Thermal oxide-silicate conversion processes

Abstract

A method is provided comprising providing at least one of a calcium-containing salt and calcium-containing mineral. A silicate material that contains a ratio of O to Si greater than 2:1. A mixture of the at least one of the calcium-containing salt and the calcium-containing mineral and silicate material is heated to consume at least some at least one of the calcium-containing salt and the calcium-containing mineral and the silicate material to form a calcium-enriched silicate.

Description

THERMAL OXIDE-SILICATE CONVERSION PROCESSESGOVERNMENT RIGHTS

[0001] This invention was made with Government support under contract (ONR-N0014-18- 2659) awarded by the Office of Naval Research. The Government has certain rights in the invention.CROSS REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority under 35 U.S.C. §119 from U.S. Application No. 63 / 518,038, entitled THERMAL PROCESS TO TRANSFORM SILICATE MINERALS INTO ALKALINE SOLIDS FOR CARBON REMOVAL, by Kanan et al., which is incorporated herein by reference for all purposes.BACKGROUND

[0003] The background description provided here is for the purpose of generally presenting the context of the disclosure. Information described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.

[0004] The removal of CO2 from the atmosphere (CDR) on the multi-hundred gigaton (Gton) scale this century is an essential component of nearly all carbon management strategies designed to limit global temperature rises to less than 2° C above pre-industrial levels, yet CDR is currently limited to a few small demonstration projects because existing CDR technologies are energy-intensive and prohibitively expensive. To contribute meaningfully to global management, new methods are needed to remove CO2 from air and safely sequester it while minimizing the energy and resource inputs.SUMMARY

[0005] To achieve the foregoing and in accordance with the purpose of the present disclosure, a method is provided comprising providing at least one of a calcium-containing salt and calcium-containing mineral. A silicate material that contains a ratio of O to Si greater than 2:1 is provided. A mixture of the at least one of the calcium-containing salt and the calcium- containing mineral and silicate material is heated to consume at least some at least one of the calcium-containing salt and the calcium-containing mineral and the silicate material to form a calcium-enriched silicate.

[0006] In another manifestation, a method is provided comprising providing at least one of a calcium-containing salt and calcium-containing mineral. A silicate material that contains a ratio of O to Si greater than 2: 1 is provided. A mixture of the at least one of the calcium-containingsalt and the calcium-containing mineral and silicate material is heated to consume at least some at least one of the calcium-containing salt and the calcium-containing mineral and the silicate material to form a calcium-enriched silicate. CO2 is provided to form at least one of CaCCh and dissolved Ca2+and bicarbonate (HCO ) ions from the CO2 and the calcium-enriched silicate.

[0007] In another manifestation, a method is provided comprising providing at least one of an alkali metal-containing salt and alkali metal -containing mineral. A silicate material comprising magnesium is provided. A mixture of the at least one of the alkali metal-containing salt and alkali metal-containing mineral with the silicate material is heated to consume some of the at least one of the alkali metal-containing salt and alkali metal-containing mineral and the silicate material to form an alkali metal-enriched silicate.

[0008] In another manifestation, a method is provided comprising providing at least one of a calcium-containing salt and calcium-containing mineral. A silicate material that contains a ratio of O to Si greater than 2: 1 is provided. A mixture of the at least one of a calcium- containing salt and calcium-containing mineral with the silicate material is heated to consume some of the at least one of a calcium-containing salt and calcium-containing mineral and the silicate material to form a product comprising calcium-enriched silicate. The product is added to soil to provide plant available Si.

[0009] These and other features of the present invention will be described in more detail below in the detailed description of the disclosure and in conjunction with the following figures.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The present disclosure is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which:

[0011] Figure 1 is a high-level flow chart of a process that may be used in some embodiments.

[0012] Figure 2 is a table that shows reactions for olivine, serpentine, and Augite for different experiments.

[0013] Figure 3A is a table showing entry numbers of different experiments, additives, additive wt%, and phases observed by pXRD.

[0014] Figure 3B is a stacked plot of the pXRD patterns for the product mixtures of the reactions using different additives.

[0015] Figure 4 shows a plot of the pXRD pattern for a product mixture of an embodiment.

[0016] Figure 5 shows a plot of the pXRD pattern for a product mixture of another embodiment.

[0017] Figure 6A is a plot of stacked pXRD patterns corresponding to three different time points (2 weeks, 4 weeks, and 7 weeks) provided by an embodiment.

[0018] Figure 6B shows three overlaying plots of TGA-MS data of the 7 week timepoint of the embodiment used for Figure 6A.

[0019] Figure 7 shows three overlaying plots of TGA-MS data of an embodiment.

[0020] Figure 8A is a plot of the pXRD pattern of the reaction products of an embodiment indicating complete consumption of olivine and NazCOs and NazMgSiCh and MgO as the only observed phases in an embodiment.

[0021] Figure 8B shows a plot of the pXRD pattern for the solids separated by centrifugation in the embodiment shown in Figure 8A.

[0022] Figure 9 shows the results of the measured soluble Si in some embodiments.

[0023] In the drawings, like reference numerals are sometimes used to designate like structural elements. It should also be appreciated that the depictions in the figures are diagrammatic and not to scale.DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS

[0024] The reaction of silicate minerals with CO2 to form carbonates or dissolved bicarbonates has been proposed as a way to achieve permanent CO2 removal to counteract anthropogenic CO2 emissions. The vast geological reserves of ultramafic and mafic rocks containing olivine ((Mg,Fe)2SiO4), serpentine (MgsSizOslOH)^, and pyroxene((Ca,Mg,Fe)2Si2Oe) have the capacity to provide >100,000 Gt of CDR. Moreover, there are >400 Mt of ultramafic / mafic mine tailings generated annually worldwide. Silicates remove CO2 from the atmosphere under wet conditions via a process known as weathering, but natural weathering is very slow. It has been shown that the carbonation of silicates found in ultramafic rocks can be achieved within hours at high temperature and high CO2 pressure (185° C, 155 bar CO2), but little or no reactivity occurs at ambient temperature and 1 bar CO2 pressure.

