Method of making a calcium carbonate product

Abstract

The present invention relates to methods of making calcium carbonate products. Such calcium carbonate products are useful as strengthening additives for cementitious materials.

Description

[0001] Method of Making a Calcium Carbonate Product

[0002] The present invention relates to methods of making calcium carbonate products. Such calcium carbonate products are useful as strengthening additives for cementitious materials.

[0003] Background

[0004] Cement is a commonly used construction material that is used to bind other materials together, for example, aggregates in the production of concrete. It is traditionally produced by first milling raw materials, typically limestone and clay, to form raw meal. The raw meal is calcined causing the decomposition of limestone into lime, and the precalcined meal is sintered to form clinker. The clinker is cooled, ground, and mixed with additives depending on the type of cement being produced. Portland cement (e.g., Ordinary Portland cement or OPC) is the most common cementitious material used in construction. OPC contains mainly calcium silicates and may be classified by the British / European standard BS EN 197-1:2019 (Part 1: Composition, specifications and conformity criteria for common cements').

[0005] Cement production is responsible for 3 billion tonnes of CO2 annually, accounting for around 8% of global CO2 emissions. During manufacture, CO2 is released from raw meal during the calcination of limestone (CaCOs), which is converted into lime (CaO). Moreover, the manufacturing process is highly energy intensive, and the energy production further contributes to the overall CO2 emissions, for example, by the burning of fossil fuels. Methods of making cementitious products with reduced CO2 emissions are needed.

[0006] Limestone provides a source of calcium carbonate in the calcite polymorph, which is one of the three main polymorphs of calcium carbonate together with vaterite and aragonite. Their relative thermodynamic stability is as follows: calcite > aragonite > vaterite. Each of these polymorphs of calcium carbonate may be added to cementitious materials to improve compressive strength; however, vaterite is more reactive than calcite and would be expected to yield an even greater compressive strength in the subsequent cured products. The flowability and workability of cementitious materials is also expected to be improved where vaterite is added instead of calcite, in part ascribed to the spherulitic morphology of vaterite, compared with the rhombohedral morphology of calcite.The literature discloses processes wherein limestone is calcined to release carbon dioxide and generate calcium oxide, which is subsequently reacted with CO2 to generate calcium carbonate that comprises vaterite. For example, in W02021016200A1, a method of calcining limestone to form carbon dioxide and calcium oxide or hydroxide is disclosed, followed by the treatment with a recycled N-containing salt, whereby it is subjected to carbonation with carbon dioxide. Similarly, in US 11,945,758 B2, a method of producing a cement composition is disclosed, comprising dissolving limestone in a N-containing salt solution to produce an aqueous solution comprising calcium salt and a gaseous stream comprising carbon dioxide; and treating the aqueous solution comprising calcium salt with the gaseous stream comprising carbon dioxide to form a composition comprising bimodal distribution of reactive vaterite cement.

[0007] One of the issues with using limestone in the manner described in the literature is that the process liberates carbon dioxide from the limestone during the conversion process from calcite into the vaterite form. Whilst the conversion of limestone, in the calcite form, to the more reactive vaterite with a defined particle size distribution is valuable, a considerable issue regarding this method is the limitation on the emissions benefit as no CO2 is effectively ‘captured’ within the process. The problem with limestone as a calcium source for strength additives in cementitious products is that, in order to obtain the more useful vaterite polymorph instead of the calcite which is inherently present, carbon dioxide is released to the atmosphere. Even where recaptured and utilised in the precipitation of vaterite from the remaining Ca2+rich solution, this achieves little potential CO2 sequestration impact. Therefore, there is a need for an alternative Ca-based sources which do not liberate CO2.

[0008] There is a large amount of waste gypsum produced industrially from which it would be desirable to make use of the calcium content in many applications. Gypsum is, however, a form of calcium sulfate, rather than calcium carbonate. If it were possible to make use of a calcium source which is not calcium carbonate based in the first instance, then the issue of carbon dioxide release is eliminated, and a reactive calcium carbonate product is produced which incorporates exogenously sourced CO2, such as from flue-gas.

[0009] The presence of sulfate ions, however, incurs several key challenges; the requirement to remove sulfate from a recycled N-base carbonation solution prior to reuse, modulated carbonation reaction kinetics, and potential issues with sulfate inclusion in the final product which affects its application as a cementitious additive.Kang, D et al. Chemical conversion of carbon dioxide via target metal separation using seawater-derived wastewater, 2018, 3, 30, 8628-8636 describes the formation of calcium carbonate from seawater- based wastewater. Sodium sulfate was used to separate calcium ions from the seawater and form calcium sulfate dihydrate (gypsum). Carbon dioxide is converted to ionic form by reaction with alkanolamines, before carbonation of the calcium sulfate dihydrate. The calcium carbonate is produced exclusively in the calcite and aragonite polymorphs, which are less useful as additives for cementitious materials than the vaterite polymorph.

[0010] Accordingly, there is a need for new methods of making cementitious products having a lower carbon footprint. Ideally, these methods would also result in cementitious products having advantageous mechanical properties for applications such as construction. It is an object of the present invention to provide an improved method of enhancing the strength of products comprising cementitious material which utilises waste gypsum or similar calcium sulfate material as the calcium source.

[0011] Summary of the Invention

[0012] In a first aspect, the invention provides a method of making a calcium carbonate product, the method comprising the steps of:

[0013] a] providing a calcium source comprising calcium sulfate; and

[0014] b] (i) combining the calcium source with a nitrogenous base comprising at least one amine functional group in the presence of at least 1 mole equivalent of carbon dioxide relative to the moles of calcium in the calcium source to yield a calcium carbonate product and a nitrogenous-base salt byproduct, wherein the ratio of moles of amine functional groups in the nitrogenous base to moles of calcium in the calcium source is 2:1 or more; or

[0015] (ii) carbonating a nitrogenous base comprising at least one amine functional group by reacting the nitrogenous base with carbon dioxide to form a pre-carbonated nitrogenous base, and combining the calcium source with the pre-carbonated nitrogenous base to yield a calcium carbonate product and a nitrogenous-base salt byproduct, wherein the average number of amine functional groups per molecule of the nitrogenous base before carbonation is x and the calcium source is combined with at least (2 / x) moles of pre-carbonated nitrogenous base relative to the moles of calcium in the calcium source;wherein the nitrogenous base is selected from an alkylamine, an alkanolamine, an amino acid or salt thereof, a polyamine, or combinations thereof;

[0016] wherein the nitrogenous base comprises an amine group bonded to a carbon atom, wherein said carbon atom is substituted by at least one hydrogen atom; and wherein the median particle diameter of the calcium carbonate product is less than or equal to 20 pm.

[0017] The inventors have found that this method converts a calcium source comprising calcium sulfate into calcium carbonate particles having a controlled particle morphology and size, which can be used as a strengthening additive in a cementitious product. Because the reaction to form calcium carbonate consumes CO2, the method has the potential to be carbon negative. By contrast, starting from a CC>2-yielding calcium source, e.g., CaCOs, does not have this potential. When the calcium carbonate product of the invention is used in a cementitious product, it can offset emissions from other cementitious materials that may be present. For example, when the calcium carbonate product of the invention at least partially replaces OPC in a cementitious product, there is a reduction in CO2 emissions both due to the CO2 sequestration and because less OPC (which is manufactured via a carbon intensive process as explained above) is required. Therefore, the calcium carbonate product obtained by the method of the invention may be added to a cementitious material to form a cementitious product having a reduced carbon footprint and improved mechanical properties, such as a higher compressive strength.

[0018] A particular advantage of the present invention is that the resulting calcium carbonate product contains vaterite. Without being bound by theory, the inventors believe that the vaterite in the cementitious material may cause mineralisation of CO2 within several calcium and aluminium based species within cementitious materials, which directly or indirectly results in the long-term strength enhancement achieved in the eventual product. It is also especially beneficial from a compressive strength perspective that the calcium carbonate product has a small median (D50) particle diameter of less than 20 pm.

[0019] A further advantage of the present invention is that the resulting calcium carbonate product comprising vaterite has excellent stability to polymorphic conversion. Typically, the metastable vaterite polymorph would convert to the more stable calcite polymorph, e.g., when cured under high relative humidity such as 80% RH. However, the inventors have found that the calcium carbonate product produced by the process of the presentinvention comprising vaterite is stable and does not convert to calcite or aragonite when cured, as shown in the examples.

[0020] Accordingly, in a second aspect, the invention provides a method of making a cementitious product, the method comprising the steps of: making a calcium carbonate product according to the method of the first aspect; and adding the calcium carbonate product to a cementitious material.

[0021] In a third aspect, the invention provides the use of a calcium carbonate product obtained by the method of the first aspect to strengthen a cementitious product or work as a partial substitute for cementitious material content.

[0022] Summary of the Figures

[0023] Figure 1 shows the effect of the mole equivalent of monoethanolamine (i.e. , the mole equivalent of amine functional groups) on the median particle diameter of the calcium carbonate product.

[0024] Figure 2 shows the effect of the mole equivalent of monoethanolamine (i.e., the mole equivalent of amine functional groups) on the proportion of vaterite in the calcium carbonate product.

[0025] Figure 3 shows the phase composition of calcium carbonate synthesised from Na2COs and CaCl2.6H2O over time.

[0026] Figure 4 shows the effect of the median particle diameter of the calcium carbonate product on the flowability of the cementitious product.

[0027] Definitions

[0028] As used herein, the term “about” means approximately, in the region of, roughly, or around. The term “about” in relation to a numerical value x is optional and means, for example, x ± 5%. Numerical values disclosed with the term “about” include the specifically identified value. For example, “about 100” means a number ranging from 95 to 105, including 95, 100, and 105.

[0029] An ‘alkylamine’ is a C2 to C10 linear or branched alkane having one, two, or three amine groups, wherein the amine groups are primary, secondary, or tertiary amine groups, preferably primary or secondary amine groups.An ‘alkanolamine’ is a C2 to C10 linear or branched alkane having one, two, or three amine groups and one, two, or three hydroxyl groups, wherein the amine groups are primary, secondary, or tertiary amine groups, preferably primary or secondary amine groups.

[0030] A ‘mineral acid’ is an acid derived from one or more inorganic compounds, for example, sulfuric acid, hydrochloric acid, or nitric acid. A ‘concentrated mineral acid’ as used herein is a mineral acid having a molarity of more than 5M, for example, 10M or more. A ‘dilute mineral acid’ is a mineral acid having a molarity of 5M or less, for example, 1 M or less.

