System and process for recovering a lithium compound from a saltwater

Abstract

A process for recovering a lithium compound from a saltwater. Lithium in the saltwater is extracted through a first direct lithium extraction process to produce a lithium recovery solution containing boron, magnesium, and calcium impurities. The lithium recovery solution is purified through softening and nanofiltration to reduce those impurities, thereby reducing calcium and magnesium hardness, and to produce a boron-depleted lithium recovery solution and a boron-rich brine. The boron-depleted lithium recovery solution is concentrated using a brine concentrator such as a low-salt-rejection reverse osmosis unit to produce a concentrated lithium solution with lithium concentration in the range of 10.0 g / L – 25.0 g / L.

Description

SYSTEM AND PROCESS FOR RECOVERING A LITHIUM COMPOUND FROM A SALTWATERCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority to United States provisional patent application no. 63 / 555,700, filed on February 20, 2024, and entitled, “System and Process for Recovering and Purifying a Lithium Chloride Solution”, and to United States provisional patent application no. 63 / 644,712, filed on May 9, 2024, and entitled, “System and Process for Recovering a Lithium Compound”, the entireties of which are hereby incorporated by reference herein.TECHNICAL FIELD

[0002] The present disclosure relates to systems, processes and techniques for recovering a lithium compound from a saltwater.BACKGROUND

[0003] Lithium is a crucial component of lithium ion batteries, which are employed in electric vehicles and power storage systems. Natural resources containing lithium include saltwaters from various sources, such as salt lakes, geothermal brines, and produced water resulting from oil / gas production. Most of these saltwaters are considered low-grade lithium resources due to their low lithium concentrations (e g., less than 300 mg / L) and high impurity levels (e.g., a mass ratio of lithium content to total dissolved solids content of not more than 0.005). Direct lithium extraction (DLE), a process that selectively extracts dissolved lithium out of saltwater while leaving impurities behind, has been explored to recover lithium from these low- grade lithium-containing saltwaters.SUMMARY

[0004] According to a first aspect, there is provided a process for recovering a lithium compound from a saltwater, the process comprising: extracting lithium from a lithium-extraction stream comprising the saltwater by applying a first direct lithium extraction process to the lithium- extraction stream to produce a lithium recovery solution, the lithium recovery solution comprising boron, magnesium and calcium impurities, wherein the first direct lithium extraction process comprises at least one of a selective lithium adsorption process, a selective lithium-ion exchangeprocess, or an electrochemical lithium extraction process; removing at least some of the magnesium and calcium from the lithium recovery solution to produce a softened lithium recovery solution comprising a calcium concentration of 50 mg / L or lower; and removing at least some of the boron from the softened lithium recovery solution by applying a boron removal nanofiltration process to produce a boron-depleted lithium recovery solution and a boron-rich brine, wherein the boron removal nanofiltration process comprises: adjusting pH of a first nanofiltration feed comprising the softened lithium recovery solution to a pH range of 8.5 - 11; and subjecting the first nanofiltration feed to a first nanofiltration to produce a first nanofiltration permeate and a first nanofiltration retentate as the boron-rich brine.

[0005] The boron removal nanofiltration process may further comprise: subjecting a second nanofiltration feed comprising the first nanofiltration permeate to a second nanofiltration to produce a second nanofiltration retentate and a second nanofiltration permeate; and recycling the second nanofiltration retentate as at least a part of the first nanofiltration feed.

[0006] The boron removal nanofiltration process may further comprise: subjecting the second nanofiltration permeate to a third nanofiltration to produce a third nanofiltration retentate and a third nanofiltration permeate; and recycling the third nanofiltration retentate as at least a part of the second nanofiltration feed.

[0007] The removing of at least some of the magnesium and calcium impurities may be through at least one of chemical softening, nanofiltration softening, or ion exchange softening.

[0008] The process may further comprise recycling the boron-rich brine as at least a part of the lithium-extraction stream comprising the saltwater.

[0009] The process may further comprise concentrating the boron-depleted lithium recovery solution using low- salt-rejection reverse osmosis to produce a concentrated boron- depleted lithium solution with a lithium concentration in the range of 10.0 g / L - 25.0 g / L.

[0010] The process may further comprise polishing the concentrated boron-depleted lithium solution using a chelating ion exchange resin comprising at least one of iminodiacetic functional groups, amino phosphonic functional groups, or N-Methylglucamine functional groups.

[0011] The process may further comprise converting the lithium in the polished concentrated lithium solution to produce lithium carbonate and a blowdown liquor.

[0012] The process may further comprise extracting the lithium by applying a second direct lithium extraction process to produce a lithium-rich blowdown liquor and a lithium-depleted blowdown liquor, and the second direct lithium extraction process may comprise at least one of a selective lithium adsorption process, a selective lithium-ion exchange process, or an electrochemical lithium extraction process.

