Electrochemical carbon removal from water by carbon mineralization.

Abstract

Ca 2+ ions and Mg 2+ Calcium carbonate (CaCO 3 ) and magnesium hydroxide (Mg(OH) 2 A method for recovering CaCO3 from solution is provided, the method comprising: introducing the aqueous solution into an electrochemical cell having a chamber containing a photoactive cathode and an anode; and then carrying out process steps (a) and (b). Process step (a) comprises introducing a source of (bi)carbonate anions into the cell, applying a voltage to the cell resulting in the water reduction reaction of process step (a) at the cathode, and recovering solid CaCO3 from the solution, facilitated by hydroxide ions generated from the water reduction reaction of process step (a). 3 Process step (b) involves applying a voltage to the cell, resulting in the water reduction reaction of process step (b) at the cathode, and precipitation of solid Mg(OH) from solution, facilitated by hydroxide ions produced from the water reduction reaction of process step (b). 2 and carrying out precipitation of the compound.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 269,143, filed March 10, 2022, the entire contents of which are incorporated herein by reference. [Background technology]

[0002] Greenhouse gases are gases that absorb heat from the atmosphere and have a wide range of adverse environmental and health effects.

[0003] Nearly all of the increase in greenhouse gases to their current dangerous levels is the result of human activities.

[0004] Carbon dioxide (CO2) is estimated to account for 76% of global greenhouse gas emissions. AR5 Climate Change 2014: Climate Change Mitigation. While the combustion of fossil fuels (e.g. for heat, electricity, and transport) is the primary source of CO2, other sources include deforestation, burning of solid waste, and other industrial processes.

[0005] The oceans absorb about 30% of the carbon dioxide released into the atmosphere. As atmospheric carbon dioxide levels increase, the amount of carbon dioxide absorbed by the oceans also increases, resulting in ocean acidification.

[0006] Ocean acidification refers to the continuing decrease in the pH of ocean waters caused by the uptake of carbon dioxide from the atmosphere, with dire consequences for marine ecosystems, marine life, and associated commerce and industry.

[0007] Carbon dioxide is naturally removed from the atmosphere when it is absorbed by plants as part of the biological carbon cycle, but plants alone cannot remove excessive levels of carbon dioxide from the atmosphere.

[0008] A variety of technologies exist for water treatment and carbonate precipitation processes; however, none can adequately address the continuing need for carbon dioxide reduction.

[0009] US Patent No. 4,115,219 uses a sodium carbonate (Na2CO3) / sodium hydroxide (NaOH) purification process in which raw brine is contacted sequentially with sodium carbonate and sodium hydroxide for precipitation of impurities, and the treated brine is then used in a mercury electrolysis cell to produce chlorine. Unlike the present invention, US Patent No. 4,115,219 is directed to a chlor-alkali process, which is an industrial process for the electrolysis of sodium chloride (NaCl) solution, which is used to produce chlorine and sodium hydroxide (caustic soda). Generally, there are three chlor-alkali production processes currently in use: the mercury cell, the diaphragm cell, and the membrane cell as described in US Patent No. 4,115,219. The mercury cell process (also called the amalgam process because mercury is the cathode and sodium is produced there to form an amalgam with the mercury) has been largely phased out because of the large amounts of mercury used, which have serious environmental problems (emitted mercury accumulates in the environment; furthermore, the chlorine and sodium hydroxide produced by the mercury cell chlor-alkali process themselves contain traces of mercury).

[0010] US Patent No. 11,465,925 relates to a method for capturing carbon from seawater. Seawater is subjected to reverse osmosis to produce fresh water and brine. In a next step, hydroxides are produced by a cation exchange membrane electrolysis cell process using the fresh water and the brine. The cation exchange membrane electrolysis cell has an anode chamber and a cathode chamber separated by a membrane. Brine is fed to the electrolysis cell. An electric current is passed through the brine and the fresh water to produce a hydroxide solution in the cathode chamber of the electrolysis cell. The hydroxide solution is collected and placed in a communicating chamber, and fresh seawater is introduced. A precipitate is produced, containing at least calcium carbonate and magnesium carbonate.

[0011] EP 0 995 719 A1 relates to a method for purifying a sol, which involves precipitating and removing magnesium as magnesium hydroxide and calcium as calcium carbonate from the sol. Similar to US 4,115,219, but different from the present invention, the aim of EP 0 995 719 A1 is to purify the brine before using it in a chlor-alkali (amalgam) process to produce chlorine. The aim is to remove cationic impurities, such as calcium, magnesium and iron, from the brine prior to electrolysis in a cell, as these impurities are called "electrolysis poisons". The reference discloses that "surprisingly, it has been found that by adjusting the calcium:magnesium ratio in the brine, purification of the brine can be made much more effective and more economically feasible". Thus, according to this reference, the ratio of calcium to magnesium in the brine prior to precipitation of magnesium and calcium is adjusted to 1-7:1.

[0012] US Patent No. 5,356,610 relates to a method for purifying various liquids produced or obtained in an alkali metal chlorate process, which allows replacing a significant ion exchange capacity and high performance filter with precipitation and co-separation of compounds. The method includes the steps of adding carbonate ions and iron-containing compounds to the liquid in order to precipitate calcium carbonate, forming and precipitating a complex of iron ions and silicon compounds, and then co-separating the precipitate from the thus purified liquid. Alkali metal chlorates are produced by electrolysis of an electrolyte containing alkali metal chlorides. Impurities such as calcium ions, magnesium ions, and fluoride ions as well as silicon compounds cause harmful deposits on the cathode during electrolysis. This reference therefore aims to remove calcium ions and silicon compounds from the chlorate electrolyte.

[0013] French Patent Application FR 2 142 731 A1 relates to a method for purifying a crude aqueous sodium chloride solution. More specifically, this reference relates to an improvement of the process step for purifying a crude aqueous sodium chloride solution containing mercury and to a method for reducing the amount of mercury lost in the co-precipitation state.

[0014] WO 2009 / 006295 relates to a desalination process involving precipitation of carbonate compounds, in which the feed water is subjected to carbonate precipitation conditions prior to desalination. In this process, the carbonate precipitation step is carried out such that the feed water and / or the waste brine of the desalination process is subjected to carbonate precipitation conditions.

[0015] WO 2022 / 216741 relates to a method for converting waste and low-value minerals into carbon dioxide (CO2)-neutral materials.

[0016] WO 2022 / 197954 relates to electrochemical systems and methods for producing acid and base solutions, such as for use in carbon capture. The disclosed method involves generating acid and base using an electrochemical acid-base generator; dissolving a mineral in the acid to produce a mineral-rich solution and separating silica from the mineral-rich solution to form a silica-depleted solution; adding a first portion of base to the silica-depleted solution to remove impurities by precipitation, adding a second portion of base until ferrous hydroxide (Fe(OH)2) precipitates, then pausing base addition to remove the ferrous hydroxide precipitate from the solution; then adding a third portion of base to the iron-depleted solution to precipitate magnesium hydroxide (Mg(OH)2) and / or calcium hydroxide (Ca(OH)2); then recovering the salt solution and transferring the recovered salt solution to an electrochemical acid-base generator to generate fresh acid and fresh base.

[0017] WO 2012 / 085552 relates to a treatment apparatus and method for desalination and greenhouse gas (GHG) sequestration. The treatment apparatus includes an electrochemical separation cell in fluid communication with a separate cathode reaction cell, and a separate anode reaction cell. The separation cell contains a first aqueous solution containing ions. The cathode reaction cell contains a second aqueous solution that includes cathode products from the electrochemical separation of the first aqueous solution.

[0018] US Patent No. 9,493,368 relates to a method for precipitating scale from water, comprising providing an electrochemical cell having a primary cathode chamber containing a first electrode, a primary anode chamber containing a second electrode, and a cation exchange membrane separating the primary cathode chamber from the primary anode chamber. A feed water stream is split into separate input streams to the primary cathode chamber and the primary anode chamber, respectively. The pH of the water in the primary anode chamber is decreased by electrolysis. The pH of the water in the primary cathode chamber is increased by electrolysis, and cations are removed from the water in the primary cathode chamber by the formation of scale on the first electrode of the primary cathode chamber. The separate treated water discharge streams from each of the primary cathode chamber and the primary anode chamber are combined into a single conditioned water stream.

[0019] US Patent No. 10,407,327 relates to a bioelectrochemical system capable of removing multivalent ions from seawater. The bioelectrochemical system comprises an anode chamber with an anode for receiving electrons generated when treating organic material in wastewater with microorganisms; a cathode chamber with a cathode for receiving electrons from the anode to produce hydroxide ions by reacting the electrons with oxygen and water supplied from an external source and using the hydroxide ions to deposit multivalent ions in an electrolyte; and an anion exchange membrane for preventing the migration of multivalent ions in the electrolyte to the anode chamber. Electrochemically active bacteria are attached to the anode.

[0020] US Patent No. 11,413,578 relates to a method for removing carbon dioxide from a water or gas stream by: contacting the gas stream containing carbon dioxide, if present, with an aqueous solution containing ions capable of forming insoluble carbonate salts; contacting the aqueous solution containing carbon dioxide with an electroactive mesh which causes its alkalinization, thereby forcing the precipitation of carbonate solids from the solution and removing dissolved inorganic carbon by electrolysis; and removing the precipitated carbonate solids from the solution or from the surface of the mesh on which the carbonate solids may be deposited.