[0031] Molecular weight is determined by size exclusion chromatography, specifically gel permeation chromatography (GPC), with a monodisperse polystyrene equivalent molecular weight calibration standard and GPC columns (optionally manufactured by PSS (Polymer Standards Service-USA, Inc), applied column combination: SDV 5pm 1000A, SDV 5pm 500A, SDV 5pm 100A). The flow rate in the columns is 1.0 ml / min, eluent: tetrahydrofuran, column temperature: 40°C, a differential refractive index detector (Rl) and a UV-detector (254nm) were used. The dispersibility DISP = (Mw / Mn) is the quotient of molecular weight average and number average and was calculated from the measurement results. Unless otherwise stated, the molecular weight of polymeric and oligomeric compounds is the number average molecular weight.

[0032] The terms ‘particle diameter’ or ‘particle size’ refer to the equivalent spherical diameter (esd), i.e. , the diameter of a sphere having the same volume as a given particle. The terms “Dn” and “Dnparticle diameter” refer to the diameter below which n% by volume of the particle population is found. Thus, the terms “D50” and “D50 particle diameter” refer to the volume-based median particle diameter below which 50% by volume of the particle population is found, the terms “D90” and “D90 particle diameter” refer to the particle diameter below which 90% by volume of the particle population is found, and the terms “D10” and “D10 particle diameter” refer to the particle diameter below which 10% by volume of the particle population is found. The term ‘median’ or ‘average’ when applied to a ‘particle diameter’ or ‘particle size’ herein refers to the D50 particle diameter, i.e., the ‘median particle diameter’ is the diameter below which 50% by volume of the particle population is found. Particle diameters can be determined by laser diffraction, for example using Mie theory. Particle diameters can be determined in accordance with ISO 13322-2:2021. Particle size distribution measurements as specified or reported herein are typically measured by Malvern Instruments’ conventional Malvern Mastersizer 3000+Ultra particle size analyzer. The analyte may be prepared as a paste using a dilute aqueous NaOH solution (e.g., 1 g NaOH in 10 L).

[0033] A ’polyamine’ is a linear or branched oligomer or polymer having a repeat unit comprising an amine group having a molecular weight of 100 Da to 100 kDa. A preferred example of a polyamine that may be used in the method of the invention is polyethyleneimine. Polyethyleneimine is a linear or branched oligomer or polymer with a repeating unit Of -CH2CH2NH-.

[0034] Any percentage amount values disclosed herein are on a weight percentage basis unless otherwise specified.

[0035] Detailed Description of the invention

[0036] Method of Making a Calcium Carbonate Product

[0037] The method of making a calcium carbonate product according to the first aspect comprises the following steps:

[0038] a] providing a calcium source comprising calcium sulfate; and

[0039] b] (i) combining the calcium source with a nitrogenous base comprising at least one amine functional group in the presence of at least 1 mole equivalent of carbon dioxide relative to the moles of calcium in the calcium source to yield a calcium carbonate product and a nitrogenous-base salt byproduct, wherein the ratio of moles of amine functional groups in the nitrogenous base to moles of calcium in the calcium source is 2:1 or more ; or

[0040] (ii) carbonating a nitrogenous base comprising at least one amine functional group by reacting the nitrogenous base with carbon dioxide to form a pre-carbonated nitrogenous base, and combining the calcium source with the pre-carbonated nitrogenous base to yield a calcium carbonate product and a nitrogenous-base salt byproduct, wherein the average number of amine functional groups per molecule of the nitrogenous base before carbonation is x and the calcium source is combined with at least (2 / x) moles of pre-carbonated nitrogenous base relative to the moles of calcium in the calcium source; wherein the nitrogenous base is selected from an alkylamine, an alkanolamine, an amino acid or salt thereof, a polyamine, or combinations thereof; and

[0041] wherein the nitrogenous base comprises an amine group bonded to a carbon atom, wherein said carbon atom is substituted by at least one hydrogen atom.This method typically provides a calcium carbonate product having a median particle diameter of less than or equal to 20 pm. In other words, performing the method described above enables the production of calcium carbonate having such a median particle diameter. Accordingly, this method produces a calcium carbonate product that has a small, controlled particle size and contains a significant proportion of vaterite, whilst also sequestering CO2. Although vaterite is metastable relative to calcite and aragonite, the vaterite within the calcium carbonate product of the process of the invention is stable to conversion to calcite or aragonite. The calcium carbonate product is therefore particularly advantageous for use in a cementitious product due to its compressive strengthenhancing effect and its carbon negative method of manufacture.

[0042] Furthermore, the method produces a nitrogenous-base salt byproduct, for example monoethanolammonium sulfate, that may be used in a further step to regenerate the nitrogenous base and precipitate a salt byproduct suitable for use as a fertiliser, such as potassium sulfate. Fertiliser production is typically carbon intensive, so the method also advantageously provides a carbon negative method for producing fertiliser. The regenerated nitrogenous base can be recycled in the method of making a calcium carbonate product of the invention, further improving the sustainability of the method.

[0043] In step b](i), the conversion of calcium sulfate to calcium carbonate may be represented by the following equation (in the case where the nitrogenous base is an alkylamine (AlkNF ); other nitrogenous bases encompassed by the invention would react similarly):

[0044] CO2+ CaS04+ 2AlkNH2+ H2O CaC03+ AlkNH3)2S04

[0045] The calcium sulfate reacts with the carbon dioxide in the presence of the nitrogenous base, here, a primary alkylamine, typically in the presence of water. There must be at least one molar equivalent of the carbon dioxide and a molar excess of amine groups in the nitrogenous base, relative to the moles of calcium in the calcium source, for the reaction to occur.

[0046] As an alternative to step b](i), step b](ii) can be performed instead. In step b](ii), the nitrogenous base is carbonated using carbon dioxide to form a pre-carbonated nitrogenous base. Typically, the amount of carbon dioxide absorbed into the solution comprising the nitrogenous base is 1-15 wt.%, more preferably 6-12 wt%. This precarbonated nitrogenous base is reacted with the calcium source to form the calcium carbonate product.The combination of the calcium source comprising calcium sulfate with at least 1 mole equivalent, preferably at least 1.2 mole equivalents, more preferably 2-10 mole equivalents, of carbon dioxide, or at least (2 / x) moles of a pre-carbonated nitrogenous base (where x is the average number of amine functional groups per molecule of the nitrogenous base before carbonation) relative to the moles of calcium in the calcium source means that there is a high conversion rate of calcium sulfate into calcium carbonate, which ameliorates the possible effects of residual sulfate in the calcium carbonate lattice on properties such as workability, setting time, compressive strength, and expansion upon hydration.

[0047] Calcium Source

[0048] The calcium source comprises calcium sulfate. It is advantageous to use calcium sulfate as the calcium source in the controlled production of calcium carbonate because there is no carbon dioxide release, unlike when limestone, i.e., calcium carbonate, is used as the calcium source. Not only does this eliminate a carbon dioxide release mechanism, the conversion of calcium sulfate into calcium carbonate consumes carbon dioxide, and therefore the method of the invention is intrinsically carbon negative.

[0049] The calcium source may comprise at least 50% or at least 60% by weight calcium sulfate. At lower amounts, the calcium carbonate product may contain a lower proportion of vaterite.

[0050] The calcium source may comprise a hydrate of calcium sulfate, such as gypsum. Preferably, most of the calcium source, for example, at least 90 wt.% or at least 99 wt.%, is calcium sulfate or a hydrate thereof.

[0051] The calcium source may be gypsum, bassanite, anhydrite, ora combination thereof. The calcium source may be provided in the bassanite or anhydrite forms, since these are readily available. Preferably, the calcium source is gypsum. The use of gypsum is advantageous because it has limited commercial uses that do not require further processing of the material.

[0052] The calcium source comprising calcium sulfate, such as gypsum, may be obtained from the waste products of other industrial processes which further improves the sustainability of the method. Accordingly, when the calcium source is gypsum, the gypsum is preferably waste gypsum from an industrial process, such as phosphogypsum. Wastegypsum is the preferred calcium sulfate source, since it typically has the lowest commercial value and fewest uses without additional processing. The calcium source may be selected from phosphogypsum, flue gas desulfurization (FGD) gypsum, building waste gypsum, and combinations thereof. The calcium source may be selected from flue gas desulfurization (FGD) gypsum, building waste gypsum, and combinations thereof.

[0053] The calcium source may comprise less than 0.10 wt% of magnesium, for example, less than 0.05 wt%, or less than 0.01 wt%. The calcium source may comprise less than 0.10 wt% of magnesium in a form that is soluble in water at 25°C, for example, less than 0.05 wt%, or less than 0.01 wt% magnesium in a form that is soluble in water at 25°C. Magnesium may interact with the calcium carbonate during precipitation, reducing the proportion of vaterite in the final calcium carbonate product and increasing the proportion of aragonite. Higher amounts of magnesium may be observed from certain calcium sources, such as sources derived from seawater. Accordingly, the calcium source is preferably not derived from seawater.

[0054] The calcium source may be pre-processed by at least one of: washing with a concentrated mineral acid; washing with dilute mineral acid; gravimetric separation techniques; sieving; alkaline treatment; and filtration. The pre-treatment process purifies the calcium source prior to reaction, for example, by removing heavy metal ions or other toxic contaminants, as well as other mineral phases, which improves the purity of the resulting calcium carbonate product and thereby improved the compressive strength of the final cementitious product.

[0055] In one preferred example, during step a], the calcium source is pre-processed by alkaline treatment with a hydroxide (e.g. an alkali metal hydroxide) to convert the calcium sulfate to calcium hydroxide (i.e., portlandite), and during step b], the calcium hydroxide is combined with the nitrogenous base or pre-carbonated nitrogenous base. Ca(OH)2may be isolated simply by filtering the post reaction suspension, and washing the solid with water and isopropanol.

[0056] In another example, the calcium source is pre-processed by washing with a mineral acid, preferably a strong mineral acid in an amount of around 10-50 wt.% relative to the calcium source such as gypsum. Suitable mineral acids include sulfuric acid, hydrochloric acid, and nitric acid. The acid wash step will typically take around 10-600 minutes, whilst the calcium source is agitated. The solid residue can then be rinsed withwater to remove residual acid impurities, preferably until the pH of the washing material is greater than 6. This pre-processing step removes impurities from the calcium source.

[0057] Other pre-processing treatments could be considered, such as a dilute mineral acid wash, gravimetric separation techniques, sieving, and filtering.

[0058] Nitrogenous Base

[0059] The nitrogenous base used in the method of the first aspect comprises at least one amine functional group. This nitrogenous base acts as a directing agent for the vaterite polymorph of calcium carbonate. The precipitation of calcium carbonate at ambient temperatures occurs typically through the Oswald step rule, whereby amorphous calcium carbonate is initially precipitated, which dissolves and reprecipitates as vaterite, before finally dissolving to reprecipitate as calcite. The nitrogenous bases (also referred to herein as vaterite directing agents) are therefore associated with the surface association to vaterite particles, slowing their redissolution and thus calcite formation. As a result, they are therefore also closely related to limiting the particle sizing of vaterite particles produced in the process, which has been clearly demonstrated through process evaluation, through surface association with the as-nucleated vaterite particles.

