Electrochemical Extraction and Conversion of Metals from Liquid Solutions

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. § 119 (e) of U.S. Provisional Patent Application 63/677,051 (Attorney Docket No. EELIP001P) by Mert Akin, titled: “Electrochemical Extraction and Conversion of Metals from Liquid Solutions”, filed on 2024 Jul. 30, which is incorporated herein by reference in its entirety for all purposes.

FIELD OF TECHNOLOGY

The present disclosure generally relates to the electrified extraction of lithium from liquid sources and, more specifically, to apparatuses, systems, and methods for lithium extraction from brine (e.g., natural, geothermal, and synthetic brines, leachate solutions from minerals, clays, and recycled products) in a lithium-extraction reactor and subsequent direct conversion to lithium-containing products (e.g., lithium carbonate, lithium hydroxide, or lithium-containing salt forms) in a lithium-conversion reactor.

BACKGROUND

Lithium, a critical element for batteries and other technologies, can be found in the form of hard-rock ore, brine, and clay. The majority of lithium compounds (such as lithium chloride (LiCl), lithium carbonate (Li₂CO₃), and lithium hydroxide (LiOH)) are extracted from hard-rock ores (e.g., spodumene or lithium aluminum silicate) through traditional mining and lithium-containing continental brines—also called salars or saltwater.

Currently, on the commercial scale, evaporative approaches, often referred to as solar evaporation, are used to extract lithium from continental brines. In these approaches, a brine is concentrated in an open-air evaporation pond (e.g., over a year) to crystallize alkali salts. These salts may then be purified through a series of chemical processes with the addition of chemicals, such as calcium carbonate (CaCO₃), calcium oxide (CaO), sodium carbonate (Na₂CO₃), and sodium hydroxide (NaOH). Later, the concentrated lithium chloride solution is transferred to the chemical carbonation plant, wherein the lithium chloride (LiCl) solution is converted into lithium carbonate (Li₂CO₃) via chemical carbonization with the addition of sodium carbonate (Na₂CO₃) and then, if applicable, to lithium hydroxide (LiOH) using calcium hydroxide (Ca(OH)₂).

The conventional lithium carbonate (Li₂CO₃) and lithium hydroxide (LiOH) productions through solar evaporation coupled with chemical conversion processes suffer from lengthy recovery time (10-24 months), low recovery efficiency (˜30%), and high operational expenses (˜5000 $/ton of Li₂CO₃). More importantly, this method consumes tremendous amounts of fresh water (˜500,000 gallons/ton of Li₂CO₃) and carbon emissions (3 tons/ton of Li₂CO₃). Therefore, this process poses an enormous burden on the environment due to carbon emissions, water consumption, and waste generation.

Yet another challenge is the geographical distribution of lithium around the world. High-grade brines with an approximately 50 to 80% lithium concentration are present in geographically restricted locations, specifically in the lithium triangle (the region of Argentina, Bolivia, and Chile) and China. On the other hand, there are abundant low-grade, low-concentration, liquid lithium sources in geothermal brines, oilfield brines, closed-basin brines, and seawater. Unfortunately, the extraction of lithium from low-grade sources through the conventional solar evaporation process is not efficient and economically viable. Because of this technological challenge, most of the low-grade sources remain untapped.

Therefore, there is a need for methods and devices to enable efficient, economical, sustainable, and scalable lithium extraction from abundant low-grade sources with minimal environmental impact.

SUMMARY

Described herein are tandem methods for producing a lithium-containing product from a lithium-containing solution and systems for performing. A method may involve supplying the lithium-containing solution into a lithium-extraction reactor and applying a negative potential to the working electrode, thereby electrochemically incorporating lithium into the working electrode. The lithium-containing solution may then be replaced with a recovery solution and a positive potential to the working electrode, thereby extracting lithium from the working electrode into the recovery solution. The recovery solution comprising lithium cations is then transferred to a lithium-conversion reactor, and a conversion potential is applied between the electrodes, thereby converting the lithium cations into a lithium-containing product, such as lithium carbonate (Li₂CO₃), lithium hydroxide (LiOH), lithium chloride (LiCl), and lithium sulfate (Li₂SO₄). For example, carbon dioxide (CO₂) may be pumped through the recovery solution while applying the conversion potential to lithium carbonate (Li₂CO₃).

Clause 1. A tandem method for producing a lithium-containing product from a lithium-containing solution, the tandem method comprising: supplying the lithium-containing solution comprising lithium cations (Li⁺) into a lithium-extraction reactor, wherein the lithium-extraction reactor comprises a working electrode and a counter electrode; applying a negative potential to the working electrode, relative to the counter electrode, thereby electrochemically incorporating the lithium cations (Li⁺) into the working electrode; removing the lithium-containing solution from the lithium-extraction reactor; supplying a recovery solution to the lithium-extraction reactor; applying a positive potential to the working electrode, relative to the counter electrode, thereby extracting the lithium cations (Li⁺) from the working electrode into the recovery solution; transferring the recovery solution comprising the lithium cations (Li⁺) to a lithium-conversion reactor, wherein the lithium-conversion reactor comprises a cathodic electrode, an anodic electrode, and an ionic exchange membrane positioned between the cathodic electrode and the anodic electrode; and applying a conversion potential between the cathodic electrode and the anodic electrode, thereby converting the lithium cations (Li⁺) in the recovery solution into the lithium-containing product.

Clause 2. The tandem method of clause 1, wherein the recovery solution comprises water.

Clause 3. The tandem method of clause 1, wherein the lithium-containing product comprises lithium hydroxide (LiOH).

Clause 4. The tandem method of clause 3, wherein applying the conversion potential between the cathodic electrode and the anodic electrode comprises water splitting into hydrogen gas (H₂) and hydroxide ions (OH⁻) at the cathodic electrode and reacting the hydroxide ions (OH⁻) with the lithium cations (Li⁺) to form lithium hydroxide (LiOH).

Clause 5. The tandem method of clause 1, further comprising supplying carbon dioxide (CO₂) into the lithium-conversion reactor while applying a conversion potential between the cathodic electrode and the anodic electrode, wherein the lithium-containing product comprises lithium carbonate (Li₂CO₃).

Clause 6. The tandem method of clause 5, wherein applying the conversion potential between the cathodic electrode and the anodic electrode comprises: water splitting into hydrogen gas (H₂) and hydroxide ions (OH⁻) at the cathodic electrode, reacting hydroxide ions (OH⁻) with the carbon dioxide (CO₂) to form bicarbonate anions (HCO₃⁻), and reacting the bicarbonate anions (HCO₃⁻) with the lithium cations (Li⁺) to form lithium carbonate (Li₂CO₃).

Clause 7. The tandem method of clause 5, wherein applying the conversion potential between the cathodic electrode and the anodic electrode is performed for an electrode-saturation period of time prior to supplying the carbon dioxide (CO₂) into the lithium-conversion reactor.

Clause 8. The tandem method of clause 1, wherein: the working electrode comprises one or more materials selected from the group consisting of lithium selective compounds, including but not limited to, manganese oxide (MnO₂), lithium cobalt oxide (Li_1-xCoO₂ such that 0≤x<1), lithium cobalt phosphate (Li_1-xCoPO₄ such that 0≤x<1), lithium manganese oxide (Li_1-xMn₂O₄ such that 0≤x<1), lithium nickel oxide (Li_1-xNiO₂ such that 0≤x<1), lithium nickel cobalt manganese oxide (LiNi_xMn_yCo_1-x-yO₂ such that 0≤x≤1, 0≤y≤1, and 0≤x+y≤1), lithium iron phosphate (Li_1-xFePO₄ such that 0≤x<1), lithium manganese phosphate (Li_1-xMnPO₄ such that 0≤x<1), lithium vanadium oxide (Li_1-xV₂O₅ such that 0≤x<1 or Li₃V₃O₈), lithium vanadium phosphate (Li₃V₂(PO₄)₃), iron phosphate (FePO₄), and vanadium phosphate (V₂O₅).

Clause 9. The tandem method of clause 1, wherein, in addition to the lithium cations (Li⁺), the lithium-containing solution comprises one or more anions selected from the group consisting of chloride (Cl⁻), sulfate (SO₄²⁻), bicarbonate (HCO₃⁻), borate (B(OH⁻)₄⁻), bromide (Br⁻), nitrate (NO₃⁻), and fluoride (F⁻).

Clause 10. The tandem method of clause 9, wherein applying the negative potential to the working electrode, relative to the counter electrode, further comprises electrochemical incorporating the anions into the counter electrode.

Clause 11. The tandem method of clause 10, wherein the counter electrode comprises a material selected from the group consisting of cobalt, a cobalt compound, lithium cobalt oxide (LiCoO₂), lithium manganese oxide (Li_1-xMn₂O₄), lithium nickel cobalt manganese oxide (LiNi_xMn_yCo_1-x-yO₂), lithium iron phosphate (LiFePO₄), polyaniline (PANI), polypyrrole (PPy), silver (Ag), a silver alloy, silver chloride (AgCl), and a Prussian blue analog.

Clause 12. The tandem method of clause 10, wherein applying the negative potential to the working electrode, relative to the counter electrode, further comprises electrochemically incorporating the anions into the counter electrode.

Clause 13. The tandem method of clause 12, wherein the counter electrode comprises one or more materials selected from the group consisting of activated carbon, carbon paper, carbon nanotubes, conductive polymer, diamond, doped diamond, graphite, graphene, gold, and platinum (Pt).

Clause 14. The tandem method of clause 1, wherein the negative potential for the incorporation of the lithium cations (Li⁺) into the working electrode is in a range of −0.01 mV to −10 V (vs reversible hydrogen electrode).

Clause 15. The tandem method of clause 1, wherein the positive potential for releasing the lithium cations (Li⁺) from working electrodes is in a range of 0.01 mV to 10 V (vs reversible hydrogen electrode).

Clause 16. The tandem method of clause 1, wherein the recovery solution comprises one or more materials selected from the group consisting of water (H₂O), acetone (C₃H₆O), acetonitrile, diethyl carbonate (C₅H₁₀O₃), dimethyl carbonate (C₃H₆O₃), ethyl methyl carbonate (C₄H₈O₃), methyl acetate (C₃H₆O₂), ethyl acetate (C₄H₈O₂), dimethoxyethane (C₄H₁₀O₂), tetrahydrofuran (C₄HgO), ethanol (C₂H₆O), methanol (CH₃OH), isopropanol (C₃H₈O), dimethylformamide (C₃H₇NO), dimethyl sulfoxide (C₂H₆OS), and N-methyl-2-pyrrolidone (CH₇NO).

Clause 17. The tandem method of clause 1, wherein the conversion potential is in a range of 0.1 mV to 2 V (vs a reversible hydrogen electrode).

Clause 18. The tandem method of clause 1, wherein the cathodic electrode comprises one or more catalytically active materials performing a hydrogen evolution reaction (HER) from the group consisting of platinum, platinum-containing catalysts, platinum-supported materials, palladium, palladium-containing catalysts, palladium-supported materials, gold, gold-containing catalysts, gold-supported materials, carbon, carbon-containing catalysts, carbon-supported materials, silver, silver-containing catalysts, and silver supported materials; one or more catalyst support materials selected from the group consisting of carbon papers, carbon clots, and metallic substrates; and one or more polymeric binder selected from the group consisting of anion- or cation-exchange ionomers or a combination of both.

Clause 19. The tandem method of clause 1, wherein the anodic electrode comprises one or more catalytically active materials performing an oxygen evolution reaction (OER) selected from the group consisting of nickel, nickel-containing catalysts, nickel-supported materials, iridium, iridium-containing catalysts, iridium-supported materials, ruthenium, ruthenium-containing catalysts, ruthenium supported materials, platinum, platinum-containing catalysts, platinum supported materials, metal borides/borates, palladium, palladium-containing catalysts, palladium supported materials, rhodium, rhodium-containing catalysts, rhodium supported materials, cobalt, cobalt-containing catalysts, cobalt supported catalysts; one or more catalyst support materials selected from the group consisting of carbon papers, carbon clots, and metallic substrates; and one or more polymeric binder selected from the group consisting of anion-exchange ionomers or cation-exchange ionomers or a combination of both.

Clause 20. The tandem method of clause 1, wherein the ionic exchange membrane is an anion-selective membrane or a cation-selective membrane.

Clause 21. The tandem method of clause 1, wherein the temperature of the lithium-extraction reactor is in a range of −40° C. to 150° C.

Clause 22. The tandem method of clause 1, wherein the temperature of the lithium-conversion reactor is in a range of −40° C. to 150° C.

Clause 23. The tandem method of clause 1, wherein the lithium-containing product is selected from the group consisting of lithium carbonate (Li₂CO₃), lithium hydroxide (LiOH), lithium chloride (LiCl), and lithium sulfate (Li₂SO₄).

Clause 24. A tandem method for producing a lithium-containing product from a lithium-containing solution, the tandem method comprising: supplying the lithium-containing solution comprising lithium cations (Li⁺) into a lithium-extraction reactor, wherein the lithium-extraction reactor comprises a working electrode and a counter electrode; applying a negative potential to the working electrode, relative to the counter electrode, thereby electrochemically incorporating the lithium cations (Li⁺) into the working electrode; removing the lithium-containing solution from the lithium-extraction reactor; supplying a recovery solution to the lithium-extraction reactor while applying a positive potential to the working electrode, relative to the counter electrode, thereby extracting the lithium cations (Li⁺) from the working electrode into the recovery solution; transferring the recovery solution comprising the lithium cations (Li⁺) to a lithium-conversion reactor; supplying carbon dioxide (CO₂) into the lithium-conversion reactor; and heating the recovery solution to at least 30° C. while stirring the recovery solution in the lithium-conversion reactor thereby converting the lithium cations (Li⁺) in the recovery solution into the lithium-containing product comprising lithium carbonate (Li₂CO₃).

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are illustrations of a lithium-extraction reactor configured for the selective recovery of metals or, more specifically, metal cations, from various solutions, in accordance with some examples.

FIG. 1C is an expanded schematic view of a cell assembly used in a lithium-extraction reactor in FIGS. 1A-1B, in accordance with some examples.