[0021] US Patent No. 4,839,003 relates to a method for producing alkali hydroxide, chlorine and hydrogen by electrolysis of an aqueous alkali chloride solution in a membrane cell, comprising dissolving impurity-containing high NaCl solid salt in water in a salt dissolver, adding a chemical precipitant to the salt solution to precipitate the impurities, and feeding the resulting mixture to a concentrator, from which the precipitate and clear raw brine are separately recovered, the raw brine is subjected to refinement, the refined brine is fed to a membrane electrolysis cell, and the spent brine is fed to the salt dissolver.

[0022] GB 822,990 A relates to a method for the evaporation of an aqueous solution such as seawater, in which the formation of scale containing calcium carbonate and magnesium hydroxide is reduced or prevented by adjustment of the hydrogen ion concentration of the solution before or during evaporation. The method involves adding to the solution hydrogen ions generated in the anode compartment of a battery operating with an evaporator from a solution containing ions such as sulfate, nitrate or phosphate in sufficient concentration, resulting in the release of mainly hydroxide ions at the anode of the cell with the liberation of oxygen and / or promotion of an oxidation reaction at the anode with the consequent production of hydrogen ions.

[0023] US Patent No. 8,333,944 and US Patent No. 7,887,694 relate to methods for sequestrating carbon dioxide by precipitating a storage-stable carbon dioxide sequestration product from water containing alkaline earth metals and then disposing of the product.

[0024] U.S. Patent No. 9,302,216 relates to a method and apparatus for fixing carbon dioxide gas, which comprises electrolyzing seawater, separating anodic electrolytic water and cathodic electrolytic water produced by the electrolysis of seawater, introducing an alkaline substance into the anodic electrolytic water to adjust the pH, blowing carbon dioxide gas into the cathodic electrolytic water to fix the carbon dioxide gas as carbonate, mixing the anodic electrolytic water after the pH adjustment and the cathodic electrolytic water after the carbonate fixation, and releasing the mixed water in a state where the pH of the mixed water matches the pH of seawater.

[0025] US Patent No. 8,470,281 relates to a method for producing carbonate salts, comprising the steps of: providing a water-containing solution containing cations that undergo a precipitation reaction with carbonate ions and then precipitate in the form of a salt; and generating carbon dioxide microbubbles having a diameter of 50 μm or less in the water-containing solution to cause a precipitation reaction between the cations and the carbonate ions.

[0026] Similar to some of the above mentioned techniques, U.S. Patent No. 4,336,232 relates to the purification of salt brines, and in particular to a method and apparatus for treating salt brines such that the total calcium and magnesium hardness of the brine is reduced to an acceptable level. Preferably, the brine is treated with sodium carbonate (soda ash) to convert the calcium ions to calcium carbonate, and with caustic soda (sodium hydroxide) to convert the magnesium ions to magnesium hydroxide, and the resulting flocculant is separated by filtration. Amounts of sodium carbonate and sodium hydroxide in excess of the stoichiometric ratio are metered into the brine.

[0027] U.S. Patent Application No. 5,409,680 relates to a method for removing alkaline earth metal impurities (e.g., calcium and magnesium ions) from an aqueous alkali metal chlorate solution, which comprises adding sufficient alkali metal carbonate or hydroxide, or both, to the impurity-containing solution to raise the pH above about 9 to form an alkaline earth metal precipitate, and then removing the precipitate from the pH-adjusted solution (e.g., by microfiltration).

[0028] Ho et al., Separation and Purification Technology, (The Netherlands), 2023, Vol. 307, provides a review of mineral carbonation using seawater for carbon dioxide sequestration and utilization.

[0029] Diaz Nieto et al., Water Research, (Netherlands), 2019, Vol. 154, p. 117-124, report on the extraction of Mg from lithium-rich brine. 2+ and Ca 2+ This invention relates to electrolysis using a membrane for removing

[0030] Hasson et al., Desalination, (The Netherlands), 2008, Vol. 230, p. 329-342, relates to electrochemical descaling techniques for desalination applications.

[0031] Sharifian et al., Chemical Engineering Journal, (Netherlands), 2022, Vol. 438, 135326, on marine carbon capture by electrochemical in situ carbonate mineralization using bipolar membranes.

[0032] None of the aforementioned techniques provide a method that results in the precipitation of high purity Mg(OH)2 and CaCO3 as provided herein.

[0033] Conventional carbon mineralization, which involves dissolving Ca / Mg-bearing solids and CO2 in water, is severely limited by the lack of availability of homogeneous minerals with low reactivity. Several factors have been reported to affect the dissolution kinetics of alkaline minerals, including temperature, liquid-solid ratio, solvent, and particle size. At ambient temperature and pressure, the kinetics is often too slow for industrial applications and therefore needs to be accelerated. High temperatures (>100°C) or special solvents (such as acids and amines) have been reported to alleviate this inherent slow kinetics. Moreover, the heterogeneous nature of various alkaline sources is another factor to consider when using these materials in conventional carbon mineralization.

[0034] The problem of mineral dissolution can be addressed by using water rich in Ca and Mg as the alkali source since the desired cations are already solubilized in the aqueous phase. Brine, the waste product of reverse osmosis desalination, is rich in Mg. 2+ and Ca 2+ It is well known that brine is rich in calcium and is considered a potential source for carbon mineralization. Brine is a type of hypersaline water with total dissolved solids (TDS) that can reach up to 70,000 ppm. Currently, most desalination plants discharge brine directly into the ocean, which has proven to be dangerous for marine ecosystems. The successful utilization of brine for carbon mineralization can not only obviate the hazards associated with the disposal of saltwater, but also recover valuable elements such as magnesium and calcium. However, the Ca content is low. 2+ Precipitation of CO2 as carbonate is limited by the lack of dissolved CO2 in the brine solution. Direct carbonation of atmospheric CO2 with brine solutions, a thermodynamically unfavourable reaction process, is still of limited applicability to carbon mineralisation.

[0035] Combining electrolysis with CO2 mineralization enhances the carbonation of Ca and Mg ions from the brine or hard water. - (aq) , Cl 2(g) and H 2(g)We were able to produce OH - The in situ generation of accelerates carbonate formation in aqueous solution, leading to an enhancement of the carbonation reaction process. Electrochemical CO2 mineralization differs significantly from existing CO2 capture and storage strategies due to several attributes. First, electrochemical mineralization occurs at the Earth's surface and proceeds as an ex situ mineral storage process of CO2 by carbonate formation. This differs from traditional geological methods that require CO2 to be concentrated, compressed, and injected underground. Second, the reaction process is not constrained by reactivity variations or heterogeneity of the feed material that affects dissolution. Traditional carbon storage relies heavily on the dissolution properties of the alkaline source. During the past decades, the extraction of Ca from seawater or hard water has been widely used. 2+ and Mg 2+ Several membrane electrolysis methods have been proposed for mineralization and recovery of calcium carbonate. In principle, an anion exchange membrane is used to separate the cathode and anode compartments, and the hydroxyl radicals generated at the cathode govern the pH. The dissolution of CO2 in water becomes accelerated as the pH increases. More recently, membrane-free electrolysis has been investigated to simplify the device and save capital investment. Lalia and co-authors report that a titania-coated graphite cathode was found to be effective for selective CaCO3 precipitation as a stable calcite polymorph using brine in the presence of CO2, followed by selective Mg removal as brucite using a new graphite cathode / anode. Lalia, BS; Khalil, A.; Hashaikeh, R., “Selective Electrochemical Separation and Recovery of Calcium and Magnesium from Brine.” Separation and Purification Technology, (Netherlands), 2021, Vol.264, 118416. However, the complexity of fabricating the titania-coated graphite cathode and the costs associated with modifying the process for subsequent brucite precipitation make it difficult to scale up industrially.

[0036] Thus, there remains a need for improved methods that contribute to carbon dioxide mitigation, including marine carbon removal by electrochemical mineralization.

[0037] Although certain aspects of the prior art have been discussed to facilitate disclosure of the present invention, the applicant is not in any way denying these technical aspects, and it is contemplated that the present invention as claimed may include one or more of the prior art aspects discussed herein.

[0038] Where a document, act, or item of knowledge is referenced or discussed in this application, such reference or discussion is not an admission that that document, act, or item of knowledge, or any combination thereof, was publicly available, known, or part of the common general knowledge as of the priority date, or that it otherwise constitutes prior art under any applicable statutory provision; or that it was known to be relevant to any attempt to solve any problem to which this specification is concerned. Summary of the Invention

[0039] Briefly, embodiments of the present invention provide methods / processes that contribute to carbon dioxide reduction through carbon mineralization, the process by which carbon dioxide becomes solid minerals such as carbonates. Embodiments further provide a process to produce magnesium hydroxide.

