Electrolytic precipitation of high purity hydroxides using seawater

Abstract

The present disclosure relates to systems and methods for preparing highly pure brucite compositions.

Description

[0001] ELECTROLYTIC PRECIPITATION OF HIGH PURITY HYDROXIDES USING SEAWATER CROSS REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of priority to U. S. Provisional Application No.

[0003] 63 / 713,682, filed October 30, 2024, the contents of which are herein incorporated by reference in their entirety.

[0004] BACKGROUND

[0005] Brucite (Mg(0H)2) is an important chemical feedstock for production of cementitious materials, and a promising species relevant to carbon dioxide capture and sequestration. Brucite for industrial uses can be obtained as a result of natural processes, e.g., through the hydration of MgO produced from calcining magnesium carbonate, or by precipitation from seawater. Brine solutions, e.g., ocean water, contain a high amount of Mg2+ions, particularly in the form of chloride and sulfate salts. Thus, these brines can be a source for industrial brucite production via processes involving alkalinization and precipitation. However, many such brines also contain a number of other dissolved metal cations (e.g., Ca2+) which are difficult and / or energy-intensive to separate from aqueous Mg2+target ions by traditional means. Accordingly, there is a need for efficient methods of producing pure brucite from brine solutions.

[0006] SUMMARY OF THE INVENTION

[0007] In certain aspects, provided herein are systems and methods for producing brucite (MgOH2) which has substantially decreased concentrations of contaminants, e.g., those comprising calcium. In certain embodiments, the systems and methods described herein further comprise producing Ca(OH)2.

[0008] In certain aspects, a system is provided comprising:

[0009] a first electrochemical cell comprising:

[0010] a first cathodic chamber, comprising:

[0011] a first cathode;

[0012] a first target ion feed inlet;

[0013] a first cathodic gas outlet;

[0014] a first catholyte mixture outlet;

[0015] a first anodic chamber, comprising:

[0016] a first anode; a first anolyte feed inlet;

[0017] a first anodic gas outlet;

[0018] at least one primary acidic anolyte outlet;

[0019] a first membrane disposed between the first cathodic chamber and the first anodic chamber;

[0020] a first solid separation chamber, comprising:

[0021] a first catholyte mixture inlet coupled to the first catholyte mixture outlet;

[0022] a first solid collection outlet; and

[0023] a first supernatant outlet;

[0024] wherein the first cathodic chamber and the first anodic chamber are in ionic communication.

[0025] In certain aspects, a method of preparing Mg(0H)2, comprising:

[0026] providing:

[0027] a first target ion solution comprising Mg2+and at least one non-target ion to a first anodic chamber and a first cathodic chamber of a first electrochemical cell; the first electrochemical cell further comprising:

[0028] a first anode disposed within the first anodic chamber;

[0029] a first cathode disposed within the first cathodic chamber; and a first membrane disposed between and configured to separate the first cathodic chamber and the first anodic chamber;

[0030] wherein the first anodic chamber and the first cathodic chamber are in fluid communication; and

[0031] performing a first electrochemical process, comprising:

[0032] applying a first voltage to the first cathode and the first anode; thereby producing: a first acidic anolyte and an anodic gas at the first anode; and

[0033] a first catholyte mixture and a cathodic gas at the first cathode;

[0034] wherein the first catholyte mixture comprises the Mg(0H)2.

[0035] BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Fig- 1 shows a process flow diagram detailing an exemplary system and process of the disclosure. Seawater is fed to the anode cell of an electrochemical cell to decrease its pH and degas the dissolved CO2. The resulting CO2-depleted seawater is treated to separate the calcium from the solution and increase its pH back to 7-8. The solution is then fed to the cathode cell of the electrolyzer to increase its pH to 11 and precipitate the magnesium ions as magnesium hydroxide (brucite). The solid brucite is then separated from the liquid supernatant.

[0037] Fig- 2 shows a process flow diagram detailing an exemplary system and process of the disclosure. In the exemplary process, a precipitant is added to induce precipitation of non-target ions (e.g., Ca2+)

[0038] Fig- 3 shows a plot of Saturation Index (SI) of CaCO3(as calcite) as a function of pH using seawater. The darker star represents the initial SI of the seawater. Because of the high Mg2+concentration in seawater, seawater is typically supersaturated (SI > 0) toward calcite. If the pH of the seawater is increased directly (direct path d.p., represented by darker trace in the graph), the SI will increase, inducing calcite precipitation and brucite contamination. Certain embodiments of the processes described herein (lighter trace, steps 1-3) allow the production of high grade brucite as follows: (1) Seawater acidification in the anode cell of the electrolyzer to pH 1 to degas the CO2, (2) Alkalinization of the resulting degassed solution to pH 7 before reaching the cathode cell of the electrolyzer via mineral dissolution, and (3) Alkalinization in the cathodic chamber to increase the pH to 11 and precipitate brucite (Mg(0H)2).

[0039] Fig- 4 shows total dissolved carbon as a function of pH. The concentrations were calculated using PhreeqC and the Pritzer database on a solution of seawater. Pritzer was chosen because of the high ionic strength of the seawater. A typical pH of seawater is 8.2. If the pH drops below 7.9 (non-shaded region), the solution will degas CO2. Below pH 4, the degassing is maximal and allows to reach a low carbonate concentration in solution. Degassing via acidification is explored to increase the brucite purity starting with a solution of seawater composition.

[0040] Fig. 5 shows the percent of Ca and Mg ion removal, as well as solution pH, as function of moles of precipitant (NaHCO3) added. The data also indicate the selectivity of the precipitant for Ca removal.

[0041] Fig. 6 shows the percent of Ca and Mg ion removal, as well as solution pH, as function of moles of precipitant (ISfeCCh) added. The data also indicate the selectivity of the precipitant for Ca removal.

[0042] Fig. 7 shows a process flow diagram of a representative system and process according to certain embodiments of the disclosure. This system provides advantages when using feed streams with high concentrations of dissolved Ca2+, COs2', HCCh', and CO2. For feeds with low concentrations of Ca2+, carbonate ions, and CO2, the pH control is challenging, and CAPEX becomes undesirably higher for the first stage. For sea water this approach with pre- precipitation of CaCO3is limited by the availability of carbonate ions and CO2. Thus, some Ca2+will remain in the liquid feed that is entering the second electrolyzer. As long as the pH is appropriately selected (approximately 10.5) in the second electrolyzer, Ca2+will not precipitate as Ca(OH)2 (which precipitates around pH 13) in the second electrolyzer, and Mg(0H>2 is obtained in good purity.

[0043] Fig- 8 shows a process flow diagram of a representative system and process according to certain embodiments of the disclosure. Instead of precipitating out CaCO3before increasing the pH to 10.5 for Mg(0H>2 precipitation, COs2', HCCh’ and CO2 can be degassed (limited by equilibrium) by using a stripping gas that has a low CO2 concentration or is CCh-free. This way the precipitation of CaCO3is suppressed by removing one of the reactants that lead to the formation of CaCO3. As an alternative to H2, O2 from the electrolyzer, air, or an external gas supply (e.g., N2) may be used as the stripping gas.

[0044] Fig- 9 shows a process flow diagram of a representative system and process according to certain embodiments of the disclosure. Using a portion of the acidic anolyte and adding it upstream of the degassing / stripping unit can shift the equilibrium to increase the amount of degassing (removing COs2', HCCh' and CO2, which are reactants that can lead to the formation of CaCO3inside the electrolyzer). Combining acidification with gas stripping can substantially increase the favorability of the degassing equilibrium and kinetics. Degassing can also be done without the introduction of a stripping gas in an open vessel that is in equilibrium with the atmosphere, but the process would be slower.

[0045] Fig. 10 shows a process flow diagram of a representative system and process according to certain embodiments of the disclosure. If it is desirable to recover Ca2+in the form of CaCO3as byproduct, the alkaline stream leaving the Mg(0H)2 separator can be brought into contact with a CCh-containing stream (e.g. from the degassing unit to recapture CO2 emissions or directly from air). This configuration reduces the risk of CaCO3contamination, due to upstream CaCO3precipitation, in the Mg(0H)2 product. CaCO3precipitate is very fine and can potentially slip through the filter and contaminate the Mg(0H)2 this risk is mitigated in this design. CaCO3co-production is also possible downstream of the CCh-capture chamber.

[0046] Fig- 11 shows a process flow diagram of a representative system and process according to certain embodiments of the disclosure. Using an additive such as, for example, NaHCO3or Na3PO4h can induce a precipitation reaction that can selectively remove Ca2+ions from the feed water stream and reduce calcium concentration down to trace amounts, thereby minimizing the risk of CaCO3precipitation in the electrolyzer. In this example the additive is a solid, but can also be a dissolved solid, liquid or gaseous compound.

[0047] Fig. 12 shows a process flow diagram of a representative system and process according to certain embodiments of the disclosure. This setup uses the filtered catholyte to increase the pH of the target ion source feed and induce CaCO3formation. Additionally, CO2 is added to the mixture to enhance Ca removal and provide a stronger driving force for CaCO3precipitation.

[0048] Fig. 13 shows a process flow diagram of a representative system and process according to certain embodiments of the disclosure. Doing the carbonation directly in the recycle provides better process control as the CO2 contacting chamber (or “carbonation” chamber) can be run in under-stochiometric conditions (to still provide enough alkalinity for CaCO3formation and precipitation), and carbonation can be controlled on the air flow side.

[0049] Fig. 14 shows a process flow diagram of a representative system and process according to certain embodiments of the disclosure. Using the catholyte before Mg(0H)2 separation leads to substantially lower power consumption due to reduced pumping power of the recycle stream although the streams before and after Mg(0H)2 separation have the same pH. This is because Mg(0H)2 solids can replenish OH- ions during carbonation.

[0050] Fig. 15 shows a process flow diagram of a representative system and process according to certain embodiments of the disclosure. This configuration provides a simpler configuration of the process shown in Figs. 12-14. If there is no interest in CO2 capture or maximizing CaCOs co-production, this configuration provides a cheaper alternative.

[0051] Fig. 16 shows a process flow diagram of a representative system and process according to certain embodiments of the disclosure. This configuration provides a simpler configuration of the process shown in Figs. 12-14. To reduce pumping power consumption this configuration is attractive, but also poses the risk of MgCCh shell formation on the Mg(0H)2, passivating the OH' that could be released by Mg(0H)2 in solution.

[0052] Fig. 17 shows a process flow diagram of a representative system and process according to certain embodiments of the disclosure. This configuration provides a simpler configuration of the process shown in Figs. 12-14 and only recycles the solid Mg(0H)2 as a source for alkalinity inducing CaCOs precipitation.

[0053] Fig. 18 shows a process flow diagram of a representative system and process according to certain embodiments of the disclosure. This configuration can reduce power consumption by having this new equation shown in the anode occurring in parallel to the previously shown anodic reaction, H2O

[0054]

[0055] 2H + 2e + O.5O2. Additionally, less feed water is needed in this configuration. One of ordinary skill in the art will appreciate that this modification may be readily incorporated into other embodiments described herein to reduce power consumption.

[0056] Fig. 19 shows a process flow diagram of a representative system and process according to certain embodiments of the disclosure. Using an anion exchange membrane (AEM) can reduce power consumption by reducing cross-over. H+is a small ion and it is easy to crossover in cation exchange membranes (CEM). The cross-over risk is reduced when using an AEM as OH', which is too large to cross over effectively. One of ordinary skill in the art will appreciate that this modification may be readily incorporated into other embodiments described herein to reduce power consumption.

[0057] Fig.20 shows a process flow diagram of a representative system and process according to certain embodiments of the disclosure. In cases with Mg(OH)2 precipitation, using a cathode recycle loop as shown here is surprisingly more efficient. While one might assume that a higher inlet pH (resulting from the cathode recycle loop) would induce a stronger overall driving force for cross-over of H+ions, the resultant increase in conductivity of the cathode feed stream, and the higher flow rate, which minimizes electrode fouling due to precipitation and the faster removal of gas bubbles due to the higher liquid flow rate, outweigh the effect of higher H+cross-over and lead to advantages in higher overall efficiency and higher outlet pH. Other advantages: if unfiltered catholyte is recycled, the introduction of “seeds,” which can provide a preferential nucleation site for Mg(OH)2, is beneficial and reduces precipitation / fouling on the electrode. This will also lead to larger particles at the outlet that can be separated more easily in a downstream solids separation unit. This recycle loop can be achieved directly around the electrolyzer or as a bigger loop (e.g., around the pre-precipitation of CaCOs) making use of at least one of the above-mentioned advantages.

[0058] Fig.21 shows a process flow diagram of a representative system and process according to certain embodiments of the disclosure. In general, this concept of having an electrochemical Ca(OH)2 reactor downstream of the electrochemical Mg(OH)2 reactor can be applied to all process configuration but gives the greatest Ca(OH)2 yield in configurations where no CaCO3pre-precipitation is performed. Since, in the shown configuration, CO2 and Mg have already been removed, it is now easy to access the Ca in the seawater and produce Ca(OH)2 downstream of the Mg(OH)2 separation. Using seawater in both electrolyzers has the advantage of providing higher amounts of electrolyte to the anode of the second electrolyzer, specifically Na+ions. Fig.22 shows a process flow diagram of a representative system and process according to certain embodiments of the disclosure. In this configuration, the catholyte of the downstream electrolyzer is used as anode feed in same electrolyzer to recover the energy from the OH' that is still in solution after precipitate recovery. The OH' was produced at the cathode.

[0059] Fig.23 shows a process flow diagram of a representative system and process according to certain embodiments of the disclosure. This configuration enables CO2 capture in aqueous form as NaHCO3 / lSfeCCh without the formation of solids (caused by divalent cations such as Ca / Mg) which enables different sequestration options such as ocean sequestration or liquid underground injection.

[0060] Fig. 24 is a schematic of an exemplary continuous flow electrolysis set up.

[0061] Fig. 25 is schematic depicting an exemplary bubble column and vertical falling film column.

[0062] Fig. 26 is a graph illustrating the effect of current density on catholyte pH for both deaeration configurations: bubble and film.

[0063] Fig.27 is a graph illustrating representative x-ray diffraction patterns of film and bubble cases.

[0064] Fig. 28A-B are graphs illustrating (a) The purity of Mg(0H)2 as a function of current density for the bubble degassing tank (blue diamonds) and film column (red triangles) configurations and (b) CaCCE content of the precipitates for each case as a function of current density.

[0065] Fig. 29A-B are graphs illustrating (a) Mg2+removal efficiency of Case 1 and Case 2 experiments as a function of current density and (b) Mg2+removal efficiency as a function of pH measured in catholyte supernatant / effluent.

[0066] Fig 30A-C are graphs illustrating (a) Mg(0H)2 precipitation selectivity (i.e., Mg2+reacted with OH- in an electrolyzer, yielding Mg(0H)2, (b) Mg(0H)2 experimental yield (i.e., utilization of total Mg2+to precipitate final mass yield of Mg(0H)2), and solid recovery rates.

[0067] Fig. 31 are SEM images of representative samples of from left to right: (a) bubble column, 320 A / m2(b) bubble column, 400 A / m2(c) bubble column, 480 A / m2(d) film column, 320 A / m2(e) film column, 400 A / m2and (f) film column, 480 A / m2.

[0068] Fig. 32A-B are graphs illustrating (a) surface area measured by the Brunauer-Emmett-Teller (BET) method as current density increases and (b) particle size distribution (D50) as current density increases. Fig. 33A-C are graphs illustrating (a) cathodic Faradaic Efficiency (FEcathodic) as a function of current density, calculated from total OH- produced by the electrolyzer taking into account Mg2+removed and Mg2+precipitation (b) Voltage efficiency as a function of current density (c) Total efficiency as a product of FEcathodic and Voltage efficiency.

[0069] Fig.34A-B are graphs illustrating (a) MgOH2 yield (g / L) and (b) Energy consumption.

