Process and system for recovering lithium carbonate from a saltwater

Abstract

A process and system for recovering lithium carbonate from a saltwater with an increased yield. Lithium in the saltwater is extracted through a first direct lithium extraction (DLE) process to produce a first lithium recovery solution. A second lithium recovery solution is created by processing a mother liquor generated when producing the first lithium recovery solution using a second DLE process. The second lithium recovery solution is recycled by mixing it with more of the first lithium recovery solution to create a mixed brine. Lithium, in the form of lithium carbonate, is subsequently also extracted from the mixed brine. The additional mother liquor that results from extracting lithium carbonate from the mixed brine may similarly be processed by the second DLE process to create more of the second lithium recovery solution, which can be mixed with more of the first lithium recovery solution, in order to extract additional lithium carbonate.

Description

PROCESS AND SYSTEM FOR RECOVERING LITHIUM CARBONATE FROM ASALTWATERCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority to United States provisional application no. 63 / 609,223, filed on December 12, 2023, and entitled, “Recovering Lithium Carbonate from a Saltwater”, and United States provisional application no. 63 / 552,503, filed on February 12, 2024, and entitled, “Recovering Lithium Carbonate from a Saltwater”, the entireties of both of which are hereby incorporated by reference herein.TECHNICAL FIELD

[0002] The present disclosure relates to systems, processes and techniques for recovering lithium carbonate from a saltwater. More particularly, the present disclosure relates to systems, processes and techniques for recovering lithium carbonate from a saltwater with an increased yield by extracting lithium from a mother liquor waste product that itself resulted from precipitating lithium carbonate.BACKGROUND

[0003] Lithium is a key element of lithium ion batteries, which are used for electric cars and power storage equipment. Although the Earth is abundant in lithium, there are relatively few lithium resources where lithium is found in concentrations sufficient for cost-effective production of lithium products, such as lithium carbonate, which is the core raw materials for cathode active materials of lithium-ion batteries.SUMMARY

[0004] According to a first aspect, there is provided a process for recovering lithium carbonate from a saltwater, the process comprising: applying a first direct lithium extraction (DLE) process to the saltwater to produce a first lithium recovery solution and a first lithium- depleted brine; adding sodium carbonate to the first lithium recovery solution to form a first lithium carbonate solid and a mother liquor; harvesting the first lithium carbonate solid; after the harvesting, applying a second DLE process to the mother liquor to produce a second lithium recovery solution and a salty waste solution; mixing the second lithium recovery solution with the first lithium recovery solution to produce a mixed lithium recovery brine, wherein the firstlithium recovery solution that is mixed with the second lithium recovery solution has not yet been mixed with any of the second lithium recovery solution; mixing the mixed lithium recovery brine with sodium carbonate to form a second lithium carbonate solid and more of the mother liquor; and harvesting the second lithium carbonate solid.

[0005] According to another aspect, there is provided a process for recovering lithium carbonate from a saltwater, the process comprising: applying a first direct lithium extraction (DLE) process along a main flow path to the saltwater to produce a first lithium recovery solution and a first lithium-depleted brine; adding sodium carbonate to the first lithium recovery solution to form a first lithium carbonate solid and a mother liquor; harvesting the first lithium carbonate solid; after the harvesting, applying a second DLE process along a recycle flow path to the mother liquor to produce a second lithium recovery solution and a salty waste solution; mixing the second lithium recovery solution with the first lithium recovery solution to produce a mixed lithium recovery brine at an intersection of the main and recycle flow paths upstream of where the harvesting occurs; mixing the mixed lithium recovery brine with sodium carbonate to form a second lithium carbonate solid and more of the mother liquor; and harvesting the second lithium carbonate solid.

[0006] The process may further comprise: performing hardness removal by causing the first lithium recovery solution to flow through a strong acid cation exchange resin; and regenerating the strong acid cation exchange resin by mixing the salty waste solution with the strong acid cation exchange resin.

[0007] The mixing of the salty waste solution with the strong acid cation exchange resin may be performed continuously.

[0008] The mixing of the salty waste solution with the strong acid cation exchange resin may be controlled by a remotely controlled valve.

[0009] Each of the first and the second DLE processes may be selected from the group consisting of: a selective lithium adsorption process, a selective lithium-ion exchange process, and an electrochemical lithium extraction process.

[0010] The process may further comprise processing the mixed lithium recovery brine through a low-salt-rejection reverse osmosis (LSRRO) unit to a lithium concentration range of 10.0 g / L - 25.0 g / L, the LSRRO comprising an upstream RO module and a downstream RO module fluidly coupled to each other in series, wherein membranes in the downstream RO module have lower salt rejection and higher salt permeation than membranes in the upstream RO module, wherein the downstream RO module receives as at least a portion of feed thereto retentate of the upstream RO module, and wherein the upstream RO module receives at least a portion of feed thereto permeate of the downstream RO membrane.

[0011] The process may further comprise performing reverse osmosis on at least one of the first lithium recovery solution or the mixed lithium recovery brine.

[0012] The first DLE process may be a selective lithium adsorption process and the second DLE process may be an electrochemical lithium extraction process.

[0013] The process may further comprise causing at least one of the first lithium recovery solution or the second lithium recovery solution to flow through at least one of a strong acid cation exchange resin, a weak acid cation exchange resin, or a nanofiltration membrane prior to the mixing the first and second lithium recovery solutions together.

[0014] The process may further comprise causing at least one of the first lithium recovery solution or the second lithium recovery solution to flow through at least one of an aluminum oxide adsorbent, an iron oxide adsorbent, or a zinc oxide adsorbent, prior to the mixing of the first lithium recovery solution with the second lithium recovery solution.

[0015] The process may further comprise causing the first lithium recovery solution to flow through a chemical precipitation unit to remove at least one of calcium, magnesium, or boron prior to being mixed with the second lithium recovery solution.

