magnesium carbonate formation unit may be a suitable reactor such as a stirred tank precipitator (e.g. CSTR-type). A series of reactors may be used if desired. Alternatives include a fluidized-bed crystallizer, or MSMPR crystallizer.

[1065] As discussed above, one or more parameters such as temperature, pH, pressure, pressure, CO2partial pressure, and conductivity may be monitored. The system may for example include appropriate monitoring and / or sampling sites.

[1066] In some embodiments, the alkaline earth metal carbonate formation unit and / or the magnesium carbonate formation unit comprises a seeded crystalliser or a staged precipitation train configured to control carbonate polymorph and particle size distribution, optionally wherein it further comprises solid-liquid separation and washing configured to reduce residual chloride in recovered carbonate solids.

[1067] In some embodiments, the system comprises:

[1068] D ') a mineral feedstock activation unit configured to react the hydrohalic acid with a magnesium -containing mineral to produce a magnesium species which is magnesium halide, for use in C’”).

[1069] In some embodiments, the system comprises:

[1070] E”) a recycle pathway configured to recycle alkali metal halide produced in C’”), to the electrochemical unit, and

[1071] wherein the system is configured to be substantially closed-loop with respect to halide.

[1072] The discussion above in preceding aspects in relation to features such as mineral feedstock activation units and recycle pathways, applies equally to this aspect.

[1073] In some embodiments, the mineral feedstock activation unit is configured to receive a mineral feedstock selected from basalt, peridotite, dunite, harzburgite, serpentinised ultramafic rock, and mixtures thereof, and / or industrial residues comprising steel slag, red mud, mine tailings, fly ash, cement kiln dust, including partially altered or weathered forms of the foregoing, and including mixtures thereof, optionally wherein the mineral feedstock activation unit is configured to receive a weathered form of the foregoing which has undergone particle size reduction.

[1074] In some embodiments, the system is incorporated into a power station, a wastewater treatment facility, a municipal waste processing facility, a mine site, a chemical or biotechnological plant, a gasification and / or pyrolysis system, or a cement and / or concrete manufacturing facility.In some embodiments, the system is configured to receive a carbon dioxide-containing feed selected from the group consisting of air, a power station exhaust stream, a biogas CO2-containing stream, a diesel, petrol, LPG, natural gas or biogas generator exhaust stream, a pyrolysis exhaust stream, an industrial furnace exhaust stream, a methane pyrolysis exhaust stream, a cement kiln exhaust stream, and a metallurgical smelter exhaust stream.

[1075] In some embodiments, the system is configured as a retrofit module for direct mineralisation of flue gas from a generator set or combined heat-and-power (CHP) unit, wherein the carbon dioxide capture unit is arranged as an exhaust scrubber receiving flue gas and discharging a C Ch-depleted exhaust stream.

[1076] In some embodiments, the retrofit module is transportable and comprises an exhaust connection interface, a recirculating alkaline loop, and a neutralised discharge mode in which an aqueous effluent is discharged or reused when pH and oxidant residual meet predetermined thresholds.

[1077] In some embodiments, the system is configured for biogas upgrading, wherein in use a raw biogas stream is contacted with the aqueous alkali metal hydroxide or alkaline earth metal hydroxide to remove CO2and produce an upgraded methane stream, and wherein removed CO2is mineralised to carbonate in the carbonate formation unit.

[1078] In some embodiments, the system comprises a central processing facility configured to receive a carbonate -bearing and / or bicarbonate-bearing liquor generated by one or more distributed retrofit modules and to perform precipitation, solids finishing, and / or brine regeneration at a centralised scale.

[1079] Processes For Producing An Alkali Metal or Alkaline Earth Metal Carbonate

[1080] Also provided herein are processes which are adapted for producing alkali metal- and alkaline earth metal-carbonates, preferably stable carbonate forms such as magnesite and / or hydromagnesite.

[1081] Accordingly, in another aspect, there is provided a process for producing an alkali metal or alkaline earth metal carbonate, comprising:contacting a carbon dioxide-containing feed with aqueous alkali metal hydroxide or with alkaline earth metal hydroxide, wherein one or more of pH, temperature, pressure, CO2 partial pressure, and contact time, is controlled, thereby producing a stable solid alkali metal carbonate or alkaline earth metal carbonate.

[1082] The discussion above in preceding aspects in relation to process involving contacting a carbon dioxide-containing feed with aqueous alkali metal hydroxide or with alkaline earth metal hydroxide, applies equally to this aspect.

[1083] In some embodiments, the carbon dioxide-containing feed is contacted with aqueous magnesium hydroxide or sodium hydroxide.

[1084] In some embodiments, the pH is between 8 and 14, preferably 9 to 13, and in some embodiments 10 to 12.5, sufficient to promote conversion of dissolved CO2 to carbonate species.

[1085] In some embodiments, the temperature ranges from 0 °C to 90 °C, preferably 5 °C to 60 °C, and in some embodiments ambient temperature (10-35 °C).

[1086] In some embodiments, the total pressure ranges from 0.01 bar to 20 bar, preferably 0.9 bar to 10 bar, and in some embodiments near atmospheric pressure. In some embodiments, the CO2 partial pressurethe CO2 partial pressure ranges from 0.0004 bar to 10 bar, preferably 0.001 bar to 5 bar, and in some embodiments 0.004-1 bar.

[1087] In some embodiments, the contact time seconds to weeks, preferably 10 seconds to 12 hours, and in some embodiments 1 minute to 6 hours.

[1088] In some embodiments, alkali metal carbonate or alkaline earth metal carbonate is precipitated and separated.

[1089] In some embodiments, the alkali metal carbonate or alkaline earth metal carbonate is stable upon exposure to ambient conditions for at least at least 6 months, and in some embodiments at least 12 months or longer under dry storage. Stability may be assessed by retention of the solid carbonate phase without substantial dissolution, deliquescence, or decomposition when stored at temperatures of 5-40 °C and relative humidity of 20-80%. In some embodiments, stability is confirmed by no more than 10% mass loss and no substantial change in crystalline phase composition as determined by X-ray diffraction, ICP and TGA.

[1090] In some embodiments, the alkaline earth metal carbonate is used to produce a cementitious material, optionally wherein the cementitious material is a geopolymer or Portland cement.

[1091] Also provided herein is a process for capturing carbon dioxide in a closed electrochemical loop, comprising: electrochemically generating an alkaline stream and an acidic or halogen -containing stream from an alkali metal halide electrolyte; contacting carbon dioxide with the alkaline stream to produce carbonate species; removing carbonate as a solid or dissolved export stream; and recycling halide-containing electrolyte to the electrochemical step, wherein alkali metal and halide ions are substantially retained within a circulating electrolyte inventory.

[1092] In some embodiments, halogen gas (e.g. chlorine) evolution from the process is substantially avoided. In some embodiments, where halogen (e.g. chlorine) gas is produced, it is substantially converted to halide (e.g. to HC1 or chloride) without net halogen export.

[1093] Also provided herein is a system configured to operate a closed electrochemical loop for carbon dioxide mineralisation, comprising: (i) an electrochemical unit configured to generate acidity and alkalinity from a halide electrolyte; (ii) a carbonate formation unit configured to convert carbon dioxide to carbonate species using the alkalinity; (iii) a mineral activation or cation source module; and (iv) a recycle pathway configured to return halide-containing electrolyte to the electrochemical unit while exporting carbonate solids.

[1094] In some embodiments of the processes and systems discussed herein chlorine, hypochlorite, chlorate, or hydrochloric acid generated in the electrochemical step is reacted within the process boundary to regenerate halide for recycle.

[1095] In various embodiments of the processes and systems discussed herein, halide ions and alkali metal ions are retained within a circulating working electrolyte while carbonate is exported from the process. Methods of Producing Solid CarbonatesIn another aspect, there is provided a method of producing solid carbonates including steps of: providing a hydroxide solution to a column having a first end and an opposing second end; injecting carbon dioxide through a gas injection portion connected at or adjacent the first end; recirculating carbon dioxide gas through a recirculation assembly into the column at or adjacent the first end; to thereby produce solid carbonates.

[1096] In another aspect, there is provided a method of producing solid carbonates including steps of: providing a hydroxide solution to a column having a first end and an opposing second end; and injecting carbon dioxide through a gas injection portion connected at or adjacent the first end; to thereby produce solid carbonates.

[1097] In some embodiments of the above aspects, the method comprises recirculating at least a portion of gas discharged from the column to the gas injection port through a recirculation assembly to increase carbon dioxide conversion.

[1098] In some embodiments, the hydroxide solution is sodium hydroxide or potassium hydroxide. In some embodiments, the sodium hydroxide is obtained through a chlor-alkali process from sodium chloride solution.

[1099] In some embodiments, the sodium chloride solution is obtained through a reverse osmosis process. In some embodiments, the carbon dioxide-containing gas is passed through two or more columns arranged in series.

[1100] In some embodiments, the carbon dioxide-containing gas comprises exhaust gas from a generator set or CHP unit and is treated in a once-through mode without recirculation of discharged gas to the gas injection port.

[1101] Systems For Preparing Carbonates

[1102] In another aspect, there is provided a system (100) for preparing carbonates comprising: a column (110) having a first end (111) and an opposing second end (112); a gas injection port (120) connected to the column (110) at or adjacent the first end (111) and configured to introduce a carbon dioxide-containing gas stream into the column (110); a gas outlet (130) connected to the column (110) at or adjacent the second end (112) and configured to discharge gas from the column (110); a liquid outlet (140) connected to the column (110) at or adjacent the first end (111) and configured to withdraw liquid from the column (110); and a solids collection chamber (150) connected to the column (110) at or adjacent the first end (111) and configured to collect precipitated carbonate solids or a carbonate-containing slurry comprising precipitated carbonate solids; wherein the column (110) is configured to receive a hydroxide reactant for reaction with the carbon dioxide-containing gas stream to form carbonate species, bicarbonate species, precipitated carbonate solids, or combinations thereof.

[1103] In another aspect, there is provided a system (100) for preparing carbonates comprising: a column (110) having a first end (111) and an opposing second end (112); a gas injection portion (120) connected at or adjacent the first end (111); a gas outlet (130) connected at or adjacent the second end (112), wherein the gas outlet (130) comprises a valve connection adapted to control fluid flow between a recirculationassembly (135) and an expended gas outlet (139), wherein the recirculation assembly (135) is connected at or adjacent the first end (111); a liquid outlet (140) connected at or adjacent the first end (111); and a solid carbonate collection chamber (150) connected at or adjacent the first end (111).

[1104] Embodiments of the present disclosure include a system for producing carbonate material. Accordingly, the device, system or method steps have been illustrated in the drawings, showing only those specific details that are necessary for understanding the embodiments of the present disclosure, but so as not to obscure the disclosure with excessive detail that will be readily apparent to those of ordinary skill in the art having the benefit of the present description.