[0070] DETAILED DESCRIPTION OF THE INVENTION

[0071] The processes described herein are based on electrolysis and take advantage of the acid / base production in an electrolyzer, where acidity is produced at the anode and basicity at the cathode following the general reaction:

[0072]

[0073] First, seawater is fed into the anode cell of the electrolyzer where a current is applied, causing the water molecules to split, effectively forming protons (H+) and decreasing the pH of the solution in the anode cell (herein referred to as the “anolyte”) to a pH of ~l-2. The solution is then stored in an open agitated tank to allow the dissolved CO2 to degas and to equilibrate with the atmosphere. After equilibration, the CO2 depleted solution is processed before reaching the cathode cell of the electrolyzer. First, to favor a high purity of the final solid precipitated, Ca is removed from the solution using a selective ion exchange resin. Second, the solution is concentrated using a nanofiltration system. A membrane like the FilmTec™ NF90 concentrates divalent ions in the retentate while concentrations of other elements are substantially unaffected. This step allows to increase the Mg concentration, making it easier to precipitate Mg in the electrolyzer as magnesium hydroxide; the higher the Mg concentration, the higher the saturation index of the solution towards Mg(0H)2. Finally, the pH of the solution is increased to a neutral pH using the catholyte solution obtained after solid separation. The higher the Mg concentration after this step, the higher the faradaic efficiency of the electrolyzer. Each of these steps is preferably performed without contact with the atmosphere or other CO2 sources to avoid CO2 dissolution. Finally, the solution is directed to the cathode cell of the electrolyzer to increase its pH to about 10 to about 11, where magnesium precipitates as brucite (magnesium hydroxide). Based on thermodynamic simulations, assuming an average composition of seawater and a pH of 11, 54.7 mol / L(seawater) of brucite can be precipitated, which represents a weight of 3.19 g (0.11 oz). An alternative to the dilution of the anolyte with the catholyte for the pH increase step prior to the precipitation step is rock dissolution. As an example, the dissolution of periclase - a magnesium oxide mineral - following the reaction MgO + 2 H+ Mg2++ H2O, neutralizes H+ (49.63 mol(H+) / kg(MgO)), hence increases the pH, while introducing more Mg into solution to be precipitated as brucite in the electrolyzer. This could replace the NF and pH adjustment step of the process flow diagram (Figure 2).

[0074] The membrane barrier separates the catholyte and the anolyte in order to: (1) Avoid neutralization reactions from occurring between the catholyte and anolyte (i.e., by proton crossover), thus maintaining a substantially constant cathode pH and favorable conditions for Mg(0H)2 precipitation; (2) Promote higher reactor energy efficiency; and (3) Facilitate the collection of gas streams (H2 and O2). Ch gas, which is a common byproduct of electrolysis when the solution used contains high concentration of CF ions (e.g., in seawater), can be avoided if an oxygen selective electrode is used. If such an electrode is not used, the gas stream can be directed into a granulated activated carbon tank to reduce the chlorine concentration. The same technique can be used to treat the chlorine in the anolyte stream.

[0075] In certain embodiments, the electrolyzer / electrochemical cell may possess a single inlet, which provides seawater to both the anode and cathode. For example, and without limitation, the inlet may be a single piece of piping which splits into two pieces of piping, e.g., by a Y-fitting. In other examples, the inlet may merely be a single piece of piping that leads to the electrochemical cell.

[0076] In certain embodiments, the inlet of the electrolyzer / electrochemical cell may comprise two separate pieces of piping which both lead from a seawater source and to the anodic chamber and cathodic chamber, respectively.

[0077] Solution alkalinity plays an important role in this process due to the potential for calcite (calcium carbonate, CaCO3) precipitation that would decrease brucite purity. The alkalinity of seawater - in the form of bicarbonate ion (HCO3) is about 2 mmol / L (Table 1).

[0078] Table 1. Average Concentration of Seawater Components from Millero, etal. 2008.

[0079] Species Concentration

[0080] Na 486.1

[0081] Mg 54.7

[0082] Ca 10.7

[0083] K 10.6

[0084] Sr 0.1

[0085] Cl 565.8

[0086] SO429.3

[0087] HCO3 2.0

[0088]

[0089] B 0.4

[0090] F 0.07

[0091] As a result of this high alkalinity, any increase in pH beyond what is needed to precipitate Mg(0H)2 can initiate precipitation of calcium carbonate (Figure 3).

[0092] Due to the high Mg concentration in seawater (~55 mmol / L), seawater is supersaturated (SI > 0) toward calcite (SI = 0.77). Increasing the pH of seawater to 11 would further increase the solution saturation index such that SI = 1.75, which would force calcite precipitation, thus decreasing brucite purity. To guarantee the production of high purity brucite, the saturation index of the seawater solution should be controlled and, preferably, stay below the thermodynamic equilibrium. The saturation index is a function of the activity of the species forming the mineral:

[0093]

[0094] where (Ca2+) and (CO32) are the activity of Ca2+and CO32, respectively, and Kspis the solubility product of calcite (thermodynamic constant). To reduce the saturation index of seawater toward calcite, it is possible to: (1) decrease the Ca2+concentration, and / or (2) decrease the CO32concentration.

[0095] The alkalinity (i.e., the carbonate concentration) of the seawater can be adjusted using the relationship between the carbonate system and the pH (Figure 4). Based on thermodynamic simulations using PhreeqC, a controlled decrease in pH could induce a decrease of the carbonate ions in solution. If the pH reaches 7.9, the solution begins to degas CO2. CO2 degassing peaks at for pH values below 4. As a consequence of the degassing, the carbonate concentration in solution drops to 12.8 pmol / L at pH 1-2. To avoid redissolving CO2 from the atmosphere into the solution when re-increasing the pH, the process may be performed in a closed or inert environment (e.g., under N2 flow) once the seawater has degassed. This will assist in controlling the carbonate concentration, and thus the saturation index of the solution toward calcite would remain below 0 (essentially no precipitation possible) at pH 7 (SI = -2.72) and pH 11 (-0.14).

[0096] Higher magnesium concentrations in the electrolyzer inlet foster efficient brucite production. A method for increasing magnesium concentration - and thus brucite precipitation - is nanofiltration (NF). After the pH adjustment step (Figure 1), the solution passes through nanofiltration membranes (e.g., FilmTec™ NF90) to concentrate the divalent ions in the retentate. The retentate stream is then directed towards an electrolyzer cathode to produce brucite at low temperatures, while the permeate is to be either recirculated after treatment, used as utility water, or disposed of depending on the process considered. The precipitated brucite is then recovered in a settling tank and the supernatant could be redirected to the dissolution circuit.

[0097] NF can increase the concentration of both magnesium and calcium, as both are divalent ions. An increase of the calcium concentration would result in an increase of the saturation index of the solution with respect to calcite to a point where calcite may precipitate; thermodynamic modeling suggests that doubling the concentration of Ca in seawater is sufficient to induce calcite precipitation. To favor higher brucite purity (e.g., limited calcite formation), Ca can be separated from Mg prior to or after the NF step using a cation exchange resin (e.g., Amberlite IR120) that can effectively reduce the calcium concentration without significantly affecting the magnesium concentration.

[0098] Alternative to degassing CO2 to remove the carbonates to avoid calcium precipitation during electrolysis, a precipitant is added to selectively remove the calcium ion prior to electrolysis. Substantial or preferably complete removal of calcium ion prior to electrolysis ensures production of brucite which is free of calcium carbonate contamination. Precipitants include but are not limited to sodium carbonate, sodium bicarbonate and oxalic acid or an oxalate salt.

[0099] Compared to the addition of lye (NaOH) to precipitate Mg(0H)2, adding selective precipitants, such as NaHCO3or Na2COs, (a) will not precipitate magnesium, at a controlled dose, (b) costs less for the precipitant per ton of Mg(0H)2 produced, and (c) requires less postprocessing if calcium is removed prior to Mg(0H)2 precipitation, whereas in the addition of lye for Mg(0H)2 production, the calcium must be separated from the Mg(0H)2 solid. If NaHCO3or Na2COs is used as a precipitant, elevated off-gassing of CO2 will occur at the anode during electrolysis.

[0100] In the present disclosure, certain components of these systems are described as being “coupled” to one another. As will be appreciated, the term “coupled” as used herein describes components that are operationally linked to one another, but does not preclude the presence of intervening components between those said to be coupled to one another. In certain embodiments, components that are described as “coupled” to one another are in fluidic and / or gaseous communication. Additionally, as will be appreciated, various system components are described as “having” certain features. Such descriptions do not preclude, and specifically contemplate, the presence of additional features, such as inlets, outlets, valves, control mechanisms, measurement devices, heating and / or cooling systems, etc. Additionally, in the systems of the present disclosure, certain components are described as having one or more outlets or inlets. Such outlets and inlets may represent separate structural elements, or may be combined into a single inlet or outlet as suitable. The person of skill in the art will recognize that, once the important features and operating conditions of systems such as those described herein are understood, the detailed design and operation of such systems involved many choices, such as specific reagent flows, separation steps, etc. While the present disclosure provides a number of specific embodiments, any suitable combination of these design choices may be made.

[0101] In certain aspects, a system is provided, comprising:

[0102] a first electrochemical cell comprising:

[0103] a first cathodic chamber, comprising:

[0104] a first cathode;

[0105] a first target ion feed inlet;

[0106] a first cathodic gas outlet;

[0107] a first catholyte mixture outlet;

[0108] a first anodic chamber, comprising:

[0109] a first anode;

[0110] a first anolyte feed inlet;

[0111] a first anodic gas outlet;

[0112] at least one primary acidic anolyte outlet;

[0113] a first membrane disposed between the first cathodic chamber and the first anodic chamber;

[0114] a first solid separation chamber, comprising:

[0115] a first catholyte mixture inlet coupled to the first catholyte mixture outlet;

[0116] a first solid collection outlet; and

[0117] a first supernatant outlet;

[0118] wherein the first cathodic chamber and the first anodic chamber are in ionic communication.

[0119] In certain embodiments, the system further comprises at least one target ion feed concentrator, comprising: a first target ion source inlet; and a first concentrated feed outlet coupled to the first target ion feed inlet of the first cathodic chamber. In certain embodiments, the system comprises one target ion feed concentrator. In certain embodiments, the at least one target ion feed concentrator comprises: a first target ion feed concentrator, comprising the first target ion source inlet and the first concentrated feed outlet; and a second target ion feed concentrator, comprising a second target ion feed inlet coupled to the first concentrated feed outlet and a second concentrated feed outlet coupled to the first target ion feed inlet of the cathodic chamber.

[0120] In certain embodiments, the at least one target ion feed concentrator further comprises at least one nanofiltration chamber. In certain such embodiments, the at least one target ion feed concentrator comprises one nanofiltration chamber. In other such embodiments, the at least one target ion feed concentrator comprises two nanofiltration chambers. In certain alternative embodiments, the at least one target ion feed concentrator comprises at least one reverse osmosis chamber. In certain such embodiments, the at least one target ion feed concentrator comprises one reverse osmosis chamber. In other such embodiments, the at least one target ion feed concentrator comprises two reverse osmosis chambers. In certain alternative embodiments, the at least one target ion feed concentrator comprises at least one evaporation chamber. In certain such embodiments, the at least one target ion feed concentrator comprises one evaporation chamber. In other such embodiments, the at least one target ion feed concentrator comprises two evaporation chambers.

[0121] In certain embodiments, the at least one target ion feed concentrator is configured to increase a concentration of at least one target ion in an aqueous solution comprising the at least one target ion. For example, the at least one target ion feed concentrator may be configured to increase a concentration of Mg2+in the aqueous solution comprising the at least one target ion.

[0122] In certain embodiments, the system further comprises a degassing tank, comprising: an acidic anolyte inlet coupled to the at least one primary acidic anolyte outlet of the anodic chamber; a CO2 outlet at a top of the degassing tank, configured to allow a gaseous fluid to flow from the degassing tank; and a degassed anolyte outlet.

[0123] In certain embodiments, the system further comprises a degassing tank, comprising: a degassing feed inlet; a CO2 outlet at a top of the degassing tank, configured to allow a gaseous fluid to flow from the degassing tank; and a degassed mixture outlet coupled to the first target ion feed inlet of the first cathodic chamber.

[0124] In certain embodiments, the at least one target ion feed concentrator is present, and degassing feed inlet is coupled to the first concentrated feed outlet of the at least one target ion feed concentrator. In certain embodiments, the CO2 outlet is configured to allow passive exit of a fluid comprising CO2 from an aqueous solution comprising at least one target ion. In certain embodiments, the degassing tank further comprises a stripping gas inlet at a top of the degassing tank, wherein the stripping gas inlet is configured to provide a stripping gas to the degassing chamber. In certain embodiments, the stripping gas inlet is coupled to the first cathodic gas outlet of the first cathodic chamber. In certain embodiments, the stripping gas enhances removal of CO2 from an aqueous solution comprising at least one target ion. In certain embodiments, the stripping gas is air (e.g., atmospheric air or compressed air). In some embodiments, the degassing feed inlet further comprises an acid inlet coupled to the at least one primary acidic anolyte outlet of the first anodic chamber.

[0125] In various embodiments, the system further comprises a first carbonation chamber, comprising: a first supernatant inlet coupled to the first supernatant outlet of the first solid separation chamber; a first carbonation feed inlet configured to flow a fluid comprising CO2 into the first carbonation chamber; a first carbonated mixture outlet; and a first gas outlet; and a second solid separation chamber, comprising: a first carbonated mixture inlet coupled to the first carbonated mixture outlet of the first carbonation chamber; a second solid collection outlet; and a second supernatant outlet.

[0126] In certain embodiments, the first carbonation chamber is configured to produce a carbonate of a second target ion. For example, the first carbonation chamber may be configured to produce CaCO3.

[0127] In certain embodiments, the system further comprises: a first additive chamber, comprising: a second target ion feed inlet; a first additive inlet; and an additive mixture outlet; a third solid separation chamber, comprising: an additive mixture inlet coupled to the additive mixture outlet of the first additive chamber; a third solid collection outlet; and a third supernatant outlet; wherein the third supernatant outlet is coupled to the first target ion feed inlet.

[0128] In certain embodiments, the first additive inlet is configured to combine an additive with a first target ion feed. In certain embodiments, the first additive chamber is configured to produce a first solid comprising at least one non-target ion. In certain embodiments, the first solid comprises calcium [e.g., CaCO3or Ca3(PO4)2]. The additive may comprise [CO3]2-, [PO4]3-, or a combination thereof. For example, the additive may comprise NaHCO3, Na3PO4, or a combination thereof. In certain embodiments, the first target ion feed comprises Ca2+. The additive may be in a solid phase, an aqueous solution phase, a liquid phase, or a gas phase. In certain preferred embodiments, the additive is in a solid phase. In certain embodiments, the at least one target ion feed concentrator is present and the second target ion feed inlet of the first additive chamber is coupled to the first concentrated feed outlet of the at least one target ion feed concentrator.

[0129] In certain embodiments, the system further comprises: a first blending tank, comprising: a third target ion feed inlet; a first blended mixture outlet; and a first supernatant inlet coupled to the first supernatant outlet of the first solid separation chamber; and a fourth solid separation chamber, comprising: a first blended mixture inlet coupled to the first blended mixture outlet of the first blending tank; a fourth solid collection outlet; and a fourth supernatant outlet coupled to the first target ion feed inlet of the first cathodic chamber. In certain such embodiments, the first blending tank is configured to combine a first supernatant from the first solid separation chamber with a first target ion feed, thereby producing a blended mixture comprising a precipitate of at least one non-target ion. In certain embodiments, the fourth solid separation chamber is configured to separate the precipitate of the at least one non-target ion from the blended mixture.

