Passive and forced synthesis of Mg(OH)2 to provide magnesium-based CO2 capture

Abstract

The present invention relates to a method for capturing carbon dioxide and sequestering it as calcium carbonate. The method involves the use of an aqueous magnesium hydroxide solution as a carbon dioxide uptake fluid. The magnesium hydroxide in the uptake fluid is produced by two different pathways: a forced decomposition pathway and a passive dissolution pathway. The combined use of the forced decomposition pathway and the passive dissolution pathway is a major contributing factor to the low energy consumption of the carbon dioxide capture and sequestration method.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority to U.S. Provisional Patent Application No. 63 / 400,604, filed August 24, 2022, which is incorporated herein by reference in its entirety.

[0002] FIELD OF THE INVENTION The present invention relates generally to methods for carbon dioxide capture and sequestration. [Background technology]

[0003] background The majority of energy use in the United States and around the world is based on the combustion of nonrenewable fossil fuels, which results in the emission of carbon dioxide (CO2) into the atmosphere. The continued and increasing release of carbon dioxide into the atmosphere has been shown to have adverse effects on the climate. Global temperatures have risen by 0.14°F (0.08°C) per decade since 1880, but the rate of warming has more than doubled since 1981 to 0.32°F (0.18°C) per decade. The nine years from 2013 to 2021 ranked among the warmest decades on record. While many alternatives to combustion are being considered, the fact is that combustion will remain a dominant component of the global energy system for decades to come.

[0004] Energy-efficient and scalable carbon dioxide capture is one of the greatest challenges facing modern energy researchers. The idea of ​​separating carbon dioxide from flue gases originated as an economically valuable means of carbon dioxide recovery to improve oil reuse rates. The power industry explored the use of various chemical adsorbents and found monoethanolamine to be a functional capture agent. Amine-based carbon dioxide capture was evaluated as an early-stage technology and was deemed unacceptable due to the high material costs and energy losses. Although the technology has since improved, high costs and low efficiency remain a problem.

[0005] The impact of continuing carbon dioxide emissions into the atmosphere remains one of the most troubling problems facing humanity. Existing carbon capture technologies are costly and energy intensive, and new developments are needed to improve efficiency and attract investors. Energy-efficient, carbon-negative methods of capturing carbon dioxide are needed in the industry. Summary of the Invention

[0006] overview Alkaline solutions, such as monoethanolamine solutions, act as sinks for carbon dioxide capture and have been the focus of much emission reduction research. For example, an aqueous solution of magnesium hydroxide is an alkaline solution that can capture gaseous carbon dioxide and sequester it in the form of magnesium carbonate salt. Based on this principle, the inventors have devised a hybrid carbon dioxide capture and sequestration method that employs two different routes to generate the carbon dioxide capture agent, magnesium hydroxide. The two different routes include a forced decomposition route and a passive dissolution route. The forced decomposition route involves the high-temperature decomposition of magnesium chloride hydrate to produce magnesium hydroxide. The passive dissolution route involves the dissolution of mineral oxides, which immediately form hydroxides and chloride salts from the mineral oxides. In this method, both chemicals required for capture (magnesium hydroxide) and precipitation (calcium) using the SkyCycle process sequence are prepared for use in the process from magnesium chloride, which is spontaneously produced by the precipitation process in the same SkyCycle sequence. These oxide minerals, including geological and industrial wastes (CaO is the primary example for producing both high-quality calcium carbonate, but oxides of other Group 2 metals, or oxides with a 1:1 metal-to-oxygen ratio, such as MgO or FeO, can be used in passive dissolution). In contrast, forced decomposition is not a spontaneous reaction sequence, requires more energy (and a carbon footprint if that energy is provided by a carbon source), and requires multiple steps to achieve the production of magnesium hydroxide and the working Group 2 chloride; specifically, the decomposition of MgCl salt occurs in two steps with different high heat requirements, requiring the condensation and generation of HCl acid from the condensation of gaseous HCl, followed by a separate dissolution process using the generated HCl to produce CaCl or XCl, specifically from calcite (CaCO) or any non-carbonate Ca / X-containing material (where X is a metal or metalloid other than calcium).By employing a combination of forced decomposition and passive dissolution pathways, the inventors have developed a carbon dioxide capture and sequestration process that has significantly less energy penalty than other carbon dioxide capture systems, with the added advantage that the passive process benefits from low energy hydroxide / chloride production for all local / available minerals, oxides, and waste materials (e.g., ash, slag, dust, etc.) that can serve as feedstock for the passive process by first operating the forced decomposition system using available sources of metal oxides to achieve reactions that allow the process to be forced into stoichiometric balance and to operate as an industrial process.