[0040] In a first aspect, the present invention provides a method for the preparation of calcium ions (Ca 2+ ) and magnesium ions (Mg 2+ The present invention provides a method for recovering calcium carbonate (CaCO3) and magnesium hydroxide (Mg(OH)2) from an aqueous solution containing calcium carbonate (CaCO3) and magnesium hydroxide (Mg(OH)2), the method comprising:

[0041] introducing the aqueous solution into an electrochemical cell comprising a chamber containing a photoactive cathode and an anode, the cathode and the anode not being separated by a membrane; Processing step (a): introducing a gaseous source of (bi)carbonate anions into the cell; Applying a voltage to the cell to effect the water reduction reaction of process step (a) at the cathode; and Precipitating solid CaC0 from solution, facilitated by hydroxide ions produced from the water reduction reaction of process step (a); and Separately from the step of carrying out process step (a), in the same chamber, process step (b): Applying a voltage to the cell to effect the water reduction reaction of process step (b) at the cathode; and Precipitation of solid Mg(OH)2 from solution, facilitated by hydroxide ions produced from the water reduction reaction of process step (b). and Includes. The above and other objects, features and advantages of the present invention will become apparent from the following detailed description of the various aspects of the invention taken in conjunction with the accompanying drawings. [Brief description of the drawings]

[0042] [Figure 1] 1A and 1B are diagrams illustrating embodiments of process steps (a) and (b), respectively.

[0043] [Diagram 2] Part a shows that the concentrations of Mg2+ and Ca2+ in aqueous solution vary with pH. As the pH increases, the concentrations start to decrease with the onset of precipitation. Part b shows the carbon speciation in a closed system. The concentrations of H2CO3* (aq), HCO3- (aq), and CO3 2- (aq) are functions of pH and are calculated based on an ambient atmosphere with a CO2 partial pressure of 1 atm.

[0044] [Diagram 3]Part a is a schematic diagram of an embodiment of the two-mode electrochemical mineralization (where mode 1 corresponds to process step (b) and mode 2 corresponds to process step (a)). The two modes can be switched by supplying or not supplying CO2 to the cell. Part b is the XRD pattern of the Ti mesh (inset: photo of the Ti mesh electrode used in the experiment).

[0045] [Figure 4] Figure 1 shows ICP-OEM results of Ca and Mg in brine and the corresponding recovery efficiencies. Part a shows the results obtained after electrolysis of process step (b). Part b shows the results obtained after electrolysis of process steps (b) and (a). Note that in part b, each electrolysis was applied to both process steps (b) and (a). Thus, the concentration of Mg2+ in part b is almost the same as in part a.

[0046] [Diagram 5] Figure 1 shows ICP-OEM results and the corresponding recovery efficiencies. Part a shows the results obtained after electrolysis with CO2 (i.e. process step (a)) for various lengths of operation. Part b shows the results obtained after an additional electrolysis without CO2 (i.e. process step (b)), where each electrolysis period applies to both process steps.

[0047] [Figure 6] Figure 1 shows ICP-OEM results for 20 electrolyses for each of process steps (a) and (b), where -3 V (vs. Ag / AgCl) was applied for process step (b).

[0048] [Figure 7]Figure 1 shows XRD patterns and FTIR spectra of precipitates. Mode 1 in the figure corresponds to process step (b) and mode 2 in the figure corresponds to process step (a). XRD patterns of precipitates from (part a) mode 1 and (part b) mode 2 operated for 20 hours; and FTIR spectra of precipitates from (part c) mode 1 and (part d) mode 2 electrolyzed for 20 hours are shown.

[0049] [Figure 8] Figure 2 shows TGA curves of precipitates from (part a) mode 1 (process step (b)) and (part b) mode 2 (process step (a)) run for 20 h.

[0050] [Figure 9] Figure 1 shows (part a) SEM image, (part b) magnified image (area marked with box) and corresponding EDS mapping for (part c) Mg, (part d) Ca and (part e) EDS spectrum of the precipitate from Mode 1 (process step (b)) test; and (part f) SEM image (inset: magnified image of area marked with box), (part g) magnified image (area marked with box) and corresponding EDS mapping for (part h) Mg, (part i) Ca and (part j) EDS spectrum of the precipitate from Mode 2 (process step (a)) test.

[0051] [Figure 10] Figure 1. LSV curves obtained for (part a) CO2-free and (part b) CO2-saturated electrolytes (inset: zoomed in curve for TiO2 mesh). Detailed Description of the Invention

[0052] In the following description, reference is made to the accompanying drawings and text which form a part hereof and which show by way of illustration specific embodiments which may be practiced. These embodiments are described in detail to enable one skilled in the art to practice the invention, but it should be understood that other embodiments may be utilized and that structural, logical, and electrical changes may be made without departing from the scope of the invention. Thus, the following and example description of the embodiments should not be taken in a limiting sense, and the scope of the invention is defined by the appended claims.

[0053] The present invention relates to a method for the preparation of calcium ions (Ca 2+ ) and magnesium ions (Mg 2+ According to an embodiment of the present invention, Ca and Mg can be selectively recovered by electrolytic processing steps in a single cell without modification of the cell.

[0054] Carbon mineralization is a thermodynamically downhill reaction process that can potentially put the industry into a negative carbon emission state. By combining electrochemical strategies with carbon mineralization (e.g., via seawater), it is possible to both circumvent the desalination problem and facilitate the recovery of value-added elements such as magnesium. Furthermore, while traditional carbon mineralization is still limited by the lack of availability of homogeneous minerals and their inactivity under ambient conditions, embodiments of the present invention utilize electrochemical methods for carbon mineralization through the use of magnesium- and calcium-rich waters such as brines, which are effective under ambient conditions. The embodiments utilize a bimodal electrolysis strategy that allows selective magnesium and calcium precipitation to produce brucite and calcite / aragonite, respectively. Carbon dioxide can be captured and stored in the form of carbonates during electrolysis. Compared to traditional carbon mineralization, embodiments of the present invention overcome the problems of mineral dissolution and the lack of availability of homogeneous feed materials. Furthermore, there are thermodynamic disadvantages for traditional routes due to the capture of CO2 from air or flue gases and the subsequent release of CO2 from solid or liquid substrates. In the sorption-desorption process, energy consumption is essential to overcome the entropy decrease of CO2 sorption and the enthalpy increase of CO2 desorption. In contrast, carbon mineralization, as provided by embodiments of the present invention, is a thermodynamically favorable reaction process.

[0055] In a first aspect, the present invention provides a method for the preparation of calcium ions (Ca 2+ ) and magnesium ions (Mg 2+ The present invention provides a method for recovering calcium carbonate (CaCO3) and magnesium hydroxide (Mg(OH)2) from an aqueous solution containing calcium carbonate (CaCO3) and magnesium hydroxide (Mg(OH)2), the method comprising: introducing the aqueous solution into an electrochemical cell comprising a chamber containing a photoactive cathode and an anode, the cathode and the anode not being separated by a membrane; Processing step (a): introducing a gaseous source of (bi)carbonate anions into the cell; Applying a voltage to the cell to effect the water reduction reaction of process step (a) at the cathode; and Precipitating solid CaC0 from solution, facilitated by hydroxide ions produced from the water reduction reaction of process step (a); and performing the steps of: Separately from the step of carrying out process step (a), in the same chamber, process step (b): Applying a voltage to the cell to effect the water reduction reaction of process step (b) at the cathode; and Precipitation of solid Mg(OH)2 from solution, facilitated by hydroxide ions produced from the water reduction reaction of process step (b). and Includes.

[0056] Process steps (a) and (b) may be considered to be two modes of the method of the present invention. However, as discussed herein, in various embodiments process step (a) is contemplated to be mode 1 (i.e., the mode performed first), while in other embodiments process step (b) is contemplated to be mode 1.

[0057] In some embodiments, process step (a) is carried out before process step (b).

[0058] In another embodiment, process step (b) is carried out before process step (a).

[0059] The process step (a) removes CO2 from the aqueous solution. Upon undergoing the process step (a), the aqueous solution becomes CaCO3-rich by the formation of CaCO3 precipitate. 2+ An embodiment of process step (a) is shown in Figure 1A.

[0060] In process (b), Mg is extracted from the aqueous solution. 2+ After treatment step (b), the aqueous solution is free of Mg(OH)2 by the formation of a precipitate. 2+An embodiment of process step (b) is shown in Figure IB. Although Figures 1A and B show a graphite anode, any art accepted material may be used for the anode.

[0061] An embodiment of the method of the present invention is 2+ ions and Ca 2+ It utilizes the difference in solvation behavior of ions. For example, Mg 2+ The ion is Ca 2+ ion. As a result, the formation of Mg(OH)2 is highly favored. However, in the presence of carbonate ions (from a gaseous (bi)carbonate anion source in process step (a)), the formation of Ca 2+ Ion is Mg 2+ Ca 2+ The ion is Mg 2+ As a result, process step (a) favors the formation of calcium carbonate in the presence of CO and carbonate ions.

[0062] In process step (a), a gaseous source of (bi)carbonate anions (e.g. a CO2 supply) is introduced to the cell differently from process step (b) (hence, in an embodiment of the invention, process step (b) does not include the step of introducing a source of (bi)carbonate anions to the cell). The hydroxide ions generated from the reduction of water promote the formation of calcium carbonate in the presence of CO2 in process step (a) and magnesium hydroxide in the absence of CO2 in process step (b).

[0063] When treatment step (a) is carried out before treatment step (b), treatment step (a) may further include the step of introducing calcium ions (Ca 2+ ) and magnesium ions (Mg 2+ As a result of the treatment step (a), the aqueous solution is extracted with Ca 2+ ions are depleted, and then the process step (b) uses the Ca 2+ It is carried out on an ion-depleted aqueous solution.

[0064] When treatment step (b) is carried out before treatment step (a), treatment step (b) may further include the step of adding calcium ions (Ca 2+ ) and magnesium ions (Mg 2+ As a result of the treatment step (b), Mg is extracted from the aqueous solution. 2+ ions are depleted, and then the process step (a) is 2+ It is carried out on an ion-depleted aqueous solution. Carrying out process step (b) before process step (a) has the advantage that it results in Mg(OH)2 of higher purity.