[0025] Disclosed is a method for transforming a silicate reactant and a metal salt reactant into a product mixture comprising a product silicate that is enriched in the metal cation from the metal salt reactant. The silicate reactant comprises a silicate material other than SiO2 such that the ratio of O to Si atoms (O:Si ratio) is greater than 2:1, and there are other metal cations besides Si4+. The metal salt reactant comprises a metal cation and an inorganic anion. The product silicate enriched in the metal cation from the metal salt reactant is a silicate with a higher wt% of the metal cation from the metal salt reactant compared to the silicate reactant. In some embodiments, the method further comprises the formation of a metal oxide product comprising one or more metal cations other than Si4+that is derived from the silicate reactant.The products of the transformation have advantageous chemical and / or physical properties. In some embodiments, the products are used for carbon dioxide (CO2) removal from a gas. In some embodiments, the products are added to soil to improve agricultural output.

[0026] In order to facilitate understanding, Figure 1 is a high level flow chart of a process that may be used in some embodiments. At least one of an alkali metal-containing salt or alkali metal-containing mineral is provided (step 104). In the specification and claims, an alkali metalcontaining salt includes alkali metal-containing minerals. In some embodiments, the alkali metal-containing salt or mineral comprises at least one of magnesium (Mg), calcium (Ca), iron (Fe), titanium (Ti), zirconium (Zr), vanadium (V), chromium (Cr), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), lithium (Li), sodium (Na), potassium (K), and aluminum (Al). In some embodiments, the alkali metal-containing salt or mineral is a calcium containing salt or mineral. A silicate material is provided (step 108), wherein the silicate material has a ratio of oxygen (O) to silicon (Si) of greater than 2: 1, by the number of atoms. In some embodiments, the silicate comprises silicon, oxygen, and at least one of Mg, Ca, Fe, Ti, Zr, V, Cr, Co, Ni, Cu, Zn, Li, Na, K, and Al. The alkali metal-containing salt or mineral and the silicate are mixed together and heated (step 112) resulting in the consumption of the alkali metal-containing salt or mineral and the silicate forming an alkali metal-enriched silicate product. For example, if a calcium- containing salt or mineral is used, the product is a calcium-enriched silicate, so that the product silicate has a higher concentration of calcium than the reactant silicate. Other products such as metal oxides, such as magnesium oxide (MgO), may be formed. In some embodiments, the heating may be provided by at least one of an electrical source, a combustion source, and a thermal energy storage system source The products may then be used (step 116). In some embodiments, at least one of the metal oxide calcium-enriched silicate product and metal oxide product may be used for CO2 sequestration. In some embodiments, the silicate that is calcium enriched may be used for plant fertilization to provide plant available Si or may be used to improve the soil. In some embodiments, the product may be used for thin film deposition.

[0027] In some embodiments, the silicate reactant comprises one or more metal cations and one or more silicate anions of general formula SiCU4-(orthosilicate), SirO?6-(sorosilicate), SiO (cyclosilicate or chain silicate), Si20s4-(phyllosilicate). In some embodiments, the silicate reactant is a tectosilicate other than silicon dioxide (SiCL) comprising, in addition to Si4+cations, Al3+cations, and at least one other metal cation. In some embodiments, the silicate reactant further comprises other anions such as O2-, OH-, or X-, where X- is a halide. In some embodiments, the metal salt reactant comprises a calcium cation and an inorganic anion. In some embodiments, the metal salt reactant is calcium carbonate (CaCOs), calcium sulfate (CaSO4),calcium oxide (CaO), or calcium hydroxide (Ca(OH)p. In other embodiments, the metal salt reactant comprises an alkali cation salt. In some embodiments, the alkali cation salt is M2CO3, where M+is Li+, Na+, K+, Rb+, or Cs+.

[0028] When the silicate reactant and the metal salt reactant are combined and heated to an appropriate temperature, the reactants are transformed into a silicate product comprising a silicate that is enriched in the metal cation from the metal salt reactant. In some embodiments, the transformation further comprises the formation of a metal oxide product comprising one or more metal cations other than Si4+from the silicate reactant.

[0029] In some embodiments, the particle size of the silicate reactant is reduced by crushing and / or grinding prior to the reaction. In some embodiments, the silicate reactant is ground such that the median particle diameter (D50) is <1 mm. In some embodiments, the silicate reactant is ground such that the D50 is <500 pm. In some embodiments, the silicate reactant is ground such that the D50 is <250 pm. In some embodiments, the silicate reactant is ground such that the D50 is <100 pm. In some embodiments, the silicate reactant is ground such that the D50 is <75 pm. In some embodiments, the silicate reactant is ground such that the D50 is <50 pm.

[0030] In some embodiments, the particle size of the metal salt reactant is reduced by crushing and / or grinding prior to the reaction. In some embodiments, the metal salt reactant is ground such that the median particle diameter (D50) is <1 mm. In some embodiments, the metal salt reactant is ground such that the D50 is <500 pm. In some embodiments, the metal salt reactant is ground such that the D50 is <250 pm. In some embodiments, the metal salt reactant is ground such that the D50 is <100 pm. In some embodiments, the metal salt reactant is ground such that the D50 is <75 pm. In some embodiments, the metal salt reactant is ground such that the D50 is <50 pm.

