Method for concentrating divalent cations in aqueous solutions for portlandite and brucite production

Abstract

Provided herein are low-carbon dioxide-producing methods and systems for divalent metal hydroxide production (e.g., portlandite and / or brucite).

Description

[0001] METHOD FOE CONCENTEA TLNG DL VALENT CA TLONS LN A QUEOUS SOLOTLONS FOE POETLANDLTE AND EE VOLTE PEODOCTLON

[0002] RELATED APPLICATIONS

[0003] This application claims the benefit of U.S. Provisional Application No. 63 / 543,854, filed October 12, 2023, and U.S. Provisional Application No. 63 / 543,839, filed October 12, 2023, each of which is hereby incorporated by reference in its entirety.

[0004] BACKGROUND

[0005] Brucite and Portlandite are industrially important materials. Portlandite, in particular, could serve as a low carbon feedstock in PC production but, the conventional method for portlandite production involves limestone tCaCOs) thermal 1500°C decomposition (CaCOa) CaO + CO2) followed by slaking. Concrete is the second most used material globally after water. However, the production of cement (Portland Cement, PC), the binding agent in concrete, results in ~ 1 tonne [t] of CO2 emitted per t of PC produced. The direct CO2 emissions derive ~ 60 % from the thermochemical decomposition of CaCOa to produce CaO (“process emissions”, CaCOa CaO(S) + CO2(g), T - 800 °C, p = 1 bar) and ~ 40 % from the combustion of fossil fuels to heat the kiln to - 1500 °C (“combustion emissions”) to ensure the clinkering reactions typically requiring > 1 MWh of thermal energy per t of CaO produced.

[0006] Additionally, typical cement plant operations use ~ 10 % of electrical energy input and contribute - 10 % of indirect CO2 emissions. As a consequence, the annual global production of - 4.5 billion t of PC - from an installed capital asset base of > $ 400 billion including cement plants, adjacent limestone quarries, transport infrastructure, etc. - results in 8-to-10 % of anthropogenic CO2 emissions. Unfortunately, decarbonizing the heat source alone, e.g., through renewable heat, is insufficient to decarbonize PC production and supply constrained by the availability of renewable energy.

[0007] Accordingly, there is a need for low-carbon methods of producing portlandite and brucite.

[0008] SUMMARY OF THE INVENTION

[0009] In some aspects, the present disclosure provides in various embodiments electrolytic methods of portlandite and / or brucite production, comprising: (a) combining a mineral source comprising at least one divalent metal salt, an aqueous solution, and a chelating agent to produce a leachate comprising chelated divalent metal cations;

[0010] (b) subjecting the leachate to nanofiltration to produce a retentate comprising the divalent metal cations and a permeate comprising contaminant aqueous species;

[0011] (c) acidifying the retentate to release the chelating agent and produce a concentrated divalent metal cation solution;

[0012] (d) electrolyzing the concentrated divalent metal cation solution in an electrochemical cell to produce a) an anolyte and b) a catholyte comprising a solid divalent metal cation hydroxide and a catholyte supernatant; and

[0013] (e) separating the divalent metal cation hydroxide from the catholyte supernatant.

[0014] Another aspect of the present disclosure provides in various embodiments systems for producing portlandite and / or brucite, comprising: a single- or multi-step dissolution tank for contacting rocks with an aqueous solution and a chelating agent thereby producing a leachate comprising chelated divalent metal cations, wherein the multi-step dissolution tank comprises a rock inlet, a water inlet, a recycled anolyte inlet, a recycled catholyte supernatant inlet, and a leachate outlet; a filtration tank for filtering the leachate, wherein the filtration tank comprises a leachate inlet and a filtrate outlet; wherein the leachate outlet from the multi-step dissolution tank is coupled to the leachate inlet; and a nanofiltration tank for concentrating the chelated divalent metal cations in the leachate to produce a retentate comprising the chelated divalent metal cations, wherein the nanofiltration tank comprises a nanofiltration membrane a filtrate inlet, a retentate outlet, and a permeate outlet; wherein the filtrate inlet is coupled to the filtrate outlet from the filtration tank; and a separation tank for recovering the chelating agent as a solid and the divalent calcium as free ions in solution by acidification of the retentate (e.g., by mixing the retentate with a recycled anolyte stream); and an electrochemical cell for generating portlandite and / or brucite from the chelated divalent metal cations, wherein the electrochemical cell comprises an anode, a cathode, a retentate inlet, a permeate inlet, a catholyte outlet, and a recycled anolyte outlet; wherein the retentate inlet is coupled to the retentate outlet from the nanofiltration tank and is configured to pass the retentate from the nanofiltration tank into the electrochemical cell, the permeate inlet is coupled to the permeate outlet and is configured to pass the permeate from the nanofiltration tank into the electrochemical cell and the recycled anolyte outlet is coupled to the recycled anolyte inlet on the multi-step dissolution tank and is configured to pass recycled anolyte from the electrochemical cell to the multi-step dissolution tank; a settling / separation / filtration tank for separation of the portlandite and / or brucite from the catholyte comprising a catholyte inlet, a portlandite and / or brucite outlet, and a recycled catholyte supernatant outlet; wherein the catholyte inlet is coupled to the catholyte outlet from the electrochemical cell and is configured to receive catholyte from the electrochemical cell into the settling tank, and the recycled catholyte outlet is coupled to the recycled catholyte supernatant inlet on the multi-step dissolution tank and is configured to pass recycled catholyte from the settling tank into the multi-step dissolution tank.

[0015] In certain aspects, the present disclosure provides in various embodiments an electrolytic method of producing divalent metal hydroxide, comprising:

[0016] (a) combining a mineral source comprising at least one divalent metal salt with an aqueous solution to produce a leachate comprising divalent metal ions;

[0017] (b) capturing the divalent metal cations from the leachate;

[0018] (c) releasing the divalent metal cations, thereby producing a concentrated divalent metal cation solution;

[0019] (d) electrolyzing the concentrated divalent metal ion solution in an electrochemical cell to produce a) an anolyte and b) a catholyte comprising a solid divalent metal hydroxide and a catholyte supernatant; and

[0020] (e) separating the solid divalent metal hydroxide from the catholyte supernatant. Another aspect of the disclosure provides an electrolytic method of producing divalent metal hydroxide, comprising:

[0021] (a) combining a mineral source comprising minerals with an aqueous solution to produce an aqueous solution comprising divalent metal cations;

[0022] (b) passing the aqueous solution comprising divalent metal cations through an ion exchange material that retains the divalent metal cations; (c) releasing the divalent cations from the ion exchange material, thereby producing a concentrated divalent metal cation solution and regenerating the ion exchange material;

[0023] (d) electrolyzing the concentrated divalent metal cation solution in an electrochemical cell to produce a) an anolyte and b) a catholyte comprising a divalent metal hydroxide and a catholyte supernatant; and

[0024] (e) separating the divalent metal hydroxide from the catholyte supernatant.

[0025] In yet another aspect, the disclosure provides an electrolytic method of producing divalent metal hydroxide, comprising:

[0026] (a) combining a mineral source comprising minerals with an aqueous solution to produce an aqueous solution comprising divalent metal cations;

[0027] (b) contacting the aqueous solution comprising divalent metal cations with a chelating agent to produce a chelated divalent metal cation solution;

[0028] (c) subjecting the chelated divalent metal cation solution to nanofiltration to provide a retentate comprising divalent metal ions and a permeate comprising contaminant species;

[0029] (d) subjecting the retentate to an acidic pH swing to precipitate, recover, and recirculate the chelating agent and to produce a concentrated divalent metal cation solution;

[0030] (e) electrolyzing the concentrated divalent metal cation solution in an electrochemical cell to produce a) an anolyte and b) a catholyte comprising a solid divalent metal hydroxide and a catholyte supernatant; and

[0031] (f) separating the solid divalent metal hydroxide from the catholyte supernatant.

[0032] The present disclosure further provides systems for the production of divalent metal hydroxides.

[0033] BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a high-level process schematic for electrolytic production of portlandite according to embodiments described herein.

[0035] Figure 2 is the speciation of EDTA as a function of pH, showing its ability to form a complex with calcium at pH above 4.1,2

[0036] Figure 3 is (a) the dissolution rate of calcite at various pH in DIW, as compiled from Arvidson et al.,3(b) the equilibrium, thermodynamically modeled solubility limit of calcite as a function of pH, showing CO2 emission below pH 6, (c) the equilibrium, thermodynamically modeled speciation of carbonate species in solution as a function of pH.

[0037] Figure 4 is (a) the dissolution rate of calcite at pH 12 in the presence of increasing EDTA concentration4compared to a system devoid of EDTA,3(b) the dissolution rate of calcite at various pH, without3and with EDTA (0.25 M),4(c) calcium concentration observed by dissolving calcite in the presence of EDTA5compared to calcite equilibrium, thermodynamically modeled solubility limit.

[0038] Figure 5 shows (a) the rejection of calcium in a pure calcium (10 ppm) solution vs a calcium (10 ppm) + EDTA (100 ppm) solution as a function of pH,6(b) the rejection ratio between Ca-EDTA and NaHCOa as a function of pH.6

[0039] Figure 6 is a high-level process schematic for electrolytic production of solid divalent metal hydroxides (portlandite is exemplified) according to certain embodiments described herein. Figure 7 shows (a) The dissolution rate of several silicates as a function of pH, (b) the equilibrium, thermodynamically modeled solubility limit of a silica and calcium containing system as a function of pH (initial Ca / Si = 2).

[0040] Figure 8 shows the effect of pH on removal of Ca, and Mg using (a) Amberlite IRC 748,7(b) Duolite C206A resin,8and (c) Lewatit TP 207 and TP 208.9

[0041] Figure 9 The dissolution of calcite at room temperature in the presence of EDTA. (a) The increased solubility of calcite (i.e., Ca concentration) as a function of pH across a range of EDTA concentrations. The black dashed line shows the thermodynamically modeled solubility of calcite in a system devoid of EDTA. (b) The degassing of CO2 expressed as a molar percentage of total amount of aqueous and mineralized carbonates in the system as a function of the EDTA concentration and the initial pH of the solution. The dashed black line shows the thermodynamically modeled CO2 emission from calcite in a system devoid of EDTA, and the blue dotted line shows the CO2 emission of calcite in a system containing EDTA calculated, (c) The Ca-concentration at equilibrium at pH 9.5 and in the presence of 100 mmol / L of EDTA in MQW, a 0.5 mol / L NaCl solution, and simulated seawater (“Instant Ocean Seawater: IOSW”) for reagent calcite (AR Calcite) or limestone rock.

[0042] Figure 10 (a) The “initial” dissolution rate of calcite at high undersaturation (i.e., far from dissolution equilibrium) as a function of the initial pH of the solution across a range of EDTA concentrations. The data for dissolution occurring in MQW (“0 mmol / L EDTA”) are taken from the literature, (b) The measured and fitted relationship between the dissolution rate and the [Ca] / [EDTA] (molar) ratio, and (c) the dissolution rates of reagent grade calcite and limestone rock at pH 9.5 and in the presence of 100 mmol / L of EDTA in MQW, 0.5 mol / L NaCl, and simulated seawater (IOSW).

[0043] Figure 11 is a process schematic for electrolytic production of portlandite according to certain embodiments described herein.