[0016] The selective lithium adsorption process may comprise contacting at least one of the saltwater or the mother liquor with a lithium alumina intercalate resin.

[0017] The lithium alumina intercalate resin may comprise lithium aluminum layered double hydroxide chloride.

[0018] The selective lithium ion exchange process may comprise contacting at least one of the saltwater or the mother liquor with at least one of manganese oxide-based or titanium oxide-based lithium ion exchange resins.

[0019] Each of the exchange resins may comprise at least one of MnCh OAHiO, Hi.eMni.eC , H4MnsOi2, H2TiO3, or H4Ti50i2.

[0020] The electrochemical lithium extraction process may comprise contacting at least one of the saltwater or the mother liquor with a lithium-deintercalated electrode comprising at least one ofLi1.6Mm 6O4, Li1.33Mm.67O4, T-MnCh. FePO4, LixMmO4, or LixFeO4, where 0 < x < 1.0.

[0021] According to another aspect, there is provided a system for recovering lithium carbonate from a saltwater, the system comprising: a first direct lithium extraction (DLE) unit configured to receive the saltwater and to produce a first lithium recovery solution and a first lithium-depleted brine therefrom; a mixing vessel fluidly coupled to the first DLE unit to receive the first lithium recovery solution therefrom, wherein a first lithium carbonate solid and a mother liquor are formed in the mixing vessel when sodium carbonate is added to the first lithium recovery solution in the mixing vessel; and a second DLE unit fluidly coupled to the mixing vessel, wherein the second DLE unit is configured to receive the mother liquor from the mixing vessel and to produce a second lithium recovery solution and a salty waste solution therefrom, wherein the second DLE unit is fluidly coupled to the first DLE unit such that the first and second lithium recovery solutions are mixed to form a mixed lithium recovery brine for delivery to the mixing vessel for mixing with the sodium carbonate to form a second lithium carbonate solid and more of the mother liquor, and such that the first lithium recovery solution that is mixed with the second lithium recovery solution has not yet been mixed with any of the second lithium recovery solution.

[0022] According to another aspect, there is provided a system for recovering lithium carbonate from a saltwater, the system comprising: a first direct lithium extraction (DLE) unit located along a main flow path and configured to receive the saltwater and to produce a first lithium recovery solution and a first lithium-depleted brine therefrom; a mixing vessel fluidly coupled to the first DLE unit to receive the first lithium recovery solution therefrom, wherein afirst lithium carbonate solid and a mother liquor are formed in the mixing vessel when sodium carbonate is added to the first lithium recovery solution in the mixing vessel; and a second DLE unit located along a recycle flow path and fluidly coupled to the mixing vessel, wherein the second DLE unit is configured to receive the mother liquor from the mixing vessel and to produce a second lithium recovery solution and a salty waste solution therefrom, wherein the main and recycle flow paths are fluidly coupled upstream of the mixing vessel such that the first and second lithium recovery solutions are mixed to form a mixed lithium recovery brine for delivery to the mixing vessel for mixing with the sodium carbonate to form a second lithium carbonate solid and more of the mother liquor.

[0023] The system may further comprise: a strong acid cation exchange resin unit; and a three-way valve fluidly coupling the second DLE unit to the strong acid cation exchange resin unit and to a discharge conduit, wherein the salty waste solution is deliverable to the strong acid cation exchange resin via the three-way valve.

[0024] Each of the first and the second DLE units may be selected from the group consisting of: a selective lithium adsorption unit, a selective lithium ion exchange unit, and an electrochemical lithium extraction unit.

[0025] The system may further comprise a low-salt-rejection reverse osmosis (LSRRO) unit comprising at least an upstream RO module and a downstream RO module fluidly coupled in series, wherein membranes in the downstream RO module have lower salt rejection and higher salt permeation than membranes in the upstream RO module, wherein permeate from the downstream RO module is routed to the upstream RO module as feed for the upstream RO module, and wherein retentate from the upstream RO module is routed to the downstream RO module as feed for the downstream RO module.

[0026] The system may further comprise a reverse osmosis unit fluidly coupled between the mixing vessel and at least one of the first DLE unit or the second DLE unit to perform reverse osmosis on at least one of the first lithium recovery solution or the mixed lithium recovery brine.

[0027] The first DLE unit may be a selective lithium adsorption unit and the second DLE unit may be an electrochemical lithium extraction unit.

[0028] The system may further comprise at least one of a strong acid cation exchange resin unit, a weak acid cation exchange resin unit, or a nanofiltration membrane unit, fluidly coupled to at least one of the first DLE unit to process the first lithium recovery solution, or to the second DLE unit to process the second lithium recovery solution, prior to the first and second lithium recovery solutions being mixed.

[0029] The system may further comprise a silica adsorbent unit fluidly coupled to at least one of the first DLE unit to process the first lithium recovery solution, or to the second DLE unit to process the second lithium recovery solution, prior to the first and second lithium recovery solutions being mixed, wherein the silica adsorbent unit comprises at least one of an aluminum oxide adsorbent, an iron oxide adsorbent, or a zinc oxide adsorbent.

[0030] The system may further comprise a chemical precipitation unit fluidly coupled to the first DLE unit to process the first lithium recovery solution prior to the mixing of the first lithium recovery solution and the second lithium recovery solution.

[0031] One or more of the DLE units may be a lithium alumina intercalate resin unit.

[0032] The lithium alumina intercalate resin may comprise lithium aluminum layered double hydroxide chloride.

[0033] One or more of the DLE units may be one of manganese oxide-based or titanium oxide-based lithium ion exchange resins.

[0034] The ion exchange resin is at least one of Mn02 O.5H2O, H1.6Mn1.6O4, H4MnsOi2, H2TiOi, or H4Ti50i2.

