Systems and methods for direct lithium hydroxide production

Abstract

The present disclosure provides systems and methods for the direct production of lithium hydroxide by utilizing cation-selective membranes, monovalent selective membranes, or preferably lithium-selective membranes that have high lithium selectivity over multivalent and other monovalent ions, thus preventing magnesium precipitation during electrodialysis (ED) and also addressing the presence of sodium in most natural brine or mineral-based lithium production processes.

Description

[Technical field]

[0001] This application claims the benefit of priority to U.S. Provisional Application No. 63 / 147,656, filed February 9, 2021, the entire contents of which are incorporated herein by reference.

[0002] Field The present disclosure relates to a simplified, low-cost process for the direct production of high purity lithium products, in particular lithium hydroxide monohydrate, without the need to produce lithium carbonate precursors from brine and mineral sources. [Background technology]

[0003] background The largest lithium resources and producing areas in the world are the lithium-bearing brines of South America. Lithium demand pressures have already made previously uneconomic hard rock lithium resources now viable, and a significant proportion of new supply is coming from these sources, which are primarily located in Australia. There has also been a shift in the demand forecast for the lithium precursors, namely lithium carbonate and lithium hydroxide, with future projections favoring lithium hydroxide.

[0004] To produce lithium from any of the above sources, a lithium carbonate precursor must currently be produced and subsequently converted to lithium hydroxide. This presents a large and potentially unnecessary cost if the ultimate goal is lithium hydroxide. However, this is necessary as no direct commercially viable route to lithium hydroxide is currently available. Some of the potential benefits of bypassing lithium carbonate production have been described by (Grageda et al., 2020), who demonstrate the feasibility of this technique using very clean brines with very low Li / Na,K and Li / Mg,Ca ratios compared to realistic brines before pre-polishing or removal of impurity ions. Despite the use of such clean brines, Grageda et al. report significant contamination of their lithium hydroxide product with monovalent impurity cations.

[0005] Naturally occurring lithium brine concentrates, e.g., pond evaporation brines, contain mostly non-lithium cations such as Na, K, Mg, and Ca. In particular, Na ions are prevalent during the lithium extraction process, and lithium-containing brines are virtually always saturated with NaCl along with large amounts of KCl. In some hard-rock sources, such as jadarite, Na is part of the lithium mineral itself. Caustic leaching of spodumene also introduces a large excess of Na. Even in the more common acid roasting of spodumene, the Na content in the leach is typically more than 25% of the lithium content. When the above resource materials are processed, Na2CO3 is added to remove Ca, and then lithium carbonate is eventually precipitated, which also adds more Na to the process.

[0006] Purified lithium chloride or lithium sulfate brines can be subjected to membrane electrodialysis to produce relatively clean lithium hydroxide and acid solutions, but the membrane pre-purification step can be costly. Membrane electrodialysis for the separation of lithium from brines is reviewed in Gmar & Chagnes, 2019. Conventional cation-selective electrodialysis (ED) membranes are not selective between Li and Na, K, Ca or Mg. Thus, in the presence of non-lithium impurity cations, the membranes pass the impurity cations along with lithium to produce mixed hydroxides, reducing the current utilization efficiency for lithium production (Zhao et al., 2020). As a result, ED in high-sodium lithium brines not only results in Na contamination of the LiOH product, but also in the depletion of Li. + Along with ions, undesirable Na + Excessive electricity is consumed to transport the ions, and even more importantly, divalent hydroxides are highly insoluble and will precipitate within the ED cell, making the operation impossible.

[0007] Nemaska ​​Lithium Inc. has researched and tested a process to produce LiOH directly from spodumene from the Whabouchi deposit in Canada. To achieve this, a very deep cleanup of the leachate is utilized, including primary and secondary impurity removal steps followed by ion exchange, prior to membrane electrodialysis (Bourassa et al., 2020). The feed to the electrodialysis membrane contained 5.8 mg / L Ca and 0.2 mg / L Mg, with a Li / Na ratio of 4. The catholyte (LiOH stream) contained a similar Li / Na ratio, indicating little selectivity between the two. The highest reported catholyte Ca and Mg had a [OH] ratio of nearly 2 M. - ] background were 4 mg / L and 0.55 mg / L, respectively. In the catholyte in 6% LiOH solution, Ca levels averaged 3.8 mg / L and Mg was below the detection limit of 0.07 mg / L.

[0008] (2020) also specify feed brines for the electrodialysis of lithium hydroxide using conventional ED membranes, including very stringent requirements of no more than 150 ppb Mg+Ca (preferably less than 50 ppb each). Conventional ED membranes are not monovalent-divalent selective. Even more modern selective membranes often have Li-Mg selectivities only in the range of 8-33 (Gmar & Chagnes, 2019).

[0009] Qiu et al., 2019 demonstrate a five-step separation process in a sodium / potassium-free feed brine utilizing two-step electrodialysis with monovalent selective membranes, precipitation and ion exchange to separate Mg from Li, and then bipolar electrodialysis to produce LiOH. Several studies have reported the ability to use bipolar membrane electrodialysis (BPMED) to produce LiOH from clean solutions containing lithium (Bunani, Arda, et al., 2017; Bunani, Yoshizuka, et al., 2017; Jiang et al., 2014). Bipolar membrane electrodialysis is similar to membrane electrodialysis, in which anions and cations are selectively transported across a semipermeable membrane under an electric potential to drive ions and achieve their separation from a carrier such as water. Bipolar membranes typically contain a cation exchange membrane and an anion exchange membrane sandwiched together with a hydrophilic interface at their junction. Under an applied electric current, water molecules migrating to the hydrophilic junction are transported as H + ions and OH - ions, which migrate to produce acids and bases with other anions and cations. Bunani, Arda, et al., 2017, achieved separation of Li and B as LiOH and boric acid at 99.6% and 88.3%, respectively, using a bipolar electrodialysis membrane. Elsewhere, Bunani, Yoshizuka, et al., 2017, also demonstrated high recovery rates while achieving a Li concentration factor of approximately 10x. However, the Na concentration in solution was + In the presence of other cations such as , only low Li-Na selectivities of about 2 were achieved. This presents a significant challenge for pursuing a direct LiOH production route, especially based on natural resources that do not undergo significant prior purification steps.