[1105] The present disclosure is predicated, at least in part, on the finding that the present invention can be utilized to prepare carbonates from carbon dioxide. In this regard, it is postulated that the present system can be retrofitted to present industrial processes to sequester carbon dioxide in the form of solid carbonates. Furthermore, it will be envisaged that many of the reagents that are utilized in the present disclosure can be obtained as by-products of other processes. The produced carbonates are envisaged to be utilized in many different fields.

[1106] Shown in figures 3 and 4 is an example of a system for preparing carbonates from carbon dioxide. The system (100) comprises a column (110) having a first end (111) and an opposing second end (112). In an embodiment, the column (110) may be a packed column or a bubble column. The system (100) further comprises a gas injection port (120) adapted to feed carbon dioxide into the column (110). The gas injection port ( 120) is suitably connected to the column ( 110) at or adj acent the first end (111). The apparatus (100) further comprises a gas outlet (130) adapted to receive gas from the column (110). The gas outlet (130) is located at or adjacent the second end (112). In one embodiment, the gas injection portion comprises a one way valve. It will be appreciated by the person skilled in the art that any one-way valve can be utilized to avoid backflow of fluid. It is postulated that a one-way valve will minimize or alleviate the impact of any pressure changes. Additionally, or alternatively, the gas injection more may suitably comprise a blower fan to assist with feeding carbon dioxide.

[1107] The gas outlet (130) suitably comprises a valve (131). The gas outlet (130) is suitably connected to a recirculation assembly (135) and / or an expended gas outlet (139). The valve (131) is adapted to control fluid control between the recirculation assembly (135) and the expended gas outlet (139). The expended gas outlet (139) is adapted to remove gas whereby the carbon dioxide has been consumed through the reaction process. The recirculation assembly (135) is adapted direct gas to recirculate through the column (110) to ensure that a majority or a substantial amount of the carbon dioxide fed into the system is substantially reacted in the column (110). Once the carbon dioxide has been exposed to the hydroxide reactant in the column for a sufficient amount of time, or if a sensor detects that the amount of carbon dioxide has dropped to a predetermined amount, then the expended gas can be removed from the system. In one embodiment, the system further comprises a carbon dioxide sensor or indicator (not shown). The carbon dioxide sensor or indicator may be in communication with the valve, or a control unit in communication with the valve, to direct gas towards either the expended gas outlet or the recirculationassembly based on the carbon dioxide content thereof. In one embodiment, the present system converts greater than about 90%, greater than about 95%, greater than about 97%, greater than about 98% or greater than about 99% of the carbon dioxide in the form of carbonate. Additionally, or alternatively, the gas outlet may further comprise an extraction device. In an embodiment, the extraction device comprises or is an extraction fan.

[1108] In one embodiment, the carbon dioxide is present in the gas in an amount of between about 200 ppm and about 1,000,000 ppm, between about 200 ppm and about 100,000 ppm. In one embodiment, the carbon dioxide is a 100% by volume of carbon dioxide. In one embodiment, the carbon dioxide is present in the gas in an amount of between 30% and about 99%, or between about 90% and about 99.9%, by volume of carbon dioxide. In one embodiment, the carbon dioxide is present in the gas in an amount between 350 ppm and 1500 ppm. It is envisaged that the present system can be applied to removing atmospheric carbon dioxide.

[1109] In an embodiment, it is envisaged that the gas injection port may further comprise a carbon dioxide condenser to increase the concentration of carbon dioxide being fed into the system.

[1110] The system (100) further comprises a liquid outlet (140). The liquid outlet (140) is connected to or adjacent the first end (111) of the column (110). Similar to the above, the liquid outlet (140) is adapted to remove expended hydroxide reactant from the column (100). Once the hydroxide reactant has been exposed to carbon dioxide for a sufficient amount of time, or if a sensor detects that the amount of hydroxide (pH) has dropped to a predetermined amount, then the spent hydroxide reactant can be removed from the system. In an embodiment, the hydroxide reactant is hydroxide solution. In embodiments, the hydroxide solution is suitably sodium hydroxide solution, potassium hydroxide and / or magnesium hydroxide solution. In an embodiment, the apparatus further comprises a pH sensor (not shown).

[1111] In one embodiment, the gas outlet is provided with a carbon dioxide sensor. The carbon dioxide sensor can be utilized to determine the amount of carbon dioxide in the system, and can determined when the reaction between the hydroxide solution and the carbon dioxide is complete or substantially complete. It will be appreciated that the pH sensor may also be utilized in a similar manner.

[1112] In an embodiment, the system comprises a scrubber. In an embodiment, the gas injection port suitably comprises a scrubber to remove undesirable impurities from the carbon dioxide. In one embodiment, the gas outlet suitably comprises a scrubber to remove undesirable impurities from the expended gas. In one embodiment, the scrubber is utilized as the pre-scrubbing medium.

[1113] The system (100) further comprises a solid carbonate collection chamber (150). The solid carbonate collection chamber (150) is adapted to collect the solid carbonate formed from the reaction in the column (110). As the gaseous carbon dioxide reacts with the hydroxide reactant (e.g., NaOH), carbonate is formed which precipitates from the solution, and this precipitate is collected by virtue of gravity at the bottom or lower end of the column where the solid carbonate collection chamber (150) resides. In one embodiment, the solid carbonate collection chamber (150) is connected to or adjacent the first end (111).The recirculation assembly (135) may further comprise one or more pumps (136) adapted to recirculate the gas back through the column (110). Non-limiting examples of the pumps include diaphragm pumps, centrifugal pumps and hose pumps. It will be appreciated by the person skilled in the art that any pump can be utilized with the presently claimed invention.

[1114] The column (110) is suitably an elongate member having a bore therethrough. The column (110) is suitably packed with a substrate. Non-limiting examples of the substrate include stainless steel random packing, composite random packing and / or anti-fouling packing. It will be appreciated that any packing can be utilized in the column to maximise surface area that allows for solid particles and liquid transport through the column. It will also be appreciated that the packing preferably minimizes pressure drop and accumulated solids / fouling of the packing / contact medium where the gas flow countercurrently to the solvent in the reaction zone. Non limiting examples of the packing include non-reactive plastic packing and ceramic random packing.

[1115] In use, it will be appreciated that a hydroxide reactant is provided to the column. In a preferred embodiment, the hydroxide reactant is sodium hydroxide (NaOH) solution. The sodium hydroxide solution resides in the column (110). That is, in one embodiment, sodium hydroxide can be added to the column. In one embodiment, the system further comprises a hydroxide inlet. In one embodiment, the hydroxide inlet is adjacent or at the first end of the column. In a preferred embodiment, the hydroxide inlet is adjacent or at the second of the column. The hydroxide inlet may comprise a spray or similar device to distribute the hydroxide. In one embodiment, the system further comprises a liquid recirculation device adapted to circulate hydroxide from the first end of the column to the second end of the column. Carbon dioxide is injected into the column (110) through the gas injection portion (120), whereby the carbon dioxide is bubbled through the sodium hydroxide solution to form sodium carbonate (Na2CO3) and / or sodium hydrogen bicarbonate (NaHCO3) and water (H2O). The carbon dioxide gas is bubbled through sodium hydroxide solution in the column (110), and any remaining carbon dioxide or gas can be directed through the recirculation assembly (135) to be bubbled through the sodium hydroxide solution repeated until a majority or substantial amount of the carbon dioxide has reacted with the sodium hydroxide to form sodium carbonate. Once a majority or a substantial amount of carbon dioxide has been consumed in the reaction, the spent gas can be directed towards the expended gas outlet (139) to be removed from the system. The sodium carbonate has limited solubility in the solution and will precipitate out of solution. As such, the sodium carbonate will fall to the bottom of the column due to gravity and collect in the solid carbonate collection chamber (150). Furthermore, the collected solid sodium carbonate can be removed from the system through the solid carbonate collection chamber (150). Furthermore, once the majority or substantial amount of the sodium hydroxide solution has been consumed in the reaction, the expended solution can be removed from the system through the liquid outlet (140). Alternatively, hydroxide solution may be added to the expended solution to increase the hydroxide content / concentration thereof.

[1116] In an embodiment, the sodium hydroxide solution is between about 1% and about 70%, between about 7% and about 50%, between about 9% and about 50%, between about 0.1% and about 33.2%,between about 18% and about 33.2%, between about 18% and about 30%, or between about 29% and about 33.2% by weight of sodium hydroxide (aq). Preferably, the hydroxide solution is fed into the column at a counter current to the gas exhaust feed.

[1117] It will be appreciated that the hydroxide reacts with the carbon dioxide in the column, and the hydroxide and carbon dioxide may be recycled through the column until the reaction has proceeded towards an acceptable point. In this regard, it is postulated that the ratio of recycled hydroxide contacting carbon dioxide may be high. In this regard, the inventors postulate that there is an excess of hydroxide contacting the carbon dioxide. In one embodiment, the ratio of hydroxide contacting the carbon dioxide is 10:1 to 35:1.

[1118] In one embodiment, the system is adapted to run the column at a temperature range of below about 90°C or about 35°C. It is postulated that this temperature is important as the solubility of carbonate decreases when below this temperature. As such, maintaining the system and the temperature thereof above results in higher carbonate concentrations so that the reaction occurs in the aquas phase and the solids don’t accumulate in the packing of the column. The solids when cooled at or adjacent the first end will result in the carbonate species precipitating from solution.

[1119] It is envisaged that the present apparatus can be utilized to convert about 0.45 kg of carbon dioxide per kg of hydroxide solvent.

[1120] In one embodiment, calcium or magnesium can be utilized to form calcium carbonate or magnesium carbonate which are useful products in industry. In one embodiment, the carbonate is treated with calcium in the form of calcium chloride to form calcium carbonate. In an embodiment, the carbonate is treated with magnesium in the form of magnesium chloride to form magnesium carbonate. It is envisaged that the present system can be utilized as a retrofitted system for existing infrastructure. For instance, it is envisaged that the system can be connected to the flue outlet of an established exhaust to capture the carbon dioxide as solid carbonate. Non-limiting examples of existing infrastructure include generator sets, combined heat and power stations in manufacturing, agriculture, power stations, metal refineries, petroleum refineries, chemical manufacturing facilities, fermentations tanks, bioreactors and anaerobic digesters. Furthermore, it is postulated that the sodium hydroxide solution can be obtained in any manner. In one embodiment, the sodium hydroxide solution can be obtained from brine or salt water.

[1121] In one embodiment, the system comprises more than one column. In one embodiment, the system comprises three columns (a first column, a second column and a third column). In the first column, sodium hydroxide reacting with carbon dioxide is the dominate reaction (packed / bubble column). In the second column, sodium hydroxide reactant and sodium carbonate both react with carbon dioxide (packed / bubble column). In the third column, a sodium carbonate precipitates to bicarbonate (bubble column). Solids formed in the columns are removed via a combination of sedimentation and filtration.