[0035] The electrochemical lithium extraction unit may comprise a lithiumdeintercalated electrode comprising at least one of Li1.6Mn1.6O4, Li1.33Mm.67O4, .-MnO2, FePO4, LixMn2O4, or LixFeO4, where 0 < x < 1.0.

[0036] 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

[0037] Further features and advantages of the present disclosure will become apparent from the following detailed description, taken in combination with the appended drawings, in which:

[0038] FIGS. 1 to 3 are schematic diagrams illustrating first through third embodiments of a lithium recovery system including two integrated direct lithium extraction (“DLE”) units for recovering lithium carbonate with an increased production yield.

[0039] FIG. 4 is a schematic diagram illustrating an example embodiment of a low-salt- rejection reverse osmosis unit used in the lithium recovery system of FIGS. 1 to 3.

[0040] It will be noted that throughout the appended drawings, like features are identified by like reference numerals.DETAILED DESCRIPTION

[0041] As used herein: i) “Saltwater” includes salt lake water, brine, geothermal brine, or waste water from oil or gas production with ionic salt(s) dissolved therein. ii) “Polishing” refers to the removal of unwanted calcium and magnesium to a higher degree than “hardness removal”. “Hardness” in water is a term describing the degree to which the water has dissolved minerals in it such as calcium and magnesium. More specifically, in the embodiments described herein, “hardness removal” may refer to removal of calcium and magnesium such that each is at a concentration of < 100 mg / L, while “polishing” may refer to removal of calcium and magnesium such that each is at a concentration of < 10 mg / L. iii) “Mother liquor” is the liquid that remains after lithium has been substantially recovered through reacting a lithium-containing liquid with sodium carbonate to precipitate lithium as lithium carbonate. Mother liquor is created in great excess of the precipitated lithium carbonate (e.g., about 1.4 - 2.5 g / L of lithium and 70 - 120 g L1of sodium).iv) “Flow path” refers to a pipe or conduit that transports fluid to run in one direction at a time subject to intentional closure or blockage. “Upstream”, in the context of a fluid being transported, refers to the direction from which the flow is coming, and “downstream” refers to the direction to which the flow is going. The flow and / or flow direction can be controlled by gravity and / or pumps.

[0042] Lithium may be found naturally in saltwater. Saltwater typically contains less than 300 mg / L of lithium and an excess of non-lithium dissolved solids, and / or has a mass ratio of lithium content to total dissolved solids content of less than 0.005. In at least some embodiments, there is provided a lithium recovery system comprising two integrated direct lithium extraction (“DLE”) units fluidly coupled on separate flow paths (a “main flow path” and a “recycle flow path”), to recover lithium recursively. In other words, lithium is recovered directly from a saltwater (along the main flow path) and directly from a mother liquor (along the recycle flow path) produced during initial harvesting of lithium from the saltwater along the main flow path, thereby permitting recycling of the mother liquor. This results in an increased overall production yield of lithium, and more particularly lithium carbonate in at least some of the example embodiments described herein. More particularly and as discussed further below, the first DLE unit is fluidly coupled along the main flow path, while the second DLL unit is fluidly coupled along the recycle flow path. The first DLE unit produces a first lithium recovery solution from the saltwater input to the system, and lithium is recovered from the first lithium recovery solution by precipitating out lithium carbonate, which also results in mother liquor. A second lithium recovery solution is then generated by the second DLE unit from the mother liquor, and that second lithium recovery solution is mixed with the first lithium recovery solution to produce a mixed lithium recovery brine, and lithium carbonate is also precipitated out of that brine, which again also produces mother liquor. The mother liquor can be recycled again, resulting in lithium being recovered “recursively”.