[0060] The nitrogenous base comprises an amine group bonded to a carbon atom, wherein said carbon atom is substituted by at least one hydrogen, preferably at least two hydrogens. It will be understood that this requires that the N-atom of the amine functional group is bonded to a carbon atom, wherein said carbon atom is substituted by at least one hydrogen. Preferably, the nitrogenous base comprises an amine group bonded to a methylene moiety (-CH2-). The amine group may be a primary amine (for example, in monoethanolamine), a secondary amine (for example, in diethanolamine), or a tertiary amine (for example, in triethanolamine). Preferably, the nitrogenous base comprises a primary amine group or a secondary amine group, most preferably a primary amine group (-NH2). The primary or secondary amine group is preferably bonded to a methylene moiety (-CH2-).

[0061] Accordingly, the nitrogenous base contains at least one amine group that is not bonded to a tertiary carbon centre. It therefore cannot be a compound such as 2-aminomethyl-2-propan-1-ol. Preferably, the nitrogenous base contains no amine groups bonded to a tertiary carbon centre. Without being bound by theory, it is believed that the steric hindrance that occurs when the amine is bonded to a bulky carbon centre (such as thetertiary carbon centre in 2-aminomethyl-2-propan-1-ol) may result in the exclusive formation of the calcite polymorph of calcium carbonate without any of the vaterite polymorph.

[0062] In order to provide a calcium carbonate product having a suitable particle size and a significant proportion of vaterite from step b](i) of the method of the invention, the ratio of moles of amine functional groups in the nitrogenous base to moles of calcium in the calcium source is 2:1 or more, preferably about 3:1 or more. Optionally the ratio of moles of amine functional groups in the nitrogenous base to moles of calcium in the calcium source is from about 2: 1 to about 10:1, preferably from about 3: 1 to about 8: 1. Figures 1 and 2 shows that a mole equivalent of monoethanolamine (i.e., a mole equivalent of amine functional groups) of between 3:1 to about 8:1 provides a calcium carbonate product that is almost entirely vaterite and has a median particle diameter below 10 pm.

[0063] When the nitrogenous base is pre-carbonated (i.e. when using step b](ii)), the average number of amine functional groups per molecule of the nitrogenous base before carbonation is defined as ‘x’ and the calcium source is combined with at least (2 / x) moles, preferably at least (3 / x) moles, of pre-carbonated nitrogenous base relative to the moles of calcium in the calcium source. In the case where only one nitrogenous base is used, it will be understood that x is simply the number of amine functional groups per molecule. For example, if the nitrogenous base is triethylenetetramine (TETA), x = 4 as there are four amine functional groups per molecule of TETA, and the calcium source is combined with at least 0.5 moles, preferably at least 0.75 moles, of pre-carbonated nitrogenous base relative to the moles of calcium in the calcium source. Typically, the nitrogenous base is a monoamine (e.g. monoethanolamine), where x = 1, and therefore the calcium source is preferably combined with at least 2 moles, preferably at least 3 moles, of precarbonated nitrogenous base relative to the moles of calcium in the calcium source.

[0064] The calcium source may be combined with (2 / x) to (10 / x), preferably (3 / x) to (8 / x), moles of pre-carbonated nitrogenous base relative to the moles of calcium in the calcium source.

[0065] In the case where a combination of nitrogenous bases is used, it is necessary to calculate the average number of amine functional groups per molecule of nitrogenous base. It will naturally be understood from a chemical standpoint that the average is typically a weighted average based on the relative number of moles of the different compounds that are used as nitrogenous bases, when more than one nitrogenous base is present, ‘x’may be calculated as the sum of the percentage of each nitrogenous base in the combination of nitrogenous bases on a molar basis multiplied by the number of amine functional groups in each molecule of that nitrogenous base. For example, if the nitrogenous base is 75 mol% monoethanolamine and 25 mol% hexamethylenediamine, x = 1.25 as there is a weighted average of 1.25 amine functional groups per molecule of nitrogenous base (75% x 1 amine functional group in monoethanolamine + 25% x 2 amine functional groups in hexamethylenediamine), and therefore the calcium source is combined with a total of at least 1.6 moles, preferably at least 2.4 moles, of nitrogenous base relative to the moles of calcium in the calcium source.

[0066] In step b](ii), the nitrogenous base may be diluted in water and contacted with carbon dioxide (e.g., in flue gas) in a CO2 absorber to form the pre-carbonated nitrogenous base. This CO2 absorber can be of any design as is well known in the art but is preferably an absorber tower, typically filled with packing. The packing may be of structured type, for example, the packing may have 100 to 500 m2 / m3, 150 to 400 m2 / m3, or 200 to 250 m2 / m3of specific surface area. After reaction with the calcium source, the nitrogenous base may be regenerated and reused in the CO2 absorber. This process setup is advantageous as it allows water control in the recycled nitrogenous base, by means of controlling the temperature in the top of the CO2 absorber. Other embodiments of CO2 absorber that are well known in the art are feasible but not preferred, as they add to equipment or operational cost and / or increase the footprint of the plant unnecessarily.

[0067] After the nitrogenous base is combined with carbon dioxide, the pre-carbonated nitrogenous base may be a carbamate, carbonate, or bicarbonate. Most commonly, the pre-carbonated nitrogenous base is a carbamate.

[0068] The nitrogenous base is selected from an alkylamine, an alkanolamine, an amino acid or salt thereof, a polyamine, or combinations thereof. As used herein in connection with the nitrogenous base, the term “combinations thereof” encompasses combinations of more than one base from the same class of bases, for example the nitrogenous base may be a combination of two or more alkanolamines or two or more alkylamines.

[0069] The nitrogenous base may be selected from the list of: branched and linear C2-C8 alkanolamine, branched and linear C2-C8 alkylamine, an amino acid or an alkali metal salt thereof (e.g., glycine or an alkali metal salt thereof, asparagine or an alkali metal salt thereof, arginine or an alkali metal salt thereof, lysine or an alkali metal salt thereof), branched or linear polyamine with a molecular weight of 100 Da to 100 kDa, andcombinations thereof. Preferably, the nitrogenous base is selected from the list of: branched and linear C2-C8 alkanolamine, branched and linear C2-C8 alkylamine, an amino acid or an alkali metal salt thereof (e.g., glycine or an alkali metal salt thereof, lysine or an alkali metal salt thereof), and combinations thereof. The nitrogenous base may comprise an alkanolamine, preferably a primary alkanolamine.

[0070] The nitrogenous base may be selected from the list of: monoethanolamine, diethanolamine, triethanolamine, / V-methyldiethanolamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentaamine, glycine or an alkali metal salt thereof, lysine or an alkali metal salt thereof, arginine or an alkali metal salt thereof, branched or linear polyethyleneimine with a molecular weight of 100 Da to 100 kDa, and combinations thereof. Preferably, the nitrogenous base is selected from the list of: monoethanolamine, diethanolamine, triethanolamine, / V-methyl diethanolamine, hexamethylenediamine, diethylenetriamine, glycine or an alkali metal salt thereof, lysine or an alkali metal salt thereof, and combinations thereof.

[0071] The nitrogenous base may be selected from monoethanolamine, diethanolamine, triethanolamine, and combinations thereof, optionally wherein the nitrogenous base consists of: 0-40% by weight of diethanolamine and 0-10% by weight of triethanolamine, with the balance being monoethanolamine. The nitrogenous base may consist of a combination of monoethanolamine, diethanolamine, and triethanolamine, optionally wherein the nitrogenous base consists of 10-40% by weight of diethanolamine and 1-10% by weight of triethanolamine with the balance being monoethanolamine.

[0072] Preferably, the nitrogenous base is at least 60% by weight monoethanolamine, optionally wherein the nitrogenous base is at least 90% by weight monoethanolamine.

[0073] Monoethanolamine is the most preferred nitrogenous base to use in the present invention. Therefore, most preferably, the nitrogenous base is monoethanolamine.

[0074] The use of a nitrogenous base according to the invention is advantageous over the use of ammonia because use of latter presents specific challenges. Capture of CO2 from a gas stream using a solution of ammonia can result in significant ammonia slippage, necessitating use of considerable post-capture washing steps and / or chilling of the capture solution to prevent emissions - the so-called Chilled Ammonia Process typically operates at around 5 °C in the absorber. This chilling adds considerably to the CAPEX and OPEX of the process to both buy and operate the chilling apparatus. The product ofthe reaction would be ammonium sulfate, which is itself a relatively low value product, and although reacting this to form higher value potassium sulfate is possible, it obliges additional steps handling highly volatile ammonia, increasing the likelihood of losses between cycles. Use of less volatile nitrogenous bases, such as ethanolamines, obviates this risk.

[0075] Reaction of the nitrogenous base with the calcium source results in a nitrogenous base salt byproduct, in particular a nitrogenous base sulfate byproduct given that the calcium source comprises calcium sulfate. When the nitrogenous base is an alkylamine, the nitrogenous-base salt byproduct is an alkylammonium sulfate byproduct. If there is a molar excess of nitrogenous base, unreacted nitrogenous base will also be present after the reaction is complete.

[0076] To further increase the sustainability of the process, the nitrogenous base can be regenerated and reused in the method of making a calcium carbonate. The regeneration of the nitrogenous base may produce a sulfate salt, which can be used as a fertiliser. Therefore, the method provides a carbon negative process for producing calcium carbonate, which may at least partially replace OPC in cement and thereby reduce the net carbon emissions associated with its production, whilst also producing fertiliser. This is an additional benefit of the method of the invention because fertiliser production is also typically carbon intensive. Moreover, the step of recycling of the nitrogenous base prevents the build-up of sulfate ions and the subsequent reduction in gypsum solubility. Thus, the nitrogenous component chosen within the present invention may be recyclable, allowing for easy regeneration and re-use within the methods disclosed. The present invention thus provides a second product stream which yields valuable fertilizers in addition to the gypsum-based additive for cementitious materials. This greatly increases the commercial utility of the method outlined, whilst also allowing for recycling of the nitrogenous base.