[0010] Based on existing literature, extensive reduction of divalent / multivalent ions is necessary before ED is attempted, traditionally attempted by lime addition followed by softening. However, this still leaves a significant amount of Mg, depending on the liming pH as well as the amount of Ca in solution. Also, monovalent impurities such as Na and K remain in solution, and the Na content actually increases with the addition of Na for Ca removal. This approach still faces the same drawbacks, despite potentially reducing precipitation and scaling issues. The product is still a mixture of LiOH and NaOH, requiring more extensive processing using multiple fractional crystallizations and ion exchange. Even if divalent / multivalent cations are removed to ultra-low levels using ion exchange prior to electrodialysis, high Na levels result in low current efficiency, producing a mixed hydroxide product. Meng et al., 2021 outlines such an approach for producing lithium carbonate and lithium hydroxide.

[0011] Due to the above and related challenges, the only commercially implemented route to LiOH production involves multiple steps to produce the intermediate product, lithium carbonate, as shown in Figure 1a below. Concentrated brines from evaporation ponds with Li content of about 2%-6% contain significant amounts of B, Mg, and Ca in addition to Na. Boron is traditionally removed from the brine by solvent extraction using a water-insoluble alcohol solvent. Mg and Ca are subsequently removed by precipitation using a lime soda softening process. The brine is treated with lime Ca(OH2) at a pH above 10 to precipitate magnesium, iron, silica, and other heavy metal impurities. The precipitate is voluminous and requires extensive solid / liquid separation to separate the brine from the solids. Multiple stages of countercurrent washing and filtration are required to minimize lithium loss in the solution adhering to the solids. The brine is then saturated with Ca, which is precipitated as CaCO3 by the addition of a controlled amount of soda ash (Na2CO3) to prevent co-precipitation of lithium carbonate. The brine is relatively clean, containing essentially Li and Na cations, with less than 10 ppm Mg and less than 30 ppm Ca. Separation of Na from Li is difficult to do in a way that leaves Li aqueous. Therefore, Li is precipitated as lithium carbonate to separate it from the sodium, which remains aqueous. The lithium carbonate product is crude and must be purified. For this, the lithium carbonate is dissolved under CO2 to increase its solubility. The dissolved solution is filtered to remove small amounts of insoluble matter, followed by ion exchange to remove small amounts of dissolved impurities such as Na. The CO2 from the clean brine is then stripped with clean steam to reprecipitate battery grade lithium carbonate. To produce LiOH, the battery grade lithium carbonate is redissolved, causticized with lime, then separated from the precipitate, and the resulting LiOH solution is evaporated and crystallized. Due to the re-addition of some impurities along with the lime, the lithium hydroxide product may need to be redissolved and polished further using ion exchange and recrystallization. In some instances, the crude lithium carbonate is carried directly to the LiOH process. However, in these situations, due to the higher impurity loading, additional ion exchange of LiOH and multiple recrystallizations are required. These steps are shown in Figure 1a.

[0012] Another emerging approach for lithium brine enrichment utilizes thermal evaporation instead of mechanical separation and solar evaporation and is called direct lithium extraction (DLE). Figure 2 shows the general process, which involves crude separation of Li from major impurities such as Na, K, Mg, and Ca using ion exchange, ion sorption or solvent extraction. This is followed by further removal of multivalent ions using nanofiltration. The brine (Li with residual impurities) is then concentrated using reverse osmosis by separating the water to a point where the pressure required to drive reverse osmosis becomes infeasible. Concentration of additional Li and impurities then follows using thermal evaporation. The concentrated brine then flows into the processing plant, following the same steps as shown in Figure 1a.

[0013] What is needed is a more efficient process for producing LiOH from mixtures containing Li, especially natural sources such as brines, without the need for pre-purification of the feed brine to the ED or separation membrane, and especially without the need for the production of the intermediate product lithium carbonate. Summary of the Invention

[0014] overview By using an appropriate membrane such as LiTAS™, some or most of the processing steps currently used can be eliminated, resulting in a much more efficient production of lithium hydroxide from lithium-containing sources such as direct lithium extraction processes, brine evaporation ponds, or concentrated feeds from other means such as rock leachates.

[0015] The present disclosure provides a method for producing a substantially pure LiOH solution directly from a mixture containing Li and one or more impurities by feeding the mixture to an electrodialysis cell or BPMED cell containing an ion selective membrane and functioning the ion selective membrane under a potential difference to obtain a separate LiOH solution, the separate LiOH solution containing about 2% to about 14% by weight LiOH, Mg in the range of about 0 ppm to about 3 ppm, and Ca in the range of about 0 ppm to about 5 ppm. Other LiOH concentrations in the separated LiOH solution are possible. In a preferred embodiment, the ion selective membrane is included with a BPMED cell.