[0065] The aqueous solution is Ca 2+ ions and Mg 2+ The aqueous solution may be any aqueous solution that contains ions, hi some embodiments, the aqueous solution comprises seawater or process water (e.g., brine) from an industrial processing process.

[0066] In some embodiments, the Ca in the aqueous solution treated in treatment step (a) and / or treatment step (b) is 2+The concentration of ions is 100mg / L to 1500mg / L (e.g., 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400, 410, 420, 430, 440, 450, 460, 470, 480, 490, 500, 510, 520, 530, 540, 550, 560, 570, 580, 590, 600, 610, 620, 630, 640, 650, 660, 670, 680, 690, 700, 710, 720, 730, 740, 750, 760, 770, 780, 790, 800, 810, 820, 830, 840, 850, 860, 870, 880, 890, 900, 910, 920, 930, 940, 950, 960, 970, 980, 990, 1000, 1000, 1000, 1010, 1020, 10 0, 490, 500, 510, 520, 530, 540, 550, 560, 570, 580, 590, 600, 610, 620, 630, 640, 650, 660, 670, 680, 690, 700, 710, 720, 730, 740, 750, 760, 770, 780, 790, 800, 810, 820, 830, 840, 850, 860, 870, 880, 890, 900, 910, 920, 930, 94 0, 950, 960, 970, 980, 990, 1000, 1010, 1020, 1030, 1040, 1050, 1060, 1070, 1080, 1090, 1100, 1110, 1120, 1130, 1140, 1150, 1160, 1170, 1180, 1190, 1200, 1210, 1220, 1230, 1240, 1250, 1260, 1270, 1280, 1290, 1300, 1310, 1 320, 1330, 1340, 1350, 1360, 1370, 1380, 1390, 1400, 1410, 1420, 1430, 1440, 1450, 1460, 1470, 1480, 1490, or 1500 mg / L), including all ranges and subranges therein (e.g., 300 mg / L to 1500 mg / L, 400 mg / L to 1500 mg / L, 400 mg / L to 1400 mg / L, etc.).

[0067] In some embodiments, the Ca in the aqueous solution treated in treatment step (a) and / or treatment step (b) is 2+The concentration of ions is 300 mg / L or more (e.g., 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400, 410, 420, 430, 440, 450, 460, 470, 480, 490, 500, 510, 520, 530, 540, 550, 560 , 570, 580, 590, 600, 610, 620, 630, 640, 650, 660, 670, 680, 690, 700, 710, 720, 730, 740, 750, 760, 770, 780, 790, 800, 810, 820, 830, 840, or 850 mg / L or more).

[0068] In some embodiments, the Mg in the aqueous solution treated in process step (a) and / or process step (b) is 2+The concentration of ions is 100mg / L to 1500mg / L (e.g., 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400, 410, 420, 430, 440, 450, 460, 470, 480, 490, 500, 510, 520, 530, 540, 550, 560, 570, 580, 590, 600, 610, 620, 630, 640, 650, 660, 670, 680, 690, 700, 710, 720, 730, 740, 750, 760, 770, 780, 790, 800, 810, 820, 830, 840, 850, 860, 870, 880, 890, 900, 910, 920, 930, 940, 950, 960, 970, 980, 990, 1000, 1000, 1000, 1010, 1020, 10 0, 490, 500, 510, 520, 530, 540, 550, 560, 570, 580, 590, 600, 610, 620, 630, 640, 650, 660, 670, 680, 690, 700, 710, 720, 730, 740, 750, 760, 770, 780, 790, 800, 810, 820, 830, 840, 850, 860, 870, 880, 890, 900, 910, 920, 930, 94 0, 950, 960, 970, 980, 990, 1000, 1010, 1020, 1030, 1040, 1050, 1060, 1070, 1080, 1090, 1100, 1110, 1120, 1130, 1140, 1150, 1160, 1170, 1180, 1190, 1200, 1210, 1220, 1230, 1240, 1250, 1260, 1270, 1280, 1290, 1300, 1310, 1 320, 1330, 1340, 1350, 1360, 1370, 1380, 1390, 1400, 1410, 1420, 1430, 1440, 1450, 1460, 1470, 1480, 1490, or 1500 mg / L), including all ranges and subranges therein (e.g., 300 mg / L to 1500 mg / L, 400 mg / L to 1500 mg / L, 400 mg / L to 1400 mg / L, etc.).

[0069] In some embodiments, the Mg in the aqueous solution treated in process step (a) and / or process step (b) is 2+The concentration of ions is 300 mg / L or more (e.g., 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400, 410, 420, 430, 440, 450, 460, 470, 480, 490, 500, 510, 520, 530, 540, 550, 560, 570, 580, 590, 600, 610, 620, 630, 640, 650, 660, 670, 680, 690, 700, 710, 720, 730, 740, 750, 760 , 770, 780, 790, 800, 810, 820, 830, 840, 850, 860, 870, 880, 890, 900, 910, 920, 930, 940, 950, 960, 970, 980, 990, 1000, 1010, 1020, 1030, 1040, 1050, 1060, 1070, 1080, 1090, 1100, 1110, 1120, 1130, 1140, 1150, 1160, 1170, 1180, 1190, or 1200 mg / L or more).

[0070] In some embodiments, for process step (a) and / or process step (b), the aqueous solution contains Ca such that the solubility limit for forming solid carbonate and / or solid hydroxide under ambient conditions is not reached. 2+ Ion concentration and / or Mg 2+ It has an ion concentration.

[0071] In some embodiments, the aqueous solution treated in treatment step (a) and / or treatment step (b) may contain Ca. 2+ ions and / or Mg 2+The concentration of ions is 0 to 100,000 ppm (e.g., 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400, 410, 420, 430, 440, 450, 460, 470, 480, 490, 500, 510, 520, 530, 540, 550, 560, 570, 580 , 590, 600, 610, 620, 630, 640, 650, 660, 670, 680, 690, 700, 710, 720, 730, 740, 750, 760, 770, 780, 790, 800, 810, 820, 830, 840, 850, 860, 870, 880, 890, 900, 910, 920, 930, 940, 950, 960, 970, 980, 990, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000, 11000, 12000, 13000, 14000, 15000, 1600 0, 17000, 18000, 19000, 20000, 21000, 22000, 23000, 24000, 25000, 26000, 27000, 28000, 29000, 30000, 31000, 32000, 33000, 34000, 35000, 36000, 370 00, 38000, 39000, 40000, 41000, 42000, 43000, 44000, 45000, 46000, 47000, 48000, 49000, 50000, 51000, 52000, 53000, 54000, 55000, 56000, 57000, 58 000, 59000, 60000, 61000, 62000, 63000, 64000, 65000, 66000, 67000, 68000, 69000, 70000, 71000, 72000, 73000, 74000, 75000, 76000, 77000, 78000, 7 9000, 80000, 81000, 82000, 83000, 84000, 85000, 86000, 87000, 88000, 89000, 90000, 91000, 92000, 93000, 94000, 95000, 96000, 97000, 98000, 99000,or 100,000 ppm), including any range or subrange therein. As will be readily appreciated by those of skill in the art, the Ca, 2+ ions and Mg 2+ The initial concentration of the ion will be higher than the concentration after carrying out process steps (a) and (b). If process step (a) is carried out first, the solution treated in process step (b) will be depleted of calcium due to the precipitation of CaCO3 during process step (a). On the other hand, if process step (b) is carried out first, the solution treated in process step (a) will be depleted of magnesium due to the precipitation of Mg(OH)2 during process step (b).

[0072] In some embodiments, the treatment step (a) is carried out to remove Ca in the aqueous solution. 2+ The ion concentration is determined by the following: Ca in the solution before performing the treatment step (a) 2+ A reduction occurs corresponding to a removal efficiency of at least 60% (e.g., at least 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, or 98%) based on the initial concentration of the ion.

[0073] In some embodiments, the treatment step (b) is carried out to remove Mg from the aqueous solution. 2+ The ion concentration in the solution before carrying out the treatment step (b) is 2+ A reduction occurs corresponding to a removal efficiency of at least 60% (e.g., at least 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, or 98%) based on the initial concentration of the ion.

[0074] In some embodiments, the treating step (a) is carried out continuously for a period of 1 to 48 hours (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, or 48 hours) and all ranges and subranges therein (e.g., 1 to 20 hours).

[0075] In some embodiments, treating step (b) is carried out continuously for a period of 1 to 48 hours (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, or 48 hours) and all ranges and subranges therein (e.g., 1 to 20 hours).

[0076] In some embodiments, the invention includes carrying out process step (a) independently of process step (b), or includes carrying out process step (b) independently of process step (a). At least for such embodiments, when process step (a) is carried out, the aqueous solution introduced into the cell contains Ca 2+ ions (e.g., in the concentrations described herein) and, if process step (b) is performed, the aqueous solution introduced into the cell may contain Mg 2+ ions (eg, in the concentrations described herein).

[0077] In some embodiments, the methods of the invention include applying a voltage (e.g., a voltage that results in water oxidation) to the cell during processing step (a) and / or processing step (b) in the range of −4.5 V to −2.0 V (e.g., −4.5, −4.4, −4.3, −4.2, −4.1, −4.0, −3.9, −3.8, −3.7, −3.6, −3.5, −3.4, −3.3, −3.2, −3.1, −3.0, −2.9, −2.8, −2.7, −2.6, −2.5, −2.4, −2.3, −2.2, −2.1, or −2.0 V) and all ranges and subranges therein (e.g., −3.5 V to −2.0 V).