[0044] DETAILED DESCRIPTION OF THE INVENTION

[0045] In certain embodiments, described herein is a low-(CO2)-emissions pathway that makes use of limestone within an aqueous electrochemical paradigm to produce portlandite (Ca(OH)2), which can be used as low-carbon feedstock for Portland Cement (PC) production. In some embodiments, the process described herein obviates the need for carbon capture and storage (CCS) for cement / lime decarbonization. Accordingly, described herein in various embodiments is a cost-effective, accessible, and scalable electrified solution for cement decarbonization at the site and scale of existing cement plants.

[0046] In some embodiments, the process described herein uses CaCCE as a Ca-source to make portlandite at ambient conditions (p,T) — while nearly eliminating direct CO2(g) emissions. In some embodiments, the process emits as low as 1.5 mol.% of the CO2 in the precursor CaCCh, equivalent to 9 kg CO2(g) per ton of Ca(OH)2.

[0047] The process advantageously may use a range of mineral sources, such as calcium and / or magnesium rock sources (such as those containing calcium or magnesium carbonate), to produce solid metal hydroxides such as portlandite and / or brucite with low or no CO2 emissions when carbonate mineral sources are used. In some embodiments, the process involves one, or a series of cascading dissolution reactors that extract divalent metal cations, from carbonate and / or silicate rocks. In certain embodiments, the filtrate passes through several nanofiltration stages to concentrate the metal cations in the retentate, targeting a range of 20 mM to 500 mM of calcium (as Ca2+) or greater. In some embodiments, the filtrate passes through several separation steps to separate the calcium and / or the magnesium from the various impurities present in solution (e.g., aqueous carbonate species, aqueous silica species, etc.), and includes several nanofiltration stages to concentrate the target ions in the retentate, targeting a range of 20 mM to 500 mM or greater of calcium (as Ca2+) and / or magnesium (as Mg2+). The retentate stream is then directed towards an electrolyzer cathode to produce brucite and / or portlandite at low temperatures (T < 40 °C), while the permeate is either recirculated after treatment or disposed depending on the process. The precipitated solid is then recovered, e.g., by filtration, settling, or centrifugation, and the supernatant may be redirected to the dissolution circuit. In some embodiments, efficient portlandite and / or brucite production can be fostered by favoring high cation concentrations in the electrolyzer.

[0048] In certain embodiments, the process comprises combining a mineral source comprising at least one divalent metal salt, particularly a divalent metal carbonate salt), an aqueous solution, and a chelating agent to produce a leachate comprising chelated divalent metal cations. In some embodiments, the process comprises combining a mineral source comprising at least one divalent metal salt with an aqueous solution to produce a leachate comprising divalent metal ions and capturing the divalent metal ions from the leachate.

[0049] Process comprising producing a leachate comprising chelated divalent metal cations.

[0050] In certain embodiments, the process comprises combining a mineral source comprising at least one divalent metal salt, an aqueous solution, and a chelating agent to produce a leachate comprising chelated divalent metal cations. Figure 1 presents an exemplary block flow diagram of certain embodiments of this process.

[0051] To assist with calcium and / or magnesium enrichment, ethylenediaminetetraacetic acid (EDTA) - a chelating agent - is proposed to increase the concentration of the divalent calcium and / or magnesium ions in the feed to the electrolyzer unit. EDTA has varying pKa values associated with several complexes of varying charge as follows:

[0052] 2.0 (H4EDTA HsEDTA + H+)

[0053] 2.7 (H3EDTA H2EDTA2+ H+)

[0054] 6.16 (H2EDTA2HEDTA3+ H+)

[0055] 10.26 (HEDTA3EDTA4+ H+)

[0056] EDTA may react with calcium and / or magnesium ions, effectively sequestering them in larger complexes1, provided that the EDTA is in a form with at least two negative charges (i.e., above pH 4, see the below illustration of the complexation of calcium with EDTA, and Figure 2).

[0057]

[0058] In certain embodiments, the mineral source comprises carbonate rocks, silicate rocks, or a combination thereof. In further embodiments, the mineral source comprises calcium- containing solids, magnesium-containing solids, or a combination thereof. In some embodiments, the mineral source comprises calcium carbonate. Calcium carbonate (i.e., CaCOa, calcite) dissolution rate (Figure 3a3) and solubility limit (Figure 3b) are both enhanced by acidic pH. But, at acidic pH, aqueous carbonate is present in solution primarily as H2CO3 (Figure 3c), which is typically at equilibrium with atmospheric CO2. As a result, calcite dissolution at acidic pH often generates CO2 gas, as modeled in Figure 3b. By maintaining a pH above 6, calcite may be dissolved without releasing CO2, but this is linked to a notable decrease in dissolution rate and solubility, as shown in Figure 3a3and Figure 3b, respectively.

[0059] Calcium complexation by EDTA has been shown to enhance calcite dissolution rates even at low EDTA concentration (Figure 4a3’4) and within a broad pH range (Figure 4b3’4). Thus, in certain embodiments of the process described herein, it is expected that EDTA will interact with calcium at a pH above 6 directly in the dissolution tank. In addition, calcium complexation with EDTA in the dissolution tank would remove its ability to precipitate, effectively increasing the solubility limit of the mineral (Figure 4c5).

[0060] Following complexation, the dissolution circuit effluent would then be filtered and concentrated further using a nanofiltration membrane, to reach the target 200 to 400 mM calcium concentration. The complexation of calcium (Ca mass = 40.08 Da) by EDTA yields large molecules (Ca-EDTA complex mass = 330.30-332.30 Da depending on its speciation2), which are approximately 8x larger than calcium ions. The complexation to a larger molecule increases the probability of calcium rejection by nanofiltration, thus resulting in more efficient concentration of calcium (Figure 5a6). In addition, EDTA can initially be introduced in di-sodium form, hence the feed solution may contain an excess of sodium cations (Na+), in addition to the Na+coming from the electrolyte salt. As a result, carbonate aqueous species - present primarily as HCOa2-in the pH range of interest of 6 to 8 (Figure 3c) - will tend to pair in solution with Na+to form aqueous NaHCOa. Thus, the larger EDTA-Ca complex may be separated from aqueous NaHCOa using a nanofiltration membrane that would help retain EDTA-Ca complex, all while allowing NaHCOa (mass = 84.01 Da) to pass though. The preferential retention of Ca- EDTA vis-a-vis NaHCOa has been observed in the literature using a commercial FilmTec NF40 membrane (Figure 5b6). This type of membrane was shown to be particularly efficient in retaining Ca-EDTA while allowing NaHCOa to pass through in the pH range of 6 to 8.6This would effectively concentrate calcium species in the retentate while separating it from carbonate species that could induce carbonate precipitation instead of portlandite formation in the later stages. A currently commercially available nanofiltration membrane useful in the present methods are commercially available, such the Sterlitech XN45 (Polypiperazine amide with pore size of -500 Da).

[0061] Following this, the EDTA could be separated from calcium by acid addition (Figure 2) and recovered and recycled upstream for re-use in the process. The retentate, high in divalent cations and low or lacking in EDTA and any undesirable species, then serves as the feed to the cathode, either directly or after another pH swing (for example by utilizing a recycled catholyte stream) to neutralize the acidified stream. The permeate would either be recirculated after treatment or disposed of depending on the process considered.

[0062] Accordingly, the provided herein in various embodiments are electrolytic methods of producing portlandite and / or brucite, comprising:

[0063] (a) combining a rock source comprising rocks, an aqueous solution, and a chelating agent to produce a leachate comprising chelated divalent calcium and / or magnesium ions;

[0064] (b) filtering the leachate to produce a filtrate comprising the chelated divalent calcium and / or magnesium ions;

[0065] (c) subjecting the filtrate to nanofiltration to produce a retentate comprising the divalent calcium and / or magnesium ions and a permeate;

[0066] (d) electrolyzing the retentate in an electrochemical cell to produce a) an anolyte and b) a catholyte comprising calcium and / or magnesium hydroxide and a catholyte supernatant; and (e) separating the calcium and / or magnesium hydroxide from a catholyte supernatant.

[0067] In certain embodiments, the mineral source comprises carbonate rocks, silicate rocks, or a combination thereof. In further embodiments, the mineral source comprises calcium- containing solids, magnesium-containing solids, or a combination thereof. The aqueous solution may comprise fresh water, catholyte supernatant, anolyte, or any combination thereof. In certain embodiments, the aqueous solution comprises fresh water, salt water, or seawater. In some embodiments, the aqueous solution comprises softened seawater, i.e., seawater preprocessed by nanofiltration to remove divalent cations such as magnesium that may complex with EDTA. The dissolution of the rock source and chelation to the chelating agent may occur in separate steps.

[0068] In certain embodiments, the leachate comprises greater than about 2 mM divalent calcium ions. In certain embodiments, the leachate comprises greater than about 5 mM divalent calcium ions. In certain embodiments, the leachate comprises greater than about 10 mM divalent calcium ions. In certain embodiments, the leachate comprises greater than about 25 mM divalent calcium ions. In certain embodiments, the leachate comprises greater than about 50 mM divalent calcium ions. In further embodiments, the leachate comprises greater than about 100 mM divalent calcium ions. In yet further embodiments, the leachate comprises greater than about 150 mM divalent calcium ions. In still further embodiments, the leachate comprises greater than about 200 mM divalent calcium ions. In certain embodiments, the leachate comprises greater than about 250 mM divalent calcium ions. In further embodiments, the leachate comprises greater than about 300 mM divalent calcium ions. In yet further embodiments, the leachate comprises greater than about 350 mM divalent calcium ions.

[0069] In certain embodiments, the leachate has a pH from about 0.5 and about 13.5. In further embodiments, the leachate has a pH of about 3 to about 11. In further embodiments, the leachate has a pH of about 3. In yet further embodiments, the leachate has a pH of about 4. In still further embodiments, the leachate has a pH of about 5. In certain embodiments, the leachate has a pH of about 6. In further embodiments, the leachate has a pH of about 7. In yet further embodiments, the leachate has a pH of about 8. In still further embodiments, the leachate has a pH of about 9. In certain embodiments, the leachate has a pH of about 10. In further embodiments, the leachate has a pH of about 11. In certain embodiments, the method further comprises filtering the leachate to prior to the nanofiltration step.

[0070] In certain embodiments, the filtrate has a pH from about 5 to about 6.

[0071] In certain embodiments, the retentate comprises greater than about 5 mM divalent metal cations. In certain embodiments, the retentate comprises greater than about 10 mM divalent metal cations. In certain embodiments, the retentate comprises greater than about 20 mM divalent metal cations. In certain embodiments, the retentate comprises greater than about 25 mM divalent metal cations. In certain embodiments, the retentate comprises greater than about 50 mM divalent metal cations. In further embodiments, the retentate comprises greater than about 100 mM divalent metal cations. In yet further embodiments, the retentate comprises greater than about 200 mM divalent metal cations. In still further embodiments, the retentate comprises greater than about 300 mM divalent metal cations. In certain embodiments, the retentate comprises greater than about 350 mM divalent metal cations.

[0072] In certain embodiments, the retentate has a pH from about 7 to about 12. In further embodiments, the retentate has a pH of about 7. In yet further embodiments, the retentate has a pH of about 8. In still further embodiments, the retentate has a pH of about 9. In certain embodiments, the retentate has a pH of about 10. In further embodiments, the retentate has a pH of about 11. In yet further embodiments, the retentate has a pH of about 12.