[0016] In one case, the mixture contains lithium in an amount of about 1,500 ppm to about 60,000 ppm. In another case, the mixture contains impurity ions selected from the group consisting of monovalent and divalent cations and divalent anions. The impurity ions can be selected from the group consisting of Mg, Ca, Na, and K ions. In one aspect, the mixture contains a ratio of Li / Mg ions in the range of about 3 to about 20. In another aspect, the mixture contains a ratio of Li / Ca ions in the range of about 5 to about 10. In yet another aspect, the mixture contains a ratio of Li / Na ions and Li / K ions in the range of about 1.5 to about 70. Preferably, the mixture is a concentrated lithium brine from a process selected from the group consisting of pond evaporation, direct lithium extraction, and leaching of lithium minerals using water or acid. The mixture can include rock leachates from spodumene, jadarite, hectorite clay, Zinnwaldite, or other lithium-bearing minerals.

[0017] In one aspect, the ion selective membrane is selected from the group consisting of a lithium selective membrane, a monovalent cation selective membrane, or a cation selective membrane for anions. In a preferred embodiment, the ion selective membrane is a lithium selective membrane having a selectivity in the range of 10 to 100. In a particularly preferred embodiment, the ion selective membrane is a lithium selective membrane comprising a polymer matrix and metal organic framework (MOF) particles dispersed therein. In another embodiment, the cation selective membrane is a cation selective membrane for anions, and liming is performed prior to feeding the mixture into an ED cell containing the membrane.

[0018] In a preferred embodiment, the process bypasses or at least significantly reduces the need for the formation of lithium carbonate as a precursor to LiOH. In another aspect, the process is substantially free of lithium carbonate formation as a precursor to LiOH. In another aspect, partial lithium separation as lithium carbonate, phosphate, oxalate or other precipitates may be produced from the feed brine, and the remaining lithium-containing feed then proceeds through electrodialysis to produce LiOH directly. Preferably, the resulting lithium hydroxide solution is then crystallized to produce lithium hydroxide monohydrate having a purity in the range of about 95% to about 99.9% by weight. In another aspect, the lithium hydroxide solution contains lithium hydroxide in the range of 5% to 14% by weight.

[0019] In another embodiment, boron solvent extraction is performed prior to feeding the mixture to the ED cell or ED membrane. In yet another embodiment, the mixture is an evaporative concentrate from a series of brine ponds, and the method further comprises membrane separation of Mg and recycling the separated Mg to a previous pond for precipitation to produce a Li-enriched feed brine with lower Mg content, substantially as disclosed in co-pending U.S. patent application Ser. No. 17 / 602,808, entitled Systems and Methods for Recovering Lithium from Brines, which is incorporated herein by reference in its entirety.

[0020] The present disclosure also provides a system configured to directly produce LiOH without substantially producing lithium carbonate precursors. The system includes an ED cell or BPMED cell including an ion selective membrane selected from the group consisting of a lithium selective membrane, a monovalent selective membrane, or a cation selective membrane for anions; a feed inlet upstream of the membrane and configured to receive a mixture including a concentrated lithium brine from a process selected from the group consisting of pond evaporation, direct lithium extraction, and leaching of lithium minerals using water or acid; and an outlet downstream of the membrane configured to carry a LiOH solution containing about 2 wt.% to about 14 wt.% LiOH, less than 25 ppm Mg, and less than 50 ppm Ca. In some embodiments, the LiOH solution contains less than 20 ppm, less than 15 ppm, less than 10 ppm, and less than 5 ppm Mg. The LiOH solution may contain about 1 ppm to about 50 ppm Mg, about 2.5 ppm to about 75 ppm Mg, about 5 ppm to about 50 ppm Mg, or about 5 ppm to about 25 ppm Mg. In some embodiments, the LiOH solution contains less than 50 ppm, less than 45 ppm, less than 40 ppm, less than 35 ppm, less than 30 ppm, less than 25 ppm, less than 20 ppm, less than 15 ppm, less than 10 ppm, and less than 5 ppm Ca. The LiOH solution may contain about 1 ppm to about 50 ppm Ca, about 2.5 ppm to about 75 ppm Ca, about 5 ppm to about 50 ppm Ca, or about 5 ppm to about 25 ppm Ca.

[0021] In a preferred embodiment, the system includes a membrane that is a lithium-selective membrane. In one aspect, the membrane is a lithium-selective membrane that includes a polymer matrix and MOF particles dispersed therein. In another aspect, the lithium-selective membrane has a selectivity within the Li / Mg,Ca range of at least 10 and the Li / Na,K range of at least 3. [Brief description of the drawings]

[0022] [Figure 1a]FIG. 1 shows (a) a conventional process for LiOH production, (b) a simplified low-cost lithium-selective ED membrane-based manufacturing process for LiOH production, and (c) application of the membrane-based process of (b) optionally after feed brine liming and softening. [Figure 1b] See legend to Figure 1a. [Figure 1c] See legend to Figure 1a. [Diagram 2] FIG. 2 shows a typical direct lithium extraction (DLE) process block flow diagram illustrating the general steps of mechanically concentrating lithium and separating it from impurities instead of using solar evaporation ponds. [Diagram 3] FIG. 3 shows bipolar membrane electrodialysis of feed brine containing undesirable monovalent and divalent cations and divalent anions using a highly Li-selective membrane, such as a LiTAS™ membrane, to directly produce clean LiOH solution. [Figure 4a] FIG. 4 shows bipolar membrane electrodialysis of a typical low sulfate Chilean evaporation pond concentrated lithium feed brine using (a) a conventional cation-selective electrodialysis membrane, (b) a lithium-selective membrane, and (c) bipolar membrane electrodialysis using a cation-selective membrane for anions after lime-soda softening of the feed brine to remove multivalent impurities such as Mg and Ca. [Figure 4b] See legend to Figure 4a. [Figure 4c] See legend to Figure 4a. [Figure 5a] FIG. 5 shows bipolar membrane electrodialysis of a typical Argentine evaporation pond concentrated lithium feed brine using (a) a conventional cation-selective electrodialysis membrane, (b) a lithium-selective membrane, and (c) a cation-selective membrane for anions after lime-soda softening of the feed brine. [Figure 5b] See legend to Figure 5a. [Figure 5c] See legend to Figure 5a. [Figure 6a]FIG. 6 shows bipolar membrane electrodialysis of spodumene sulfuric acid roasting leaching using (a) conventional cation-selective electrodialysis membrane, (b) lithium-selective membrane, and (c) cation-selective membrane for anions after lime-soda softening. [Figure 6b] See legend to Figure 6a. [Figure 6c] See legend to Figure 6a. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS By using suitable selective membranes, some or most of the processing steps currently used can be eliminated, resulting in much more efficient production of lithium hydroxide from lithium-containing sources such as evaporated brines and rock leachates. "Selectivity," for example with respect to lithium selectivity, is defined herein as the ratio of recovered Li ions / feed Li concentration to the ratio of other ions recovered / other ion feed concentrations.