[0130] In certain embodiments, the first catholyte mixture outlet comprises a primary catholyte mixture outlet and secondary catholyte mixture outlet, and the system further comprises: a first blending tank, comprising: a third target ion feed inlet; a first blended mixture outlet; and a first catholyte mixture inlet coupled to the secondary catholyte mixture outlet of the first cathodic chamber; and a fourth solid separation chamber, comprising: a first blended mixture inlet coupled to the first blended mixture outlet of the first blending tank; a fourth solid collection outlet; and a fourth supernatant outlet coupled to the first target ion feed inlet of the first cathodic chamber; wherein the primary catholyte mixture outlet is coupled to the first catholyte mixture inlet of the first solid separation chamber. In certain embodiments, the first solid separation chamber is configured to separate a solid of a target ion from a first portion of a first catholyte mixture; and the first blending tank is configured to combine a second portion of the first catholyte mixture with a first target ion feed; thereby producing a blended mixture comprising a precipitate of at least one non-target ion. In certain embodiments, the fourth solid separation chamber is configured to separate the precipitate of the at least one non-target ion from the blended mixture. In various embodiments, the system further comprises a first carbonation chamber, comprising: a second blended mixture inlet coupled to the first blended mixture outlet of the first blending tank; a first carbonation feed inlet configured to flow a fluid comprising CO2 into the first carbonation chamber; a first carbonated mixture outlet coupled to the first blended mixture inlet of the fourth solid separation chamber; and a first gas outlet. In certain embodiments, the system further comprises a first carbonation chamber, comprising: a second supernatant inlet coupled to the first supernatant outlet of the first solid separation chamber; a first carbonation feed inlet configured to flow a fluid comprising CO2 into the first carbonation chamber; a first carbonated mixture outlet coupled to the third target ion feed inlet of the first blending tank; and a first gas outlet. In certain embodiments, the system further comprises a first carbonation chamber, comprising: a first catholyte mixture inlet coupled to the secondary catholyte mixture outlet of the first cathodic chamber; a first carbonation feed inlet configured to flow a fluid comprising CO2 into the first carbonation chamber; a first carbonated mixture outlet coupled to the third target ion feed inlet of the first blending tank; and a first gas outlet.

[0131] In certain embodiments, the first carbonation chamber is configured to is configured to produce a carbonate of at least one non-target ion. For example, the first carbonation chamber may be configured to produce CaCO3. In certain embodiments, the system comprises the at least one target ion feed concentrator, and the first concentrated feed outlet of the at least one target ion feed concentrator is coupled to the third target ion feed inlet of the first blending tank. In certain embodiments, the first anodic chamber further comprises a first recycle inlet coupled to the first supernatant outlet of the first solid separation chamber.

[0132] In certain embodiments, the first recycle inlet is configured to flow a first supernatant from the first solid separation chamber to the first anodic chamber. In certain embodiments, the first catholyte mixture outlet further comprises a first catholyte recycle outlet, the first target ion feed inlet comprises a first catholyte recycle inlet, and the first catholyte recycle outlet is coupled to the first catholyte recycle inlet. In certain such embodiments, the first catholyte recycle outlet and first catholyte recycle inlet are configured to flow a portion of a first catholyte mixture from the first catholyte mixture outlet to the first target ion feed inlet.

[0133] In certain embodiments, the system comprises a single electrochemical cell. In alternative embodiments, the system further comprises a second electrochemical cell comprising: a second cathodic chamber, comprising: a second cathode; a second target ion feed inlet coupled to the first supernatant outlet of the first solid separation chamber; a second cathodic gas outlet; a second catholyte mixture outlet; a second anodic chamber, comprising: a second anode; a second anolyte feed inlet coupled to the at least one primary acidic anolyte outlet; a second anodic gas outlet; at least one secondary acidic anolyte outlet; a second membrane disposed between the second cathodic chamber and the second anodic chamber; a fifth solid separation chamber, comprising: a second catholyte mixture inlet coupled to second first catholyte mixture outlet; a second solid collection outlet; and a second supernatant outlet; wherein the second cathodic chamber and the second anodic chamber are in ionic communication.

[0134] In certain embodiments, the first electrochemical cell is configured to produce a carbonate of at least one non-target ion, preferably wherein the carbonate of at least one nontarget ion is CaCO3. In certain embodiments, the second electrochemical cell is configured to produce a hydroxide of a first target ion. For example, the second electrochemical cell may be configured to produce Mg(0H)2.

[0135] In certain embodiments, the system further comprises a second electrochemical cell comprising: a second cathodic chamber, comprising: a second cathode; a second target ion feed inlet coupled to the first supernatant outlet of the first solid separation chamber; a second cathodic gas outlet; a second catholyte mixture outlet; a second anodic chamber, comprising: a second anode; a second anolyte feed inlet; a second anodic gas outlet; at least one secondary acidic anolyte outlet; a second membrane disposed between the second cathodic chamber and the second anodic chamber; a second solid separation chamber, comprising: a second catholyte mixture inlet coupled to second first catholyte mixture outlet; a second solid collection outlet; and a second supernatant mixture outlet; wherein the second cathodic chamber and the second anodic chamber are in ionic communication. In certain embodiments, the first electrochemical cell is configured to produce a hydroxide of a first target ion. For example, the first electrochemical cell may be configured to produce Mg(0H)2.

[0136] In certain embodiments, the second electrochemical cell is configured to produce a hydroxide of a second target ion. For example, the second electrochemical cell may be configured to produce Ca(0H)2. In certain embodiments, the second supernatant outlet of the second solid separation chamber is coupled to the second anolyte feed inlet of the second anodic chamber.

[0137] In certain embodiments, the system further comprises: a third carbonation chamber, comprising: a third supernatant mixture inlet coupled to the second supernatant mixture outlet of the second solid separation chamber; a third carbonation feed inlet configured to flow a fluid comprising CO2 into the third carbonation chamber; a third carbonated mixture outlet; and a third gas outlet. In certain embodiments, the first membrane and, when present, the second membrane comprise: a cation exchange membrane (CEM, e.g., sulfonated tetrafluoroethylene based fluoropolymer-copolymer), anion exchange membrane (AEM), a non-selective barrier material, or a combination thereof. In certain embodiments, the first membrane and, when present, the second membrane comprise a cation exchange membrane. In certain such embodiments, the first membrane and, when present, the second membrane are selective for the passage of Na+ions from the anodic chamber to the cathodic chamber. In certain alternative embodiments, the first membrane is an anion exchange membrane and / or the second membrane is an anion exchange membrane. In certain such embodiments, the first membrane and, when present, the second membrane are selective for the passage of Cl from the first cathodic chamber to the first anodic chamber, and, when present, from the second cathodic chamber to the second anodic chamber.

[0138] In certain embodiments, the first anode and, when present, the second anode are oxygen-selective anodes. In certain embodiments, the first anode and, when present, the second anode, are in the form of a plate. Alternatively, the first anode and, when present, the second anode, may be in the form of a mesh. In various embodiments, the first cathode and, when present, the second cathode, comprise iron, iron alloy, nickel, nickel alloy, cobalt, cobalt alloy, titanium, titanium alloy, aluminum, aluminum alloy, platinum, or a combination thereof. In certain preferred embodiments, the first cathode and, when present, the second cathode, further comprise a coating comprising platinum, nickel phosphate, or molybdenum sulfate. In various embodiments, the first cathode and, when present, the second cathode, are in the form of a mesh, plate, or rod. In certain embodiments, the first cathode and, when present, the second cathode, are in the form of a mesh. In certain such embodiments, the first cathode and, when present, the second cathode, are mesh comprising Pt and Ti. In certain embodiments, the first cathode and, when present, the second cathode are mesh comprising stainless steel (e.g., a 316 stainless steel mesh). In certain alternative embodiments, the first cathode and, when present, the second cathode are plates. In certain such embodiments, the first cathode and, when present, the second cathode are plates comprising Ti having a coating comprising Pt. In certain alternative embodiments, the first cathode and, when present, the second cathode are plates comprising Ni. In various embodiments, the first anode and, when present, the second anode comprise a group VIII metal, a group IX metal, a group X metal, titanium clad with a group VIII metal, titanium clad with a group IX metal, titanium clad with a group X metal, titanium clad with mixed metal oxide, or a combination thereof. In certain particular embodiments, the first anode and, when present, the second anode further comprise iridium, tin, cobalt, manganese, tantalum, ruthenium, graphite, graphene, or carbon nanotube(s).

[0139] In certain embodiments, the first electrochemical cell and, when present, the second electrochemical cell are configured to produce an anodic gas comprising O2 at the first anode and, when present, the second anode. In certain such embodiments, the anodic gas further comprises Ch. In certain embodiments, the first electrochemical cell and, when present, the second electrochemical cell are configured to produce a cathodic gas comprising th at the first cathode and, when present, the second cathode. In certain embodiments, the first electrochemical cell and, when present, the second electrochemical cell are configured to produce hydroxides of one or more target ions at the first cathode and, when present, the second cathode. In certain such embodiments, the first electrochemical cell is configured to produce Mg(0H)2 at the first cathode.

[0140] In certain embodiments, the at least one nano filtration chamber comprises a nanofiltration membrane comprising a plurality of pores, and each of the plurality of pores has a pore diameter of from about 0.001 to about 0.01 pm. In certain embodiments, the at least one nanofiltration membrane is a polyamide thin-film composite. In certain such embodiments, the at least one nanofiltration membrane is a FilmTec™ NF90 Nanofiltration membrane.

[0141] In certain embodiments, the system is configured to produce calcium hydroxide. In certain alternative embodiments, the system is configured to produce magnesium hydroxide. In yet other embodiments, the system is configured to produce magnesium hydroxide and calcium hydroxide.

[0142] In certain embodiments, the first target ion feed inlet and first anolyte feed inlet of the first electrochemical cell is a single, combined inlet coupled to the first anodic chamber and the first cathodic chamber.

[0143] In certain embodiments, the Mg(OH)2 concentration of the first catholyte mixture is sufficient (e.g., saturated) to pre-precipitate Mg(OH)2.

[0144] In certain embodiments, a first dosing vessel is disposed between the first catholyte recycle outlet and first catholyte recycle inlet configured to pre-precipitate CaCO3. In certain such embodiments, a second dosing vessel is disposed between the first catholyte recycle outlet and first catholyte recycle inlet configured to pre-precipitate Mg(0H)2.

[0145] In certain embodiments, the system comprises an electrochemical cell depicted in Figure 19 or 20.

[0146] In certain embodiments, the system is configured to produce a hydroxide of a target ion from an aqueous solution comprising the target ion and at least one non-target ion. In certain embodiments, the aqueous solution is selected from seawater, desalination brine, industrial brine, and natural brine. In certain such embodiments, the aqueous solution is a product of an industrial process. In alternative such embodiments, the aqueous solution is or is derived from seawater.

[0147] In certain embodiments, systems of the disclosure comprise two electrochemical cells (e.g., electrolyzers) that are each configured to produce a hydroxide of a target ion from a mixture comprising at least two target ions. As will be understood by one of ordinary skill in the art, the pH of the catholyte solutions in each of the electrochemical cells may be maintained at a value that is favorable for the selective precipitation of one hydroxide species over another - allowing the precipitation of a distinct hydroxide species in each electrolyzer [e.g., Mg(OH)2 in a first electrochemical cell and Ca(OH)2 in a second electrochemical cell] or only one hydroxide species (e.g., only Ca(OH)2). For example, a catholyte pH of about 10 favors production and precipitation of Mg(OH)2 from solutions comprising Mg(OH)2 and Ca(OH)2. Precipitation of Ca(OH)2 does not occur until a pH of about 12.5 is reached. Thus, sequential recovery of Mg(OH)2 and Ca(OH)2 from solutions comprising Mg(OH)2 and Ca(OH)2 is possible, whereby Mg(OH)2 is recovered first when increasing the pH from low to high. One of ordinary skill in the art will readily understand how to configure the systems of the disclosure (e.g., by selecting suitable operating conditions and system components) to selectively produce a hydroxide of a first target ion in a first electrochemical cell and a hydroxide of a second target ion in a second electrochemical cell.

[0148] In certain embodiments, when Mg-concentration is high it may be of economic value to use two sequential electrolyzers to reduce recycle pumping power consumption, while with low Mg concentrations it might be more economical to provide OH' via a recycle rather than using capital intensive electrolyzer hardware. Thus, one of skill in the art would be able to adapt the disclosed systems and methods based on Mg2+concentration to select a suitable configuration for any constraints of dimension or economy.

[0149] In certain embodiments, systems and methods of the disclosure comprise membranes separating a cathodic chamber from an anodic chamber. In further embodiments, the membrane is suitable for separating divalent cations from mixtures of cations. In certain embodiments, the membrane comprises Nafion™. In certain embodiments, the membrane comprises a polyamide active layer. In further embodiments, the polyamide active layer is an active filtration layer comprising a cross-linked polyamide. As will be understood by one of skill in the art, in certain such embodiments, this layer is responsible for the membrane’s nanofiltration properties, providing high salt rejection while allowing permeation of water and small solutes. In some embodiments, the polyamide active layer comprises a polyamide network formed through interfacial polymerization of m-phenylenediamine (MPD) and trimesoyl chloride (TMC). The resulting polyamide network comprises a dense, cross-linked structure that offers high selectivity based on size and charge exclusion. The structure of this polyamide layer affects the ability of the membrane to reject divalent ions (e.g., calcium and magnesium) and organic compounds, while still permitting the passage of monovalent ions (e.g., sodium and chloride), depending on their hydration state.

[0150] In some embodiments, the membrane further comprises a support layer. In further embodiments, the support layer is a porous polysulfone support layer. This layer provides mechanical strength without significantly impeding water flow. Polysulfone has a robust structure and is chemically resistant, which enhances the overall durability of the membrane.

[0151] In certain embodiments, the membrane further comprises a microporous substrate. In preferred embodiments, the microporous substrate comprises a non-woven fabric layer, which supports the polysulfone and polyamide layers, adding to the mechanical integrity and allowing the membrane to withstand operational pressures.

[0152] Preferred membranes for use with systems and methods of the present disclosure are capable of effectively retaining (rejecting) a complex comprising calcium [e.g., a calcium-EDTA (Ethylenediaminetetraacetate) complex], selectively, while having a reduced rejection of monovalent ions (Na+and HCO3 ). This degree of separation (between retention of calcium and monovalent ions) is a function of the charge density and pore size of the active layer (e.g., comprising polyamide) of the membrane, located at the membrane / water interface. For example, such a membrane was identified (XN45), which showed excellent Ca-EDTA rejection, while showing only moderate rejection (20%) of monovalent ions. This active layer is formed on the porous polysulfone support by reacting a water-soluble monomer amine (piperazine) with an organic solvent-soluble acyl chloride (trimesoyl chloride). A condensation reaction between these monomers takes place at the interface of the water and organic solvent, and is self-limiting (by the diffusivity of piperazine in the organic solvent). Thus, a thin-film forms on the surface of the polysulfone, which has the requisite transport properties for monovalent / divalent separation. The best membrane evaluated (XN45) has a pore size of -500 Da, which allows the majority of the monovalent ions to pass, while rejecting divalent ions and larger complexed and charged species.

[0153] In certain embodiments, systems and methods of the disclosure comprise anodes that are selective for the Oxygen-Evolution Reaction (OER). Suitable anodes may be found, for example, in published U. S. Patent Application Publication No. US 2024 / 0254640 Al, the contents of which is fully incorporated by reference herein..

[0154] In certain aspects, a method of preparing Mg(0H)2 using a system of the present disclosure is provided, the method comprising the steps of:

[0155] providing:

[0156] an electrolyte solution to the first anodic chamber; and

[0157] a first target ion stream to the first cathodic chamber;

[0158] performing a first electrochemical process, comprising:

[0159] applying a voltage to the first cathode and the first anode; thereby producing: a first acidic anolyte and an anodic gas at the first anode; and

[0160] a first catholyte mixture and a cathodic gas at the first cathode;

[0161] wherein:

[0162] the first target ion stream comprises Mg2+; and

[0163] the first catholyte mixture comprises Mg(0H)2.

[0164] A method of preparing Mg(0H)2, comprising:

[0165] providing:

[0166] a first target ion solution comprising Mg2+and at least one non-target ion to a first anodic chamber and a first cathodic chamber of a first electrochemical cell; the first electrochemical cell further comprising:

[0167] a first anode disposed within the first anodic chamber;

[0168] a first cathode disposed within the first cathodic chamber; and a first membrane disposed between and configured to separate the first cathodic chamber and the first anodic chamber;

[0169] wherein the first anodic chamber and the first cathodic chamber are in fluid communication; and

[0170] performing a first electrochemical process, comprising:

[0171] applying a first voltage to the first cathode and the first anode; thereby producing: a first acidic anolyte and an anodic gas at the first anode; and

[0172] a first catholyte mixture and a cathodic gas at the first cathode;

[0173] wherein the first catholyte mixture comprises the Mg(0H)2.