[0077] Accordingly, in one preferred example, the method further comprises a step, subsequent to step b](i) or b(ii), of adding a hydroxide compound, thereby causing precipitation of a sulfate salt byproduct. The hydroxide compound may be an alkali metal hydroxide, thereby causing precipitation of an alkali metal sulfate. The alkali metal hydroxide may be potassium hydroxide, thereby causing precipitation of potassium sulfate. Optionally, from about 0.3 to about 10 mole equivalents of alkali metal hydroxide may be added relative to the moles of calcium in the calcium source. When a primary alkylamine is usedas the nitrogenous base and potassium hydroxide is added after step b](i) or b](ii), the regeneration may be represented by the following equation:

[0078] (AlkNH3~)2S04+ 2K0H -> 2AlkNH2+ K2S04+ 2H2O

[0079] The nitrogenous base may be reused, thus creating the following cycle:

[0080] >

[0081]

[0082] In another example, the method further comprises a step c], subsequent to step b](i) or b(ii), of passing the nitrogenous-base salt byproduct through a sulfate-selective ion exchange resin to regenerate the nitrogenous base for recycling. The method may further comprise a step d], subsequent to step c], of regenerating the sulfate-selective ion exchange resin to output a salt byproduct suitable for use as a fertiliser. The regeneration of the sulfate-selective ion exchange resin may be performed using potassium hydroxide, the salt byproduct being potassium sulfate. The advantage of using an ion exchange resin and regenerating the ion exchange resin with potassium hydroxide is the production of high-purity potassium sulfate, which may be used as a fertiliser.

[0083] The method may comprise a step, subsequent to step b](i) or b(ii), of adding a hydroxide compound, thereby causing precipitation of a sulfate salt byproduct and regeneration of the nitrogenous base; and passing the regenerated nitrogenous base through a sulfateselective ion exchange resin to remove any residual sulfate.

[0084] Reaction Conditions

[0085] The reactants can be brought together in typical reaction equipment well known in the art, like continuous stirred reactors, batch reactors, plug flow reactors but not limited to these.

[0086] An alternative configuration of the process layout that this invention allows is to contact the nitrogenous base agent, calcium sulfate, and carbon dioxide (e.g., in flue gas) together in a non-fouling liquid gas contactor. Preferentially this non-fouling liquid gas contactor is a trayed column, but not limited to this.The calcium source comprising calcium sulfate can be carbonated in a reactor chamber, for example, wherein the total volume of the solution in the reactor chamber is about 3m3to 10m3per tonne of purified gypsum material.

[0087] Typically, the calcium source is combined with the nitrogenous base and carbon dioxide, or with the pre-carbonated nitrogenous base, in water.

[0088] The reaction to form the calcium carbonate product between the calcium source and the nitrogenous base and carbon dioxide, or with the pre-carbonated nitrogenous base, may be conducted under the following conditions:

[0089] • The Ca2+concentration may be from about 1 to about 500 mM, or from about 10 to about 300 mM, or from about 20 to about 150 mM, or from about 50 to about 120 mM.

[0090] • The CO2 delivery rate may be from about 0.5 litres per minute to about 2.5 litres per minute, or from about 1 litre per minute to about 2 litres per minute, per litre of the reaction mixture formed by combining the calcium source with the nitrogenous base and carbon dioxide. For example, for a 1 L reaction mixture in a 1.5 L jacketed reactor, the CO2delivery rate may range from about 0.5 litres per minute to about 2.5 litres per minute, or from about 1 litre per minute to about 2 litres per minute. This delivery rate would be expected to scale proportionally with the volume of the reaction mixture in larger or smaller reactors.

[0091] • Preferably, step b](i) and b](i i) take place at a temperature of from about 20°C to about 60°C, more preferably from about 20°C to about 35°C.

[0092] • The reaction mixture formed by combining the calcium source with the nitrogenous base and carbon dioxide or with the pre-carbonated nitrogenous base may be stirred at from 50 to 500 rpm, or from 100 to 200 rpm.

[0093] • The pH value of the reaction mixture formed by combining the calcium source with the nitrogenous base and carbon dioxide or with the pre-carbonated nitrogenous base may be between 7 to 12, preferably between 7 to 9.5.

[0094] • The reaction time of the calcium source with the nitrogenous base and carbon dioxide or with the pre-carbonated nitrogenous base may be between 5 minutes and 6 hours.The solid to liquid ratio in the reaction mixture formed by combining the calcium source with the nitrogenous base and carbon dioxide or with the pre-carbonated nitrogenous base may be from 0.05:1 to 0.4:1, optionally from 0.05:1 to 0.2:1.

[0095] The above reaction conditions are general features of the method of the invention which may be combined with one another. Accordingly, the reaction may have the following conditions: a temperature of from about 20°C to about 60°C and a pH value of between 7 to 9.5 Optionally, the reaction may have the following conditions: a Ca2+concentration of from about 1 to about 500 mM, a temperature of from about 20°C to about 60°C, a stirring speed (i.e. , agitation / shear rate) of from 50 to 500 rpm, a pH value of between 7 to 9.5 a reaction time of between 5 minutes and 6 hours, a solid to liquid ratio of 0.05:1 to 0.4:1, and, when applicable, a CO2 delivery rate may be from about 0.5 litres per minute to about 2.5 litres per minute per litre of the reaction mixture.

[0096] During step b](i) or b(ii), a further base may be added in addition to the nitrogenous base, for example, when the nitrogenous base is a mixture of monoethanolamine and other alkanolamines. The increase in pH value, for example to pH 9 or above, may preferentially encourage formation of the vaterite polymorph within the mixture, rather than calcite or aragonite, in addition to enhancing other factors such as carbon dioxide solubility.

[0097] The reaction products may be filtered to remove impurities or to extract the solid residue.

[0098] Calcium Carbonate Product

[0099] The calcium carbonate product is formed by the method of invention. As shown in the examples, the small size of the particles and the presence of the vaterite polymorph in the calcium carbonate product results in a compressive strength improvement when it is used as an additive in a cementitious product.

[0100] The median particle diameter (D50) of the calcium carbonate product is typically less than or equal to 20 pm, preferably less than or equal to 10 pm, more preferably less than or equal to 7 pm, even more preferably less than or equal to 5 pm. A D50 of less than or equal to 20 pm is beneficial for increasing compressive strength when used as an additive in a cementitious product, and within the range of less than or equal to 20 pm, a smaller D50 results in a greater increase in compressive strength. Optionally the median particle diameter of the calcium carbonate product is from 0.2 to 20 pm, preferably from0.5 m to 10 pm, more preferably from 0.8 pm to 7 pm, even more preferably from 2 pm to 5 pm. Particle diameters within these ranges result in a good balance between the flowability of the cementitious material before hydration and compressive strength of the cementitious product after hydration.

[0101] The D particle diameter of the calcium carbonate product may be less than or equal to 4 pm, optionally from 0.1 pm to 4 pm. The Dgo particle diameter of the calcium carbonate product is less than or equal to 60 pm, optionally from 10 pm to 60 pm. The calcium carbonate product may have the following particle size distribution: D : less than or equal to 4 pm; D50: less than or equal to 20 pm; Dgo: less than or equal to 60 pm. The calcium carbonate product may have the following particle size distribution: Dw: 0.1-4 pm; D50: 0.5-10 pm; Dgo: 10-60 pm.

[0102] As explained above, a particular advantage of the method of the invention is that it produces a calcium carbonate product which includes the vaterite polymorph, which is especially useful for strengthening cementitious materials. The calcium carbonate product may comprise 30-100 wt.%, 70-100 wt.%, 90-100 wt.%, 99-100 wt.%, 99.5-100 wt.%, or 100 wt.% of the vaterite polymorph, preferably wherein the balance is the calcite and / or aragonite polymorphs. Typically, the reaction produces a calcium carbonate product which comprises at least 70 wt.% vaterite, which is especially beneficial, preferably at least 90 wt% vaterite. Vaterite provides for greater reactivity in the cementitious material compared with aragonite or calcite, enhancing the physical properties of cementitious products, such as compressive strength, whilst the spherulitic morphology of the vaterite also improves flowability of the cement when compared with calcite in particular. The reaction may produce a calcium carbonate product which comprises up to 15 wt.% calcite, for example, up to 10 wt% calcite.

[0103] The polymorphism of the calcium carbonate product may be verified using X-ray diffraction, typically obtained from a Cu Ka source, as is widely known. For example, X-ray diffraction patterns obtained from the calcium carbonate product can be compared to known X-ray diffraction patterns to confirm the polymorph. For example, vaterite may be identified by having a characteristic peak at 20 = 27.0 ± 0.2 in a Cu Ka X-ray diffraction pattern, and calcite may be identified by having a characteristic peak at 20 = 29.4 ± 0.2 in a Cu Ka X-ray diffraction pattern.In a preferred example, the calcium carbonate product comprises 70-100 wt.% vaterite and has a median particle size (D50) of 0.5 pm to 10 pm, more preferably comprises 90-100 wt.% vaterite and has a median particle size (D50) of 0.8 to 7 pm.

[0104] Furthermore, the level of impurities in the calcium carbonate product is typically much lower than in the calcium source. Table 1 shows the level of impurities in the starting material and product when waste gypsum is used as the calcium source.

[0105] Table 1: Level of impurities in waste gypsum

[0106] <

[0107] <

[0108] <

[0109] <

[0110] < <

[0111] <

[0112] < <

[0113] <

[0114]

[0115] Method of Making a Cementitious Product

[0116] The method of making a cementitious product according to the second aspect comprises the following steps: making a calcium carbonate product according to the method of the first aspect; and adding the calcium carbonate product to a cementitious material. The cementitious material may comprise ordinary Portland cement. In this case, the calcium carbonate product may be added at a quantity of 2 to 50 wt.% with respect to a weight of ordinary Portland cement in the cementitious material. The cementitious material may be CEM I cement, CEM II cement, or CEM III cement. Preferably, the cementitious material is CEM I cement or CEM III cement. More preferably, the cementitious material is CEM I cement.CEM I cement comprises at least 95% by mass of ordinary Portland cement, preferably 100% by mass of ordinary Portland cement. CEM I cement may comprise up to 5% by mass of additional constituents such as gypsum.

[0117] CEM II cement comprises at least 65% and up to 94% by mass of ordinary Portland cement. Typically, there is a main secondary constituent in CEM II cement (for example, blast furnace slag, fly ash, or limestone) that is added to provide certain properties.

[0118] CEM III cement comprises at least 5% and up to 64% by mass of ordinary Portland cement, with the remainder mainly comprising blast furnace slag.

[0119] The addition of the carbon-negative calcium carbonate product of the invention offsets the carbon dioxide emitted in the production of other cementitious materials, such as OPC. Since the calcium carbonate produced by the method of the invention, which is carbon negative, can be used to replace at least some of the calcium salts present in OPC, the addition of calcium carbonate formed by the method of the present invention can significantly reduce the carbon footprint of the cement and any concrete that is made using the cement. As shown in the examples, the addition of a calcium carbonate product produced by the method of the invention improves the compressive strength of the resulting cementitious product.

[0120] The cementitious material may include any of mortar, plaster, paste or concrete which contains at least in part ordinary Portland cement (OPC) clinker and optionally aggregate or other admixtures.