FIG. 1D is a block diagram of a lithium-extraction reactor and a lithium-conversion reactor used for a tandem method for producing a lithium-containing product from a lithium-containing solution, in accordance with some examples.

FIG. 2 is a process flowchart corresponding to a tandem method for producing a lithium-containing product from a lithium-containing solution using a lithium-extraction reactor and a lithium-conversion reactor, in accordance with some examples.

FIG. 3 is a block diagram corresponding to various materials used in the tandem method of FIG. 2, in accordance with some examples.

FIGS. 4A-4D are schematic illustrations of different stages of the method in FIG. 2 while producing lithium-containing products, such as lithium carbonate.

FIGS. 5A-5D are schematic illustrations of different stages of the method in FIG. 2 while producing lithium-containing products, such as lithium hydroxide

DETAILED DESCRIPTION

Introduction

As noted above, conventional methods of lithium extraction are slow and/or require highly concentrated brines. Tandem methods for producing lithium-containing products, described herein, provide an efficient and sustainable path for efficient and selective lithium extraction and recovery from low-grade lithium-containing solutions (e.g., natural, geothermal, and synthetic brines, leachate solutions from minerals, clays, and recycled products) with zero or even negative carbon emissions. For example, carbon dioxide (CO₂) may be used and consumed while producing lithium-containing products such as lithium carbonate (Li₂CO₃).

A method, described herein, may involve supplying a lithium-containing solution into a lithium-extraction reactor and applying a negative potential to the working electrode, thereby electrochemically incorporating lithium into the working electrode. As such, lithium (initially provided in the lithium-containing solution) is separated or, more specifically, electrochemically separated from other components of the lithium-containing solution. The lithium-containing solution may then be replaced with a recovery solution. Specifically, the recovery solution is added to the lithium-extraction reactor. At this stage, lithium remains embedded in the working electrode in that reactor. A positive potential is then applied to the working electrode, thereby extracting lithium from the working electrode into the recovery solution. The recovery solution comprising lithium cations is then transferred to a lithium-conversion reactor. The lithium-conversion reactor uses different types of electrodes than the lithium-extraction reactor. A conversion potential is then applied between the electrodes of the lithium-conversion reactor, thereby converting the lithium cations into a lithium-containing product. Various examples of lithium-containing products are within the scope, e.g., lithium carbonate (Li₂CO₃), lithium hydroxide (LiOH), lithium chloride (LiCl), and lithium sulfate (Li₂SO₄).

The lithium-extraction reactor comprises a working electrode formed from lithium-selective intercalation compounds (e.g., lithium iron phosphate, lithium cobalt oxide, manganese oxide) that reversibly incorporate and release lithium cations from a lithium-containing solution under applied electrochemical potentials. In contrast, the lithium-conversion reactor comprises a cathodic electrode and an anodic electrode, each comprising electrocatalytically active materials configured to facilitate water-splitting reactions (e.g., platinum for the hydrogen evolution reaction and nickel-based materials for the oxygen evolution reaction) separated by an ionic exchange membrane. This structural and functional distinction reflects the different electrochemical mechanisms employed in these two reactors: (1) selective ion intercalation and de-intercalation in the lithium-extraction reactor versus (2) electrochemical conversion of lithium into lithium-containing products (e.g., lithium bicarbonate (LiHCO₃⁻), to lithium carbonate (Li₂CO₃)) in the lithium-conversion reactor.

The composition of the lithium-containing product (formed in the lithium-conversion reactor) depends on the composition of the recovery solution. Additional factors influencing product composition include, but are not limited to, the concentration of lithium cations in the recovery solution, the presence and flow rate of carbon dioxide (CO₂) (e.g., when carbon dioxide (CO₂) is used), electrolyte pH, temperature, and the materials of the cathodic and anodic electrodes. For instance, lithium carbonate (Li₂CO₃) formation is favored when the recovery solution contains carbon dioxide (CO₂) and high lithium cation concentrations (above 200 ppm), typically exceeding the solubility limit of intermediate lithium bicarbonate (LiHCO₃⁻), under a conversion potential of 1.5-1.8 V vs. RHE. Stirring and elevated temperatures above 30° C. facilitate the decomposition of lithium bicarbonate (LiHCO₃⁻) to lithium carbonate (Li₂CO₃). Conversely, when carbon dioxide (CO₂) is excluded and the electrolyte is highly alkaline (e.g., pH>12), LiOH formation is promoted via reaction of lithium cations (Li⁺) with electrochemically generated hydroxide anions (OH⁻). Therefore, tuning the lithium concentration, gas input/flow rates, reactor/recovery solution temperature, and electrode materials enables the selective production of lithium carbonate (Li₂CO₃) or lithium hydroxide (LiOH), and/or other lithium-containing products.

The processes in the lithium extraction and lithium conversion reactors described above can also be separate systems or can be coupled with other alternative systems to produce alkaline, alkaline earth, and transition metal products (salts and compounds), including but not limited to cesium chloride (CsCl), cesium carbonate (Cs₂CO₃), cesium hydroxide (CsOH), cesium sulfate (Cs₂SO₄), cobalt chloride (CoCl₂), cobalt carbonate (CoCO₃), cobalt hydroxide (Co(OH)₂), cobalt sulfate (CoSO₄), francium chloride (FrCl), francium carbonate (Fr₂CO₃), francium hydroxide (FrOH), francium sulfate (Fr₂SO₄), potassium chloride (KCl), potassium carbonate (K₂CO₃), potassium hydroxide (KOH), potassium sulfate (K₂SO₄), sodium chloride (NaCl), sodium carbonate (Na₂CO₃), sodium hydroxide (NaOH), sodium sulfate (Na₂SO₄), rubidium chloride (RbCl), rubidium carbonate (Rb₂CO₃), rubidium hydroxide (RbOH), rubidium sulfate (Rb₂SO₄), barium chloride (BaCl₂), barium carbonate (BaCO₃), barium hydroxide (Ba(OH)₂), barium sulfate (BaSO₄), beryllium chloride (BeCl₂), beryllium carbonate (BeCO₃), beryllium hydroxide (Be(OH)₂), beryllium sulfate (BeSO₄), calcium chloride (CaCl₂)), calcium carbonate (CaCO₃), calcium hydroxide (Ca(OH)₂), calcium sulfate (CaSO₄), magnesium chloride (MgCl₂), magnesium carbonate (MgCO₃), magnesium hydroxide (Mg(OH)₂), magnesium sulfate (MgSO₄), manganese carbonate (MnCO₃), manganese hydroxide (Mn(OH)₂), manganese sulfate (MnSO₄), nickel chloride (NiCl₂), nickel carbonate (NiCO₃), nickel hydroxide (Ni(OH)₂), nickel sulfate (NiSO₄), strontium chloride (SrCl₂), strontium carbonate (SrCO₃), strontium hydroxide (Sr(OH)₂), strontium sulfate (SrSO₄), radium chloride (RaCl₂), radium carbonate (RaCO₃), radium hydroxide (Ra(OH)₂), radium sulfate (RaSO₄), and other transition metal products (salts and compounds).

These and other variations are described in more detail below.

FIGS. 1A-1D: System Examples

FIGS. 1A-1D illustrates various components and aspects of a tandem reactor system 190 for producing a lithium-containing product from a lithium-containing solution, in accordance with some examples. The tandem reactor system 190 may comprise a lithium-extraction reactor 100 and a lithium-conversion reactor 150, as well as a power supply 192, gas supply lines 194, and liquid supply lines 196. The tandem reactor system 190 may also comprise a system controller 198 for controlling various operations of the above-referenced components, e.g., potentials applied between the electrodes in each reactor, duration, temperatures, and other processing conditions. The system controller 198 may comprise a memory 199a (configured to store various instructions associated with the tandem method 200 described below) and a processor 199b (configured to process these instructions and to control the operations).

The lithium-extraction reactor 100 comprises a working electrode 110 and a counter electrode 120. The lithium-extraction reactor 100 is configured to extract lithium cations 312 from the lithium-containing solution 310, e.g., by supplying the lithium-containing solution 310 into the lithium-extraction reactor 100 and applying a negative potential to the working electrode 110, thereby driving and incorporating the lithium cations 312 into the working electrode 110. This operation may be referred to as the selective recovery of lithium cations 312 from the lithium-containing solution 310, which may also be referred to as brine.

The working electrode 110 comprises one or more materials selected from the group consisting of lithium-selective compounds, including but not limited to, manganese oxide (MnO₂), lithium cobalt oxide (Li_1-xCoO₂ such that 0≤x<1), lithium cobalt phosphate (Li_1-xCoPO₄ such that 0≤x<1), lithium manganese oxide (Li_1-xMn₂O₄ such that 0≤x<1), lithium nickel oxide (Li_1-xNiO₂ such that 0≤x<1), lithium nickel cobalt manganese oxide (LiNi_xMn_yCo_1-x-yO₂ such that 0≤x≤1, 0≤y≤1, and 0≤x+y≤1), lithium iron phosphate (Li_1-xFePO₄ such that 0≤x<1), lithium manganese phosphate (Li_1-xMnPO₄ such that 0≤x<1), lithium vanadium oxide (Li_1-xV₂O₅ such that 0≤x<1 or Li₃V₃O₈), lithium vanadium phosphate (Li₃V₂(PO₄)₃), iron phosphate (FePO₄), and vanadium phosphate (V₂O₅). The listed materials offer distinct benefits depending on structure and application needs. It should also be noted that the negative potential applied for the incorporation (e.g., intercalation) depends on the type, physical and chemical properties, and scale of the working electrode 110. For example, spinel-type oxides (e.g., Li_1-xMn₂O₄) are low-cost, thermally stable, and operate at relatively positive potentials (−0.4 to −0.6 V vs. RHE), making them ideal for scalable systems. Layered oxides (e.g., Li_1-xCoO₂, Li_1-xNiO₂) provide high lithium sorption capacity and electrochemical reversibility but may require more negative potentials (−0.6 to −0.8 V vs. RHE). Phosphate-based materials (e.g., Li_1-xFePO₄, Li_1-xMnPO₄) exhibit excellent cyclic and mechanical stability, with flat voltage profiles and minimal degradation. Vanadium-based compounds (e.g., Li_1-xV₂O₅, Li₃V₂(PO₄)₃) offer multielectron redox reactions, enabling higher capacity, though with increased cost and complexity. These examples allow tailoring electrode selection to cost, stability, or performance targets in the lithium-extraction reactor. In this disclosure, the term “0≤x<1” refers to the stoichiometric range of lithium content in the electrode material, where x=0 corresponds to the fully lithiated (charged) state of the working electrode before lithium intercalation, and x approaching 1 corresponds to the fully delithiated (discharged) state after lithium extraction. The extent of intercalation or de-intercalation is defined by the electrochemical capacity of the host material and may be controlled by the applied potential, current density, or predefined cut-off voltage in the lithium-extraction reactor 100.

The materials of the working electrode 110 are selected to be electrochemically stable within the operating voltage window, e.g., ranging from +0.4 V to −0.8 V vs RHE (approximately +0.2 V to −1.0 V vs. SHE), depending on pH and reference conditions. This voltage range is used for selective lithium intercalation while minimizing side reactions such as hydrogen evolution and avoiding phase transformations, lattice collapse, or dissolution that could impair lithium uptake or shorten cycle life. Thermal stability above 20° C. may be used to enhance ion transport and kinetics under elevated temperatures (above 30° C.), while ensuring mechanical and electrochemical integrity. Candidate materials may be characterized by high reversibility and cycling durability to maintain performance over repeated charge/discharge cycles and reduce maintenance costs. The specific negative potential required for lithium intercalation varies based on the thermodynamic and kinetic characteristics of the electrode material. For example, spinel-type oxides (e.g., Li_1-xMn₂O₄) typically intercalate lithium at more positive potentials (−0.4 to −0.6 V vs RHE), while layered oxides (e.g., Li_1-xCoO₂ or Li_1-xNiO₂) may require more negative potentials (−0.6 to −0.8 V vs RHE) to drive effective incorporation. Phosphate-based materials (e.g., Li_1-xFePO₄ or Li_1-xMnPO₄) often exhibit narrow and well-defined intercalation plateaus, enabling operation within tighter voltage margins. Accordingly, the applied potential is tuned to the electrochemical signature of each material to achieve efficient lithium uptake without exceeding the stability limits of the electrode or electrolyte system.

In some examples, the working electrode 110 may be configured to enhance lithium ion intercalation kinetics, mechanical durability, and operational stability. For example, the geometry and morphology of the working electrode 110 can include planar, layered, or three-dimensional (3D) porous structures to maximize active surface area. The 3D porous structures may include, but are not limited to, interconnected pore networks, foam-like matrices, inverse opal structures, nanowire arrays, or hierarchical morphologies combining macro-, meso-, and micropores. In some examples, the specific surface area of the working electrode 110 is characterized by a surface area-to-projected area ratio in the range of 2:1 to 100:1, more specifically in the range of 5:1 to 50:1, or even in the range of 10:1 to 30:1. In further examples, the active intercalation material is deposited onto a woven or nonwoven carbon cloth substrate, which serves as both the mechanical backbone and current collector. The carbon cloth may comprise conductive carbon fibers (e.g., polyacrylonitrile-derived) thermally treated to enhance crystallinity, with a typical fiber diameter in the range of 5-15 micrometers, porosity in the range of 60-90%, and thickness in the range of 100-500 micrometers. The carbon cloth provides high tensile strength, electrochemical stability, low sheet resistance (<10 Ω/sq), and dimensional flexibility, making it suitable for large-area manufacturing and long-term cycling. Its open-mesh architecture promotes uniform electrolyte infiltration and minimizes mass transport limitations, while the high surface area facilitates conformal coating of active material layers via slurry casting, vacuum filtration, or spray deposition. A higher specific surface area facilitates faster charge transfer and improves rate capability, particularly beneficial for high-throughput or continuous operation modes. These configurations may be engineered to improve electrolyte accessibility, reduce polarization losses, and increase the number of electrochemically accessible active sites while maintaining mechanical robustness and interfacial integrity over repeated cycles.