[0024] As shown in Figure 1b, brine or mineral leach solutions (e.g., lithium chloride or lithium sulfate solutions) can be directly subjected to electrodialysis using lithium-selective cation membranes. The lithium-selective cation membrane allows the migration of mostly only lithium ions, producing a highly concentrated lithium hydroxide solution ready for evaporative crystallization. Thus, for example, application of a highly Li / Na-selective ED membrane could provide a route to direct LiOH production from less concentrated and impure brines, eliminating the intermediate Li2CO3 processing requirement as well as the associated capital and operating costs.

[0025] As shown in Figure 1c, if the feed brine has high Mg,Ca loading, a lime-soda softening step may optionally be performed prior to direct electrodialysis of LiOH, again bypassing the intermediate Li2CO3 processing requirement. Significant capital and operating cost savings are still maintained with this process.

[0026] "Direct" or "directly" herein with respect to LiOH production refers to systems and processes that can substantially bypass the production of intermediate lithium carbonate precursors to LiOH, and in most cases, can also bypass pre-polishing of feed from natural brines, Li-bearing rock leachates, or DLE processes. Advantageously, the methods and systems taught herein have been found to produce highly concentrated LiOH from Li-bearing feedstocks containing natural impurities and / or other impurities with a substantially reduced number of processing steps. The resulting LiOH solution can be readily crystallized, for example, by evaporation, to produce substantially pure (e.g., 95% to 99.9% pure) lithium hydroxide monohydrate. In some embodiments, the methods or systems produce a final lithium product, such as LiOH that is greater than about 90% by weight, greater than 92.5% by weight, greater than 95% by weight, greater than 96% by weight, greater than 97% by weight, greater than 98% by weight, greater than 99% by weight, greater than 99.5% by weight, greater than 99.9% by weight, or more pure. In some embodiments, the method or system produces a final lithium product that is about 90% to about 99.999% pure by weight, about 92.5% to about 99.99% pure by weight, about 95% to about 99.9% pure by weight, or about 96% to about 99% pure by weight.

[0027] As used herein, the terms "cation selective electrodialysis membrane" or "cation exchange membrane" or "cation selective membrane for anions" refer to a membrane that is selective between cations and anions, but not between cations, such as between Li and Na, K, Ca or Mg. Thus, in the presence of non-lithium impurity cations, such membranes will pass the impurity cations along with lithium to produce mixed hydroxides. "Monovalent selective membrane" or "monovalent selective cation exchange membrane" refers to a membrane that is selective between monovalent and divalent ions, thus accepting monovalent ions such as Na, K and Li and retarding divalent / multivalent cations such as Ca or Mg. "Monovalent selective membrane" also refers to a membrane that is selective between Cl and divalent ions, such as Na, K and Li, and retarding divalent / multivalent cations such as Ca or Mg. - or F - It allows the passage of essentially monovalent anions such as SO4 2-The membrane may be a monovalent selective anion exchange membrane that retards divalent anions such as cations and anions. By "conventional electrodialysis membrane" is meant a membrane that distinguishes between cations and anions and is essentially non-selective between monovalent and divalent ions.

[0028] "Electrodialysis" means the use of one or more ion exchange membranes to separate ions from a feed stream into a different ion stream under an applied potential difference. Any suitable potential difference, e.g., 400 A / m 2 ~About 3000A / m 2 A current in the range of, but not limited to, may be used.

[0029] "Bipolar membrane electrodialysis" or BPMED refers to an electrodialysis process or system in which anions and cations are selectively transported across a semipermeable membrane under an electric potential that drives the ions and achieves their separation from a carrier, such as water. A bipolar membrane typically includes a cation exchange membrane and an anion exchange membrane sandwiched together with a hydrophilic interface at their junction. Under an applied electric current, water molecules that migrate to the hydrophilic junction are transported as H + ions and OH - ions, which migrate to produce acids and bases with other anions and cations. A typical BPMED system used herein is shown in Figure 3 by way of example only, and a variety of other BPMED configurations are possible using the teachings herein.

[0030] Feed compositions herein may include impurity ion ratios of Li / Mg typically greater than 3, more typically greater than 5, and Li / Ca ratios greater than 1.5, typically greater than 3.5. Feed lithium content is typically greater than 1,000 ppm, greater than 5,000 ppm, or greater than 10,000 ppm. For example, feeds used herein may have compositions containing undesirable impurity ions (such as monovalent and divalent cations and divalent anions) with Li / Mg impurity ion ratios of 3 to 20, typically 5 to 15, and Li / Ca ratios of 5 to 100, typically 20 to 50, and Li / Na,K ratios of 1.5 to 10, typically 3.5 to 7.5, and feed lithium content typically 1000 ppm to 60,000 ppm, preferably 5000 ppm to 25,000, and for pond evaporated brines typically 10,000 ppm to 60,000 ppm.