[0078] In some embodiments, applying a voltage to the cell during process step (a) comprises pulsing the voltage by switching between a high voltage and a low voltage.

[0079] In some embodiments, applying a voltage to the cell during process step (b) comprises pulsing the voltage by switching between a high voltage and a low voltage.

[0080] In some embodiments, the methods of the invention include conducting a process step (a) to produce a precipitation reaction product comprising solid CaC0, the precipitation reaction product from process step (a) comprising: - containing 80 wt% or more CaCO3 (e.g. 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99 wt% or more CaCO3); and / or - containing 80 wt.% or more of CaCO3 in the calcite polymorph (e.g., 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99 wt.% or more of CaCO3 calcite), optionally with the remaining CaCO3 (e.g., at least 99%, 98%, or 97% of the remaining CaCO3 being present in the form of aragonite); and / or - containing 10 wt% or less Mg(OH)2 (e.g., 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, or 0.5 wt% or less Mg(OH)2); and / or - Characterized by an infrared (IR) spectrum that does not show any peaks corresponding to Mg(OH)2.

[0081] In some embodiments, the methods of the invention include performing a process step (a) to precipitate solid CaC0, wherein at least 80 wt% (e.g., at least 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99 wt%) of the solid CaC0 is calcite.

[0082] In some embodiments, the methods of the invention include performing a process step (a) to precipitate solid CaC03, wherein less than 20 wt% (e.g., less than 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 wt%) of the solid CaC03 is aragonite, and / or vaterite, and / or combinations thereof.

[0083] In some embodiments, the methods of the invention include carrying out a process step (b) to produce a precipitation reaction product comprising solid Mg(OH), the precipitation reaction product from process step (b) comprising: - containing 80 wt% or more Mg(OH)2 (e.g., 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99 wt% or more Mg(OH)2); and / or - having a purity of 80 wt% or more of Mg(OH)2 (e.g., a purity of 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99 wt% or more); and / or - containing 80 wt. % or more Mg(OH)2 in the crystalline form of brucite (e.g., 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99 wt. % or more Mg(OH)2 in the crystalline form of brucite); and / or - 110~160m2 g -1 (e.g. 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159, or 160 m) 2 g -1 ), and any range or subrange therein (e.g., 135-155 m 2 g -1 and / or - containing 10 wt% or less CaCO3 (e.g., 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0.5, or 0.1 wt% or less CaCO3); and / or - Characterized by an infrared (IR) spectrum that does not show any peaks corresponding to CaCO3.

[0084] In some embodiments, the gaseous (bi)carbonate anion source is a bicarbonate anion source (e.g., gaseous CO, air, flue gas, etc.).

[0085] In some embodiments, the gaseous (bi)carbonate anion source is obtained directly from air and / or emissions from point sources and / or post-combustion CO2 capture.

[0086] In some embodiments, the gaseous (bi)carbonate anion source is a carbonate anion source.

[0087] In some embodiments, the gaseous (bi)carbonate anion source is a gaseous carrier (e.g., air, flue gas, etc.) having a CO2 concentration in the range of 400 ppm to 1,000,000 ppm (1,000,000 ppm corresponds to pure CO2) (e.g., 400, 401, 402, 403, 404, 405, 406, 407, 408, 409, 410, 411, 412, 413, 414, 415, 416, 417, 418, 419, 420, 421, 422, 423, 424, 425, 426, 427, 428, 429, 430, 431, 432, 433, 434, 435, 436, 437, 438, 439, 440, 441, 442, 443, 444, 445, 446, 447, 448, 449, 450, 451, 452, 453, 454, 455, 456, 457, 458, 459, 460, 461, 462, 463, 464, 465, 466, 467, 468, 469, 470, 471, 472, 473, 474, 475, 476, 477, 478, 479, 480, 481, 482, 483, 484, 65, 466, 467, 468, 469, 470, 471, 472, 473, 474, 475, 476, 477, 478, 479, 480, 481, 482, 483, 484, 485, 486, 487, 488, 489, 490, 491, 492, 493, 494, 495, 49 6, 497, 498, 499, 500, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000, 11000, 12000, 13000, 14000, 15000, 16000, 17000, 18000, 19000, 20 000, 21000, 22000, 23000, 24000, 25000, 26000, 27000, 28000, 29000, 30000, 31000, 32000, 33000, 34000, 35000, 36000, 37000, 38000, 39000, 40000, 4 1000, 42000, 43000, 44000, 45000, 46000, 47000, 48000, 49000, 50000, 51000, 52000, 53000, 54000, 55000, 56000, 57000, 58000, 59000, 60000, 61000, 62000, 63000, 64000, 65000, 66000, 67000, 68000, 69000, 70000, 71000, 72000, 73000, 74000, 75000, 76000, 77000, 78000, 79000, 80000, 81000, 82000,83000, 84000, 85000, 86000, 87000, 88000, 89000, 90000, 91000, 92000, 93000, 94000, 95000, 96000, 97000, 98000, 99000, 100000, 200000, 300000, 400000, 500000, 600000, 700000, 800000, 900000, or 1000000 ppm), and all ranges and subranges therein.

[0088] In some embodiments, the (bi)carbonate anion source is a gaseous carrier (e.g., air, flue gas, etc.) with 0.04 volume percent (vo.%) to 100 vol% CO2 (e.g., 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 1 2, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, or 100 vol.% CO2), as well as all ranges and subranges therein.

[0089] In some embodiments, the (bi)carbonate anion source is introduced into the cell by a pressurized gas stream.

[0090] In some embodiments, process step (a) and / or process step (b) do not include a step of introducing a solid material into the aqueous solution. In some embodiments, the method of the invention does not include a step of introducing a solid material into the aqueous solution.

[0091] In some embodiments, treating step (a) and / or treating step (b) does not include the step of introducing an alkaline substance into the aqueous solution.

[0092] In some embodiments, process step (a) and / or process step (b) do not include a step of producing NaOH or HCl.

[0093] In some embodiments, process steps (a) and (b) are carried out without adjusting the ratio of Mg and Ca in the aqueous solution, apart from the reduction caused by depletion of Mg and Ca by precipitation formation.

[0094] In some embodiments, treating step (a) and / or treating step (b) do not include adding iron or an iron-containing compound to the aqueous solution.

[0095] In some embodiments, the aqueous solution treated in process step (a) and / or process step (b) is free of solids. In some embodiments, the aqueous solution treated in process step (a) and / or process step (b) contains less than 1 wt. % solids (e.g., less than 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0.09, 0.08, 0.07, 0.06, 0.05, 0.04, 0.03, 0.02, or 0.01 wt. %).

[0096] In some embodiments, both the solid CaCO3 precipitate and the solid Mg(OH)2 precipitate are collected from the chamber simultaneously.

[0097] In some embodiments, the solid CaCO precipitate and the solid Mg(OH) precipitate are collected separately from the chamber.

[0098] In some embodiments, process step (a) and process step (b) are performed sequentially (starting with one process step) without removing the aqueous solution from the chamber between steps of performing the two process steps.

[0099] In some embodiments, performing process step (a) and / or performing process step (b) includes stirring the aqueous solution in the chamber (e.g., by use of one or more stirring elements) (e.g., while applying a voltage to the cell).

[0100] In various embodiments, the photoactive cathodes used in the methods of the invention are made from or include photoactive materials that promote the decomposition of water into hydroxide species. Such materials can be readily identified and selected by one of skill in the art. The photoactive material may be, for example, as described in Eftekhari A, Babu VJ, Ramakrishna S, “Photoelectrode nanomaterials for photoelectrochemical water splitting.” Int J Hydrog Energy, (Netherlands), 2017, Vol. 42, p. 11078-11109; Yao B, Zhang J, Fan X, He J, Li Y., “Surface Engineering of Nanomaterials for Photo-Electrochemical Water Splitting.” Small., (USA), January 2019, Vol. 15, No. 1, p. 1803746; Li D, Shi J, Li C., “Transition-Metal-Based Electrocatalysts as Cocatalysts for Photoelectrochemical Water Splitting: A Mini Review.” Small., (USA), June 2018, Vol. 14, No. 23, p. 1704179; and Ji L, Lv C, Chen Z, Huang Z, Zhang C., “Nickel-Based (Photo)Electrocatalysts for Hydrogen Production.”, Adv Mater., (USA), April 2018, Vol. 30, No. 17, p. 1705653.

[0101] In some embodiments, the photoactive cathode comprises a metal, a mixed metal composition, or a (mixed) metal oxide. Examples of cathode materials include, but are not limited to, materials comprising titanium (e.g., titanium dioxide TiO2), copper, or steel, and functional and / or synthetic photoactive materials, such as titanium copper, or steel. In some embodiments, the cathode comprises a metal. In some embodiments, the cathode comprises titanium, tungsten, carbon, copper, steel, nickel, platinum, palladium, iron, iridium, molybdenum, cobalt, gold, or silver. In some embodiments, the cathode comprises titanium, carbon, copper, or steel. In some embodiments, the cathode comprises an oxide coating (e.g., a metal oxide coating, such as molybdenum disulfide-zinc oxide, including metal oxides of the metals discussed herein, e.g., NiO). In certain embodiments, the cathode comprises a titanium mesh (e.g., a TiO2 mesh).