[0073] In certain embodiments, the permeate comprises less than about 10 mM divalent metal cations. In further embodiments, the permeate comprises less than about 9 mM divalent metal cations. In yet further embodiments, the permeate comprises less than about 8 mM divalent metal cations. In still further embodiments, the permeate comprises less than about 7 mM divalent metal cations. In certain embodiments, the permeate comprises less than about 6 mM divalent metal cations. In further embodiments, the permeate comprises less than about 5 mM divalent metal cations. In yet further embodiments, the permeate comprises less than about 4 mM divalent metal cations. In still further embodiments, the permeate comprises less than about 3 mM divalent metal cations. In certain embodiments, the permeate comprises less than about 2 mM divalent metal cations. In further embodiments, the permeate comprises less than 1 mM divalent metal cations.

[0074] In certain embodiments, the permeate has a pH from about 7 to about 9. In further embodiments, the permeate has a pH of about 7. In yet further embodiments, the permeate has a pH of about 8. In still further embodiments, the permeate has a pH of about 9. In certain embodiments, the catholyte supernatant comprises less than about 50 mM divalent metal cations. In further embodiments, the catholyte supernatant comprises less than 40 mM divalent metal cations. In yet further embodiments, the catholyte supernatant comprises less than 30 mM divalent metal cations. In still further embodiments, the catholyte supernatant comprises less than 20 mM divalent metal cations. In certain embodiments, the catholyte supernatant comprises less than 10 mM divalent metal cations. In further embodiments, the catholyte supernatant comprises less than 1 mM divalent metal cations.

[0075] In certain embodiments, the catholyte has a pH less than about 12.

[0076] In certain embodiments, the chelating agent is selected from ethylene-diamine- tetraacetic acid (EDTA), diethylene triamine penta methylene phosphonic acid (DTMPA, DTPMP), hydroxy-ethane diphosphonic acid (HEDP), ethylenediamine N,N'-disuccinic acid (EDDS), methyl glycine di-acetic acid (MGDA), diethylenetriaminepentaacetic acid (DTPA), propylene diamine tetraacetic acid (PDTA), 2-hydroxypyridine-N-oxide (HPNO), methyl glycine diacetic acid (MGDA), glutamic acid N.N-diacetic acid (N,N-dicarboxymethyl glutamic acid tetrasodium salt (GLDA) and nitrilotriacetic acid (NTA), glucose, fructose, galactose, sucrose, lactose, mannose, and any combination thereof. In further embodiments, the chelating agent is ethylenediaminetetraacetic acid.

[0077] In certain embodiments, the concentration of the chelating agent, preferably EDTA, is from about 10 mM to about 500 mM. In further embodiments, the concentration of the chelating agent is about 10 mM. In yet further embodiments, the concentration of the chelating agent is about 100 mM. In still further embodiments, the concentration of the chelating agent is about 200 mM. In certain embodiments, the concentration of the chelating agent is about 300 mM. In further embodiments, the concentration of the chelating agent is about 400 mM. In yet further embodiments, the concentration of the chelating agent is about 500 mM.

[0078] In certain embodiments, the chelating agent is introduced stoichiometrically vis-a-vis calcium and or / magnesium. In further embodiments, in the case of carbonate rock dissolution - the bicarbonate in solution is charge compensated by sodium, allowing the separation of the Ca-EDTA or Mg-EDTA complex (retentate) and Na-carbonate / bicarbonate (depending on the pH). This inhibits CO2 from degassing from the solution such that the sodium carbonate / bicarbonate is then discarded in the effluent stream. This can further be fostered by the addition of Na (e.g., in the form of a soluble salt such as sodium chloride) as an additive. In certain embodiments, the production of divalent metal hydroxide occurs at a temperature from about 20 °C to about 40 °C. In further embodiments, the production of divalent metal hydroxide occurs at a temperature of about 20 °C. In yet further embodiments, the production of divalent metal hydroxide occurs at a temperature of about 25 °C. In still further embodiments, the production of divalent metal hydroxide occurs at a temperature of about 30 °C. In certain embodiments, the production of divalent metal hydroxide occurs at a temperature of about 35 °C. In further embodiments, the production of divalent metal hydroxide occurs at a temperature of about 40 °C.

[0079] In certain embodiments, the nanofiltration is accomplished using a nanofiltration membrane. Pressure-driven membrane technology has become increasingly prevalent, notably nanofiltration owing to its unique properties: tailored selectivity, lower pressure, higher flow rates, and lower investment and operating costs vis-a-vis well-established reverse osmosis. Non-limiting examples of nanofiltration membranes are provided in Table 1. In some embodiments, the nanofiltration membrane is selected from the nanofiltration membranes listed in Table 1.

[0080] Table 1. Commercially available nanofiltration membranes including the nominal pore size, pure water normalized flux, and divalent and monovalent salt rejections.

[0081] In some embodiments, the nanofiltration membrane has a pore size in a range of about 500 Da to about 1000 Da. In yet further embodiments, the nanofiltration membrane has a pore size in a range of about 500 Da. In still further embodiments, the nanofiltration membrane has a pore size in a range of about 600 Da. In certain embodiments, the nanofiltration membrane has a pore size in a range of about 700 Da. In further embodiments, the nanofiltration membrane has a pore size in a range of about 800 Da. In yet further embodiments, the nanofiltration membrane has a pore size in a range of about 900 Da. In still further embodiments, the nanofiltration membrane has a pore size in a range of about 1000 Da.

[0082] In certain embodiments, the method further comprises recycling the catholyte supernatant back to step (a). In further embodiments, the method further comprises recycling the anolyte back into step (a) and / or step (c). In yet further embodiments, the method further comprises recovering the chelating agent prior to step (d). In still further embodiments, the method further comprises recycling the chelating agent back into step (a).

[0083] Those of skill in the art will recognize that recycling of waste streams can be accomplished with a variety of configurations, of which the particular configurations disclosed herein are merely exemplary. The recycling may be performed across two or more parallel streams, e.g., wherein the waste from one stream is recycled into a second, whose waste may then be recycled back onto the first. In other embodiments, such as when multiple series of dissolution tanks or multiple filtration tanks are employed, the waste streams may be arranged so that waste from one is recycled to the next, which is recycled to the next, and the last one is recycled back to the first. Any such configurations will be understood to be within the spirit and intent of the systems and methods disclosed herein.

[0084] In some embodiments, the divalent metal cation comprises a divalent alkaline earth metal cation. In preferred embodiments, the divalent metal cation comprises Ca2+, Mg2+, or both. In some embodiments, the divalent metal hydroxide comprises calcium hydroxide, magnesium hydroxide, or both.

[0085] In some embodiments, the process emits less than 20 mol % of the of the CChfrom the mineral source (e.g., CaCCh or MgCCh). In some embodiments, the process emits less than 15 mol % of the of the CO2 from the mineral source. In some embodiments, the process emits less than 10 mol % of the of the CO2 from the mineral source. In some embodiments, the process emits less than 5 mol % of the of the CO2 from the mineral source. In some embodiments, the process emits less than 4 mol % of the of the CO2 from the mineral source. In some embodiments, the process emits less than 3 mol % of the of the CO2 from the mineral source. In some embodiments, the process emits less than 2 mol % of the of the CO2 from the mineral source. In some embodiments, the process emits less than 1 mol % of the of the CO2 from the mineral source. In some embodiments, the process emits as low as 1.5 mol % of the of the CO2 from the mineral source. In some embodiments, the process emits as low as 1 mol % of the of the CO2 from the mineral source. In some embodiments, the process emits as low as 0.5 mol % of the of the CO2 from the mineral source.

[0086] In some aspects, provided herein are systems for producing portlandite and / or brucite, comprising: a single- or multi-step dissolution tank for contacting rocks with an aqueous solution and a chelating agent thereby producing a leachate comprising chelated divalent metal cations, wherein the multi-step dissolution tank comprises a rock inlet, a water inlet, a recycled anolyte inlet, a recycled catholyte supernatant inlet, and a leachate outlet; a filtration tank for filtering the leachate, wherein the filtration tank comprises a leachate inlet and a filtrate outlet; wherein the leachate outlet from the multi-step dissolution tank is coupled to the leachate inlet; and a nanofiltration tank for concentrating the chelated divalent metal cations in the leachate to produce a retentate comprising the chelated divalent metal cations, wherein the nanofiltration tank comprises a nanofiltration membrane, a filtrate inlet, a retentate outlet, and a permeate outlet; wherein the filtrate inlet is coupled to the filtrate outlet from the filtration tank; and a separation tank for recovering the chelating agent as a solid and the divalent calcium as free ions in solution by acidification of the retentate (e.g., by mixing the retentate with a recycled anolyte stream); and an electrochemical cell for generating portlandite from the chelated divalent metal cations, wherein the electrochemical cell comprises an anode, a cathode, a retentate inlet, a permeate inlet, a catholyte outlet, and a recycled anolyte outlet; wherein the retentate inlet is coupled to the retentate outlet from the nanofiltration tank and is configured to pass the retentate from the nanofiltration tank into the electrochemical cell, the permeate inlet is coupled to the permeate outlet and is configured to pass the permeate from the nanofiltration tank into the electrochemical cell and the recycled anolyte outlet is coupled to the recycled anolyte inlet on the multi-step dissolution tank and is configured to pass recycled anolyte from the electrochemical cell to the multi-step dissolution tank; a settling / separation / filtration tank for separation of the portlandite from the catholyte comprising a catholyte inlet, a portlandite outlet, and a recycled catholyte supernatant outlet; wherein the catholyte inlet is coupled to the catholyte outlet from the electrochemical cell and is configured to receive catholyte from the electrochemical cell into the settling tank, and the recycled catholyte outlet is coupled to the recycled catholyte supernatant inlet on the multi-step dissolution tank and is configured to pass recycled catholyte from the settling tank into the multi-step dissolution tank.

[0087] Process comprising producing a leachate comprising divalent metal ions, and capturing the divalent metal ions from the leachate.

[0088] In some embodiments, the process comprises combining a mineral source comprising at least one divalent metal salt with an aqueous solution to produce a leachate comprising divalent metal ions, and capturing the divalent metal ions from the leachate. Figure 6 presents an exemplary block flow diagram of the process according to certain embodiments. In some embodiments, the process uses ion exchange to assist with concentrating the divalent metal cations by passing an aqueous divalent cation solution through an ion exchange material. In further embodiments, a combination of selective ion-exchange materials and a chelating agent, such as ethylenediaminetetraacetic acid (EDTA), may be used to increase the concentration of the divalent calcium and / or magnesium ions in the feed to the electrolyzer unit. Both divalent ions can effectively be chelated by EDTA above pH 4. EDTA is only one of many examples of potential chelating agents. Chelating agents useful in the present methods include, without limitation, ethylene-diamine-tetraacetic acid (EDTA), diethylene triamine penta methylene phosphonic acid (DTMPA, DTPMP), hydroxy-ethane diphosphonic acid (HEDP), ethylenediamine N,N'-disuccinic acid (EDDS), methyl glycine di-acetic acid (MGDA), diethylene triamine pentaacetic acid (DTPA), propylene diamine tetraacetic acid (PDTA), 2-hydroxypyridine-N-oxide (HPNO), methyl glycine diacetic acid (MGDA), glutamic acid N.N-diacetic acid (N,N-dicarboxymethyl glutamic acid tetrasodium salt (GLDA) nitrilotriacetic acid (NTA), glucose, fructose, galactose, sucrose, lactose, mannose, or any combination thereof.