[0174] In certain embodiments, the second acidic anolyte portion is discharged. As used herein, the term “discharge” does not necessarily preclude the presence of additional downstream system components or method steps involving the second acidic anolyte portion. For example, as will be appreciated by one of skill in the art, the second portion of the acidic anolyte may be neutralized at or after the point of generation, or used in downstream applications where acidic solutions are useful (e.g., as a disinfectant or sterilizing solution).

[0175] In certain embodiments, as will be appreciated by one of ordinary skill in the art, separating the Mg(0H)2 from the first catholyte mixture comprises precipitating Mg(0H)2. Said precipitation may occur optionally within the cathodic chamber (e.g, resulting in a suspension of the hydroxide of the at least one target ion within the cathodic chamber) or outside of the cathodic chamber (e.g, in a hydroxide isolation chamber or precipitation chamber fluidly coupled to an outlet of the cathodic chamber).

[0176] In certain aspects, provided herein are systems, comprising:

[0177] an electrochemical cell, comprising:

[0178] a cathodic chamber, comprising:

[0179] a cathode;

[0180] a neutral retentate inlet;

[0181] a cathodic gas outlet; and

[0182] a target mixture outlet;

[0183] wherein the cathodic chamber is configured to facilitate the passage of a neutral retentate through the cathodic chamber, contact the neutral retentate with the cathode, and produce a target mixture comprising a target precipitate and a first supernatant;

[0184] an anodic chamber, comprising:

[0185] an anode;

[0186] an aqueous feed inlet;

[0187] an anodic gas outlet; and

[0188] an acidic anolyte outlet;

[0189] wherein the anodic chamber is configured to facilitate the passage of an aqueous feed comprising target ions, non-target ions, and CO2 through the anodic chamber, contact the aqueous feed with the anode, and produce an acidic anolyte solution; and

[0190] an electrochemical membrane disposed between the cathodic chamber and the anodic chamber;

[0191] wherein the cathodic chamber and the anodic chamber are in ionic communication; a degassing tank coupled to the anodic chamber, comprising: an acidic anolyte inlet coupled to the acidic anolyte outlet of the anodic chamber; a CO2 outlet at a top of the degassing tank, configured to allow passive exit of CO2 from the acidic anolyte solution;

[0192] a degassed anolyte outlet;

[0193] a separation chamber coupled to the degassing tank, comprising;

[0194] an ion exchange resin disposed within the separation chamber, configured to separate at least one of the non-target ions from the degassed anolyte and produce a depleted anolyte solution comprising the target ions; and

[0195] a depleted anolyte outlet;

[0196] at least one nanofiltration chamber coupled to the separation chamber, comprising;

[0197] a depleted anolyte inlet disposed at a first end of the at least one nanofiltration chamber and coupled to the depleted anolyte outlet of the separation chamber;

[0198] a permeate outlet disposed at a second end of the at least one nanofiltration chamber; an acidic retentate outlet disposed at the first end of the at least one nanofiltration chamber; and

[0199] at least one nanofiltration membrane disposed within the at least one nanofiltration chamber, configured to:

[0200] separate the permeate outlet and the second end of the at least one nanofiltration chamber from the acidic retentate outlet and the first end of the at least one nanofiltration chamber; and

[0201] produce an acidic retentate comprising the target ions at the first end of the at least one nanofiltration chamber;

[0202] a pH adjustment chamber coupled to the at least one nanofiltration chamber, comprising; an acidic retentate inlet coupled to the acidic retentate outlet of the at least one nanofiltration chamber;

[0203] a spent catholyte inlet; and

[0204] a neutral retentate outlet coupled to the retentate inlet of the cathodic chamber; wherein the pH adjustment chamber is configured to facilitate adjustment of a pH of the acidic retentate to from about 6 to about 8 and produce a neutral retentate comprising the target ions;

[0205] a clarifying tank coupled to the cathodic chamber of the electrochemical cell, comprising: a target mixture inlet coupled to the target mixture outlet of the cathodic chamber; a target precipitate outlet disposed at a bottom of the clarifying tank, configured to allow removal of the target precipitate;

[0206] a first supernatant outlet disposed at a top of the clarifying chamber.

[0207] An exemplary system according to these aspects is depicted in Figure 1.

[0208] In other aspects, provided herein are systems comprising:

[0209] a mixing chamber, comprising:

[0210] an aqueous feed inlet;

[0211] a precipitant feed inlet; and

[0212] a first feed mixture outlet;

[0213] wherein the mixing chamber is configured to mix an aqueous feed with a precipitant feed, thereby producing a first feed mixture comprising a non-target precipitate and a first supernatant comprising target ions;

[0214] a first clarifying chamber coupled to the mixing chamber, comprising:

[0215] a first feed mixture inlet coupled to the first feed mixture outlet of the mixing chamber; a non-target precipitate outlet disposed at a bottom of the first clarifying chamber; and a first supernatant outlet disposed at a top of the first clarifying chamber; wherein the first clarifying chamber is configured to separate the non-target precipitate from the first supernatant;

[0216] an electrochemical cell coupled to the first clarifying chamber, comprising:

[0217] a cathodic chamber coupled to the first clarifying chamber, comprising:

[0218] a cathode;

[0219] a first supernatant inlet coupled to the first supernatant outlet of the first clarifying chamber;

[0220] a cathodic gas outlet; and

[0221] a target mixture outlet;

[0222] wherein the cathodic chamber is configured to facilitate the passage of the first supernatant through the cathodic chamber, contact the first supernatant with the cathode, and produce a target mixture comprising a target precipitate and a second supernatant;

[0223] an anodic chamber coupled to the cathodic chamber and the clarifying tank, comprising;

[0224] an anode;

[0225] a first supernatant inlet coupled to the first supernatant outlet of the clarifying chamber; an anodic gas outlet; and

[0226] an anolyte outlet;

[0227] wherein the anodic chamber is configured to facilitate the passage of the first supernatant through the anodic chamber and contact the first supernatant with the anode; and

[0228] an electrochemical membrane disposed between the cathodic chamber and the anodic chamber;

[0229] wherein the cathodic chamber and the anodic chamber are in ionic communication; and the cathode and the anode are separated by an interelectrode distance of less than about 20 mm;

[0230] a second clarifying chamber coupled to the electrochemical cell, comprising:

[0231] a target mixture inlet coupled to the target mixture outlet of the cathodic chamber; a target precipitate outlet configured to allow collection of the target precipitate; and a second supernatant outlet;

[0232] wherein the second clarifying tank is configured to separate the target precipitate from the second supernatant.

[0233] An exemplary system according to these aspects is provided in Fig. 2.

[0234] In some aspects, provided herein are methods of preparing a hydroxide of a target ion, comprising:

[0235] providing an aqueous feed comprising the target ion, non-target ions, and CO2 to an anodic chamber of an electrochemical cell, the electrochemical cell further comprising:

[0236] a cathode disposed within a cathodic chamber;

[0237] an anode disposed within the anodic chamber; and

[0238] an electrochemical membrane disposed between and configured to separate the cathodic chamber and the anodic chamber;

[0239] wherein the cathodic chamber and the anodic chamber are in ionic communication;

[0240] performing an electrochemical process comprising:

[0241] applying a voltage to the cathode and the anode, thereby producing:

[0242] an acidic anolyte solution and O2 at the anode; and

[0243] H2 and a target mixture comprising a target precipitate and a first supernatant at the cathode;

[0244] wherein the target precipitate comprises a hydroxide of the target ion; passing the acidic anolyte solution into a degassing tank configured to allow passive exit of CO2 from the acidic anolyte solution, thereby forming a degassed anolyte; passing the degassed anolyte into a separation chamber, the separation chamber having an ion exchange resin disposed therein and configured to separate at least one of the non-target ions from the degassed anolyte, thereby producing a depleted anolyte solution comprising the target ions;

[0245] passing the depleted anolyte solution into at least one nanofiltration chamber configured to separate the depleted anolyte solution into a permeate and an acidic retentate, the acidic retentate comprising the target ions;

[0246] adjusting a pH of the acidic retentate to from about 6 to about 8, thereby producing a neutral retentate comprising the target ions;

[0247] passing the neutral retentate to the cathodic chamber of the electrochemical cell;

[0248] passing the target mixture to a clarifying tank configured to separate the target precipitate from the first supernatant; and

[0249] collecting the target precipitate.

[0250] In other aspects, provided herein are methods of preparing a hydroxide of a target ion, comprising:

[0251] passing an aqueous feed and a precipitant feed into a mixing chamber configured to mix the aqueous feed and the precipitant feed, thereby producing a first feed mixture comprising a non-target precipitate and a first supernatant comprising a target ion;

[0252] passing the first feed mixture into a first clarifying chamber configured to separate the non- target precipitate from the first supernatant;

[0253] passing the first supernatant via a first supernatant outlet into an electrochemical cell; performing an electrochemical process comprising:

[0254] applying a voltage to a cathode and anode disposed within the electrochemical cell; contacting the cathode with the first supernatant, thereby forming H2 and a target mixture, the target mixture comprising a second supernatant and a target precipitate, the target precipitate comprising the hydroxide of a target ion; contacting the anode with the first supernatant, thereby forming O2 and an acidic anolyte solution;

[0255] passing the target mixture via a target mixture outlet into a second clarifying chamber configured to separate the target precipitate from the second supernatant; and collecting the target precipitate. In certain embodiments, the disclosure provides a method of preparing Mg(0H)2, comprises providing: a first target ion solution comprising Mg2+and at least one non-target ion to a first anodic chamber and a first cathodic chamber of a first electrochemical cell; the first electrochemical cell further comprising: a first anode disposed within the first anodic chamber; a first cathode disposed within the first cathodic chamber; and a first membrane disposed between and configured to separate the first cathodic chamber and the first anodic chamber; wherein the first anodic chamber and the first cathodic chamber are in fluid communication; and performing a first electrochemical process, comprising: applying a first voltage to the first cathode and the first anode; thereby producing: a first acidic anolyte and an anodic gas at the first anode; and a first catholyte mixture and a cathodic gas at the first cathode; wherein the first catholyte mixture comprises the Mg(0H)2.

[0256] In certain such embodiments, the method further comprises separating the Mg(0H)2 from the first catholyte mixture, thereby producing a first supernatant and a first solid comprising Mg(0H)2. For example, separating the Mg(0H)2 from the first catholyte mixture may comprise filtering the first catholyte mixture. In certain embodiments, the at least one nontarget ion comprises calcium, iron, sodium, potassium, or a combination thereof. In certain other embodiments, the at least one non-target ion comprises calcium. For example, the at least one non-target ion may be Ca2+.

[0257] In certain embodiments, the first target ion solution is or is derived from seawater, or comprises seawater. In certain preferred embodiments, the first target ion solution is seawater. In other embodiments, the first target ion solution is a naturally occurring brine solution. In certain such embodiments, the first target ion solution is an industrial brine solution (e.g., produced water).

[0258] In certain embodiments, the method further comprises increasing a concentration of Mg2+in the first target ion solution. In certain such embodiments, increasing the concentration of Mg2+in the first target ion solution comprises performing at least one concentration step, and each of the at least one concentration steps increases the concentration of Mg2+in the first target ion solution.

[0259] In certain embodiments, the at least one concentration step comprises nanofiltration. In certain such embodiments, the nanofiltration comprises passing the first target ion solution through a nanofiltration membrane, thereby producing a first permeate, comprising the at least one non-target ion, and a first retentate, comprising the Mg2+. In various embodiments, the at least one concentration step comprises performing reverse osmosis on the first target ion solution.

[0260] In certain embodiments, the at least one concentration step comprises evaporating water from the first target ion solution. In certain embodiments, the method comprises one concentration step. In other embodiments, the method comprises two concentration steps. In certain embodiments, the method further comprises removing CO2 from the first acidic anolyte, thereby producing a first degassed solution comprising Mg2+and the at least one non-target ion. In certain embodiments, the method further comprises removing CO2 from the first target ion solution, thereby forming a first degassed solution comprising Mg2+and the at least one non-target ion.

[0261] In certain embodiments, removing CO2 from the first target ion solution comprises allowing CO2 to passively exit the target ion solution. In certain embodiments, removing CO2 from the first target ion solution comprises contacting the first target ion solution with a stripping gas, and wherein the stripping gas enhances removal of CO2 from the first target ion solution. In certain embodiments, the stripping gas is air (e.g., atmospheric air or compressed air). In certain embodiments, the first supernatant further comprises the at least one non-target ion, and the method further comprises contacting the first supernatant with a fluid comprising CO2, thereby producing a first carbonate mixture comprising a carbonate of the at least one non-target ion.

[0262] In certain embodiments, the method further comprises separating the carbonate of the at least one non-target ion from the first carbonate mixture. For example, the carbonate of the at least one non-target ion may be CaCO3. In certain embodiments, the method further comprises contacting the target ion solution with an additive, thereby producing an additive mixture comprising a second solid comprising the at least one non-target ion. In certain embodiments, the method further comprises separating the second solid comprising the at least one non-target ion from the additive mixture. The additive may comprise [CO3]2-, [PO4]3-, or a combination thereof. For example, the additive may comprise NaHCO3, Na3PO4, or a combination thereof. In certain embodiments, the second solid comprising the at least one non-target ion comprises calcium. In certain embodiments, the additive is in a solid phase, an aqueous solution phase, a liquid phase, or a gaseous phase, preferably wherein the additive is in a solid phase.

[0263] In certain embodiments, the method further comprises contacting the first supernatant with the first target ion solution, thereby forming a mixture comprising a third solid comprising the at least one non-target ion. In certain embodiments, the method further comprises contacting a portion of the first catholyte mixture with the first target ion solution, thereby forming a mixture comprising a third solid comprising the at least one non-target ion.

[0264] In certain embodiments, the method further comprises combining a portion of the solid comprising Mg(OH)2 with the first target ion solution, thereby forming a mixture comprising a third solid comprising the at least one non-target ion. In certain such embodiments, the method further comprises contacting the mixture comprising the third solid with a fluid containing CO2.

[0265] In certain embodiments, the method further comprises contacting the first supernatant with a fluid containing CO2, thereby forming a first carbonated mixture, and contacting the first carbonated mixture with the first target ion solution, thereby forming the mixture comprising the third solid. In certain embodiments, the method further comprises contacting the portion of the first catholyte mixture with a fluid containing CO2, thereby forming a first carbonated mixture, and contacting the first carbonated mixture with the first target ion solution, thereby forming the mixture comprising the third solid.

[0266] In certain embodiments, the method further comprises separating the third solid from the mixture. For example, the third solid comprising the at least one non-target ion may comprise calcium. In certain such embodiments, the third solid comprising the at least one non-target ion is CaCO3. In certain embodiments, the fluid comprising CO2 is a gas. In certain embodiments, the method further comprises providing the first supernatant to the first anodic chamber. In certain embodiments, the first membrane is selective for the passage of anions from the first cathodic chamber to the first anodic chamber. In certain embodiments, the method further comprises recycling a portion of the first catholyte mixture to the first cathodic chamber, thereby forming a catholyte recycle stream.

[0267] In certain embodiments, the method further comprises: providing: a second target ion solution comprising Ca2+and at least one non-target ion to a second anodic chamber and a second cathodic chamber of a second electrochemical cell; the second electrochemical cell further comprising: a second anode disposed within the second anodic chamber; a second cathode disposed within the second cathodic chamber; and a second membrane disposed between and configured to separate the second cathodic chamber and the second anodic chamber; wherein the second anodic chamber and the second cathodic chamber are in fluid communication; and performing a second electrochemical process, comprising: applying a second voltage to the second cathode and the second anode; thereby producing: a second acidic anolyte and an anodic gas at the second anode; and a second catholyte mixture and a cathodic gas at the second cathode; wherein the second catholyte mixture comprises calcium.