[0102] In some embodiments, industrial titanium mesh (e.g., TiO2 mesh) is used as an electrode for efficient CO2 mineralization and selective recovery of valuable metals in the form of Mg(OH)2 and CaCO3.

[0103] In some embodiments, the cathode may be, for example, a mesh surface, a porous surface, an etched surface, or a nanostructure (e.g., between 2 nm and 1000 nm, e.g., 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400, 410, 420, 430, 440, 450, 460, 470, 480, 490, 500, 510, 520, 530, 540, 550, 560, 570, 580, 590, 600, 610, 620, 630, 640, 650, 660, 670, 680, 690, 700, 710, 720, 730, 740, 750, 760, 770, 780, 790, 800, 810, 820, 830, 840, 850, 860, 870, 880, 89 90, 500, 510, 520, 530, 540, 550, 560, 570, 580, 590, 600, 610, 620, 630, 640, 650, 660, 670, 680, 690, 700, 710, 720, 730, 740, 750, 760, 770, 780, 790, 800, 810, 820, 830, 840, 850, 860, 870, 880, 890, 900, 910, 920, 930, 940, 950, 960, 970, 980, 990, or 1000 nm, and all ranges and subranges therein.

[0104] The anode may be of any material accepted in the art. In some embodiments, the anode comprises a metal, a mixed metal composition, or a (mixed) metal oxide composition. In some embodiments, the anode comprises carbon (e.g., graphite). In some embodiments, the anode comprises nickel, platinum, palladium, iron, iridium, molybdenum, cobalt, gold, or silver.

[0105] Certain embodiments of the method of the present invention provide a convenient electrochemical strategy for carbon mineralization carried out in a single chamber cell.

[0106] In some embodiments where process step (b) is performed before process step (a), OH by electrolysis - The formation of Mg increases the alkalinity of the solution (see Equation 1 in Table I below). 2+Ions are determined by the solubility product constant (K sp ) is significantly lower, so it is thermodynamically preferred to precipitate as Mg(OH)2 (see Eqs. 2 & 3 in Table I). sp is the equilibrium state of Mg 2+ and OH - in water and is therefore also known as the equilibrium constant. Following the implementation of process step (b), process step (a) is carried out in which CO2 is bubbled through a Ca-rich electrolyte (which has been depleted of Mg through process step (b)). Assuming most of the Mg has already been removed in process step (b), the continuously produced OH - ions help accelerate the dissolution of CO2 and bicarbonate ions (H2CO3 * ) than carbonate ions (CO3 2- ) (see Eqs. 4-6 in Table I). Finally, the produced CO3 2- The ions react with calcium to produce insoluble calcium carbonate (see Equations 7 & 8 in Table I). [Table 1] EXAMPLES

[0107] The invention will now be illustrated, but not limited, by reference to specific embodiments described in the following examples.

[0108] Materials and Methods

[0109] Chemicals: Sodium chloride (NaCl, ≥99%, Sigma-Aldrich), magnesium chloride (MgCl2, 99%, Alfa Aesar), calcium chloride dihydrate (CaCl2·2H2O, ~99%, MP) were used without further purification. In addition, magnesium hydroxide (Mg(OH)2, ≥95%, Fisher chemical), calcium hydroxide (Ca(OH)2, ≥98%, Fisher chemical), magnesium carbonate (approximately 4MgCO3·Mg(OH)2·5H2O, content (as MgO): 40.0–43.5%, Spectral) and calcium carbonate (CaCO3, research grade, Ward's science) were used as standard chemicals. Deionized water (18.2 MΩ·cm, Millipore) was used throughout the experiments.

[0110] <Solution preparation>: Ca 2+ and Mg 2+ is the most abundant divalent cation in natural waters and often in industrial waters such as brines and reaction products. - Anions usually provide charge compensation to cations in these systems. In this study, 10 g of NaCl, 2.21 g of CaCl2 2H2O, and 2.04 g of MgCl2 were dissolved in 200 mL of deionized water to give 3000 mg / L CaCl, respectively. 2+ and 2600 mg / L Mg 2+ The pH was measured to be 8.42, but when CO2 was dissolved and saturated, it dropped to 4.41.

[0111] Electrochemical measurements: All electrochemical measurements were performed using a potentiostat (Interface1010E, Gamry instruments). Electrolysis was performed in a three-electrode system. The working electrode (cathode) had an area of ​​1 × 1 cm. 2The electrode was a piece of titanium mesh (0.1 mm thick with 0.8 × 1.5 mm openings). The reference and counter electrodes (anodes) were Ag / AgCl and platinum wire, respectively. The prepared artificial brine was used as the electrolyte (60 mL), and the applied voltage was controlled at -2.5 V vs. Ag / AgCl (all potential differences in this work are vs. Ag / AgCl unless otherwise specified).

[0112] Product characterization: All precipitates collected after the reaction were centrifuged, washed with deionized water, and then dried at 80°C. The structural features are examined using X-ray diffraction (XRD, Bruker D8 Advance ECO powder diffractometer) at a voltage of 40 V and a current of 25 A. The obtained data are analyzed by Jade software, and the crystal species are identified by the International Center for Diffraction Data (ICCD) database. The important functional groups are measured using Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR, Thermo Fisher Nicolet iS50). The volatile content is measured using Thermogravimetric Analysis (TGA, TA Instruments, SDT650). During the TGA measurement, the temperature is increased from room temperature to 1000°C in 10°C increments under N2 atmosphere. Morphological studies are performed by scanning electron microscopy (SEM, Zeiss LEO 1550 FESEM). The concentrations of metal cations in the liquids are measured by inductively coupled plasma optical emission spectrometry (ICP-OEM, Spectro Analytical Instruments).

[0113] Thermodynamics of Dissolution and Precipitation: In aqueous solution, Ca 2+ Concentration and Mg 2+ The dependence of the concentration on pH is sp(Equations 2 & 3; see Table I above) are used to determine the separation of these two most abundant cations in brines and often in industrial waters. It has been demonstrated that the separation can be achieved simply by using pH. When the pH is in the range of 10.36 to 12.34, Mg 2+ The concentration of -4 While the Ca 2+ is 10 -2 M, demonstrating the technical feasibility of separating these two divalent cations using only pH. The thermodynamic driving force for precipitation is given by the degree of saturation (Ω), where Ω is the ion activity product (IAP) and K sp It is equal to the ratio of (Ω=IAP / K sp For example, the IAP of brucite is [Mg 2+ ] and [OH - ] squared. When Ω reaches a critical point, precipitation begins.

[0114] In aqueous solutions, the speciation of CO2 in water results in HCO3 - and CO3 2- Both occur and exist in equilibrium. The chemical species formation reactions and dissociation constants representing the CO2-H2O system are listed in Table I above as Equations 4-6, where H2CO3 * represents the sum of CO2(aq) and H2CO3. The dissociation of aqueous CO2 can be visualized by the Bjerrum diagram. As can be seen in part b of Figure 2, CO3 2- The anion activity depends on the pH in the closed system. Calculations are based on an atmosphere with a CO2 pressure of 1 atm. Under neutral conditions (pH=7), the proportion of carbonates is about 1% of the total dissolved carbon, while an estimated 84% of the carbon exists as bicarbonate. However, when the pH is increased to 10.33, the carbonate ion becomes dominant. Thus, increasing the pH favors carbon mineralization as a result of accelerated carbonate formation.

[0115] <Results and Discussion>

[0116] Electrochemical CO2 mineralization and selective magnesium and calcium recovery are carried out in a single-chamber device (Figure 3, part a) equipped with a three-electrode system. An industrial titanium mesh (Figure 3, part b, inset) is used as the working electrode due to its excellent performance and stability against acids or alkalis. A constant potential of -2.5 V is applied throughout the electrochemical experiments. In general, the hydroxyl groups (OH - ) is continuously produced around the cathode (Equation 1). OH - The production of Mg leads to a local pH increase, which in turn leads to selective Mg production depending on the pH range, as explained in part a of Figure 2. 2+ and Ca 2+ More specifically, the recovery process proceeds in two modes, here process step (b) followed by process step (a), both modes being carried out in the same cell under similar conditions.

[0117] Recovery of only Mg cations can be achieved by bulk electrolysis. During the first stage of electrolysis (here process step (b)), the hydroxyl radicals produced from the decomposition of water are converted to Mg 2+ and results in the formation of Mg(OH)2. This reaction has a lower K than the formation of Ca(OH)2. sp (Equation 2), Mg(OH)2 is thermodynamically favored to precipitate exclusively without other solid compounds. At the end of process step (b), Mg(OH)2 can be easily removed from the solution by filtration or centrifugation.

