Process and system for preparing lithium carbonate with energy recovery

Abstract

Processes and systems for preparing lithium carbonate with energy recovery. Various fluid streams are directed to one or more energy recovery devices to improve energy efficiency and system performance during lithium carbonate production. Lithium in a saltwater is extracted by applying direct lithium extraction to produce a lithium recovery solution. The lithium recovery solution is concentrated by a membrane concentrator and heated, and chelating ion exchange is used to purify the heated lithium recovery solution by removing multivalent cations and / or boron from it. The concentrated and purified lithium recovery solution is then reacted with sodium carbonate at a temperature of at least 70 °C to produce a lithium carbonate slurry, which is separated into lithium carbonate solids and a mother liquor. Prior to purification, the concentrated lithium recovery solution is heated using heat from at least one of the unconcentrated lithium recovery solution or the mother liquor.

Description

PROCESS AND SYSTEM FOR PREPARING LITHIUM CARBONATE WITH ENERGY RECOVERYCROSS-REFERENCE TO RELATED APPLICATION

[0001] The present application claims priority to United States provisional application no. 63 / 625,554 filed on January 26, 2024, and entitled “Process and System for Lithium Carbonate with Energy Recovery”, the entirety of which is hereby incorporated by reference herein.TECHNICAL FIELD

[0002] The present disclosure relates to systems, processes, and techniques for preparing lithium carbonate while recovering energy. More particularly, the present disclosure relates to systems and processes for producing lithium carbonate involving direct lithium extraction, membrane concentration, chelating ion exchange, lithium carbonate conversion and energy recovery.BACKGROUND

[0003] Lithium carbonate is a core ingredient for making cathode active materials of lithium-ion batteries. The demand for lithium carbonate increases as the market for lithium-ion batteries grows due to decarbonization efforts being undertaken in certain key industries. Lithium carbonate is generally produced through reacting sodium carbonate with a purified lithium solution, which is recovered from primary lithium resources, such as lithium-containing saltwaters and lithium ores. Lithium-containing saltwaters contain lithium and other impurities such as sodium, potassium, calcium, magnesium, chloride, and sulfate ions. Existing methods for extracting lithium from lithium-containing saltwaters include solar evaporation and direct lithium extraction (DLE). Solar evaporation involves pumping a lithium-containing saltwater into large solar ponds, where water is evaporated and impurities (e.g., salts) are crystallized out of the lithium-containing saltwater to produce a concentrated and purified lithium solution. Solar evaporation processes have mainly been deployed in South America for lithium-containing saltwaters with a high lithium concentration (e.g., > 600 mg / L lithium) and a high purity (e.g., a lithium content to total dissolved solids content ratio [Li / TDS ratio] > 0.005). DLE includes processes such as selective lithium adsorption, selective lithium ion exchange, and electrochemical lithium extraction that selectively recover lithium from a lithium-containing saltwater whileleaving behind water and most of the impurities dissolved in the saltwater. DLE can recover lithium from a low-grade lithium saltwater having a lithium content less than 300 mg / L and a high proportion of impurities, with Li / TDS ratio of not more than 0.005.SUMMARY

[0004] According to a first aspect, there is provided a process for preparing lithium carbonate, the process comprising: extracting lithium from a saltwater through applying direct lithium extraction to produce a lithium recovery solution and a lithium-depleted brine; concentrating the lithium recovery solution using a membrane concentrator to produce a concentrated lithium recovery solution; heating the concentrated lithium recovery solution to produce a heated lithium recovery solution; removing, through chelating ion exchange, multivalent cations and / or boron from the heated lithium recovery solution to form a purified lithium recovery solution; reacting the purified lithium recovery solution with sodium carbonate at a temperature of at least 70 °C to produce a lithium carbonate slurry; and separating the lithium carbonate slurry into lithium carbonate solids and a mother liquor, wherein the heating of the concentrated lithium recovery solution is performed by transferring heat from at least one of the lithium recovery solution or the mother liquor to the concentrated lithium recovery solution.