[0013] The removing of magnesium and calcium impurities may be performed using ion exchange softening, and the process may further comprise regenerating resins used for the ion exchange softening using the lithium-depleted blowdown liquor.

[0014] The selective lithium adsorption process may comprise contacting the saltwater with a lithium alumina intercalate resin.

[0015] The lithium alumina intercalate resin may comprise lithium aluminum layered double hydroxide chloride.

[0016] The process may further comprise concentrating the lithium recovery solution using reverse osmosis after the first direct lithium extraction process and prior to the removing of at least some of the magnesium and calcium impurities.

[0017] The boron-depleted lithium recovery solution may have a boron concentration of100 mg / L of less.

[0018] According to another aspect, there is provided a system for recovering a lithium compound from a saltwater, the system comprising: a first direct lithium extraction unit for receiving the saltwater and configured to extract lithium from the saltwater to produce a lithium recovery solution comprising boron, magnesium, and calcium impurities, wherein the first direct lithium extraction unit comprises at least one of a selective lithium adsorption unit, a selective lithium ion exchange unit, or an electrochemical lithium extraction unit; a magnesium and calcium hardness reducing unit fluidly coupled to the first direct lithium extraction unit and configured to reduce magnesium and calcium hardness in the lithium recovery solution to produce a softenedlithium recovery solution comprising a calcium concentration of 50 mg / L or less; a nanofiltration assembly configured to remove boron from the softened lithium recovery solution to produce a boron-depleted lithium recovery solution and a boron-rich brine, wherein the nanofiltration assembly comprises: a pH adjustment unit fluidly coupled to the magnesium and calcium hardness reducing unit and configured to adjust pH of a first nanofiltration feed comprising the softened lithium recovery solution to a pH range of 8.5 - 11; and a first nanofiltration unit fluidly coupled to the pH adjustment unit and configured to separate the first nanofiltration feed once within the pH range of 8.5 - 11 into a first nanofiltration permeate as the boron-depleted lithium recovery solution, and a first nanofiltration retentate as the boron-rich brine.

[0019] The first nanofiltration unit may be fluidly coupled to the first direct lithium extraction unit to recycle the boron-rich brine as at least a part of the lithium-extraction stream comprising the saltwater.

[0020] The system may further comprise a low-salt-rej ection reverse osmosis unit fluidly coupled to the first nanofiltration unit to concentrate the boron-depleted lithium recovery solution to produce a concentrated boron-depleted lithium solution with a lithium concentration in the range of 10.0 g / L - 25.0 g / L.

[0021] The system may further comprise: a chelating ion exchange unit comprising a resin that comprises at least one of iminodiacetic functional groups, amino phosphonic functional groups, or N-Methylglucamine functional groups, and the chelating ion exchange unit may be fluidly coupled to the low-salt-rejection reverse osmosis unit to polish the concentrated boron- depleted lithium solution; and a lithium carbonate reactor fluidly coupled to the chelating ion exchange unit and configured to convert the polished concentrated boron-depleted lithium solution into lithium carbonate and a blowdown liquor.

[0022] The system may further comprise a second direct lithium extraction unit fluidly coupled to the lithium carbonate reactor and configured to produce a lithium-rich blowdown liquor and a lithium-depleted blowdown liquor from the blowdown liquor.

[0023] The magnesium and calcium hardness reducing unit may comprise an ion exchange softening unit, and the second direct lithium extraction unit may be fluidly coupled tothe ion exchange softening unit to direct the lithium-depleted blowdown liquor to the ion exchange softening unit to regenerate resins therein.

[0024] This summary does not necessarily describe the entire scope of all aspects. Other aspects, features and advantages will be apparent to those of ordinary skill in the art upon review of the following description of specific embodiments.BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In the accompanying drawings, which illustrate one or more example embodiments:

[0026] FIGS 1A and IB are schematic diagrams illustrating lithium recovery systems for recovering a lithium compound, according to example embodiments.

[0027] FIG. 2 is a schematic diagram illustrating a low-salt-rejection reverse osmosis unit used for concentrating a lithium compound solution in the systems of FIGS. 1A and IB.

[0028] For the sake of clarity, not every component is labeled, nor is every component of each embodiment shown where illustration is unnecessary to allow those of ordinary skill in the art to understand the embodiments described herein.DETAILED DESCRIPTION

[0029] Depending on the selectivity of DLE units for lithium over other impurities, a lithium recovery solution generated using DLE units may still contain impurities such as dissolved boron, calcium and magnesium; this may result in the lithium recovery solution having a relatively high boron concentration, and relatively high calcium and magnesium hardness levels. In such instances, further purification is required prior to converting the recovered lithium into a final product. In at least some of the example embodiments disclosed herein, a lithium recovery solution generated from a DLE unit undergoes purification through softening and nanofiltration to remove at least some such boron, calcium, and magnesium purities, thereby reducing the calcium and magnesium hardness levels and boron impurities. The purified lithium recovery solution is subsequently concentrated through a low-salt-rejection reverse osmosis (LSRRO) process to obtain a concentrated lithium chloride solution.