[0043] FIG. 1 illustrates, according to one embodiment, a lithium recovery system 100 that recovers lithium from a saltwater. This example system 100 comprises the following: i) A first DLE unit 110 fluidly coupled to conduits 101, 111 and 112 to respectively receive the saltwater, output a first lithium recovery solution, and output a first lithium-depleted brine.ii) A hardness removal unit 117 coupled downstream of the first DLE unit 110 to perform hardness removal on the first lithium recovery solution output by the first DLE unit 110. The hardness removal unit 117 in FIG. 1 may comprise any one or more of a strong acid cation exchange resin, a weak acid cation exchange resin, a nanofiltration membrane, or an ion exchange unit. iii) A silica adsorbent unit 114 fluidly coupled downstream of the first DLE unit 110 to remove silica from the first lithium recovery solution after it has been processed by the hardness removal unit 117. The silica adsorbent unit 114 may comprise any one or more of an aluminum oxide adsorbent, an iron oxide adsorbent, or a zinc oxide adsorbent. The silica adsorbent may be regenerated for reuse, or be disposable. iv) A reverse osmosis (“RO”) unit 120 fluidly coupled to, and downstream of, the silica adsorbent unit 114. The RO unit 120 is used to concentrate a mixed lithium recovery brine, which is generated by mixing the first lithium recovery solution and a second lithium recovery solution output by a second DLE unit 170 along conduit 171, as described below. In some embodiments, the system 100 may further comprise a reverse osmosis unit (RO) 120 downstream of the first DLE unit 110 and upstream of wherein the lithium recovery solutions are mixed together (e g., along conduit 111). v) A concentrator 140 fluidly coupled to, and downstream of, the reverse osmosis unit 120. The concentrator is used to further concentrate the mixed lithium recovery brine. The concentrator 140 may be, for example, a membrane concentrator or an evaporation concentrator. According to some embodiments, the concentrator 140 comprises a low salt rejection reverse osmosis (LSRRO) unit as described in respect of FIG. 4, below. vi) A chelating ion exchange unit 150 fluidly coupled to, and downstream of, the concentrator 140. In some embodiments, the chelating ion exchange unit 150 may be upstream of the concentrator 150. The chelating ion exchange unit 150 removes minerals such as calcium, magnesium and boron from the concentrated mixed lithium recovery brine prior to lithium carbonate precipitation. The chelating ion exchange unit 150 may comprise resins having one or more of iminodiacetic (IDA) functional groups, amino phosphonic (AMP) functional groups, or N-methylglucamine functional groups, each of which is a chelator forcalcium, magnesium and other divalents for IDA and AMP; and boron for N- methylglucamine functional groups. vii) A mixing vessel 160, fluidly coupled to, and downstream of, the chelating ion exchange unit 150. Sodium carbonate is added to one or both of the first lithium recovery solution or the mixed lithium recovery brine in the mixing vessel 160 to result in the precipitation of lithium carbonate and generation of the mother liquor. viii) A second DLE unit 170, fluidly coupled to receive the mother liquor from the mixing vessel 160, and to output the second lithium recovery solution (transferred via conduit 171) to the output of the silica adsorbent unit 114 for subsequent treatment by the reverse osmosis unit 120. The second lithium recovery solution is combined with the output of the silica adsorbent unit 114, which is the first lithium recovery solution after it has been processed by the hardness removal unit 117 and the silica adsorbent unit 114. Mixing the first and second lithium recovery solutions results in the mixed lithium recovery brine. In some embodiments, including as shown in FIG. 1, the second lithium recovery solution in conduit 171 is already very low in silica and hardness and can therefore enter the main flow path immediately upstream of the RO unit 120 (i.e., in conduit 116 in FIG. 1) without having first been processed by the hardness removal unit 117 and / or the silica adsorbent unit 114. In other embodiments, the second lithium recovery solution may be fluidly coupled immediately upstream of the silica-adsorbent unit 114 (i.e., along conduit 113) and / or immediately upstream of the hardness remover 117 (i.e., along conduit 111), for example, or in any other suitable position that results in eventual mixing of the recovery solutions.As a byproduct of generating the second lithium recovery solution, the second DLE unit 170 also outputs a salty waste solution along conduit 172, which can be directed to the hardness removal unit 117 via valve 172 and conduit 174 to regenerate the ion exchange resin in the hardness removal unit 117 when the hardness removal unit 117 comprises an ion exchange unit. For example, in at least some embodiments the salty waste solution 172 is recirculated back to a strong acid cation exchange resin to regenerate it.

[0044] While FIG. 1 depicts all of the foregoing components, in other embodiments (not depicted) the system 100 may comprise fewer components. For example, in at least some other embodiments, the system 100 comprises the first and second DLE units 110, 170 and the mixing vessel 160, and omits the remaining components. In still further embodiments, the system 100 may comprise the first and second DLE units 110, 170 and the mixing vessel 160, and any one or more of the hardness removal unit 117, silica adsorbent unit 114, RO unit 120, concentrator 140, or the chelating ion exchange unit 150.

[0045] The present disclosure is also directed at a process for recovering lithium carbonate from a saltwater. In at least some embodiments, an example process comprises the following: i) Causing the saltwater to flow through the first DLE unit 110 so as to apply a first DLE process to the saltwater to produce the first lithium recovery solution (output along conduit 111 in FIG. 1) and a first lithium-depleted brine (output along conduit 112). ii) Causing the first lithium recovery solution to flow to the mixing vessel 160, and adding sodium carbonate to the mixing vessel 160 to form a first lithium carbonate solid (for discharge along conduit 162) and a mother liquor (for discharge along conduit 161). iii) Harvesting the first lithium carbonate solid along conduit 162. iv) Diverting the mother liquor using conduit 161 to the second DLE unit 170 via the recycle flow path so as to apply a second DLE process to that mother liquor to produce a second lithium recovery solution (discharged along conduit 171) and a salty waste solution (discharged along conduit 172). v) Causing the second lithium recovery solution to flow, along the recycle flow path (via conduit 171), back into the main flow path to produce a mixed lithium recovery brine with an upstream volume of the first lithium recovery solution (i .e., a portion of the first lithium recovery solution that has not yet been mixed with the second lithium recovery solution). vi) Causing the salty waste solution to flow into a hold tank (not depicted) via conduit 162. vii) Causing the mixed lithium recovery brine to flow to the mixing vessel 160, and once in the mixing vessel 160 mixing the mixed lithium recovery brine with sodium carbonate to forma second lithium carbonate solid (harvestable using conduit 162) and more of the mother liquor. viii) Harvesting the second lithium carbonate solid 162 and repeating steps iv) to viii) for any desired number of cycles.

[0046] In at least some additional embodiments, there is provided a system 100 for recovering lithium carbonate from a saltwater, with the system comprising the first DLE unit 110, the mixing vessel 160, and the second DLE unit 170, and with: i) A first conduit comprising conduit 101 in FIG. 1 for flowing the saltwater through the first DLE unit 110 to produce a first lithium recovery solution and a discard solution. ii) A second conduit comprising conduits 111, 113, 116, 131, 141, and 151 in FIG. 1 for conveying the first lithium recovery solution to the mixing vessel 160. The main flow path comprises this second conduit. iii) A third conduit comprising conduit 162 in FIG. 1 for harvesting the lithium carbonate solid from the mixing vessel 160. iv) A fourth conduit comprising conduit 161 for diverting the mother liquor from the mixing vessel 160 after the harvesting to the second DLE unit 170. v) A fifth conduit comprising conduit 171 for conveying a second lithium recovery solution 171 from the second DLE unit 170 back to the second conduit to combine with the first lithium recovery solution. The recycle flow path comprises the fourth and fifth conduits. vi) A sixth conduit comprising conduits 172 and 174, and valve 173 therebetween, for a salty waste solution output by the second DLE unit 170.