[0005] The process may further comprise washing the separated lithium carbonate solids with a washing water at a temperature of at least 50 °C to produce washed lithium carbonate solids and a washing discharge.

[0006] The process may further comprise heating the washing water before the washing of the separated lithium carbonate solids.

[0007] The heating of the washing water may comprise flowing the washing water through a first portion of a washing-water heat exchanger and the washing discharge through a second portion of the washing-water heat exchanger.

[0008] The process may further comprise cooling the saltwater to less than 70 °C before extracting the lithium through applying the direct lithium extraction.

[0009] The cooling may comprise flowing the saltwater through a first portion of a feedingsaltwater heat exchanger and the lithium-depleted brine through a second portion of the feedingsaltwater heat exchanger.

[0010] The separating and the washing of the lithium carbonate solids may be performed with a peeler centrifuge and / or a pusher centrifuge.

[0011] The direct lithium extraction may comprise contacting the saltwater with a lithium alumina intercalate resin to extract the lithium from the saltwater and onto the lithium alumina intercalate resin.

[0012] The direct lithium extraction may comprise eluting the extracted lithium from the lithium alumina intercalate resin using an elution water to produce the lithium recovery solution.

[0013] The process may further comprise heating the elution water to at least 40 °C before eluting the extracted lithium.

[0014] The elution water may be heated to about 70 °C before eluting the extracted lithium.

[0015] The heating of the elution water may comprise flowing the elution water through a first portion of an elution water heat exchanger and the lithium-depleted brine through a second portion of the elution water heat exchanger.

[0016] The heating may comprise transferring heat from only one of the lithium recovery solution or the mother liquor to the concentrated lithium recovery solution.

[0017] The concentrated lithium recovery solution may be heated to at least 40 °C.

[0018] According to another aspect, there is provided a system for preparing lithium carbonate, the system comprising: a direct lithium extraction unit configured to extract lithium from a saltwater to produce a lithium recovery solution and a lithium-depleted brine; a membrane concentrator fluidly coupled to the direct lithium extraction unit and configured to concentrate the lithium recovery solution to produce a concentrated lithium recovery solution; at least one concentrated lithium recovery solution heat exchanger fluidly coupled to the membrane concentrator and configured to heat the concentrated lithium recovery solution to produce a heatedlithium recovery solution; a chelating ion exchange unit fluidly coupled to the concentrated lithium recovery solution heat exchanger and configured to remove multivalent cations and / or boron from the heated lithium recovery solution to produce a purified lithium recovery solution; a reactor unit fluidly coupled to the chelating ion exchange unit for reacting the purified lithium recovery solution with sodium carbonate at a temperature of at least 70 °C to produce a lithium carbonate slurry; and a solids-liquid separation unit fluidly coupled to the reactor unit and configured to receive and separate the lithium carbonate slurry into lithium carbonate solids and a mother liquor, wherein the membrane concentrator is thermally coupled through the at least one concentrated lithium recovery solution heat exchanger to at least one of the direct lithium extraction unit or the solids-liquid separation unit so that heat is transferred from at least one of the lithium recovery solution or the mother liquor to the concentrated lithium recovery solution through the at least one concentrated lithium recovery solution heat exchanger.

[0019] The system may further comprise a washing-water heat exchanger fluidly coupled to the solids-liquid separation unit to receive and heat a washing water that is used to wash lithium carbonate solids within the solids-liquid separation unit to produce a washing discharge. The washing-water heat exchanger may have first and second portions configured to receive the washing water through the first portion and the washing discharge through the second portion so that heat in the washing discharge is transferred to the washing water through the washing-water heat exchanger.

[0020] The system may further comprise a feeding-saltwater heat exchanger fluidly coupled to the direct lithium extraction unit to cool the saltwater directed to the direct lithium extraction unit. The feeding-saltwater heat exchanger may have first and second portions configured to receive the saltwater through the first portion and the lithium-depleted brine through the second portion so that heat in the saltwater is transferred to the lithium-depleted brine through the feeding-saltwater heat exchanger.