[0030] Referring now to FIG. 1A, there is depicted an example embodiment of a system 100a to recover a lithium compound from a saltwater. The system 100a comprises: i) a first direct lithium extraction unit 110 configured to extract lithium from the saltwater to produce a lithium recovery solution comprising boron, magnesium and calcium impurities, wherein the first direct lithium extraction unit comprises at least one of a selective lithium adsorption unit, a selective lithium ion exchange unit, or an electrochemical lithium extraction unit; ii) a magnesium and calcium hardness reducing unit 130 fluidly coupled to the first direct lithium extraction unit 110 and configured to reduce the magnesium and calcium hardness in the lithium recovery solution (i.e., to reduce the magnesium and calcium impurities in the solution) to produce a softened lithium recovery solution comprising a calcium concentration of 50 mg / L or less; and iii) a nanofiltration assembly 140 fluidly configured to remove boron from the softened lithium recovery solution to produce a b or on-depl eted lithium recovery solution and a boron-rich brine, wherein the nanofiltration assembly 140 comprises: a) a pH adjustment unit 141 fluidly coupled to the magnesium and calcium hardness reducing unit 130 and configured to adjust pH of a first nanofiltration feed comprising the softened lithium recovery solution to a pH range of 8.5 - 11; and b) a first nanofiltration unit 143 fluidly coupled to the pH adjustment unit 141 and configured to separate the first nanofiltration feed once within the above pH range into a first nanofiltration permeate as the boron-depleted lithium recovery solution, and a first nanofiltration retentate as the boron-rich brine.

[0031] According to at least some embodiments, the nanofiltration assembly 140 may further comprise a second nanofiltration unit 147 fluidly coupled in series to the first nanofiltration unit 143 and configured to separate a second nanofiltration feed comprising the first nanofiltration permeate to produce a second nanofiltration retentate and a second nanofiltration permeate; and a conduit 146 fluidly coupled to the second nanofiltration unit 147 and to recycle the second nanofiltration retentate as a part of the first nanofiltration feed. The nanofiltration assembly 140 may further comprise a third nanofiltration unit (not shown in FIG. 1) fluidly coupled to the second nanofiltration unit 147 and configured to separate the second nanofiltration permeate into a third nanofiltration retentate and a third nanofiltration permeate, and a conduit (not shown in FIG. 1)fluidly coupling the second nanofiltration unit 147 and the third nanofiltration unit to recycle the third nanofiltration retentate as at least a portion of the second nanofiltration feed.

[0032] As shown in FIG. 1 A, the system 100a may further comprise a first reverse osmosis unit 120 downstream of the first direct lithium extraction unit 110 and upstream of the hardness reducing unit 130, which is configured to concentrate the lithium recovery solution from the direct lithium extraction unit 110; a second reverse osmosis unit 150 downstream of the nanofiltration assembly 140 to concentrate the boron-depleted lithium recovery solution; a brine concentrator 160 downstream of the second reverse osmosis unit 150 to further concentrate the boron-depleted lithium recovery solution to produce a concentrated lithium compound solution; a chelating ion exchange unit 170 downstream of the brine concentrator 160 to polish the concentrated lithium compound solution and to produce a purified lithium compound solution; and a lithium carbonate reactor 180 downstream of the chelating ion exchange unit 170 and configured to convert the lithium compound into lithium carbonate product. The brine concentrator 160 may comprise a LSRRO unit, as described further below in respect of FIG. 2. Additionally or alternatively, the brine concentrator 160 may comprise any one or more of ultra-high pressure reverse osmosis unit operated at a pressure of more than 1,200 psi, an osmotically assisted reverse osmosis unit, or an evaporator.

[0033] In embodiments in which the first DLE unit 110 comprises a selective lithium adsorption unit, the selective lithium adsorption unit may comprise a lithium alumina sorbent resin that is put into contact with the saltwater and that, through that contact, adsorbs lithium from the saltwater onto the resin. The adsorbed lithium is then eluted from the resin as the lithium recovery solution using fresh water or a diluted lithium chloride solution. Suitable lithium alumina sorbent resins include, but are not limited to, resins comprising hydrated alumina or lithium aluminum layered double hydroxide chloride. Example preparation processes of the lithium alumina sorbent resins are described, for example, in U.S. Pat. Nos. 4,348,295; 4,461,714; 6,280,693; and 8,753,594. A lithium alumina sorbent resin may be prepared through incorporating one or both of hydrated alumina or lithium aluminum layered double hydroxide chloride with at least one of an ion exchange resin, a zeolite or a polymeric binder. The lithium alumina sorbent resins are packed into columns or beds into which saltwater comprising lithium is pumped to facilitate selective lithium adsorption. A continuous countercurrent adsorption and desorption process may be usedwhen operating a selective lithium adsorption unit; an example continuous countercurrent adsorption and desorption process is described in U.S. Pat. Pub. No. 2019 / 0256368.