[1122] Shown in Figures 5 and 6 are examples of schematics utilizing the present systems in different orientations.

[1123] Figure 5 shows an embodiment of a schematic whereby the present system can be utilized with saline water which undergoes brine pretreatment, e.g. in feed treatment unit (210). The resultant brine isutilized in the chlor-alkali electrolysis process, e.g. carried out in an electrochemical unit having a chloralkali electrolysis unit (220) to form chlorine gas and hydrogen gas. The chlorine gas and hydrogen gas can be utilized to form hydrochloric acid, for example in hydrohalic acid generation unit (230). The chlor-alkali electrolysis process also produces sodium hydrogen which can undergo purification, e.g. in NaOH purification unit (213). The sodium hydroxide solution can then be reacted with carbon dioxide to produce carbonate precipitation, e.g. in carbon dioxide capture unit 100a. The resulting precipitated carbonate and / or bicarbonate can be recovered in carbonate filtration unit (214).

[1124] Figure 6 shows an embodiment whereby the present system can be utilized with saline water which undergoes salt crystallization, e.g. in NaCl crystallization unit 215. The salt can be crystalized using evaporation ponds, by employing traditional thermal crystallization techniques (e.g., crystallizers which utilize steam to heat the brine solution to create a saturated brine solution), and / or by adding hydrochloric acid to reduce the solubility of sodium chloride in solution and filtering / concentrating the sodium chloride crystals that have formed. The result salt can be hydrated to form a saturated brine solution, and if desired subjected to feed treatment, e.g. in chloralkali feed treatment unit 210a, and utilized in the chlor-alkali electrolysis process to produce sodium hydroxide, e.g. in chloralkali electrolysis unit 211. Chlorine gas and hydrogen gas are produced and can be utilized in producing hydrochloric acid. The sodium hydroxide solution from the chlor-alkali process can then be reacted with carbon dioxide to produce carbonate precipitate, e.g. in carbon dioxide capture unit 100a, with carbonate precipitation.

[1125] In certain embodiments, the CO2capture unit may operate across a wide range of alkali concentrations depending on deployment constraints. In one embodiment, the capture unit comprises a flow-through or conduit-based contactor configured to provide plug-flow-like behaviour (e.g., a tubular reactor, channel reactor, static-mixer reactor, or wetted-wall contactor) operated with a concentrated alkali solution, for example sodium hydroxide at about 1-70 wt%, preferably 5-50 wt%. In higher-concentration embodiments (e.g., greater than about 50 wt%), operability measures may be employed including heated and / or insulated reservoirs and lines, positive-displacement pumping, controlled residence time, and solids-management measures (e.g., controlled bleed, filtration, staged dilution, or operation as a deliberate slurry reactor) to mitigate viscosity and carbonate scaling while maintaining net CO2absorption.

[1126] In other embodiments, the capture unit comprises a pressurised water scrubbing absorber operated with a recirculating aqueous solvent at elevated pressure, optionally including a low-dose alkali additive to increase alkalinity and CO2loading capacity. For example, sodium hydroxide may be present at about 0.001-5 wt%, preferably 0.01-1 wt%, and in some embodiments about 0.1 wt%, optionally metered under pH control into the feed and / or recirculation loop. Such embodiments may include optional bleed, regeneration, filtration, or hardness management to mitigate scaling. These alternative configurations enable adaptation of the capture system to volume-constrained, water-constrained, or pressurised industrial environments while remaining compatible with the closed electrochemical architecture. In some embodiments, regeneration of the circulating absorption medium is achieved by electrochemical, thermal, pressure-swing, or combined processes configured to restore reactive capacity while maintaining thesubstantially closed-loop retention and recycling of reactive ionic species. Regeneration units may be integrated or distributed, provided that regenerated medium is returned to the loop and only inert products cross the system boundary. In some embodiments, the method is paired with any of the following from MOF, PSA, VSA and gas separation techniques.

[1127] In some embodiments, the system is configured to capture carbon dioxide from ambient air (direct air capture; DAC) by contacting an ambient-air stream with an alkaline absorbent within a low pressuredrop gas-liquid contactor. In some embodiments the electrolyte / ions are employed enabling electrochemical direct air capture adsorption / absorption. The contactor may comprise any one or more of a packed column, structured packing, random packing, wetted-wall surfaces, spray / film contactors, or combinations thereof, configured to provide gas-liquid interfacial area while minimizing pressure drop and resisting fouling by carbonate precipitation.

[1128] In the ambient-air configuration, the gas stream may for example be driven through the contactor by one or more of (i) natural draft, (ii) wind-driven flow, (iii) buoyancy / stack effect, and / or (iv) a mechanical gas mover (e.g., fan or blower) operated at mild forced convection. In some embodiments, the system is installed or oriented to take advantage of naturally high airflow locations (e.g., ventilation corridors, elevated exposures, or building-induced pressure gradients) such that the gas flow is achieved with minimal or no powered air handling. In embodiments employing a mechanical gas mover, the contactor and associated ducting are configured for low pressure drop such that the specific energy associated with gas movement is reduced relative to high-pressure-drop collectors.

[1129] The liquid phase comprises an alkaline solution, suspension, or slurry capable of absorbing CO2(e.g., alkali metal hydroxide, alkaline earth hydroxide, carbonate-rich liquors, or combinations thereof), which is distributed over the contactor by gravity feed, trays, spray bars, headers, or weirs, and is recirculated at a rate sufficient to maintain wetting of the contact surfaces and to transport absorbed inorganic carbon to downstream conversion steps. In some embodiments, absorbed CO2is converted to bicarbonate and / or carbonate species in solution, and the carbonate species is subsequently precipitated as a solid carbonate product via reaction with one or more alkaline earth metal cations or alkaline earth metalcontaining solids (e.g., Mg2+and / or Ca2+supplied from a mineral activation step, a chloride exchange step, or a mineral slurry), thereby exporting carbon as a stable solid carbonate.

[1130] In some embodiments, the ambient-air configuration is operated as part of a closed electrochemical / electromineral loop (CEL) in which alkalinity is regenerated electrochemically and halide ions are substantially retained and recycled within the process. For example, an electrochemical regeneration module may generate one or more of an alkali metal hydroxide and an acid stream, wherein the hydroxide stream is supplied to the contactor for CO2absorption and the acid stream is consumed internally for mineral activation, impurity control, and / or ion management. In some embodiments, the process is configured such that a principal mass export comprises stable carbonate solids, while electrolyte salts (including halide salts) are substantially retained within the loop.In some embodiments, optional sensors are used to monitor ambient-air operation, including one or more of CO2concentration (e.g., NDIR), pH, conductivity, alkalinity, oxidation-reduction potential (ORP), flow, and differential pressure across the contactor. In some embodiments, the system is operable across multiple CO2concentration regimes, including ambient-air DAC and enriched-air or point-source gas streams, by selection of contactor geometry, gas driving mechanism (passive or active), and liquid circulation conditions.

[1131] The present invention can be installed onsite or retrofitted to existing infrastructure. The carbonate and products produced can be utilized in the same infrastructure (if required or necessary). It is envisaged that the present invention will reduce emissions of the infrastructure and will assist in the consumer being eligible for carbon rebates. Additionally, another advantage of the present invention is that flue gas is scrubbed of harmful particulates and this results in a net benefit to the environment and general health of the population. Consumers can also benefit from sustainable branding because of the utilization of the present invention which allows for carbon neutral or carbon reduced manufacturing.

[1132] Column Design Example

[1133] Column design considerations are as follows. The ratio of the rate of reaction and the fluid transport rate can be represented as a dimensionless number called the Hatta number (Ha).

[1134] Ha = √(knCB,bulkDCO2) / kLHEIGHT="38" WIDTH="129" SRC="imgf000088_0001.tif" / >

[1135] If the reaction rate is low Ha>0.3, a bubble column should be utilized; for larger values, a packed column is sufficient. For the selected design which features NaHCCT equilibrium condition the Ha is low (<0.1) whereas the for precipitation NazCOs Ha is >100. Therefore, an intermediate design is recommended between a bubble column and a packed tower. The objective of the design is to maximise the CO2 absorption efficiency (yn)

[1136] , Q>ut,n (100 — Co)

[1137] yn= 1 - - - —

[1138]

[1139] c0(100 — couCn)

[1140] To alter the absorption efficiency three variables can be manipulated:

[1141] 1) the height of the column;

[1142] 2) the gas flow rate and injection point; and

[1143] 3) the injection point of recycled liquid.

[1144] At the bench-scale, a ratio of 0.71 between the acid gas reactor column height and alkaline solvent column and recycle configured on the injected column achieved the highest conversion efficiency.

[1145] In one embodiment, the apparatus further comprises a sodium hydroxide generator. In this regard, the sodium hydroxide generator is a generator that produces sodium hydroxide. One particularly useful example is utilizing the chlor-alkali process. In this regard, the chlor-alkali process is an electrolysisreaction that produces chlorine gas, hydrogen gas and sodium hydroxide. The chloro-alkali process utilizes brine or salt water as a starting material.

[1146] In the chlor-alkali process, the main processes are as follows:

[1147] Anode

[1148]

[1149] 2Cl−(aq) → Cl2(g) + 2e−

[1150] Cathode

[1151]

[1152] 2H2O (l) + 2e−→ H2(g) + 2HO−(aq)

[1153] In solution

[1154] Na+(aq) +−OH (aq) → NaOH (aq)

[1155] Overall

[1156] 2NaCl (aq) + 2H2O (l) → Cl2(g) + H2(g) + 2NaOH (aq)

[1157] The chlor-alkali process is typically utilized to produce chlorine gas from brine. The chlorine gas and hydrogen gas are typically collected, and are useful products utilized in a wide variety of industries. It is envisaged that the sodium hydroxide obtained from the chlor-alkali process (which is usually treated as waste) can be utilized in the present apparatus. In this regard, it is envisaged that the brine solution utilized for the chlor-alkali process can be obtained as waste materials from an existing infrastructure such a reverse osmosis system, waste brine from desalination plants, salt from seawater brine evaporation ponds, and brine waste from bauxite refining (brine tailings). It is also envisaged that the brine solution can be obtained from manufactured pure salt crystals mixed with water.

[1158] The inventors also envisage that the energy or electricity required for the chlor-alkali process can be obtained using renewable sources. Non-limiting examples of these renewable sources include PV solar, wind, fusion, geothermal, bioenergy (organic matter burned as fuel) and hydroelectricity. Further examples of energy sources include but are not limited to nuclear, heavy fuel oil paired with CCS and natural gas power stations.

[1159] Figure 7 provides a schematic of a system for preparing carbonates. The system shown in figure 7 is a carbon dioxide capture unit, and can be used as part of a larger system, e.g including additional units such as a mineral dissolution unit and a chloralkali electrolysis unit. The system contains a column reactor (110), having an inlet near the bottom of the reactor for introduction of a carbon dioxide -containing feed. The carbon dioxide-containing feed may be introduced via a suitable conduit / line, for example which is optionally equipped with heat exchanger (216) and / or a fan / blower (217). The column also has an outlet at or near the top for treated gas to exit the reactor.