[0089] Calcium carbonate’s (i.e., CaCOa, calcite) dissolution rate (Figure 3a1) and solubility limit (Figure 3b) are both enhanced at acidic pH. But, at acidic pH, aqueous carbonate is present in solution primarily as H2CO3 (Figure 3c) and is typically at equilibrium with atmospheric CO2. As a result, calcite dissolution at acidic pH can release CO2 gas, as modeled in Figure 3b. By maintaining a pH above 6, calcite may be dissolved without releasing CO2, but this is linked to a notable decrease in dissolution rate and solubility, as shown in Figure 3a3and Figure 3b, respectively.

[0090] The dissolution rate and solubility limit of silicate rocks is also pH limited, where high dissolution rates are typically observed at very low pH (Figure 7a). But, at acidic to neutral pH, the solubility of silicate rocks is limited by the low solubility limit of amorphous silica (Figure 7b). The dissolution rate of silicates as a function of pH follows a V-shape, hence high dissolution rates are also observed at higher pH (Figure 7a). However, in that instance, silicate solubility is limited by the formation of calcium silicate hydrate (C-Si-H) compounds that will consume the calcium in solution (Figure 7b), which is to be avoided. For this reason, it is preferable to work in acidic conditions.

[0091] A proposed pathway to concentrate calcium and / or magnesium while separating them from other ionic species in solution is to use an ion-exchange material that is selective toward divalent cations. An ion-exchange material would be used after the carbonate / silicate dissolution step to retain calcium and / or magnesium while allowing the aqueous contaminant species to pass through. Calcium and / or magnesium may then be released and concentrated during the regeneration step by using a strongly acidic stream produced at the anode of the electrolyzer; the amount of acid solution for regenerating the ion-exchange / -chelation material is pH, and material dependent, and utilizes a solution with a very low pH, which advantageously captures the divalent metal ion in a smaller solution volume than initially used in the dissolution step. Note that, for carbonate rocks, CO2 emissions during the process can be reduced or prevented by using a dissolution medium at pH >6, meaning that it is preferable to work with sodium-containing ion exchange material instead of protonated ionexchange material. In such embodiments, the method may include two regeneration steps: first with a strongly acidic stream to recover calcium, then with a strongly basic NaOH solution to replace H+by Na+within the ion exchange material.

[0092] A range of ion exchange materials are commercially available for the purposes detailed above. To selectively capture Ca and / or Mg ions dissolved in some solutions, cation exchange resins with chelating functional groups such as iminodiacetic acid (IDA) or strongly acidic sulfonic groups can be used. Non-limiting examples of commercially available ion exchange resins and zeolite are listed in Table 2. All are suitable for this type of process, and acid strength may be varied during regeneration depending on the ion exchange material used. The conditions for resin regeneration are dependent on the resin type and the corresponding functional group. For example, a weakly acidic resin (pKa 4 to 9) may act more favorably in lower acid concentrations for regeneration than strongly acidic resins.

[0093] Table 2. Commercially available ion exchange materials and their properties. Gibbs free energies highlighted with the symbol * were estimated from the values provided at 15, 35, and 45 °C in the references.

[0094] As shown in Figure 8, the pH for capturing alkaline-earth metals varies according to the type of cation exchange material used. This is noteworthy for the process detailed above, as the pH of the feed solution may vary between 6 and 8 for carbonate dissolution, and below 2 for silicate rocks. Alternatively, pH swing may be used for silicate rocks dissolution feed for more efficient concentration steps. The pH swing is preferably conducted by contacting the filtered aqueous solution with high-pH (e.g., pH 13) recirculated catholyte. With some feedstocks, the pH of the filtered aqueous solution may naturally increase up to near-neutral pH during the rock dissolution. The type of resin should be selected based on (A) its capacity to remove divalent cations from solution at the pH of interest for carbonate dissolution (e.g., pH 6 to 8), and for silicate dissolution (e.g., pH below 2 with potential pH swing), and (B) its capacity to be efficiently regenerated using a strongly acidic stream.

[0095] Following that step, further divalent metal cation concentration may be performed. The enriched feed may be recirculated into multiple dissolution tanks following multiple ion exchange steps: the removal of one or multiple aqueous limiting species (e.g., carbonate species for carbonate rocks dissolution, or aqueous silica for silicate rocks dissolution) will help promote the dissolution of the various feed rocks. In such embodiments, increasing ion exchange material may advantageously be used at each step.

[0096] Alternatively, or jointly, the concentrated divalent metal cation feed may be further concentrated using nanofiltration (NF) to attain the target concentration of 20 to 500 mM, or greater. Utilizing a chelating agent, such as EDTA, may help increase the efficiency of the NF step, whereby the complexation - for example - of calcium (Ca mass = 40.08 Da) by EDTA (Ca-EDTA average complex mass = 331.30 Da between pH 4 and 121 7) yields larger molecules, compared to calcium ions alone, rendering the sized-based concentration step of the NF much more efficient at neutral pH (a).

[0097] Accordingly, the present invention provides in various embodiments electrolytic methods of producing divalent alkaline metal hydroxide, comprising: (a) combining a mineral source comprising at least one divalent metal salt with an aqueous solution to produce a leachate comprising divalent metal ions;

[0098] (b) capturing the divalent metal cations from the leachate;

[0099] (c) releasing the divalent metal cations, thereby producing a concentrated divalent metal cation solution;

[0100] (d) electrolyzing the concentrated divalent metal ion solution in an electrochemical cell to produce a) an anolyte and b) a catholyte comprising a solid divalent metal hydroxide and a catholyte supernatant; and

[0101] (e) separating the solid divalent metal hydroxide from the catholyte supernatant.

[0102] Any method of capturing a divalent metal cation form an aqueous solution may be suitable in the present methods. Capturing the cations refers to reversible formation of a complex with the cations that facilitates their separation from other components of the solution, either by size, charge, or by being fixed in position relative to the flowable solution. Any approach to selective and reversible capture of the divalent cations can be employed in the methods and systems disclosed herein. For example, capturing a divalent metal cation can include chelating the divalent metal cations using a chelating agent, passing the aqueous divalent metal cation solution through an ion exchange membrane, contacting the aqueous solution with a divalent metal cation binding agent, contacting the aqueous solution with a divalent metal cation adsorbing agent, or any combination thereof.

[0103] In more particular embodiments, the present invention provides electrolytic methods of producing divalent alkaline metal hydroxide, comprising:

[0104] (a) combining a mineral source comprising minerals with an aqueous solution to produce an aqueous solution comprising divalent metal cations;

[0105] (b) passing the aqueous solution comprising divalent metal cations through an ion exchange material that retains the divalent metal cations;

[0106] (c) releasing the divalent cations from the ion exchange material, thereby producing a concentrated divalent metal cation solution and regenerating the ion exchange material;

[0107] (d) electrolyzing the concentrated divalent metal cation solution in an electrochemical cell to produce a) an anolyte and b) a catholyte comprising a divalent metal hydroxide and a catholyte supernatant; and

[0108] (e) separating the divalent metal hydroxide from the catholyte supernatant. In some embodiments, the present invention provides electrolytic methods of producing divalent metal hydroxide, comprising:

[0109] (a) combining a mineral source comprising minerals with an aqueous solution to produce an aqueous solution comprising divalent metal cations;

[0110] (b) contacting the aqueous solution comprising divalent metal cations with a chelating agent to produce a chelated divalent metal cation solution;

[0111] (c) subjecting the chelated divalent metal cation solution to nanofiltration to provide a retentate comprising divalent metal ions and a permeate comprising contaminant species;

[0112] (d) subjecting the retentate to an acidic pH swing to produce a concentrated divalent metal cation solution;

[0113] (e) electrolyzing the concentrated divalent metal cation solution in an electrochemical cell to produce a) an anolyte and b) a catholyte comprising a solid divalent metal hydroxide and a catholyte supernatant; and

[0114] (f) separating the solid divalent metal hydroxide from the catholyte supernatant.

[0115] In some embodiments, releasing the divalent metal cation from the ion exchange material comprises contacting the ion exchange material with an acidic solution. In some embodiments, subjecting the retentate to an acidic swing also assists in precipitating and recovering the chelating agent. The recovered chelating agent may further be recirculated back in to the process.

[0116] In certain embodiments, the mineral source comprises calcium, magnesium, or both. In some embodiments, the mineral source comprises carbonate rocks, silicate rocks, slags, or fly ashes. In some embodiments, the method further comprises filtering the aqueous solution comprising divalent metal cations prior to step (b). In some embodiments, the aqueous solution of step (a) comprises water, catholyte supernatant, anolyte, or any combination thereof. In some embodiments, the aqueous solution of step (a) further comprises a sodium soluble salt. In certain embodiments, the aqueous solution comprises of step (a) comprises fresh water, salt water, or seawater. In some embodiments, the aqueous solution of step (a) comprises softened seawater, i.e., seawater preprocessed by nanofiltration to remove divalent cations such as magnesium that may complex with EDTA. In preferred embodiments, the divalent metal cation is a divalent metal cation, preferably Ca2+, Mg2+, or both. In various embodiments, the aqueous solution comprising divalent metal cations comprises greater than about 2 mM divalent metal cations. In some embodiments, the aqueous solution comprising the divalent metal cations comprises greater than about 50 mM divalent metal cations. In some embodiments, the aqueous solution from step (a) has a pH from about 0.5 to about 12. In certain embodiments, the mineral source comprises carbonate rocks. In certain such embodiments, the aqueous solution from step (a) has a pH from about 6 to about 8. In other embodiments, the mineral source comprises silicate rocks. In certain such embodiments, the aqueous solution from step (a) has a pH less than 2.

[0117] In certain embodiments, the ion exchange material is a protonated ion exchange material. In further embodiments, the ion exchange material is a sodium-containing ion exchange material. In yet further embodiments, the method further comprises contacting the ion exchange material with sodium hydroxide after the contacting with the acidic solution. In still further embodiments, the ion exchange material comprises iminodiacetic acid, sulfonic acid, or both. In certain embodiments, the ion exchange material is zeolite A.

[0118] In certain embodiments, the chelating agent is selected from ethylene-diamine- tetraacetic acid (EDTA), diethylene triamine penta methylene phosphonic acid (DTMPA, DTPMP), hydroxy-ethane diphosphonic acid (HEDP), ethylenediamine N,N'-disuccinic acid (EDDS), methyl glycine di-acetic acid (MGDA), diethylene triamine pentaacetic acid (DTPA), propylene diamine tetraacetic acid (PDTA), 2-hydroxypyridine-N-oxide (HPNO), methyl glycine diacetic acid (MGDA), glutamic acid N.N-diacetic acid (N,N- dicarboxymethyl glutamic acid tetrasodium salt (GLDA) nitrilotriacetic acid (NTA), glucose, fructose, galactose, sucrose, lactose, mannose, and any combination thereof.

[0119] In certain embodiments, the chelating agent is ethylenediaminetetraacetic acid. In further embodiments, the concentration of ethylenediaminetetraacetic acid is from about 10 to about 1000 mM. In further embodiments, ethylenediaminetetraacetic acid is stoichiometrically introduced vis-a-vis calcium and / or magnesium. In the case of carbonate rock dissolution, the bicarbonate in solution is charge-compensated by sodium, allowing the separation of the Ca-EDTA or Mg-EDTA complex (retentate) and Na-carbonate / bicarbonate (depending on the pH). This inhibits CO2 from degassing from the solution such that the sodium carbonate / bicarbonate is then discarded in the effluent stream. This can further be fostered by the addition of Na (e.g., in the form of a soluble salt) as an additive. Thus, the present methods can advantageously extract metal species from carbonate rocks without releasing CO2. For example, portlandite may be produced using limestone as a feedstock without degassing CO2.