[0034] In embodiments in which the first DLE unit 110 comprises a selective lithium ion exchange unit, the selective lithium ion exchange unit may comprise at least one of manganese oxide-based or titanium oxide-based lithium ion exchange resins. Suitable manganese oxide-based and titanium oxide-based lithium ion exchange resins include, but are not limited to, resins comprising at least one of MnCh O.SFhO, H1.6Mm.6O4, HjMmOn, ^TiOs or lUTisOn. Example preparation processes of manganese oxide-based and titanium oxide-based lithium ion exchange resins are described, for example, in U.S. Pat. Nos. 6,764,584 and 10,150,056. The manganese oxide-based resin may be prepared by incorporating manganese oxide-based compounds with a polymeric matrix, and the titanium oxide-based lithium ion exchange resin may be prepared by incorporating titanium oxide-based compounds with a polymeric matrix. At least one of the manganese oxide-based or titanium oxide-based lithium ion exchange resins are packed into columns or beds into which saltwater comprising lithium is pumped to facilitate selective lithium ion exchange. The manganese oxide-based and titanium oxide-based lithium ion exchange resins may be first prepared in a lithiated format and then be converted into a proton format through acid treatment. When the resins in proton format are contacted with a saltwater, lithium in the saltwater selectively exchanges with protons so that lithium adsorbs onto the resin and protons are released from the resin into the saltwater. The adsorbed lithium is then eluted from the resin as the lithium recovery solution using an acid solution (e.g. a hydrochloric acid solution). A continuous countercurrent adsorption and desorption process may be used when operating a selective lithium adsorption unit; an example continuous countercurrent adsorption and desorption process is described in U.S. Pat. No. 9,771,632.

[0035] In embodiments in which the first DLE unit 110 comprises an electrochemical lithium extraction unit, the electrochemical lithium extraction unit may comprise a lithiumdeintercalated electrode. Suitable lithium-deintercalated electrodes include, but are not limited to, compositions comprising at least one of Li1.6Mn1 eO4, Lii.33Mni.67O4 -MnO2, FePO4, LixMn2O4, or LixFeO4, where 0 < x < 1.0. Example electrochemical lithium extraction units that may be used for the first direct lithium extraction unit 110 are described, for example, in International Pat. Pub. Nos. WO 2014 / 047347, and WO 2012 / 065361. During electrochemical lithium extraction, thelithium-deintercalated electrode is coupled with another electrode that can adsorb an anion or release a cation to form an electrochemical device. In some embodiments of electrochemical lithium extraction, both electrodes may be submerged in a solution comprising lithium, and an anion or cation exchange membrane may be positioned in the solution such that any ions originating at one the electrodes need to pass through the membrane in order to reach the other electrode. The lithium-deintercalated electrode selectively extracts lithium from the saltwater when a potential is applied to the coupled electrodes.

[0036] The hardness removal unit 130 may comprise at least one of a chemical or nanofiltration membrane softening unit 131, or an ion exchange softening unit 134. The chemical softening unit 131 may comprise a base addition unit (not shown in FIG. 1) to reduce magnesium hardness and a sodium carbonate addition unit (not shown in FIG. 1) to reduce calcium hardness. The ion exchange softening unit 134 may comprise a strong acid cation exchange resin, a weak acid cation exchange resin, and a resin comprising one of iminodiacetic functional groups, amino phosphonic functional groups.

[0037] For example, the nanofiltration membrane softening unit 131 may be structurally similar to a reverse osmosis unit, except with a nanofiltration membrane specifically designed to reject calcium and magnesium ions so that the permeate has a lower hardness than the retentate. More particularly, example membranes may comprise polymer thin films and be sourced, for example, from DuPont de Nemours, Inc. or Hydronautics - a Nitto Group Company. Similarly, the base addition unit may comprise a base dosing tank with a pump to meter in base (such as NaOH or lime) and controlled via pH to precipitate out magnesium from the solution, thereby reducing magnesium hardness. The sodium carbonate addition unit may comprise a chemical storage tank to hold the sodium carbonate in either solid or liquid form, and suitable transfer equipment (e.g., a pump or solids dosing equipment) to add the sodium carbonate to the solution to precipitate out calcium, thereby reducing calcium hardness.

[0038] Additionally, according to at least some embodiments: i) the system 100a may further comprise a conduit 145 fluidly coupling the first nanofiltration unit 143 and the first direct lithium extraction unit 110 to recycle the boron-rich brine such that it is mixed with the saltwater fed to the direct lithium extraction unit 110;ii) as described in more detail in respect of FIG. 2 below, the brine concentrator unit 160 may comprise a LSRRO unit; and / or iii) the chelating ion exchange unit 170 may comprise resins having iminodiacetic functional groups, amino phosphonic functional groups, or N-Methylglucamine functional groups.