[1160] The column may if desired also have an inlet for introduction of additional gas via a gas line, for example to assist in maintaining desired pressure.

[1161] The column also contains an inlet / outlet loop for circulation of aqueous alkali metal hydroxide. At or near the top of the column is an inlet for introduction of aqueous alkaline metal hydroxide. The aqueous alkali metal hydroxide is passed through heat exchanger (216a) prior to introduction into the column, allowing the temperature of the solution introduced to the column to be controlled. At or near the bottomof the column is an outlet for aqueous alkali metal hydroxide to exit the column. The loop also contains a recirculation pump (218) to circulate the aqueous alkali metal hydroxide. Thus, in the embodiment shown, the aqueous alkali metal hydroxide can trickle downwards through the column, contacting with the carbon dioxide in the carbon dioxide -containing feed as it travels upwards.

[1162] The system is also equipped with feed tank (219) which supplies additional aqueous alkali metal hydroxide into the loop as needed, by transfer pump (218a).

[1163] The column reactor is further provided with an outlet at or near the bottom of the column reactor for discharge of alkali metal carbonate and / or bicarbonate that forms as a result of the reaction. This can be transferred to discharge tank (220) together with any accompanying spent solution and, after settling, the liquid and solid components can be separated, with the liquid transferred by means of transfer pump (218b).

[1164] Figure 8 provides a further schematic of an embodiment of a system for producing carbonates. As with the system depicted in figure 7, the system shown in figure 8 represents a carbon dioxide capture unit, and can be used as part of a larger system, e.g including additional units such as a mineral dissolution unit and a chloralkali electrolysis unit. As shown in the figure, carbon dioxide -containing gas is introduced via gas inlet pipe (221) (e.g. equipped with heat exchanger, flange fittings elbow and butterfly valve connected to gas source), and enters the column via gas inlet tee (222) which is at the base of the column. The column has a packing region / wet contacting region (223), which contains packing (224), that can be periodically replaced, and / or for which there a clean in place requirements for gas-liquid contacting. The column also has a top assembly (225) containing for example a column outlet tee and a liquid inlet tee, and there is a gas outlet assembly (226) connected to the top assembly. Thus, carbon dioxide -containing gas can enter the column via the gas inlet tee, pass upwards through the column packing, and exit via the column outlet tee and the gas outlet assembly. The system also contains a loop for introduction / reintroduction of liquid aqueous alkali metal hydroxide. For example, the column is also equipped with a liquid holding vessel (227), having for example an outlet fitting connected to the suction side of a recirculating pump, and a butterfly valve at the bottom of the column for discharging contents (e.g. spent solution). Liquid can exit the column near its bottom via liquid holding vessel (227) into a recirculation line and be reintroduced via liquid inlet (228) and the liquid inlet tee. The recirculation line contains one or more liquid recirculation pumps (229), and a liquid line heater assembly (230) and heater valve (231) to control the temperature of the liquid entering the column. Thus, liquid (i.e. aqueous alkali metal hydroxide) can enter the top of the column reactor and flow downwards over the column packing, and contact the carbon dioxide-containing feed travelling upwards, to produce carbonate and / or bicarbonate. Liquid can then be recirculated via the liquid holding vessel near the bottom of the column and the recirculation line, or when spent, spent liquid can be discharged via the butterfly valve (232). The recirculation line also contains a liquid feed funnel (233), equipped with a shut off valve to seal the inlet from the atmosphere on the suction side. The feed funnel allows introduction of additional aqueous alkali metal hydroxide as needed.

[1165] Stable Carbon Dioxide-Containing MaterialsThe present disclosure also provides stable carbon dioxide -containing materials, which provide for an effective means of storing carbon dioxide, and / or provide materials useful for other purposes, such as in cementitious materials. Such materials are producible using the processes and systems defined herein.

[1166] Accordingly, in another aspect, there is provided a magnesium carbonate material produced by a process as defined herein, wherein the magnesium carbonate material is or comprises one or more of magnesite, nesquehonite, hydromagnesite, dypingite, and amorphous magnesium carbonate.

[1167] In another aspect, there is provided a crystalline form of magnesium carbonate, wherein the crystalline form is produced or producible by a process as defined herein.

[1168] In another aspect, there is provided an aluminosilicate material, comprising: an aluminosilicate; and an alkaline earth metal carbonate; wherein the alkaline earth metal carbonate is obtained by a process as defined herein.

[1169] Uses of Carbon Dioxide-Containing Materials

[1170] One end product of the present invention is the formation of chalk, e.g. gym chalk. In one embodiment, the chalk is eco-friendly exercise chalk. Exercise chalk is primary magnesium carbonate. In relation to magnesium carbonate, it should be noted that 80% of the worlds’ supply is mined in China (Liaoning, Shandong & Shaanxi Province). The present disclosure allows for the synthesis of magnesium carbonate which is prepared by reaction of any soluble magnesium salt and sodium bicarbonate or through the reaction of magnesium hydroxide and gaseous carbon dioxide. As such, mining of such materials can be alleviated by the present invention. A further end product is use of the alkaline earth metal carbonate and / or the alkali metal carbonate in cementitious materials and / or geopolymers. Silicon-based byproducts of the process may also find use in such materials. The products may find use as for example additives and / or fillers in products, such as cosmetic compositions or toothpastes. The products may be used as a store for carbon, i.e. providing a stable sink for carbon dioxide. They may also be utilized for uses such as mine site backfilling, or soil amendment.

[1171] In one embodiment, the system is for use in producing carbonate material. In another embodiment, the system when used in producing carbonate material.

[1172] The above description of various embodiments of the present invention is provided for purposes of description to one of ordinary skill in the related art. It is not intended to be exhaustive or to limit the invention to a single disclosed embodiment.

[1173] As mentioned above, numerous alternatives and variations to the present invention will be apparent to those skilled in the art of the above teaching. Accordingly, while some alternative embodiments have been discussed specifically, other embodiments will be apparent or relatively easily developed by those of ordinary skill in the art. Accordingly, this invention is intended to embrace all alternatives, modifications and variations of the present invention that have been discussed herein, and other embodiments that fall within the spirit and scope of the above described invention.

[1174] ExamplesThe present invention is further described with reference to the following non-limiting examples. The examples demonstrate formation of stable alkaline earth metal carbonate materials as produced by the processes described herein, confirming that the disclosed carbonation pathways yield durable solid phases suitable for long-term storage and / or material utilisation as well as demonstrating operation of a closed electrochemical carbon mineralisation architecture with ionic regeneration and carbonate export.

[1175] Example 1: Demonstration of carbonate formation from generator / exhaust

[1176] Methodology

[1177] Introduction

[1178] Sodium carbonate, as evidenced by the titration results shown in Figure 9, was produced using the methodology described below.

[1179] The aqueous speciation of dissolved carbon dioxide is governed by pH, as illustrated by a Bjerrum plot: at low pH (<6), carbonic acid (H2CO3) dominates; at intermediate pH, bicarbonate (HCO₃⁻) is the dominant species; and at high pH (> 10), carbonate (CO₃²⁻) predominates.

[1180] Most industrial wet scrubbers operate under alkaline conditions, making them well suited for direct conversion of CO2 in exhaust gases into carbonate species. Producing carbonate via alkaline wet scrubbing is a suitable method for enabling durable carbon capture at the emission source while generating a valuable product suitable for use as a fdler material or as a precursor for further processing. The following describes a method for producing carbonate via contact between alkaline sorbent solutions and generator exhaust gas.

[1181] Background Theory

[1182] Alkalinity generation

[1183] Alkalinity used in the scrubbing process may be generated electrochemically, for example via a chlor-alkali process:

[1184] A) Anode: 2Cl⁻ → Cl₂ + 2e⁻

[1185] B) An ion-exchange membrane allows for migration of Na from the anode compartment to the cathode compartment.

[1186] C) Cathode: 2 H₂O + 2e⁻ → H₂ + 2OH⁻

[1187] Overall reaction: 2NaCl + 2H₂O → Cl₂ + H₂ + 2NaOH

[1188] Carbonate Precipitation

[1189] Reaction chemistry considerations for CO2 acid-gas removal are as follows. CO2 gas dissolves in water according to liquid-film mass-transfer kinetics and its solubility limit. Dissolved CO2 subsequently participates in carbonic acid equilibria:

[1190] CO2+ H2O H2CO3 (aq) (1) H2CO3 (aq) «-> HCO3-(aq) + H+(aq) (2) HCO3- (aq) CO32+ H+(aq) (3)

[1191] The equilibrium constant

[0023] at 25 degrees °C for eq. (2) and (3) the equilibrium K values can be written as:

[1192] Ki = [HCO3 ] [H+] / [H2CO3] = 10−6.73, K2= [CO32] [H+] / [HCO3 ] = 10−10.26(4)Under a pseudo-steady-state assumption, where C total = [H2CO3] + [HCO₃⁻] + [CO32"], the mole fraction of each carbonate species may be expressed as a function of pH. The relationship between these equilibrium constants and the resulting distribution of carbonate species with respect to pH is commonly referred to as a Bjerrum plot. For improved accuracy, activity coefficients for each ion and species may be introduced.

[1193] Further to this regarding the formation of carbonate a few additional factors must be considered, specifically, the pH balance in solution via counter ions. As an example, when carbon dioxide is dissolved in deionized water, it does not remain electrically neutral but instead undergoes hydration and partial dissociation to form carbonic acid and associated ionic species. Specifically, dissolved CO2 establishes equilibria producing bicarbonate (HCO₃⁻) and protons (H+), resulting in weak self-ionisation and stabilisation of the solution at mildly acidic pH (typically ~5-6). Although this process generates ions internally and preserves electroneutrality within the solution, the extent of ion formation is limited by the absence of additional counter-ions. As proton concentration increases, further dissociation is suppressed, rendering the process self-limiting and preventing the establishment of a sustained pH gradient or continued CO2 uptake beyond Henry’s-law solubility. In the absence of mobile spectator cations (e.g., Na+, K+, Ca2+), there is no practical mechanism under sustained conditions to accommodate additional charge separation or to stabilise higher-alkalinity conditions, and consequently no practical pathway to sustained carbonate (CO32−) formation. Accordingly, while CO2 dissolution in deionized water generates ions via carbonic acid equilibria, sustained alkaline capture and carbonate precipitation require the presence of counter-ions to maintain charge balance and to preserve hydroxide activity.