[0268] In certain embodiments, the method further comprises separating a fourth solid comprising calcium from the second catholyte mixture, thereby producing a second supernatant and the fourth solid comprising calcium.

[0269] In certain embodiments, the second acidic anolyte comprises Mg2+and is provided to the first anodic chamber. In certain embodiments, the second supernatant comprises Mg2+and is provided to the first cathodic chamber. In certain embodiments, the compound comprising calcium is CaCO3. In certain embodiments, the first target ion solution and the second target ion solution are the same solution. In certain embodiments, the first target ion solution and the second target ion solution are different solutions. In certain embodiments, the first supernatant is provided to the second cathodic chamber. In certain embodiments, the method further comprises contacting the second supernatant with a fluid comprising CO2, thereby producing a carbonate mixture comprising a carbonate of at least one monovalent cation. In certain such embodiments, the carbonate mixture comprises NaHCO3or Na2COs, or a combination thereof.

[0270] In certain embodiments, the second catholyte mixture comprises Ca(0H)2. In certain embodiments, the method further comprises contacting the first acidic anolyte and, when present, the second acidic anolyte with a basic material, thereby neutralizing the first acidic anolyte and, when present, the second acidic anolyte. In certain embodiments, the basic material comprises a fifth solid or a solution comprising OH ions.

[0271] In certain embodiments, the second target ion solution is or is derived from seawater, or comprises seawater. In certain preferred embodiments, the second target ion solution is seawater. In other embodiments, the second target ion solution is a naturally occurring brine solution. In alternative embodiments, the second target ion solution is an industrial brine solution (e.g., produced water).

[0272] In certain embodiments, the first target ion feed inlet and first anolyte feed inlet of the first electrochemical cell is a single, combined inlet coupled to the first anodic chamber and the first cathodic chamber. In certain embodiments, the Mg(0H)2 concentration of the first catholyte mixture is sufficient (e.g., saturated) to pre-precipitate Mg(0H)2. In certain embodiments, the method further comprises: pre-precipitating CaCO3by a first dosing vessel disposed along the catholyte recycle stream. In various embodiments, the method further comprises pre-precipitating Mg(0H)2 by a second dosing vessel disposed along catholyte recycle stream. In certain embodiments, one or more of the electrochemical cells is the electrochemical cell depicted in Figure 19 or 20.

[0273] In certain embodiments, the first solid comprising Mg(OH)2 has a purity of greater than about 90%, greater than about 95%, or greater than about 99%. In certain embodiments, the first solid comprising Mg(OH)2 has a purity of from about 90% to 100%, from about 95% to 100%, or from about about 99% to 100%. In certain embodiments, the first solid comprising Mg(OH)2 comprises less than about 5% Ca, less than about 1% Ca, less than about 0.8% Ca, less than about 0.5% Ca, or less than about 0.1% Ca.

[0274] In certain embodiments, the first solid comprising Mg(OH)2 comprises substantially no calcium or comprises trace amounts of calcium. In certain other embodiments, the first solid comprising Mg(OH)2 is substantially pure Mg(OH)2.

[0275] In certain embodiments, the method is performed using the system of any one of systems described above.

[0276] Experimental data obtained by carrying out the processes shown in Figs. 7, 9, 11, 13, 15 (labeled Case 1, 2, 3, 4, 5, respectively) is depicted in Table 2 below:

[0277] Table 2: Summary of Simulation Results for Main Process Configurations

[0278]

[0279] *1: Electrolyzer Energy Intensity, *2: Overall Energy Intensity

[0280] Table 3, below, shows the simulation results of overall process (RO system + main process) for Case 2 and Case 5 with three different RO configurations.

[0281] Table 3: Summary of Simulation Results for Overall Process Configurations

[0282]

[0283]

[0284] Definitions

[0285] 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. Generally, nomenclature used in connection with, and techniques of, chemistry, chemical engineering, electrical engineering and civil engineering described herein, are those well- known and commonly used in the art.

[0286] The methods and techniques of the present disclosure are generally performed, unless otherwise indicated, according to conventional methods well known in the art and as described in various general and more specific references that are cited and discussed throughout this specification.

[0287] 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).

[0288] All 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.

[0289] As used herein, the term “particle size” refers to the mean particle size (dso) as determined through, e.g., dynamic light scattering.

[0290] As used herein, the term “production capacity” refers to the upper boundary of the dry mass of pure product equivalents that may be produced per unit of time. As used herein, the term “spent solution" refers to the residual solution utilized in a prior step of a process (e.g., nanofiltration or electrolysis) which may optionally be re-used or discarded depending on the user’s needs and the configuration of the system.

[0291] As used herein the term gEEI refers to gross Electrical Energy Intensity, which is a measure of the total electrical energy required by a process to produce a given amount of a product [e.g., a metric tonne (MT) of Mg(0H)2]. gEEI values referred to in the present disclosure are calculated according to the formula: gEEI = [(current applied) (voltage)] / (mass of Mg(0H)2 produced), which also includes the production of any co-products such as EE. In methods of the present disclosure, the value of the electric potential (voltage) applied to the cathode and anode in the electrochemical positively correlates with the gEEI of the process. For example, a process having a gEEI of about 4 MWh / MTMg(0H)2 would be considered more energy efficient than a process having a gEEI of 5 MWh / MTMg(0H)2 by one of skill in the art.

[0292] As used herein, the term “hydrodynamic separation” refers to the physical separation of two fluid feed streams or processes that are usually or may be combined. For example, the term may refer to, e.g., separation of an anolyte from a catholyte stream in an electrochemical process. The term “hydrodynamic separation” may also be used herein to refer to the separation of an electrolysis chamber (e.g., where H+and OH' ions are produced from aqueous solutions) and a precipitation chamber (e.g., where an aqueous ionic species comprising the OH' ions is precipitated from solution) such that the precipitation of the hydroxide species occurs in the precipitation chamber instead of in the electrolysis chamber.

[0293] As used herein, the term “interelectrode distance” refers to the magnitude of the minimum distance between an outer face of a first conductive element and an outer face of a second conductive element.

[0294] The term “target ion,” as used herein, refers to an ion that is desired or “targeted” for concentration, preparation, and / or isolation by the systems and methods disclosed herein. For example, the systems and methods of the disclosure may favor the separation, concentration of Mg2+(an exemplary target ion) from mixtures comprising Mg2+and at least one additional “non-targef ’ ion. Additionally, as will be appreciated by one of ordinary skill in the art, the use of the term “target” to modify other terms such as “mixture” and “precipitate” signifies that the mixture or precipitate comprises target ion(s).

[0295] The term “non-target ion,” as used herein, refers to an ion that is not desired or targeted for concentration, preparation, and / or isolation by the systems and methods disclosed herein. For example, non-target ions involved in the systems and methods disclosed herein may be selected from Ca2+, Fe2+, and Na+, and combinations thereof. For example, systems and methods of the disclosure may involve the separation and concentration of Mg2+(a target ion) from mixtures comprising Mg2+and at least one additional “non-target” ion, such as Ca2+, Fe2+, and Na+.

[0296] The term “stripping gas” as used herein refers to a fluid (preferably a gaseous fluid) that may be present in the dissolution chamber when contacting an acid (e.g., a portion of the acidic anolyte) with a carbonate source (e.g., CaCO3), thereby producing CO2 and a solution comprising the target ion (e.g., Ca2+). The stripping gas may aid the decarbonation of the carbonate source by facilitating or assisting in the removal of CO2 from the dissolution chamber, thereby affecting decarbonation equilibria in favor of the products e.g. CO2 and aqueous target ions). As a non-limiting example, the stripping gas may be air, or air that is substantially free of CO2 (e.g, the gas produced by a CO2 capture process), or any other gas low in or free of CO2, e.g, the anodic gas, cathodic gas or a mixture of anodic and cathodic gases.

[0297] The terms “anodic gas” and “cathodic gas” as used herein refer to gaseous products that are produced at the anode and cathode, respectively. For example, an anodic gas may comprise O2, and a cathodic gas may comprise H2.

[0298] The term “source” as used herein in connection with chemical elements (e.g., calcium) refers to a composition that comprises the element.

[0299] The term “ionic communication” as used herein refers to the ability for ions to freely flow between two objects or regions of an object, e.g., between the cathodic chamber and anodic chamber of an electrochemical cell, in accordance with local chemical gradients. Nonlimiting examples of such gradients include flow of ions from an area of high electrical potential to low electrical potential, from high ion concentration to low ion concentration, and from high chemical potential to low chemical potential. In certain embodiments, two objects or regions may be physically separated by a semi-permeable barrier (e.g., not in fluid communication) but still be in ionic communication, e.g., by virtue of ion diffusion or transport through the barrier.

[0300] The term “produced water” as used herein refers to an aqueous solution that is obtained from underground sources as a byproduct of oil and / or natural gas extraction. INCORPORATION BY REFERENCE

[0301] 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.

[0302] EQUIVALENTS

[0303] 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.

[0304] EXAMPLES

[0305] This example contemplates a continuous flow electrolytic method of producing alkalinity to synthesize Mg(0H)2 from untreated seawater. Mg(0H)2 precipitation experiments were conducted to identify the most efficient operating conditions to produce high-purity Mg(0H)2 powders by modulating current, voltage, reagent pH, gas flow rate, and degassing configurations in a pilot-scale, continuous-flow electrolysis system using real, unprocessed seawater acidified by recycled anolyte as feedstock.

[0306] Unprocessed natural seawater used in this study was filtered once through a.45 pm pore size nylon filter to remove any particulate impurities, and refrigerated until ready for usage.

[0307] Seawater was first pumped from an acidification / degassing tank, where it was mixed with recycled anolyte from the electrolyzer to convert bicarbonates into carbon dioxide, which was subsequently removed from the influent brine with a controlled stream of 400 ppm CO2 gas by one of two deaeration modules (bubbling column with sparger or falling film column). The pH of the degassed acidified brine was controlled by adjusting the ratio of recycled anolyte to incoming seawater, providing tunable control of the feedstock chemistry and pH. The preconditioned electrolyzer feed was then collected in a buffer tank before being simultaneously fed by peristaltic pumps into the anode and cathode chambers of the electrolyzer unit at 4.5 mL / min. The resultant Mg(OH)2-rich slurry was discharged from the catholyte outlet into a dedicated collection tank while the anolyte effluent was collected into a separate tank and recirculated back into the degassing / acidification tank. The complete system was supported by a set of auxiliary components including 6 peristaltic pumps for fluid movement and five pH meters positioned in the tanks.

[0308] Inlet seawater was conditioned to pH ~3.0 through CO2 sparging and recycled anolyte mixing, while catholyte pH reached values 11 to 11.6 during electrolysis, enabling effective Mg(0H)2 precipitation with minimal Ca2+-product impurities. Anolyte pH remained between pH 0.9-1.2, maintaining desired acidity for feedstock recirculation.

[0309] Decarbonation pre-treatment was achieved by (1) acidifying the seawater feed and (2) degassing 400-ppm CO2. By lowering the brine’s pH to 3, HCO3' was converted into CO2 gas, significantly reducing the concentration of carbonate ions in solution. Degassing took place in one of two deaeration configurations: by a bubbling column and a vertical falling film column (See Table 4 below). The decarbonation pretreatment aimed to deter the formation of CaCO3or Mgi-xCaxCO3, which would otherwise more predominantly occur at the elevated pH in the presence of DIC achieved during electrolysis.

[0310] The bubble column was chosen as a preliminary lab-scale proof of concept while the falling film column served as an analogue to industrial vertical degassing columns to demonstrate the capability of this system to advance to larger scales. The bubble column consisted of a 1-L plastic bottle through which 400 ppm-CCh gas was bubbled in the bubble column by a sparger at the bottom at a constant rate of 0.15 L / min (Fig. 25). The falling film column was a tall, vertical borosilicate-glass tube in which the acidified seawater trickled as a thin film down the inner wall (~18 cm) while a counter-current 400 ppm-CCh stream stripped out dissolved CO2. In the latter case, enough acidified seawater was allowed to accumulate in the inner tube to allow for constant flow for 5 minutes before beginning the degassing process, during which CO2 gas was supplied at 3 L / min (Fig. 25).

[0311] Experiments were conducted using a custom-built two-compartment electrochemical flow reactor constructed from chemically resistant acrylic and titanium hardware and a proton exchange membrane (PEM). A titanium-felt platinum-coated cathode (25 cm2) and Ruthenium-coated titanium mesh oxygen-selective anode (OSA) (25 cm2) were used. The liquid fill section for each electrolyzer chamber was 14.58 cm3, separated by the PEM. Inlet and outlet ports on both compartments allowed continuous flow operation and the acidified degassed seawater solution was used as the electrolyte.

[0312] Electrolytic water splitting in the flow electrolyzer follows the half-cell anodic OER (1) and HER cathodic reactions (3). Due to the usage of an OSA, the usually favorable C1ER (2) is -99% circumvented. Anode Half-Reaction (OER)

[0313] 2 H20 - 02+ 4H++ 4e" E° = +1.229 V vs SHE (1) Chlorine Evolution Reaction (OSA favors OER)

[0314] 2C ^ Cl2+ 2e~ E° = +1.36Vvs SHE (2) Cathode (hydroxide generation) / Cathode Half-reaction (HER) 2 H2O + 2e~ -► H2+ 4OH~ E° = -0.828 V vs SHE (3) The OH- generated at the cathode reacted with Mg2+from the CO2-depleted seawater (pH ~ 11):

[0315] Mg2++ 2 OH Mg(OH)2(s) (4)

[0316] Meanwhile, minute amounts of CaCO3, MgxCai-xCO3, and Ca(OH)2 were generated according to Equations 5-8, though less favorably than Mg(OH)2 in a carbonate-depleted environment:

[0317] HCO3- + OH- CO3- + H2O (5)

[0318] CO32’ + Ca2+CaCO3(s) (6)

[0319] 2 OH’ + Ca2+Ca(OH)2(s) (7)

[0320]

[0321] Electrolysis experiments were conducted under galvanostatic control by a DC power supply. Current densities ranged from 320-480 A / m2, with a typical cell voltage of 2.98 to 3.81 V. Measurements were performed with a potentiostat. Table 1 shows operating conditions for different cases / experiments carried out.

[0322] Table 4, Experimental variables listed for all experimental cases including current density, voltage, CO2 flow rate, and purity / yield averaged results.

[0323]

[0324] All experimental data was derived from triplicate measurements at a minimum unless otherwise noted, and the reported mean and standard error were derived from all data points. The system was run for a minimum of 120 minutes to achieve steady state operation before collection. The system was operated in continuous-flow mode with matched flow rates of 4.5 mL / min through the cathode and anode, producing a residence time of approximately 3.24 minutes in each chamber. Voltage and current data were recorded in real time.

[0325] Liquid samples were collected from the seawater tank, degassing acidification tank, electrolyzer feed holding tank, anolyte collection tank, and catholyte collection tank during each run and analyzed by titration and ICP-OES for pH and ionic composition respectively. Inductively coupled plasma optical emission spectroscopy (ICP-OES) was performed using an analyzer for multi-elemental analysis to quantify Mg2+, Ca2+, Na+, and K+concentrations in a 5% trace-metal-grade HNO3 matrix. Titration was conducted on catholyte and anolyte effluents.

[0326] Anionic components of seawater were measured using a photospectrometer.

[0327] Mg(OH)2-containing slurry from the cathode was collected in glass 1-L bottles. The suspension was allowed to settle for 24 hours then centrifuged in 50-mL centrifugation tubes and washed using a deionized water volume at least equal to that of the filtered suspension, then centrifuged again after which the supernatant was discarded; this process was repeated a minimum of five times to eliminate coprecipitated contaminants such as NaCl and / or KC1. Washed slurries were then filtered using a Buchner funnel and.45 pm pore size nylon filter. The cake was then allowed to dry to completion.

[0328] Mg(0H)2 purity was determined by digesting processed precipitates in 1:2 molar ratio of solid to high purity 37 wt% HC1 (assuming 100 wt% Mg(0H)2), diluted with HNO3 to a known volume, filtered with.45 pm pore size nylon filters, and measured with ICP-OES.