[0047] FIGS. 2 and 3 show alternative embodiments of the system 100. The system 100a of FIG. 2 is analogous to the system 100 of FIG. 1, with the hardness removal unit 117 and silica- adsorbent unit 114 removed, and a chemical precipitation unit 130 added to, the main flow path for the first lithium recovery solution as it flows to the mixing vessel 160. The system 100b of FIG. 3 is similar to the system 100b of FIG. 2, except that the second lithium recovery solution isdelivered via conduit 171 immediately upstream of the concentrator 140 as opposed to the RO unit 120.

[0048] More particularly, as shown in FIGS. 2 and 3, the systems 100a and 100b include a reverse osmosis unit (RO) 120 downstream of the first DLE unit 110 to concentrate the first lithium recovery solution, and in the case of the system 100a shown in FIG. 2, the mixed lithium recovery brine. In the embodiments of FIGS. 2 and 3, a chemical precipitation unit 130 is fluidly coupled to and downstream of the RO unit 120. The chemical precipitation unit 130 removes calcium and magnesium impurities in the RO-concentrated first lithium recovery solution (for the system 100b of FIG. 3) or the RO-concentrated mixed lithium recovery brine (for the system 100a of FIG. 2) as shown in FIG. 2. In some embodiments, the concentrator 140 is downstream of the chemical precipitation unit 130, and a chelating ion exchange unit 150 is downstream of the concentrator 140 and upstream of the mixing vessel 160. In other embodiments, the chemical precipitation unit 130 is downstream of the concentrator 140, and is used to further remove calcium, magnesium and boron from the membrane-concentrated mixed lithium recovery brine prior to recovering lithium carbonate. The chemical precipitation unit 130 may be a reactor wherein pH is adjusted with NaOH (or an equivalent) to increase the pH to precipitate out Mg(0H)2 and other metal hydroxides. Silica is also co-precipitated in this process. Na2CCh (or an equivalent) is added to precipitate out divalent cations as carbonate salt.

[0049] As with the system 100 of FIG. 1, any one or more of the RO unit 120, chemical precipitation unit 130, concentrator 140, or chelating ion exchange unit 150 may be omitted from the systems 100a, 100b, in various embodiments.

[0050] Also as with the system 100 of FIG. 1, the second DLE 170 is on the recycle flow path, which sends the second lithium recovery solution upstream (relative to the mixing vessel 160) along the main flow path to permit mixing of the first and second lithium recovery solutions. This increases the efficiency of the overall lithium harvest as compared to mere linking of two DLE units in series.

[0051] As described above, each of the first and second DLE units 110, 170 may include one or more types of a selective lithium adsorption unit, a selective lithium-ion exchange unit, oran electrochemical lithium extraction unit. Each of these different kinds of DLE units 110, 170 is described in further detail below.

[0052] While in some embodiments, the first and second DLE units 110, 170 are the same type of selective lithium adsorption unit, in other embodiments they are different types of units. For example, the first DLE unit 110 may include a selective lithium adsorption unit, and the second DLE unit 170 may include an electrochemical lithium extraction unit. In other embodiments, this order may be reversed.

[0053] A selective lithium adsorption unit includes a lithium alumina sorbent resin which adsorbs lithium from solutions it comes into contact with. Suitable lithium alumina sorbent resins include, but are not limited to, one or more of 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 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 adsorptions. A continuous countercurrent adsorption and desorption process is used in some embodiments when operating a selective lithium adsorption unit; an example continuous countercurrent adsorption and desorption process is described in U.S. Pat. Pub. No. 2019 / 0256368.

[0054] A selective lithium ion exchange unit includes at least one of manganese oxidebased 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 MnCh O.SFbO; Hi.eMni.gCU; LEMmOn; FETiCh or FLTisOi . 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 oxidebased compounds with a polymeric matrix.

[0055] In a selective lithium ion exchange unit, at least one of the manganese oxide-based or titanium oxide-based lithium ion exchange resins are packed into columns or beds into which lithium-containing saltwater is pumped to accomplish selective lithium ion exchange. In some embodiments, the manganese oxide-based and titanium oxide-based lithium-ion exchange resins are first prepared in a lithiated format and then converted into a protonated form through acidification. When the resins in protonated form 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. A continuous countercurrent adsorption and desorption process is used when operating a selective lithium adsorption unit in some embodiments; an example continuous countercurrent adsorption and desorption process is described in U.S. Pat. No. 9,771,632.

[0056] An electrochemical lithium extraction unit comprises a lithium-deintercalated electrode in some embodiments. Suitable lithium-deintercalated electrodes include, but are not limited to, compositions comprising one or more of Li1.6Mn1.6O4, Li1.33Mn167O4, X-MnO?. FePO4, LixMn2O4, or LixFeO4, where 0 < x < 1.0. Example electrochemical lithium extraction units that are used for one or both of the first or second DLE units 110, 170 in some embodiments are described, for example, in PCT Publication Nos. WO 2014 / 047347 and WO 2012 / 065361. During electrochemical lithium extraction, the lithium-deintercalated electrode is coupled with another electrode which can absorb an anion or release a cation to form an electrochemical device. In some embodiments, both electrochemical lithium extraction electrodes may be submerged in saltwater and / or mother liquor, and an anion or cation exchange membrane is positioned in the solution such that any ions originating at one the electrodes must pass through the membrane to reach the other electrode. Thus, the lithium-deintercalated electrode selectively extracts lithium from a saltwater when an electric potential is applied to the coupled electrodes.