[0039] Referring again to FIG. 1 A, according to at least some embodiments a process for recovering a lithium compound from the saltwater may comprise: i) extracting lithium from the saltwater by applying a first direct lithium extraction process to produce a lithium recovery solution comprising boron, magnesium and calcium impurities, wherein the first direct lithium extraction process comprises at least one of a selective lithium adsorption process, a selective lithium ion exchange process, or an electrochemical lithium extraction process; ii) reducing magnesium and calcium hardness in the lithium recovery solution to produce a softened lithium recovery solution comprising a calcium content of 50 mg / L or less; and iii) removing boron from the softened lithium recovery solution by applying a boron nanofiltration process to produce a boron-depleted lithium recovery solution and a boron-rich brine, wherein the boron nanofiltration process comprises: a) adjusting pH of a first nanofiltration feed comprising the softened lithium recovery solution to a pH range of 8.5 - 11; and b) subjecting the first nanofiltration feed to a first nanofiltration to produce a first nanofiltration permeate and a first nanofiltration retentate as the boron-rich brine.

[0040] The boron nanofiltration process may further comprise subjecting a second nanofiltration feed comprising the first nanofiltration permeate to a second nanofiltration to produce a second nanofiltration retentate and a second nanofiltration permeate; and recycling the second nanofiltration retentate as at least a part of the first nanofiltration feed. The boron nanofiltration process may further comprise subjecting the second nanofiltration permeate to a third nanofiltration to produce a third nanofiltration retentate and a third nanofiltration permeate such that the third nanofiltration permeate becomes the boron-depleted lithium recovery solution when the boron concentration in the third nanofiltration permeate is 100 mg / L or less; and recycling the third nanofiltration retentate as at least a part of the second nanofiltration feed. Moregenerally, nanofiltration may be performed until the boron content in the permeate resulting from the boron nanofiltration process is 100 mg / L or less, regardless of whether one, two, three, or more nanofiltrations are required to achieve this target.

[0041] Additionally, according to at least some embodiments: i) the process may further comprise recycling the boron-rich brine by mixing it with the saltwater fed to the first direct lithium extraction process; ii) the process may further comprise concentrating the lithium recovery solution using reverse osmosis after the lithium recovery solution is generated using the first direct lithium extraction process and prior to reducing magnesium and calcium hardness of the lithium recovery solution; and / or iii) the removing of magnesium and calcium hardness may be performed through any one or more of a chemical softening, nanofiltration membrane softening or ion exchange softening.

[0042] During operation of the lithium recovery system 100a, the saltwater is fed via conduit 101 to the system 100 and the first direct lithium extraction unit 110. The saltwater may be a salt lake brine, a geothermal brine, or a produced water resulting from oil / gas production, for example. The saltwater has a lithium content of less than 300 mg / L and a relatively high impurity level, with a mass ratio of lithium content to total dissolved solids content of not more than 0.005. The saltwater may be pretreated using at least one pretreatment unit (not shown in FIG. 1 A), such as a gas flotation unit, a sedimentation unit, a media filter, a microfilter, or heating / cooling units. Lithium in the saltwater is extracted by the first direct lithium extraction unit 110, producing the lithium recovery solution and the lithium-depleted brine. The lithium-depleted brine comprises the water and impurities from the saltwater and is discharged via conduit 112 out of the system 100. The lithium recovery solution is directed via conduit 111 to the first reverse osmosis unit 120, which concentrates the lithium recovery solution to produce a permeate discharged via conduit 122 and a concentrate directed via conduit 121 to the hardness reducing unit 130. Magnesium and calcium hardness in the lithium recovery solution are reduced by the magnesium and calcium hardness reducing unit 130. More particularly, as shown in FIG. 1A the magnesium and chemicalhardness reducing unit 130 comprises a chemical or nanofiltration membrane softening unit 131, and then by an ion exchange softening unit 134 fluidly coupled in series with the chemical or nanofiltration membrane softening unit 131. A chemical softening unit may comprise, for example, reactor tank(s), a base addition unit to dose solution with base (e.g., NaOH) to precipitate out magnesium, thereby reducing magnesium hardness; and a sodium carbonate addition unit to add sodium carbonate to the solution to precipitate out calcium, thereby reducing calcium hardness. During chemical softening, magnesium hardness is reduced by reacting the lithium recovery solution with a base (e.g. a sodium hydroxide solution) to precipitate magnesium hydroxide. Silica in the lithium recovery solution may be removed together with magnesium hydroxide precipitates. Calcium hardness is reduced by reacting the lithium recovery solution with a sodium carbonate solution to precipitate calcium carbonate. Alternatively, magnesium and calcium hardness may be removed using a nanofiltration membrane. The lithium recovery solution after the softening unit 131 is directed via conduit 133 to the ion exchange softening unit 134, where the hardness may be further reduced. The ion exchange softening unit 134 may comprise columns with resins selected to bind to divalent ions such as calcium and magnesium and exchange a monovalent cation. The calcium and magnesium impurities are discharged via conduits 132 and 135 out of the system 100a. The softened lithium recovery solution contains a calcium content of 50 mg / L or less, which is beneficial for the subsequent boron removal performed using the nanofiltration assembly 140 to reduce the risk of possible calcium borate scaling.