[1194] On the other hand, maintenance of the alkaline pH gradient required for sustained carbonate formation necessitates the presence and transport of counter-ions to preserve overall electroneutrality of the aqueous phase. As hydroxide ions are consumed during reaction with dissolved CO2, charge balance is maintained by the corresponding presence and mobility of alkali metal cations (e.g., Na+) within the solution. In the absence of sufficient counter-ion availability, local charge imbalance would suppress effective hydroxide activity and limit further pH-driven carbonate formation. Accordingly, sustained carbonate precipitation under alkaline conditions requires not only hydroxide availability but also adequate counter-ion inventory and transport to maintain the pH gradient and ionic balance within the system.

[1195] As indicated above, under highly alkaline conditions (pH 10), dissolved CO2 reacts preferentially with hydroxide to form sodium carbonate (Na2CO3). At elevated CO2 partial pressure and saturation levels resulting in a more moderate pH, sodium bicarbonate ions may form (NaHCO₃). Eq. (5), (6).

[1196] Reaction 1: 2NaOH + CO2 (g) ---> Na₂CO₃ (aq) + H₂O (l) (5) Reaction 2: Na₂CO₃ (aq) + H₂O + CO₂ → 2NaHCO₃ (aq) (6)

[1197] As can be inferred from the above, depending on the pH, CO2 partial pressure and saturation levels of carbonate species either H2CO3, HCO3, or CO32species predominate.

[1198] MethodologyTo evaluate this behaviour under industrially relevant conditions, a laboratory-scale test was conducted in which an alkaline NaOH solution was contacted with CO2 to confirm that carbonate is the dominant species under highly alkaline conditions. To further verify that the mechanism could function under industrial exhaust conditions, flue gas from a generator was used to assess whether partially combusted particulates materially impacted carbonate formation or the carbonic equilibrium.

[1199] Step 1: Producing the carbonate slurry solution for analysis

[1200] A bench scale carbonate reactor / modified packed column wet scrubber (see figures 1 and 2) was assembled with components as described in the detailed description. The unit was cleaned with a first pass wash of sodium hydroxide and wiped down until the stainless-steel vessel, fittings and tubing were mostly free of residue. A solution of NaOH sorbent was prepared by mixing 1 kg of pure sodium hydroxide CAS Number: 1310-73-2 (caustic, balance water flakes) with approximately 12.5 L of water. The contents were well mixed and placed until all the caustic dissolved in solution and then the liquid sorbent was transferred into the column via the funnel as seen in the image of the apparatus (figure 1). From here the apparatus pumps as shown in figure 1 were turned on and the solution was allowed to run through the column and create a film on the aluminium packing.

[1201] Next, a 6.5 KVA 240 V 25 amps petrol genset was turned on and left in standby mode. A reading of the petrol generator exhaust CO2 content was taken using a handheld NDIR device. The reading of approx. 45,000 PPM was obtained. From here the unit was connected to the apparatus via the stainless-steel piping (120). As soon as the exhaust is connected the reaction began to proceed in the packing section of the column and bubbling was observed. The system eventually reached steady state observed by gas rapidly bubbling through the column while water trickles through the packing indicating suitable gas-liquid contacting and avoiding flooding. At the base of the column an exhaust atmosphere forms above (150) which creates further contacting space for carbonate and the CO2 containing gas to associate with the CO2 dissolving in solution and reaching a saturated dissolved CO2 steady state condition which is continuously replenished via contact occurring in the column as the liquid in the tank is continuously pumped through the column and contacts the CO2 containing gas from the generator. A reading at the exhaust was taken of 691 PPM indicating approximately 98% CO2 removal efficiency based on inlet and outlet NDIR measurements by the liquid solution via the column apparatus. The exhaust of the apparatus was continuously monitored by the handheld NDIR device. The reading held relatively constant at 650 ppm until about 15 minutes into the run where the reading began to rise, once the reading exceeded 10,000 ppm for 2 minutes the run was ended the generator was turned off. The results were verified by checking the air flow via a stroke to air flow conversion method to get the air flow through the generator exiting via the exhaust this was applied to the NDIR reading to get the volume of CO2 passing through the column which lead to the finding that approximately 0.63 m3 / min gas flow occurred through genset at 4.5% CO2 volume. The 1kg hydroxide solution effectively prevented emissions for about 15 minutes. At this point the run was stopped, and the contents of the column were drained at the base of the column (140) via the butterfly valve into an IBC. The vessel was sealed and the contents were transported to the lab for analysis.Step 2. Titration Data

[1202] To generate the titration curves shown in figure 9, Wagner’s EFC lab performed a standard potentiometric acid titration on each sample (and on reference materials), recording pH as a function of cumulative HC1 volume added. The resulting curves were then used to identify the characteristic alkalinity transitions and to infer the relative contributions of free hydroxide (NaOH), carbonate (Na₂CO₃), and bicarbonate (NaHCO₃).

[1203] The method is fundamentally the same as a conventional “total alkalinity / carbonate alkalinity” titration used in water and process chemistry, with two operational reference endpoints:

[1204] • pH 8.3 (carbonate-to-bicarbonate transition region)

[1205] • pH 4.5 (total alkalinity endpoint region)

[1206] Potentiometric acid titration was used to generate the pH-volume curves shown in figure 9 and to infer alkaline speciation in carbonate capture liquors and slurries, reported as NaOH, Na₂CO₃, and NaHCOs on a mass-percent basis of total alkaline material. Solids content (wt%) was determined separately by drying representative aliquots at 105 °C to constant mass and calculating the dry-to-wet mass ratio. Two capture samples (Sample 1 and Sample 2) were analysed alongside a commercial soda ash (Na2COs) reference. A synthetic “mimic” solution corresponding to the inferred Sample 1 alkaline composition (approximately 20% NaOH and 80% Na2COs on an alkaline-material basis) was prepared and titrated under the same procedure to validate interpretation by curve overlay. Upon receipt, each sample container was homogenised prior to subsampling. Liquid or slurry samples were titrated as representative aliquots of the as-received material. For the “dried Sample 2” condition, dried material was re-dissolved in deionised water prior to titration; slow dissolution kinetics and transient pH excursions were observed during analysis. For titration, a clean beaker was charged with sufficient deionised water for stable electrode immersion and stirring, and a fixed aliquot of sample was added. The mixture was stirred continuously to maintain homogeneity. A calibrated pH electrode was immersed and the initial pH recorded. Standard hydrochloric acid (HC1) of known molarity was delivered incrementally from a burette. After each addition, the solution was allowed to stabilise, the pH recorded, and the cumulative titrant volume logged, with smaller increments used near inflection regions. Titration proceeded to an acidic endpoint (pH < 2), and the recorded data pairs of cumulative HC1 volume versus pH were used to generate the titration curves. Two operational endpoints were extracted from each curve: Vs.3 (the titrant volume at pH 8.30 corresponding to the carbonate-to-bicarbonate transition region) and V4.5 (the titrant volume at pH 4.50 corresponding to the total alkalinity endpoint). The relationship between these volumes was used to partition alkalinity using standard carbonate system relationships, where Vs.3 > 'ZA^.s indicates the presence of free hydroxide (NaOH + Na₂CO₃ system), Vs.3 < ‘AVt.s indicates bicarbonate presence (Na₂CO₃ + NaHCO system), and Vs.3 ~ ‘AV4.5 indicates carbonate-dominant behaviour. Acid equivalents were converted to moles and masses of NaOH, Na₂CO₃, and NaHCO using standard stoichiometry and molar masses (NaOH 40.00 g / mol, Na₂CO₃ 105.99 g / mol, NaHCOs 84.01 g / mol). Results were reported as mass percent of alkaline material, defined as the sum of the calculated masses of NaOH, Na₂CO₃, and NaHCO.A synthetic Na0H / Na₂CO₃ solution at the inferred Sample 1 ratio (20 / 80 on an alkaline-material basis) was titrated using the same procedure and compared by curve overlay to confirm the inferred composition within method resolution.

[1207] Wagner’s EFC performed standard potentiometric HC1 titrations on homogenised aliquots (and reference standards), recording pH versus cumulative titrant volume to pH ~ 2; endpoint volumes at pH 8.3 and 4.5 were used to partition hydroxide / carbonate / bicarbonate alkalinity and report NaOH / Na2CO3 / NaHCC>3 mass fractions of the alkaline material.

[1208] Figure 9 shows: Sample 1 (-10 wt% solids) with alkaline fraction -20% NaOH / 80% Na₂CO₃ and high starting pH; Sample 2 (-13.8 wt% solids) with alkaline fraction -64% Na₂CO₃ / 36% NaHCO₃ and lower starting pH; and a dried Sample 2 condition exhibiting slow re-solubility with broadened bicarbonate region and transient pH excursions.

[1209] Sample 1

[1210] • -10% solids

[1211] • Alkaline fraction approx. 20% NaOH / 80% Na₂CO₃

[1212] • High starting pH

[1213] • “Mimic” solution prepared (20% NaOH / 80% Na₂CO₃) confirmed behaviour

[1214] • Represents generator exhaust scrubbing, run -15 min at -8% vol CO2, producing predominantly sodium carbonate

[1215] Sample 2

[1216] • -13.8% solids

[1217] • Alkaline fraction approx. 64% Na₂CO₃ / 36% NaHCO

[1218] • Lower starting pH

[1219] • Produced by bubbling pure CO2 through solution to drive bicarbonate formation

[1220] • Dried sample showed bicarbonate region broadening and slower re-solubility

[1221] In further trials, the scrubber was evaluated across a range of gas-flow regimes to assess suitability for industrial air-treatment applications. In one embodiment, the apparatus was operated as an air scrubber for integration with ventilation systems, including particulate filtration assemblies (e.g., HEPA bag filters) and controlled underground air environments where removal of combustion-derived exhaust gases is required.

[1222] For this evaluation, the scrubber was connected to a 0.75 kW blower delivering approximately 150 m3 / h of airflow. During startup, transient liquid entrainment was observed; however, within approximately 30 seconds a stable high gas-flow operating regime was established. This regime differed from the low-flow trickling mode observed at reduced gas velocities. At elevated gas flow, bubbling through the packed section and partial fluidisation of the wetted packing occurred, increasing gas-liquid interfacial contact. A similar hydrodynamic regime was observed during direct attachment of the scrubber inlet to a generator exhaust source. Under these conditions, ambient CO2 concentration within the laboratory environment was elevated to approximately 1100 ppm (NDIR measurement). Upon operation of the scrubber in the high-flow regime, the measured ambient CO2 concentration decreased to approximately 550 ppm and remained within that range for approximately 5-10 minutes under the tested conditions. The liquid phase comprised approximately 1 kg sodium hydroxide dissolved in 10 L of demineralised water. These results demonstrate operability of the scrubber under high-throughput forced-convection conditions and confirm that the apparatus can transition between low-flow trickling and high-flow bubbling or partially fluidised regimes as a function of gas velocity.