[0007] In this regard, a method for recovering carbon dioxide from a gas stream and sequestering the carbon dioxide in the form of calcium carbonate is disclosed herein. In some aspects, the method includes a first step of decomposing a magnesium chloride-containing material to form a first mixture containing magnesium hydroxide and a second mixture containing gaseous hydrogen chloride and water; a second step of mixing calcium oxide with a magnesium chloride brine to produce a third mixture containing magnesium hydroxide and calcium chloride; a third step of mixing the first mixture with the third mixture to obtain a fourth mixture containing magnesium hydroxide and calcium chloride; and a fourth step of contacting the fourth mixture with carbon dioxide to produce a product mixture containing calcium carbonate and an aqueous solution of magnesium chloride. In some aspects, substantially no heat is provided as an input for the second step. In some aspects, the calcium carbonate is a solid precipitate and is separated from the aqueous solution of magnesium chloride. In some aspects, the aqueous solution of magnesium chloride is dehydrated to obtain the magnesium chloride-containing material. For example, the aqueous solution of magnesium chloride can be dehydrated to obtain magnesium chloride hydrate.

[0008] In some aspects, the fourth mixture contains approximately equal amounts of magnesium hydroxide produced in the first step and magnesium hydroxide produced in the second step. In some aspects, the magnesium hydroxide in the fourth mixture is a ratio of the magnesium hydroxide produced in the first step to the magnesium hydroxide produced in the second step of 1:99, 2:98, 3:97, 4:96, 5:95, 6:94, 7:93; 8:92, 9:91, 10:90, 11:89, 12:88, 13:87, 14:86, 15:85, 16:84, 17:83, 18:82, 19:81, 20:80, 21:79, 22:78, 23:77, 24:76, 25: 75, 26:74, 27:73, 28:72, 29:71, 30:70, 31:69, 32:68, 33:67, 34:66, 35:65, 36:64, 37:63, 38:62, 39:61 40:60, 41:59, 42:58, 43:57, 44:56, 45:55, 46:54, 47:53, 48:52, 49:51, 50:50, 51:49, 52:48, 53:47, 54:46, 55:45, 56:44, 57:43, 58:42, 59:41, 60:40, 61:39, 62:38, 63:37, 64:36, 65:35, 66:34, 67:33, 68:32, 69:31, 70:30, 71:29, 72:28, 73:2 and any one of, less than, greater than, between, or any range of weight to weight ratios of 7, 74:26, 75:25, 76:24, 77:23, 78:22, 79:21, 80:20, 81:19, 82:18, 83:17, 84:16, 85:15, 86:14, 87:13, 88:12, 89:11, 90:10, 91:9, 92:8, 93:7, 94:6, 95:5, 96:4, 97:3, 98:2, and 99:1.

[0009] In some aspects, the magnesium chloride-containing material is magnesium chloride hydrate. The magnesium chloride hydrate can include magnesium chloride dodecahydrate, octahydrate, hexahydrate, tetrahydrate, dihydrate, and combinations thereof. In some aspects, the magnesium chloride hydrate includes magnesium chloride tetrahydrate or magnesium chloride dihydrate. In some aspects, the magnesium chloride hydrate contains 2.0 to 2.1 molar equivalents of water of hydration. All of these forms of magnesium chloride can be used in both forced decomposition and passive dissolution methods to produce magnesium hydroxide and the corresponding metal oxide chlorides. Passive dissolution can be achieved in magnesium chloride brines, while forced decomposition can only be achieved in the crystalline form of magnesium chloride. This elimination of the energy required to crystallize and decompose magnesium chloride salts (because the passive dissolution step is spontaneous and does not require these energies) contributes significantly to the low-energy nature of the combination of the two processes in the precursor chemicals fed to the SkyCycle process.

[0010] In some aspects, the first mixture is substantially free of magnesium chloride hydroxide. In some aspects, the first mixture is substantially free of magnesium oxide. In some aspects, the magnesium chloride-containing material decomposed in the first step includes at least a portion of the magnesium chloride produced in the fourth step.