[0043] The softened lithium recovery solution is directed via conduit 136 to the nanofiltration assembly 140, which is used for boron removal. The nanofiltration assembly 140 cannot remove boron species efficiently in the softened lithium recovery solution when boron is in the form of boric acid. Accordingly, the boron in the softened lithium recovery solution is converted from boric acid to polyborates by controlling the pH of the softened lithium recovery solution fed to the nanofiltration assembly 140 to be within a range of 8.5 - 11, inclusive of endpoints. A pH control unit 141 adds a base or an acid through conduit 142 to the first nanofiltration feed, which comprises the softened lithium recovery solution and the second nanofiltration retentate. The pH control unit 141 may comprise, for example, an online pH measurement device and a doser that adds acid (e.g., HC1) or a base (e.g., NaOH) in response to the measured and the targeted pH. The first nanofiltration unit 143 rejects 40 - 60% of the boron in the first nanofiltration feed at a pH range of 8.5 - 11 to produce the first nanofiltration retentateas the boron-rich brine, which is recycled by mixing it with the saltwater fed to the direct lithium extraction unit 110. At least a portion of the boron in the boron-rich brine is rejected by the first direct lithium extraction unit 110 and discharged together with other impurities from the saltwater via conduit 112 out of the system 100a. The second nanofiltration feed comprising the first nanofiltration permeate is directed via conduit 145 to the second nanofiltration unit 147 for further boron removal. In at least some embodiments, the second nanofiltration permeate discharged by the second nanofiltration unit 147 has a boron concentration of 100 mg / L or less, following which it is subsequently treated as the boron-depleted lithium recovery solution. As mentioned above, nanofiltrations may be performed until the boron concentration reaches 100 mg / L or less, or another desired boron concentration target.

[0044] The boron-depleted lithium recovery solution is directed via conduit 148 to the second reverse osmosis unit 150, which concentrates the boron-depleted lithium recovery solution and produces a concentrated boron-depleted lithium recovery solution and an RO permeate. The RO permeate is discharged via conduit 152. The concentrated boron-depleted lithium recovery solution is directed via conduit 151 to the brine concentrator 160. The brine concentrator 160 further concentrates lithium in the lithium recovery solution to a concentration range of 10.0 g / L - 25.0 g / L (inclusive of endpoints). The brine concentrator 160 also produces a permeate discharged via conduit 162. The concentrated lithium recovery solution from the brine concentrator 160 is directed via conduit 161 to the chelating ion exchange unit 170 to further remove calcium, magnesium, and / or boron, producing a purified and concentrated lithium brine. The impurities removed by the chelating ion exchange unit 170 are discharged via conduit 172. The purified and concentrated lithium solution is directed via conduct 171 to the lithium carbonate reactor 180, where lithium reacts with sodium carbonate to produce a lithium carbonate product and a mother liquor blowdown. The lithium carbonate product is discharged via conduit 183, and the mother liquor blowdown is recycled via conduit 181 to be mixed with the saltwater fed to the direct lithium extraction unit 110. An acid (e.g. hydrochloric acid) may be used to neutralize the carbonate in the mother liquor blowdown before it is mixed with the saltwater.

[0045] FIG. IB illustrates, according to an example embodiment, another system 100b to recover a lithium compound from a saltwater. The system 100b is analogously constructed as the system 100a of FIG. 1A, and relative to the system 100a of FIG. 1A further comprises a seconddirect lithium extraction unit 182 to recover lithium from the mother liquor blowdown. The second direct lithium extraction unit 182 outputs a lithium-rich blowdown solution and a lithium-depleted blowdown solution. The lithium-rich blowdown solution is mixed with the boron-depleted lithium recovery solution from the nanofdtration assembly 140 used for boron removal and this mixture is fed to the second reverse osmosis 150 for further lithium purification. The lithium-depleted blowdown solution is rich in sodium chloride and is directed via conduct 183 to the ion exchange softening unit 134 to regenerate its resins. Like the first direct lithium extraction unit 110, the second direct lithium extraction unit 182 may comprise any of a selective lithium adsorption unit, a selective lithium ion exchange unit, or an electrochemical lithium extraction unit.