[0121] The cementitious material may comprise supplementary cementitious materials (SCMs), such as fly ash, ground granulated blast furnace slag (GGBS) or other metal-byproduct slags, mining tailings, milled limestone, and / or metakaolin / other calcined clay. SCMs typically contain a variety of silicates, aluminosilicates, ferroaluminates either as crystalline or amorphous materials. When used to partially replace Portland cement, SCMs are associated with providing species to react with produced portlandite in an alkali-activated pozzolanic reaction to produce further mineral hydrates which contribute significantly to compressive strength. By providing aluminate and silicate sources, the use of supplementary cementitious materials (SCMs) in combination with the calcium carbonate product produced from the method of the invention results in an increase in the extent to which the calcium carbonate product improves the compressive strength of related materials (relative to a comparable cementitious material comprised of the sameSCM / OPC blend where the calcium carbonate byproduct has not been used). This particularly applies to SCM blends with high aluminate content.

[0122] The calcium carbonate product may be added in conjunction with a reaction control agent. The reaction control agent is an additive that modifies the hydration reaction of the cementitious product. Reaction control agents, such as polycarboxylate-ether high-range water reducer (HRWR) admixtures, can be used to adjust the water demand of the binder mixture and can result in enhanced compressive strength, according to the needs of the user.

[0123] Thus, the third aspect of the invention is the use of a calcium carbonate product obtained by the method of the first aspect to strengthen a cementitious product or work as a partial substitute for cementitious material content.

[0124]

[0125] Example 1 (Formulation IC5-1.1)

[0126] Gypsum (172 g, 1 mol; CaSO4.2H2O, 99% pure) was added to a 1.5 L jacketed reactor and charged with 1 L of a 2 M solution of monoethanolamine (MEA, 120.8 ml; 2:1 molar MEA ratio to calcium) in water. The slurry was stirred at 250 rpm and CO2 was delivered via a tube to the bottom of the reactor vessel at a rate of 1 litre per minute over the course of the reaction.

[0127] Following completion as determined by the calcium strip method (calcium concentration in solution < 40 ppm), the reaction slurry was filtered and washed with 500 mL of deionised water and subsequently 500 mL of isopropanol, and dried at 40 °C, yielding 120 g of gypsum-derived additive product as a fine white powder.

[0128] This equates to a 96% molar conversion rate from calcium sulfate to calcium carbonate.

[0129] Example 2 (Formulation IC5-1.2)

[0130] Gypsum (172 g, 1 mol; CaSO4.2H2O, 99% pure) was added to a 1.5 L jacketed reactor and charged with 1 L of a 3 M solution of monoethanolamine (MEA, 181.1 ml; 3:1 molar MEA ratio to calcium) in water. The slurry was stirred at 250 rpm and CO2 was deliveredvia a tube to the bottom of the reactor vessel at a rate of 1 litre per minute over the course of the reaction.

[0131] Following completion as determined by the calcium strip method (calcium concentration in solution ~0 ppm), the reaction slurry was filtered and washed with 500 mL of deionised water and subsequently 500 mL of isopropanol, and dried at 40 °C, yielding 99.8 g of gypsum-derived additive product as a fine white powder.

[0132] This equates to an 80% molar conversion rate from calcium sulfate to calcium carbonate.

[0133] Example 3 (Formulation IC5-1.3)

[0134] Gypsum (172 g, 1 mol; CaSO4.2H2O, 99% pure) was added to a 1.5 L jacketed reactor and charged with 1 Lof an 8 M solution of monoethanolamine (MEA, 483.0 ml; 8:1 molar MEA ratio to calcium) in water. The slurry was stirred at 250 rpm and CO2 was delivered via a tube to the bottom of the reactor vessel at a rate of 1 litre per minute over the course of the reaction.

[0135] Following completion as determined by the calcium strip method (calcium concentration in solution ~0 ppm), the reaction slurry was filtered and washed with 500 mL of deionised water and subsequently 500 mL of isopropanol, and dried at 40 °C, yielding 99.6 g of gypsum-derived additive product as a fine white powder.

[0136] This equates to an 80% molar conversion rate from calcium sulfate to calcium carbonate.

[0137] Example 4 (Formulation IC5-2.1)

[0138] Gypsum (172 g, 1 mol; CaSO4.2H2O, 99% pure) was added to a 1.5 L jacketed reactor and charged with 1 L of a 3 M solution of monoethanolamine (MEA, 181.1 ml; 3:1 molar MEA ratio to calcium) in water. The slurry was stirred at 250 rpm and CO2 was delivered via a tube to the bottom of the reactor vessel at a rate of 0.5 litre per minute over the course of the reaction.

[0139] Following completion as determined by the calcium strip method (calcium concentration in solution ~0 ppm), the reaction slurry was filtered and washed with 500 mL of deionised water and subsequently 500 mL of isopropanol, and dried at 40 °C, yielding 99.9 g of gypsum-derived additive product as a fine white powder.

[0140] This equates to an 80% molar conversion rate from calcium sulfate to calcium carbonate.Example 5 (Formulation IC5-2.2)

[0141] Gypsum (172 g, 1 mol; CaSO4.2H2O, 99% pure) was added to a 1.5 L jacketed reactor and charged with 1 L of a 3 M solution of monoethanolamine (MEA, 181.1 ml; 3:1 molar MEA ratio to calcium) in water. The slurry was stirred at 250 rpm and CO2 was delivered via a tube to the bottom of the reactor vessel at a rate of 2 litres per minute over the course of the reaction.

[0142] Following completion as determined by the calcium strip method (calcium concentration in solution ~0 ppm), the reaction slurry was filtered and washed with 500 mL of deionised water and subsequently 500 mL of isopropanol, and dried at 40 °C, yielding 100 g of gypsum-derived additive product as a fine white powder.

[0143] This equates to an 80% molar conversion rate from calcium sulfate to calcium carbonate.

[0144] Example 6 (Formulation IC5-3.1)

[0145] Gypsum (86 g, 0.5 mol; CaSO4.2H2O, 99% pure) was added to a 1.5 L jacketed reactor and charged with 1 L of a 3 M solution of monoethanolamine (MEA, 181.1 ml; 6:1 molar MEA ratio to calcium) in water. The slurry was stirred at 250 rpm and CO2 was delivered via a tube to the bottom of the reactor vessel at a rate of 1 litre per minute over the course of the reaction.

[0146] Following completion as determined by the calcium strip method (calcium concentration in solution ~0 ppm), the reaction slurry was filtered and washed with 500 mL of deionised water and subsequently 500 mL of isopropanol, and dried at 40 °C, yielding 48.4 g of gypsum-derived additive product as a fine white powder.

[0147] This equates to a 77% molar conversion rate from calcium sulfate to calcium carbonate.

[0148] Example 7 (Formulation IC5-3.2)

[0149] Gypsum (344 g, 2 mol; CaSO4.2H2O, 99% pure) was added to a 1.5 L jacketed reactor and charged with 1 Lof a 3 M solution of monoethanolamine (MEA, 181.1 ml; 1.5:1 molar MEA ratio to calcium) in water. The slurry was stirred at 250 rpm and CO2 was delivered via a tube to the bottom of the reactor vessel at a rate of 1 litre per minute over the course of the reaction.Following completion as determined by the calcium strip method (calcium concentration in solution ~0 ppm), the reaction slurry was filtered and washed with 500 mL of deionised water and subsequently 500 mL of isopropanol, and dried at 40 °C, yielding 198 g of gypsum-derived additive product as a fine white powder.

[0150] This equates to a 79% molar conversion rate from calcium sulfate to calcium carbonate.

[0151] Example 8 (Formulation IC5-4.1)

[0152] Gypsum (172 g, 1 mol; CaSO4.2H2O, 90% pure) was added to a 1.5 L jacketed reactor and charged with 1 L of a 3 M solution of monoethanolamine (MEA, 181.1 ml; 3:1 molar MEA ratio to calcium) in water. The slurry was stirred at 250 rpm and CO2 was delivered via a tube to the bottom of the reactor vessel at a rate of 1 litre per minute over the course of the reaction.

[0153] Following completion as determined by the calcium strip method (calcium concentration in solution ~0 ppm), the reaction slurry was filtered and washed with 500 mL of deionised water and subsequently 500 mL of isopropanol, and dried at 40 °C, yielding 110.1 g of gypsum-derived additive product as a fine white powder.

[0154] This equates to a 97% molar conversion rate from calcium sulfate to calcium carbonate, or an 87% conversion ratio based on the gypsum weight.

[0155] Example 9 (Formulation IC5-4.2)

[0156] Flue gas desulfurisation gypsum (FGD gypsum) (172 g) was added to a 1.5 L jacketed reactor and charged with 1 L of a 3 M solution of monoethanolamine. The slurry was stirred at 250 rpm and CO2 was delivered via a tube to the bottom of the reactor vessel at a rate of 1 litre per minute over the course of the reaction.

[0157] FGD gypsum is a synthetic gypsum produced from gas captured during emission control systems at coal-fired electric utility plants.

[0158] Following completion as determined by the calcium strip method (calcium concentration in solution ~0 ppm), the reaction slurry was filtered and washed with 500 mL of deionised water and subsequently 500 mL of isopropanol, and dried at 40 °C, yielding 97.0 g of gypsum-derived additive product as a fine white powder.

[0159] This equates to a 77% molar conversion rate from calcium sulfate to calcium carbonate.Comparative Example 10* (Formulation 3M-AMP-IC)

[0160] Gypsum (172 g, 1 mol; CaSO4.2H2O, 99% pure) was added to a 1.5 L jacketed reactor and charged with 1 Lof a 3 M solution of 2-amino-2-methyl-propan-1-ol (AMP, 286.3 ml; 3:1 molar ratio AMP to calcium) in water. The slurry was stirred at 250 rpm and CO2 was delivered via a tube to the bottom of the reactor vessel at a rate of 1 litre per minute over the course of the reaction.

[0161] Following completion as determined by the calcium strip method (calcium concentration in solution ~0 ppm), the reaction slurry was filtered and washed with 500 mL of deionised water and subsequently 500 mL of isopropanol, and dried at 40 °C, yielding 105 g of gypsum-derived additive product as a fine white powder.

[0162] This equates to an 84% molar conversion rate from calcium sulfate to calcium carbonate.

[0163] Comparative Example 11* (Formulation 2M-AMP / sucrose-IC)

[0164] Gypsum (172 g, 1 mol; CaSO4.2H2O, 99% pure) was added to a 1.5 L jacketed reactor and charged with 1 Lof a 2 M solution of 2-amino-2-methyl-propan-1-ol (AMP, 191.8 ml; 2:1 molar ratio AMP to calcium) and sucrose (171.5 g, 0.5 mol) in water. The slurry was stirred at 250 rpm and CO2 was delivered via a tube to the bottom of the reactor vessel at a rate of 1 litre per minute over the course of the reaction.