[0031] In some embodiments, the silicate reactant and metal salt reactant are granulated prior to the reaction to improve the flow of the reactants in the reaction vessel.

[0032] In some embodiments, the transformation takes place when the silicate reactant and metal salt reactant are heated to a temperature of >800 °C. In some embodiments, the transformation takes place when the silicate reactant and metal salt reactant are heated to a temperature of >900 °C. In some embodiments, the transformation takes place when the silicate reactant and metal salt reactant are heated to a temperature of >1000 °C. In some embodiments, the transformation takes place when the silicate reactant and metal salt reactant are heated to a temperature of >1100 °C. In some embodiments, the transformation takes place when the silicate reactant and metal salt reactant are heated to a temperature of >1200 °C. In some embodiments, the transformation takes place when the silicate reactant and metal salt reactant are heated to atemperature of >1300 °C.

[0033] The transformation can be performed in the presence of any of a variety of gases. In some embodiments, the transformation is performed under air. In some embodiments, the transformation is performed under an inert gas such as nitrogen gas (N2) or argon (Ar). In some embodiments, the transformation is performed under CO2. The transformation may be performed under a flowing gas, static gas, or vacuum.

[0034] In some embodiments, an additive in the form of a second metal salt is used to enable the reaction between the silicate reactant and the metal salt reactant to be performed at a lower temperature than without the additive. In some embodiments, the additive forms a molten phase that facilitates the reaction at a lower temperature than what is required in the absence of the non-reactant metal salt. In some embodiments, an additive in the form of a second metal salt is used to accelerate the reaction between the silicate reactant and the metal salt reactant. In some embodiments, the additive is sodium sulfate (Na2SO4), potassium sulfate (K2SO4), sodium perborate (NaBC ), sodium borate (Na2B4O?) (borax), potassium perborate (KBO2), potassium borate (K2B4O7), sodium hydroxide (NaOH), potassium hydroxide (KOH), sodium chloride (NaCl), or potassium chloride (KC1). In some embodiments, the additive is added as a minor component of the transformation. In some embodiments, the additive is added at <10 wt%. In some embodiments, the additive is added at <5 wt%. In some embodiments, the additive is added at <1 wt%. In some embodiments, the additive can be recovered after the transformation by separation from the products and reused in a subsequent transformation. In some embodiments, the reaction is performed with an additive at a temperature between 800 °C and 1300 °C. In some embodiments, the reaction is performed with an additive at a temperature between 900 °C and 1200 °C.

[0035] The transformation can be performed in any apparatus capable of reaching the appropriate temperature, such as a muffle furnace, a tunnel kiln, a shuttle kiln, a roller hearth kiln, an elevator kiln, a shaft kiln, an indirect rotary calciner, a direct-fired rotary calciner, an indirect rotary kiln, or a direct-fired rotary kiln. In some embodiments, the transformation is performed in a direct-fired rotary kiln or calciner wherein the heat is provided by the combustion of a carbon-based fuel such as natural gas, petroleum, biogas, syngas, coal, biomass, or char. In some embodiments, the transformation is performed in a direct-fired rotary kiln or calciner using oxyfuel combustion wherein the kiln or calciner is supplied with fuel and pure oxygen gas (O2) or a gas enriched in O2 such that the flue gas from the kiln has a high concentration of CO2 that facilitates its separation and sequestration.

[0036] In some embodiments, the metal salt reactant comprises a calcium compound. Insome embodiments, the metal salt reactant comprises CaO or another calcium compound that serves as a source of CaO, such as a calcium salt (CaY, where Y is an anion or anions with 2- charge, such O2-, (NO3O2, OH’, CO32’, and SO42-), such as CaCOs, CaSO4, Ca(OH)2, calcium nitrate (Ca(NO3)2). In some embodiments, the metal salt reactant is a calcium-containing mineral such as limestone. Heating the metal salt reactant comprising an appropriate calcium compound or calcium-containing mineral with the silicate reactant results in the formation of a Ca-enriched silicate product, meaning a silicate with a higher wt% of Ca than the silicate reactant. When a calcium compound other than CaO is used, the transformation is accompanied by the release of a gaseous byproduct derived from the calcium salt. For example, when CaCXF or limestone is used, CO2 is formed as a byproduct. When CaSO4 is used, sulfur dioxide (SO2) and O2, and / or sulfur trioxide (SO3) are formed as byproducts. In some embodiments, the calcium compound is heated to form CaO and a gaseous byproduct in a first step and then the CaO is combined with the silicate reactant and heated with the silicate reactant in a second step to form a Ca-enriched silicate. In some embodiments, the calcium compound is heated with the silicate reactant directly without a first step to form CaO. The decomposition of the calcium compound to form CaO and the gaseous byproduct may occur at a lower temperature than the temperature of the reaction between CaO and the silicate reactant. For example, CaCOs typically decomposes to form CaO and CO2 at temperatures ranging from 600-900 °C, whereas the reaction with CaO and a silicate reactant generally takes place at 900 °C or greater. In some embodiments, the decomposition of the calcium compound to release the gaseous byproducts is concomitant with its reaction with the silicate reactant. For example, in some embodiments in which CaSO4 is used as the metal salt reactant, CaO is not observed as an intermediate.