[0046] FIG. 2 illustrates, according to another example embodiment, the brine concentrator 160 as a LSRRO assembly for concentrating the lithium recovery brine to result in a concentrated lithium chloride solution with a lithium concentration in a range of 10.0 g / L - 25.0 g / L (inclusive of endpoints). The LSRRO assembly 160 comprises at least an upstream RO module 160a and a downstream RO module 160b fluidly coupled in series so that the downstream RO module 160b receives a brine concentrated by the upstream RO module 160a via conduit 163 and a permeate generated by the downstream RO module 160b is returned via conduit 164 to the inlet of the upstream RO module 160a, in which membranes in the downstream RO module 160b have a lower salt rejection rate and a higher salt passage rate than membranes in the RO module 160a. The membrane of the upstream RO module 160a has at least a 95% rejection rate for sodium chloride under testing conditions of 32,000 mg / L sodium chloride solution as the input to the first RO module 160a, an operation pressure of 800 psi, an operation temperature of 25 °C, and 10% permeate recovery. The membrane of the downstream RO module 160b has a 30% to 75% rejection rate for sodium chloride under testing conditions of 100,000 mg / L sodium chloride solution as the feed water, an operation pressure of 1,000 psi, an operation temperature of 25 °C, and 10% permeate recovery. As another example, the membranes used in the RO module 160a may be seawater reverse osmosis membranes and the membranes used in the membrane module 160b may be nanofiltration membranes.

[0047] The terminology used herein is only for the purpose of describing particular embodiments and is not intended to be limiting. Accordingly, as used herein, the singular forms “a”, “an”, and “the” are intended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms “comprises” and “comprising”, when used in this specification, specify the presence of one or more stated features, integers, steps, operations, elements, and components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and groups. Directional terms such as “top”, “bottom”, “upwards”, “downwards”, “vertically”, and “laterally” are used in the following description for the purpose of providing relative reference only, and are not intended to suggest any limitations on how any article is to be positioned during use, or to be mounted in an assembly or relative to an environment. Additionally, the term “connect” and variants of it such as “connected”, “connects”, and “connecting” as used in this description are intended to include indirect and direct connections unless otherwise indicated. For example, if a first device is connected to a second device, that coupling may be through a direct connection or through an indirect connection via other devices and connections.

[0048] Use of language such as "at least one of X, Y, and Z," "at least one of X, Y, orZ," "at least one or more of X, Y, and Z," "at least one or more of X, Y, and / or Z," or "at least one of X, Y, and / or Z," is intended to be inclusive of both a single item (e.g., just X, or just Y, or just Z) and multiple items (e g., {X and Y}, {X and Z}, {Y and Z}, or {X, Y, and Z }). The phrase "at least one of' and similar phrases are not intended to convey a requirement that each possible item must be present, although each possible item may be present. The term "or" is generally employed in its sense including "and / or" unless the content clearly dictates otherwise.

[0049] As used herein, unless the context indicates otherwise a reference to a parameter being “about” or “approximately” a particular value means that parameter is within 10% of that value.

[0050] It is contemplated that any part of any aspect or embodiment discussed in this specification can be implemented or combined with any part of any other aspect or embodiment discussed in this specification, so long as such implementation or combination is not performed using mutually exclusive parts.

[0051] One or more example embodiments have been described by way of illustration only. This description is presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the form disclosed. It will be apparent to persons skilled in the artthat a number of variations and modifications can be made without departing from the scope of the claims.

Claims

CLAIMS1. A process for recovering a lithium compound from a saltwater, the process comprising: i) extracting lithium from a lithium-extraction stream comprising the saltwater by applying a first direct lithium extraction process to the lithium-extraction stream to produce a lithium recovery solution, the lithium recovery solution comprising boron, magnesium and calcium impurities, wherein the first direct lithium extraction process comprises at least one of a selective lithium adsorption process, a selective lithium-ion exchange process, or an electrochemical lithium extraction process; ii) removing at least some of the magnesium and calcium from the lithium recovery solution to produce a softened lithium recovery solution comprising a calcium concentration of 50 mg / L or lower; and iii) removing at least some of the boron from the softened lithium recovery solution by applying a boron removal nanofiltration process to produce a boron-depleted lithium recovery solution and a boron-rich brine, wherein the boron removal nanofiltration process comprises: a) adjusting pH of a first nanofiltration feed comprising the softened lithium recovery solution to a pH range of 8.5 - 11; and b) subjecting the first nanofiltration feed to a first nanofiltration to produce a first nanofiltration permeate and a first nanofiltration retentate as the boron-rich brine.

2. The process of claim 1, wherein the boron removal nanofiltration process further comprises: i) subjecting a second nanofiltration feed comprising the first nanofiltration permeate to a second nanofiltration to produce a second nanofiltration retentate and a second nanofiltration permeate; and ii) recycling the second nanofiltration retentate as at least a part of the first nanofiltration feed.

3. The process of claim 2, wherein the boron removal nanofiltration process further comprises: i) subjecting the second nanofiltration permeate to a third nanofiltration to produce a third nanofiltration retentate and a third nanofiltration permeate; andii) recycling the third nanofiltration retentate as at least a part of the second nanofiltration feed.

4. The process of any one of claims 1 to 3, wherein the removing of at least some of the magnesium and calcium impurities is through at least one of chemical softening, nanofiltration softening, or ion exchange softening.