In some examples, the working electrode 110 is porous with porosity in the range of 25-90% or, more specifically, 30-80%, or even 40-60%. These porosity levels balance between ionic accessibility and mechanical integrity. Higher porosity enhances lithium ion diffusion and electrolyte penetration into the bulk of the electrode, which improves charge transfer kinetics and increases effective surface area for intercalation. However, excessive porosity (e.g., above 90%) may reduce structural strength, lead to delamination during cycling, or diminish electronic conductivity. Conversely, low porosity (e.g., less than 25%) may limit ion transport and reduce utilization of the active material. Specified porosity ranges are suitable for achieving high lithium recovery efficiency, stable electrode performance, and long cycle life in practical operating conditions.

In some examples, the working electrode 110 is fabricated using one or more techniques selected from the group consisting of roll-to-roll coating, doctor blading, slurry casting, vacuum filtration, or spray deposition. The working electrode 110 may be formed by applying a slurry comprising an active material, a polymeric binder, a conductive additive, and an organic solvent onto a substrate or current collector, followed by drying under controlled environmental conditions. In some examples, the active material comprises one or more compounds selected from the group consisting of: (i) lithium-selective intercalation compounds, including but not limited to spinel-type oxides, layered transition metal oxides, phosphate-based compounds, and vanadium-based materials; (ii) lithium-compatible insertion compounds, such as Prussian blue analogs and hexacyanoferrates; and (iii) pseudocapacitive materials, such as conductive polymers and cobalt-containing redox-active compounds. The active material is selected to enable reversible lithium ion intercalation under electrochemical cycling in the lithium-extraction reactor 100. In some examples, the working electrode 110 comprises a current collector selected from the group consisting of carbon cloth, carbon paper, stainless steel mesh, aluminum foil, copper foil, titanium foil, and nickel foam. In further examples, the working electrode 110 is configured as a freestanding electrode, wherein the conductive substrate (e.g., carbon cloth) functions both as the mechanical support and current collector. The carbon cloth may comprise a woven carbon fiber mesh with a porosity in the range of 60% to 90%, a thickness in the range of 100 μm to 500 μm, and an area-specific contact resistance of 0.7 Ω·cm² or less, more specifically 0.5 Ω·cm² or less, or even 0.2 Ω·cm² or less. The binder may comprise one or more polymers selected from the group consisting of polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA), polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), polyurethane (PU), polyethylene (PE), acrylic resin, epoxy resin, and alkyd resin. In some examples, the binder content in the slurry is in a range of 1 wt % to 10 wt %, more specifically 1.5 wt % to 3 wt %. One or more conductive carbon additives, such as carbon black, Super P, or carbon nanotubes, may be added to the slurry to enhance in-plane electrical conductivity and maintain percolation pathways throughout the electrode layer. The organic solvent may include one or more solvents selected from the group consisting of n-methyl-2-pyrrolidone (NMP), acetone, methyl ethyl ketone (MEK), acetonitrile, cyclohexanone, butyronitrile, ethanol, methanol, and dimethyl sulfoxide (DMSO). The solvent is selected based on compatibility with the binder system and the desired rheological and coating characteristics of the slurry. In some examples, the coated electrode layer has a thickness of 50-2000 micrometers, more specifically 500-1500 micrometers, or even 700-1000 micrometers. For ultra-thick electrodes (e.g., >500 micrometers), the slurry may be applied in a wet state and subsequently dried at a substantially uniform rate to prevent cracking, delamination, and internal resistive gradients. Controlling the drying rate may include regulating the environmental humidity and temperature using one or more of: a humidifier, misted liquid (e.g., water or organic solvent), ambient gas ventilation, dry gas injection, or thermal regulation via resistive heating, oven drying, or heated gas circulation. The drying temperature may be maintained in a range of 30° C. to 100° C., more specifically 40° C. to 80° C., depending on the slurry formulation, coating thickness, and reactor configuration. The resulting electrode layer may exhibit a contact resistivity of 0.7 Ω·cm² or less, more specifically 0.5 Ω·cm² or less, 0.3 Ω·cm² or less, or even 0.2 Ω·cm² or less, depending on the electrode composition and processing parameters. These configurations are selected to ensure high ionic and electronic conductivity, mechanical integrity, and stable interfacial contact during operation in the lithium-extraction reactor 100.

In some examples, the counter electrode 120 comprises a material selected from the group consisting of: (i) non-faradaic capacitive materials, such as activated carbon, carbon paper, carbon nanotubes, graphite, graphene, and conductive polymers, wherein charge storage occurs predominantly through electrostatic ion adsorption at the electrical double layer; (ii) pseudocapacitive materials, including polyaniline (PANI), polypyrrole (PPy), and cobalt compounds, wherein ion storage occurs via surface or near-surface redox reactions with fast kinetics; (iii) battery-type or faradaic insertion materials, such as Prussian blue analogs (e.g., K₂MnFe(CN)₆, K₂NiFe(CN)₆, K_0.1-0.2FeFe(CN)₆) and nickel hexacyanoferrate, which can selectively intercalate cations and/or anions through redox-mediated bulk reactions; (iv) redox-active halide-reactive electrodes, including silver, silver chloride, and silver alloys, which may participate in reversible redox reactions to capture halide anions (e.g., Cl⁻) via Ag/AgCl cycling; and (v) electrochemically inert or stable materials, such as platinum, gold, and doped diamond, which offer high corrosion resistance and serve primarily as charge-balancing or reference electrodes in high-potential or corrosive environments. The selection of counter electrode material influences the mechanism of anion removal or charge compensation during lithium intercalation into the working electrode and thereby affects the required negative potential applied. In some examples, non-faradaic capacitive materials are used for lithium-extraction reactors due to their fast response, wide potential windows, and high cycling stability. Pseudocapacitive and redox-active electrodes may be selected when co-adsorption of halides or redox selectivity may be used. Battery-type and halide-reactive materials may be used to enable selective anion removal or secondary ion capture, while inert electrodes may serve control or benchmarking purposes.

The morphology and structure of the counter electrode 120, such as porosity (e.g., 25% to 90%), specific surface area (e.g., 5 m²/g to 200 m²/g), thickness (e.g., 50 μm to 2000 μm), and geometric configuration (e.g., planar sheet, porous mesh, or structured foam), may be engineered to improve ionic mass transport, minimize polarization losses, and maintain mechanical integrity over repeated electrochemical cycles. In some examples, the counter electrode 120 is fabricated as a thick or ultra-thick structure, where the thickness exceeds 500 micrometers, to increase ion storage capacity and extend service life in high-capacity configurations. For example, capacitive or pseudocapacitive counter electrodes comprising activated carbon, carbon paper, or conductive polymers may be fabricated with high porosity (e.g., >70%), specific surface area in the range of 100 m²/g to 200 m²/g, and a thickness of 100-1000 micrometers. These structures may exhibit interconnected pore networks with pore diameters of 10-100 nanometers and tortuosity between 1.5 and 3.5 to promote electrolyte infiltration and uniform ion flux across the electrode—electrolyte interface. In contrast, redox-active or halide-reactive counter electrodes—such as those comprising Prussian blue analogs, silver/silver chloride, or transition metal-based materials—may be fabricated with lower porosity (e.g., 25% to 45%) and compact morphology. In such cases, electrode thickness may be 500-2000 micrometers. These ultra-thick electrodes may be prepared by applying the electrode slurry in a wet state and drying it at a substantially uniform rate to prevent cracking, interlayer delamination, or pore collapse. The drying process may include controlling environmental humidity and temperature by using one or more of: a humidifier, misted liquids (e.g., water or organic solvents), airflow regulation, or heated gas injection. The drying temperature may be maintained in a range of 30-100° C., more specifically in a range of 40-80° C., depending on the composition, geometry, and binder system. These process parameters are selected to ensure uniform solvent evaporation, minimize mechanical stress gradients, and maintain electrode porosity and contact integrity during scale-up. In some examples, the counter electrode 120 shares the same structural configuration as the working electrode 110 and may be fabricated using the same materials, layer architecture, and processing techniques. The counter electrode 120 may be integrated with additional components, including but not limited to porous membranes (e.g., separators) and electrically conductive current collectors (e.g., metallic foils or meshes), depending on reactor configuration.

The positive potential applied for lithium release (e.g., de-intercalation) depends on the type, physical and chemical properties, and scale of the working electrode 110, as well as the characteristics of the counter electrode 120. For example, when the working electrode 110 comprises lithium iron phosphate (LiFePO₄), de-intercalation typically occurs at potentials between +0.3 V and +0.5 V versus the reversible hydrogen electrode (RHE). In such cases, non-faradaic capacitive counter electrodes, such as activated carbon or carbon paper, operate effectively in a range of +0.3 V to +0.6 V vs. RHE. When the working electrode comprises lithium manganese oxide (LiMn₂O₄), de-intercalation occurs at higher potentials, typically between +0.8 V and +1.0 V vs. RHE. For these applications, faradaic counter electrodes such as Prussian blue analogs (e.g., K₂MnFe(CN)₆ or K₂NiFe(CN)₆) or nickel hexacyanoferrate may be employed, operating in the range of +0.6 V to +1.1 V vs. RHE. The redox properties and electrochemical stability of the counter electrode influence the accessible voltage window, lithium extraction efficiency, and suppression of undesired side reactions. In some examples, the positive potential is applied in a controlled manner, using a voltage ramp rate in the range of 0.1 mV/s to 100 mV/s (equivalent to 6 mV/min to 6000 mV/min, or 0.36 V/hour to 360 V/hour), more commonly between 0.5 mV/s and 10 mV/s (i.e., 30 mV/min to 600 mV/min, or 1.8 V/hour to 36 V/hour), until one or more endpoint conditions are met. These conditions may include reaching a target lithium concentration in the recovery solution 310 (e.g., 100-500 ppm, or 0.01-0.05 M), a predefined total charge input, or a terminal current density threshold (e.g., 0.1-10 A/m², more preferably 0.5-2 A/m²). This controlled voltage increase minimizes overpotentials, promotes uniform de-intercalation, and reduces risks of irreversible phase transitions, gas evolution, or electrode degradation. The electrochemical de-intercalation step may be performed under constant current (galvanostatic), constant voltage (potentiostatic), or pulsed potential/current modes. Constant current conditions are most commonly employed for their simplicity and scalability. In such configurations, the system may operate at C-rates ranging from C/10 to 10C, with a preferred operating window between C/10 and 1C. Here, “C-rate” refers to the current required to achieve full de-intercalation of lithium from the working electrode in one hour (1C), such that a C/10 rate corresponds to a 10-hour process and a 2C rate corresponds to a 30-minute process. For example, when the working electrode has a lithium capacity of 100 mAh/g, a 1C rate corresponds to 100 mA/g of applied current. Slower rates (e.g., C/10) are typically used in high-selectivity or durability-focused applications, while higher C-rates may be applicable to accelerated processing or short-cycle operations. In some examples, pulsed current or pulsed voltage profiles may be employed to enhance lithium ion transport kinetics, reduce concentration polarization, and suppress side reactions such as water electrolysis. For instance, a pulsed current protocol may involve a square-wave form alternating between 5 mA/cm² for 10 seconds and 0 mA/cm² for 5 seconds over a 30-minute period, enabling intermittent ion relaxation and replenishment at the electrode—electrolyte interface. Alternatively, a pulsed voltage regime may consist of applying +0.5 V for 30 seconds followed by open-circuit rest or +0.1 V for 10 seconds, repeated cyclically. These approaches can reduce electrode overpotential, improve utilization of the active material, and enable extended electrode life. In some implementations, duty cycles may range from 25% to 90%, with pulse frequencies in the range of 0.01 Hz to 10 Hz, depending on the electrode material, geometry, and diffusion coefficients of lithium ions in the host matrix. Regardless of the charging/discharging scheme, the applied electrochemical protocol is tuned to the intrinsic properties of the working and counter electrodes to enable efficient, selective, and stable lithium recovery from liquid sources.

FIGS. 1A and 1B are illustrations of a lithium-extraction reactor 100 comprising multiple electrochemical cells 130 stacked together between reactor end plates 102, in accordance with some examples. Each cell 130 may have a cell terminal 136 (for controlling the voltage applied to the cell electrodes) and a fluidic connector 139 (for supplying/removing a lithium-containing solution 310 and a recovery solution 320). A lithium-extraction reactor 100 may also comprise various fasteners for supporting/aligning various components of the lithium-extraction reactor 100.

FIG. 1C is an exploded view of a single electrochemical cell 130 of the lithium-extraction reactor 100 in FIGS. 1A and 1B, in accordance with some examples. The electrochemical cell 130 may comprise gaskets 104, current collectors 106, tunnels 108, and a working electrode 110. The tunnels 108 function as fluidic pathways that enable continuous or distributed flow of a lithium-containing solution 310 and a recovery solution 320 between individual electrochemical cells 130 within the lithium-extraction reactor 100. In some examples, the tunnels 108 also serve as conduits for pressure balancing, feedstock recirculation, or liquid removal to maintain uniform operating conditions across the reactor stack. The tunnels 108 may be made of electrically insulating materials, including but not limited to thermoplastic polymers (e.g., polypropylene, polyethylene, PVDF), thermoset plastics, or thermoset polymer composites such as glass-fiber reinforced composites, selected for their chemical resistance and structural integrity under electrochemical operating conditions.

The cell terminal 136 provides an electrical connection between the power supply 192 and the current collectors 106, enabling controlled potential application across the working and counter electrodes. In some examples, the cell terminal 136 (which may also be referred to as a ring terminal) is made of electrically conductive materials, such as copper, nickel, or tin-plated alloys, and is fastened to conductive bolts or plates to ensure stable, low-resistance current transmission during reactor operation.

The end plate 102 may be made of electrically conductive materials, including but not limited to stainless steel, steel, titanium, metallic alloys, aluminum, silver, copper, gold, nickel, nickel-plated stainless steel, and gold-plated stainless steel. The gasket 104 can be made of any type of elastic materials that ensure sealing, including but not limited to rubber, nitrile, neoprene, and silicone. The current collector 106 can be made of electrically conductive materials, including but not limited to steel and its alloys, titanium and its alloys, metallic alloys, aluminum, silver, copper, gold, nickel, nickel-plated stainless steel, and gold-plated stainless steel.