[0057] Referring now to FIG. 4, the concentrator 140 depicted therein is a membrane concentrator working on the basis that it will be performing low salt rejection reverse osmosis (LSRRO) for concentrating the mixed lithium recovery brine. As illustrated by FIG. 4, the LSRRO unit 140 comprises an upstream RO module 140a and a downstream RO module 140b fluidly coupled to each other in series so that the downstream RO module 140b receives a brine concentrated through the upstream RO module 140a via conduit 143. The permeate generatedthrough the downstream RO module 140b, whose membranes have lower salt rejection and higher salt passage than membranes in the upstream RO module 140a, is then returned via conduit 144 to the inlet of the upstream RO module 140a. According to one embodiment, the membranes used in the upstream RO module 140a reject > 98% sodium chloride at a test condition of operational pressure of 600 psi and 32,000 mg / L sodium chloride, whereas the downstream RO module 140b rejects < 95% sodium chloride at the same test conditions. According to another embodiment, the membranes used in the upstream RO module 140a are seawater reverse osmosis membranes, or ultrahigh pressure reverse osmosis membranes, and the membranes used in the downstream RO module 140b are nanofiltration membranes or specialty LSSRO membranes.

[0058] As shown in the system of FIG. 1, the system 100 comprises applying the hardness removal unit 117 to the first lithium recovery solution prior to mixing the first lithium recovery solution with the second lithium recovery solution. In this example, the hardness removal unit 117 may comprise a strong acid cation exchange resin, a weak acid cation exchange resin, or a nanofiltration membrane. While not depicted in the systems 100a, 100b of FIG. 2 and 3, those systems 100a, 100b may comprise the hardness removal unit 117 in a manner analogous to that of the system 100 of FIG. 1.

[0059] During operation of the system 100 of FIG. 1, a saltwater is fed via conduit 101 to the system 100 and the first DLE unit 110. The saltwater may have a lithium content of less than 300 mg / L and an impurity content measured as a mass ratio of lithium content to total dissolved solids content of less than 0.005.

[0060] In some embodiments, the saltwater has been subjected to at least one pretreatment process (not depicted) prior to entering conduit 101, such as processing by a gas flotation unit, a sedimentation unit, a media filter, a microfilter, selective contaminant removal or heating / cooling units.

[0061] The lithium in the saltwater is extracted through the first DLE unit 110, producing the first lithium recovery solution and the first lithium-depleted brine. The first lithium-depleted brine comprises water and impurities from the saltwater and is discharged via conduit 112. The first lithium recovery solution is directed via conduit 111 to the hardness removal unit 117, and in embodiments that include the silica adsorbent unit 114 via conduit 113 to the silica adsorbent unit114. The hardness and silica removal processes also produce a hardness waste and a silica waste, which are discharged via conduits 102 and 115, respectively. The first lithium recovery solution is mixed with a second lithium recovery solution to form a mixed lithium recovery brine comprising the first lithium recovery solution and the second lithium recovery solution. In some embodiments, such as in FIG. 1, the mixing occurs, and accordingly the lithium recovery brine is generated, upstream of the silica removal unit 114 and accordingly directed through the silica removal unit 114 and then via conduit 116 to the RO unit 120, producing an RO-concentrated mixed lithium recovery brine (conduit 131) and an RO permeate. The RO permeate is discharged via the exit conduit indicated at 122. In one embodiment, the RO permeate may be directed to inputs of either or both of the first and the second DLE units 110, 170 as make-up water.

[0062] The RO-concentrated mixed lithium recovery brine may be directed via conduit 131 to the concentrator 140 for further concentration. Lithium content in the mixed lithium recovery brine after the concentrator 140 is about 10.0 g / L - 25.0 g / L. The concentrator 140 also produces a water waste product discharged via conduit 142.

[0063] The RO-concentrated mixed lithium recovery brine may then be directed to a chelating ion exchange (IX) unit 150 to polish any remaining calcium, magnesium, or boron from the solution, producing an IX-polished mixed lithium recovery brine, which is directed via conduit 151 to the mixing vessel 160, which acts as a lithium carbonate reactor. Lithium in the IX-polished mixed lithium recovery brine is converted into lithium carbonate by the addition of sodium carbonate (Na2COs) in this same vessel 160, with mixing. Lithium carbonate solids are discharged via conduit 162 and collected for harvest. The lithium carbonate precipitation waste in the form of the mother liquor is then directed via conduit 161 to the second DLE unit 170 (as in FIG. 1). The second DLE unit 170 extracts residual lithium from the mother liquor and produces the second lithium recovery solution 171. The second lithium recovery solution is then directed via conduit 171 to be mixed with the first lithium recovery solution 116 to form the mixed lithium recovery brine. A second DLE 170 also produces a second lithium-depleted brine discharged via conduits 172, 174 and control valve 173. In at least some conventional methods, this would have been a waste product; in contrast, in the presently disclosed embodiments, the control valve 173 controls the volume of high-quality sodium chloride being sent back to the hardness remover 117 to regenerate it.

[0064] In one embodiment as shown in the system 100a of FIG. 2, the first lithium recovery solution (conduit 111) and second lithium solution (conduit 171) are mixed to form the mixed lithium recovery brine, which goes through the reverse osmosis (RO) unit 120 to produce an RO- concentrated mixed lithium recovery brine and an RO permeate (conduit 122). The RO permeate is discharged via conduit 122, and out of the system 100a. Alternatively, the reverse osmosis permeate may be directed to inputs of either or both of the first and the second DLE units 110, 170 for recycling. The RO-concentrated mixed lithium recovery brine may be directed via conduit 121 to the chemical precipitation unit 130. Any calcium and / or magnesium impurities in the RO- concentrated mixed lithium recovery brine is removed by the chemical precipitation unit 130 to produce a solids sludge discharged via conduit 132 out of the system 100a, and a purified mixed lithium recovery brine moving along conduit 131. The purified mixed lithium recovery brine is directed via conduit 131 to the membrane concentrator of the concentrator 140 to concentrate lithium in the purified mixed lithium recovery brine to the range of 10.0 g / L - 25.0 g / L. The concentrator 140 also produces a permeate discharged via conduit 142 out of the system 100a. In some embodiments, the LSRRO-concentrated mixed lithium recovery brine is directed to the chelating ion exchange unit 150 to polish one or more of calcium, magnesium or boron out of the LSRRO-concentrated mixed lithium recovery brine to produce an IX-polished mixed lithium recovery brine, which is directed via conduit 151 to the mixing vessel 160, which acts as a lithium carbonate reactor. In the mixing vessel 160, the mixed lithium recovery brine is converted into lithium carbonate by reacting it with sodium carbonate (NazCO,), which is added to the mixed lithium recovery brine within the mixing vessel 160. Lithium carbonate solids are discharged via conduit 162 out of the system 100a. The lithium carbonate precipitation mother liquor is directed via conduit 161 to the second DLE unit 170. The second DLE unit 170 extracts lithium from the mother liquor and produces the second lithium recovery solution directed (conduit 171), which is mixed in some embodiments with the first lithium recovery solution and a second lithium-depleted brine discharged out the system 100a via conduit 172.