[0118] After process step (b), the aqueous solution / brine is now depleted of Mg. The Mg-free brine / electrolyte collected after process step (b) is an ideal source for CO2 mineralization. Mg 2+ After removal of Ca (treatment step (b)), 2+ becomes the predominant divalent cation in the aqueous solution / brine. Subsequent process step (a), in which continuous bubbling of CO2 near the cathode, favors dissolution of CO2 by increasing the pH. The dissolved CO2 is then partially hydrated and ionized to form H+ and HCO3 - (Equations 4 & 5). OH due to applied voltage - The continuous production of ensures the dissolution of more CO2 and at the same time the neutralization reaction (H + +OH - →H2O) by H + As a result, the equilibrium shown in equations 4-6 shifts in favor of the production of carbonate ions (Figure 2, part b). 2+ The presence of Ca 2+ is combined with carbonate ions and removed from the aqueous phase in the form of CaCO3 precipitate, allowing carbonation. This product is almost insoluble under alkaline conditions (equation 7) and is easy to separate from the solution. After treatment step (a), almost pure CaCO3 (>96%) can be obtained. Thus, Mg 2+ and Ca 2+ is separately recovered from the brine by a simple two-mode electrolysis. It is noteworthy that both modes (i.e. process step (b) and process step (a)) operate under similar conditions and can be easily switched between by passing a CO2 stream.

[0119] The liquid phases obtained before and after electrolysis in process step (b) and process step (a) were measured by inductively coupled plasma optical emission spectrometry (ICP-OEM). In process step (b), the Mg 2+ It was observed that the concentration of ions decreased significantly from an initial concentration of 2566 ppm to 335 ppm, with a removal efficiency of 87% after 20 h (Figure 4, part a). Specifically, the Mg 2+ The concentration of Ca ions dropped by 43% in the first 5 hours of operation. 2+ The concentration of Mg was almost unchanged (~1%), demonstrating the high selectivity of Mg precipitation. 2+ begins to precipitate when CO2 supply is started. During the additional 20 hours of electrolysis (step (a)), the Ca in solution 2+ It was found that the concentration of was reduced by 90% (Figure 4, part b).

[0120] Interestingly, more than 77% of this reduction was observed within the first 5 hours of electrolysis in process step (a). In summary, after 20 hours of electrolysis in each process, Mg 2+ and Ca 2+ are selectively removed from the brine by precipitation with efficiencies as high as 87% and 90%, respectively.

[0121] Mg 2+ Ca before 2+ (i.e., process step (a) precedes process step (b)), Mg 2+ and Ca 2+ The reverse order of recovery modes was also examined. As shown in Figure 5, Ca 2+ The amount of Ca in the solution was reduced by 94% in the presence of CO2, whereas Mg remained at the same concentration after 20 hours of electrolysis. 2+ Although there are signs that Mg has been removed, 2+ The concentration of Mg remains unchanged. 2+ Ca without considering the precipitation 2+ However, in the subsequent process step (b), the removal efficiency of Mg was less than 20% at the same potential (-2.5 V) (Figure 5, part b). This is because the removal of OH after electrolysis of process step (a) with CO2 - This is because the concentration of OH ions becomes low, and as a result the pH of the solution drops significantly. - The competing reaction that consumes 4OH becomes dominant. - -4e - →O2 + 2H2O), which slows down the precipitation. Therefore, more Mg 2+ A higher applied voltage is favorable for precipitation. As shown in FIG. 6, when the applied voltage is increased to −3 V in the second stage of electrolysis (process step (b)), Mg 2+ The removal efficiency of Mg reached 82%, which is almost 62 points higher than that at −2.5 V. This result shows that the recovery efficiency is highly dependent on the order of removal. Thus, some embodiments of the present invention can be used to 2+is selectively removed as Mg(OH)2, followed by Ca 2+ (i.e., process step (b) is carried out prior to process step (a)) since this provides a relatively good efficiency at the same applied voltage.

[0122] The solid precipitates collected after each treatment step were further investigated by X-ray diffraction (XRD) analysis, which allows the identification of the crystal species of these solid products. As shown in Figure 7, part a, the XRD pattern of the product collected from mode 1 (treatment step (b)) matches well with brucite (PDF#98-000-0130) and no other Bragg peaks can be observed. This indicates that only brucite crystal species are produced in mode 1 (treatment step (b)). The solid product obtained from mode 2 (treatment step (a)) shows a clear group of CaCO3 Bragg peaks (Figure 7, part b) that can be identified in the XRD pattern; these are attributed to two different CaCO3 crystal polymorphs. The major polymorph observed (85.8 wt%) was identified as calcite (PDF#01-085-1108), which is considered to be the most stable crystalline form of CaCO3, while the remainder of the Bragg peaks (14.2 wt%) can be attributed to aragonite (PDF#01-073-3251). The ratio of calcite to aragonite produced was calculated to be 6:1. These results are further confirmed by Fourier transform infrared spectroscopy (FTIR) spectra. As shown in part c of Figure 7, the FTIR spectrum of the precipitate from mode 1 (here process step (b)) demonstrates the presence of hydroxyl groups and shows a peak (3695 cm -1 ) are exactly in the same position as in commercial Mg(OH)2, which is consistent with the results obtained by XRD. At the same time, the solid product obtained from mode 2 (here, process step (a)) shows a series of typical carbonate vibrations (1805, 1400, 1090 and 870 cm -1 ) can be observed (Figure 7, part d). -1Note that the peak at 0.05 is due to aragonite. No other peaks were observed, indicating the formation of only CaCO3, which is also consistent with the XRD results. Thus, Mg and Ca are removed separately from the brine via the electrochemical formation of Mg(OH)2 and CaCO3, respectively. At the same time, CO2 is mineralized to calcite and aragonite, which can be further utilized.

[0123] Further evidence of selective Mg(OH)2 and CaCO3 formation in process steps (b) and (a), respectively, was found using thermogravimetric analysis (TGA). For the solid product obtained from mode 1 (process step (b)) (Figure 8, part a), obvious weight loss was observed as the temperature exceeded 255 °C, terminating at 415 °C. This temperature range of weight loss is similar to commercial Mg(OH)2, implying the presence of analogues. This weight loss is caused by the decomposition of Mg(OH)2 to MgO and H2O that typically occurs within that temperature range, which is in full agreement with the XRD results (not shown). Since only weight loss peaks are observed, this can be entirely attributed to the evaporation of H2O after decomposition. The purity of Mg(OH)2 is calculated to be around 96.78 wt%. For the solid product obtained from mode 2 (process step (a)), obvious weight loss was observed within the temperature range of 553 °C to 808 °C (Figure 8, part b). This weight loss can be attributed to the decomposition of CaCO3 into CaO and CO2. Similarly, the content of CaCO3 is estimated to be 96.29% based on 42.37 wt% of CO2 released during the decomposition of CaCO3. Mg(OH) 2(s) →MgO (s) +H2O (g) 200~500℃ (9) CaCO 3(s) →CaO (s) +CO 2(g) 600~800℃ (10)

[0124] Scanning electron microscopy (SEM) image (Figure 9, part a) of the solid product obtained from mode 1 (processing step (b)) shows the presence of the flake-like morphology typically found in brucite, which is clearly visualized in the magnified image (Figure 9, part b). Furthermore, Energy Dispersive X-ray Spectroscopy (EDS) mapping shows a strong signal of Mg (Figure 9, part c) and negligible noise from Ca (Figure 9, part d). The EDS spectrum shows that Mg is the main alkali metal present in the particles, with a calculated weight ratio of Mg to Ca of 51:1 (Figure 9, part e). It is noteworthy that the powder produced has a considerably large surface area of ​​144.33 m 2 g -1 The surface area of ​​the precipitates shows a large surface area, which is more than 10 times larger than that of the commercial brucite used for comparison in this study. This is beneficial for further utilization of the precipitates. For example, in CO2 capture applications, Mg(OH)2 particles with a large surface area have been found to have better reaction kinetics. At the same time, the morphology of deformed cubic calcite (Fig. 9, part f) and needle-like aragonite (Fig. 9, part g) was found in the solid product obtained from mode 2 (process step (a)). This is consistent with the XRD and FTIR results (Fig. 9, part b). In addition, EDS mapping also shows the dispersion of Ca on selected particles (Fig. 9, part i), with a weight ratio of Ca:Mg of 80:1 (Fig. 9, part j). In summary, all the results prove the selective recovery of Mg and Ca from the brine. It is worth noting that the mineralization of CO2 is carried out simultaneously with mode 2 (process step (a)).

[0125] Electrode stability and activity are important considerations in the design of the system. In this embodiment, industrial titanium mesh is used as the working electrode for long-term electrolysis and is examined to be the most active material for carbon mineralization. As shown in Figure 10, part a, the linear sweep voltammetry (LSV) curves measured for the Ti mesh electrode in CO2-free electrolyte (mode 1, process step (b)) show an onset potential near -1.5 V and a maximum potential of -300 mA cm at -2.5 V. -2 It is shown that a current density of 100000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

[0126] Furthermore, it was confirmed that the Ti mesh electrode was corrosion resistant for long-term electrolysis even in the presence of chloride anions. The equilibrium potential of the oxygen evolution reaction (OER, Eq. 9) is 130 mV more negative than that of the chlorine evolution reaction (ClER, Eq. 10), making ClER kinetically favored. OER is a four-electron oxidation, while ClER is a two-electron oxidation that proceeds more readily, requiring a lower overpotential. Thus, ClER has a much faster reaction rate and is the dominant anodic reaction. Note that the electrooxidation of chlorine (ClOR, Eq. 11) usually occurs around the anode during electrolysis, further competing with OER. As a result, the more favorable ClER reaction and the OH generation from the ClOR reaction are favored. -The suppression of consumption leads to the preferential formation of brucite and subsequent carbon mineralization in the two-mode electrolysis. Under alkaline conditions (pH = 8.42, mode 1, process step (b)), the highly reactive chloride anions can corrode the electrodes via a metal chloride-hydroxide formation mechanism. With carbon fiber cloth, a gradual corrosion can be observed accompanying the electrolysis of splitting seawater (not shown). However, the Ti mesh pieces can be reused many times without obvious corrosion, indicating their exceptional corrosion resistance and potential applications in industry. 4OH - (aq) -4e - →O 2(g) +2H2O E 0 =1.23V(vs.SHE) (9)