[0031] The LiOH solutions obtained from the methods and systems disclosed herein typically contain highly concentrated LiOH. For example, a LiOH concentration range of about 2% to about 14% LiOH by weight can be achieved. In some embodiments, the LiOH concentration is at least 5%. Other concentrations are possible. Advantageously, these concentrations can be readily crystallized to produce substantially pure lithium hydroxide monohydrate.

[0032] With reference to the embodiments of FIG. 1b and FIG. 1c, the present disclosure provides selective membrane electrodialysis to eliminate most of the current process steps (FIG. 1a) and the intermediate lithium carbonate precipitation. The inventors have found that the required membrane Li / Mg,Ca selectivity is a function of the feed Li / Mg and Li / Ca ratios. For Li / Mg and Li / Ca ratios greater than 10, typical of Chilean concentrated brines, Li / Mg,Ca selectivities greater than 10 are preferred, more preferably Li / Mg,Ca selectivities greater than 30 or even greater than 50. For feed Li / Mg ratios less than 10, as in some Argentinean brines, Li / Mg selectivities greater than 75 are preferred. For feed Li / Mg ratios in the region of 2-5, the approach shown in FIG. 1c is optionally used, including chemically precipitating Mg prior to direct electrodialysis of LiOH. In this case, the preferred Li / Mg selectivity may be approximately 10 or greater, preferably greater than 30. In all cases, higher Li / Na,K selectivities of greater than 10 are beneficial but not required, and are particularly beneficial for the approach shown in FIG. 1c. Given the teachings herein, appropriate selectivities can be selected based on the feed impurity content such that membranes of the above-mentioned selectivities directly produce non-precipitating LiOH solutions having maximum Mg and Ca contents of about 25 ppm or less and about 50 ppm or less, respectively. These Ca and Mg numbers are indicative of the K sp (Mg(OH2)) = 5.61E-12 and K spThis is higher than what can be calculated using the solubility product of (Ca(OH2)) = 5.02E-6 (Lide, 2004). However, as mentioned by Bourassa et.al. (2020), higher concentrations of Ca and Mg up to 4 mg / L and up to 0.55 mg / L were reported during extended test runs producing LiOH using electrodialysis from ultra-purified brine. Without wishing to be bound by theory, the higher levels of Ca and Mg compared to those calculated from the solubility product indicate some stabilization mechanism that allows them to remain in solution, possibly due to the activity of the components and the stabilizing influence of other impurity ions. The inventors have experimentally verified that up to 25 mg / L Mg and up to 50 mg / L Ca can remain in stable, non-precipitating solution in 5% LiOH solution.

[0033] It should be understood that membranes useful in embodiments of the present disclosure can include any membrane capable of achieving at least a partial separation of monovalent ions or lithium from one or more impurities, preferably monovalent-monovalent and / or monovalent-multivalent separation of the targets.

[0034] As an example, one particularly suitable membrane is the LiTAS™ membrane. Such membranes have been shown to have monovalent-divalent ion selectivities of 500 or greater, utilizing metal-organic framework (MOF) components. Such membranes have also demonstrated corresponding Li-Mg selectivities of 1500 (Lu et al., 2020). LiTAS™ membranes incorporating Li-Na selective MOFs, which have demonstrated selectivities of approximately 1000, may also be provided.

[0035] "LiTAS™" membrane technology refers to lithium ion transport and / or separation using metal-organic framework (MOF) nanoparticles in a polymer support. MOFs have very high internal surface areas and adjustable openings that achieve separation and transport of ions while allowing only certain ions to pass. These MOF nanoparticles are embodied as powders, but when combined with a polymer, the combined MOF and polymer can create a mixed matrix membrane with embedded nanoparticles. The MOF particles create a percolation network or channels that allow selected ions to pass through. When extracting lithium, the membrane is placed within the module housing. A feed, such as evaporated brine, is pumped through a system with one or more layers of membranes that perform effective separation even at high salinity. Current separator technologies may fall short in one area or another, but LiTAS™ is particularly preferred and effective. U.S. Patent Application No. 62 / 892,439, filed August 27, 2019, International Patent Publication No. 2019 / 113649, published June 20, 2019, and International Patent Application No. PCT / US2020 / 047955, filed August 26, 2020, for LiTAS™ membrane technology, are incorporated herein by reference in their entirety. In particular, the LiTAS™ membrane may be a polymeric membrane comprising one or more nanoparticles. In particular, the nanoparticles in the membrane may comprise one or more metal-organic frameworks (MOFs), such as UiO-66, UiO-66-(CO2H)2, UiO-66-NH2, UiO-66-SO3, UiO-66-Br, or any combination thereof. Other MOFs include ZIF-8, ZIF-7, HKUST-1, UiO-66, or combinations thereof.

[0036] Membranes for use herein can also be monovalent selective cation exchange membranes with sufficiently high lithium / divalent selectivity, depending on the feed brine Mg content and type of application (Figure 1b or Figure 1c). For example, Nie et al., 2017 mention monovalent selective membranes for Li-Mg separation from high Mg content brine, achieving high Li recovery and good selectivity of 20-33.

[0037] Another example is a membrane containing an ionophore, which is a material that transports a specific ion across a semipermeable surface or membrane, as discussed in Demeter et.al., 2020. Such ionophores are based on 14-crown-4 crown ether derivatives. Other possible examples are supported liquid membranes or ionic liquid membranes in electrodialysis, as described in the review paper by Li et al., 2019, where cation-selective membranes (Li-Mg selectivity of 8-33, Li-Ca selectivity of about 7, Li-Na selectivity of about 3, and Li-K selectivity of about 5) are described.