[0011] In some aspects, calcium-containing minerals or industrial materials are contacted with an acid to produce calcium oxide. In some aspects, the calcium-containing minerals are selected from the group consisting of alite, jaffeite, perlite, vermiculite, diopside, tremolite, combinations thereof, or any other calcium-containing silicate minerals. In some embodiments, the calcium-containing industrial materials include stone, concrete, steel furnace slag, biomass fuel production slag, spent coal fly ash, combinations thereof, and other mineral-containing wastes. In some aspects, the acid is selected from the group consisting of hydrochloric acid, sulfuric acid, and nitric acid. In some aspects, at least a portion of the acid used to dissolve the calcium-containing minerals or industrial materials is obtained from the decomposition of magnesium chloride-containing materials. In some aspects, CaO produced from the dissolution of the calcium-containing minerals or wastes is used as input to the second step.

[0012] It is specifically contemplated that any limitation discussed with respect to one embodiment of the invention may apply to any other embodiment of the invention. Furthermore, any composition of the invention may be used in any method of the invention, and any method of the invention may be used to produce or utilize any composition of the invention.

[0013] Other objects, features, and advantages of the present invention will become apparent from the following detailed description. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. DETAILED DESCRIPTION OF THE INVENTION

[0014] Detailed Description A.Definition As used herein, the term "carbonate" or "carbonate product" generally refers to a compound having a carbonate group [CO] 2-The term is therefore defined as a mineral component containing the bicarbonate group [HCO3]. Thus, the term encompasses both carbonate / bicarbonate mixtures and species containing only carbonate ions. The terms "bicarbonate" and "bicarbonate products" generally refer to the bicarbonate group [HCO3]. 1- Thus, the term encompasses both carbonate / bicarbonate mixtures and species containing only bicarbonate ions.

[0015] As used herein, "Ca / Mg" refers to either Ca alone, Mg alone, or a mixture of both Ca and Mg. The Ca to Mg ratio can range from 0:100 to 100:0, for example, 1:99, 2:98, 3:97, 4:96, 5:95, 6:94, 7:93; 8:92, 9:91, 10:90, 11:89, 12:88, 13:87, 14:86, 15:85, 16:84, 17:83, 18:84, 19:85, 20:86, 21:87, 22:88, 23:89, 24:86, 25:85, 26:84, 27:83, 28:84, 29:85, 30:89, 31:89, 32:88, 33:88, 34:86, 35:85, 36:84, 37:83, 38:84, 39:85, 40:84, 41:84, 42:84, 43:84, 45:85, 46:84, 47:84, 48:84, 49:85, 50:84, 51:84, 52:84, 53:84, 54:84, 55:85, 56:84, 57:84, 58:84, 59:85, 60:84, 61:84, 62:84, 63:84, 64:84, 65:84, 66:84, 67:84, 6 :82, 19:81, 20:80, 21:79, 22:78, 23:77, 24:76, 25:75, 26:74, 27:73, 28:72, 29:71, 30:70, 31:69, 32:68, 33:67, 34:66, 35:65, 36:64, 37:63, 38:62, 39:61 40:60, 41:59, 42:58, 43:57, 44:56, 45:55, 46:54, 47:53, 48:52, 49:51, 50:50, 51:49, 52:48, 53:47, 54:46, 55:45, 56:44, 57:43, 58:42, 59:41, 60:40, 61:39, 62:38, 63:37, 64:36, 65:35, 66:34, 67:33, 68:32, 69:3 1, 70:30, 71:29, 72:28, 73:27, 74:26, 75:25, 76:24, 77:23, 78:22, 79:21, 80:20, 81:19, 82:18, 83:17, 84:16, 85:15, 86:14, 87:13, 88:12, 89:11, 90:10, 91:9, 92:8, 93:7, 94:6, 95:5, 96:4, 97:3, 98:2, and 99:1. x Ca (1-x) " and "Ca x Mg (1-x)The symbols " and " are synonymous. The terms "Group II" and "Group 2" are used interchangeably. Magnesium chloride hydrate refers to any hydrate, including but not limited to hydrates having 2, 4, 6, 8, or 12 equivalents of water per equivalent of magnesium chloride. Depending on the context, the abbreviation "MW" means either molecular weight or megawatts. The abbreviation "PFD" is a process flow chart. The abbreviation "Q" is heat (or heat load), and heat is a type of energy. It does not include any other type of energy.

[0016] As used herein, the term "capture" is used generally to refer to techniques or practices whose partial or total effect is to remove carbon dioxide from its point of emission. As used herein, the term "sequestration" is used generally to refer to techniques or practices whose partial or total effect is to store the captured carbon dioxide in some form so as to prevent it from returning to the atmosphere. The use of these terms does not exclude any of the described embodiments from being considered capture and sequestration techniques.