[0120] In certain embodiments, the method further comprises subjecting the concentrated divalent metal cation solution to nanofiltration. In some embodiments, the nanofiltration is accomplished using a nanofiltration membrane. Nanofiltration membranes are commercially available as known to those skilled in the art. Non-limiting examples of nanofiltration membranes are provided in Table 1. In some embodiments, the nanofiltration membrane is selected from the nanofiltration membranes listed in Table 1. One of many non-limiting examples of a useful nanofiltration membrane is a Sterlitech XN45 membrane (Polypiperazine amide with pore size of -500 Da). In further embodiments, the nanofiltration membrane has a pore size in a range of about 500 Da to about 1000 Da. In yet further embodiments, the nanofiltration membrane has a pore size in a range of about 500 Da. In still further embodiments, the nanofiltration membrane has a pore size in a range of about 600 Da. In certain embodiments, the nanofiltration membrane has a pore size in a range of about 700 Da. In further embodiments, the nanofiltration membrane has a pore size in a range of about 800 Da. In yet further embodiments, the nanofiltration membrane has a pore size in a range of about 900 Da. In still further embodiments, the nanofiltration membrane has a pore size in a range of about 1000 Da.

[0121] In certain embodiments, the concentrated divalent metal ion solution comprises greater than about 2 mM divalent metal ions. In further embodiments, the concentrated divalent metal ion solution comprises greater than about 20 mM divalent metal ions. In yet further embodiments, the concentrated divalent metal ion solution comprises from about 200 to about 500 mM divalent metal ions.

[0122] In certain embodiments, the permeate has a pH from about 5 to about 10. In further embodiments, the permeate comprises less than 10 mM divalent metal ions. In yet further embodiments, the permeate comprises less than 1 mM divalent metal ions.

[0123] In certain embodiments, the retentate has a pH from about 7 to about 12. In certain such embodiments, the retentate has a pH from about 7 to about 9 for brucite production, and from about 7 to about 12 for portlandite production. In further embodiments, the retentate comprises greater than about 10 mM divalent metal ions. In yet further embodiments, the retentate comprises greater than about 200 mM divalent metal ions. In still further embodiments, the retentate comprises from about 200 to about 500 mM divalent metal ions. In certain embodiments, the catholyte comprises less than about 50 mM divalent metal ions. In further embodiments, the catholyte has a pH less than about 12.

[0124] In yet further embodiments, the production of divalent metal hydroxide occurs at less than about 40 °C. In still further embodiments, the method further comprises recycling the catholyte supernatant. In certain embodiments, the method further comprises recycling the anolyte. In further embodiments, the acidic solution of step (d) comprises recycled anolyte. In yet further embodiments, the method further comprises repeating steps (a) to (d) at least one additional time.

[0125] Those of skill in the art will recognize that recycling of waste streams can be accomplished with a variety of configurations, of which the particular configurations disclosed herein are merely exemplary. The recycling may be performed across two or more parallel streams, e.g., wherein the waste from one stream is recycled into a second, whose waste may then be recycled back onto the first. In other embodiments, such as when multiple series of dissolution tanks or multiple filtration tanks are employed, the waste streams may be arranged so that waste from one is recycled to the next, which is recycled to the next, and the last one is recycled back to the first. Any such configurations will be understood to be within the spirit and intent of the systems and methods disclosed herein.

[0126] In some embodiments, the process emits less than 20 mol % of the of the CChfrom the mineral source (e.g., CaCCh or MgCCh). In some embodiments, the process emits less than 15 mol % of the of the CO2 from the mineral source. In some embodiments, the process emits less than 10 mol % of the of the CO2 from the mineral source. In some embodiments, the process emits less than 5 mol % of the of the CO2 from the mineral source. In some embodiments, the process emits less than 4 mol % of the of the CO2 from the mineral source. In some embodiments, the process emits less than 3 mol % of the of the CO2 from the mineral source. In some embodiments, the process emits less than 2 mol % of the of the CO2 from the mineral source. In some embodiments, the process emits less than 1 mol % of the of the CO2 from the mineral source. In some embodiments, the process emits as low as 1.5 mol % of the of the CO2 from the mineral source. In some embodiments, the process emits as low as 1 mol % of the of the CO2 from the mineral source. In some embodiments, the process emits as low as 0.5 mol % of the of the CO2 from the mineral source.

[0127] In certain aspects provided herein are systems for producing a divalent metal hydroxide comprising: a multi-step dissolution tank for contacting a mineral source with an aqueous solution thereby producing an aqueous solution comprising divalent metal cations, wherein the multi- step dissolution tank comprises a mineral source inlet, an aqueous solution inlet, a recycled anolyte inlet, a recycled catholyte supernatant inlet, and an outlet; an optional filtration tank for filtering the aqueous solution comprising divalent metal cations, wherein the filtration tank comprises a filtration tank inlet and an outlet; and wherein the outlet from the multi-step dissolution tank is coupled to the filtration tank inlet; and an optional ion exchange tank for contacting the aqueous solution comprising the divalent metal cations with an ion exchange material and for contacting the ion exchange material with an acidic solution, thereby producing a concentrated divalent metal cation solution and regenerating the ion exchange material, wherein the ion exchange tank comprises an inlet to receive the aqueous solution comprising divalent metal cations and a concentrated divalent metal cation solution outlet; and wherein the outlet from the multi-step dissolution tank or the outlet from the filtration tank, when present, is coupled to the ion exchange tank inlet; and an electrochemical cell for generating the divalent metal hydroxide from the concentrated divalent metal cation solution, wherein the electrochemical cell comprises an anode, a cathode, a concentrated divalent metal cation solution inlet, a catholyte outlet, and an anolyte outlet; wherein the concentrated divalent metal cation solution inlet is coupled to outlet from the ion exchange tank, when present, the outlet from the filtration tank, when present, or the outlet from multi-step dissolution tank and is configured to pass the concentrated divalent metal cation solution from the ion exchange tank, when present, the filtration tank, when present, or the multi-step dissolution tank into the electrochemical cell, and the recycled anolyte outlet is coupled to the recycled anolyte inlet on the multi-step dissolution tank and is configured to pass anolyte supernatant from the electrochemical cell to the multi-step dissolution tank; a settling tank, filtration or centrifugation system for separation of a solid divalent metal hydroxide from the catholyte supernatant comprising a catholyte inlet, a solid metal hydroxide outlet, and a recycled catholyte supernatant outlet; wherein the catholyte supernatant inlet is coupled to the catholyte supernatant outlet from the electrochemical cell and is configured to receive catholyte from the electrochemical cell into the settling tank, and the recycled catholyte outlet is coupled to the recycled catholyte supernatant inlet on the multi-step dissolution tank and is configured to pass the catholyte supernatant from the settling tank into the multi-step dissolution tank.

[0128] In some embodiments, the system further comprises: a nanofiltration tank for further producing a chelated divalent metal ion solution, wherein the nanofiltration tank comprises a nanofiltration membrane, a concentrated divalent metal cation solution inlet, and a chelated divalent metal cation solution outlet; wherein the concentrated divalent metal ion solution inlet is coupled to the concentrated divalent metal ion solution outlet from the ion exchange tank, and the concentrated divalent metal ions outlet is coupled to the concentrated divalent metal ion inlet on the electrochemical cell.

[0129] Definitions

[0130] Unless otherwise defined herein, scientific and technical terms used in this application shall have the meanings that are commonly understood by those of ordinary skill in the art.

[0131] Chemistry terms used herein, unless otherwise defined herein, are used according to conventional usage in the art, as exemplified by “The McGraw-Hill Dictionary of Chemical Terms”, Parker S., Ed., McGraw-Hill, San Francisco, C.A. (1985).

[0132] All of the above, and any other publications, patents and published patent applications referred to in this application are specifically incorporated by reference herein. In case of conflict, the present specification, including its specific definitions, will control.

[0133] As used herein, the terms “optional” or “optionally” mean that the subsequently described event or circumstance may occur or may not occur, and that the description includes instances where the event or circumstance occurs as well as instances in which it does not.

[0134] Certain ranges are presented herein with numerical values being preceded by the term “about.” As used herein, the terms “substantially” and “about” are used to describe and account for small variations. When used in conjunction with an event or circumstance, the terms can refer to instances in which the event or circumstance occurs precisely as well as instances in which the event or circumstance occurs to a close approximation. For example, when used in conjunction with a numerical value, the terms can encompass a range of variation of less than or equal to ±10% of that numerical value, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%. As used herein, the term “nanofiltration” refers to a membrane liquid- separation technology. Nanofiltration provides high rejection of larger-sized species (e.g., above 1000 Da) and multivalent ions on a size and charge exclusion basis, and low rejection of monovalent ions on a charge exclusion basis.

[0135] As used herein, “capturing the divalent metal ions” may be accomplished using an ion exchange material, chelating agent, intercalation, and / or binding.

[0136] As used herein, “releasing the divalent metal ion” may be accomplished by lowering the pH of the solution. For example, decreasing the pH of a solution can lead to precipitation and regeneration of a chelating agent.

[0137] EXAMPLES

[0138] The invention now being generally described, it will be more readily understood by reference to the following examples which are included merely for purposes of illustration of certain aspects and embodiments of the present invention and are not intended to limit the invention.

[0139] Materials

[0140] Solids: Two calcium precursors were used: an analytical reagent grade (AR) grade calcite sample (> 99 mass %), and a high-purity limestone rock. The AR calcite was used as received. The limestone rock was ground to a fine powder in a planetary ball mill and sieved to between 30 pm and 90 pm to retrieve a particle size distribution similar to that of the AR- calcite. Both samples were fully characterized, as described below. The results are summarized in Table 3.

[0141] Solids: analytical reagent grade (AR) grade calcite (> 99 mass %) was used as received. Limestone rock was ground to a fine powder in a planetary ball mill and sieved to between 30 pm and 90 pm to retrieve a particle size distribution similar to that of the AR-calcite. Both samples were fully characterized, as described below. The results are summarized in Table 3.

[0142] Table 3. The characterization of the AR calcite and the limestone samples. The particle size distribution from light scattering analysis, the bulk oxide composition from XRF and TGA analysis, and the mineral composition from XRD analysis are provided.

[0143]

[0144] Solutions: solid H4EDTA powder (> 99 mass %) and solid NaOH powder (> 99 mass %) were used as received to prepare EDTA-containing solutions. Unless specified, all solutions were prepared with 18 MQ.cm MilliQ® water (MQW). In some instances, NaCl- containing MQW or simulated seawater (i.e., synthetic Instant Ocean© seawater) were used instead of pure MQW.

[0145] Membranes: Eight commercial NF membranes were selected for screening for separation steps 2-i, 2-ii, and 2-iii based on common performance parameters, i.e., the normalized permeate flux and observed rejections (Table 1, above).

[0146] Solid-phase analysis

[0147] Particle size distribution: The particle size distribution (PSD) of the solids was measured by light scattering from dilute suspensions of the powders in water using a Beckman Coulter light scattering analyzer LS 13-320. The uncertainty in the light scattering analysis was estimated to be - 10 % based on three measurements and assuming the density of both samples to be that of pure calcite, i.e., 2.711 g / cm3. In addition, the PSD was used to estimate the specific surface area (SSA, in cm2 / g) of the samples. X-Ray fluorescence: X-ray fluorescence (XRF) was conducted using a Hitachi X- Supreme8000 series XRF Analyzer under helium flow. The sample holders were double cleaned with isopropanol (IPA) prior to use. The solid (powder) sample was packed into the sample holder until “infinite” thickness (i.e., > 2 mm) was achieved. The helium (He) flow was maintained below 10 psi and maximum tube current maintained at < 30 kW during the analysis.