[0065] The system 100b of FIG. 3 is a variant of the system 100a of FIG. 2. In FIG. 3, the second lithium recovery solution is mixed with the first lithium recovery solution to form the mixed lithium recovery brine just upstream of the LSRRO unit 140. The first lithium recovery solution is concentrated through the RO unit 120 to produce an RO-concentrated first lithium recovery solution, which is then purified by removing one or more of calcium and magnesiumimpurities in the chemical precipitation unit 130 to produce a purified first lithium recovery solution. The purified first lithium recovery solution is mixed with the second lithium recovery solution to form mixed lithium recovery brine, which is fed to the low-salt-rejection reverse osmosis (LSRRO) 140 to concentrate the lithium in the mixed lithium recovery brine to a concentration of about of 10.0 g / L - 25.0 g / L.Example 1

[0066] A double DLE process with a recursive flow path was demonstrated for lithium recovery and results compared to a single pass DLE process previously used. Table 1 contains results for the single pass DLE process, and Table 2 contains results of the double DLE process according to an example embodiment.Table 1. LizCCh Recovery Single PassTable 2. LizCCh Recovery According to an Example EmbodimentThere is a 25% increase in overall lithium yield by weight as a result of this example embodiment.

[0067] In this disclosure the recitation of numerical ranges by endpoints includes all numbers subsumed within that range including all whole numbers, all integers and all fractional intermediates (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5 etc.). In this disclosure the singular forms an "an", and "the" include plural referents unless the content clearly dictates otherwise. Thus, for example, reference to a composition containing "a compound" includes a mixture of two or more compounds.

[0068] The terminology used herein is for the purpose of describing particular embodiments only 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 clearly indicates otherwise (e.g., a reference in the claims to “a unit” or “the unit” does not exclude embodiments in which multiple units are used). 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. Embodiments which comprise or may comprise a specified feature or variable or parameter, alternative embodiments may consist, or consist essentially of such features, or variables or parameters. 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. Similarly, if the first device is communicatively connected to the second device, communication may be through a direct connection or through an indirect connection via other devices and connections.

[0069] Use of language such as "at least one of X, Y, and Z," "at least one of X, Y, or Z," "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.

[0070] 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.

[0071] While example embodiments have been described above and illustrated in the accompanying drawings, it will be evident to those skilled in the art that modifications may be made without departing from this disclosure. Such modifications are considered as possible variants comprised in the scope of the disclosure.

Claims

CLAIMS1. A process for recovering lithium carbonate from a saltwater, the process comprising: applying a first direct lithium extraction (DLE) process along a main flow path to the saltwater to produce a first lithium recovery solution and a first lithium-depleted brine; adding sodium carbonate to the first lithium recovery solution to form a first lithium carbonate solid and a mother liquor; harvesting the first lithium carbonate solid; after the harvesting, applying a second DLE process along a recycle flow path to the mother liquor to produce a second lithium recovery solution and a salty waste solution; mixing the second lithium recovery solution with the first lithium recovery solution to produce a mixed lithium recovery brine at an intersection of the main and recycle flow paths upstream of where the harvesting occurs; mixing the mixed lithium recovery brine with sodium carbonate to form a second lithium carbonate solid and more of the mother liquor; and harvesting the second lithium carbonate solid.

2. The process of claim 1, further comprising: performing hardness removal by causing the first lithium recovery solution to flow through a strong acid cation exchange resin; and regenerating the strong acid cation exchange resin by mixing the salty waste solution with the strong acid cation exchange resin.

3. The process of claim 2, wherein the mixing of the salty waste solution with the strong acid cation exchange resin is performed continuously.

4. The process of claim 2 or 3, wherein the mixing of the salty waste solution with the strong acid cation exchange resin is controlled by a remotely controlled valve.

5. The process of any one of claims 1 to 3 wherein each of the first and the second DLE processes is selected from the group consisting of: a selective lithium adsorption process, a selective lithium-ion exchange process, and an electrochemical lithium extraction process.

6. The process of any one of claims 1 to 3, further comprising processing the mixed lithium recovery brine through a low-salt-rejection reverse osmosis (LSRRO) unit to a lithium concentration range of 10.0 g / L - 25.0 g / L, the LSRRO comprising an upstream RO module and a downstream RO module fluidly coupled to each other in series, wherein membranes in the downstream RO module have lower salt rejection and higher salt permeation than membranes in the upstream RO module, wherein the downstream RO module receives as at least a portion of feed thereto retentate of the upstream RO module, and wherein the upstream RO module receives at least a portion of feed thereto permeate of the downstream RO membrane.

7. The process of any one of claims 1 to 6, further comprising performing reverse osmosis on at least one of the first lithium recovery solution or the mixed lithium recovery brine.

8. The process of claim 5, wherein the first DLE process is a selective lithium adsorption process and the second DLE process is an electrochemical lithium extraction process.