[0329] X-ray diffraction (XRD) by a Cu-Ka source was used to detect crystal structure and phases. Scanning electron microscopy (SEM) was used to observe and image the morphology with electron dispersive spectroscopy (EDS) to qualitatively observe elemental distribution of the studied particles. Particle size distribution was obtained by SLS-PSD and surface area of the particles by Brunauer-Emmett-Teller (BET) method.

[0330] Mg2+removal efficiency was taken as “pre-washing yield” represented by the following equations: Mg2+removal (%)= 100

[0331] & v 7

[0332]

[0333] Mg2+removed (mol) = M g2+in- M g2+catholyte supernatant)

[0334]

[0335] The mass purity was calculated based on the relative mass concentrations of Mg2+, Ca2+, Na+, and K+in the digested precipitate relating them to their respective solids (Mg(0H)2, CaCO3, NaCl, and KC1) and is represented by the following equation:

[0336] Mg(OH)2Purity

[0337]

[0338] solid

[0339]

[0340]

[0341] Electrolytic conversion was calculated as a function of Mg2+(mol) and is represented by the following equation:

[0342] Mg 0H)2 precipitate selectivity (%) = 100

[0343]

[0344]

[0345] OH ^effluent (mol) [OH Jcatholyte

[0346] Mg 0H)2 experimental yield (%) = 100

[0347]

[0348] Production efficiency was taken as the ratio between amount of Mg(OH)2 collected and total Mg2+removed from the system and is represented by the following equation:

[0349] ,,, rr,,-, solid recovery rate (%) = 100

[0350]

[0351] The Faradaic efficiency (FE, unitless) of the process can be calculated in terms of the known production of OH' species, as measured by the current passed, and is represented by the following equation:

[0352] r / FE(%) =[OU ]tota\ / [OH ^theoretical *100

[0353] [OH ]theoretical (mol)—l*t / F

[0354] where [OH-]measuredis the concentration of OH' measured in the system (see later equations), F is Faraday’s constant (96485 s*A / mol), I is the current (A) and t is the time for each respective run (seconds).

[0355] Voltage efficiency is a measure of the efficiency of the cell operation, defined as the ratio of the theoretical cell voltage to the actual applied cell voltage during operation, wherein the thermodynamic minimum voltage, Vo, is defined by the OER and HER half-cell reactions, and is represented by the following equation:

[0356]

[0357] Vo = E°anode— E°cathode= 2.06 V

[0358] Electrolyzer efficiency is defined as the total efficiency product of voltaic and faradaic efficiencies and is represented by the following equation:

[0359]

[0360] Specific energy consumption (SEC) is calculated in MWH per metric tonne of Mg(0H>2 produced, based on integrated energy input, and is represented by the following equation.

[0361]

[0362] Electrolytic precipitation of Mg(0H>2 was achieved via seawater splitting using the described OSA-PEM system, leveraging accessible cathodic alkalinity to exceed the solubility product of Mg(0H)2without significant Ca2+byproducts, as shown in Fig. 27-28B. At a controlled pH >11, Mg2+ions readily formed Mg(0H>2 while Ca2+preferentially remained in solution, aligning with previously reported selective pathways. Table 5 below shows averaged results of each case: Table 5: Averaged Results of Cases 1A-2C

[0363]

[0364] Cell voltages remained effectively constant at each imposed current density after steady state was reached. The system operated without significant ohmic drift or activation losses, even under extended operation (measured up to 10 hours). The absence of progressive voltage increase suggests that the flow rates and degassing were sufficient to maintain effectively clean electrode surfaces and uniform ionic transport. Significant fouling was not observed through voltage changes nor visually observed upon electrolyzer disassembly at the end of each run. These observations align with prior seawater electrolysis reporting that stable polarization is achievable when carbonate side reactions are mostly suppressed. Cell voltages ranged from 2.9 to 3.9 V (depending on the applied current and degassing configuration, and had a linear relationship to current density.

[0365] The OSA successfully promoted OER and inhibited C1ER as observed by photospectrometry of anolyte effluent and prevented significant formation of hazardous Ch gas.

[0366] The influence of current density on catholyte alkalinity was evaluated for bubble and film configurations as shown in Fig. 26. Across the tested current density range (320-480 A / m2), catholyte pH remained between 11.02 and 11.22, exceeding the threshold for Mg(0H)2 precipitation from seawater. Bubble mode consistently exhibited higher alkalinity (pH 11.12-11.22) compared to film degassing (pH 11.02-11.12). The lower pH of the falling film column configuration may be explained by lesser elimination of CO2 and DIC in the degassing stage due to lesser residence time. Buffering arises from rapid hydration of CO2 to H2CO3, which subsequently disassociates to HCCh', decreasing pH and reducing brucite supersaturation and scaling. Evidence of this effect is supported by minor co-precipitation of carbonate byproducts in collected falling film precipitates and less so in the bubble precipitates.

[0367] After reaching steady state, the system maintained stable pH values in each feed tank with the catholyte pH roughly constant due to Mg(0H)2 and minor carbonate buffering. Bulk pH in both cathode and anode compartments remained close to the starting setpoints during steady-state operation. Lower voltages were required to maintain constant lower pH of falling film configuration, most likely due to carbonate buffering and less brucite scaling compared to the bubbling column’s higher overpotential attributed to supernucleation of brucite at the cathode.

[0368] Phase compositions of the recovered precipitates were characterized by X-ray diffraction (XRD) with representative diffractograms presented in Fig. 27. Qualitative phase analysis was conducted using Rietveld refinement using conventional software and databases. Phase composition quantification was limited by variability in crystallinity, peak overlap, and inconsistent structural distortion of mixed phases.

[0369] The presence and relative intensity of peaks varied across conditions, indicating differences in phase composition. However, brucite (Mg(0H)2) was the predominant phase across all samples, followed by aragonitic calcium carbonate (CaCO3) and trace amounts of calcitic magnesium carbonate (MgxCai-x)C03, portlandite (Ca(0H)2), potassium chloride (KC1), and sodium chloride (NaCl). (MgxCai-x)CC>3 may indicate co-precipitation of Ca2+and Mg2+with remaining carbonate in the cathode; the transformation of Mg(0H)2 into mixed carbonate phases; or the incorporation of Mg2+into the lattice structure of calcitic CaCO3, leading to an increase in calcite solubility. Additionally, clusters of aragonite are known to form during electrolytic precipitation of Mg(0H)2 from seawater and Mg2+anions can be incorporated into the structure, causing structural distortion and strain in the calcitic crystal or can be induced by precipitate drying conditions when CaCO3is present in Mg(0H)2 slurries. This mixed calcium carbonate phase was unable to be clarified as aragonitic or calcitic by XRD. However, it was found to be present in higher amounts in film column products than bubble column solids at comparable current densities.

[0370] Temporarily elevated pH and localized electrochemical conditions during precipitation may have favored temporary depletion of carbonate species, promoting the reaction of Ca2+with OH' ions prior to complete carbonate saturation despite the solubility product constants of Mg(0H)2 and CaCOs being much smaller than that of Ca(0H)2. These findings are consistent with the notion that Ca(0H)2 can persist in systems with restricted CO2 access.

[0371] The presence of NaCl and KC1 in precipitated samples may be ascribed to entrapment of non-target ions, disproportionately observed in samples with higher mass / longer run times. These salts require thorough washing to remove, and incomplete removal can reduce measured purity. Rapid nucleation under these conditions can yield denser, less porous precipitates that trap feedstock ions and resist effective filtration and washing, leaving residual soluble salts detectable in post-washing ICP-OES analysis.

[0372] ICP-OES of HCl-digested precipitates provided comprehensive and accurate quantification of total elemental content and did not suffer from the quantification limitations of XRD. Mg2+, Ca2+, Na+, and K+were measured in radial mode. Molecular identities and corresponding molecular weights were assigned based on phase identification by XRD, specifically Mg(0H)2, CaCCri, NaCl, and KC1. Calcium hydroxide and calcitic magnesium carbonate were excluded from weight contribution due to unquantifiably low abundance and lower molecular weights relative to CaCOs. By conservatively assuming CaCOs as the predominant calcium and carbonate impurity, the calculated Mg(0H)2 purity values represent a lower-bound estimate. Mg(0H)2 purity (wt%) and CaCCE content (wt%) are presented in Fig.

[0373] 28 A and 28B.

[0374] Across all experimental parameters, Mg(0H)2 purity exceeded 99.62 wt%. ICP-OES confirmed higher Ca2+ impurities in film products, bolstering qualitative XRD analyses. The reduced purity observed is attributed to inadequate gas-liquid interaction within the falling film column and thus higher carbonate content in the electrolyzer feed. Bicarbonate buffering lowered pH at the cathode and led to Ca2+co-precipitating as (MgxCai-x)C03 or in minute quantities Ca(0H)2. This effect was most pronounced in the falling film column at 320 A / m2, where the catholyte pH (11.02) was insufficiently alkaline to exclusively precipitate Mg2+, yet favorable for the formation of CaCO3due to the prevalence of CCh2under these conditions. Bubbling column yielded higher purities, ranging from 99.75 to 99.85 wt%, across the evaluated current densities while the film column set up yielded slightly lower purities, ranging from 99.62 to 99.82 wt%. Above 400 A / m2, current density and product purity had an inverse correlation across both degassing configurations. The purities reported herein are higher than previously reported for conventional electrolytically produced Mg(OH)2 from seawater without chemical or external modifications.

[0375] The removal of Mg2+from the electrolyte was calculated by analyzing the difference in Mg2+concentration between the influent electrolyzer feed and in the catholyte effluent as measured by ICP-OES after filtration, shown in Fig. 29A as an effect of current density and in Fig. 29B as an effect of catholyte pH.

[0376] Mg2+ions in the catholyte effluent were one order of magnitude less than in the feed solution (-1300 ppm) and linearly decreased with increasing current density, ranging from 252-477 ppm (bubble) and 174-434 ppm (film). As current density increased from 320-480 A / m2, removal efficiency increased from 68.37 to 81.49% (bubble) and 65.66 to 87.83% (film).

[0377] Above 400 A / m2, the film column was more efficient at Mg2+removal than the bubble column (Fig. 29 A). As pH increased for each set up, Mg2+removal increased; however, higher absolute pH values did not correlate with higher Mg2+removal (Fig. 6B). Film column data at 320 A / m2remains outside of the trend int terms of purity and yield due to higher Ca-based impurity inclusions. This may be due to CO2 presence in the electrolyzer buffering the pH and preventing scaling on the active area of the electrode, which is supported by the higher amounts of carbonate precipitates in falling film column precipitates (See Fig. 28B). Referring to Fig. 30A, Mg(0H)2 reaction selectivity was quantified as OH' content in Mg2+precipitate compared to OH' total produced by the electrolyzer to evaluate the selectivity of Mg(0H)2 precipitation. Mg2+precipitation with OH' increased with increasing current density for both configurations, and was higher for the film column from 320-400 A / m2and was within statistical overlap for 480 A / m2for both columns. This may be ascribed to the buffering environment and less supemucleation in the film column as previously discussed.

[0378] Fig. 30B reports Mg2+experimental yield was evaluated as the ratio of Mg2+from recovered precipitate (Mg2+precipitate) to the total initial Mg2+input into the system (Mg2+in). In both deaeration configurations, yields improved with increasing current density. At 320 A / m2, the bubble and film columns achieved production efficiencies of 50.21 and 49.44%, respectively; at 480 A / m2, experimental yields increased substantially to 72.61% for the bubble column and 77.68% for the film column.

[0379] Solid recovery rate was quantified as the Mg2+precipitatedas Mg(0H)2 compared to Mg2+removed from the electrolyte (Mg2+removed) by the electrolyzer to form precipitate, shown in Fig. 30C. Across all tested conditions, this rate exceeded 73.91% (Case 1, 320 A m2), reaching a maximum of 89.26 % at 480 A / m2with the bubbling column. This trend of increasing conversion with current density is consistent with the anticipated enhancement in precipitation kinetics under intensified electrochemical conditions.

[0380] The falling film configuration demonstrated superior solid recovery from 320-400 A m2, which is attributed to prolonged Mg2+availability in the acidic catholyte environment. This condition may result from incomplete CO2 degassing and limited pH buffering capacity within the electrolyzer, as previously discussed. However, this same operational regime also promoted co-precipitation of CaCO3, as confirmed by ICP-OES and XRD analyses (Fig. 27-28B), thereby reducing the purity of the recovered product. These results are consistent with trends observed in recovery / efficiency values (Fig. 30A-C), particularly for the falling film system.

[0381] The microscopic morphology of representative precipitate samples of each case parameter was studied by SEM-EDS as shown in Fig. 31. High local supersaturation levels induced by the high pH at the electrode surfaces disfavor the growth of hexagonal brucite crystals, leading to the observed nanometric globular morphology observed in Fig. 8. The precipitate of the falling film column with 320 A / m2current density (Case 2A) displayed an exaggerated globular morphology compared to the other cases and lower surface area than other falling film column precipitates. This is consistent with its lower pH at the cathode, lower purity, and increased carbonate content as detected by ICP-OES and XRD. EDS of all sample confirmed majority brucite compositions and did not detect Ca2+or other impurity elements.

[0382] In bubbling column experiments, particle size decreased from approximately 8.62 pm at 320 A m2to 7.89 pm at 480 A m2, indicating that higher current densities promote rapid nucleation and formation of fine, dispersed particles Fig. 32a. In contrast, the falling film column exhibited a slight increase in particle size with current density, from 9.01 to 9.59 pm, suggesting slower nucleation rates and enhanced crystal growth, as shown in Fig. 32A.

[0383] Figure 32B presents BET surface area trends, which further highlight differences in microstructural development. The bubbling column produced high initial surface areas (93.07 m2 / g) that declined modestly at elevated current densities, consistent with particle coarsening and agglomeration under accelerated precipitation conditions. Conversely, the falling film column showed a decrease in BET surface area from 73.87 m2 / g at 320 A m2to 78.88 m2 / g at 400 A m2, followed by a slight reduction at 480 A m2to 72.43 m2 / g. This behavior suggests that moderate current densities optimize nucleation and porosity, while excessive current densities may induce densification and reduce accessible surface area for both degassing configurations.

[0384] The electrochemical efficacy of the exemplary system was assessed by OH' Faradaic efficiency (FE), voltage efficiency, and total efficiency as reported in Fig. 33A-C. FE was calculated based on total OH' produced in the system (OH'totai) based on the stoichiometric ratio of 1 Mg2+removed2 OH' anions and OH' in the catholyte effluent based on titration, compared to OH' capable of being produced based on current and time (OH'theoreticai). FE decreased with increasing current density for bubble and film configurations, ranging from 78.63% to 60.14% for bubble and 71.16% and 62.11% for film as reported in Fig. 8a. FE was lower for the film column configuration from 320-400 A / m2, in agreement with lower pH values, shown in Fig.

[0385] 26 and other measures of efficiency. This may be ascribed to carbonate buffering until 480 A / m2 was able to overcome the presence of remnant DIC at high enough current activity. Seawater electrolysis is typically affected by reactions competing with hydroxide generation, including buffering by bicarbonate and mass transport limitations that restrict OH' availability for precipitation.

[0386] Fig. 33B shows that voltage efficiency (VE) favored the film configuration, suggesting lower energy losses despite reduced OH' conversion. Ohmic resistance increased with increasing current density (0.40 V, 0.54 V, 0.60 V) from 320-480 A / m2. Overpotential increases similarly for falling film and bubble column configurations, most likely due to in situ precipitation at the cathode blocking reaction sites. Additionally, the rate of electron transfer increased which may promote side reactions at the cathode. For example, gas evolution at the cathode is known to form bubbles that block active sites on the electrode, increasing resistance and decreasing effective active area with increasing current density. These effects were more pronounced in the bubble column VE, which was lower at all current densities.