[0037] When the metal salt reactant comprises a calcium compound, the identity of the silicate product or products can be controlled at least to some extent by the ratio of the calcium compound to the silicate reactant used in the reaction. When the ratio of calcium compound to silicate reactant is such that the ratio of the total amount of Ca to the total amount of Si is 2: 1 on a molar basis, then calcium silicate (Ca2SiO4) is the favored silicate product.

[0038] In preferred embodiments, the silicate reactant comprises an Mg -rich silicate, a silicate that has >5 wt% Mg, and the metal salt reactant comprises a calcium compound as described above. In some embodiments, the silicate comprises olivine (for which the Mg endmember has the formula magnesium silicate (Mg2SiO4) and is called forsterite), serpentine (for which the Mg endmember has the formula Mg3Si2Os(OH)4), or diopside (with formula CaMgSi2Oe). In some embodiments, the calcium compound is CaCC , CaSO4, or Ca(OH)2. In some embodiments, the silicate comprises silicon, oxygen, and at least one of Mg, Ca, iron (Fe),titanium (Ti), zirconium (Zr), vanadium (V), chromium (Cr), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), lithium (Li), sodium (Na), potassium (K), and aluminum (Al). Heating the silicate reactant with the calcium compound results in the formation of a silicate product that has a higher Ca content than the silicate reactant. In some embodiments, forming a silicate product that has a higher Ca content than the silicate reactant is accompanied by the formation of magnesium oxide (MgO). In some embodiments, MgO is reacted with CO2 to form at least one of magnesium carbonate (Mg(C03)), magnesium carbonate hydroxide (Mg5(CO3)4(OH)2 • H2O), MgCOs • H2O (where x is an integer), and dissolved Mg2+and bicarbonate (HCCL-) ions. In some embodiments, other metal oxide byproducts are formed that contain metal ions other than Mg2+that are derived from impurities in the silicate reactant or calcium compound. For example, if the silicate contains iron, the transformation can result in the formation of iron oxide byproducts such as iron (II, III) oxide (Fe iCL) or dicalcium ferrite (Ca2Fe20s). The oxidation state of the metal ion in such metal oxide byproducts may be different than the oxidation state of the metal ion from which it is derived in the silicate reactant or calcium compound reactant because the metal ion may be oxidized by O2 if the transformation is performed under air or if the product is in contact with air while it is cooling. In some embodiments, the silicate product has the formula CaiSiOs. which is the formula for the mineral alite. In some embodiments, the silicate product has the formula Ca2SiO4, which is the formula for the mineral larnite. In some embodiments, the silicate product has the formula Ca7Mg(SiO4)4, which is the formula for the mineral Bredigite. In some embodiments, the silicate product has the formula Ca3Mg(SiO4)2, which is the formula for the mineral merwinite. In some embodiments, the silicate product has the formula CaMgSiCU, which is the formula for the mineral monticellite. In some embodiments, the silicate product has the formula Ca2MgSi2O?, which is the formula for the mineral akermanite. The identity of the silicate product or products can be controlled at least to some extent by the ratio of calcium compound reactant to Mg- containing silicate used in the transformation. When the ratio of calcium compound reactant to silicate is such that the ratio of the total amount of Ca to the total amount of Si is 2:1 on a molar basis, then Ca2SiO4 is the favored silicate product.

[0039] In some embodiments, the silicate reactant comprises an Mg-rich silicate, a silicate that has >5 wt% Mg concentration, and the metal salt reactant comprises M2CO3, where M+is an alkali cation or another alkali salt that serves as a source of M2O. In some embodiments, the Mg- rich silicate is olivine (for which the Mg endmember has the formula Mg2SiO4 and is called forsterite), serpentine (for which the Mg endmember has the formula Mg3Si2Os(OH)4), or diopside (with formula CaMgSi2Oe). Heating the Mg-rich silicate reactant with the alkali saltresults in the formation of a silicate product that has a higher alkali content than the silicate reactant. In some embodiments, forming a silicate product that has a higher alkali content than the silicate reactant is accompanied by the formation of MgO. In some embodiments, the silicate product has the formula M^MgSiC , where M+is an alkali cation.

[0040] In some embodiments, the products of the reaction between the silicate reactant and the metal salt reactant are alkaline such that when the products are suspended in water the pH of the water is >10. In some embodiments, when the products are suspended in water the pH of the water is >11. In some embodiments, when the products are suspended in water the pH is >12.

[0041] The products of the transformation of the silicate reactant and the metal salt reactant, comprising a silicate product and in some embodiments further comprising a metal oxide product, can be used to remove CO2 from a gas and / or liquid by the formation of carbonates and bicarbonates. In some embodiments, the products are contacted with air to remove CO2 from the air. In some embodiments, the products are contacted with a gas containing at least 0.1% CO2 by volume to remove CO2 from the gas. In some embodiments, the products are contacted with a gas containing at least 1% CO2 by volume to remove CO2 from the gas. In some embodiments, the products are contacted with a gas containing at least 10% CO2 by volume to remove CO2 from the gas. In some embodiments, the products are contacted with a liquid comprising water that is in contact with a gas containing CO2. and the products react with dissolved inorganic carbon in the liquid to form bicarbonates and / or carbonates.