[0038] Referring now to FIG. 3, a LiTAS™ membrane applied in a BPMED setup is shown. In this setup, the electrodialysis cell is set up in three compartments in addition to the electrode rinse flow path adjacent to the end electrodes. A three compartment unit including a cation exchange membrane, a bipolar membrane and an anion exchange membrane is set up as a repeating unit. Any number of repeating units can be provided in the ED or BPMED cells contemplated herein. The cation exchange membrane in this example is a Li-selective membrane that essentially allows only lithium ions and water to pass along with small amounts of impurities. These membranes can also be monovalent selective, allowing monovalent ions such as Na, K and Li to pass and retarding divalent / multivalent cations such as Ca or Mg. The bipolar membrane is a sandwich of a cation exchange membrane and an anion exchange membrane as described above. The positively charged anion exchange membrane essentially allows only negatively charged anions to pass and repels positively charged cations. These membranes can also be monovalent selective, essentially allowing only monovalent anions such as chloride to pass over divalent anions such as sulfate.

[0039] The feed enters the central compartment of each repeating unit. The Li-selective membrane allows essentially only Li to permeate through the membrane into the adjacent base recovery compartment. Similarly, anions permeate through an anion exchange membrane into the acid recovery compartment. A bipolar membrane on the opposite side of the compartment allows H to pass through to the acid recovery compartment. + ions or to the base recovery compartment. - In this way, a clean LiOH stream can be produced directly from the feed brine or leach solution.

[0040] In another embodiment (FIG. 1c), if the feed brine contains too many multivalent ions, typically Li / Mg ratios greater than 5 and Li / Ca ratios greater than 2, respectively, BPMED can be applied after the liming step or after the liming and softening steps. However, the liming and softening steps increase the sodium content of the feed brine by replacing Mg ions with Ca and Ca ions with Na. In this case, lithium selective membranes that discriminate between Li and Na are most preferred. However, cation selective membranes for anions that only discriminate between cations and anions can also be used in some cases for viable processes, mainly after softening, to produce viable products (FIGS. 4c and 5c). In some cases, conventional ED membranes remain inviable as indicated by high Ca levels, resulting in catholyte containing high Ca levels (stream BC in the figure), which tend to precipitate in the ED cell. Even in cases where conventional ED membranes do yield potentially viable products, in most cases (Figure 5c), the products are of relatively low quality and require additional processing steps similar to those shown in Figure 1a, i.e., LiOH recrystallization and ion exchange (IX) to remove Na, K, and other trace impurities.

[0041] The inventors have surprisingly found that the use of an appropriate selective membrane during ED can reduce or eliminate most of the processing steps required for conventional LiOH production. Based on the teachings and exemplary embodiments herein, other embodiments that rearrange the process steps or include additional steps will be optional for those skilled in the art. For example, other embodiments may include solvent extraction (SX) of boron from the feed brine or IX for boron removal from the feed brine or during LiOH crystallization. EXAMPLES

[0042] Analysis method: Several real-world brine examples from various regions and sources are provided in the following paragraphs to demonstrate the applicability of the systems and methods described herein in a wide variety of cases. Based on realistic brine chemistry, electrodialysis separation was modeled with and without a lithium-selective membrane.

[0043] For the lithium-selective membrane, a Li-Mg,Ca selectivity of 100 was used based on the documented performance of LiTAS™ membranes. A Li-Na,K selectivity of 50 was used for this selective membrane. Traditional ED modeling does not have selectivity between cations. Selectivity is defined here as the ratio of recovered Li ions / feed Li concentration to the ratio of recovered other cations / other cation feed concentration. Lithium hydroxide concentration was set at 5% in all cases, close to the solubility limit. Hydrochloric acid concentration was also set at 5% exiting the ED. In the non-selective membranes, per-pass recoveries of 95% for Li and 100% for other cations were used. Other cation recoveries were set higher since Li is the major component in these brines and other cations are recovered to a higher extent as the process continues to reach 95% Li recovery. For the Li-selective membrane, the same Li recovery of 95% was used and other cation recoveries were determined based on selectivity and relative concentration. The lithium hydroxide and hydrochloric acid solutions were set to evaporate to 14% solubility limit of LiOH and 30% solubility limit of HCl, respectively. In the sulfuric acid system, the sulfuric acid was set to be concentrated to 65%. The vapors from these evaporations were condensed and returned to the ED cell as carrier fluid to recover additional LiOH and HCl / H2SO4. Thus, a steady-state mass balance model was developed incorporating BPMED separation, evaporation, lithium hydroxide monohydrate crystallization, and filtration. Different feed chemistries were run in the model to predict the system at equilibrium. In particular, impurities in the base compartment outlet stream were of interest to ensure that Mg and Ca levels remained in solution.

[0044] Example 1, Chilean Evaporation Pond Brine: The performance of cation-selective ED membranes versus Li-selective membranes working in a BPMED setup on concentrated feed brine is shown in Figure 4. The feed to the ED is pond concentrated brine, e.g., natural brine after some solar evaporation (e.g., 98% by volume). This is a typical Chilean concentrated brine composition with a Li / Mg ratio of approximately 10. Additional make-up fresh water is shown added separately to the acid and base compartments to replenish the concentrated acid and base streams, as well as the water exiting with the crystallized water in LiOH.H2O. Most of the carrier water is recirculated evaporator crystallizer vapor condensate. The Li-depleted effluent from the BPMED can be recycled to the evaporation pond. Comparison of the base compartment outlet composition between Figure 4a (non-selective membrane) and Figure 3b (selective membrane) shows a striking difference in the impurity levels of the resulting LiOH stream. In practice, a Mg concentration of approximately 1200 ppm in the base stream exiting the ED in Figure 4a is not possible as this concentration exceeds the solubility of Mg in this solution. Mg will precipitate at these concentrations, making the use of conventional ED membranes impossible. The maximum Mg and Ca levels in this stream need to be less than 3 ppm and 5 ppm, respectively, to stay in solution as achievable with Li-selective membranes. With Li-selective membranes, the impurity profile of the LiOH stream becomes amenable to direct crystallization into commercially salable lithium products, as seen in Figure 4b.