[0148] Thermo gravimetric analysis: Thermogravimetric analysis (TGA) was performed using a Perkin Elmer STA 8000 under a flow of ultrapure nitrogen in aluminum oxide crucibles. A heating ramp of 10 °C / min was used between (35 and 950) °C, after 5 min of equilibration at 35 °C.

[0149] X-ray diffraction'. X-ray diffraction (XRD) analysis was performed using a PANalytical X’PertPro diffractometer - 9-9 configuration, Cu-Ka radiation, a = 1.54 A - on powdered samples. The scans were acquired between 5° and 70° with a step size of 0.02° using a X’Celerator 2 detector. Rietveld refinement of the samples was performed using Profex and BGMN packages.

[0150] Fourier transform infrared spectroscopy: Solid-state attenuated total reflection Fourier- transform infrared spectroscopy (ATR-FTIR) was performed using a Spectrum Two FT-IR Spectrometer (Perkin Elmer). The powdered samples were pressed using around 90 N of force onto a diamond / ZnSe composite crystal to ensure good contact and generate total internal reflection. The spectra reported herein were obtained by averaging 4 scans over the wavenumber range of (4000 - 400) cm-1at a resolution of 1 cm-1.

[0151] Solution-phase analysis

[0152] Inductively coupled plasma - optical emission spectrometry: Inductively coupled plasma - optical emission spectrometry (ICP-OES) was performed using a PerkinElmer Avio 200 for multi-elemental analysis to quantify Ca and Na concentrations in solution (i.e., in a 5 vol. % trace-metal grade HNO3 matrix). All intensity measurements, measured in radial view, were converted to concentration units using a calibration curve with a blank and 7 calibration points between 0.1 ppm and 25 ppm, prepared using standard solutions (1000 ppm Inorganic Ventures). Our testing showed that the presence of trace amounts of EDTA in the samples prepared for ICP measurement does not affect the intensity reading. Note that, for the limestone sample, Mg, Fe, and Al, as elements that can all complex with EDTA, were analyzed in a following a similar method as that used for Ca analysis. In general, for both feedstocks, Mg was found to be present in trace amounts (i.e., < 1 mmol / L that corresponds to < 1 mol. % of the amount of Ca in solution) while Al and Fe were below the detection limit.

[0153] Titration'. Volumetric titrations were performed using an OrionStar T910 instrument and using HC1 as the titrant to determine the concentration of dissolved EDTA, Ca-EDTA complex, and dissolved inorganic carbon (DIC) species as analytes diluted in MQW (Milli-Q water). The HC1 titrant was prepared from 37 mass % concentrated HC1 (ACS grade), and the acid content of the titrant was determined prior to usage by titrating a carbonate standard solution (1000 ppm Inorganic Ventures). The titration procedure consists of continuous acid addition under agitation (600 rpm) until 20 mL of acid has been dispensed, or until a pH below 3 is reached, at a pace regulated by the apparatus based on the instantaneous temperature-corrected pH measurement. The start and end points are determined from the minimum of the derivative of the pH evolution as a function of the volume of acid dispensed.

[0154] UV -Visible spectrophotometry. Chloride concentrations in solution was determined using the Iron(III)-thiocyanate method with an ultraviolet visible spectrophotometer (Hach DR 1900) and DPD testing kits (TNTplus-879). After zeroing using a blank reference, sample vials were measured in the ranges of (1 - 70) mg / L and (70 - 1,000) mg / L.

[0155] Gas analysis

[0156] Gas chromatography. Gas chromatography (GC) was used to quantify CO2(g) evolution using an Inficon Micro GC Fusion instrument. The GC was calibrated using standard CO2 calibration gases of (0, 0.1, 5, and 20) mol. % CO2 with N2 for balance. The apparatus allows for a carrier gas with a known and fixed flowrate that first passes through a hermetically closed reactor vessel where the reaction of interest occurs before / while being fed into the Inficon Micro GC instrument for analysis. The concentration of CO2 in mol. % is recorded at intervals of 30 seconds for the entire reaction time and is then used to quantify the total amount of CO2 emitted during the reaction by integration from the known flowrate of the carrier gas. Thermodynamic modeling

[0157] Thermodynamic modeling of solid- and solution-phase equilibria was carried out using GEM-Selektor v.3.6 (GEMS) which incorporates the slop98.dat and Cemdatal8 thermodynamic databases. Property inputs from these databases are used to assess solid phase solubilities and aqueous speciation. To represent the non-ideality of the solutions, the activity coefficients were calculated using the Truesdell- Jones extension to the Debye-Hiickel equation that is applicable for Im~ 2 mol / L: logioTi Eq. 1 where, gi is the activity coefficient and ztthe charge of the zthaqueous species, Ayand Byare temperature and pressure dependent coefficients, XjWis the molar quantity of water, Xwis the total molar amount of the aqueous phase, and I is the molal ionic strength. A common ion size parameter (a = 3.72 A) and a short-range interaction parameter (by= 0.64 kg / mol) were used, considering NaCl as the background electrolyte.

[0158] Low Carbon Process

[0159] Ca-extraction and complexation'. The solubility and dissolution rate of the AR calcite and the limestone rock, were investigated in EDTA-containing solutions of varying pH (6 - 10) and EDTA concentration (2 - 200) mmol / L. First, the H4EDTA was fully dissolved in MQW in borosilicate beakers at room temperature under continuous agitation by the progressive addition of solid NaOH until the target pH was attained. Following the dissolution of EDTA, calcite or limestone were added so that the total calcium content in the system is slightly in excess vis-a-vis the EDTA amount, i.e., such that CaCOa (in mol) = 1.1 x EDTA (in mol). Considering solid-to-liquid ratios (s:l) on a g / g basis, where solid designates the calcium source and liquid designates the EDTA-containing solution, this corresponds to ratios of 1:4542, 1:454, and 1:45 for solutions containing (2, 20, and 200) mmol / L of EDTA, respectively. The system was agitated at room temperature until it stabilized, that is, no further change in Ca concentration is observed. The time to equilibrium, i.e., at least 95 mol. % Ca extraction, is dependent on pH and EDTA concentration but less than - 1.5 hours in all cases. The solution and the headspace gas phase were both sampled and analyzed using ICP-OES, titration, and gas-phase (GC) analysis. The evolution of the calcium concentration [Ca] (in mol / L) over time resulting from the dissolution of the calcium precursors can be modeled using a lst-order equation of the form: where, ko (in mol / L / s) and ki (in s1) are apparent rate constants that are dependent on pH and the EDTA concentration, and t is the time (s). The dissolution rate (r) (in mol / m2 / s) is calculated using the following equation:83 where, mCais the amount of calcium (in mol) dissolved during the time At (s), mCaC03is the initial mass of calcite introduced in the reactor (in g), and SSAtis the specific surface area of the sample at a time t (in m2 / g) calculated as follows:84

[0160] SSAt= SSA(1 - FSD A Eq. 4 where, SSA is the initial specific surface area calculated from the particle size distribution of the sample, and FSD is the fraction of solid dissolved (unitless) at any time t calculated as follows: where, [Ca]tis the calcium concentration at a time t, nCais the amount of calcium initially available in the solid sample (in mol), and V is the volume of solution in the reactor (in Lj.Ca / CCb separation and. Na-HCOVwater separation via nanofiltration: A Sterlitech CF042 PTFE cross-flow cel was used at a constant applied pressure of 80 psi (5.5 bar) provided by a diaphragm pump. The setup used a jacketed reactor connected to a chiller system for temperature control of the feed solution at 20 °C. The membranes were equilibrated by immersion for at least 24 h in the testing solution and stabilized / compacted under pressure for at least 1 h to achieve pseudo-steady state rejections and flux. The NF tests were carried out under batch-recirculation conditions, i.e., by circulating the retentate back to the feed tank under atmospheric pressure, at constant temperature and applied pressure at selected water recoveries. The membranes were screened based on the reported normalized permeate flux and observed rejections ( Table ), and experimental rejections and the specific energy intensity as a function of water recovery for the solution-system of interest herein. In the screening process for Ca-EDTA / Na- HCO3 separations at (10 - 20) mmol / L in MQW, with and without high NaCl salinity background matrix, five membranes - N90, TS40, NF270, XN45, and NFW - were tested at a water recovery of 0 % to limit concentration polarization effects recirculating both retentate and permeate streams, as well as at an increased water recovery of up to 50 %, without recirculation of the permeate thereafter. This allowed examination of the separation and permeability properties to select a membrane for the high water recovery target of 85 % (i.e., which yields the largest separation), typical of NF processes (80 % - 90 %). The Na-HCOa / watcr separation for process-water recycling was performed at 75 % water recovery upon screening of four membranes (NF90, TS80, SB90, and NP030).

[0161] Ca-decomplexation and EDTA recovery: Acidification using electrolytically produced HC1 is used to decomplex Ca from the EDTA, while ensuring its reprotonation into the highly insoluble H4EDTA form. Thus, HC1 was used to titrate the Ca-EDTA solutions in MQW with EDTA contents ranging from 10 mmol / E to 1000 mmol / E until HC1 (in mol) = 4 x EDTA (in mol) has been introduced (i.e., when the EDTA is tetra-protonated). The precipitate was recovered by vacuum filtration using a Buchner apparatus and filter paper (Whatman™, Grade 1, > 11 pm) and dried in a vacuum desiccator at room temperature prior to XRD and FT-IR analysis. The filtered solution was also analyzed so that the residual contents of aqueous EDTA, and Ca and Cl could be quantified by titration, ICP-OES analysis, and UV-Vis analysis, respectively.

[0162] Ca(OH)2 precipitation'. Ca(OH)2 precipitation was assessed using thermodynamic modeling and validated experimentally by titrating model “CaCh / (l-x)NaHCO3” solutions where 0.90 < x < 1.0 on a mole basis in MQW with 1 mol / L NaOH solutions. This range was selected to assess the precipitate purity in the range of Ca-EDTA / Na-HCCh separation achievable via NF in single- and double- stages. The recovered solids were dried under vacuum in glass desiccators to prevent carbonation prior to characterization.

[0163] Results and Discussion

[0164] In aqueous solution, EDTA binds cations with an increasing preference for valence and field strength - Z / ir, m1, i.e., the ratio of the valence (Z) to the ionic radius, ir. On account of its ability to bind divalent cations, EDTA substantially enhances the solubility of calcite (CaCCh: Figure 9a) by up to - 3 orders of magnitude compared to MQW. This occurs as EDTA chelates calcium species on a stoichiometric basis over a broad pH range: on average, (0.96 ± 0.04) mol of Ca are bound per mol of EDTA at equilibrium. This ensures that EDTA is fully chelated, consistent with literature reports.33The reaction of EDTA with calcite evolves some CO2 under specific conditions, 6 < pH < 9, although no CO2 evolution is observed when dissolving calcite in MQW (Figure 9b). This is because while the majority of the aqueous EDTA species are being held in the form of HEDTA3anions above pH 6 - as disclosed by in Figure 2 - minor amounts of H2EDTA2' exist in solution.