[0042] In some embodiments, the products of the transformation of the silicate reactant and the metal salt reactant, comprising a silicate product, and in some embodiments further comprising a metal oxide product, are added to agricultural soil, as a soil amendment. In some embodiments, the silicate product when added to soil acts as a source of plant available silicon, which can provide benefits to crop yield and resilience.ExamplesExample 1 : Transformation of Mg-rich silicates and CaCCh or CaSC

[0043] Natural magnesium silicates olivine, serpentine, or augite were crushed and sieved to produce samples with a particle size of 75-100 pm. Reactions were performed using 0.071 g olivine (0.50 mmol, Mgi.9 Feo.i SiC ) or 0.069 g serpentine (0.25 mmol, Mg3Si2Os(OH)4 with minor aluminum (Al), iron (Fe), and calcium (Ca) impurities) or 0.072 g augite (0.33 mmol, CaMgSi2Oe) as the silicate reactant and CaCCh (0.05 - 0.10 g; 0.5 - 1.0 mmol) or CaSC (0.136 g, 1.0 mmol) as the metal salt reactant. Reactions were performed in the presence or absence of 0.0085 g Na2SO4 (0.060 mmol) as an additive. The metal salt reactant, silicate reactant, and additive were mixed by brief grinding with a mortar and pestle, heated in a muffle furnace to thedesired temperature, held at this temperature for a fixed period of time, and then allowed to cool in air. The products were analyzed by powder X-ray diffraction (pXRD). The results are summarized in Figure 2. Figure 2 shows reactions for olivine, serpentine, and Augite and also provides a table listing entry numbers of different experiments, silicate reactant, including its end member formula and other constituent elements present in the silicate reactant, Ca salt reactant, reaction temperature, number of hours of heating, the weight percentage of any additive, and the phases observed using powder X-ray diffraction (pXRD). In the cases where there is no silicate reactant phase observed and no CaO or CaSO4 phase observed by pXRD in the product mixture, the reaction went to completion (100% yield), meaning that all the silicate reactant was converted to a Ca-enriched silicate and all the Ca compound was consumed (entries 2, 5, 6, 7, 8, 9, 10, 11, 12). More detailed descriptions of the reactions corresponding to the entries in Figure 1 are provided below.

[0044] A reaction of CaCOs with olivine (2: 1 CaC03:Mgi.9Feo.iSi04 molar ratio) at 1200 °C for 4 h resulted in the formation of the desired products Ca2SiC>4 and MgO in addition to Ca2Fe20s, which arises from the minor Fe2+cation in olivine reacting with CaO and O2 (Figure 2, Entry 1). However, substantial peaks for the olivine and CaO reactants were also present in the pXRD pattern, with phase quantification indicating that the reaction was less than 50% complete. When the reaction was performed with 5 wt% Na2SO4 as an additive, the starting material peaks disappeared and Ca2SiO4, MgO, and CWFe^O^ were the only observed phases by pXRD after just 1 h at 1200 °C (Figure 2, Entry 2). To obtain a quantitative reaction yield, the products of the reaction were carbonated under 1 atm CO2 in an aqueous suspension and the amount of carbonates formed was assessed by thermal gravimetric analysis (TGA) of the dried solids. These experiments indicated that the yield of the reaction to form Ca2SiO4 and MgO was essentially 100%.

[0045] At a lower reaction temperature of 1100 °C, the reaction produced (Ca2SiO4 and MgO after 1 h, with unreacted CaO remaining (Figure 2, Entry 3). Reaction at 1000 °C for 4 h converted 72% of the starting material to Ca2SiO4 and MgO (Figure 2, Entry 4). When the reaction was performed at 1200 °C with lower amounts of CaCOi, mixed Mg / Ca silicate phases were formed: using 1.5 or 1 equivalents of CaCO-, resulted in the formation of Ca A-lgCSKFh + MgO and CaMgSiO4 + MgO, respectively (Figure 2, Entries 5 and 6).

[0046] The reaction of 2: 1 CaS04:Mgi.9Feo.iSi04 with 5 wt% Na2SO4 at 1200 °C for 1 h resulted in complete consumption of CaSO4 and formation of Ca2SiO4 and MgO by pXRD (Figure 2, Entry 7). When the same reaction was performed at 1100 °C, the product mixture after 1 h consisted of CaMgSiO4 and MgO as well as unreacted CaSO4 and olivine, but no CaOwas observed (Figure 2, Entry 8). This result indicates a mechanistic difference between transforming the silicate with CaSO4 vs CaCOa. Whereas CaCOa decomposes to CaO prior to reacting with the silicate, the decomposition of CaSOa appears to be promoted by its reaction with the silicate.

[0047] For serpentine, a reaction with 4 molar equivalents of either CaCOa or CaSOa resulted in the disappearance of the starting material peaks and the formation of CaaSiO i and MgO (Figure 2, Entries 9 and 10). For augite, a reaction with 3 molar equivalents of either CaCOa or CaSO4 resulted in full conversion to Ca2SiO4 and MgO by pXRD (Figure 2, Entries 11 and 12).

[0048] Example 2: Transformation of olivine and CaCOa using different metal salt additives Olivine (Mgi.9 Feo.i SiO4) was crushed and sieved to produce a sample with a particle size of 75- 100 pm. 0.10 g CaCOa (1 mmol), 0.071 g olivine (0.50 mmol) and 0.0034-0.0085 g K2SO4 or NaOH or NaBO2 (2-5 wt% of the total mass of CaCOa + olivine) were ground and mixed. The mixture was heated to the desired temperature in a furnace. The reaction was held for 1 h at the desired temperature and cooled down in air. The results are summarized in Figures 3A-3B. Figure 3 A is a table showing entry numbers of different experiments, additives, additive wt%, and phases observed by pXRD. Figure 3B is a stacked plot of the pXRD patterns for the product mixtures of the reactions using different additives. The patterns all show the same product phases (Ca2SiO4, MgO, and Ca2Fe20s), and none of the reactant phases, indicating complete conversion for all cases.Example 3: Transformation of olivine and CaCCh on a kilogram scale