[0165] Following completion as determined by the calcium strip method (calcium concentration in solution ~0 ppm), the reaction slurry was filtered and washed with 500 mL of deionised water and subsequently 500 mL of isopropanol, and dried at 40 °C, yielding 110.6 g of gypsum-derived additive product as a fine white powder.

[0166] This equates to an 88.5% molar conversion rate from calcium sulfate to calcium carbonate.

[0167] Example 12 (Formulation DEA-IC)

[0168] Gypsum (172 g, 1 mol; CaSO4.2H2O, 99% pure) was added to a 1.5 L jacketed reactor and charged with 1 L of a 3 M solution of diethanolamine (DEA, 287.5 ml; 3:1 molar ratio DEA to calcium) in water. The slurry was stirred at 250 rpm and CO2 was delivered via a tube to the bottom of the reactor vessel at a rate of 1 litre per minute over the course of the reaction.Following completion as determined by the calcium strip method (calcium concentration in solution ~0 ppm), the reaction slurry was filtered and washed with 500 mL of deionised water and subsequently 500 mL of isopropanol, and dried at 40 °C, yielding 123 g of gypsum-derived additive product as a fine white powder.

[0169] This equates to a 98% molar conversion rate from calcium sulfate to calcium carbonate.

[0170] Example 13 (Formulation 3M-MEAb-IC)

[0171] Gypsum (172 g, 1 mol; CaSO4.2H2O, 99% pure) was added to a 1.5 L jacketed reactor and charged with 1 L of a solution of methanolamine (MEA, 132.2 ml; 2.19 equivalents to calcium), diethanolamine (DEA, 69.0 ml; 0.72 equivalents to calcium) and triethanolamine (TEA, 12 ml; 0.09 equivalents to calcium) in water (total molar equivalents of nitrogenous base to calcium was 3:1). The slurry was stirred at 250 rpm and CO2 was delivered via a tube to the bottom of the reactor vessel at a rate of 1 litre per minute over the course of the reaction.

[0172] Following completion as determined by the calcium strip method (calcium concentration in solution ~0 ppm), the reaction slurry was filtered and washed with 500 mL of deionised water and subsequently 500 mL of isopropanol, and dried at 40 °C, yielding 125 g of gypsum-derived additive product as a fine white powder.

[0173] This equates to a 99% molar conversion rate from calcium sulfate to calcium carbonate.

[0174] Example 14 (Formulation 2M-MEAb-IC)

[0175] Gypsum (172 g, 1 mol; CaSO4.2H2O, 99% pure) was added to a 1.5 L jacketed reactor and charged with 1 L of a solution of methanolamine (MEA, 121.0 ml; 2 equivalents to calcium), diethanolamine (DEA, 63.4 ml; 0.66 equivalents to calcium) and triethanolamine (TEA, 10.9 ml; 0.08 equivalents to calcium) in water (total molar equivalents of nitrogenous base to calcium was 2.74:1). The slurry was stirred at 250 rpm and CO2 was delivered via a tube to the bottom of the reactor vessel at a rate of 1 litre per minute over the course of the reaction.

[0176] Following completion as determined by the calcium strip method (calcium concentration in solution ~0 ppm), the reaction slurry was filtered and washed with 500 mL of deionised water and subsequently 500 mL of isopropanol, and dried at 40 °C, yielding 105 g of gypsum-derived additive product as a fine white powder.This equates to an 84% molar conversion rate from calcium sulfate to calcium carbonate.

[0177] Example 15 (Formulation MDEA-IC)

[0178] Gypsum (172 g, 1 mol; CaSO4.2H2O, 99% pure) was added to a 1.5 L jacketed reactor and charged with 1 Lof a solution of 3M / V-methyl diethanolamine (MDEA, 344.4 ml; 3:1 molar MDEA ratio to calcium) in water. The slurry was stirred at 250 rpm and CO2 was delivered via a tube to the bottom of the reactor vessel at a rate of 1 litre per minute over the course of the reaction.

[0179] Following completion as determined by the calcium strip method (calcium concentration in solution ~0 ppm), the reaction slurry was filtered and washed with 500 mL of deionised water and subsequently 500 mL of isopropanol, and dried at 40 °C, yielding 118 g of gypsum-derived additive product as a fine white powder.

[0180] This equates to a 94% molar conversion rate from calcium sulfate to calcium carbonate.

[0181] Example 16 (Formulation HMDA-IC)

[0182] Gypsum (172 g, 1 mol; CaSO4.2H2O, 99% pure) was added to a 1.5 L jacketed reactor and charged with 1 L of a solution of 3M hexamethylenediamine (HMDA, 348.6 g; 3:1 molar MDEA ratio to calcium) in water. The slurry was stirred at 250 rpm and CO2 was delivered via a tube to the bottom of the reactor vessel at a rate of 1 litre per minute over the course of the reaction.

[0183] Following completion as determined by the calcium strip method (calcium concentration in solution ~0 ppm), the reaction slurry was filtered and washed with 500 mL of deionised water, 500 mL of isopropanol, then 250 ml acetone, and dried at 40 °C yielding 126 g of gypsum-derived additive product as a fine white powder.

[0184] This equates to a >99% molar conversion rate from calcium sulfate to calcium carbonate.

[0185] Example 17 (Formulation DETA-IC)

[0186] Gypsum (172 g, 1 mol; CaSO4.2H2O, 99% pure) was added to a 1.5 L jacketed reactor and charged with 1 L of a solution of 3M diethylenetriamine (DETA, 512.6 ml; 3:1 molar DETA ratio to calcium) in water. The slurry was stirred at 250 rpm and CO2 was delivered via a tube to the bottom of the reactor vessel at a rate of 1 litre per minute over the course of the reaction.Following completion as determined by the calcium strip method (calcium concentration in solution ~0 ppm), the reaction slurry in the form of a gel was diluted with 4L of deionised water, filtered and washed with 500 mL of deionised water, followed by 500 mL of isopropanol, then 500 mL of acetone, and dried at 40 °C, yielding 120 g of gypsum-derived additive product as a fine white powder.

[0187] This equates to a 95% molar conversion rate from calcium sulfate to calcium carbonate.

[0188] Example 18 (Formulation 3M-KGIy-IC)

[0189] Gypsum (172 g, 1 mol; CaSO4.2H2O, 99% pure) was added to a 1.5 L jacketed reactor and charged with 1 Lof an aqueous solution of 3M potassium glycinate (KGIy; 3:1 molar KGIy ratio to calcium), which was previously prepared by the addition of KOH (3 mol, 168.3 g) to L-glycine (3 mol, 225.2 g) in water. The slurry was stirred at 250 rpm and CO2 was delivered via a tube to the bottom of the reactor vessel at a rate of 1 litre per minute over the course of the reaction.

[0190] Following completion as determined by the calcium strip method (calcium concentration in solution ~0 ppm), the reaction slurry was diluted with 2L of deionised water, filtered and washed with 500 mL of deionised water, followed by 500 mL of isopropanol, and dried at 40 °C, yielding 97.6 g of gypsum-derived additive product as a fine white powder.

[0191] This equates to a 77% molar conversion rate from calcium sulfate to calcium carbonate.

[0192] Example 19 (Formulation 3M-KLys-IC)

[0193] Gypsum (172 g, 1 mol; CaSO4.2H2O, 99% pure) was added to a 1.5 L jacketed reactor and charged with 1 L of an aqueous solution of 3M potassium lysinate (KLys; 3:1 molar KLys ratio to calcium), which was previously prepared by the addition of KOH (3 mol, 168.3 g) to L-lysine (3 mol, 438.6 g) in water. The slurry was stirred at 250 rpm and CO2 was delivered via a tube to the bottom of the reactor vessel at a rate of 1 litre per minute over the course of the reaction.

[0194] Following completion as determined by the calcium strip method (calcium concentration in solution ~0 ppm), the reaction slurry was diluted with 2L of deionised water, filtered and washed with 500 mL of deionised water, followed by 500 mL of isopropanol, and dried at 40 °C, yielding 103 g of gypsum-derived additive product as a fine white powder.

[0195] This equates to an 82% molar conversion rate from calcium sulfate to calcium carbonate.Example 20 (Formulation 2M-KLys-IC)

[0196] Gypsum (172 g, 1 mol; CaSO4.2H2O, 99% pure) was added to a 1.5 L jacketed reactor and charged with 1 L of an aqueous solution of 2M potassium lysinate (KLys; 2:1 molar KLys ratio to calcium), which was previously prepared by the addition of KOH (3 mol, 112.2 g) to L-lysine (2 mol, 293.9 g) in water. The slurry was stirred at 250 rpm and CO2 was delivered via a tube to the bottom of the reactor vessel at a rate of 1 litre per minute over the course of the reaction.

[0197] Following completion as determined by the calcium strip method (calcium concentration in solution ~0 ppm), the reaction slurry was filtered and washed with 500 mL of deionised water and subsequently 500 mL of isopropanol, and dried at 40 °C, yielding 124.1 g of gypsum-derived additive product as a fine white powder.

[0198] This equates to a 99% molar conversion rate from calcium sulfate to calcium carbonate.

[0199] Example 21 (Formulation 1M-KLys-IC)

[0200] Gypsum (172 g, 1 mol; CaSO4.2H2O, 99% pure) was added to a 1.5 L jacketed reactor and charged with 1 L of an aqueous solution of 1M potassium lysinate (KLys; 1:1 molar KLys ratio to calcium), which was previously prepared by the addition of KOH (1 mol, 56.11 g) to L-lysine (1 mol, 146.2 g) in water. The slurry was stirred at 250 rpm and CO2 was delivered via a tube to the bottom of the reactor vessel at a rate of 1 litre per minute over the course of the reaction.

[0201] Following completion as determined by the calcium strip method (calcium concentration in solution ~0 ppm), the reaction slurry was filtered and washed with 500 mL of deionised water and subsequently 500 mL of isopropanol, and dried at 40 °C, yielding 113 g of gypsum-derived additive product as a fine white powder.

[0202] This equates to a 90 % molar conversion rate from calcium sulfate to calcium carbonate.

[0203] Example 22 (Formulations GC003, GC008, GC020)

[0204] CO2 was bubbled through a 30 wt% aq. solution of MEA (20 kg) with stirring until loaded to 2-2.3 mol kg-1. The solution was cooled to 30-35 °C and gypsum (5.71 kg, 33.2 mol; CaSO4.2H2O, 99% pure) added. The slurry was stirred for 1h, until the sulfate concentration in the solution reached 1.3 mol kg-1(+ / - 0.1). The reaction slurry was vacuum filtered, the filter cake washed with water (10 L), and dried at 60 °C until amoisture content of <1% was recorded. Calcium carbonate (3.1 kg, 30.97 mol, 93% yield) was recovered.