[0165] At an initial pH of 9.5 and using 100 mmol / L of EDTA - conditions at which no CO2 evolution is expected - Ca extraction from limestone rock by EDTA is similar to that of analytical reagent grade (AR) calcite (Figure 9c), despite small quantities of other solutes present in the rock. Since an electrochemical process uses a conductive electrolyte, dissolution was evaluated in a 0.5 mol / L NaCl solution and in synthetic Instant Ocean® seawater to examine how salinity and ionic strength affects Ca-extraction behavior. It is noted that a “high” ionic strength alone does not affect the amount of extracted calcium in solution at equilibrium (Figure 3c). Rather, seawater is observed to strongly decrease the capacity of EDTA to extract calcium due to the native presence of - 55 mmol / L of Mg and - 10 mmol / L of Ca. These divalent “matrix cations”, particularly Mg, consume the chelation capacity of EDTA, and therefore compromise Ca-chelation by EDTA, reducing its ability to uptake Ca- species dissolved from calcite. This indicates that the use of natural brines and saline waters within the present process may improve with water softening, e.g., preprocessing by NF, to remove parasitic and competitive divalent cations such as Mg that may complex with EDTA.

[0166] Considering the effects of EDTA on calcite dissolution, it is noted that EDTA enhances the dissolution rate of calcite enormously, as compared to MQW, across a range of pHs (Figure 10a). In the presence of EDTA, increasing calcite dissolution rates are observed with decreasing pH (Figure 10a), at an EDTA dosage of - 20 mmol / L of EDTA (see Figure 4a and b), and at low [Ca] / [EDTA] ratios (see Figure 4b, where 0 < [Ca] / [EDTA] < 1, molar ratio). The highest dissolution rates at [EDTA] - 20 mmol / L arise from the competing effects of EDTA’s chelation properties (favorable) (Figure 10a) and increasing ionic strength (unfavorable) on the dissolution rate. The dissolution rates at saturation (i.e., where [Ca] / [EDTA] = 1) imply that longer times would promote saturation for 200 mmol / L of EDTA solutions as compared to 2 mmol / L or 20 mmol / L of EDTA solutions, although the former solution contains 100 or 10 times as much extracted Ca as the latter solutions. Under similar pHs and EDTA concentrations, the AR calcite and the limestone rock feature similar dissolution rates (Figure 10c). The 0.5 mol / L of NaCl solution and seawater perform similarly to each other and induce a decrease in the dissolution rate, whereby a linear decrease in the dissolution rate is observed with an increasing ionic strength.

[0167] INCORPORATION BY REFERENCE

[0168] All publications and patents mentioned herein are hereby incorporated by reference in their entirety as if each individual publication or patent was specifically and individually indicated to be incorporated by reference. In case of conflict, the present application, including any definitions herein, will control.

[0169] EQUIVALENTS

[0170] While specific embodiments of the subject invention have been discussed, the above specification is illustrative and not restrictive. Many variations of the invention will become apparent to those skilled in the art upon review of this specification and the claims below. The full scope of the invention should be determined by reference to the claims, along with their full scope of equivalents, and the specification, along with such variations.

[0171] REFERENCES

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[0173] (2) C. N. Fredd and H. S. Fogler, “Alternative Stimulation Fluids and Their Impact on Carbonate Acidizing,” SPEJournal, vol. 3, no. 01, pp. 34-41, Mar. 1998, doi: 10.2118 / 31074-PA.

[0174] (3) R. S. Arvidson, I. E. Ertan, J. E. Amonette, and A. Luttge, “Variation in calcite dissolution rates:,” Geochimica etCosmochimica Acta, vol. 67, no. 9, pp. 1623-1634, May 2003, doi: 10.1016 / S0016-7037(02)01177-8.

[0175] (4) C. N. Fredd and H. S. Fogler, “The Influence of Chelating Agents on the Kinetics of Calcite Dissolution,” J oumalof Colloid, and Interface Science, vol. 204, no. 1, pp.

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[0177] (5) E. H. Oelkers, S. V. Golubev, O. S. Pokrovsky, and P. Benezeth, “Do organic ligands affect calcite dissolution rates?,” Geochimica et Cosmochimica Acta, vol. 75, no. 7, pp. 1799-1813, Apr. 2011, doi: 10.1016 / j.gca.2011.01.002.

[0178] (6) Simpson, A. E., Kerr, C. A. & Buckley, C. A., “The effect of pH on the nanofiltration of the carbonate system in solution,” Desalination, Vol. 64, pp. 305-319, 1987, doi: 10.1016 / 0011-9164(87)90104-4.

[0179] (7) Z. Yu, T. Qi, J. Qu, L. Wang, and J. Chu, “Removal of Ca(II) and Mg(II) from potassium chromate solution on Amberlite IRC 748 synthetic resin by ion exchange,” Journal of Hazardous Materials, vol. 167, no. 1-3, pp. 406-412, Aug. 2009, doi: 10.1016 / j.jhazmat.2008.12.140.

[0180] (8) S. Mountadar, A. Hayani, A. Rich, M. Siniti, and S. Tahiri, “Equilibrium, kinetic, and thermodynamic studies of the Ca 2+ and Mg 2+ ions removal from water by Duolite C206A,” Solvent Extraction and Ion Exchange, vol. 36, no. 3, pp. 315-329, Apr. 2018, doi: 10.1080 / 07366299.2018.1478369.

[0181] (9) S. Y. Jiang, B. Gao, and B. Dong, “Ion Exchange Behaviors of Ca(II) and Mg(II) on Lewatit MonoPlus TP 207 and TP 208 Chelating Resins,” AMR, vol. 347-353, pp. 937-951, Oct. 2011, doi: 10.4028 / www. scientific.net / AMR.347-353.937.

[0182] (10) M. Windholz and Merck & Co, Eds., The Merck index: an encyclopedia of chemicals, drugs, and biologicals, 10th ed. Rahway, N.J., U.S.A: Merck, 1983. (11) B. Bandrabur, R.-E. Tataru-Farmu§, L. Lazar, and G. Gutt, “Application of a strong acid resin as ion exchange material for water softening - Equilibrium and thermodynamic analysis,” Scientific study & research, vol. 13, no. 4, 2012.

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Claims

We claim:

1. An electrolytic method of producing portlandite and / or brucite, comprising:(a) combining a mineral source comprising at least one divalent metal salt, an aqueous solution, and a chelating agent to produce a leachate comprising chelated divalent metal cations;(b) subjecting the leachate to nanofiltration to produce a retentate comprising the divalent metal cations and a permeate comprising contaminant aqueous species;(c) acidifying the retentate to release the chelating agent and produce a concentrated divalent metal cation solution;(d) electrolyzing the concentrated divalent metal cation solution in an electrochemical cell to produce a) an anolyte and b) a catholyte comprising a solid divalent metal cation hydroxide and a catholyte supernatant; and(e) separating the divalent metal cation hydroxide from the catholyte supernatant.

2. The method of claim 1, wherein the mineral source comprises carbonate rocks, silicate rocks, or a combination thereof.

3. The method of claims 1 or 2, wherein the mineral source comprises calcium- containing solids, magnesium-containing solids, or a combination thereof.

4. The method of any one of claims 1-3, wherein the aqueous solution comprises water, recycled anolyte, recycled catholyte supernatant, a sodium salt, salt water, seawater, softened seawater, or any combination thereof.

5. The method of any one of claims 1-4, wherein the leachate has a pH of from about 0.5 to about 13.5.

6. The method of any one of claims 1-5, wherein the leachate comprises greater than about 2 mM divalent metal cations.

7. The method of any one of claims 1-6, further comprising filtering the leachate prior to step (b).

8. The method of any one of claims 1-7, wherein the nanofiltration in step (b) is performed with a nanofiltration membrane.

9. The method of claim 8, wherein the nanofiltration membrane has a pore size in a range of about 500 Da to about 1000 Da.

10. The method of any one of claims 1-9, wherein the retentate comprises greater than about 5 mM divalent metal cations.

11. The method of any one of claims 1-10, wherein the retentate comprises greater than about 25 mM divalent metal cations.

12. The method of any one of claims 1-11, wherein the retentate comprises greater than about 200 mM divalent metal cations.

13. The method of any one of claims 1-12, wherein the retentate comprises greater than about 300 mM divalent metal cations.

14. The method of any one of claims 1-13, wherein the retentate has a pH from about 7 to about 12.

15. The method of any one of claims 1-14, wherein the permeate comprises less than 5 mM divalent metal cations.

16. The method of any one of claims 1-15, wherein the permeate comprises less than 1 mM divalent metal cations.

17. The method of any one of claims 1-16, wherein the permeate has a pH from about 7 to about 9.

18. The method of any one of claims 1-17, wherein the catholyte supernatant comprises less than about 50 mM divalent metal cations.

19. The method of any one of claims 1-17, wherein the catholyte supernatant has a pH less than about 12.

20. The method of claim 1-19, wherein the chelating agent is selected from ethylene- diamine-tetraacetic acid (EDTA), diethylene triamine penta methylene phosphonic acid (DTMPA, DTPMP), hydroxy-ethane diphosphonic acid (HEDP), ethylenediamine N,N'- disuccinic acid (EDDS), methyl glycine di-acetic acid (MGDA), diethylene triamine pentaacetic acid (DTPA), propylene diamine tetraacetic acid (PDTA), 2-hydroxypyridine-N- oxide (HPNO), methyl glycine diacetic acid (MGDA), glutamic acid N.N-diacetic acid (N,N- dicarboxymethyl glutamic acid tetrasodium salt (GLDA) nitrilotriacetic acid (NTA), glucose, fructose, galactose, sucrose, lactose, mannose, and any combination thereof.

21. The method of claim 1-20, wherein the chelating agent is EDTA.

22. The method of claim 21, wherein the concentration of ethylenediaminetetraacetic acid is from about 10 mM to about 500 mM.

23. The method of any one of claims 1-22, wherein the production of the divalent metal cation hydroxide occurs at a temperature from about 20 °C to about 40 °C.

24. The method of any one of claims 1-23, further comprising recycling the catholyte supernatant into step (a).

25. The method of any one of claims 1-24, further comprising recycling the anolyte into step (a) and / or step (c).

26. The method of anyone of claims 1 to 25, further comprising recovering the chelating agent prior to step (d).

27. The method of claim 26, further comprising recycling the recovered chelating agent back into step (a).

28. The method of any one of claims 1 to 27, wherein the divalent metal cation comprises Ca2+, Mg2+, or both.

29. The method of any one of claims 1 to 28, wherein the divalent metal hydroxide comprises calcium hydroxide, magnesium hydroxide, or both.

30. A system for producing portlandite and / or brucite comprising: a single- or multi-step dissolution tank for contacting rocks with an aqueous solution and a chelating agent thereby producing a leachate comprising chelated divalent metal cations, wherein the multi-step dissolution tank comprises a rock inlet, a water inlet, a recycled anolyte inlet, a recycled catholyte supernatant inlet, and a leachate outlet; a filtration tank for filtering the leachate, wherein the filtration tank comprises a leachate inlet and a filtrate outlet; wherein the leachate outlet from the multi-step dissolution tank is coupled to the leachate inlet; and a nanofiltration tank for concentrating the chelated divalent metal cations in the leachate to produce a retentate comprising the chelated divalent metal cations, wherein the nanofiltration tank comprises a nanofiltration membrane a filtrate inlet, a retentate outlet, and a permeate outlet; wherein the filtrate inlet is coupled to the filtrate outlet from the filtration tank; and a separation tank for recovering the chelating agent as a solid and the divalent calcium as free ions in solution by acidification of the retentate (e.g., by mixing the retentate with a recycled anolyte stream); and an electrochemical cell for generating portlandite and / or brucite from the chelated divalent metal cations, wherein the electrochemical cell comprises an anode, a cathode, a retentate inlet, a permeate inlet, a catholyte outlet, and a recycled anolyte outlet; wherein the retentate inlet is coupled to the retentate outlet from the nanofiltration tank and is configured to pass the retentate from the nanofiltration tank into the electrochemical cell, the permeate inlet is coupled to the permeate outlet and is configured to pass the permeate from the nanofiltration tank into the electrochemical cell and the recycled anolyte outlet is coupled to the recycled anolyte inlet on the multi-step dissolution tank and is configured to pass recycled anolyte from the electrochemical cell to the multi-step dissolution tank;a settling / separation / filtration tank for separation of the portlandite and / or brucite from the catholyte comprising a catholyte inlet, a portlandite and / or brucite outlet, and a recycled catholyte supernatant outlet; wherein the catholyte inlet is coupled to the catholyte outlet from the electrochemical cell and is configured to receive catholyte from the electrochemical cell into the settling tank, and the recycled catholyte outlet is coupled to the recycled catholyte supernatant inlet on the multi-step dissolution tank and is configured to pass recycled catholyte from the settling tank into the multi-step dissolution tank.