[0049] Olivine was crushed and sieved to produce a sample with a particle size of 75-100 pm. 1.05 kg CaCOs (10.5 mol) and 0.73 kg olivine (5.0 mol, Mgi.9 Feo.i SiO4) were mixed in a blender. The mixture was heated to 1300 °C in a muffle furnace, held at this temperature for 6 h, and then cooled down in air. The reaction was analyzed by pXRD. The results are summarized in Figure 4, which shows a plot of the pXRD pattern for the product mixture. The only phases observed in the pattern are the phases of Ca2SiC>4, MgO, and Ca2Fe20s, indicating the reaction went to completion.Example 4: Transformation of andradite and CaCO i

[0050] Andradite (CasFeaSisOi with Al and Mg impurities) was crushed and sieved to produce a sample with a particle size of 75-100 pm. 0.10 g CaCOi (1 mmol), 0.1693 g andradite (0.33 mmol) and 0.014 g Na2SO4 (5 wt% of the total mass of CaCOs + andradite) were groundand mixed. The mixture was heated to 1200 °C in a furnace and held for 1 h at this temperature, then cooled down in air. The reaction was analyzed by pXRD. The results are summarized in Figure 5, which shows a plot of the pXRD pattern for the product mixture. The only phases observed in the pattern are the phases of Ca2SiO4 and Ca2Fe20s.Example 5: Use of the products to remove CO2 from air

[0051] A reaction was performed as described in Example 1, Figure 1, Entry 2. The product was washed with water to remove Na2SO4 and then dried. 100 mg of this material, consisting of Ca2SiO4 and MgO, was placed in a vial. The material was kept wet by evenly spraying 0. 1 mL water onto it once per day and exposed to air without any agitation. A pXRD pattern of the material was obtained every week to check the progress of the carbonation. Figure 6A is a plot of stacked pXRD patterns corresponding to three different time points (2 weeks, 4 weeks, and 7 weeks). The Ca2SiO4 peaks completely disappeared and were replaced by CaCCh peaks within 7 weeks. The MgO peaks diminished in intensity. Thermal gravimetric analysis-mass spectrometry (TGA-MS) was used to quantify the extent of carbonation (Figure 6B). Figure 6B shows three overlaying plots. The plots with broken lines marked H2O and CO2 use the left y- axis and show the signals for H2O and CO2 measured by the mass spectrometer in the TGA-MS (the signals are ion currents arising from the ionization of H2O and CO2 in the mass spectrometer) versus the temperature applied by the instrument. The solid line uses the right y- axis and shows the weight loss of the sample vs temperature. The broken line plots showing the signals for H2O and CO2 enable the assignment of the origin of the weight loss feature observed in the solid line plot. The observation of peaks for the CO2 signal and the absence of peaks for the H2O signal show that the weight loss features at -400-450 °C and 600-750 °C correspond to loss of CO2 from a magnesium carbonate and CaCOs, respectively. Based on the data in Figures 6A and 6B, after 7 weeks of exposure to air, -100% of the calcium content of the material was converted to CaCOs and -25% of the Mg content was carbonated. The Mg carbonation product was not sufficiently crystalline to be quantified by pXRD, but TGA-MS analysis was consistent with the formation of hydromagnesite (Mgs(CO3)4(OH)2).Example 6: Carbonation of products using 1 atm CO2

[0052] A reaction was performed as described in Example 1. The product was washed with water to remove Na2SO4 and then dried. 100 mg of this material, consisting of Ca2SiC>4 and MgO, was suspended in 10 mL CO2-saturated water in a 20 mL vial with a stir bar. The headspace of the vial was sparged with CO2 and the vial was capped. The slurry wasultrasonicated for 1-2 minutes to achieve a better suspension. The suspension was stirred at 300- 500 rpm. The reaction was held for 1 hour at 30 °C. To analyze the carbonation extent, the slurry was heated at 135 °C until dryness. Thermal gravimetric analysis-mass spectrometry (TGA-MS) was used to quantify the extent of carbonation (Figure 7). Figure 7 shows three overlaying plots. The plots with broken lines marked H3O and CO2 use the left y-axis and show the signals for H2O and CO2 measured by the mass spectrometer in the TGA-MS (the signals are ion currents arising from the ionization of H2O and CO2 in the mass spectrometer) versus the temperature applied by the instrument. The solid line uses the right y-axis and shows the weight loss of the sample vs temperature. The broken line plots showing the signals for H2O and CO2 enable the assignment of the origin of the weight loss feature observed in the solid line plot. The observation of peaks for the CO2 signal and the absence of peaks for the H2O signal show that the weight loss features at -400-550 °C and 600-750 °C correspond to loss of CO2 from a magnesium carbonate and CaCCh, respectively. Based on the data in Figure 7, -100 % of the calcium content of the material was converted to CaCO3and -100 % of the Mg content was carbonated. The Mg carbonation product was not sufficiently crystalline to be quantified by pXRD, but TGA-MS analysis was consistent with the formation of hydromagnesite (Mg5(CO3)4(OH)2).Example 7 : Preparation and carbonation of M2MgSiO4 from olivine + alkali carbonates