[0045] Figure 4c shows the application of BPMED using a cation exchange membrane (not selective between different types of cations) to a process stream after the concentrated feed brine has been treated with lime-soda softening to precipitate multivalent cations. The LiOH concentrated stream in this case exhibits low levels of Mg and Ca, but high levels of K and elevated Na content. The production of lithium hydroxide from this stream may optionally include LiOH recrystallization and IX polishing in addition to the initial lime-soda softening. This represents a considerable improvement over conventional production processes, as lithium carbonate production is bypassed and process steps are significantly reduced. The purity of lithium hydroxide monohydrate achieved in cases a, b, and c is 95%, 99.9%, and 92%, respectively.

[0046] Example 2, Argentinean Evaporation Pond Brine: A mass balance summary of this brine processed with ED is shown in Figure 5. Figure 5a shows direct processing using a cation-selective ED membrane. The concentrate pond brine is 1.9% Li with other components as shown. Non-selective (conventional) ED produces a Mg level in the base compartment of 1662 ppm, significantly higher than the <3 ppm required to prevent precipitation. Thus, this conventional membrane separation is not preferred compared to the systems and methods taught herein using ED membranes suitable for direct LiOH production.

[0047] Figure 5b shows the process using a lithium-selective ED membrane. The Mg and Ca levels in the base compartment are below the maximum levels of 3 ppm and 5 ppm. Notably, the Na and K levels are also low, resulting in a high purity LiOH.H2O product.

[0048] Figure 5c shows the treatment of brine using a cation-selective ED membrane after it has been subjected to a lime-soda softening process for divalent and multivalent cation removal. In this case, the Mg and Ca levels in the base compartment are at acceptable levels. The process is therefore feasible; however, due to the high Na and K levels in the base compartment, a relatively crude (approximately 71% LiOH.H2O) product is produced with a 60% lower Li current efficiency.

[0049] Example 3, Hard Rock (Spodumene) Acid Roasting Leachate: A mass balance overview of processing this material via ED is shown in Figure 6. The acid roasting leachate composition as shown was taken from Bourassa, 2019. Figure 6a shows direct processing using a cation-selective conventional ED membrane. The concentrated leachate is 2.1% Li, with other components as shown. This is a typical sulfuric acid system. Cation-selective conventional ED produces Mg levels of 96 ppm and Ca levels of 263 ppm in the base compartment, which are generally not practical (Figure 6a). After the leachate has softened, the Ca and Mg levels are reduced to 2 ppm and 20 ppm, respectively, as shown in Figure 6c. The base compartment solution is now at an acceptable Mg concentration of 1.2 ppm. However, the Ca concentration of 12 ppm makes this application generally impractical for most purposes. However, by using a Li-selective membrane, a very clean LiOH.H2O product is possible (Figure 6c).

[0050] In addition to the above, additional examples of typical Bolivian and other Chilean brines are provided in Table 1. Application of Li-selective ED proves beneficial in all cases. Lithium-selective membrane electrodialysis on brines or concentrated feeds evaporated by solar or DLE means can open routes to feed brines, direct lithium extraction, and direct lithium hydroxide production from mineral leachates. In certain circumstances (hard rock spodumene excluded), softening of the feed brine is optionally performed prior to application of conventional non-cation-selective ED. However, the product in such cases is relatively crude and may be contaminated with, for example, Na and K hydroxides requiring additional purification. Also, lower lithium current efficiencies result from the recovery of impurity hydroxides.

[0051] Li-selective ED provides an efficient route to direct LiOH production in all major lithium sources, such as South American brines and spodumene, which account for nearly all of today's lithium supply. The systems and methods taught herein are also applicable to other lithium sources, such as hectorite clay, jadarite, Zinnwaldite, etc. This method significantly simplifies the process, reducing capital, operating and reagent costs, resulting in lower production costs. Other advantages include the ability to process feeds that are not significantly concentrated and obtain higher lithium recoveries, since precipitation losses are avoided both in the pond and in the processing plant.

[0052] Table 1. Concentrated LiOH (5%) solution impurity profiles of various realistic brine and hard rock sources processed using the methodology disclosed herein. BPMED used with Li-selective membrane produces the best product. BPMED used on softened feed with cation-selective membrane for anions produces a viable process in most cases, but the product purity is lower. The treated liquids are either concentrated Li-brines from evaporation ponds or leachates from spodumene roasting and leaching. In some cases, the feed liquids also include those after an initial lime-soda softening to remove multivalent cations.

[0053] [Table 1] * Precipitation that makes the process unfeasible. + Although feasible, this is less desirable due to the high amount of impurities in the product that would require rework. Table 1. Concentrated LiOH (5%) solution impurity profiles of various realistic brine and hard rock sources processed using the methodology disclosed herein. BPMED used with Li-selective membrane produces the best product. BPMED used on softened feed with cation-selective membrane for anions produces a viable process in most cases, but the product purity is lower. The treated liquids are either concentrated Li-brines from evaporation ponds or leachates from spodumene roasting and leaching. In some cases, the feed liquids also include those after an initial lime-soda softening to remove multivalent cations.