[0017] In the claims and / or specification, the use of the words "a" or "an," when used in conjunction with the word "comprising," may mean "one," but is also consistent with the meanings of "one or more," "at least one," and "one or more."

[0018] Throughout this application, the term "about" is used to indicate that a value includes the inherent variation of error for the device, method, or study subject variation employed to determine the value.

[0019] The terms "comprise," "have," and "include" are open-ended linking verbs. Any form or tense of one or more of these verbs, such as "comprises," "comprising," "has," "having," "includes," and "including," are also open-ended. For example, any method that "comprises," "has," or "includes" one or more steps is not limited to having only those one or more steps, but may also include other unlisted steps.

[0020] The above definitions take precedence over any conflicting definitions in any document incorporated herein by reference. However, the fact that certain terms are defined should not be construed as indicating that any undefined terms are indefinite. Rather, all terms used are believed to describe the invention in terms such that one skilled in the art can understand the scope and practice the invention.

[0021] Climate change is the defining issue of our time, and humanity faces a defining moment. From shifting weather patterns that threaten food production to rising sea levels that increase the risk of catastrophic flooding, the impacts of climate change are global in scope and unprecedented in scale. After more than a century and a half of industrialization, deforestation, and large-scale agriculture, atmospheric carbon dioxide levels have risen to record levels not seen in 3 million years. Carbon capture and sequestration are widely recognized as key strategies for limiting atmospheric emissions of carbon dioxide from power plants and other large-scale industrial polluters.

[0022] Over the past 30 years, significant efforts have been made to improve the technical feasibility of various carbon dioxide capture and sequestration methods. Major drawbacks of carbon dioxide capture processes are their high cost and energy requirements, and extensive research has been conducted to address energy utilization, operational considerations, product value, and economics in order to propose profitable business models. One promising decarbonization technology is mineral carbonation, which replicates natural weathering with faster reaction rates and improved conversion efficiency at industrial scale.

[0023] While researching carbon capture systems based on mineral carbonation, the inventors developed a unique method that employs a combination of two sources and processes to obtain magnesium hydroxide. The method employs a combination of passive dissolution and forced decomposition to provide magnesium hydroxide. The end result is a system that reduces reliance on forced decomposition of magnesium chloride while maintaining the required chloride balance.

[0024] The carbon capture systems disclosed herein employ a combination of passive dissolution and forced decomposition elements. In some embodiments, the passive dissolution element involves contacting mineral-containing material, preferably waste containing leachable minerals, with acid and, optionally, water to leach mineral ion salts from the mineral material into a brine or slurry. The mineral ion salts from the brine or slurry can then be used as a carbon dioxide capture and / or carbon dioxide mineral storage reagent. In some embodiments, the waste serves as a source of calcium cations, particularly calcium oxide. In some embodiments, the mineral-containing material includes calcium oxide. In some embodiments, the mineral-containing material is or includes calcium-containing silicate minerals. In some embodiments, the mineral-containing material includes alite, japhite, perlite, vermiculite, diopside, tremolite, combinations thereof, or any other calcium-containing silicate minerals. In some embodiments, the mineral-containing material includes stone, concrete, steel furnace slag, biomass fuel production slag, spent coal fly ash, combinations thereof, and other mineral-containing waste. In some embodiments, calcium oxide obtained by passive dissolution can be combined with magnesium chloride to produce magnesium hydroxide and calcium chloride. The magnesium chloride can be obtained externally or internally from another element of the carbon capture system. The reaction between calcium oxide obtained by passive dissolution and magnesium chloride is shown below: CaO + MgCl2+ H2O → Mg(OH)2+ CaCl2(1)

[0025] In some embodiments, the forcible decomposition element comprises conductive heat-driven decomposition magnesium chloride. In some embodiments, a hydrate of magnesium chloride is employed, and any hydrated form of magnesium chloride may be used, including magnesium chloride dodecahydrate, octahydrate, hexahydrate, tetrahydrate, and dihydrate. In some embodiments, magnesium chloride dihydrate is selected as the starting material.