5. The process of claim 1, further comprising recycling the boron-rich brine as at least a part of the lithium-extraction stream comprising the saltwater.

6. The process of any one of claims 1 to 5, further comprising concentrating the boron-depleted lithium recovery solution using low-salt-rejection reverse osmosis to produce a concentrated boron-depleted lithium solution with a lithium concentration in the range of 10.0 g / L - 25.0 g / L-7. The process of claim 6, further comprising polishing the concentrated boron-depleted lithium solution using a chelating ion exchange resin comprising at least one of iminodiacetic functional groups, amino phosphonic functional groups, or N-Methylglucamine functional groups.

8. The process of claim 7, further comprising converting the lithium in the polished concentrated lithium solution to produce lithium carbonate and a blowdown liquor.

9. The process of claim 8, further comprising extracting the lithium by applying a second direct lithium extraction process to produce a lithium-rich blowdown liquor and a lithium-depleted blowdown liquor, wherein the second direct lithium extraction process comprises at least one of a selective lithium adsorption process, a selective lithium-ion exchange process, or an electrochemical lithium extraction process.

10. The process of claim 9, wherein the removing of magnesium and calcium impurities is performed using ion exchange softening, and wherein the process further comprises regenerating resins used for the ion exchange softening using the lithium-depleted blowdown liquor.

11. The process of any one of claims 1 to 10, wherein the selective lithium adsorption process comprises contacting the saltwater with a lithium alumina intercalate resin.

12. The process of claim 11, wherein the lithium alumina intercalate resin comprises lithium aluminum layered double hydroxide chloride.

13. The process of any one of claims 1 to 12, further comprising concentrating the lithium recovery solution using reverse osmosis after the first direct lithium extraction process and prior to the removing of at least some of the magnesium and calcium impurities.

14. The process of claim 1, wherein the boron-depleted lithium recovery solution has a boron concentration of 100 mg / L of less.

15. A system for recovering a lithium compound from a saltwater, the system comprising: i) a first direct lithium extraction unit for receiving the saltwater and configured to extract lithium from the saltwater to produce a lithium recovery solution comprising boron, magnesium, and calcium impurities, wherein the first direct lithium extraction unit comprises at least one of a selective lithium adsorption unit, a selective lithium ion exchange unit, or an electrochemical lithium extraction unit; ii) a magnesium and calcium hardness reducing unit fluidly coupled to the first direct lithium extraction unit and configured to reduce magnesium and calcium hardness in the lithium recovery solution to produce a softened lithium recovery solution comprising a calcium concentration of 50 mg / L or less; iii) a nanofiltration assembly configured to remove boron from the softened lithium recovery solution to produce a boron-depleted lithium recovery solution and a boron-rich brine, wherein the nanofiltration assembly comprises:(a) a pH adjustment unit fluidly coupled to the magnesium and calcium hardness reducing unit and configured to adjust pH of a first nanofiltration feed comprising the softened lithium recovery solution to a pH range of 8.5 - 11; and(b) a first nanofiltration unit fluidly coupled to the pH adjustment unit and configured to separate the first nanofiltration feed once within the pH range of 8.5 - 11 into a first nanofiltration permeate as the boron-depleted lithium recovery solution, and a first nanofiltration retentate as the boron-rich brine.

16. The system of claim 15, wherein the first nanofiltration unit is fluidly coupled to the first direct lithium extraction unit to recycle the boron-rich brine as at least a part of the lithium-extraction stream comprising the saltwater.

17. The system of claim 16, further comprising a low-salt-rejection reverse osmosis unit fluidly coupled to the first nanofiltration unit to concentrate the boron-depleted lithium recovery solution to produce a concentrated boron-depleted lithium solution with a lithium concentration in the range of 10.0 g / L - 25.0 g / L.

18. The system of claim 17, further comprising: i) a chelating ion exchange unit comprising a resin that comprises at least one of iminodiacetic functional groups, amino phosphonic functional groups, or N-Methylglucamine functional groups, wherein the chelating ion exchange unit is fluidly coupled to the low-salt-rejection reverse osmosis unit to polish the concentrated boron-depleted lithium solution; and ii) a lithium carbonate reactor fluidly coupled to the chelating ion exchange unit and configured to convert the polished concentrated boron-depleted lithium solution into lithium carbonate and a blowdown liquor.

19. The system of claim 18, further comprising a second direct lithium extraction unit fluidly coupled to the lithium carbonate reactor and configured to produce a lithium-rich blowdown liquor and a lithium-depleted blowdown liquor from the blowdown liquor.

20. The system of claim 19, wherein the magnesium and calcium hardness reducing unit comprises an ion exchange softening unit, and wherein the second direct lithium extraction unit is fluidly coupled to the ion exchange softening unit to direct the lithium-depleted blowdown liquor to the ion exchange softening unit to regenerate resins therein.