[0053] Olivine was crushed and sieved to produce a sample with a particle size of 75-100 pm. 0.12 g Na2CO3(1.1 mmol) and O.145 g olivine (l mmol, Mgi.85 Feo.15 SiC ) were ground and mixed. The mixture was heated to 900 °C in a muffle furnace, held at this temperature for 1 h, and cooled down in air. The reaction products were analyzed by pXRD. Figure 8A is a plot of the pXRD pattern of the reaction products indicating complete consumption of olivine and Na3CO3and Na2MgSiO4 and MgO as the only observed phases. To react the products with CO2, 100 mg of the product mixture consisting of MgO + Na2MgSiO4 was placed in a vial and suspended in 10 mL of deionized water that had been saturated with CO2. The headspace of the vial was filled with CO2. The reaction was kept at 50 °C for 2 hours and then centrifuged to separate the solid component (SiO2) from the liquid supernatant. The supernatant was heated at 100 °C under air, which caused precipitation of a white solid. The slurry was centrifuged again to separate the solid from the supernatant. The solid separated by centrifugation was analyzed by pXRD. Figure 8B, solid line, shows a plot of the pXRD pattern for the solid separated by centrifugation. The solid was identified as hydromagnesite (Mgs(CO3)4(OH)2). The final supernatant was heated until dryness to recover a second solid, which was also analyzed bypXRD. Figure 8B, dashed line, shows a plot of the pXRD pattern of the solid obtained by evaporating the supernatant to dryness. The solid was identified as Na2CO3.Example 8: Plant available Si assay

[0054] This example demonstrates the use of the disclosed method to transform a Mg-rich silicate into a Si fertilizer. Two different products were prepared from the reaction of CaCCh with olivine. Product 1 was prepared by crushing and sieving 0.73 kg olivine to produce a sample with particle size 75-100 pm and mixing it with 1.08 kg CaCCb. The mixture was heated to 1300 °C under air and held at reaction temperature for 6 hours before cooling to room temperature. The product mixture was analyzed by pXRD and found to consist of Ca2SiC>4 and MgO with a minor amount of Ca2Fe20s. Product 2 was prepared by crushing and sieving 0.73 kg olivine to produce a sample with particle size 75-100 pm and mixing it with 0.54 kg CaCO i. The mixture was heated to 1300 °C under air and held at reaction temperature for 6 hours before cooling to room temperature. The product was analyzed by pXRD and found to consist of CaMgSiCU, MgO, and minor amounts of Ca3Mg(SiO4)2 and Fe3O4. Aliquots of Product 1 and Product 2 were analyzed by using a 5-day soluble Si assay. For comparison, a sample of the olivine starting material and a sample of wollastonite, a standard Si fertilizer, were also assayed. The assay consists of incubating 0.2 g of the sample with an extractant solution composed of 100 ml of 0.094 M sodium carbonate solution and 100 ml of 0.2 M ammonium nitrate solution for 5 days and then analyzing the extractant solution by spectrophotometry using the heteropoly blue method to determine the amount of Si extracted as soluble silicic acid, also known as plant available Si. Figure 9 shows the results of the measured plant available Si for the 4 samples. Shown are the average and standard deviation for 6 replicate measurements performed for each sample. The results are shown as the Si wt% of the sample that was solubilized as silicic acid. The assay results showed no soluble Si for olivine and 2.21% for the standard Si fertilizer wollastonite. Substantially higher soluble Si values were measured for Product 1 and Product 2 despite the lower Si content of these materials.

[0055] While this invention has been described in terms of several preferred embodiments, there are alterations, permutations, modifications, and various substitute equivalents, which fall within the scope of this invention. It should also be noted that there are many alternative ways of implementing the methods and apparatuses of the present invention. It is therefore intended that the following appended claims be interpreted as including all such alterations, permutations, modifications, and various substitute equivalents as fall within the true spirit and scope of the present invention. As used herein, the phrase “A, B, or C” should be construed to mean a logical(“A OR B OR C”), using a non-exclusive logical “OR,” and should not be construed to mean ‘only one of A or B or C. Each step within a process may be an optional step and is not required. Different embodiments may have one or more steps removed or may provide steps in a different order. In addition, various embodiments may provide different steps simultaneously instead of sequentially.

Claims

CLAIMSWhat is claimed is:

1. A method, comprising: a. providing at least one of a calcium-containing salt and calcium-containing mineral; b. providing a silicate material that contains a ratio of O to Si greater than 2:1; and c. heating a mixture of the at least one of the calcium-containing salt and the calcium-containing mineral and silicate material to consume at least some at least one of the calcium-containing salt and the calcium-containing mineral and the silicate material to form a calcium-enriched silicate.

2. The method, as recited in claim 1, wherein the silicate material comprises Mg2+ions.

3. The method, as recited in claim 2, wherein the silicate material has a magnesium concentration of at least 5 wt%.

4. The method, as recited in claim 2, wherein the heating the mixture forms magnesium oxide (MgO).

5. The method, as recited in claim 4, further comprising e) reacting MgO with CO2 to form at least one of Mg(COj), Mgs(CO3)4(OH)2, MgCO3 xH2O (where x is an integer), and dissolved Mg2+and bicarbonate (HCO3O ions.

6. The method of claim 1, wherein the calcium-containing salt comprises CaO.

7. The method of claim 1, wherein the providing the calcium-containing salt comprises heating a calcium salt CaY to form CaO and a gaseous byproduct, wherein Y is an anion or anions with 2- charge.

8. The method of claim 7, wherein CaY is at least one of CaCOs, CaSOr, Ca(NO3)2, and Ca(OH)2.

9. The method of claim 1, further comprising: before step (c) providing an additive; and during step (c) heating the additive, wherein the additive at least one of accelerates a reaction in step (c) and lowers a temperature required for the reaction in step (c).

10. The method of claim 9, wherein the additive comprises at least one of Na2SO4, K2SO4, NaOH, KOH, NaBO2, KBO2, NaCl, or KC1.