[0054] References: TIFF2024509488000002.tif213151TIFF2024509488000003.tif140150

Claims

1. 1. A method for producing a LiOH solution from a mixture containing Li and one or more impurities, comprising: (A) providing the mixture to an ED cell containing an ion selective membrane; and (B) applying a potential difference across the ion selective membrane to obtain a separate LiOH solution. Including, the separate LiOH solution contains LiOH, less than about 25 ppm Mg, and less than about 50 ppm Ca; method.

2. 2. The method of claim 1, wherein the LiOH solution contains about 5 ppm to about 25 ppm Mg.

3. 3. The method of claim 1 or claim 2, wherein the LiOH solution contains about 5 ppm to about 50 ppm Ca.

4. 4. The method of any one of claims 1 to 3, wherein the separate LiOH solution comprises about 2% to about 14% LiOH and water.

5. The method of any one of claims 1 to 4, wherein the ion selective membrane is contained within a bipolar membrane electrodialysis cell.

6. 6. The method of any one of claims 1 to 5, wherein the mixture contains lithium in an amount of about 1,000 ppm to about 60,000 ppm.

7. 7. The method of any one of claims 1 to 6, wherein the mixture contains impurity ions selected from the group consisting of monovalent and divalent cations and divalent anions.

8. The method according to any one of claims 1 to 7, wherein the mixture contains impurity ions selected from the group consisting of K ions, Na ions, Mg ions, and Ca ions.

9. The method of claim 8, wherein the impurity ion is K.

10. 9. The method of claim 8, wherein the impurity ion is Na.

11. 9. The method of claim 8, wherein the impurity ion is Mg.

12. 9. The method of claim 8, wherein the impurity ion is Ca.

13. 13. The method of any one of claims 1 to 12, wherein the mixture comprises a ratio of Li / Mg ions greater than about 2.

14. 14. The method of any one of claims 1 to 13, wherein the mixture comprises a ratio of Li / Ca ions greater than about 3.

15. 15. The method of any one of claims 1 to 14, wherein the mixture comprises a ratio of Li / Na ions greater than about 1.

5.

16. 16. The method of any one of claims 1 to 15, wherein the mixture comprises a ratio of Li / K ions greater than about 1.

5.

17. 17. The method of any one of claims 1 to 16, wherein the mixture is a concentrated lithium brine from a process selected from the group consisting of pond evaporation, direct lithium extraction, and leaching of lithium minerals using water, base or acid.

18. 18. The method of claim 17, wherein the mixture is evaporated pond saltwater.

19. 20. The method of claim 17, wherein the mixture comprises rock leachate.

20. 20. The method of claim 17, wherein the mixture is a DLE-produced brine.

21. The method of any one of claims 17 to 20, wherein the mixture has been treated to remove impurities.

22. The method of any one of claims 17 to 20, wherein the mixture is unprocessed.

23. 23. The method of any one of claims 1 to 22, wherein the ion selective membrane is selected from the group consisting of lithium selective membranes, monovalent selective membranes, and cation selective membranes for anions.

24. 24. The method of any one of claims 1 to 23, wherein the ion selective membrane is a lithium selective membrane.

25. 25. The method of any one of claims 1 to 24, wherein the ion selective membrane is a lithium selective membrane having a selectivity in the Li / Mg,Ca range of at least 10.

26. 26. The method of any one of claims 1 to 25, wherein the ion selective membrane is a lithium selective membrane having a selectivity in the Li / Na,K range of at least 3.

27. 27. The method of any one of claims 1 to 26, wherein the ion-selective membrane is a lithium-selective membrane comprising a polymer matrix.

28. 28. The method of any one of claims 1 to 27, wherein the ion-selective membrane is a lithium-selective membrane comprising a polymer matrix and MOF particles dispersed therein.

29. 29. The method of any one of claims 1 to 28, wherein the ion selective membrane is a cation selective membrane for anions and liming or softening is performed prior to feeding the mixture into the ED cell.

30. 30. The method of any one of claims 1 to 29, wherein the process is substantially free of lithium carbonate precursors to LiOH.

31. 31. The method of any one of claims 1 to 30, further comprising precipitating a portion of said mixture as a lithium precipitate prior to feeding said mixture to said ED cell, such that at least a portion of the feed then proceeds through electrodialysis to directly produce LiOH.

32. 32. The method of any one of claims 31, wherein the lithium precipitate comprises a material selected from the group consisting of lithium carbonate, lithium phosphate, and lithium oxalate.

33. The method of any one of claims 1 to 32, further comprising subjecting the lithium hydroxide solution to crystallization to produce lithium hydroxide monohydrate.

34. 34. The method of any one of claims 1 to 33, wherein the lithium hydroxide solution comprises in the range of about 2% to about 14% lithium hydroxide.

35. 35. The method of any one of claims 1 to 34, wherein the lithium hydroxide monohydrate has a purity in the range of greater than 95% to 99.9% by weight.

36. 36. The method of claim 35, wherein the lithium hydroxide monohydrate has a purity in the range of 95% to 99.9% by weight.

37. 37. The method of claims 1-36, further comprising the step of performing boron solvent extraction or ion exchange prior to providing said mixture to said membrane.

38. 38. The method of any one of claims 1 to 37, wherein the mixture is an evaporative concentrate from a series of saltwater ponds, and the method further comprises membrane separation of Mg and recycling the separated Mg to a previous pond for precipitation to produce a lower Mg content feed to the ED cell.

39. 39. The method of any one of claims 1 to 38, wherein the mixture is subjected to liming and softening to remove multivalent ions prior to feeding the mixture to the ED cell.

40. 40. The method of any one of claims 1 to 39, further comprising subjecting the LiOH solution to ion exchange.

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