[0026] Magnesium chloride has an enthalpy of formation (Δ fThe ΔH° of magnesium hydroxide (solid) is -601.58 kJ / mol. f The H° solid is -924.66 kJ / mol. Because solid magnesium hydroxide lies in an energy valley relative to the magnesium chloride starting material, heat can be captured from the decomposition of magnesium chloride to magnesium hydroxide. The captured heat can be utilized internally, thereby contributing to a low energy loss in the carbon dioxide capture and sequestration process. The enthalpy difference between the initial and final steps in the above equation is 0.0465 kWh, excluding the enthalpy of the exothermic absorption of HCl in water, approximately 55 kJ / mol HCl. This includes the formation of two moles of HCl, or 110 kJ (0.031 kWh). The total is 0.0155 kWh. Each mole of magnesium hydroxide can react with one mole of CO2, resulting in a theoretical minimum energy requirement of 0.0155 / 0.044 = 0.35 kWh / kg CO2.

[0027] In some embodiments, the magnesium chloride forced decomposition process is carried out in a manner that avoids the formation of magnesium chloride hydroxide partial decomposition products. The magnesium chloride forced decomposition process is carried out such that the decomposition reaction proceeds substantially to completion and the magnesium hydroxide product is substantially free of magnesium chloride hydroxide.

[0028] In some aspects, the magnesium chloride forced decomposition process is carried out in a manner that avoids the formation of magnesium oxide decomposition products. The magnesium chloride forced decomposition process is carried out so that the magnesium hydroxide product is substantially free of magnesium oxide. Magnesium oxide is a dehydrated form of magnesium hydroxide (Mg(OH)≡MgO + HO). Additional energy is required to remove lone water molecules from magnesium hydroxide to produce magnesium oxide. Employing magnesium hydroxide as an intermediate in the forced decomposition element and avoiding the complete dehydration of magnesium to magnesium oxide can save energy and contribute to lower energy losses in the carbon dioxide capture and sequestration process.

[0029] The magnesium hydroxide produced by the forced decomposition of magnesium chloride can be combined with the magnesium hydroxide produced from the reaction of magnesium chloride with calcium oxide, i.e., the product of passive dissolution (Reaction 1 above). The combined magnesium hydroxide (in solution) can then be used as the uptake fluid for the absorption of carbon dioxide.

[0030] Combining magnesium hydroxide obtained from passive dissolution with magnesium hydroxide obtained by forced decomposition of magnesium chloride reduces the amount of magnesium chloride that is decomposed. Reducing the amount of magnesium chloride that is decomposed reduces the total energy input required for the decomposition of magnesium chloride. Reducing the total energy input required for the decomposition of magnesium chloride contributes to a favorable thermodynamic energy penalty in the carbon capture process.

[0031] The combination of magnesium hydroxide obtained from passive dissolution and magnesium hydroxide obtained by the forced decomposition of magnesium chloride allows the carbon capture and sequestration system to utilize mineral-containing materials that might otherwise be disposed of as unwanted waste. Employing waste as a mineral source contributes to the environmentally friendly nature of the carbon capture process.

[0032] The magnesium hydroxide obtained by the combination of passive dissolution and forced decomposition can be mixed with water and exposed to flue gas in a bubble column. Energy is used to compress the flue gas, which contains approximately 12–19% carbon dioxide and additional components, primarily nitrogen. At least a portion of the carbon dioxide in the flue gas is absorbed into the magnesium hydroxide solution, or intake liquid, to form magnesium carbonate. Calcium chloride present in the intake liquid reacts with the magnesium carbonate through an "ion switch" reaction to form calcium carbonate. The calcium carbonate spontaneously precipitates from solution, leaving magnesium chloride in solution. Although the calcium chloride solution in the intake liquid is an indirect product of passive dissolution, additional calcium chloride can be added to the intake liquid. Sourcing calcium chloride from the passive dissolution of industrial waste materials contributes to the environmentally friendly nature of the carbon capture process. The solid precipitated calcium carbonate (PCC) is then isolated to yield a PCC and magnesium chloride solution. Various methods can be used to separate the PCC from the solution. In one example, the PCC and solution are separated by passive hydrostatic pressure, i.e., gravity drainage via hydrostatic head filtration. The spontaneous formation of PCC is an exothermic reaction, and the heat released from this reaction may be recycled. The recycled heat from the calcium chloride formation "ion switch" reaction contributes to the low energy loss of the carbon capture process. The recycled heat may be used internally to generate steam, thereby contributing to the favorable thermodynamic energy loss of the carbon capture process.