[0205] Characterisation of calcium carbonate product

[0206] Particle size analysis was performed on a Malvern Panalytical Mastersizer Ultra 3000+ laser diffraction instrument, in wet dispersion mode. The system was initialised and backgrounded using a dilute aqueous NaOH solution (1 g NaOH in 10 L). A paste of the analyte sample was prepared using the same NaOH solution, which was added to the measurement beaker to achieve an obscuration between 3-3.5 %. The mixture was subsequently sonicated for 30 seconds, before additional sample was added to achieve a target obscuration between 4-4.5 %, followed by a further sonication for 30 seconds. After a 30 second delay the measurement was started.

[0207] Table 2. A summary of the characteristics of the gypsum-based additive products of Examples 1 to 20 is provided below.aAragonite was also formed in this reaction (34.6 %).bK2Ca(SC>4)2.H2O was also formed in this reaction (3.5%).CK2SO4 was also formed in this reaction (22.1%).dK2Ca(SC>4)2.H2O (0.9%) and K2SO4 (25.3%) were also formed in this reaction.eK2Ca(SC>4)2.H2O was also formed in this reaction (6.6%).

[0208]

[0209]

[0210]

[0211] *Comparative examples.

[0212] All of the example methods according to the invention resulted in a calcium carbonate product having a D50 particle diameter of less than 20 pm and containing a significantproportion of vaterite. Comparative examples 10 and 11, wherein the nitrogenous base was 2-aminomethyl-2-propan-1-ol (in which the amine group is bonded to a tertiary carbon), resulted in the production of no or very little vaterite.

[0213] Polymorphic conversion data

[0214] Calcium carbonate was synthesised via a precipitation reaction by adding a solution of calcium chloride hexahydrate (CaCl2'6H20, 3.284 kg, 15 mol) dissolved in water (13.1 litres) to a stirred solution of sodium carbonate (Na2COs, 1.589 kg, 15 mol) in 15 litres of water. The resulting suspension was filtered and washed with water (10 litres) and then dried using a vacuum filtration process. The filter cake was analysed by powder X-ray diffraction (pXRD) and was shown to be composed of primarily vaterite and calcite polymorphs. The water-washed filter cake was subjected to curing in a climatic chamber maintained at 20°C and 80% relative humidity for up to 20.5 hours. Samples were collected at time intervals and analysed using XRD to determine the phase composition of the material. The relative proportions of these polymorphs were quantified through Rietveld refinement analysis, with the results presented in Figure 3.

[0215] The XRD analysis revealed a progressive transformation from vaterite to calcite over the curing period. Initially, the filter cake contained 83.3 wt.% vaterite and 16.7 wt.% calcite, but by 20.5 hours, vaterite decreased to 5.9 wt.%, while calcite increased to 94.1 wt.%. The most significant transformation occurred within the first 5.5 hours, with a notable decrease in vaterite content and a corresponding increase in calcite. The dissolution of metastable vaterite and reprecipitation into the more stable calcite is consistent with the known thermodynamic stability of calcium carbonate polymorphs.

[0216] Analogous curing treatment of samples containing a high proportion of vaterite, synthesised according to Examples 1-9, 13, 14, 16-21, showed no transformation of vaterite to calcite (or to any other CaCOs polymorph). Therefore, a benefit of the claimed process is that the calcium carbonate product is stable to polymorphic conversion. As a result, the advantageous vaterite polymorph in the product produced by the process of the invention is stable and should remain available for use as an additive in a cementitious product even after storage and transportation of the product.Compressive strength data

[0217] The formulations provided were then tested to show the effects of the gypsum-based additive as strength enhancers for cementitious materials such as concrete.

[0218] Table 3 details the resulting compressive strengths of various concretes, with comparison to their respective references wherein the respective gypsum-based additive has substituted 20% or 10% of the CEM-based binder. For completion and demonstration, the application of reaction control agents has been included in these examples, in the form of proprietary polycarboxylate-ether HRWR admixtures: MasterGlenium (MG- ACE480), ISOFLOW, ISOFLEX.

[0219] Table 3. Compressive strength testing data for different cementitious concretes incorporating IC5 product, relative to reference sample (i.e. containing no IC5 material).

[0220]

[0221]

[0222]

[0223]

[0224] limestone) Binder “C”: CEM III (70% OPC + 30% ground granulated blast-furnace slag (GGBS)); Binder “D”: CEM IV (80% OPC + 20% calcined clay (metakaolin)); Binder “E”: CEM III (50% OPC + 50% ground granulated blast-furnace slag), wherein, in “E-Ref’, 5 10% of the binder “E” has been substituted with commercially available milled limestone.

[0225] Binder

[0226] In investigating formulations of the gypsum-based additive, the clear relationship between particle sizing and calcium carbonate polymorph is detailed, whereby IC5-1.3 exhibits superior strength enhancement properties over other formulations. Strength 0 enhancements are notably reflected in the CEM III series (70% OPC + 30% groundgranulated blast-furnace slag (GGBS)), which incorporates a high aluminate pozzolan into the binder blend.

[0227] Furthermore, the clear relationship between particle sizing, surface area and concrete rheology detailed by slump-testing of mixes as produced in these examples. Concrete slump refers to the workability and / or consistency of the concrete mix. The paste viscosity increased, evaluated by a decrease in concrete slump, versus reference where the application of 20 % of IC blends with particle sizing in excess of 10 pm, whereupon smaller particle sizes greatly reduced the workability of the concretes. This is shown in Figure 4. This is attributed to the relationship between surface area and water-demand to wet the associated IC materials, alongside changes in particle packing relative to cement particles in addition to a variety of other effects. Calcium carbonate morphology is also closely interrelated and investigated, with vaterite workability considerably improved compared to equivalent particle sizes of calcite.

[0228] It is therefore possible to provide a method of improving the strength of products formed from cementitious materials, by the use of a gypsum-derived additive, that is, a calcium carbonate product which is formed from calcium sulfate and preferably precipitated from solution so as to have vaterite polymorphism. This provides improved strength in the eventual product, as well as providing greater flowability for the cementitious material.

[0229] Numbered embodiments

[0230] 1. A method of improving the strength of a product comprising cementitious material, the method comprising the steps of:

[0231] a] providing a calcium source comprising calcium sulfate;

[0232] b] combining the calcium source with a nitrogenous base in the presence of least 1 mole equivalent of carbon dioxide relative to the calcium source to yield a calcium carbonate product and a nitrogenous-base salt byproduct, wherein a median particle diameter of the calcium carbonate product is less than or equal to 20pm; and

[0233] c] utilising the calcium carbonate product at least in part as a binder for a cementitious material for enhancing the strength of the subsequent product.

[0234] 2. A method of numbered embodiment 1, wherein the calcium source is gypsum, bassinite, anhydrite, or a combination thereof.3. A method of numbered embodiment 1, wherein the calcium source is waste gypsum from an industrial process.

[0235] 4. A method of any one of the preceding numbered embodiments, wherein the median particle diameter of the calcium carbonate product is less than or equal to 10pm.

[0236] 5. A method of any one of the preceding numbered embodiments, wherein the median particle diameter of the calcium carbonate product is between 0.8pm and 1 ,5pm.

[0237] 6. A method of any one of the preceding numbered embodiments, wherein the calcium carbonate product has a particle size distribution centred on the median particle diameter within a range of ±50pm

[0238] 7. A method of any one of the preceding numbered embodiments, wherein, during step a], the calcium source is pre-processed by at least one of: washing with a concentrated mineral acid; washing with dilute mineral acid; gravimetric separation techniques; sieving; alkaline treatment; and filtration.

[0239] 8. A method of numbered embodiment 7, wherein during step a], the calcium source is pre-processed by alkaline treatment with a hydroxide to convert the calcium sulfate to calcium hydroxide, and during step b], the calcium hydroxide is combined with the nitrogenous base.

[0240] 9. A method of any one of the preceding numbered embodiments, wherein the calcium carbonate product comprises microscale calcium carbonate particles.

[0241] 10. A method of any one of the preceding numbered embodiments, wherein the calcium carbonate product comprises 20-100 wt.% vaterite.

[0242] 11. A method of any one of the preceding numbered embodiments, wherein during step c], the calcium carbonate product is provided in a quantity of 2 to 50 wt.% with respect to a weight of ordinary Portland cement in the cementitious material.

[0243] 12. A method of any one of the preceding numbered embodiments, wherein the nitrogenous base comprises an alkylamine or alkanolamine.

[0244] 13. A method of numbered embodiment 12, wherein the nitrogenous base is selected from the list of: monoethanolamine; diethanolamine; triethanolamine; branched andlinear C2-C8 alkanolamines, branched and linear C2-C8 alkylamines, glycine; asparagine, arginine, lysine, tetreethylenepentaamine; and branched or linear polyethyleneimine with a molecular weight of 100 Da to 100 KDa.

[0245] 14. A method of any one of the preceding numbered embodiments, wherein the nitrogenous base is introduced in at least a 2 to 3 mole equivalent amount to the calcium sulfate.

[0246] 15. A method of any one of the preceding numbered embodiments, wherein, during step b], a further base is added.

[0247] 16. A method of numbered embodiment 15, wherein a total base amount is introduced in a 0.3 to 10 mole equivalent amount to the calcium sulfate.

[0248] 17. A method of any one of the preceding numbered embodiments, wherein the nitrogenous-base salt byproduct is an alkylammonium sulfate byproduct.

[0249] 18. A method of any one of the preceding numbered embodiments, further comprising a step d], subsequent to step b], of passing the nitrogenous-base salt byproduct through a sulfate-selective ion exchange resin to regenerate the nitrogenous base for recycling.

[0250] 19. A method of numbered embodiment 18, further comprising a step e], subsequent to step d], of regenerating the sulfate-selective ion exchange resin to output a salt byproduct suitable for use as a fertiliser.

[0251] 20. A method of numbered embodiment 19, wherein the regeneration is performed using potassium hydroxide, the salt byproduct being potassium sulfate.

[0252] 21. A method of any one of the preceding numbered embodiments, further comprising a step subsequent to step b], of adding a hydroxide compound to directly precipitate a salt byproduct.

[0253] 22. A method of any one of the preceding numbered embodiments, wherein, during step c], the calcium carbonate product is added in conjunction with a reaction control agent.23. A method of numbered embodiment 22, wherein the reaction control agent is selected from a group comprising: a carbon-dioxide-loaded alkanolamine; triisopropanolamine; triethanolamine; other organic alkanolamines; sodium gluconate; and polycarboxylates.