[0021] The system may further comprise an elution water heat exchanger fluidly coupled to the direct lithium extraction unit to heat an elution water that is used to elute lithium from the direct lithium extraction unit. The elution-water heat exchanger may have first and second portions configured to receive the elution water through the first portion and the lithium-depleted brinethrough the second portion so that heat in the lithium-depleted brine is transferred to the elution water.

[0022] The direct lithium extraction unit may comprise lithium alumina intercalate resin.

[0023] The solids-liquid separation unit may comprise a peeler centrifuge and / or a pusher centrifuge.

[0024] The membrane concentrator may be thermally coupled through the at least one concentrated lithium recovery solution heat exchanger to either of the direct lithium extraction unit or the solids-liquid separation unit such that heat is transferred from either the lithium recovery solution or the mother liquor to the concentrated lithium recovery solution.

[0025] The membrane concentrator may be thermally coupled through the at least one concentrated lithium recovery solution heat exchanger to both of the direct lithium extraction unit and the solids-liquid separation unit such that heat is sequentially transferred from both of the lithium recovery solution and the mother liquor to the concentrated lithium recovery solution.

[0026] The concentrated lithium recovery solution heat exchanger may be configured to heat the concentrated lithium recovery solution to at least 40 °C.

[0027] According to another aspect, there is provided a process for preparing lithium carbonate, the process comprising: extracting lithium from a saltwater through applying direct lithium extraction to produce a lithium recovery solution and a lithium-depleted brine; concentrating the lithium recovery solution using a membrane concentrator to produce a concentrated lithium recovery solution; heating the concentrated lithium recovery solution to produce a heated lithium recovery solution; removing, through chelating ion exchange, at least one of multivalent cations or boron from the heated lithium recovery solution to form a purified lithium recovery solution; reacting the purified lithium recovery solution with sodium carbonate at a temperature of at least 70°C to produce a lithium carbonate slurry; and separating the lithium carbonate slurry into lithium carbonate solids and a mother liquor; wherein the heating of the concentrated lithium recovery solution comprises flowing the concentrated lithium recovery solution through a first portion of a concentrated-brine heat exchanger and one of the lithiumrecovery solution from direct lithium extraction or the mother liquor through the second portion of the concentrated-brine heat exchanger.

[0028] According to another aspect, there is provided a system for preparing lithium carbonate, the system comprising: a direct lithium extraction unit configured to extract lithium from a saltwater to produce a lithium recovery solution and a lithium-depleted brine; a membrane concentrator fluidly coupled to the direct lithium extraction unit and configured to concentrate the lithium recovery solution to produce a concentrated lithium recovery solution; a concentrated lithium recovery solution heat exchanger fluidly coupled to the membrane concentrator and configured to heat the concentrated lithium recovery solution to produce a heated lithium recovery solution; a chelating ion exchange unit fluidly coupled to the first heat exchanger and configured to remove at least one of multivalent cations or boron from the heated lithium recovery solution to produce a purified lithium recovery solution; a reactor unit fluidly coupled to the chelating ion exchange unit for reacting the purified lithium recovery solution with sodium carbonate at a temperature of at least 70°C to produce a lithium carbonate slurry; and a solids-liquid separation unit fluidly coupled to the reactor unit and configured to receive and separate the lithium carbonate slurry into lithium carbonate solids and a mother liquor; wherein the membrane concentrator is thermally coupled through the concentrated-brine heat exchanger to at least one of the direct lithium extraction unit or the solids-liquid separation unit so that the concentrated-lithium recovery solution heat exchanger heats the concentrated lithium recovery solution through flowing the concentrated lithium recovery solution through a first portion of the concentrated-brine heat exchanger and one of the lithium recovery solution or the mother liquor through the second portion of the concentrated-brine heat exchanger.