11. The method of claim 9, wherein the additive is not consumed.

12. The method of claim 1, after c further comprising providing CO2 to form at least one of CaCCh and dissolved Ca2+and bicarbonate HCO from the CO2 and the calcium-enriched silicate.

13. The method of claim 1, wherein the heating the mixture uses heat provided by at least one of an electrical source, a combustion source, and a thermal energy storage system source.

14. The method of claim 1, wherein the silicate material comprises silicon, oxygen, and at least one of Mg, Ca, Fe, Ti, Zr, V, Cr, Co, Ni, Cu, Zn, Li, Na, K, and Al.

15. The method of claim 1, wherein the calcium-containing salt comprises at least one of O2-, (NO3")2, OH , CO32; and SO42".

16. The method of claim 1, further comprising using the calcium-enriched silicate for at least one of CO2 mineralization by sequestering CO2, plant fertilization, and thin fdm deposition.

17. A method of sequestering CO2, comprising: a. providing a calcium-containing salt; b. providing a silicate material that contains a ratio of O to Si greater than 2: 1 ; c. heating a mixture of the calcium-containing salt and silicate material to consume some of the calcium-containing salt and silicate material to form a product comprising calcium- enriched silicate; and d providing CO2 to form at least one of CaCO3and dissolved Ca2+ and bicarbonate (HCO3“) ions from the CO2 and the calcium-enriched silicate.

18. The method, as recited in claim 17, wherein the silicate material comprises magnesium and where step c further forms MgO.

19. The method, as recited in claim 18, wherein step d forms at least one of Mg(CO3), Mg5(CO3)4(OH)2. MgCO3• XH2O Mg5(CO3)4(OH)2 • xH3O (where x is an integer), and dissolved Mg2+and bicarbonate (HCO3“) ions.

20. A method, comprising: a. providing at least one of an alkali metal-containing salt and alkali metalcontaining mineral; b. providing a silicate material comprising magnesium; and c. heating a mixture of the at least one of the alkali metal-containing salt and alkali metal-containing mineral with the silicate material to consume some of the at least one of the alkali metal-containing salt and alkali metal-containing mineral and the silicate material to form an alkali metal -enriched silicate.

21. The method, as recited in claim 20, wherein step c further forms MgO.

22. The method, as recited in claim 21, further comprising reacting MgO with CO2 to form at least one of Mg(CO3), Mg5(CO3)4(OH)2, MgCO3• xH3O Mgs(CO3)4(OH)2 • xH O (where x is an integer), and dissolved Mg2+and bicarbonate (HCO3“) ions.

23. The method, as recited in claim 20, wherein the silicate material has a magnesium concentration of at least 5 wt%.

24. The method of claim 20, further comprising: before step (c) providing an additive; and during step (c) heating the additive, wherein the additive at least one of accelerates a reaction in step (c) and lowers a temperature required for the reaction in step (c).

25. The method of claim 24, wherein the additive comprises at least one of Na3SO4, K2SO4, NaOH, KOH, NaBO2, KBO2, NaCl, or KC1.

26. A method, comprising: a. providing at least one of a calcium-containing salt and calcium-containing mineral; b. providing a silicate material that contains a ratio of O to Si greater than 2:1; c. heating a mixture of the at least one of a calcium-containing salt and calcium- containing mineral with the silicate material to consume some of the at least one of a calcium- containing salt and calcium-containing mineral and the silicate material to form a product comprising calcium-enriched silicate; and d. adding the product to soil to provide plant available Si.

27. The method, as recited in claim 26, wherein the silicate material comprises Mg2+ions.

28. The method, as recited in claim 27, wherein the silicate material has a magnesium concentration of at least 5 wt%.

29. The method, as recited in claim 27, wherein the heating the mixture forms magnesium oxide (MgO).

30. The method, as recited in claim 29, further comprising e) reacting MgO with CO2 to form at least one of Mg(CO3), Mg5(CO3)4(OH)2. MgCO3• xH20 Mg5(CO3)4(OH)2• xH20 (where x is an integer), and dissolved Mg2+and bicarbonate (HCO3“) ions.

31. The method of claim 26, wherein the calcium-containing salt comprises CaO.

32. The method of claim 26, wherein the providing the calcium-containing salt comprises heating a calcium salt CaY to form CaO and a gaseous byproduct, wherein Y is an anion or anions with 2- charge.

33. The method of claim 32, wherein CaY is at least one of CaCO3, CaSO4, Ca(NO3)2, and Ca(OH)2.

34. The method of claim 26, further comprising: before step (c) providing an additive; and during step (c) heating the additive, wherein the additive at least one of accelerates a reaction in step (c) and lowers a temperature required for the reaction in step (c).

35. The method of claim 34, wherein the additive comprises at least one of Na2SC>4, K2SO4, NaOH, KOH, NaBO2, KBO2, NaCl, or KC1.

36. A soil amendment comprising at least 2% plant available Si made by a method comprising: a. providing at least one of a calcium-containing salt and calcium-containing mineral; b. providing a silicate material that contains a ratio of O to Si greater than 2:1; and c. heating a mixture of the at least one of a calcium-containing salt and calcium- containing mineral with the silicate material to consume some of the at least one of a calcium- containing salt and calcium-containing mineral and the silicate material to form a product comprising calcium-enriched silicate.

37. The soil amendment, as recited in claim 36, wherein the silicate material comprises Mg2+ions.

38. The soil amendment, as recited in claim 37, wherein the silicate material has a magnesium concentration of at least 5 wt%.

39. The soil amendment, as recited in claim 37, wherein the heating the mixture forms magnesium oxide (MgO).

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