[0254] 24. A method of preparing a gypsum-based additive for a cementitious material suitable for improving the strength of a product formed from the cementitious material, the method comprising the steps of:

[0255] a] providing a calcium source derived from gypsum;

[0256] b] combining the calcium source with a nitrogenous base in the presence of carbon dioxide to yield a calcium carbonate product and a nitrogenous-base salt byproduct, wherein a median particle diameter of the calcium carbonate product is less than or equal to 20pm.

[0257] 25. A strengthening additive for a cementitious product, the strengthening additive comprising calcium carbonate having a median particle diameter of less than or equal to 20pm, wherein the calcium carbonate has been formed by precipitation.

Claims

Claims1. A method of making a calcium carbonate product, the method comprising the steps of:a] providing a calcium source comprising calcium sulfate; andb] (i) combining the calcium source with a nitrogenous base comprising at least one amine functional group in the presence of at least 1 mole equivalent of carbon dioxide relative to the moles of calcium in the calcium source to yield a calcium carbonate product and a nitrogenous-base salt byproduct, wherein the ratio of moles of amine functional groups in the nitrogenous base to moles of calcium in the calcium source is 2:1 or more; or(ii) carbonating a nitrogenous base comprising at least one amine functional group by reacting the nitrogenous base with carbon dioxide to form a pre-carbonated nitrogenous base, and combining the calcium source with the pre-carbonated nitrogenous base to yield a calcium carbonate product and a nitrogenous-base salt byproduct, wherein the average number of amine functional groups per molecule of the nitrogenous base before carbonation is x and the calcium source is combined with at least (2 / x) moles of pre-carbonated nitrogenous base relative to the moles of calcium in the calcium source; wherein the nitrogenous base is selected from an alkylamine, an alkanolamine, an amino acid or salt thereof, a polyamine, or combinations thereof;wherein the nitrogenous base comprises an amine group bonded to a carbon atom, wherein said carbon atom is substituted by at least one hydrogen atom; and wherein the median particle diameter of the calcium carbonate product is less than or equal to 20 pm.

2. The method of claim 1 , wherein, in step b] (i) , the ratio of moles of amine functional groups in the nitrogenous base to moles of calcium in the calcium source is from about 2:1 to about 10:1.

3. The method of any one of the preceding claims, wherein, in step b](i) , the ratio of moles of amine functional groups in the nitrogenous base to moles of calcium in the calcium source is about 3:1 or more, optionally from about 3:1 to about 8:1.

4. The method of any one of the preceding claims, wherein, in step b](ii), the calcium source is combined with (2 / x) to (10 / x) moles of pre-carbonated nitrogenous base relative to the moles of calcium in the calcium source.

5. The method of any one of the preceding claims, wherein, in step b](ii), the calcium source is combined with (3 / x) to (8 / x) moles of pre-carbonated nitrogenous base relative to the moles of calcium in the calcium source.

6. The method of any one of the preceding claims, wherein the calcium source comprises at least 50% or at least 60% by weight calcium sulfate.

7. The method of any one of the preceding claims, wherein the calcium source is gypsum, bassanite, anhydrite, or a combination thereof.

8. The method of any one of the preceding claims, wherein the calcium source is gypsum, optionally waste gypsum from an industrial process.

9. The method of any one of the preceding claims, wherein the median particle diameter of the calcium carbonate product is less than or equal to 10 pm, optionally from 0.5 pm to 10 pm.

10. The method of any one of the preceding claims, wherein the median particle diameter of the calcium carbonate product is less than or equal to 7 pm, optionally from 0.8 pm to 7 pm.

11. The method of any one of the preceding claims, wherein the median particle diameter of the calcium carbonate product is less than or equal to 5 pm, optionally from 2 pm to 5 pm.

12. The method of any one of the preceding claims, wherein the D particle diameter of the calcium carbonate product is less than or equal to 4 pm, optionally from 0.1 pm to 4 pm.

13. The method of any one of the preceding claims, wherein the Dgo particle diameter of the calcium carbonate product is less than or equal to 60 pm, optionally from 10 pm to 60 pm.

14. The method of any one of the preceding claims, wherein, during step a], the calcium source is pre-processed by at least one of: washing with a concentrated mineral acid; washing with dilute mineral acid; gravimetric separation techniques; sieving; alkaline treatment; and filtration.

15. The method of claim 14, wherein during step a], the calcium source is pre-processed by alkaline treatment with a hydroxide to convert the calcium sulfate to calcium hydroxide, and during step b], the calcium hydroxide is combined with the nitrogenous base or pre-carbonated nitrogenous base.

16. The method of any one of the preceding claims, wherein the calcium carbonate product comprises 30-100 wt.%, 70-100 wt.%, 90-100 wt.%, 99-100 wt.%, 99.5-100 wt.%, or 100 wt.% of the vaterite polymorph;preferably wherein the balance is at least one of the calcite and aragonite polymorphs.

17. The method of any one of the preceding claims, wherein the nitrogenous base is selected from the list of: branched and linear C2-C8 alkanolamine, branched and linear C2-C8 alkylamine, an amino acid or an alkali metal salt thereof, branched or linear polyamine with a molecular weight of 100 Da to 100 kDa, and combinations thereof.

18. The method of any one of the preceding claims, wherein the nitrogenous base comprises an amine group bonded to -CH2-.

19. The method of any one of the preceding claims, wherein the nitrogenous base comprises a primary or secondary amine group, preferably a primary or secondary amine group bonded to -CH2-.

20. The method of any one of claims 1-19, wherein the nitrogenous base is selected from the list of: monoethanolamine, diethanolamine, triethanolamine, / V-methyldiethanolamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentaamine, glycine or an alkali metal salt thereof, lysine or an alkali metal salt thereof, arginine or an alkali metal salt thereof, branched or linear polyethyleneimine with a molecular weight of 100 Da to 100 kDa, and combinations thereof.

21. The method of any one of claims 1-19, wherein the nitrogenous base is selected from monoethanolamine, diethanolamine, triethanolamine, and combinations thereof,optionally wherein the nitrogenous base consists of: 0-40% by weight of diethanolamine and 0-10% by weight of triethanolamine, with the balance being monoethanolamine.

22. The method of any one of claims 1-21, wherein the nitrogenous base is at least 60% by weight monoethanolamine, optionally wherein the nitrogenous base is at least 90% by weight monoethanolamine.

23. The method of any one of claims 1-19, wherein the nitrogenous base is monoethanolamine.

24. The method of any one of the preceding claims, wherein, in step b](ii) , the precarbonated nitrogenous base is a carbamate, carbonate, or bicarbonate, optionally wherein the pre-carbonated nitrogenous base is a carbamate.

25. The method of any one of the preceding claims, wherein a further base is added during step b],26. The method of any one of the preceding claims, wherein the nitrogenous-base salt byproduct is an alkylammonium sulfate byproduct.

27. The method of any one of the preceding claims, further comprising a step, subsequent to step b](i) or b](ii), of adding a hydroxide compound, thereby causing precipitation of a sulfate salt byproduct.

28. The method of claim 27, wherein the hydroxide compound is an alkali metal hydroxide, thereby causing precipitation of an alkali metal sulfate.

29. The method of claim 28, wherein from about 0.3 to about 10 mole equivalents of alkali metal hydroxide is added relative to the moles of calcium in the calcium source.

30. The method of claim 28 or claim 29, wherein the alkali metal hydroxide is potassium hydroxide, thereby causing precipitation of potassium sulfate.

31. The method of any one of claims 28-30, further comprising a step c], subsequent to the step of adding the hydroxide compound, of passing any residual nitrogenous-base salt byproduct through a sulfate-selective ion exchange resin to regenerate the nitrogenous base for recycling.

32. The method of any one of claims 1-26, further comprising a step c], subsequent to step b](i) or b](ii), of passing the nitrogenous-base salt byproduct through a sulfateselective ion exchange resin to regenerate the nitrogenous base for recycling.

33. The method of claim 31 or claim 32, further comprising a step d], subsequent to step c], of regenerating the sulfate-selective ion exchange resin to output a salt byproduct suitable for use as a fertiliser.

34. The method of claim 32, wherein the regeneration is performed using potassium hydroxide, the salt byproduct being potassium sulfate.

35. The method of any one of the preceding claims, wherein, during step b](i) or b](ii) , the Ca2+concentration is from about 1 to about 500 mM, or from about 10 to about 300 mM, or from about 20 to about 150 mM, or from about 50 to about 120 mM.

36. The method of any one of the preceding claims, wherein, in step b](i), the CO2 delivery rate is from about 0.5 litres per minute to about 2.5 litres per minute, or from about 1 litre per minute to about 2 litres per minute, per litre of the reaction mixture formed by combining the calcium source with the nitrogenous base and carbon dioxide.

37. The method of any one of the preceding claims, wherein step b](i) and b](ii) take place at a temperature of from about 20°C to about 60°C, optionally from about 20°C to about 35°C.

38. The method of any one of the preceding claims, wherein, during step b](i) or b](ii) , the reaction mixture formed by combining the calcium source with the nitrogenous base and carbon dioxide or with the pre-carbonated nitrogenous base is stirred at from 50 to 500 rpm, or from 100 to 200 rpm.

39. The method of any one of the preceding claims, wherein, during step b](i) or b](ii) , the pH value of the reaction mixture formed by combining the calcium source with the nitrogenous base and carbon dioxide or with the pre-carbonated nitrogenous base is between 7 to 12, or between 7 to 9.5.

40. The method of any one of the preceding claims, wherein, during step b](i) or b(ii), the reaction time of the calcium source with the nitrogenous base and carbon dioxide or with the pre-carbonated nitrogenous base is between 5 minutes and 6 hours.

41. The method of any one of the preceding claims, wherein the solid to liquid ratio in the reaction mixture formed by combining the calcium source with the nitrogenous base and carbon dioxide or with the pre-carbonated nitrogenous base is 0.05:1 to 0.4:1, optionally from 0.05:1 to 0.2:1.

42. The method of any one of the preceding claims, wherein at least 90 wt.% or at least 99 wt.% of the calcium source is calcium sulfate or a hydrate thereof.

43. A method of making a cementitious product, the method comprising the steps of:making a calcium carbonate product according to the method of any one of the preceding claims; andadding the calcium carbonate product to a cementitious material.

44. A method of claim 43, wherein the cementitious material comprises ordinary Portland cement.

45. A method of claim 44, wherein the cementitious material is CEM I cement, CEM II cement, or CEM III cement.

46. A method of claim 44 or claim 45, wherein the calcium carbonate product is added at a quantity of 2 to 50 wt.% with respect to a weight of ordinary Portland cement in the cementitious material.

47. A method of any one of claims 43-46, wherein the calcium carbonate product is added in conjunction with a reaction control agent.

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