In some examples, the lithium-extraction reactor 100 does not include any membranes between the working electrode 110 and the counter electrode 120. Such a reactor may be referred to as a membraneless electrochemical lithium extraction reactor. The absence of a membrane allows direct ionic communication between the electrodes, which lowers the internal ohmic resistance and enables higher current densities at reduced applied potentials (e.g., <0.8 V vs. RHE), thereby improving overall energy efficiency during lithium intercalation and deintercalation. Additionally, removing the membrane eliminates the risk of membrane fouling, scaling, or degradation-standard failure modes in high-salinity or silica-rich brines (e.g., geothermal or oilfield brines). The simplified architecture reduces manufacturing complexity and capital costs, and allows for easier cleaning and modular replacement of electrochemical cells. Moreover, the membraneless design is compatible with a wide range of brine chemistries and pH values (e.g., pH 4-10), including those containing multivalent ions (e.g., Ca²⁺, Mg²⁺, Fe³⁺) or organics, which may compromise the selectivity or durability of ion-selective membranes. The reactor may also be more amenable to continuous-flow operation when coupled with flow-directing components (e.g., channel baffles or flow distributors) that maintain separation between the working and counter electrode reactions via hydrodynamic control.

In some examples, a lithium-extraction reactor 100 further comprises a lithium-extraction membrane 135 positioned between the working electrode 110 and the counter electrode 120. The lithium-extraction membrane 135 may be either ion-selective or non-ion-selective. An ion-selective membrane, such as a cation or anion exchange membrane, permits the selective transport of target ions (e.g., Li⁺ or Cl⁻) while blocking others, thereby reducing undesired side reactions and cross-contamination in feedstocks containing interfering species (e.g., Na⁺, Mg²⁺, SO₄²⁻). A non-ion-selective membrane, such as a porous polymer separator, allows broader ionic transport and may be used when operating in simplified electrolytes or where minimizing internal resistance and cost is prioritized. The choice depends on feedstock complexity, purity requirements, and cell design trade-offs between selectivity and conductivity.

In some examples, the lithium-extraction membrane 135 comprises one or more electronically non-conductive porous polymeric materials, including, but not limited to, sulfonated tetrafluoroethylene-based fluoropolymers, sulfonated poly(ether ether ketone), polybenzimidazole, poly(phenylene oxide), polystyrene-divinylbenzene resins, quaternized polyolefins, polyethylene, polypropylene, polyvinylidene fluoride, polytetrafluoroethylene, cellulose, glass fiber, and composite nonwoven polymers. The specific selection of membrane composition and type may depend on the chemical composition of the feed solution, operational pH, temperature, and desired selectivity of electrochemical extraction.

In some examples, the lithium-extraction membrane 135 comprises one or more electronically non-conductive porous polymeric materials, including, but not limited to, sulfonated tetrafluoroethylene-based fluoropolymers, sulfonated poly(ether ether ketone), polybenzimidazole, poly(phenylene oxide), polystyrene-divinylbenzene resins, quaternized polyolefins, polyethylene, polypropylene, polyvinylidene fluoride, polytetrafluoroethylene, cellulose, glass fiber, and composite nonwoven polymers. The specific selection of the lithium-extraction membrane 135 composition and type may depend on one or more processing parameters, including: (i) the chemical composition of the lithium-containing solution, (ii) the operational pH, (iii) temperature, and (iv) the desired selectivity and ionic conductivity during electrochemical extraction. For example, in low-pH, high-chloride geothermal brines, the lithium-extraction membrane 135 may comprise a cation exchange membrane such as sulfonated fluoropolymer or SPEEK to permit selective lithium cation (Li⁺) transport while limiting anionic crossover and withstanding acidic corrosion. In brines rich in scaling species, such as calcium (Ca²⁺), magnesium (Mg²⁺), or iron (Fe³⁺), the lithium-extraction membrane 135 may be selected from chemically resistant porous membranes (e.g., PTFE or PVDF) optionally reinforced with glass fiber or nonwoven backing to enhance structural integrity and fouling resistance. In examples where elevated operational temperature is required (e.g., >60° C.), the lithium-extraction membrane 135 may be fabricated from thermally stable fluorinated polymers, polyolefins, or ceramic-polymer composites.

In some examples, the lithium-extraction membrane 135 is a multilayer membrane comprising a mechanically robust porous support layer and a surface-selective functional layer. For instance, the lithium-extraction membrane 135 may comprise a nonwoven polypropylene or polyethylene substrate coated with a sulfonated polystyrene layer or a quaternized poly(phenylene oxide) surface, allowing for tailored cation selectivity and wettability. In some examples, the lithium-extraction membrane 135 may include inorganic additives, such as silica (SiO₂), titania (TiO₂), or zirconia (ZrO₂) nanoparticles, dispersed within the membrane matrix to enhance chemical and mechanical durability under high ionic strength and flow conditions.

In some examples, the lithium-extraction membrane 135 further comprises one or more surface-active coatings or tethered functional groups configured to suppress fouling or enhance lithium ion affinity. These coatings may include zwitterionic polymers, hydrophilic brushes (e.g., polyethylene glycol), or crown ether-functionalized ligands that promote lithium-selective facilitated transport across the membrane. Such modifications may be introduced via grafting, layer-by-layer deposition, or plasma-enhanced surface functionalization.

The lithium-extraction membrane 135 may exhibit porosity in the range of 30-85% and a thickness of 10-200 micrometers, depending on the flow rate, pressure differential, and desired lithium recovery rate. In some examples, the pore size distribution of the lithium-extraction membrane 135 is between 10-1,000 nanometers, such as 50-500 nanometers, selected to balance ionic permeability and mechanical strength. In further examples, the lithium-extraction membrane 135 may be configured to be physically removable or modular, such that it can be replaced or regenerated without requiring disassembly of the entire lithium-extraction reactor 100. In such cases, the lithium-extraction membrane 135 may be held within a membrane holder or alignment frame that ensures secure sealing and precise positioning between the working electrode 110 and the counter electrode 120.

The lithium-extraction membrane 135 may be deposited or assembled using fabrication techniques including, but not limited to, spray-coating, doctor blading, dip-coating, roll-to-roll casting, thermal lamination, or ultrasonic welding. In some examples, the lithium-extraction membrane 135 is pre-treated with deionized water or an alcohol-based solution to enhance hydration, reduce surface charge hysteresis, or minimize contact resistance prior to electrochemical operation.

The lithium-conversion reactor 150 comprises a cathodic electrode 160, an anodic electrode 170, and an ionic exchange membrane 180 such that the ionic exchange membrane 180 is positioned between the cathodic electrode 160 and the anodic electrode 170.

In some examples, the cathodic electrode 160 comprises one or more cathodic catalytically active materials 162 configured to perform a hydrogen evolution reaction (HER). The catalysts may be selected from the group consisting of platinum, platinum-containing catalysts, platinum-supported materials, palladium, palladium-containing catalysts, palladium-supported materials, gold, gold-containing catalysts, gold-supported materials, carbon, carbon-containing catalysts, carbon-supported materials, silver, silver-containing catalysts, and silver-supported materials. These are all examples of HER catalysts. However, platinum and platinum-supported materials may also be used due to their superior catalytic activity, high current efficiency, and corrosion resistance under aqueous electrochemical conditions. In some examples, palladium- and gold-based catalysts may also be used depending on cost, availability, and specific electrolyte conditions, though they typically exhibit lower HER activity compared to platinum.

The cathodic electrode 160 may further comprise one or more cathodic catalyst support materials 164 selected from the group consisting of carbon papers, carbon cloths, and metallic substrates. These support materials 164 provide mechanical integrity, high electrical conductivity, and a high surface area for catalyst dispersion. In addition, the cathodic electrode 160 may comprise one or more cathodic polymeric binders 166 selected from the group consisting of anion-exchange ionomers, cation-exchange ionomers, or a combination thereof. The polymeric binders serve to mechanically adhere the catalyst particles to the support substrate, ensure ionic conductivity within the catalyst layer, and maintain structural integrity during prolonged electrochemical operation. For example, anion-exchange ionomers may enhance OH⁻ transport for HER in alkaline media, while cation-exchange ionomers may be used in acidic environments to facilitate proton exchange.

In some examples, the anodic electrode 170 comprises one or more anodic catalytically active materials 172 (catalysts) configured to perform an oxygen evolution reaction (OER). The catalysts may be selected from the group consisting of nickel, nickel-containing catalysts, nickel-supported materials, iridium, iridium-containing catalysts, iridium-supported materials, ruthenium, ruthenium-containing catalysts, ruthenium-supported materials, platinum, platinum-containing catalysts, platinum-supported materials, metal borides and borates, palladium, palladium-containing catalysts, palladium-supported materials, rhodium, rhodium-containing catalysts, rhodium-supported materials, cobalt, cobalt-containing catalysts, and cobalt-supported catalysts. These are all examples of OER catalysts. However, nickel and nickel-based materials may be used due to their favorable activity under alkaline conditions, abundance, low cost, and ease of scale-up for large-area electrodes. In some examples, iridium- and ruthenium-based catalysts may be used for applications requiring higher intrinsic activity or operation in acidic or neutral electrolytes, although such materials may increase system cost and reduce sustainability.

The anodic electrode 170 may further comprise one or more anodic catalyst support materials 174 selected from the group consisting of carbon papers, carbon cloths, and metallic substrates, which provide mechanical support, enhance electrical conductivity, and improve catalyst dispersion and utilization. The anodic electrode 170 may also comprise one or more anodic polymeric binders 176 selected from the group consisting of anion-exchange ionomers, cation-exchange ionomers, or a combination thereof. These polymeric binders serve to maintain the structural integrity of the catalyst layer, provide ionic conductivity within the electrode, and promote long-term mechanical adhesion of the catalyst to the support during extended electrochemical operation.

Various combinations of anodic catalytically active materials 172 and cathodic catalyst support materials 164 may depend on performance, durability, and cost considerations. For example, a cathodic electrode 160 comprising platinum on carbon paper is paired with an anodic electrode 170 comprising nickel hydroxide on a metallic substrate, providing a high-performance system suitable for alkaline electrolysis with stable long-term operation. In another example, a cathodic electrode 160 comprising silver-supported materials is paired with an anodic electrode 170 comprising iridium oxide, enabling operation in neutral pH environments where stability against oxidative degradation is desired. In yet another example, a cathodic electrode 160 comprising palladium-containing catalysts is used in conjunction with an anodic electrode 170 comprising cobalt boride, offering a noble-metal-reduced configuration while maintaining catalytic efficiency and structural robustness.

In some examples, the ionic exchange membrane 180 is selected from the group consisting of anion-selective and cation-selective membranes configured to permit selective transport of anions or cations, respectively, while physically and electronically separating the cathodic electrode 160 and the anodic electrode 170. In more specific examples, the ionic exchange membrane 180 is an anion-selective membrane configured to permit the transport of hydroxide ions (OH⁻) from the cathodic electrode 160 to the anodic electrode 170. The use of anion-selective membranes may facilitate the formation of lithium hydroxide (LiOH) or lithium carbonate (Li₂CO₃) by enabling selective anion migration, suppressing parasitic crossover reactions, and maintaining ionic charge balance within the lithium conversion reactor 150. Suitable anion-selective membranes may comprise, but are not limited to, quaternized poly(phenylene oxide), polystyrene-divinylbenzene resins, quaternized polyolefins, and other polymeric materials incorporating anion-exchange functional groups. In some examples, the ionic exchange membrane 180 exhibits ionic conductivity in the range of 5 to 200 mS/cm and a thickness between 25 μm and 200 μm. The selection of membrane type and composition may depend on the chemistry of the recovery solution 320, operational pH, temperature, and the target lithium-containing product.

The cathodic electrode 160 performing a hydrogen evolution reaction (HER) is a layered structure with porosity in the range of 25-90%, more specifically in the range of 40-60%, depending on the composition and architecture of the electrode. In some examples, the cathodic electrode 160 comprises a platinum-group catalyst, including but not limited to platinum, palladium, or their alloys, supported on a substrate such as carbon paper, carbon cloth, or metallic foam. For instance, platinum nanoparticles may be spray-deposited on a carbon cloth support with ˜70% porosity to enhance catalytic activity, promote hydrogen gas detachment, and increase the electrochemically active surface area. In other examples, palladium or platinum-palladium alloys are deposited on carbon felt or metallic mesh substrates, providing structural robustness and high HER efficiency under alkaline or neutral pH conditions. The cathodic electrodes can be prepared by depositing materials, including but not limited to platinum, iridium, gold, ruthenium, and their alloys, onto substrates, including but not limited to carbon papers and cloths, felts, foams, and any type of electrically conductive substrates.

The anodic electrode 170 performing an oxygen evolution reaction (OER) is a layered structure with porosity in the range of 25-90%, more specifically in the range of 35-75%, depending on the catalyst composition and deposition method. In some examples, the anodic electrode 170 comprises nickel-based catalysts, including but not limited to nickel hydroxide (Ni(OH)₂), nickel oxyhydroxide (NiOOH), or nickel borate (Ni-Bx), supported on substrates such as nickel foam, titanium mesh, or carbon cloth. For instance, nickel hydroxide may be electrodeposited onto a porous nickel foam support with ˜80% porosity to facilitate a high active surface area, efficient oxygen bubble detachment, and sustained catalytic activity under alkaline conditions. In other examples, nickel oxyhydroxide is formed in situ on titanium mesh via thermal or electrochemical oxidation, producing a conformal high-surface-area film that promotes OER kinetics while maintaining structural stability during prolonged operation.

The anodic electrode 170 can be prepared by depositing materials, including but not limited to iridium and iridium oxide and their alloys, ruthenium, ruthenium oxide, and their alloys, platinum and their alloys, nickel-based hydroxides or nickel-based catalysts, cobalt-based catalysts, iron-based catalysts onto substrates including but not limited to carbon papers and carbon clots, but papers, cloths, felts and foams of any type electrically conductive materials.