[0387] The overall system’s energy efficiency is defined here as the product of voltage efficiency and Faradaic efficiency with respect to the production of OH- species by the electrolyzer and ranged from 48.81-30.81% for bubble column and 49.26-39.28% for film configuration as current density increased from 320-480 A / m2(Fig. 33C). VE compensated for lower FE OH' production

[0388] To summarize, the example described herein demonstrates the viability of scaling up a lab-scale continuous flow electrolysis pilot to industrial levels by comparing the efficacy and efficiency of a vertically oriented falling film column configuration for CO2 removal from unprocessed seawater acidified with recycle anolyte. Discussed above and Fig. 34A-B. The system achieved ultrahigh purity in the resulting brucite precipitates, comparable to that obtained using a laboratory-scale bubbling column. Notably, the falling film column exhibited superior total efficiency, highlighting its potential for industrial scalability without compromising yield or selectivity. Furthermore, one of ordinary skill in the art will appreciate that once the falling film column is scaled up from lab size to industrial size, active area for CCE-degassing will increase and therefore be even more effective than demonstrated herein.

[0389] Electrochemical performance metrics including FE, VE, and TE confirmed the effectiveness of the system in generating a high-pH gradient with an oxygen selective anode electrolyzer, offering a low-cost pathway to alkalinity generation compared to conventional chloro-alkaline methods. Thus, electrochemical precipitation ofMg(OH)2 from seawater using scalable degassing and an OSA can serve as a sustainable and cost-effective strategy for generation of alkalinity.

Claims

1. We claim:

1. A system, comprising:3.a first electrochemical cell comprising:4.a first cathodic chamber, comprising:5.a first cathode;6.a first target ion feed inlet;7.a first cathodic gas outlet;8.a first catholyte mixture outlet;9.a first anodic chamber, comprising:10.a first anode;11.a first anolyte feed inlet;12.a first anodic gas outlet;13.at least one primary acidic anolyte outlet;14.a first membrane disposed between the first cathodic chamber and the first anodic chamber;15.a first solid separation chamber, comprising:16.a first catholyte mixture inlet coupled to the first catholyte mixture outlet;17.a first solid collection outlet; and18.a first supernatant outlet;19.wherein the first cathodic chamber and the first anodic chamber are in ionic communication.

2. The system of claim 1, further comprising at least one target ion feed concentrator, comprising:21.a first target ion source inlet; and22.a first concentrated feed outlet coupled to the first target ion feed inlet of the first cathodic chamber.

3. The system of claim 2, wherein the system comprises one target ion feed concentrator.

4. The system of claim 2, wherein the at least one target ion feed concentrator comprises:a first target ion feed concentrator, comprising the first target ion source inlet and the first concentrated feed outlet; and25.a second target ion feed concentrator, comprising a second target ion feed inlet coupled to the first concentrated feed outlet and a second concentrated feed outlet coupled to the first target ion feed inlet of the cathodic chamber.

5. The system of any one of claims 2-4, wherein the at least one target ion feed concentrator further comprises at least one nanofiltration chamber.

6. The system of claim 5, wherein the at least one target ion feed concentrator comprises one nanofiltration chamber.

7. The system of claim 6, wherein the at least one target ion feed concentrator comprises two nanofiltration chambers.

8. The system of any one of claims 2-7, wherein the at least one target ion feed concentrator comprises at least one reverse osmosis chamber.

9. The system of any one of claims 2-8, wherein the at least one target ion feed concentrator comprises one reverse osmosis chamber.

10. The system of any one of claims 2-8, wherein the at least one target ion feed concentrator comprises two reverse osmosis chambers.

11. The system of any one of claims 2-10, wherein the at least one target ion feed concentrator comprises at least one evaporation chamber.

12. The system of any one of claims 2-11, wherein the at least one target ion feed concentrator comprises one evaporation chamber.

13. The system of any one of claims 2-11, wherein the at least one target ion feed concentrator comprises two evaporation chambers.

14. The system of any one of claims 2-13, wherein the at least one target ion feed concentrator is configured to increase a concentration of at least one target ion in an aqueous solution comprising the at least one target ion.

15. The system of claim 14, wherein the at least one target ion feed concentrator is configured to increase a concentration of Mg2+in the aqueous solution comprising the at least one target ion.

16. The system of any one of claims 1-15, further comprising:37.a degassing tank, comprising:38.an acidic anolyte inlet coupled to the at least one primary acidic anolyte outlet of the anodic chamber;39.a CO2 outlet at a top of the degassing tank, configured to allow a gaseous fluid to flow from the degassing tank; and40.a degassed anolyte outlet.

17. The system of any one of claims 1-15, further comprising:42.a degassing tank, comprising:43.a degassing feed inlet;44.a CO2 outlet at a top of the degassing tank, configured to allow a gaseous fluid to flow from the degassing tank; and45.a degassed mixture outlet coupled to the first target ion feed inlet of the first cathodic chamber.

18. The system of claim 17, wherein the at least one target ion feed concentrator is present, and degassing feed inlet is coupled to the first concentrated feed outlet of the at least one target ion feed concentrator.

19. The system of any one of claims 16-18, wherein the CO2 outlet is configured to allow passive exit of a fluid comprising CO2 from an aqueous solution comprising at least one target ion.

20. The system of any one of claims 16-18, wherein the degassing tank further comprises a stripping gas inlet at a top of the degassing tank, wherein the stripping gas inlet is configured to provide a stripping gas to the degassing chamber.

21. The system of claim 20, wherein the stripping gas inlet is coupled to the first cathodic gas outlet of the first cathodic chamber.

22. The system of claim 20 or 21, wherein the stripping gas enhances removal of CO2 from an aqueous solution comprising at least one target ion.

23. The system of any one of claims 20-22, wherein the stripping gas is air (e.g., atmospheric air or compressed air).

24. The system of any one of claims 17-23, wherein the degassing feed inlet further comprises an acid inlet coupled to the at least one primary acidic anolyte outlet of the first anodic chamber.

25. The system of any one of claims 17-24, further comprising:53.a first carbonation chamber, comprising:54.a first supernatant inlet coupled to the first supernatant outlet of the first solid separation chamber;55.a first carbonation feed inlet configured to flow a fluid comprising CO2 into the first carbonation chamber;56.a first carbonated mixture outlet; and57.a first gas outlet; and58.a second solid separation chamber, comprising:59.a first carbonated mixture inlet coupled to the first carbonated mixture outlet of the first carbonation chamber;60.a second solid collection outlet; and61.a second supernatant outlet.

26. The system of claim 25, wherein the first carbonation chamber is configured to produce a carbonate of a second target ion.

27. The system of claim 25 or 26, wherein the first carbonation chamber is configured to produce CaCO3.

28. The system of any one of claims 1-27, further comprising:64.a first additive chamber, comprising:65.a second target ion feed inlet;66.a first additive inlet; and67.an additive mixture outlet;68.a third solid separation chamber, comprising:69.an additive mixture inlet coupled to the additive mixture outlet of the first additive chamber;70.a third solid collection outlet; and71.a third supernatant outlet;72.wherein the third supernatant outlet is coupled to the first target ion feed inlet.

29. The system of claim 28, wherein the first additive inlet is configured to combine an additive with a first target ion feed.

30. The system of claim 28 or 29, wherein the first additive chamber is configured to produce a first solid comprising at least one non-target ion.

31. The system of claim 30, wherein the first solid comprises calcium [e.g., CaCO3or Ca3(PO4)2].

32. The system of any one of claims 29-31, wherein the additive comprises [CO3]2-, [PO4]3-, or a combination thereof.

33. The system of claim 32, wherein the additive comprises NaHCO3, Na3PO4, or a combination thereof.

34. The system of any one of claims 29-33, wherein the first target ion feed comprises Ca2+.

35. The system of any one of claims 29-33, wherein the additive is in a solid phase, an aqueous solution phase, a liquid phase, or a gas phase.

36. The system of claim 35, wherein the additive is in a solid phase.

37. The system of any one of claims 28-36, wherein the at least one target ion feed concentrator is present and the second target ion feed inlet of the first additive chamber is coupled to the first concentrated feed outlet of the at least one target ion feed concentrator.

38. The system of any one of claims 1-15, further comprising:82.a first blending tank, comprising:83.a third target ion feed inlet;84.a first blended mixture outlet; and85.a first supernatant inlet coupled to the first supernatant outlet of the first solid separation chamber; and86.a fourth solid separation chamber, comprising:87.a first blended mixture inlet coupled to the first blended mixture outlet of the first blending tank;88.a fourth solid collection outlet; and89.a fourth supernatant outlet coupled to the first target ion feed inlet of the first cathodic chamber.

39. The system of claim 38, wherein the first blending tank is configured to combine a first supernatant from the first solid separation chamber with a first target ion feed, thereby producing a blended mixture comprising a precipitate of at least one non-target ion.

40. The system of claim 39, wherein the fourth solid separation chamber is configured to separate the precipitate of the at least one non-target ion from the blended mixture.

41. The system of any one of claims 1-15, wherein the first catholyte mixture outlet comprises a primary catholyte mixture outlet and secondary catholyte mixture outlet, and the system further comprises:93.a first blending tank, comprising: a third target ion feed inlet;94.a first blended mixture outlet; and95.a first catholyte mixture inlet coupled to the secondary catholyte mixture outlet of the first cathodic chamber; and96.a fourth solid separation chamber, comprising:97.a first blended mixture inlet coupled to the first blended mixture outlet of the first blending tank;98.a fourth solid collection outlet; and99.a fourth supernatant outlet coupled to the first target ion feed inlet of the first cathodic chamber;100.wherein the primary catholyte mixture outlet is coupled to the first catholyte mixture inlet of the first solid separation chamber.

42. The system of claim 41, wherein:102.the first solid separation chamber is configured to separate a solid of a target ion from a first portion of a first catholyte mixture; and103.the first blending tank is configured to combine a second portion of the first catholyte mixture with a first target ion feed;104.thereby producing a blended mixture comprising a precipitate of at least one non-target ion.

43. The system of claim 42, wherein the fourth solid separation chamber is configured to separate the precipitate of the at least one non-target ion from the blended mixture.

44. The system of any one of claims 36-41, further comprising:107.a first carbonation chamber, comprising:108.a second blended mixture inlet coupled to the first blended mixture outlet of the first blending tank;109.a first carbonation feed inlet configured to flow a fluid comprising CO2 into the first carbonation chamber;110.a first carbonated mixture outlet coupled to the first blended mixture inlet of the fourth solid separation chamber; and111.a first gas outlet.

45. The system of any one of claims 38-40, further comprising:112.a first carbonation chamber, comprising:113.a second supernatant inlet coupled to the first supernatant outlet of the first solid separation chamber;114.a first carbonation feed inlet configured to flow a fluid comprising CO2 into the first carbonation chamber;115.a first carbonated mixture outlet coupled to the third target ion feed inlet of the first blending tank; and116.a first gas outlet.

46. The system of any one of claims 41-43, further comprising:118.a first carbonation chamber, comprising:119.a first catholyte mixture inlet coupled to the secondary catholyte mixture outlet of the first cathodic chamber;120.a first carbonation feed inlet configured to flow a fluid comprising CO2 into the first carbonation chamber;121.a first carbonated mixture outlet coupled to the third target ion feed inlet of the first blending tank; and122.a first gas outlet.

47. The system of any one of claims 44-46, wherein the first carbonation chamber is configured to produce a carbonate of at least one non-target ion.

48. The system of claim 47, wherein the first carbonation chamber is configured to produce CaCO3.

49. The system of any one of claims 38-48, wherein the system comprises the at least one target ion feed concentrator, and the first concentrated feed outlet of the at least one target ion feed concentrator is coupled to the third target ion feed inlet of the first blending tank.

50. The system of any one of claims 1-49, wherein the first anodic chamber further comprises a first recycle inlet coupled to the first supernatant outlet of the first solid separation chamber.

51. The system of claim 50, wherein the first recycle inlet is configured to flow a first supernatant from the first solid separation chamber to the first anodic chamber.

52. The system of any one of claims 1-51, wherein the first catholyte mixture outlet further comprises a first catholyte recycle outlet, the first target ion feed inlet comprises a first catholyte recycle inlet, and the first catholyte recycle outlet is coupled to the first catholyte recycle inlet.

53. The system of claim 52, wherein the first catholyte recycle outlet and first catholyte recycle inlet are configured to flow a portion of a first catholyte mixture from the first catholyte mixture outlet to the first target ion feed inlet.

54. The system of claim 53, wherein the first catholyte mixture comprises Mg(OH)2.

55. The system of any one of claims 1-54, wherein the system comprises a single electrochemical cell.

56. The system of any one of claims 1-54, further comprising:132.a second electrochemical cell comprising:133.a second cathodic chamber, comprising:134.a second cathode;135.a second target ion feed inlet coupled to the first supernatant outlet of the first solid separation chamber;136.a second cathodic gas outlet;137.a second catholyte mixture outlet;138.a second anodic chamber, comprising:139.a second anode;140.a second anolyte feed inlet coupled to the at least one primary acidic anolyte outlet;141.a second anodic gas outlet;142.at least one secondary acidic anolyte outlet;143.a second membrane disposed between the second cathodic chamber and the second anodic chamber; a fifth solid separation chamber, comprising:144.a second catholyte mixture inlet coupled to second first catholyte mixture outlet; a second solid collection outlet; and145.a second supernatant outlet;146.wherein the second cathodic chamber and the second anodic chamber are in ionic communication.

57. The system of claim 56, wherein the first electrochemical cell is configured to produce a carbonate of at least one non-target ion, preferably wherein the carbonate of at least one non-target ion is CaCO3.

58. The system of any one of claims 56-57, wherein the second electrochemical cell is configured to produce a hydroxide of a first target ion.

59. The system of any one of claims 56-58, wherein the second electrochemical cell is configured to produce Mg(0H)2.

60. The system of any one of claims 17-24, further comprising:151.a second electrochemical cell comprising:152.a second cathodic chamber, comprising:153.a second cathode;154.a second target ion feed inlet coupled to the first supernatant outlet of the first solid separation chamber;155.a second cathodic gas outlet;156.a second catholyte mixture outlet;157.a second anodic chamber, comprising:158.a second anode;159.a second anolyte feed inlet;160.a second anodic gas outlet;161.at least one secondary acidic anolyte outlet;162.a second membrane disposed between the second cathodic chamber and the second anodic chamber;163.a second solid separation chamber, comprising: a second catholyte mixture inlet coupled to second first catholyte mixture outlet; a second solid collection outlet; and164.a second supernatant mixture outlet;165.wherein the second cathodic chamber and the second anodic chamber are in ionic communication.

61. The system of claim 60, wherein the first electrochemical cell is configured to produce a hydroxide of a first target ion.

62. The system of claim 60 or 61, wherein the first electrochemical cell is configured to produce Mg(OH)2.

63. The system of any one of claims 60-62, wherein the second electrochemical cell is configured to produce a hydroxide of a second target ion.

64. The system of any one of claims 60-63, wherein the second electrochemical cell is configured to produce Ca(OH)2.

65. The system of any one of claims 60-64, wherein the second supernatant outlet of the second solid separation chamber is coupled to the second anolyte feed inlet of the second anodic chamber.

66. The system of any one of claims 60-64, further comprising:172.a third carbonation chamber, comprising:173.a third supernatant mixture inlet coupled to the second supernatant mixture outlet of the second solid separation chamber;174.a third carbonation feed inlet configured to flow a fluid comprising CO2 into the third carbonation chamber;175.a third carbonated mixture outlet; and176.a third gas outlet.

67. The system of any one of claims 1-66, wherein the first membrane and, when present, the second membrane comprise: a cation exchange membrane (CEM, e.g., sulfonatedtetrafluoroethylene based fluoropolymer-copolymer), anion exchange membrane (AEM), a non-selective barrier material, or a combination thereof.

68. The system of claim 67, wherein the first membrane and, when present, the second membrane comprise a cation exchange membrane.

69. The system of any one of claims 1-68, wherein the first membrane and, when present, the second membrane are selective for the passage of Na+ions from the anodic chamber to the cathodic chamber.

70. The system of any one of claims 1-67, wherein the first membrane is an anion exchange membrane.

71. The system of any one of claims 1-67 and 70, wherein the second membrane is an anion exchange membrane.

72. The system of claim 70 or 71, wherein the first membrane and, when present, the second membrane are selective for the passage of Cl from the first cathodic chamber to the first anodic chamber, and, when present, from the second cathodic chamber to the second anodic chamber.