[1223] In a further trial, the scrubber was evaluated for operation in a direct air capture (DAC) mode using ambient air as the gas source. An aqueous alkaline solution was prepared comprising approximately 1 kg sodium hydroxide dissolved in approximately 10 L of demineralised water. The initial pH of the circulating liquid prior to operation was approximately 13.3. The apparatus was operated with a blower (0.75 kW) providing forced convection at an airflow of approximately 150 m3 / h for approximately 30 minutes under ambient laboratory conditions. During operation, NDIR measurements indicated inlet CO2 concentrations of approximately 500 ppm. Outlet readings exhibited variable reductions consistent with ambient-level CO2 and the high superficial gas velocity, with intermittent measurements ranging between approximately 0 and 500 ppm. Following the run, the circulating liquid pH was measured at approximately 13.14, indicating consumption of alkalinity. After shutdown and settling, carbonate precipitates were observed within portions of the apparatus, and partial impairment of liquid flow was observed in low-velocity regions. Based on (i) the measured airflow and representative inlet / outlet CO2 concentration differential, and (ii) the observed change in liquid pH, the CO2 uptake during the trial was estimated to be on the order of approximately 26 g over 30 minutes of operation.

[1224] These results demonstrate that the column apparatus is capable of removing CO2 from ambient air streams. The results further indicate that operation under high forced airflow in IOW-CO2 ambient conditions is not the most energy-efficient configuration. In some embodiments, the apparatus is preferentially deployed for higher-CCE gas streams (e.g., enclosed or semi-enclosed environments, industrial ventilation scrubbing, or point-source exhaust streams containing approximately 3-8% by volume CO2), where masstransfer driving force is greater. In alternative embodiments directed to ambient-air DAC, energy efficiency may be improved through reduced pressure-drop contactor geometries, increased gas-liquid contact area, reduced superficial gas velocity, and / or operation under natural draft or mild forced convection.

[1225] Example 2. Closed Electrochemical Loop (CEL)

[1226] The Closed Electrochemical Loop (CEL) is an electrochemically driven ionic regeneration architecture in which acidity and alkalinity equivalents are generated, consumed, and regenerated within a conserved working electrolyte while carbonate product is selectively exported as a solid phase. Because carbonate is exported as a neutral solid phase, ionic charge carriers of the working electrolyte remain in solution and are conserved for reuse. The following describes the CEL architecture and illustrative laboratory demonstrations that support enablement of the disclosed embodiments.

[1227] CEL DescriptionIn the absence of mobile counter-ions, locally generated hydroxide and proton species rapidly recombine, suppressing sustained ionic conductivity and preventing maintenance of a stable pH gradient. Accordingly, deionised water, which contains only very low concentrations of charge carriers, cannot sustain meaningful ionic charge transport under typical operating conditions.

[1228] To maintain a pH gradient suitable for carbonate formation and precipitation, dissolved ionic species must be present to support conductivity and to stabilise alkalinity equivalents in solution. In illustrative embodiments, alkali and / or alkaline earth cations present in the working electrolyte enable the persistence of hydroxide alkalinity and facilitate conversion of dissolved CO2 into carbonate and / or bicarbonate species, which may subsequently form solid carbonate phases.

[1229] Continuous or periodic regeneration of alkalinity is required to sustain these conditions in a flowing or continuous process environment. Because pH and ionic speciation are linked to local charge balance, the system is configured to conserve and recycle working electrolyte ions while selectively exporting solid phase carbonate product. In this manner, the process maintains favourable conditions for ongoing carbonate production while preserving the ionic inventory required for sustained electrochemical operation.

[1230] In illustrative embodiments, the CEL controls carbonate speciation via pH while maintaining electroneut...

Claims

1. Claims1. A process for capturing carbon dioxide, comprising:a) electrochemically treating an alkali metal halide and water to produce aqueous alkali metal hydroxide and hydrohalic acid;b) contacting a carbon dioxide -containing feed with aqueous alkali metal hydroxide from a), to produce an alkali metal carbonate and / or bicarbonate;c) reacting hydrohalic acid from a), with an alkaline earth metal-containing mineral feedstock to produce alkaline earth metal chloride; andd) reacting alkali metal carbonate and / or bicarbonate from b) with alkaline earth metal chloride from c) in the presence of water to produce solid alkaline earth metal carbonate and alkali metal chloride;wherein alkali metal halide produced in d) is recycled to a), andwherein the process is substantially closed-loop with respect to halide.

2. A process as claimed in claim 1, wherein the halide is chloride.

3. A process as claimed in claim 1 or 2, wherein the process is substantially closed-loop with respect to alkali metal.

4. A process as claimed in any of claims 1 to 3, wherein ionic species are substantially conserved within the process, whilst carbonate is exported from the process.

5. A process as claimed in any of claims 1 to 4, wherein the products exported from the process are substantially electrically neutral, and net ionic species are substantially retained within the process.

6. A process as claimed in any of claims 1 to 5, wherein the alkali metal is sodium.

7. A process as claimed in claim 6, wherein the halide is chloride, and sodium chloride is obtained from seawater.

8. A process as claimed in any of claims 1 to 7, wherein the alkaline earth metal is magnesium or calcium, optionally magnesium.

9. A process as claimed in claim 8, wherein the solid alkaline earth metal carbonate is or comprises magnesite or hydromagnesite.

10. A process as claimed in any of claims 1 to 9, wherein the alkaline earth metal-containing mineral feedstock is selected from the group consisting of nickel laterite tailings, brucite, serpentine, olivine, pyroxene, hydrotalcite, basaltic materials, ultramafic rocks, industrial tailings, and oxide / hydroxide phases occurring in mining residues, including partially altered or weathered forms of the foregoing, and including mixtures thereof, optionally wherein the alkaline earth metal-containing mineral feedstock is a weathered form of the foregoing which has undergone particle size reduction.

11. A process as claimed in any of claims 1 to 10, wherein the alkaline earth metal-containing mineral feedstock is a silicon-containing alkaline earth metal-containing mineral feedstock, and wherein a silicon-containing byproduct is exported from the process, optionally wherein the silicon containing byproduct is a silicic acid or silicon oxide.

12. A process as claimed in claim 11, wherein the alkaline earth metal-containing mineral feedstock is an alkaline earth metal silicate and step c) produces alkaline earth metal halide and a silicic acid.

13. A process as claimed in claim 12, wherein the silicic acid is dehydrated to produce silicon oxide.

14. A process as claimed in any of claims 1 to 13, wherein one or more of pH, temperature, pressure, contact time, and CO2partial pressure is set so as to control production of carbonate and / or bicarbonate species.

15. Aprocess as claimed in any of claims 1 to 14, wherein alkali metal carbonate and / or bicarbonate is precipitated and separated.

16. Aprocess as claimed in any of claims 1 to 15, wherein alkaline earth metal carbonate is precipitated and separated.

17. A process as claimed in any of claims 1 to 2 and 3 to 15, wherein at least a portion of the alkali metal carbonate and / or bicarbonate produced in b) is used to produce a cementitious material, optionally wherein the cementitious material is a geopolymer.

18. A process as claimed in any of claims 11 to 17, wherein at least a portion of the silicon-containing byproduct is used to produce a cementitious material, optionally wherein the cementitious material is a geopolymer or Portland cement.

19. A process for producing an alkaline earth metal carbonate, comprising:a’) electrochemically treating an alkali metal halide and water to produce aqueous alkali metal hydroxide and hydrohalic acid;b’)reacting hydrohalic acid from a’), with an alkaline earth metal -containing mineral feedstock to produce alkaline earth metal halide; and reacting the alkaline earth metal halide with alkali metal hydroxide from a’), to produce alkaline earth metal hydroxide and alkali metal halide;orreacting alkali metal hydroxide from a’) with an alkaline earth metal -containing mineral feedstock, wherein the alkaline earth metal -containing mineral feedstock is a silicate-containing alkaline earth metal-containing mineral feedstock, to produce alkaline earth metal hydroxide and an alkali metal silicate; and reacting the alkali metal silicate with hydrohalic acid from a’) to produce a silicic acid and alkali metal halide;andc’) contacting a carbon dioxide-containing feed with aqueous alkaline earth metal hydroxide from b’), to produce solid alkaline earth metal carbonate;wherein alkali metal halide produced in b’) is recycled to a’), andwherein the process is substantially closed-loop with respect to halide.

20. A process as claimed in claim 19, wherein the halide is chloride.

21. A process as claimed in claim 19 or 20, wherein the process is substantially closed-loop with respect to alkali metal.

22. A process as claimed in any of claims 19 to 21, wherein ionic species are substantially conserved within the process, whilst carbonate is exported from the process.

23. A process as claimed in any of claims 19 to 22, wherein the products exported from the process are substantially electrically neutral, and net ionic species are substantially retained within the process.

24. A process as claimed in any of claims 19 to 23, wherein the alkali metal is sodium.

25. A process as claimed in claim 24, wherein the halide is chloride, and sodium chloride is obtained from seawater.

26. A process as claimed in any of claims 19 to 25, wherein the alkaline earth metal is magnesium or calcium, optionally magnesium.

27. A process as claimed in claim 26, wherein the solid alkaline earth metal carbonate is or comprises magnesite or hydromagnesite.

28. A process as claimed in any of claims 19 to 27, wherein the alkaline earth metal -containing mineral feedstock is selected from the group consisting of nickel laterite tailings, brucite, serpentine, olivine, pyroxene, hydrotalcite, basaltic materials, ultramafic rocks, industrial tailings, and oxide / hydroxide phases occurring in mining residues, including partially altered or weathered forms of the foregoing, and including mixtures thereof, optionally wherein the alkaline earth metal-containing mineral feedstock is a weathered form of the foregoing which has undergone particle size reduction.

29. A process as claimed in any of claims 19 to 28, wherein the alkaline earth metal-containing mineral feedstock is a silicon-containing alkaline earth metal-containing mineral feedstock, and wherein a silicon-containing byproduct is exported from the process, optionally wherein the silicon containing byproduct is a silicic acid or silicon oxide.

30. A process as claimed in claim 29, wherein the alkaline earth metal -containing mineral feedstock is an alkaline earth metal silicate, and step b’) involves reaction with hydrohalic acid to produce alkaline earth metal halide and a silicic acid.

31. A process as claimed in claim 29, wherein the alkaline earth metal -containing mineral feedstock is an alkaline earth metal silicate, and step b’) involves reaction with alkali metal hydroxide followed by reaction with hydrohalic acid to produce a silicic acid.

32. A process as claimed in claim 30 or 31, wherein the silicic acid is dehydrated to produce silicon oxide.

33. A process as claimed in any of claims 19 to 32, wherein one or more of pH, temperature, pressure, contact time, and CO2partial pressure is set so as to control production of alkaline earth metal carbonate.

34. A process as claimed in any of claims 19 to 33, wherein alkaline earth metal carbonate is precipitated and separated.

35. A process as claimed in any of claims 19 to 34, wherein at least a portion of the silicic acid, silicon oxide, or silicon-containing byproduct, is used to produce a cementitious material, optionally wherein the cementitious material is a geopolymer or Portland cement.