[0029] 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

[0030] In the accompanying drawings, which illustrate one or more example embodiments:

[0031] FIGS. 1 to 3 are schematic diagrams illustrating systems for preparing lithium carbonate, according to example embodiments.

[0032] 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

[0033] Depending on the selectivity of the particular DLE process used for lithium over other ion impurities, a lithium recovery solution generated by applying DLE may contain significant amounts of impurities that require further purification and refining treatments before converting the recovered lithium into lithium carbonate. The purification and refining treatments consume heat energy, increasing the production cost for the lithium carbonate. The example embodiments disclosed herein provide systems and methods to prepare lithium carbonate while also performing energy recovery. Various embodiments are directed to features such as directing various fluids to one or more energy recovery devices, such as heat exchangers, to improve energy efficiency and system performance.

[0034] FIG. 1 illustrates, according to one example embodiment, a system 100 for preparing lithium carbonate. The system 100 comprises: i) a direct lithium extraction unit 110 configured to extract lithium from a saltwater received through a conduit 103 to produce a lithium recovery solution and a lithium-depleted brine; ii) a membrane concentrator 120 fluidly coupled to the direct lithium extraction unit 110 and configured to concentrate the lithium recovery solution to produce a concentrated lithium recovery solution; iii) a concentrated lithium recovery solution heat exchanger 130 fluidly coupled to the membrane concentrator 120 and configured to heat the concentrated lithium recovery solution to produce a heated lithium recovery solution; iv) a chelating ion exchange unit 140 fluidly coupled to the concentrated lithium recovery solution heat exchanger 130 and configured to remove at least one of multivalent cations or boron from the heated lithium recovery solution to produce a purified lithium recovery solution;v) a reactor unit 150 fluidly coupled to the chelating ion exchange unit 140 for reacting the purified lithium recovery solution with sodium carbonate at a temperature of at least 70 °C to produce a lithium carbonate slurry; and vi) a solids-liquid separation unit 160 fluidly coupled to the reactor unit 150 and configured to receive and separate the lithium carbonate slurry into lithium carbonate solids and a mother liquor.

[0035] The membrane concentrator 120 is thermally coupled through the concentrated lithium recovery solution heat exchanger 130 to the solids-liquid unit 160 so that the concentrated lithium recovery solution heat exchanger 130 heats the concentrated lithium recovery solution by flowing the concentrated lithium recovery solution received by conduit 122 from the membrane concentrator 120 through a first portion of the concentrated lithium recovery solution heat exchanger 130 and the mother liquor received by conduit 161 from the solids-liquid separation unit 160 through the second portion of the concentrated lithium recovery solution heat exchanger 130.

[0036] The system 100 as depicted in FIG. 1 further comprises a washing-water heat exchanger 170 fluidly coupled to the solids-liquid separation unit 160 to receive and heat a washing water. The heated washing water is then delivered to the solids-liquid separation unit 160 and used to wash lithium carbonate solids within the solids-liquid separation unit 160 to produce washed lithium carbonate solids and a washing discharge. The washing-water heat exchanger has a first and a second portion configured respectively to receive the washing water, which arrives through conduit 171, through the first portion and the washing discharge, which is delivered through conduit 173, through the second portion so that heat in the washing discharge is transferred to the washing water through the washing-water heat exchanger 170.

[0037] The system 100 further comprises a feeding-saltwater heat exchanger 102 fluidly coupled to the direct lithium extraction unit 110 to cool the saltwater fed to the direct lithium extraction unit 110 to a designated temperature. The feeding-saltwater heat exchanger 102 has a first and a second portion configured respectively to receive the saltwater received through conduit 101 through the first portion and the lithium-depleted brine received through conduit 104 from theDLE unit 110 through the second portion so that heat in the saltwater is transferred to the lithium- depleted brine through the feeding-saltwater heat exchanger 102.

[0038] The heat exchangers 102, 130 and 170 may comprise conduits and / or plates manufactured from a heat-conductive material (e.g., titanium) with the outside and the interior of the conduits and / or plates as a first portion and a second portion of the heat exchangers, respectively.