73. The system of any one of claims 1-66, wherein the first anode and, when present, the second anode are oxygen-selective anodes.

74. The system of any one of claims 1-73, wherein the first anode and, when present, the second anode, are in the form of a plate.

75. The system of any one of claims 1-73, wherein the first anode and, when present, the second anode, are in the form of a mesh.

76. The system of any one of claims 1-75, wherein the first cathode and, when present, the second cathode, comprise iron, iron alloy, nickel, nickel alloy, cobalt, cobalt alloy, titanium, titanium alloy, aluminum, aluminum alloy, platinum, or a combination thereof.

77. The system of any one of claims 1-76, wherein the first cathode and, when present, the second cathode, further comprise a coating comprising platinum, nickel phosphate, or molybdenum sulfate.

78. The system of any one of claims 1-77, wherein the first cathode and, when present, the second cathode, are in the form of a mesh, plate, or rod.

79. The system of any one of claims 1-77, wherein the first cathode and, when present, the second cathode, are in the form of a mesh.

80. The system of any one of claims 1-78, wherein the first cathode and, when present, the second cathode, are mesh comprising Pt and Ti.

81. The system of any one of claims 1-80, wherein the first cathode and, when present, the second cathode are mesh comprising stainless steel (e.g., a 316 stainless steel mesh).

82. The system of any one of claims 1-79, wherein the first cathode and, when present, the second cathode are plates.

83. The system of claim 82, wherein the first cathode and, when present, the second cathode are plates comprising Ti having a coating comprising Pt.

84. The system of claim 82, wherein the first cathode and, when present, the second cathode are plates comprising Ni.

85. The system of any one of claims 1-84, wherein the first anode and, when present, the second anode comprise a group VIII metal, a group IX metal, a group X metal, titanium clad with a group VIII metal, titanium clad with a group IX metal, titanium clad with a group X metal, titanium clad with mixed metal oxide, or a combination thereof.

86. The system of claim 85, wherein the first anode and, when present, the second anode further comprise iridium, tin, cobalt, manganese, tantalum, ruthenium, graphite, graphene, or carbon nanotube(s).

87. The system of any one of claims 1-86, wherein the first electrochemical cell and, when present, the second electrochemical cell are configured to produce an anodic gas comprising O2 at the first anode and, when present, the second anode.

88. The system of claim 87, wherein the anodic gas further comprises Ch.

89. The system of any one of claims 1-88, wherein the first electrochemical cell and, when present, the second electrochemical cell are configured to produce a cathodic gas comprising H2 at the first cathode and, when present, the second cathode.

90. The system of any one of claims 1-88, wherein the first electrochemical cell and, when present, the second electrochemical cell are configured to produce hydroxides of one or more target ions at the first cathode and, when present, the second cathode.

91. The system of any one of claims 1-90, wherein the first electrochemical cell is configured to produce Mg(0H)2 at the first cathode.

92. The system of any one of claims 5-91, wherein the at least one nano filtration chamber comprises a nanofiltration membrane comprising a plurality of pores, and each of the plurality of pores has a pore diameter of from about 0.001 to about 0.01 pm.

93. The system of claim 92, wherein the at least one nanofiltration membrane is a polyamide thin-film composite.

94. The system of claim 92 or 93, wherein the at least one nanofiltration membrane is a FilmTec™ NF90 Nanofiltration membrane.

95. The system of any one of claims 1-94, wherein the system is configured to produce calcium hydroxide.

96. The system of any one of claims 1-95, wherein the system is configured to produce magnesium hydroxide.

97. The system of any one of claims 1-96, wherein the system is configured to produce magnesium hydroxide and calcium hydroxide.

98. The system of any one of claims 1-97, wherein the first target ion feed inlet and first anolyte feed inlet of the first electrochemical cell is a single, combined inlet coupled to the first anodic chamber and the first cathodic chamber.

99. The system of any one of claims 1-97, wherein the Mg(0H)2 concentration of the first catholyte mixture is sufficient (e.g., saturated) to pre-precipitate Mg(0H)2.

100. A system of claim 99, further comprising: a first dosing vessel disposed between the first catholyte recycle outlet and first catholyte recycle inlet configured to pre-precipitate CaCO3.

101. A system of claim 100, further comprising: second dosing vessel disposed between the first catholyte recycle outlet and first catholyte recycle inlet configured to pre-precipitate Mg(0H)2.

102. The system of any one of claims 1-97, wherein the system is configured to produce a hydroxide of a target ion from an aqueous solution comprising the target ion and at least one non-target ion.

103. The system of claim 102, wherein aqueous solution is selected from seawater, desalination brine, industrial brine, and natural brine.

104. The system of claim 102, wherein the aqueous solution is a product of an industrial process.

105. The system of claim 102, wherein the aqueous solution is or is derived from seawater.

106. A method of preparing Mg(0H)2 using the system of any one of claims 1-105, the method comprising the steps of:214.providing:215.an electrolyte solution to the first anodic chamber; and a first target ion stream to the first cathodic chamber;216.performing a first electrochemical process, comprising:217.applying a voltage to the first cathode and the first anode; thereby producing: a first acidic anolyte and an anodic gas at the first anode; and a first catholyte mixture and a cathodic gas at the first cathode; wherein:218.the first target ion stream comprises Mg2+; and219.the first catholyte mixture comprises Mg(0H)2.

107. A method of preparing Mg(0H)2, comprising:221.providing:222.a first target ion solution comprising Mg2+and at least one non-target ion to a first anodic chamber and a first cathodic chamber of a first electrochemical cell; the first electrochemical cell further comprising:223.a first anode disposed within the first anodic chamber;224.a first cathode disposed within the first cathodic chamber; and a first membrane disposed between and configured to separate the first cathodic chamber and the first anodic chamber;225.wherein the first anodic chamber and the first cathodic chamber are in fluid communication; and226.performing a first electrochemical process, comprising:227.applying a first voltage to the first cathode and the first anode; thereby producing:228.a first acidic anolyte and an anodic gas at the first anode; and a first catholyte mixture and a cathodic gas at the first cathode; wherein the first catholyte mixture comprises the Mg(0H)2.

108. The method of claim 107, further comprising separating the Mg(0H)2 from the first catholyte mixture, thereby producing a first supernatant and a first solid comprising Mg(0H)2.

109. The method of claim 108, wherein separating the Mg(0H)2 from the first catholyte mixture comprises filtering the first catholyte mixture.

110. The method of any one of claims 107-109, wherein the at least one non-target ion comprises calcium, iron, sodium, potassium, or a combination thereof.

111. The method of any one of claims 107-110, wherein the at least one non-target ion comprises calcium.

112. The method of any one of claims 107-111, wherein the at least one non-target ion is Ca2+.

113. The method of any one of claims 107-112, wherein the first target ion solution is or is derived from seawater, or comprises seawater.

114. The method of any one of claims 107-113, wherein the first target ion solution is seawater.

115. The method of any one of claims 107-112, wherein the first target ion solution is a naturally occurring brine solution.

116. The method of any one of claims 107-112, wherein the first target ion solution is an industrial brine solution (e.g., produced water).

117. The method of any one of claims 107-116, further comprising increasing a concentration of Mg2+in the first target ion solution.

118. The method of claim 117, wherein increasing the concentration of Mg2+in the first target ion solution comprises performing at least one concentration step, and each of the at least one concentration steps increases the concentration of Mg2+in the first target ion solution.

119. The method of claim 118, wherein the at least one concentration step comprises nanofiltration.

120. The method of claim 119, wherein the nanofiltration comprises passing the first target ion solution through a nanofiltration membrane, thereby producing a first permeate, comprising the at least one non-target ion, and a first retentate, comprising the Mg2+.

121. The method of any one of claims 118-120, wherein the at least one concentration step comprises performing reverse osmosis on the first target ion solution.

122. The method of any one of claims 118-121, wherein the at least one concentration step comprises evaporating water from the first target ion solution.

123. The method of any one of claims 118-122, wherein the method comprises one concentration step.

124. The method of any one of claims 118-122, wherein the method comprises two concentration steps.

125. The method of any one of claims 107-124, further comprising removing CO2 from the first acidic anolyte, thereby producing a first degassed solution comprising Mg2+and the at least one non-target ion.

126. The method of any one of claims 107-124, further comprising removing CO2 from the first target ion solution, thereby forming a first degassed solution comprising Mg2+and the at least one non-target ion.

127. The method of claim 125 or 126, wherein removing CO2 from the first target ion solution comprises allowing CO2 to passively exit the target ion solution.

128. The method of claim 125 or 126, wherein removing CO2 from the first target ion solution comprises contacting the first target ion solution with a stripping gas, and wherein the stripping gas enhances removal of CO2 from the first target ion solution.

129. The method of claim 128, wherein the stripping gas is air (e.g., atmospheric air or compressed air).

130. The method of any one of claims 108-129, wherein the first supernatant further comprises the at least one non-target ion, and the method further comprises contacting the first supernatant with a fluid comprising CO2, thereby producing a first carbonate mixture comprising a carbonate of the at least one non-target ion.

131. The method of claim 130, further comprising separating the carbonate of the at least one non-target ion from the first carbonate mixture.

132. The method of claim 130 or 131, wherein the carbonate of the at least one non-target ion is CaCO3.251.133 The method of any one of claims 107-132, further comprising contacting the target ion solution with an additive, thereby producing an additive mixture comprising a second solid comprising the at least one non-target ion.

134. The method of claim 133, further comprising separating the second solid comprising the at least one non-target ion from the additive mixture.

135. The method of claim 133 or 134, wherein the additive comprises [CO3]2-, [PO4]3-, or a combination thereof.

136. The method any one of claims 133-135, wherein the additive comprises NaHCO3, Na3PO4, or a combination thereof.

137. The method of any one of claims 133-136, wherein the second solid comprising the at least one non-target ion comprises calcium.

138. The method of any one of claims 133-137, wherein the additive is in a solid phase, an aqueous solution phase, a liquid phase, or a gaseous phase, preferably wherein the additive is in a solid phase.

139. The method of any one of claims 107-132, further comprising contacting the first supernatant with the first target ion solution, thereby forming a mixture comprising a third solid comprising the at least one non-target ion.

140. The method of any one of claims 107-132, further comprising contacting a portion of the first catholyte mixture with the first target ion solution, thereby forming a mixture comprising a third solid comprising the at least one non-target ion.

141. The method of any one of claims 108-132, further comprising combining a portion of the solid comprising Mg(OH)2 with the first target ion solution, thereby forming a mixture comprising a third solid comprising the at least one non-target ion.

142. The method of any one of claims 139-141, further comprising contacting the mixture comprising the third solid with a fluid containing CO2.

143. The method of claim 139, further comprising contacting the first supernatant with a fluid containing CO2, thereby forming a first carbonated mixture, and contacting the first carbonated mixture with the first target ion solution, thereby forming the mixture comprising the third solid.

144. The method of claim 140, further comprising contacting the portion of the first catholyte mixture with a fluid containing CO2, thereby forming a first carbonated mixture, and contacting the first carbonated mixture with the first target ion solution, thereby forming the mixture comprising the third solid.

145. The method of any one of claims 139-144, further comprising separating the third solid from the mixture.

146. The method of any one of claims 139-145, wherein the third solid comprising the at least one non-target ion comprises calcium.

147. The method of any one of claims 139-146, wherein the third solid comprising the at least one non-target ion is CaCO3.

148. The method of any one of claims 142-147, wherein the fluid comprising CO2 is a gas.

149. The method of any one of claims 107-148, further comprising providing the first supernatant to the first anodic chamber.

150. The method of any one of claims 107-149, wherein the first membrane is selective for the passage of anions from the first cathodic chamber to the first anodic chamber.

151. The method of any one of claims 107-150, further comprising recycling a portion of the first catholyte mixture to the first cathodic chamber, thereby forming a catholyte recycle stream.

152. The method of any one of claims 107-151, further comprising:269.providing:270.a second target ion solution comprising Ca2+and at least one non-target ion to a second anodic chamber and a second cathodic chamber of a second electrochemical cell;271.the second electrochemical cell further comprising:272.a second anode disposed within the second anodic chamber;273.a second cathode disposed within the second cathodic chamber; and a second membrane disposed between and configured to separate the second cathodic chamber and the second anodic chamber;274.wherein the second anodic chamber and the second cathodic chamber are in fluid communication; and275.performing a second electrochemical process, comprising:276.applying a second voltage to the second cathode and the second anode; thereby producing:277.a second acidic anolyte and an anodic gas at the second anode; and278.a second catholyte mixture and a cathodic gas at the second cathode; wherein the second catholyte mixture comprises calcium.

153. The method of claim 152, further comprising separating a fourth solid comprising calcium from the second catholyte mixture, thereby producing a second supernatant and the fourth solid comprising calcium.

154. The method of claim 152 or 153, wherein the second acidic anolyte comprises Mg2+and is provided to the first anodic chamber.

155. The method of claim 153 or 154, wherein the second supernatant comprises Mg2+and is provided to the first cathodic chamber.

156. The method of any one of claims 152-155, wherein the compound comprising calcium is CaCO3.

157. The method of claim 152 or 153, wherein the first target ion solution and the second target ion solution are the same solution.

158. The method of claim 152 or 153, wherein the first target ion solution and the second target ion solution are different solutions.

159. The method of any one of claims 152, 153, 158, wherein the first supernatant is provided to the second cathodic chamber.

160. The method of any one of claims 153 and 157-159, further comprising contacting the second supernatant with a fluid comprising CO2, thereby producing a carbonate mixture comprising a carbonate of at least one monovalent cation.

161. The method of claim 160, wherein the carbonate mixture comprises NaHCO3or Na2CC>3, or a combination thereof.

162. The method of any one of claims 157-161, wherein the second catholyte mixture comprises Ca(OH)2.

163. The method of any one of claims 107-162, further comprising contacting the first acidic anolyte and, when present, the second acidic anolyte with a basic material, thereby neutralizing the first acidic anolyte and, when present, the second acidic anolyte.

164. The method of claim 163, wherein the basic material comprises a fifth solid or a solution comprising OH ions.

165. The method of any one of claims 152-164, wherein the second target ion solution is or is derived from seawater, or comprises seawater.

166. The method of any one of claims 152-165, wherein the second target ion solution is seawater.

167. The method of any one of claims 152-164, wherein the second target ion solution is a naturally occurring brine solution.

168. The method of any one of claims 152-164, wherein the second target ion solution is an industrial brine solution (e.g., produced water).

169. The method of any one of claims 106-168, wherein the first target ion feed inlet and first anolyte feed inlet of the first electrochemical cell is a single, combined inlet coupled to the first anodic chamber and the first cathodic chamber.

170. The method of any one of claims 106-168, wherein the Mg(OH)2 concentration of the first catholyte mixture is sufficient (e.g., saturated) to pre-precipitate Mg(OH)2.

171. The method of any one of claims 106-168 and 170, further comprising: preprecipitating CaCO3by a first dosing vessel disposed along the catholyte recycle stream.

172. The method of claim 171, further comprising: pre-precipitating Mg(OH)2 by a second dosing vessel disposed along the catholyte recycle stream.

173. The method of any one of claims 107-172, wherein the first solid comprising Mg(OH)2 has a purity of greater than about 90%, greater than about 95%, or greater than about 99%.

174. The method of any one of claims 107-173, wherein the first solid comprising Mg(OH)2 has a purity of from about 90% to 100%, from about 95% to 100%, or from about about 99% to 100%.

175. The method of any one of claims 107-173, wherein the first solid comprising Mg(OH)2 comprises less than about 5% Ca, less than about 1% Ca, less than about 0.8% Ca, less than about 0.5% Ca, or less than about 0.1% Ca.

176. The method of any one of claims 107-175, wherein the first solid comprising Mg(OH)2 comprises substantially no calcium.

177. The method of any one of claims 107-175, wherein the first solid comprising Mg(OH)2 comprises trace amounts of calcium.

178. The method of any one of claims 107-175, wherein the first solid comprising Mg(OH)2 is substantially pure Mg(OH)2.

179. The method of any one of claims 107-177, performed using the system of any one of claims 1-105.

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