FIGS. 2-3, 4A-4D, and 5A-5D: Methods of Producing Lithium-Containing Products

FIG. 2 is a process flowchart corresponding to a tandem method 200 for producing a lithium-containing product 390 from a lithium-containing solution 310 using a lithium-extraction reactor 100 and a lithium-conversion reactor 150. Various examples of these reactors are described above with reference to FIGS. 1A-1D. Various materials involved in this tandem method 200 are illustrated in FIG. 3. Furthermore, FIGS. 4A-4D are schematic illustrations of different stages of the method in FIG. 2 while producing one example of lithium-containing product 390, such as lithium carbonate. FIGS. 5A-5D are schematic illustrations of different stages of the method in FIG. 2 while producing another example of lithium-containing product 390, such as lithium hydroxide

Supplying a Lithium-Containing Solution

The tandem method 200 comprises (block 210) supplying the lithium-containing solution 310 comprising lithium cations 312 into a lithium-extraction reactor 100. In some examples, the concentration of the lithium cations 312 in the lithium-containing solution 310 may be in a range of 1 ppm to 2,000 ppm or, more specifically, 10 ppm to 1,000 ppm. The lithium-containing solution 310 may originate from natural, geothermal, or synthetic brines, leachate solutions from minerals, clays, or recycled products. Exemplary sources include geothermal brines (e.g., Salton Sea), oilfield brines, seawater, closed-basin brines, or leachates obtained from lithium-ion battery recycling processes.

In some examples, the lithium-containing solution 310 may undergo one or more pre-treatment operations, such as mechanical filtration, pH adjustment, ion-exchange, or membrane separation, prior to electrochemical processing. In some examples, in addition to lithium cations 312, the lithium-containing solution 310 comprises one or more anions 314 selected from the group consisting of chloride (Cl⁻), sulfate (SO₄²⁻), bicarbonate (HCO₃⁻), borate (B(OH⁻)₄⁻), bromide (Br⁻), nitrate (NO₃⁻), and fluoride (F⁻), which are commonly present in lithium-bearing brines. The purpose of this pre-treatment is to collect and/or remove suspended solids, colloidal silica, and interfering ionic species, including but not limited to monovalent cations (e.g., sodium, potassium) and divalent or multivalent cations (e.g., calcium, magnesium, manganese, zinc, and iron).

In some cases, the lithium-containing solution 310 may further comprise one or more additives 316, such as alkali metals (e.g., Na⁺, K⁺), alkaline earth metals (e.g., Mg²⁺, Ca²⁺), or transition metals (e.g., Mn²⁺, Fe²⁺), depending on the origin and composition of the feedstock. For example, geothermal brines from the Salton Sea region contain approximately 200 ppm to 250 ppm lithium cations (Li⁺), in addition to high concentrations of chloride (Cl⁻), sodium (Na⁺), potassium (K⁺), and calcium (Ca²⁺) ions, as well as trace elements such as manganese (Mn²⁺) and zinc (Zn²⁺).

The lithium-containing solution 310 comprises one or more source-solution solvents 318. For example, water may be used source-solution solvent 318, i.e., the lithium-containing solution 310 is an aqueous solvent system in which water (H₂O) is the primary solvent. In other examples, the lithium-containing solution 310 may comprise a combination of multiple source-solution solvents 318 (which may be referred to as a mixed solvent system), including water and one or more co-solvents such as ethanol (EtOH), methanol (CH₃OH), or dimethyl sulfoxide (DMSO), depending on the target electrochemical or transport properties. For purposes of these disclosures, the terms “lithium-containing solution” and “brine” are used interchangeably to refer to any liquid-phase medium containing lithium cations 312, regardless of its origin, composition, or prior treatment.

Applying Negative Potential to the Working Electrode

Referring to FIG. 2, the tandem method 200 proceeds with (block 220) applying a negative potential to the working electrode 110, relative to the counter electrode 120, thereby (block 222) electrochemically incorporating the lithium cations 312 into the working electrode 110. For example, the lithium cations 312 may intercalate into the working electrode 110. The purpose of this electrochemical incorporation of the lithium cations 312 into the working electrode 110 is to separate the lithium cations 312 from the rest of the materials in the lithium-containing solution 310, especially one or more anions 314. In some examples, the working electrode 110 undergoes an electrochemical transformation upon lithium intercalation. For instance, when the working electrode 110 comprises lithium iron phosphate (Li_1-xFePO₄, such that 0≤x<1), lithium cations 312 are inserted into the olivine lattice, converting Fe³⁺ to Fe²⁺, and forming lithium-rich LiFePO₄ during lithiation. As another example, when the working electrode 110 comprises lithium manganese oxide (Li_1-xMn₂O₄, such that 0≤x<1), lithium cations 312 are intercalated into the spinel framework, leading to redox transitions between Mn₄+ and Mn³⁺ as x varies. These intercalation reactions are typically reversible under electrochemical cycling and may be tuned by the applied potential, porosity of the working electrode, and electrolyte composition.

In some examples, the negative potential for the incorporation (e.g., intercalation) of lithium cations (Li⁺) into the working electrode 110 is in a range of −0.01 V to −1.2 V versus the reversible hydrogen electrode (RHE), more specifically in a range of −0.05 V to −0.8 V vs. RHE, or even more specifically in a range of −0.1 V to −0.6 V vs. RHE. These voltage ranges are selected based on the electrochemical redox characteristics of the intercalation host material. For example, lithium iron phosphate (Li_1-xFePO₄) typically undergoes lithium insertion around-0.4 V to −0.6 V vs. RHE, while layered oxides such as lithium cobalt oxide (Li_1-xCoO₂) or lithium nickel oxide (Li_1-xNiO₂) may require more negative potentials, generally between-0.6 V and −0.8 V vs. RHE. Spinel-type materials such as lithium manganese oxide (Li_1-xMn₂O₄) may intercalate lithium at slightly more positive voltages, typically between-0.3 V and −0.5 V vs. RHE. The applied potential is tuned to match the specific redox potential of the working electrode, while avoiding undesirable side reactions such as hydrogen evolution or phase degradation. In some examples, the negative potential is applied under a controlled voltage ramp to ensure gradual lithiation. The ramp rate may be in the range of 0.1 mV/s to 100 mV/s (i.e., 6 mV/min to 6000 mV/min, or 0.36 V/hour to 360 V/hour), more commonly between 0.5 mV/s and 10 mV/s (i.e., 30 mV/min to 600 mV/min, or 1.8 V/hour to 36 V/hour), depending on electrode thickness, lithium ion diffusivity, and electrolyte conductivity. This allows for stable intercalation kinetics while minimizing internal stress, resistive heating, and lithium plating. The voltage ramp may be terminated once the potential reaches a defined cutoff value or a terminal current density plateau is observed. Alternatively or additionally, lithium intercalation may be performed under constant current (galvanostatic), constant voltage (potentiostatic), or pulsed regimes. Under galvanostatic control, the current density may be in the range of 0.1 mA/cm² to 10 mA/cm², more typically between 0.5 mA/cm² and 5 mA/cm², corresponding to approximate C-rates from C/10 to 5C depending on the active mass loading and material capacity. For example, a 1C rate corresponds to full lithiation within 1 hour for a given theoretical capacity (e.g., 170 mAh/g for LiFePO₄), and a C/10 rate corresponds to a 10-hour cycle. Lower C-rates may be preferred to ensure high selectivity and maximize lithium utilization, particularly in brines with competing cations or multivalent species. In some implementations, pulsed current or pulsed voltage profiles are applied to improve lithium ion transport, relieve concentration gradients, and suppress gas evolution at the electrode interface. For instance, a pulsed current regime may consist of applying 2 mA/cm² for 15 seconds, followed by 0 mA/cm² for 5 seconds (i.e., a 75% duty cycle at 0.05 Hz), while a pulsed voltage strategy may apply −0.5 V for 10 seconds followed by an open-circuit or rest period of 10 seconds. Pulse frequencies may range from 0.01 Hz to 10 Hz, and duty cycles from 20% to 90%, depending on the electrode porosity, interfacial kinetics, and system resistance. These strategies can also reduce parasitic hydrogen evolution, improve lithium diffusion into bulk electrode material, and mitigate structural fatigue over repeated cycles. Regardless of the applied protocol, the lithiation process is conducted under electrochemical conditions designed to maximize lithium uptake efficiency, maintain electrode structural integrity, and support high reversibility across multiple cycles.

In some examples, the temperature of the lithium-extraction reactor 100 or, more specifically, of the lithium-containing solution 310 (provided in the lithium-extraction reactor 100) is maintained in a range of −40° C. to 120° C., more specifically, in a range of 15° C. to 80° C., or even more specifically, in a range of 20° C. to 60° C. These temperature ranges are selected based on the trade-off between improved lithium intercalation kinetics and the electrochemical, thermal, and mechanical stability of the working electrode 110 and the counter electrode 120. For example, temperatures above 20° C. may enhance ionic conductivity and lithium cation diffusion, thereby accelerating lithium incorporation into the working electrode 110. Conversely, temperatures exceeding 90° C. may lead to degradation of one or more electrode components, including: (i) phase distortion or transformation in active materials (e.g., Li_1-xMn₂O₄, Li_1-xFePO₄, or Li_1-xCoO₂); (ii) binder softening or detachment (e.g., in polyvinylidene fluoride (PVDF)-based polymeric binders); and (iii) loss of mechanical or electrical contact between active particles, conductive additives, and current collector substrates. In some examples, the lithium-containing solution 310 is heated prior to or within the lithium-extraction reactor 100 using one or more heating elements, including, but not limited to, a recirculating water bath, an inline heat exchanger, a resistive heating jacket, or an integrated thermal control assembly. The temperature may be monitored and regulated by the system controller 198 during reactor operation.

In some examples, the negative potential is applied to the working electrode 110 until a defined endpoint is reached, such as a target coulombic input, a threshold current density (e.g., less than 0.1 mA/cm²), or a maximum intercalation duration in a range of 1 minute to 12 hours, more specifically, in a range of 5 minutes to 6 hours, or even more specifically, in a range of 10 minutes to 2 hours. In some examples, the lithium-containing solution 310 comprises lithium cations (Li⁺) in a concentration in a range of 10 ppm to 1,000 ppm, more specifically, in a range of 50 ppm to 500 ppm, or even more specifically, in a range of 100 ppm to 250 ppm.

In some examples, (block 220) applying the negative potential to the working electrode 110, relative to the counter electrode 120, further comprises (block 224) inducing a compensatory anion response at the counter electrode 120. Specifically, one or more anions 314 (e.g., Cl⁻, SO₄²⁻, HCO₃⁻) present in the lithium-containing solution 310 may migrate toward and become physically adsorbed onto, or electrochemically stabilized within, the counter electrode 120 to maintain charge neutrality during lithium cation intercalation at the working electrode 110. The mechanism of anion compensation depends on the material properties of the counter electrode 120. For example, when the counter electrode 120 comprises a non-faradaic capacitive material (e.g., activated carbon, carbon paper, or graphene), the anions 314 are primarily stored via electrostatic adsorption at the electrical double layer. In contrast, when the counter electrode 120 comprises a pseudocapacitive or redox-active material (e.g., polyaniline, silver/silver chloride, or a Prussian blue analog), the anions 314 may participate in partial or reversible faradaic reactions and may be inserted into the bulk or near-surface regions of the material through redox-mediated processes. In either case, the anion response enables electrochemical charge balancing without the need for external electrolyte modification or sacrificial reagents, and may be tuned by selecting counter electrode materials with appropriate surface area, redox activity, or ion affinity.

Removing Lithium-Containing Solution from the Lithium-Extraction Reactor

Referring to FIG. 2, the tandem method 200 proceeds with (block 230) removing the lithium-containing solution 310 from the lithium-extraction reactor 100. In some examples, this removal is performed by draining the lithium-containing solution 310 and flushing the internal volume of the reactor with a rinse medium, such as deionized (DI) water, to displace residual brine and minimize cross-contamination. For example, the DI water flush is applied in sufficient volume to ensure conductivity falls below a predetermined threshold (e.g., <100 uS/cm), thereby confirming effective purging. It should be noted that during this operation, while the lithium-containing solution 310 is removed, the lithium cations 312 remain retained within the working electrode 110. In particular, lithium cations 312 are electrochemically intercalated into the crystal structure of the working electrode 110, such as in Li_1-xFePO₄ or Li_1-xMn₂O₄, where 0≤x<1. The amount of lithium cations 312 present in the working electrode 110 at this stage may correspond to a stoichiometric intercalation level wherein x ranges from 0.05 to 0.80, depending on the specific electrode material, applied potential, and intercalation time. This corresponds to approximately 20% to 95% of the theoretical lithium storage capacity of the working electrode 110, as measured by charge passed during the intercalation step or inferred from open-circuit potential. The removal operation thus isolates the intercalated lithium from the residual non-lithium constituents in the original brine, and prepares the lithium-extraction reactor 100 for the subsequent lithium release step, wherein a recovery solution 320 is supplied and a positive potential is applied to extract the lithium cations 312 into the recovery medium.

The lithium incorporation (e.g., intercalation) and release (e.g., de-intercalation) steps may be performed in a single cycle or repeated in multiple sequential cycles. In some examples, a fresh lithium-containing solution 310 is supplied during each cycle to replenish lithium cations 312, while the same recovery solution 320 may be reused until the lithium concentration reaches a threshold value, such as in a range of 100 ppm to 500 ppm. The number of cycles may be in a range of 1 to 6 cycles or, more specifically, in a range of 1 to 2 cycles when using the disclosed system, to reduce process time, minimize solvent usage, and lower overall operating costs. The number of cycles may be selected based on the lithium uptake capacity of the working electrode 110, the concentration of lithium cations 312 in the lithium-containing solution 310 (e.g., in a range of 10 ppm to 1,000 ppm), and the target lithium concentration required in the recovery solution 320 to enable efficient electrochemical formation of lithium-containing products, such as lithium carbonate (Li₂CO₃) or lithium hydroxide (LiOH), in the lithium-conversion reactor 150.