[0039] The direct lithium extraction unit 110 comprises a lithium alumina intercalate resin. Suitable lithium alumina intercalate resins include, but are not limited to, resins comprising hydrated alumina or lithium aluminum layered double hydroxide chloride. Example preparation processes for the lithium alumina intercalate resin 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 intercalate 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 intercalate resin is 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 used 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.

[0040] The membrane concentrator 120 may comprise a reverse osmosis unit, an osmotically assisted reverse osmosis unit and a low salt rejection reverse osmosis (LSRRO) unit for concentrating the lithium recovery solution produced from the direct lithium extraction unit 110. The membrane concentrator 120 may further comprise pretreatment units (not shown in FIG. 1) to remove membrane scaling chemicals such as Ca, Mg, and suspended particles. Suitable pretreatment units include, but are not limited to, an ultrafiltration unit, an ion exchange unit, and a chemical precipitation unit.

[0041] The chelating ion exchange unit 140 may comprise ion exchange resins having one of aminomethylphosphonic acid functional groups, iminodiacetic acid functional groups, N- methylglucamine functional groups to remove at least one of multivalent cations or boron from the heated lithium recovery solution. The chelating ion exchange resins used herein can selectivelyremove the multivalent cations and / or boron with minimum lithium loss during the chelating ion exchange process.

[0042] The solids-liquid separator 130 may comprise any suitable type of centrifuge, such as any one or more of a peeler centrifuge, a pusher centrifuge, or a decanter centrifuge. For example, when considering the same amount of pure water for use in lithium carbonate washing, each of the peeler and pusher centrifuges does a better job of lithium carbonate washing than the decanter centrifuge. More particularly, in comparison to a decanter centrifuge, lithium carbonate washed using the peeler / pusher centrifuge may have 80% fewer sodium chloride impurities than lithium carbonate washed with a decanter centrifuge. This can make lithium carbonate washed using a peeler or pusher centrifuge better suited for use as recycled lithium carbonate seed crystals and as a final lithium carbonate product.

[0043] According to at least some embodiments, and with reference to FIG 1, an example process for preparing lithium carbonate comprises: i) extracting lithium from a saltwater through applying direct lithium extraction to produce a lithium recovery solution and a lithium-depleted brine; ii) concentrating the lithium recovery solution using the membrane concentrator 120 to produce a concentrated lithium recovery solution; iii) heating the concentrated lithium recovery solution to produce a heated lithium recovery solution; iv) removing through chelating ion exchange at least one of multivalent cations or boron from the heated lithium recovery solution to form a purified lithium recovery solution; v) reacting the purified lithium recovery solution with sodium carbonate at a temperature of at least 70 °C to produce a lithium carbonate slurry; and vi) separating the lithium carbonate slurry into lithium carbonate solids and a mother liquor.

[0044] The heating of the concentrated lithium recovery solution comprises flowing the concentrated lithium recovery solution through a first portion of the concentrated lithium recovery solution heat exchanger 130 and the mother liquor through the second portion of the concentrated lithium recovery solution heat exchanger 130. In at least some embodiments, the concentrated lithium recovery solution may be heated to at least 40 °C.

[0045] During operation of the system 100 for preparing lithium carbonate, a lithium- containing saltwater is fed via conduit 101 to the system 100. The lithium-containing saltwater may be a brine (e.g., a geothermal brine or a produced water produced from an oil / gas field) from a confined aquifer where the lithium-containing saltwater is heated to a temperature of above 80 °C by the Earth's interior. The hot lithium-containing saltwater is directed to the feeding-saltwater heat exchanger 102, which cools the lithium-containing saltwater to a temperature of less than 70 °C. The cooled saltwater is fed via conduit 103 to the direct lithium extraction unit 110. Lithium in the saltwater is selectively extracted through adsorption onto lithium alumina intercalate resins within the direct lithium extraction unit 110 and the saltwater after the DLE process, and consequently the saltwater becomes a lithium-depleted brine. The lithium-depleted brine is directed via conduit 104 to the feeding-saltwater heat exchanger 102 so that lithium-containing saltwater delivered via conduit 101 flows through a first portion of a feeding-saltwater heat exchanger 102 and the lithium-depleted saltwater from the DLE unit 110 via conduit 104 flows through a second portion of the feeding-saltwater heat exchanger 102. Heat in the lithium- containing saltwater is transferred through the feeding-saltwater heat exchanger 102 into the lithium-depleted brine, which is discharged via conduit 105 out of the system 100.