[0033] The magnesium chloride solution can be dehydrated to regenerate magnesium chloride or its hydrates. In an exemplary dehydration process, waste heat from a concurrently operating plant or process can be used to drive water removal. In one embodiment, steam can be used to remove water from a magnesium chloride solution. This exemplary process employs a two-stage dehydration process, whereby in the first stage, a boiler / evaporator is used to remove at least a portion of the water from the magnesium chloride solution, and in the second stage, a spray dryer is used to remove at least a portion of the remaining water. The boiler / evaporator can be employed to remove at least a portion of the water in the magnesium chloride solution, producing an intermediate fluid having approximately 3 molar equivalents of water of hydration. This intermediate fluid is then transferred to a spray dryer and heated to a temperature of ≥105°C. The fluid is then flashed under pressure, during which the water / steam separates as vapor, and magnesium chloride hydrate crystals having approximately 2.0-2.1 molar equivalents of water of hydration are collected. Heat recycled from various segments of the carbon dioxide capture and sequestration process, or from a co-operating power plant, can be used in the evaporation or spray-drying steps to dehydrate the magnesium chloride solution. For example, steam generated from recycled heat can be used to heat the drying gas used to spray-dry the magnesium chloride solution. Spray-drying conditions can be adjusted to regenerate solid magnesium chloride with the desired degree of hydration. The regenerated magnesium chloride hydrate can then be transferred to a magnesium chloride forced decomposition reactor for decomposition.

[0034] In some embodiments, the carbon dioxide capture and sequestration process employs carbon dioxide collected from a carbon dioxide emission source, for example, from the flue gas of a power generation facility. In some embodiments, heat is collected from the flue gas of the carbon dioxide emission source. Traditionally, flue gas from a power generation facility is released into the atmosphere. The flue gas contains carbon dioxide, water in the form of water vapor or steam, and other gases. This waste flue gas can be utilized to recycle heat. The carbon dioxide capture and sequestration process described herein can utilize externally co-generated heat to further reduce energy input requirements. The recycled heat can then be used to generate electricity, power a compressor, generate steam, and / or increase the temperature of steam. Excess heat from various high-heat elements can be utilized and introduced into heat-input or heat-sink (heat-negative) elements. By linking various heat-excess and heat-deficit process elements, reliance on external heat sources is reduced. This not only reduces the net energy loss of the process, but also reduces energy input costs due to the reduced use of external energy sources. Combining the elements of carbon sequestration and heat reuse and transfer results in an efficient carbon dioxide capture and sequestration process with significantly reduced energy losses.

Claims

1. CO from the gas stream 2 and CO 2 CaCO 3 1. A method for isolating a tissue in the form of (a) Mg(OH) 2 A first mixture containing HCl and H 2 to form a second mixture containing 2000 and MgCl 2 decomposing the contained materials; (b) Mg(OH) 2 and CaCl 2 to produce a third mixture containing CaO and MgCl 2 mixing with salt water; (c) Mg(OH) 2 and CaCl 2 mixing the first mixture with the third mixture to obtain a fourth mixture comprising: (d) CaCO 3 and MgCl 2 and a fourth mixture containing CO to produce a product mixture comprising an aqueous solution of 2 contacting with The method comprising:

2. 10. The method of claim 1, wherein substantially no heat is provided as an input for step (b).

3. Mg(OH) in step (c) 2 is the Mg(OH) produced in step (a) 2 and Mg(OH) produced in step (b). 2 and , in approximately equal amounts.

4. MgCl 2 Containing material is MgCl 2 10. The method of claim 1, wherein the compound is a hydrate.

5. MgCl 2 5. The method of claim 4, wherein the hydrate comprises 2.0 to 2.1 molar equivalents of water of hydration.

6. 10. The method of claim 1, wherein the first product mixture is substantially free of Mg(OH)Cl.

7. MgCl 2 The material containing MgCl produced in step (d) 2 10. The method of claim 1, comprising at least a portion of:

8. 10. The method of claim 1, further comprising dissolving calcium-containing minerals or waste materials with an acid to produce CaO.

9. 9. The method of claim 8, wherein CaO produced from the dissolution of calcium-containing minerals or waste materials is used as input for step (b).

10. 9. The method of claim 8, wherein the acid is hydrochloric acid, nitric acid, or sulfuric acid.

11. 10. The method of claim 9, wherein at least a portion of the hydrochloric acid is obtained from step (a).

12. 9. The method of claim 8, wherein the calcium-containing mineral is selected from the group consisting of alite, jaffeite, perlite, vermiculite, diopside, tremolite, and combinations thereof.

13. 9. The method of claim 8, wherein the calcium-containing waste material is selected from the group consisting of stone, concrete, steel furnace slag, biomass fuel production slag, spent coal fly ash, and combinations thereof.

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