Once the working electrode 110 is removed/separated from the lithium-containing solution 310, the working electrode 110 may be cleaned of residual impurities by submerging the working electrode 110 into a recovery solution and applying a negative potential. In some examples, the recovery solution comprises deionized water or a polar aprotic solvent (e.g., dimethyl sulfoxide (DMSO), N-methyl-2-pyrrolidone (NMP), or isopropanol (IPA)), optionally containing up to 1 wt % of a supporting electrolyte (e.g., lithium chloride (LiCl) or sodium sulfate (Na₂SO₄)) to enhance ionic conductivity. A negative potential in the range of −0.01 V to −1.0 V (vs. reversible hydrogen electrode) or, more specifically, −0.05 V to −0.8 V, or even more specifically, −0.1 V to −0.6 V may be applied. The cleaning operation may be performed for a duration in the range of 1 minute to 60 minutes or, more specifically, 2 to 30 minutes, or even more specifically, 5 to 20 minutes. The counter electrode used during this cleaning operation may comprise a material selected from the group consisting of platinum, graphite, carbon felt, or other electrochemically stable and inert conductors. Typical impurities removed during this cleaning step may include residual divalent or multivalent cations (e.g., calcium (Ca²⁺), magnesium (Mg²⁺), iron (Fe³⁺), manganese (Mn₂+)) and anions (e.g., chloride (Cl⁻), sulfate (SO₄²⁻), and borate (B(OH⁻) 4″)) that may be weakly bound to the surface or present in the porous structure of the working electrode 110.

Supplying a Recovery Solution to the Lithium-Extraction Reactor

The tandem method 200 comprises (block 240) supplying a recovery solution 320 to the lithium-extraction reactor 100. In some examples, the recovery solution 320 comprises one or more recovery-solution solvents 322. Some examples of suitable recovery-solution solvents 322 include, but are not limited to, inorganic solvents (e.g., water (H₂O)) and organic solvents (e.g., acetone (C₃H₆O), acetonitrile, diethyl carbonate (C₅H₁₀O₃), dimethyl carbonate (C₃H₆O₃), ethyl methyl carbonate (C₄H₈O₃), methyl acetate (C₃H₆O₂), ethyl acetate (C₄H₈O₂), dimethoxyethane (C₄H₁₀O₂), tetrahydrofuran (C₄H₈O), ethanol (C₂H₆O), methanol (CH₃OH), isopropanol (C₃H₈O), dimethylformamide (C₃H₇NO), dimethyl sulfoxide (C₂H₆OS), and N-methyl-2-pyrrolidone (C₅H₇NO)). In some examples, recovery-solution solvents 322 comprise a combination of two or more of these solvents.

In some examples, water (e.g., deionized water) is used as one of the recovery-solution solvents 322, and the concentration of water in the recovery solution 320 is at least 80 vol %, at least 90 vol %, or even at least 95 vol %. DI water offers favorable lithium ion solubility, low cost, and compatibility with subsequent electrochemical conversion reactions in the lithium-conversion reactor 150. In some examples, organic or mixed solvents may be used as recovery-solution solvents 322 to modify lithium transport properties, enhance solvent-electrode interactions, or accommodate specific feedstock compositions. In further examples, the recovery solution 320 may additionally comprise one or more supporting electrolytes 324 selected from the group consisting of lithium chloride (LiCl), lithium sulfate (Li₂SO₄), lithium hydroxide (LiOH), and sodium sulfate (Na₂SO₄). The concentration of one or more supporting electrolytes 324 may be 0.001 M to 1.0 M or, more specifically, in a range of 0.01 M to 0.5 M. These supporting electrolytes enhance ionic conductivity and promote efficient electrochemical release of lithium cations 312 from the working electrode 110. The specific composition of the recovery solution 320 may be selected based on the lithium loading of the working electrode 110, the set lithium concentration in solution, and the requirements for product formation in the lithium-conversion reactor 150.

Applying Positive Potential to the Working Electrode

The tandem method 200 comprises (block 250) applying a positive potential to the working electrode 110, relative to the counter electrode 120, thereby extracting the lithium cations 312 from the working electrode 110 into the recovery solution 320. In some examples, the positive potential is in a range of +0.01 V to +1.2 V versus the reversible hydrogen electrode (RHE), more specifically in a range of +0.22 V to +0.8 V vs. RHE, depending on the electrochemical characteristics of the active material. For instance, when the working electrode 110 comprises lithium iron phosphate (Li_1-xFePO₄), lithium de-intercalation typically occurs at potentials between +0.4 V and +0.5 V vs. RHE. This corresponds to the oxidation of LiFePO₄ to FePO₄ and the release of lithium cations 312 into the surrounding electrolyte. Other materials, such as lithium manganese oxide (Li_1-xMn₂O₄), may require higher potentials, typically in the range of +0.8 V to +1.0 V vs. RHE, for effective lithium release. In some examples, the positive potential is applied as a constant value (potentiostatic mode), a constant current (galvanostatic mode), a voltage ramp, or as part of a pulsed waveform. In potentiostatic operation, the potential may be held at a fixed value (e.g., +0.5 V vs. RHE) until the system reaches a steady-state current density threshold, such as a drop to 1% to 5% of the initial current. In galvanostatic mode, the current density may range from 0.1 mA/cm² to 10 mA/cm², more typically between 0.5 mA/cm² and 5 mA/cm², corresponding to C-rates of approximately C/10 to 5C, depending on the electrode capacity. In some examples, the positive potential is applied under a controlled voltage ramp, such as 0.1 mV/s to 100 mV/s (i.e., 0.36 V/hour to 360 V/hour), more preferably 0.5 mV/s to 10 mV/s (i.e., 1.8 V/hour to 36 V/hour), allowing gradual delithiation and minimization of structural degradation, parasitic reactions, or overshoot. In additional implementations, pulsed voltage or pulsed current profiles may be used to enhance lithium-ion transport and minimize overpotentials. For example, a pulsed voltage protocol may apply +0.6 V for 20 seconds, followed by an open circuit or +0.2 V rest for 10 seconds. A pulsed current profile may involve cycles of 2 mA/cm² for 15 seconds followed by 0 mA/cm² for 5 seconds. Pulse frequencies may range from 0.01 Hz to 10 Hz, with duty cycles between 25% and 90%, tailored to the porosity and diffusivity of the electrode. The lithium release operation may continue until a defined endpoint is reached. This endpoint may include a target lithium concentration in the recovery solution 320 (e.g., 100 ppm to 500 ppm or 0.01-0.05 M), a predefined coulombic charge transfer (based on electrode capacity), or a minimum current density threshold as noted above. The charge passed may be integrated and monitored to ensure full extraction of lithium to the extent defined by the electrode's electrochemical capacity. In some examples, the temperature of the recovery solution 320 is maintained in a range of 15° C. to 80° C., more specifically 20° C. to 60° C., to enhance ionic conductivity, diffusion rates, and delithiation kinetics. Stirring or continuous flow of the recovery solution 320 may be employed to improve mass transport and maintain concentration gradients across the electrode interface. The recovery solution 320 may optionally comprise one or more supporting electrolytes (e.g., lithium chloride, lithium sulfate) at a concentration of 0.01 M to 0.5 M to ensure sufficient ionic conductivity and promote electrochemical stability during lithium release. Regardless of the mode of operation, the applied potential and processing conditions are selected to enable efficient lithium de-intercalation, minimize parasitic reactions, and preserve the structural and electrochemical reversibility of the working electrode 110 over repeated cycles.

Transfer the Recovery Solution to the Lithium-Conversion Reactor

The tandem method 200 comprises (block 260) transferring the recovery solution 320 comprising the lithium cations 312 to a lithium-conversion reactor 150. The lithium-conversion reactor 150 comprises a cathodic electrode 160, an anodic electrode 170, and an ionic exchange membrane 180 positioned between the cathodic electrode 160 and the anodic electrode 170. In some examples, the lithium-conversion reactor 150 or, more specifically, the recovery solution 320 (while present in the lithium-conversion reactor 150) is maintained at a temperature in a range of −40° C. to 120° C. or, more specifically, in a range of 15° C. to 90° C., or even more specifically, in a range of 20° C. to 80° C. These broader ranges may apply to systems configured to operate with non-aqueous recovery solutions or under cryogenic or high-temperature conditions. In more specific examples, the lithium-conversion reactor 150 is maintained at a temperature in a range of 30° C. to 40° C. or, more specifically, at approximately 40° C. to enhance lithium product precipitation kinetics, gas solubility, and electrochemical conversion efficiency.

In some examples, the recovery solution 320 is pre-heated prior to entry into the lithium-conversion reactor 150 using inline heat exchangers, jacketed reservoirs, or thermal circulation loops. Alternatively, heating may be applied internally within the reactor using integrated resistive elements or external temperature control systems. The selected heating method may depend on system scale, throughput requirements, and the thermal properties of the recovery solution 320.

In further examples, the concentration of lithium cations 312 in the recovery solution 320 is maintained in a range of 200 ppm to 1,500 ppm or, more specifically, in a range of 300 ppm to 1,000 ppm to support efficient formation of lithium-containing products, such as lithium carbonate (Li₂CO₃) or lithium hydroxide (LiOH). Higher concentrations of lithium cations 312 in the recovery solution 320 enhance the electrochemical conversion efficiency by increasing the rate of reaction with hydroxide ions (OH⁻) and/or bicarbonate ions (HCO₃⁻), up to the solubility threshold of the corresponding lithium-containing product. For example, concentrations exceeding 200 ppm favor Li₂CO₃ precipitation by surpassing the solubility limit of intermediate lithium bicarbonate (LiHCO₃⁻), while elevated lithium levels in alkaline media promote more complete LiOH formation during water-splitting reactions. To reach and maintain such concentrations, the recovery solution 320 may be reused across multiple lithium release (de-intercalation) cycles. For example, 1 to 6 cycles or, more specifically, 1 to 2 cycles, wherein the working electrode is repeatedly loaded with lithium cations 312 from a fresh lithium-containing solution 310 and discharged into a common volume of recovery solution 320. In further examples, lithium-extraction reactors are operated in parallel or sequence to continuously transfer lithium cations 312 into a shared recovery reservoir. The lithium concentration in the recovery solution 320 may be monitored using one or more sensors, such as conductivity probes or ion-selective electrodes, and the recovery solution 320 is transferred to the lithium-conversion reactor once a predefined concentration threshold is reached. These strategies enable efficient process control and maintain optimal lithium cation concentrations to support selective and high-yield formation of lithium-containing products during electrochemical conversion.

Additional process parameters may include supplying carbon dioxide (CO₂) into the lithium-conversion reactor 150 at a controlled flow rate when Li₂CO₃ formation is used. The endpoint of the preceding lithium release step (block 250) may be determined based on total charge passed, residual lithium content in the working electrode 110, or the lithium concentration reached in the recovery solution 320.

Applying a Conversion Potential

The tandem method 200 comprises (block 270) applying a conversion potential between the cathodic electrode 160 and the anodic electrode 170, thereby converting the lithium cations 312 in the recovery solution 320 into the lithium-containing product 390. In some examples, the lithium-containing product 390 is selected from the group consisting of lithium carbonate (Li₂CO₃), lithium hydroxide (LiOH), lithium chloride (LiCl), and lithium sulfate (Li₂SO₄).

In some examples, the conversion potential applied between the cathodic electrode 160 and the anodic electrode 170 is in a range of 0.1 mV to 2.0 V versus the reversible hydrogen electrode (RHE) or, more specifically, in a range of 1.2 V to 2.0 V versus RHE, or even more specifically, in a range of 1.5 V to 1.8 V versus RHE. The voltage selection may depend on the type of lithium-containing product formed, the composition of the recovery solution 320, and the materials of the cathodic electrode 160, anodic electrode 170, and ionic exchange membrane 180. For example, in systems configured to produce lithium carbonate (Li₂CO₃), a conversion potential in a range of 1.5 V to 1.8 V versus RHE is typically required to drive the water-splitting reaction at the cathodic electrode 160, generating hydroxide ions (OH″) that react with dissolved carbon dioxide (CO₂) to form bicarbonate ions and ultimately precipitate lithium carbonate (Li₂CO₃). In contrast, lithium hydroxide (LiOH) formation may proceed at slightly lower potentials under alkaline conditions in the absence of carbon dioxide (CO₂).

In some examples, the conversion operation continues until the lithium cation concentration in the recovery solution 320 is reduced below a target threshold, a predetermined amount of charge has been passed (e.g., based on stoichiometric conversion of Li⁺ to Li₂CO₃ or LiOH), or the applied current decreases below a cutoff level, such as in a range of 1% to 5% of the initial current. In further examples, the carbon dioxide (CO₂) gas flow may be maintained during the conversion step and terminated based on pH, conductivity, or observed saturation behavior of the product. Additional characteristics of the conversion step may include maintaining the lithium-conversion reactor 150 at a temperature in a range of 30° C. to 40° C. or, more specifically, at approximately 40° C. to promote CO₂ solubility, enhance reaction kinetics, and improve lithium product precipitation. The selected conversion potential should remain below the water electrolysis breakdown voltage of the membrane 180, and avoid excessive oxygen evolution at the anodic electrode 170, which may cause undesirable side reactions or degradation of cell components. Accordingly, the conversion potential is selected to balance lithium product yield, energy efficiency, and material stability.

The lithium conversion reactor accommodates a water splitting reaction at the cathode through which water molecules (H₂O) are converted into hydroxide ions and hydrogen (H₂)—see equation (1):

H 2 ⁢ O + e - → OH - + 0.5 H 2 ( g ) ( 1 )

The gaseous CO₂ is then supplied to the cathode electrode, where it dissolves in the electrolyte until its saturation point is reached-see equation (2):

CO 2 ( g ) → CO 2 ( l ) ( 2 )

The hydroxide ions produced through the water splitting reaction react with the CO₂ saturated inside the catholyte, generating bicarbonate ions-see equation (3):

CO 2 ( l ) + OH - → HCO 3 - ( 3 )

The bicarbonate anions formed are then collected and mixed with the lithium cations (Li⁺) to form lithium carbonate (Li₂CO₃) in water—see equation (4):

2 ⁢ Li + + 2 ⁢ HCO 3 - → Li 2 ⁢ CO 3 + H 2 ⁢ O + CO 2 ( 4 )

The lithium carbonate (Li₂CO₃) precipitate is then collected from the lithium conversion reactor for direct use or additional purification or separation processes.