9. The process of any one of claims 1 to 8, further comprising causing at least one of the first lithium recovery solution or the second lithium recovery solution to flow through at least one of a strong acid cation exchange resin, a weak acid cation exchange resin, or a nanofiltration membrane prior to the mixing the first and second lithium recovery solutions together.

10. The process of any one of claims 1 to 9, further comprising causing at least one of the first lithium recovery solution or the second lithium recovery solution to flow through at least one of an aluminum oxide adsorbent, an iron oxide adsorbent, or a zinc oxide adsorbent, prior to the mixing of the first lithium recovery solution with the second lithium recovery solution.

11. The process of any one of claims 1 to 10, further comprising causing the first lithium recovery solution to flow through a chemical precipitation unit to remove at least one of calcium, magnesium, or boron prior to being mixed with the second lithium recovery solution.

12. The process of claim 5, wherein the selective lithium adsorption process comprises contacting at least one of the saltwater or the mother liquor with a lithium alumina intercalate resin.

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

14. The process of claim 5, wherein the selective lithium ion exchange process comprises contacting at least one of the saltwater or the mother liquor with at least one of manganese oxidebased or titanium oxide-based lithium ion exchange resins.

15. The process of claim 14, wherein each of the exchange resins comprises at least one of MnO2'0.5H2O, H1.eMn1.6O4, H4MnjOi2, H2TiOa, or H4TisOi2.

16. The process of claim 5, wherein the electrochemical lithium extraction process comprises contacting at least one of the saltwater or the mother liquor with a lithium-deintercalated electrode comprising at least one of i16Mn1 eO4, Li1.33Mn1.67O4, X-MnO2, FePO4, LixMn2O4, or LixFeO4, where 0 < x < 1.0.

17. A system for recovering lithium carbonate from a saltwater, the system comprising: a first direct lithium extraction (DLE) unit located along a main flow path and configured to receive the saltwater and to produce a first lithium recovery solution and a first lithium- depleted brine therefrom; a mixing vessel fluidly coupled to the first DLE unit to receive the first lithium recovery solution therefrom, wherein a first lithium carbonate solid and a mother liquor are formed in the mixing vessel when sodium carbonate is added to the first lithium recovery solution in the mixing vessel; and a second DLE unit located along a recycle flow path and fluidly coupled to the mixing vessel, wherein the second DLE unit is configured to receive the mother liquor from the mixing vessel and to produce a second lithium recovery solution and a salty waste solution therefrom, wherein the main and recycle flow paths are fluidly coupled upstream of the mixing vessel suchthat the first and second lithium recovery solutions are mixed to form a mixed lithium recovery brine for delivery to the mixing vessel for mixing with the sodium carbonate to form a second lithium carbonate solid and more of the mother liquor.

18. The system of claim 17, further comprising: a strong acid cation exchange resin unit; and a three-way valve fluidly coupling the second DLE unit to the strong acid cation exchange resin unit and to a discharge conduit, wherein the salty waste solution is deliverable to the strong acid cation exchange resin via the three-way valve.

19. The system of claim 17 or 18, wherein each of the first and the second DLE units is selected from the group consisting of: a selective lithium adsorption unit, a selective lithium ion exchange unit, and an electrochemical lithium extraction unit.

20. The system of any one of claims 17 to 19, further comprising a low-salt-rejection reverse osmosis (LSRRO) unit comprising at least an upstream RO module and a downstream RO module fluidly coupled in series, wherein membranes in the downstream RO module have lower salt rejection and higher salt permeation than membranes in the upstream RO module, wherein permeate from the downstream RO module is routed to the upstream RO module as feed for the upstream RO module, and wherein retentate from the upstream RO module is routed to the downstream RO module as feed for the downstream RO module.

21. The system of any one of claims 17 to 20, further comprising a reverse osmosis unit fluidly coupled between the mixing vessel and at least one of the first DLE unit or the second DLE unit to perform reverse osmosis on at least one of the first lithium recovery solution or the mixed lithium recovery brine.

22. The system of claim 19, wherein the first DLE unit is a selective lithium adsorption unit and the second DLE unit is an electrochemical lithium extraction unit.

23. The system of any one of claims 17 to 22, further comprising at least one of a strong acid cation exchange resin unit, a weak acid cation exchange resin unit, or a nanofiltration membrane unit, fluidly coupled to at least one of the first DLE unit to process the first lithium recovery solution, or to the second DLE unit to process the second lithium recovery solution, prior to the first and second lithium recovery solutions being mixed.

24. The system of any one of claims 17 to 23, further comprising a silica adsorbent unit fluidly coupled to at least one of the first DLE unit to process the first lithium recovery solution, or to the second DLE unit to process the second lithium recovery solution, prior to the first and second lithium recovery solutions being mixed, wherein the silica adsorbent unit comprises at least one of an aluminum oxide adsorbent, an iron oxide adsorbent, or a zinc oxide adsorbent.

25. The system of any one of claims 17 to 24, further comprising a chemical precipitation unit fluidly coupled to the first DLE unit to process the first lithium recovery solution prior to the mixing of the first lithium recovery solution and the second lithium recovery solution.

26. The system of claim 19, wherein one or more of the DLE units is a lithium alumina intercalate resin unit.

27. The system of claim 26, wherein the lithium alumina intercalate resin comprises lithium aluminum layered double hydroxide chloride.

28. The system of claim 19, wherein one or more of the DLE units is manganese oxide-based or titanium oxide-based lithium ion exchange resins.

29. The system of claim 28, wherein the ion exchange resin is at least one of MnCE O.5H2O, H1.6Mn1.6O4, H4Mn50i2, FLTiOi, or H4TisOi2.

30. The system of claim 19, wherein the electrochemical lithium extraction unit comprises a lithium-deintercalated electrode comprising at least one ofLi1.6Mn1.6O4, Lii.33Mni.67O4, -MnO2, FePO4, LixMn2O4, or LixFeO4, where 0 < x < 1.0.

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