[24] 2Cl - (aq) -e - →Cl 2(g) E 0 =1.36V(vs.SHE) (10)

[24] 2Cl - (aq) +2OH - (aq) -e - →2ClO - (aq) +H2O E 0 =1.72V(vs.SHE) (11)

[25]

[0127] <Conclusion>

[0128] In summary, the above tests demonstrate a bimodal electrochemical carbon mineralization process that utilizes Ca- and Mg-rich aqueous solutions and selectively extracts Ca and Mg as CaCO3 and Mg(OH)2, respectively. Magnesium hydroxide and calcium carbonate with purities as high as 96.78% and 96.29%, respectively, were obtained after bimodal electrolysis (process step (b) followed by process step (a)). This technique is able to extract the huge amount of Mg in the brine. 2+ and Ca 2+It has the potential to utilize titanium mesh to produce high value added materials while simultaneously acting as a CO2 sink. Additionally, the forgoing embodiment utilizes industrial titanium mesh as the working electrode, which has been widely reported to be scalable. Furthermore, stability testing has shown impressive anti-corrosion properties even in chlorine-containing systems, meaning that it can be reused for multiple cycles without apparent corrosion.

[0129] Mg 2+ and Ca 2+ was selectively removed by precipitation with high efficiencies of 87% and 90%, respectively, which has the potential to significantly reduce the salinity of the brine, facilitating the efficient disposal of more material, while also significantly reducing the environmental risks to aquatic ecosystems.

[0130] The terminology used herein is merely for the purpose of describing particular embodiments and is not intended to limit the present invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms unless the context clearly indicates otherwise. It is further understood that the terms "comprise" (and any form of such terms, e.g., "comprises" and "comprising"), "have" (and any form of such terms, e.g., "has" and "having"), "include" (and any form of such terms, e.g., "includes" and "including"), "contain" (and any form of such terms, e.g., "contains" and "containing"), and any other grammatical variants thereof, are open-ended linking verbs. As a result, a method or device that "comprises," "has," "includes," or "contains" one or more steps or elements possesses, but is not limited to possessing only, those one or more steps or elements. Similarly, a method step or composition or article element that "comprises," "has," "includes," or "contains" one or more features possesses, but is not limited to possessing only, those one or more features.

[0131] As used herein, the terms "comprising," "has," "including," "containing," and other grammatical variations thereof, encompass the terms "consisting of" and "consisting essentially of."

[0132] The phrase "consisting essentially of" or grammatical variations thereof, as used herein, is deemed to specify the stated features, integers, steps, or components, but does not exclude the addition of one or more additional features, integers, steps, components, or groups thereof, so long as such additional features, integers, steps, components, or groups thereof do not materially alter the basic and novel characteristics of the claimed composition, device, or method.

[0133] All publications cited in this specification are herein incorporated by reference to the same extent as if each individual publication was specifically and individually indicated to be incorporated by reference as if it were fully set forth.

[0134] Subject matter incorporated by reference is not to be considered a substitute for any claim limitation, unless expressly indicated otherwise.

[0135] Embodiments of the method of the present invention differ significantly from those disclosed in the references discussed herein, such as Carre et al., Environmental Chemistry Letters, (DE), 2020, Vol. 18, pp. 1193-1208; Rau, Environ. Sci. Technol., (US), 2008, Vol. 42, pp. 8935-8940; and Xie et al., Environ Earth Sci, (DE), 2015, Vol. 73, pp. 6881-6890.

[0136] Throughout this specification, when one or more ranges are referred to, each range is intended to be a shorthand format for presenting information, where the range is understood to include each individual point within the range, and also any subranges within that range, between any individual point within that range and any other individual point within that range, as if each was individually set forth herein.

[0137] While several aspects and embodiments of the present invention have been described and illustrated herein, alternative aspects and embodiments may be selected by those skilled in the art to accomplish the same purposes, and it is therefore intended that this disclosure and the appended claims cover all such additional and alternative aspects and embodiments that fall within the true spirit and scope of the present invention.

Claims

1. Calcium ions (Ca ２＋ ) and magnesium ions (Mg ２＋ From an aqueous solution containing ) calcium carbonate (CaCO3) ３ ) and magnesium hydroxide (Mg(OH) ２ A method for recovering ) the method being: The steps include: introducing an aqueous solution into an electrochemical cell having a chamber containing a photoactive cathode and anode, wherein the cathode and anode are not separated by a membrane; and then Processing step (a): Introducing a gaseous (bi)carbonate anion source into the cell; Applying a voltage to the cell brings about the water reduction reaction in the cathode process (a); and The reaction of solid CaCO3 from solution is facilitated by hydroxide ions produced from the water reduction reaction in processing step (a). ３ To perform precipitate formation The steps to implement: In addition to the step of carrying out processing step (a), processing step (b) is carried out in the same chamber: Applying a voltage to the cell brings about the water reduction reaction in the cathode process (b); and The reaction of solid Mg(OH) from solution is facilitated by hydroxide ions produced from the water reduction reaction in processing step (b). ２ To perform precipitate formation Steps to implement and A method that includes this.

2. The method according to claim 1, wherein the aqueous solution includes seawater or process water derived from an industrial processing step.

3. The method according to claim 1, wherein processing step (a) is performed before processing step (b).

4. The method according to claim 1, wherein processing step (b) is performed before processing step (a).

5. Regarding processing step (a) and / or processing step (b): Ca in aqueous solution ２＋ The ion concentration is 100 mg / L to 1500 mg / L; and / or Mg ２＋ The ion concentration is between 100 mg / L and 1500 mg / L. The method according to claim 1.

6. Regarding processing step (a) and / or processing step (b): The concentration of Ca ions in the aqueous solution is 300 mg / L or more; and / or ２＋ ​ Mg in aqueous solution ２＋ The ion concentration is Mg 300 mg / L or higher. ２＋ It is an ion, The aqueous solution has a Ca²⁺ ion concentration and / or Mg²⁺ ion concentration such that, under ambient conditions, it does not reach the solubility limit for forming solid carbonates and / or solid hydroxides. The method according to claim 1.

7. For processing step (a) and / or processing step (b), the aqueous solution contains Ca such that under ambient conditions it does not reach the solubility limit for forming solid carbonates and / or solid hydroxides. ２＋ Ion concentration and / or Mg ２＋ The method according to claim 1, having an ion concentration.

8. The bicarbonate anion source is gaseous CO2. ２ The method according to claim 1.

9. The method according to claim 1, comprising applying a voltage to the cell that causes oxidation of water in the range of -3.5V to -2.0V while performing processing step (a) and / or processing step (b).

10. By performing processing step (a), solid CaCO2 ３ The process includes a step of producing a precipitate reaction product comprising: CaCO4 80 wt% or more ３ Including; and / or Mg(OH) less than 10 wt% ２ Including; and / or Mg(OH) ２ The method according to claim 1, characterized by an infrared (IR) spectrum that does not show a peak corresponding to [a specific value].

11. By performing processing step (a), solid CaCO2 ３ The step includes precipitating the solid CaCO ３ The method according to claim 1, wherein at least 80 wt% of the material is calcite.

12. By performing processing step (b), the solid Mg(OH) ２ The process includes a step of producing a precipitate reaction product comprising: 80 wt% or more of Mg(OH) ２ Including; and / or CaCO3 less than 10 wt% ３ Including; and / or CaCO ３ It is characterized by an infrared (IR) spectrum that does not show a peak corresponding to, The method according to claim 1.

13. The method according to claim 1, wherein the cathode comprises a cathode of titanium, carbon, copper, iron, nickel, platinum, palladium, iron, iridium, molybdenum, cobalt, gold, or silver, and the cathode further comprises an oxide coating (e.g., a metal oxide coating).

14. The method according to claim 1, wherein the cathode comprises a textured surface, the textured surface being a mesh surface (e.g., titanium mesh), a porous surface, an etched surface, or a surface containing a nanostructure.

15. The method according to claim 1, wherein the anode includes carbon (e.g., graphite), nickel, platinum, palladium, iron, iridium, molybdenum, cobalt, gold, or silver.

16. (Heavy) carbonate anion sources include air and / or emissions from point sources and / or post-combustion CO2. ２ The method according to claim 1, wherein the (bi)carbonate anion source is obtained directly from a captured material (e.g., exhaust gas) and the gas has a CO2 concentration ranging from 400 ppm to 100 vol% CO2.

17. The method according to claim 1, wherein the method does not include the step of introducing an alkaline substance into an aqueous solution.

18. In a single step, solid CaCO3 is extracted from the chamber. ３ Mg(OH) precipitate and solid ２ The method according to claim 1, further comprising the step of collecting both of the precipitates.

19. The method according to claim 1, comprising stirring the contents of the chamber (for example, by using a stirring element) while carrying out processing step (a) and / or while carrying out processing step (b).

20. During processing step (a), the application of voltage to the cell includes pulsing the voltage by switching between high voltage and low voltage; and / or During processing step (b), the application of voltage to the cell includes pulsing the voltage by switching between high voltage and low voltage. The method according to claim 1.

Images