The cascade system overall consumes carbon dioxide (CO₂), water, and electricity to convert lithium into lithium carbonate (Li₂CO₃) while producing hydrogen (H₂)—see equation (5):

2 ⁢ Li + + CO 2 + H 2 ⁢ O + 2 ⁢ e - → Li 2 ⁢ CO 3 + H 2 ( 5 )

The lithium conversion reactor comprises cathodic electrodes performing water splitting reaction; anodic electrodes performing oxygen evolution reaction; cation or anion exchange membrane; electronically conductive electrode holders; pipeline between the lithium conversion reactor and lithium extraction reactor10; gaseous carbon dioxide (CO₂) supply; gaseous carbon dioxide (CO₂) carrying line; carbon dioxide (CO₂) diffuser; electrolyte; electrolyte chamber.

In some examples, (block 270) applying the conversion potential between the cathodic electrode and the anodic electrode comprises (block 272) splitting water into hydrogen gas (H₂) and hydroxide ions (OH⁻) at the cathodic electrode 170 and reacting the hydroxide ions (OH⁻) with the lithium cations (Li⁺) to form lithium hydroxide (LiOH) in the recovery solution 320.

Supplying Carbon Dioxide (CO₂) into the Lithium-Conversion Reactor

In some examples, (block 270) applying the conversion potential between the cathodic electrode 160 and the anodic electrode 170 comprises (block 274) supplying carbon dioxide (CO₂) into the lithium-conversion reactor 150 or, more specifically, into the recovery solution 320 while applying a conversion potential between the cathodic electrode 160 and the anodic electrode 170, wherein the lithium-containing product comprises lithium carbonate (Li₂CO₃). The carbon dioxide may be introduced from a pressurized cylinder, CO₂ capture system, or on-site generation unit and delivered either continuously or in a pulsed mode, depending on process design and reactor configuration. Specifically, (block 270) applying the conversion potential may comprise: (a) electrochemical splitting of water at the cathodic electrode 160 to generate hydrogen gas (H₂) and hydroxide ions (OH⁻); (b) chemical reaction of the hydroxide ions (OH⁻) with dissolved carbon dioxide (CO₂) to form bicarbonate anions (HCO₃⁻); and (c) reaction of the bicarbonate anions (HCO₃⁻) with lithium cations 312 in the recovery solution 320 to form lithium carbonate (Li₂CO₃), which may precipitate from the solution under appropriate conditions.

In some examples, carbon dioxide (CO₂) is introduced at a flow rate in a range of 10 sccm to 500 sccm or, more specifically, in a range of 50 sccm to 200 sccm, depending on the volume of the lithium-conversion reactor 150, the lithium concentration in the recovery solution 320, and the active surface area of the cathodic electrode 160. The gas may be dispersed using a porous sparger, gas-diffusion layer, or microbubble emitter positioned adjacent to the cathodic region to promote uniform dispersion and enhance gas-liquid mass transfer. In some examples, the lithium-conversion reactor 150 is maintained at a temperature in a range of 30° C. to 40° C. or, more specifically, at approximately 40° C., to improve CO₂ solubility, bicarbonate formation kinetics, and precipitation yield. The partial pressure of carbon dioxide may be maintained in a range of 0.8 atm to 1.2 atm to support near-saturation concentrations in the recovery solution 320. In further examples, the endpoint of the CO₂ supply operation may be determined based on achieving a target pH (e.g., in a range of 7.0 to 8.5), cessation of net CO₂ uptake, or attainment of a predefined lithium carbonate yield as determined by conductivity, turbidity, or charge-based measurements.

In some examples, (block 270) applying the conversion potential between the cathodic electrode 160 and the anodic electrode 170 is performed for an electrode-saturation period of time prior to supplying carbon dioxide (CO₂) into the lithium-conversion reactor 150. The electrode-saturation period refers to a time interval during which the electrochemical system is operated under the applied conversion potential in the absence of CO₂, such that the cathodic electrode 160 generates hydroxide ions (OH⁻) and reaches a stabilized interfacial state. This preparatory step may enhance the efficiency of subsequent CO₂ conversion by ensuring sufficient availability of hydroxide ions (OH⁻) for reaction with CO₂ upon its introduction. In some examples, the electrode-saturation period may be selected to allow the cathodic process (e.g., water reduction) to reach steady-state current, electrode wetting, and thermal equilibrium. In some examples, the electrode-saturation period is in a range of 30 seconds to 10 minutes or, more specifically, in a range of 1 minute to 5 minutes, depending on the applied potential, electrode configuration, and volume of the recovery solution 320. The timing of carbon dioxide introduction following the electrode-saturation period may be selected to balance reaction kinetics, gas utilization, and lithium carbonate (Li₂CO₃) yield. This sequencing may also mitigate premature CO₂ escape or inefficient gas absorption during initial system transients.

Heating Recovery Solution

In some examples, method 200 comprises (block 280) heating the recovery solution 320 to a temperature in a range of 30° C. to 90° C. or, more specifically, in a range of 35° C. to 50° C. or, even more specifically, to approximately 40° C., while stirring the recovery solution 320 in the lithium-conversion reactor 150, thereby converting the lithium cations 312 into a lithium-containing product comprising lithium carbonate (Li₂CO₃). Heating and agitation may promote carbon dioxide (CO₂) dissolution, accelerate bicarbonate formation, and facilitate precipitation of lithium carbonate (Li₂CO₃) by enhancing reaction kinetics and reducing induction time. The (block 280) heating operation may be performed in addition to the (block 270) conversion-potential-application operation or, in some examples, instead of it. For example, in thermochemical modes of operation, lithium carbonate formation may proceed via direct heating and CO₂ delivery without the need for electrochemical potential. Alternatively, the (block 280) heating operation may be performed concurrently with electrochemical conversion to improve product crystallization, gas-liquid equilibrium, and process efficiency. In further examples, the lithium-containing product 390 formed in the lithium-conversion reactor 150 may be separated from the recovery solution 320 by one or more downstream operations, including, but not limited to, filtration, settling, centrifugation, or membrane-based separation. The separation step may occur within the reactor or in a dedicated unit operation following completion of lithium carbonate (Li₂CO₃) precipitation.

In some examples, method 200 proceeds with the crystallization of the lithium-containing product 390. During this stage, water and/or solvents are removed from the recovery solution 320 under controlled thermal, evaporative, or reactive conditions to facilitate the formation of a solid-phase lithium-containing product 390. Crystallization conditions may be selected to promote supersaturation and controlled nucleation, including but not limited to adjusting temperature (e.g., in a range of 30° C. to 90° C.), pressure (e.g., atmospheric or reduced), and agitation rate (e.g., in a range of 100 rpm to 600 rpm). In some examples, crystallization is performed by slow evaporation, vacuum drying, or temperature-induced precipitation, optionally with the use of crystallization aids such as seeding agents or antisolvents. The resulting solid-phase lithium-containing product 390 may exhibit tunable characteristics based on crystallization kinetics, including particle morphology (e.g., platelets, rods, agglomerates), size distribution (e.g., D₅₀ in a range of 5 μm to 50 μm), and phase composition. In some examples, crystallization is conducted at alkaline pH (e.g., pH>12) to favor lithium hydroxide (LiOH) formation, or at near-neutral to mildly basic pH (e.g., pH=8-10) in the presence of dissolved carbon dioxide (CO₂) to facilitate lithium carbonate (Li₂CO₃) precipitation. In some examples, the crystallized lithium-containing product 390 is subjected to one or more purification or product finishing steps.

These may include solid-liquid separation (e.g., filtration, centrifugation, or decantation), washing with deionized water and/or organic solvents (e.g., ethanol or isopropanol) to remove residual mother liquor or soluble impurities, and thermal drying under vacuum or inert gas (e.g., nitrogen or argon) at temperatures in a range of 60° C. to 120° C. Optional purification steps may further comprise redissolution and recrystallization, chelation-based impurity removal, or treatment with ion exchange resins to meet downstream purity requirements. The resultant material may be classified as a battery-grade lithium-containing product, meeting the purity, elemental composition, and physical specifications required for lithium-ion battery applications and related electrochemical devices. As used herein, “battery-grade” refers to lithium-containing products (e.g., Li₂CO₃ or LiOH·H₂O) having a chemical purity of at least 99.5 wt %, more specifically at least 99.9 wt %, with individual metallic impurity concentrations (e.g., Na⁺, K⁺, Ca²⁺, Mg²⁺, Fe, Al) below 10 ppm and total impurities below 100 ppm, in accordance with industrial standards. Particle size distribution, tap density, and flowability may be controlled to enable compatibility with cathode precursor synthesis or electrolyte formulation in lithium-ion and solid-state battery systems. Final product finishing may include particle size adjustment (e.g., milling or sieving), surface treatment, and packaging under controlled humidity or inert atmosphere. The lithium-containing product 390 produced via method 200 is suitable for direct integration into battery-grade material supply chains, including those utilizing nickel-rich layered oxides (e.g., NCA, NMC), olivine phosphates (e.g., LFP), or advanced solid-state chemistries.

Additional Examples

In some examples, carbon dioxide (CO₂) may be supplied to the lithium-conversion reactor 150 from a point source (e.g., flue gas) or captured from ambient air. The carbon dioxide (CO₂) may be delivered into the lithium-conversion reactor 150 via a gas supply line and dispersed through a gas diffusion layer positioned adjacent to the cathodic electrode 160. The gas diffusion layer may comprise a porous, electrically conductive structure configured to enable uniform delivery of gaseous carbon dioxide (CO₂) to the local reaction environment. The gas diffusion layer may exhibit porosity in a range of 25% to 90% and may be selected from the group consisting of carbon paper, carbon cloth, carbon felt, carbon foam, and metallic mesh. The carbon dioxide (CO₂) flow rate may be regulated based on the applied current density, the electrode surface area, the composition of the recovery solution 320, and the geometry of the lithium-conversion reactor 150, such that the electrolyte pH at the cathodic electrode 160 is maintained at or above a value of 7.

In some examples, the gas diffusion layer is integrated within the cathodic electrode 160 to facilitate simultaneous gas transport and electrochemical reactivity. The structure may be freestanding or layered and may be selected from electrically conductive materials compatible with aqueous or non-aqueous electrolytes under electrochemical operation. The geometry and morphology of the gas diffusion layer may be optimized to promote carbon dioxide (CO₂) saturation, gas-liquid interface stability, and high utilization efficiency under continuous or pulsed flow conditions.

In some examples, the surface composition, pore architecture, and interfacial properties of the gas diffusion layer and cathodic electrode 160 may be modified using one or more methods selected from the group consisting of hydrophobic agent treatment (e.g., polytetrafluoroethylene coating), deposition of polymeric films, integration of ionomeric binders (e.g., anion- or cation-exchange ionomers), and surface functionalization by sputtering, alloying, or chemical etching. These modifications may be applied to enhance gas-liquid contact efficiency, suppress flooding or dry-out effects, and maintain electrochemical performance under repeated cycling in the lithium-conversion reactor 150.

In some examples, the recovery solution 320 or, more specifically, the electrolyte provided in the lithium-conversion reactor 150, may be selected to be alkaline, neutral, or acidic depending on the desired lithium-containing product and compatibility with the cathodic electrode 160, anodic electrode 170, and ionic exchange membrane 180. The electrolyte may include one or more compounds selected from the group consisting of lithium hydroxide (LiOH), lithium chloride (LiCl), lithium carbonate (Li₂CO₃), lithium sulfate (Li₂SO₄), potassium hydroxide (KOH), potassium carbonate (K₂CO₃), potassium bicarbonate (KHCO₃⁻), potassium chloride (KCl), potassium sulfate (K₂SO₄), sodium hydroxide (NaOH), sodium carbonate (Na₂CO₃), sodium bicarbonate (NaHCO₃), sodium chloride (NaCl), cesium hydroxide (CsOH), cesium carbonate (Cs₂CO₃), cesium bicarbonate (CsHCO₃⁻), cesium chloride (CsCl), cesium sulfate (Cs₂SO₄), magnesium hydroxide (Mg(OH)₂), magnesium carbonate (MgCO₃), magnesium bicarbonate (Mg(HCO₃⁻)₂), magnesium chloride (MgCl₂), magnesium sulfate (MgSO₄), hydrochloric acid (HCl), acetic acid (CH₃COOH), nitric acid (HNO₃), sulfuric acid (H₂SO₄), phosphoric acid (H₃PO₄), lactic acid (C₃H₆O₃), boric acid (H₃BO₃), oxalic acid (C₂H₂O₄), citric acid (C₆H₈O₇), carbonic acid (H₂CO₃), and hydrofluoric acid (HF). The concentration of the electrolyte may be in a range of 0.0001 M to 20 M, depending on ionic conductivity, buffer capacity, and compatibility with the system components.

In further examples, the electrolyte composition in the lithium-conversion reactor 150 is tailored to ensure appropriate pH control, buffer strength, and ionic mobility to support electrochemical conversion of lithium cations (Li⁺) into lithium-containing products, such as lithium carbonate (Li₂CO₃) or lithium hydroxide (LiOH). Buffering species may include carbonate or bicarbonate ions formed in situ via reaction of carbon dioxide (CO₂) with electrochemically generated hydroxide ions (OH⁻), or externally added to regulate pH. Organic or inorganic acids may be used to stabilize intermediate species, such as lithium bicarbonate (LiHCO₃⁻), and to optimize electrolyte composition for precipitation, crystallization, and separation of lithium-containing products. These formulations may also enhance carbon dioxide (CO₂) solubility, maintain compatibility with the ionic exchange membrane 180, and prevent degradation of the cathodic electrode 160 and anodic electrode 170 during prolonged operation.