36. A process for producing magnesium carbonate, comprising:a”) electrochemically treating an alkali metal halide and water to produce aqueous alkali metal hydroxide; b”) contacting a carbon dioxide-containing feed with aqueous alkali metal hydroxide from a”), to produce an alkali metal carbonate and / or bicarbonate; andc”) reacting alkali metal carbonate and / or bicarbonate from b”) with a magnesium species in the presence of water to produce solid magnesium carbonate.

37. A process as claimed in claim 36, wherein the alkali metal is sodium.

38. A process as claimed in claim 37, wherein the sodium chloride is obtained from seawater.

39. A process as claimed in any of claims 36 to 38, wherein the magnesium species is magnesium chloride.

40. A process as claimed in any of claims 36 to 39, wherein the magnesium of the magnesium species is obtained from seawater.

41. A process as claimed in any of claims 36 to 40, wherein c”) produces alkali metal halide, and wherein alkali metal halide produced in c”) is recycled to a”).

42. A process as claimed in claim 41, wherein the halide is chloride.

43. A process as claimed in any of claims 36 to 42, wherein a”) comprises subjecting an alkali metal halide and water to electrochemical treatment, and producing aqueous alkali metal hydroxide and hydrohalic acid.

44. A process as claimed in claim 42, wherein the halide is chloride.

45. A process as claimed in claim 39, comprising:reacting hydrohalic acid produced in a”) with a magnesium-containing mineral feedstock to produce magnesium halide, which is used in c”).

46. A process as claimed in claim 45, wherein the magnesium-containing mineral feedstock is selected from the group consisting of nickel laterite tailings, brucite, serpentine, olivine, pyroxene, hydrotalcite, basaltic materials, ultramafic rocks, industrial tailings, and oxide / hydroxide phases occurring in mining residues, including partially altered or weathered forms of the foregoing, and including mixtures thereof, optionally wherein the alkaline earth metal-containing mineral feedstock is a weathered form of the foregoing which has undergone particle size reduction.

47. A process as claimed in claim 45 or 46, wherein the magnesium-containing mineral feedstock is a silicon-containing magnesium-containing mineral feedstock, and wherein a silicon-containing byproduct is exported from the process, optionally wherein the silicon containing byproduct is a silicic acid or silicon oxide.

48. A process as claimed in claim 47, wherein the magnesium -containing mineral feedstock is a magnesium silicate and wherein reacting the magnesium silicate with hydrohalic acid produces magnesium halide and a silicic acid.

49. A process as claimed in claim 48, wherein the silicic acid is dehydrated to produce silicon oxide.

50. A process as claimed in any of claims 36 to 49, wherein the process is substantially closed-loop with respect to halide.

51. A process as claimed in any of claims 36 to 50, wherein the process is substantially closed-loop with respect to alkali metal.

52. A process as claimed in any of claims 36 to 51, wherein ionic species are substantially conserved within the process, whilst carbonate is exported from the process.

53. A process as claimed in any of claims 36 to 52, wherein the products exported from the process are substantially electrically neutral, and net ionic species are substantially retained within the process.

54. A process as claimed in any of claims 36 to 53, wherein the magnesium species is magnesium hydroxide.

55. A process as claimed in any of claims 36 to 54, wherein one or more of pH, temperature, pressure, contact time, and CO2partial pressure is set so as to control production of carbonate and / or bicarbonate species.

56. A process as claimed in any of claims 36 to 55, wherein alkali metal carbonate and / or bicarbonate is precipitated and separated.

57. A process as claimed in any of claims 36 to 56, wherein magnesium carbonate is precipitated and separated.

58. A process as claimed in any of claims 36 to 57, wherein at least a portion of the alkali metal carbonate and / or bicarbonate produced in b”) is used to produce a cementitious material, optionally wherein the cementitious material is a geopolymer.

59. A process as claimed in any of claims 47 to 58, wherein at least a portion of the silicon-containing byproduct is used to produce a cementitious material, optionally wherein the cementitious material is a geopolymer or Portland cement.

60. A process as claimed in any of claims 1 to 59, wherein following contacting of the carbon dioxidecontaining feed with aqueous alkali metal hydroxide or alkaline earth metal hydroxide, at least a portion of the remaining carbon dioxide is recirculated and re-contacted with the aqueous alkali metal hydroxide or alkaline earth metal hydroxide.

61. A process as claimed in any of claims 1 to 60, wherein the electrochemical treatment is the chloralkali process, and wherein HC1 is produced from hydrogen and chlorine obtained from the chloralkali process.

62. A process as claimed in any of claims 1 to 60, wherein the electrochemical treatment is bipolar membrane electrodialysis (EDBM).

63. A process as claimed in any of claims 1 to 62, wherein the electrochemical treatment is carried out using electricity generated from a renewable source.

64. Aprocess as claimed in any of claims 1 to 63, wherein the process is continuous or semi-continuous.

65. A process as claimed in any of claims 1 to 64, wherein the carbon dioxide-contacting step is operated in a hydroxide-dominant regime and a carbonate-dominant regime, the regime being selected by control of ion activity, pH, residence time, pressure, CO2partial pressure, or combinations thereof.

66. A process as claimed in any of claims 1 to 65, wherein a controlled purge is carried out to manage impurity accumulation.

67. A process as claimed in any of claims 1 to 66, wherein the carbon dioxide feed is air, and direct air capture is carried out.

68. A process as claimed in any of claims 1 to 67, wherein the process produces magnesium carbonate, which is used as gym chalk.

69. A process for producing an alkali metal or alkaline earth metal carbonate, comprising:contacting a carbon dioxide-containing feed with aqueous alkali metal hydroxide or with alkaline earth metal hydroxide,wherein one or more of pH, temperature, pressure, CO2 partial pressure, and contact time, is controlled, thereby producing a stable solid alkali metal carbonate or alkaline earth metal carbonate.

70. A process as claimed in claim 69, wherein the carbon dioxide-containing feed is contacted with aqueous magnesium hydroxide.

71. A process as claimed in claim 69 or 70, wherein the pH is between 8 and 14, preferably between 9 and 13.

72. A process as claimed in any of claims 69 to 71, wherein the temperature is in the range of from 0 °C to 90 °C, preferably from 5 °C to 60 °C.

73. A process as claimed in any of claims 69 to 72, wherein the pressure is in the range of from 0.001 bar to 20 bar, preferably from 0.9 bar to 10 bar.

74. A process as claimed in any of claims 69 to 73, wherein the CO2partial pressure is in the range of from 0.0004 bar to 10 bar, preferably from 0.001 bar to 5 bar.

75. A process as claimed in any of claims 69 to 74, wherein the contact time is in the range of from 10 seconds to 48 hours, preferably from 1 minute to 12 hours, to 1 month, depending on CO2 partial pressure, gas volume contacted and hydroxide concentration and volume.

76. A process as claimed in any of claims 69 to 75, wherein alkali metal carbonate or alkaline earth metal carbonate is precipitated and separated.

77. A process as claimed in any of claims 69 to 76, wherein the alkali metal carbonate or alkaline earth metal carbonate is stable upon exposure to ambient conditions for at least 6 months.

78. A process as claimed in any of claims 69 to 77, wherein the alkaline earth metal carbonate is used to produce a cementitious material, optionally wherein the cementitious material is a geopolymer or Portland cement.

79. A process as claimed in any of claims 1 to 78, wherein the carbon dioxide-containing feed is selected from the group consisting of air, a power station exhaust stream, a biogas CO2-containing stream, a diesel, petrol, LPG, natural gas or biogas generator exhaust stream, a pyrolysis exhaust stream, an industrial furnace exhaust stream, a methane pyrolysis exhaust stream, a cement kiln exhaust stream, and a metallurgical smelter exhaust stream.

80. A process as claimed in any of claims 1 to 79, which is incorporated into a power station, a wastewater treatment facility, a municipal waste processing facility, a mine site, a chemical or biotechnological plant, a gasification and / or pyrolysis system, or a cement and / or concrete manufacturing facility.

81. A system for capturing carbon dioxide, comprising:A) an electrochemical unit (211) configured to electrochemically treat an alkali metal halide and water to produce aqueous alkali metal hydroxide,wherein the electrochemical unit is configured toi) produce hydrohalic acid, orii) produce hydrogen and halogen,and wherein, when configured to produce hydrogen and halogen, the system also comprises an hydrohalic acid generation unit (212) configured to produce hydrohalic acid from the hydrogen and halogen;B) a carbon dioxide capture unit (100a) configured to contact a carbon dioxide-containing feed with the aqueous alkali metal hydroxide, to produce an alkali metal carbonate and / or bicarbonate;C) a mineral feedstock activation unit configured to react the hydrohalic acid with an alkaline earth metal-containing mineral feedstock to produce alkaline earth metal halide;D) an alkaline earth metal carbonate formation unit (240) configured to react the alkali metal carbonate and / or bicarbonate with alkaline earth metal chloride in the presence of water to produce solid alkaline earth metal carbonate and alkali metal chloride; andE) a recycle pathway configured to recycle alkali metal halide produced in D), to A), and wherein the system is configured to be substantially closed-loop with respect to halide while exporting carbonate solids.

82. A system for producing an alkaline earth metal carbonate, comprising:A’) an electrochemical unit (211) configured to electrochemically treat an alkali metal halide and water, to produce aqueous alkali metal hydroxide,wherein the electrochemical unit is configured toi) produce hydrohalic acid, orii) produce hydrogen and halogen,and wherein, when configured to produce hydrogen and halogen, the system also comprises a hydrohalic acid generation unit (212) configured to produce hydrohalic acid from the hydrogen and halogen;B’) an alkaline earth metal hydroxide production unit comprisingeithera mineral feedstock activation unit configured to react the hydrohalic acid with an alkaline earth metal-containing mineral feedstock to produce alkaline earth metal halide, and a halide exchange unit configured to react the alkaline earth metal halide with the alkali metal hydroxide to produce alkaline earth metal hydroxide and alkali metal halide;oran alkaline mineral feedstock activation unit configured to react the alkali metal hydroxide with a silicon-containing alkaline earth metal-containing mineral feedstock to produce alkaline earth metal hydroxide and an alkali metal silicate, and a silicic acid production unit configured to react the alkali metal silicate with the hydrohalic acid to produce a silicic acid and alkali metal halide; andC’) a carbon dioxide capture unit (100a) configured to contact a carbon dioxide-containing feed with the aqueous alkaline earth metal hydroxide, to produce an alkaline earth metal carbonate; and D’) a recycle pathway configured to recycle alkali metal halide produced in B’), to A’), and wherein the system is configured to be substantially closed-loop with respect to halide.