31. An electrolytic method of producing divalent metal hydroxide, comprising:(a) combining a mineral source comprising at least one divalent metal salt with an aqueous solution to produce a leachate comprising divalent metal ions;(b) capturing the divalent metal cations from the leachate;(c) releasing the divalent metal cations, thereby producing a concentrated divalent metal cation solution;(d) electrolyzing the concentrated divalent metal ion solution in an electrochemical cell to produce a) an anolyte and b) a catholyte comprising a solid divalent metal hydroxide and a catholyte supernatant; and(e) separating the solid divalent metal hydroxide from the catholyte supernatant.

32. The method of claim 31, wherein capturing the divalent metal cations comprises: chelating the divalent metal cations using a chelating agent, passing the aqueous divalent metal cation solution through an ion exchange membrane, contacting the aqueous solution with a divalent metal cation binding agent, or contacting the aqueous solution with a divalent metal cation adsorbing agent, or any combination thereof.

33. An electrolytic method of producing divalent metal hydroxide, comprising:(a) combining a mineral source comprising minerals with an aqueous solution to produce an aqueous solution comprising divalent metal cations;(b) passing the aqueous solution comprising divalent metal cations through an ion exchange material that retains the divalent metal cations;(c) releasing the divalent cations from the ion exchange material, thereby producing a concentrated divalent metal cation solution and regenerating the ion exchange material;(d) electrolyzing the concentrated divalent metal cation solution in an electrochemical cell to produce a) an anolyte and b) a catholyte comprising a divalent metal hydroxide and a catholyte supernatant; and(e) separating the divalent metal hydroxide from the catholyte supernatant.

34. An electrolytic method of producing divalent metal hydroxide, comprising:(a) combining a mineral source comprising minerals with an aqueous solution to produce an aqueous solution comprising divalent metal cations;(b) contacting the aqueous solution comprising divalent metal cations with a chelating agent to produce a chelated divalent metal cation solution;(c) subjecting the chelated divalent metal cation solution to nanofiltration to provide a retentate comprising divalent metal ions and a permeate comprising contaminant species;(d) subjecting the retentate to an acidic pH swing to precipitate, recover, and recirculate the chelating agent and to produce a concentrated divalent metal cation solution;(e) electrolyzing the concentrated divalent metal cation solution in an electrochemical cell to produce a) an anolyte and b) a catholyte comprising a solid divalent metal hydroxide and a catholyte supernatant; and(f) separating the solid divalent metal hydroxide from the catholyte supernatant.

35. The method of claim 32 or 34, wherein releasing the divalent metal cation from the ion exchange material comprises compacting the ion exchange material with an acidic solution.

36. The method of any one of claims 31 to 35, wherein the mineral source comprises calcium, magnesium, or both.

37. The method of claim 31-36, wherein the mineral source comprises carbonate rocks, silicate rocks, slags, or fly ashes.

38. The method of any one of claims 31 to 37, further comprising filtering the aqueous solution comprising divalent metal cations prior to step (b).

39. The method of any one of any one of claims 31 to 38, wherein the aqueous solution of step (a) comprises water, catholyte supernatant, anolyte, salt water, seawater, softened seawater, or any combination thereof.

40. The method of any one of claims 31 to 39, wherein the aqueous solution of step (a) further comprises a soluble sodium salt.

41. The method of any one of claims 31 to 40, wherein the divalent metal cation is a metal cation.

42. The method of claim 41, wherein the divalent metal cation is Ca2+, Mg2+, or both.

43. The method of claim 31 to 42, wherein the aqueous solution comprising the divalent metal ions comprises greater than about 1 mM divalent metal ions.

44. The method of any one of claims 31 to 43, wherein the aqueous solution comprising divalent metal cations comprises greater than about 2 mM divalent metal ions.

45. The method of any one of claims 31 to 44, wherein the aqueous solution from step (a) has a pH from about 0.5 to about 12.

46. The method of any one of claims 31 to 44, wherein the aqueous solution from step (a) has a pH less than 2.

47. The method of any one of claims 32-46, wherein the ion exchange material is a protonated ion exchange material.

48. The method of any one of claims 32 to 47, wherein the ion exchange material is a sodium-containing ion exchange material.

49. The method of claim 35, further comprising contacting the ion exchange material with a hydroxide after the contacting with the acidic solution.

50. The method of any one of claims 32 to 49, wherein the ion exchange material comprises iminodiacetic acid, sulfonic acid, or both.

51. The method of any one of claims 32 to 46, wherein the ion exchange material is zeolite A.

52. The method of any one of claims 32 to 51, wherein the chelating agent is selected from ethylene-diamine-tetraacetic acid (EDTA), diethylene triamine penta methylene phosphonic acid (DTMPA, DTPMP), hydroxy-ethane diphosphonic acid (HEDP), ethylenediamine N,N'-disuccinic acid (EDDS), methyl glycine di-acetic acid (MGDA), diethylene triamine pentaacetic acid (DTPA), propylene diamine tetraacetic acid (PDTA), 2-hydroxypyridine-N- oxide (HPNO), methyl glycine diacetic acid (MGDA), glutamic acid N.N-diacetic acid (N,N- dicarboxymethyl glutamic acid tetrasodium salt (GLDA) nitrilotriacetic acid (NTA), glucose, fructose, galactose, sucrose, lactose, mannose, and any combination thereof.

53. The method of claim 52, wherein the chelating agent is EDTA.

54. The method of any one of claims 32 to 53, wherein the concentration of the chelating agent is from about 1 mM to about 1000 mM.

55. The method of any one of claims 31 to 54, further comprising subjecting the concentrated divalent metal cation solution to nanofiltration.

56. The method of any one of claims 33-50, wherein the nanofiltration is accomplished using a nanofiltration membrane.

57. The method of any one of claims 33-50, wherein the nanofiltration membrane has a pore size in a range of about 500 Da to about 1000 Da.

58. The method of claim 57, wherein the concentrated divalent metal cation solution comprises greater than about 2 mM divalent metal ions.

59. The method of claim 58, wherein the concentrated divalent metal cation solution comprises greater than about 20 mM divalent metal cations.

60. The method of any one of claims 31-59, wherein the concentrated divalent metal cation solution comprises from about 200 to about 500 mM divalent metal cations.

61. The method of any one of claims 33-60, wherein the permeate has a pH from about 5 to about 10.

62. The method of any one of claims 33-61, wherein the permeate comprises less than 20 mM divalent metal ions.

63. The method of any one of claims 33-62, wherein the permeate comprises less than 1 mM divalent metal ions.

64. The method of any one of claims 33-63, wherein the retentate has a pH from about 7 to about 12.

65. The method of any one of claims 33-64, wherein the retentate comprises greater than about 10 mM divalent metal ions.

66. The method of any one of claims 33-65, wherein the retentate comprises greater than about 200 mM divalent metal ions.

67. The method of any one of claims 33-60, wherein the retentate comprises from about 200 to about 400 mM divalent metal ions.

68. The method of any one of claims 31-61, wherein the catholyte supernatant comprises less than about 50 mM divalent metal ions.

69. The method of any one of claims 31-68, wherein the catholyte supernatant has a pH less than about 12.

70. The method of any one of claims 31-69, wherein the production of divalent metal hydroxide occurs at less than about 40 °C.

71. The method of any one of claims 31-70, further comprising recycling the catholyte supernatant into step (a).

72. The method of any one of claims 31-71, further comprising recycling the anolyte into step (a).

73. The method of any one of claims 35-72, wherein the aqueous solution comprises the anolyte.

74. The method of any one of claims 31 to 73, further comprising repeating the process at least one additional time.

75. A system for producing a divalent metal hydroxide, comprising: a multi-step dissolution tank for contacting a mineral source with an aqueous solution thereby producing an aqueous solution comprising divalent metal cations, wherein the multi- step dissolution tank comprises a mineral source inlet, an aqueous solution inlet, a recycled anolyte inlet, a recycled catholyte supernatant inlet, and an outlet; an optional filtration tank for filtering the aqueous solution comprising divalent metal cations, wherein the filtration tank comprises a filtration tank inlet and an outlet; and wherein the outlet from the multi-step dissolution tank is coupled to the filtration tank inlet; and an optional ion exchange tank for contacting the aqueous solution comprising the divalent metal cations with an ion exchange material and for contacting the ion exchange material with an acidic solution, thereby producing a concentrated divalent metal cation solution and regenerating the ion exchange material, wherein the ion exchange tank comprises an inlet to receive the aqueous solution comprising divalent metalcations and a concentrated divalent metal cation solution outlet; and wherein the outlet from the multi-step dissolution tank or the outlet from the filtration tank, when present, is coupled to the ion exchange tank inlet; and an electrochemical cell for generating the divalent metal hydroxide from the concentrated divalent metal cation solution, wherein the electrochemical cell comprises an anode, a cathode, a concentrated divalent metal cation solution inlet, a catholyte outlet, and an anolyte outlet; wherein the concentrated divalent metal cation solution inlet is coupled to outlet from the ion exchange tank, when present, the outlet from the filtration tank, when present, or the outlet from multi-step dissolution tank and is configured to pass the concentrated divalent metal cation solution from the ion exchange tank, when present, the filtration tank, when present, or the multi-step dissolution tank into the electrochemical cell, and the recycled anolyte outlet is coupled to the recycled anolyte inlet on the multi-step dissolution tank and is configured to pass anolyte supernatant from the electrochemical cell to the multi-step dissolution tank; a settling tank, filtration or centrifugation system for separation of a solid divalent metal hydroxide from the catholyte supernatant comprising a catholyte inlet, a solid metal hydroxide outlet, and a recycled catholyte supernatant outlet; wherein the catholyte supernatant inlet is coupled to the catholyte supernatant outlet from the electrochemical cell and is configured to receive catholyte from the electrochemical cell into the settling tank, and the recycled catholyte outlet is coupled to the recycled catholyte supernatant inlet on the multi-step dissolution tank and is configured to pass the catholyte supernatant from the settling tank into the multi-step dissolution tank.

76. The system of claim 75, further comprising: a nanofiltration tank for further producing a chelated divalent metal cation solution, wherein the nanofiltration tank comprises a nanofiltration membrane, a concentrated divalent metal cation solution inlet, and a chelated divalent metal cation solution outlet; wherein the concentrated divalent metal cation solution inlet is coupled to the concentrated divalent metal cation solution outlet from the ion exchange tank, and the concentrated divalent metal cation solution outlet is coupled to the concentrated divalent metal cation inlet on the electrochemical cell.

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