Lithium Hydroxide Conversion

In some examples, the lithium-containing product 390 is lithium hydroxide (LiOH). As noted above, a working electrode 110 is used to extract lithium cations (Li⁺) from a lithium-containing solution 310 (e.g., point source, such as brine or clays). Hydroxide ions (OH⁻) and hydrogen are generated through the water-splitting reaction in a lithium conversion reactor 150, as described in Equation (1) above. The lithium cations (Li⁺) are then supplied to the lithium conversion reactor 150, where hydroxide ions (OH⁻) react with the lithium cations (Li⁺) to form lithium hydroxide (LiOH)—see equation (6):

Li + + OH - → LiOH ( 6 )

The lithium hydroxide (LiOH) is then collected from the conversion reactor.

The overall reaction of a tandem method 200 consumes water and electricity to convert lithium cations 312 into lithium hydroxide (LiOH) while producing hydrogen-see equation (7):

2 ⁢ Li + + 2 ⁢ H 2 ⁢ O + 2 ⁢ e - → 2 ⁢ LiOH + H 2 ( 7 )

The lithium hydroxide (LiOH) production process in the lithium conversion reactor enables the production of 0.5 mole of H₂ for producing 1 mole of lithium hydroxide. The processes in the lithium extraction and lithium conversion reactors described above can also be separate systems or can be coupled with other alternative systems to produce alkaline, alkaline earth, and transition metal products (salts and compounds) referenced above.

Carbonate Conversion

As noted above, the gaseous carbon dioxide (CO₂) may be supplied to the lithium-conversion reactor 150, where the carbon dioxide (CO₂) dissolves in the recovery solution 320 (which may also be referred to as electrolyte) until its saturation point is reached-see equation (8):

CO 2 ( g ) → CO 2 ( l ) ( 8 )

Carbonic acid is produced inside the aqueous solutions according to (9):

CO 2 ( l ) + H 2 ⁢ O → H 2 ⁢ CO 3 ( 9 )

Carbonic acid is dissolved inside the aqueous solutions according to (10):

H 2 ⁢ CO 3 → H + + HCO 3 - ( 10 )

By feeding lithium ions (Li⁺) to the recovery solution 320, some of the lithium ions are converted into lithium bicarbonate (11):

Li + + HCO 3 - → LiHCO 3 ( 11 )

The remaining lithium ions (Li⁺) are precipitated into lithium carbonate (Li₂CO₃) according to (12):

2 ⁢ Li + + 2 ⁢ HCO 3 - → Li 2 ⁢ CO 3 + CO 2 + H 2 ⁢ O ( 12 )

The formed lithium bicarbonate (LiHCO₃⁻) is unstable at higher temperatures (>30° C.). Therefore, lithium bicarbonate (LiHCO₃⁻) can be converted into lithium carbonate (Li₂CO₃) by heating and stirring the solution. Overall, the system consumes CO₂ and water to convert lithium into lithium carbonate (Li₂CO₃)—see equation (13).

2 ⁢ LI + + CO 2 + H 2 ⁢ O → Li 2 ⁢ CO 3 ( 13 )

In some examples, potassium carbonate (K₂CO₃) may be produced from brine in the tandem reactor system 190, e.g., in a manner similar to lithium carbonate (Li₂CO₃) described above. The potassium cations (K⁺) are recovered in a lithium-extraction reactor 100 and supplied to a lithium-conversion reactor 150, where bicarbonate ions (produced from water splitting in the conversion reactor—in a manner described above) react with the potassium cations (K⁺) to form potassium carbonate (K₂CO₃)—see equation (14):

2 ⁢ K + + 2 ⁢ HCO 3 - → K 2 ⁢ CO 3 + H 2 ⁢ O + CO 2 ( 14 )

Similar processes may be performed to produce cesium carbonate (Cs₂CO₃)—see equation (15), magnesium carbonate (MgCO₃)—see equation (16), sodium carbonate (Na₂CO₃)—see equation (17), rubidium carbonate (Rb₂CO₃)—see equation (18), francium carbonate (Fr₂CO₃)—see equation (19), calcium carbonate (Ca₂CO₃)—see equation (20), barium carbonate (BaCO₃)—see equation (21), nickel carbonate (NiCO₃—see equation (22) cobalt carbonate (CoCO₃)—see equation (23), manganese carbonate (MnCO₃)—see equation (24), beryllium carbonate (BeCO₃)—equation (25), strontium carbonate (SrCO₃)—see equation (26), radium carbonate (RaCO₃)—see equation (27).

2 ⁢ Cs + + 2 ⁢ HCO 3 - → Cs 2 ⁢ CO 3 + H 2 ⁢ O + CO 2 ( 15 ) Mg 2 + + 2 ⁢ HCO 3 - → MgCO 3 + H 2 ⁢ O + CO 2 ( 16 ) 2 ⁢ Na + + 2 ⁢ HCO 3 - → Na 2 ⁢ CO 3 + H 2 ⁢ O + CO 2 ( 17 ) 2 ⁢ Rb + + 2 ⁢ HCO 3 - → Rb 2 ⁢ CO 3 + H 2 ⁢ O + CO 2 ( 18 ) 2 ⁢ Fr + + 2 ⁢ HCO 3 - → Fr 2 ⁢ CO 3 + H 2 ⁢ O + CO 2 ( 19 ) Ca + 2 + 2 ⁢ HCO 3 - → CaCO 3 + H 2 ⁢ O + CO 2 ( 20 ) Ba + 2 + 2 ⁢ HCO 3 - → BaCO 3 + H 2 ⁢ O + CO 2 ( 21 ) Ni + 2 + 2 ⁢ HCO 3 - → NiCO 3 + H 2 ⁢ O + CO 2 ( 22 ) Co + 2 + 2 ⁢ HCO 3 - → CoCO 3 + H 2 ⁢ O + CO 2 ( 23 ) Mn + 2 + 2 ⁢ HCO 3 - → MnCO 3 + H 2 ⁢ O + CO 2 ( 24 ) Be + 2 + 2 ⁢ HCO 3 - → BeCO 3 + H 2 ⁢ O + CO 2 ( 25 ) Sr + 2 + 2 ⁢ HCO 3 - → SrCO 3 + H 2 ⁢ O + CO 2 ( 26 ) Ra + 2 + 2 ⁢ HCO 3 - → RaCO 3 + H 2 ⁢ O + CO 2 ( 27 )

Hydroxide Conversion

Potassium hydroxide (KOH) may be produced from a lithium-containing solution 310 using a tandem reactor system 190 in a manner similar to lithium hydroxide (LiOH)—see equation (28):

K + + OH - → KOH ( 28 )

Other examples include hydroxide (CsOH)—see equation (29), magnesium hydroxide (Mg(OH)₂)—see equation (30), sodium hydroxide (NaOH)—see equation (31), rubidium hydroxide (RbOH)—see equation (32), francium hydroxide (FrOH)—see equation (33), calcium hydroxide (Ca(OH)₂)—see equation (34), barium hydroxide (Ba(OH)₂)—see equation (35), nickel hydroxide (Ni(OH)₂)—see equation (36), cobalt hydroxide (Co(OH)₂)—see equation (37), manganese hydroxide (Mn(OH)₂)—see equation (38), beryllium hydroxide (Be(OH)₂)—see equation (39), strontium hydroxide (Sr(OH)₂)—see equation (40), radium hydroxide (Ra(OH)₂)—see equation (41):

Cs + + OH - → CsOH ( 29 ) Mg + 2 + 2 ⁢ OH - → Mg ⁡ ( OH ) 2 ( 30 ) Na + + OH - → NaOH ( 31 ) Rb + + OH - → RbOH ( 32 ) Fr + + OH - → FrOH ( 33 ) Ca + 2 + 2 ⁢ OH - → Ca ( OH ) 2 ( 34 ) Ba + 2 + 2 ⁢ OH - → Ba ( OH ) 2 ( 35 ) Ni + 2 + 2 ⁢ OH - → Ni ( OH ) 2 ( 36 ) Co + 2 + 2 ⁢ OH - → Co ( OH ) 2 ( 37 ) Mn + 2 + 2 ⁢ OH - → Mn ( OH ) 2 ( 38 ) Be + 2 + 2 ⁢ OH - → Be ( OH ) 2 ( 39 ) Sr + 2 + 2 ⁢ OH - → Sr ( OH ) 2 ( 40 ) Ra + 2 + 2 ⁢ OH - → Ra ( OH ) 2 ( 41 )

Chloride Conversion

In some examples, a lithium-containing product 390 is lithium chloride (LiCl), which may be produced in a tandem reactor system 190 (series integration of an extraction reactor and conversion reactor) or in a separate system using the downstream of the lithium extraction reactor. The lithium cations (Li⁺) extracted from a lithium-containing solution 310 are supplied to a reactor where chloride ions (produced either in a conversion reactor or in a separate system or obtained from a point source) react with the lithium cations (Li⁺) to form lithium chloride (LiCl)—see equation (42):

Li + + Cl - → LiCl ( 42 )

Other chloride examples that may be formed in a similar manner include potassium chloride (KCl)—see equation (43), cesium chloride (CsCl)—see equation (44), magnesium chloride (Mg(Cl)₂)—see equation (45), sodium chloride (NaCl)—see equation (46), rubidium chloride (RbCl)—see equation (47), francium chloride (FrCl)—see equation (48), calcium chloride (Ca(Cl)₂)—see equation (49), barium chloride (Ba(Cl)₂)—see equation (50), nickel chloride (Ni(Cl)₂)—see equation (51), cobalt chloride (Co(Cl)₂)—see equation (52), manganese chloride (Mn(Cl)₂)—see equation (53), beryllium chloride (Be(Cl)₂)—see equation (54), strontium chloride (Sr(Cl)₂)—see equation (55), radium chloride (Ra(Cl)₂)—see equation (56):

K + + Cl - → KCl ( 43 ) Cs + + Cl - → CsCl ( 44 ) Mg + 2 + 2 ⁢ Cl - → Mg ⁡ ( Cl ) 2 ( 45 ) Na + + Cl - → NaCl ( 46 ) Rb + + Cl - → RbCl ( 47 ) Fr + + Cl - → FrCl ( 48 ) Ca + 2 + 2 ⁢ Cl - → Ca ⁡ ( Cl ) 2 ( 49 ) Ba + 2 + 2 ⁢ Cl - → Ba ⁡ ( Cl ) 2 ( 50 ) Ni + 2 + 2 ⁢ Cl - → Ni ⁡ ( Cl ) 2 ( 51 ) Co + 2 + 2 ⁢ Cl - → Co ⁡ ( Cl ) 2 ( 52 ) Mn + 2 + 2 ⁢ Cl - → Mn ⁡ ( Cl ) 2 ( 53 ) Be + 2 + 2 ⁢ Cl - → Be ⁡ ( Cl ) 2 ( 54 ) Sr + 2 + 2 ⁢ Cl - → Sr ⁡ ( Cl ) 2 ( 55 ) Ra + 2 + 2 ⁢ Cl - → Ra ⁡ ( Cl ) 2 ( 56 )

Sulfate Conversion

In some examples, a lithium-containing product 390 is lithium sulfate (Li₂SO₄) produced either in a tandem reactor system 190 (series integration of extraction reactor and conversion reactor) or in a separate system using the downstream of the lithium extraction reactor. In order to achieve the production of lithium sulfate (Li₂SO₄), the extraction reactor (the first step of the tandem reactor system 190) can be equipped with working (intercalation) electrodes that could extract lithium cations (Li⁺) from point sources (such as brine or clays). The lithium cations (Li⁺) are then supplied to the system, where sulfate ions (produced either in a conversion reactor or in a separate system or obtained from a point source) react with the lithium cations (Li⁺) to form lithium sulfate-see equation (57):

2 ⁢ Li + + SO 4 - 2 → Li 2 ⁢ SO 4 ( 57 )

Other sulfate examples that may be formed in a similar manner include potassium sulfate (K₂SO₄)—see equation (58), cesium sulfate (Cs₂SO₄)—see equation (59), magnesium sulfate (MgSO₄)—see equation (60), sodium sulfate (Na₂SO₄)—see equation (61), rubidium sulfate (Rb₂SO₄)—see equation (62), francium sulfate (Fr₂SO₄)—see equation (63), calcium sulfate (CaSO₄)—see equation (64), barium sulfate (BaSO₄)—see equation (65), nickel sulfate (NiSO₄)—see equation (66), cobalt sulfate (CoSO₄)—see equation (67), manganese sulfate (MnSO₄)—see equation (68), beryllium sulfate (BeSO₄)—see equation (69), strontium sulfate (SrSO₄)—see equation (70), and radium sulfate (RaSO₄)—see equation (71):

2 ⁢ K + + SO 4 - 2 → K 2 ⁢ SO 4 ( 58 ) 2 ⁢ Cs + + SO 4 - 2 → Cs 2 ⁢ SO 4 ( 59 ) Mg + + SO 4 - 2 → MgSO 4 ( 60 ) Na + + SO 4 - 2 → Na 2 ⁢ SO 4 ( 61 ) 2 ⁢ Rb + + SO 4 - 2 → Rb 2 ⁢ SO 4 ( 62 ) 2 ⁢ Fr + + SO 4 - 2 → Fr 2 ⁢ SO 4 ( 63 ) Ca + + SO 4 - 2 → CaSO 4 ( 64 ) Ba + 2 + SO 4 - 2 → BaSO 4 ( 65 ) Ni + 2 + SO 4 - 2 → NiSO 4 ( 66 ) Co + 2 + SO 4 - 2 → CoSO 4 ( 67 ) Mn + 2 + SO 4 - 2 → MnSO 4 ( 68 ) Be + 2 + SO 4 - 2 → BeSO 4 ( 69 ) Sr + 2 + SO 4 - 2 → SrSO 4 ( 70 ) Ra + 2 + SO 4 - 2 → RaSO 4 ( 71 )

CONCLUSION

Although the foregoing concepts have been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the appended claims. It should be noted that there are many alternative ways of implementing processes, systems, and apparatuses. Accordingly, the present embodiments are to be considered illustrative and not restrictive.