83. A system for producing magnesium carbonate, comprising:A”) an electrochemical unit (211) configured to electrochemically treat an alkali metal halide and water, to produce aqueous alkali metal hydroxide,wherein the electrochemical unit is configured toiii) produce hydrohalic acid, oriv) produce hydrogen and halogen,and wherein, when configured to produce hydrogen and halogen, the system also comprises a hydrohalic acid generation unit (212) configured to produce hydrohalic acid from the hydrogen and halogen;B”) a carbon dioxide capture unit (100a) configured to contact a carbon dioxide-containing feed with the aqueous alkali metal hydroxide, to produce an alkali metal carbonate and / or bicarbonate; and C”) a magnesium carbonate formation unit (240) configured to react the alkali metal carbonate and / or bicarbonate with a magnesium species in the presence of water to produce solid magnesium carbonate.

84. A system as claimed in claim 83, comprising:D ') a mineral feedstock activation unit configured to react the hydrohalic acid with a magnesium -containing mineral to produce a magnesium species which is magnesium halide, for use in C’”).

85. A system as claimed in claim 83 or 84, comprisingE”) a recycle pathway configured to recycle alkali metal halide produced in C’”), to the electrochemical unit, andwherein the system is configured to be substantially closed-loop with respect to halide.

86. A system as claimed in any of claims 81 to 85, wherein the system comprises a halogen-management module including a hydrohalic acid generation unit which comprises a recombination reactor and / or an electrochemical cell configured to react hydrogen and halogen to produce hydrohalic acid for recycle to the mineral activation unit.

87. A system as claimed in claim 86, wherein the halide is chloride, and wherein the halogen-management module comprises an absorber configured to convert halogen species into one or more of hydrochloric acid, hypochlorite, chlorate, and regenerated halide salts, and optionally wherein an oxidant residual of a recycled brine stream is controlled using oxidation-reduction potential (ORP) measurement and / or free-halogen measurement.

88. A system as claimed in any of claims 81 to 87, wherein the mineral feedstock activation unit is configured to receive a mineral feedstock selected from basalt, peridotite, dunite, harzburgite, serpentinised ultramafic rock, and mixtures thereof, and / or industrial residues comprising steel slag, red mud, mine tailings, fly ash, cement kiln dust, including partially altered or weathered forms of the foregoing, and including mixtures thereof, optionally wherein the mineral feedstock activation unit is configured to receive a weathered form of the foregoing which has undergone particle size reduction.

89. A system as claimed in any of claims 81 to 88, wherein the carbon dioxide capture unit comprises a packed column, spray tower, bubble column, venturi scrubber, membrane contactor, or mechanically agitated reactor, optionally which is configured to enhance gas-liquid mass transfer and to control carbonate / bicarbonate speciation by pH and alkalinity.

90. A system as claimed in any of claims 81 to 89, wherein the alkaline earth metal carbonate formation unit and / or the magnesium carbonate formation unit comprises a seeded crystalliser or a staged precipitation train configured to control carbonate polymorph and particle size distribution, optionally wherein it further comprises solid-liquid separation and washing configured to reduce residual halide in recovered carbonate solids.

91. A system as claimed in any of claims 81 to 90, wherein the system is configured to receive a carbon dioxide-containing feed selected from the group consisting of air, a power station exhaust stream, a biogas CO₂-containing stream, a diesel, petrol, LPG, natural gas or biogas generator exhaust stream, a pyrolysis exhaust stream, an industrial furnace exhaust stream, a methane pyrolysis exhaust stream, a cement kiln exhaust stream, and a metallurgical smelter exhaust stream.

92. A system as claimed in any of claims 81 to 91, which is incorporated into a power station, a wastewater treatment facility, a municipal waste processing facility, a mine site, a chemical or biotechnological plant, a gasification and / or pyrolysis system, or a cement and / or concrete manufacturing facility.

93. A system as claimed in any of claims 81 to 92, wherein the system is configured as a retrofit module for direct mineralisation of flue gas from a generator set or combined heat-and-power (CHP) unit, wherein the carbon dioxide capture unit is arranged as an exhaust scrubber receiving flue gas and discharging a CO₂-depleted exhaust stream.

94. A system as claimed in claim 93, wherein the retrofit module is transportable and comprises an exhaust connection interface, a recirculating alkaline loop, and a neutralised discharge mode in which an aqueous effluent is discharged or reused when pH and oxidant residual meet predetermined thresholds.

95. A system as claimed in any of claims 81 to 94, wherein the system is configured for biogas upgrading, wherein in use a raw biogas stream is contacted with the aqueous alkali metal hydroxide or alkaline earth metal hydroxide to remove CO2and produce an upgraded methane stream, and wherein removed CO2is mineralised to carbonate in the carbonate formation unit.

96. A system as claimed in any of claims 81 to 95, wherein the system comprises a central processing facility configured to receive a carbonate-bearing and / or bicarbonate-bearing liquor generated by one or more distributed retrofit modules and to perform precipitation, solids finishing, and / or brine regeneration at a centralised scale.

97. A magnesium carbonate material produced by the process of any of claims 1 to 80, wherein the magnesium carbonate material is or comprises one or more of magnesite, nesquehonite, hydromagnesite, dypingite, and amorphous magnesium carbonate.

98. A crystalline form of magnesium carbonate, wherein the crystalline form is produced or producible by a process according to any of the preceding claims.

99. An aluminosilicate material, comprising:an aluminosilicate; andan alkaline earth metal carbonate;wherein the alkaline earth metal carbonate is obtained by a process of any of claims 1 to 80.

100. A method of producing solid carbonates including steps of:providing a hydroxide solution to a column having a first end and an opposing second end; injecting carbon dioxide through a gas injection portion connected at or adjacent the first end; recirculating carbon dioxide gas through a recirculation assembly into the column at or adj acent the first end;to thereby produce solid carbonates.

101. A method of producing solid carbonates including steps of:providing a hydroxide solution to a column having a first end and an opposing second end; and injecting carbon dioxide through a gas injection portion connected at or adjacent the first end; to thereby produce solid carbonates.

102. A method as claimed in claim lOO or 101, wherein the method comprises recirculating at least a portion of gas discharged from the column to the gas injection port through a recirculation assembly to increase carbon dioxide conversion.

103. A method as claimed in any of claims 100 to 102, wherein the hydroxide solution is sodium hydroxide or potassium hydroxide.

104. A method as claimed in claim 103, wherein the sodium hydroxide is obtained through a chlor-alkali process from sodium chloride solution.

105. A method as claimed in claim 103 or 104, wherein the sodium chloride solution is obtained through a reverse osmosis process.

106. A method as claimed in any of claims 100 to 105, wherein the carbon dioxide-containing gas is passed through two or more columns arranged in series.

107. A method as claimed in any of claims 100 to 106, wherein the carbon dioxide-containing gas comprises exhaust gas from a generator set or CHP unit and is treated in a once-through mode without recirculation of dischaiged gas to the gas injection port.

108. A system (100) for preparing carbonates comprising:a column (110) having a first end (111) and an opposing second end (112);a gas injection port (120) connected to the column (110) at or adjacent the first end (111) and configured to introduce a carbon dioxide-containing gas stream into the column (110);a gas outlet (130) connected to the column (110) at or adjacent the second end (112) and configured to discharge gas from the column (110);a liquid outlet (140) connected to the column (110) at or adjacent the first end (111) and configured to withdraw liquid from the column (110); anda solids collection chamber (150) connected to the column (110) at or adjacent the first end (111) and configured to collect precipitated carbonate solids or a carbonate -containing slurry comprising precipitated carbonate solids;wherein the column (110) is configured to receive a hydroxide reactant for reaction with the carbon dioxide-containing gas stream to form carbonate species, bicarbonate species, precipitated carbonate solids, or combinations thereof.

109. A system as claimed in claim 108, wherein the system comprises a spent gas outlet (139) fluidly connected to the gas outlet (130).

110. A system as claimed in claim 108 or claim 109, comprising two or more columns fluidly connected in series such that gas discharged from a gas outlet (130) of an upstream column is introduced into a gas injection port (120) of a downstream column to provide sequential carbon dioxide removal.

111. A system as claimed in any of claims 108 to 110, wherein the system is configured as an exhaust scmbber for a generator set or combined heat-and-power (CHP) unit, wherein the gas injection port (120) is configured to receive engine exhaust and the gas outlet (130) is configured to discharge treated exhaust in a once-through flow path without return of the dischaiged gas to the gas injection port (120).

112. A system as claimed in any of claims 108 to 111, wherein the system comprises a recirculation assembly (135) fluidly connecting the gas outlet (130) to the gas injection port (120) and configured to return at least a portion of gas discharged from the column (110) to the column (110).

113. A system as claimed in any of claims 108 to 112, wherein the gas outlet (130) comprises a valve arrangement (131) configured to selectively direct gas discharged from the column (110) to at least one of: (i) the spent gas outlet (139); and(ii) the recirculation assembly (135),such that the system is operable in (a) a once-through mode in which substantially all of the gas is directed to the spent gas outlet (139), and (b) a recirculation mode in which at least a portion of the gas is returned to the column ( 110) via the recirculation assembly (135).

114. A system as claimed in any of claims 108 to 113, wherein the system comprises a carbon dioxide sensor located at or downstream of the gas outlet (130) and a controller in communication with the valve arrangement (131), wherein the controller is configured to control a gas split between the once-through mode and the recirculation mode based on measured carbon dioxide concentration and / or an exposure-time criterion.

115. A system (100) for preparing carbonates comprising:a column (110) having a first end (111) and an opposing second end (112);a gas injection portion (120) connected at or adjacent the first end (111);a gas outlet (130) connected at or adjacent the second end (112), wherein the gas outlet (130) comprises a valve connection adapted to control fluid flow between a recirculation assembly (135) and an expended gas outlet (139), wherein the recirculation assembly (135) is connected at or adjacent the first end (111);a liquid outlet (140) connected at or adjacent the first end (111); and a solid carbonate collection chamber (150) connected at or adjacent the first end (111).

116. A process for capturing carbon dioxide in a closed electrochemical loop, comprising: electrochemically generating an alkaline stream and an acidic or halogen-containing stream from an alkali metal halide electrolyte;contacting carbon dioxide with the alkaline stream to produce carbonate species;removing carbonate as a solid or dissolved export stream; andrecycling halide-containing electrolyte to the electrochemical step,wherein alkali metal and halide ions are substantially retained within a circulating electrolyte inventory.

117. A system configured to operate a closed electrochemical loop for carbon dioxide mineralisation, comprising:(i) an electrochemical unit configured to generate acidity and alkalinity from a halide electrolyte;(ii) a carbonate formation unit configured to convert carbon dioxide to carbonate species using the alkalinity;(iii) a mineral activation or cation source module; and (iv) a recycle pathway configured to return halide-containing electrolyte to the electrochemical unit while exporting carbonate solids.

118. The process of any preceding claim, wherein chlorine, hypochlorite, chlorate, or hydrochloric acid generated in the electrochemical step is reacted within the process boundary to regenerate halide for recycle.

119. The process or system of any preceding claim, wherein halide ions and alkali metal ions are retained within a circulating working electrolyte while carbonate is exported from the process.

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