[0046] An elution water is fed via conduit 111 to the direct lithium extraction unit 110 to elute lithium from lithium alumina intercalate resins to produce a lithium recovery solution. The lithium recovery solution is directed via conduit 112 to the membrane concentrator 120. Some of the scaling components in the lithium recovery solution may be removed through pretreatment such as chemical precipitation, filtration, and / or ion exchange. A portion of water in the lithium recovery solution is removed by the membrane concentrator 120 and is discharged via conduit 121 out of the membrane concentrator 120. The lithium recovery solution produced by the membrane concentrator 120 is concentrated, with a lithium content in the range of 10.0 g / L - 25.0 g / L.

[0047] While lithium alumina intercalate resins are used in the example direct lithium extraction unit 110 discussed above, more generally, direct lithium extraction units 110 comprising different materials may be used in at least some other embodiments. For example, in addition to or as an alternative to lithium alumina intercalate resins, ion exchange based resins may be used. Example ion exchange resins comprise manganese oxide-based or titanium oxide-based lithium ion exchange resins.

[0048] The concentrated lithium recovery solution is directed via conduit 122 to the concentrated lithium recovery solution heat exchanger 130, which heats the concentrated lithium recovery solution. The heated lithium recovery solution is directed via conduit 141 to the chelating ion exchange unit 140. The chelating ion exchange unit 140 comprises ion exchange resins having at least one of an aminomethylphosphonic acid functional group, iminodiacetic acid functional group, or N-methylglucamine functional group, and can selectively remove at least one of calcium, magnesium or boron through a chelating mechanism and purify the heated lithium recovery solution with a minimal loss in lithium. The capacity of the chelating ion exchange unit 140 for removal of multivalent cations and boron is > 10% higher at an operating temperature of 60 °C than at an operating temperature of 20 °C. Thus, efficiency of chelating ion exchange is improved with the incorporation of the concentrated lithium recovery solution heat exchanger 130 within the system 100 to heat the concentrated lithium recovery solution. The purified lithium recovery solution from the chelating ion exchange unit 140 is directed via conduit 142 to the reactor unit 150. The purified lithium recovery solution reacts with sodium carbonate in the reactor unit 150 at a temperature of at least 70 °C to produce a lithium carbonate slurry, which is discharged via conduit 151 to the solids-liquid separation unit 160, which may comprise a peeler centrifuge or a pusher centrifuge. The solids-liquid separation unit 160 separates the lithium carbonate slurry into lithium carbonate solids and a mother liquor. The mother liquor is directed via conduit 161 to the concentrated lithium recovery solution heat exchanger 130. Heat in the mother liquor is transferred into the concentrated lithium recovery solution by flowing the concentrated lithium recovery solution, received through conduit 122 from the membrane concentrator, through a first portion of the concentrated lithium recovery solution heat exchanger 130 and by flowing the mother liquor, received by conduit 161 from the solids-liquids separation unit 160, through the second portion of the concentrated lithium recovery solution heat exchanger 130. The mother liquor is discharged via conduit 131 out of the concentrated lithium recovery solution heat exchanger 130.

[0049] A washing water is directed via conduit 171 to the system 100 and the washingwater heat exchanger 170. The washing-water heat exchanger 170 heats the washing water. The heated washing water from the washing-water heat exchanger 170 may be further heated using another heating source (not shown in FIG. 1) before being directed via conduit 172 to the solids- liquid separation unit 160 to wash lithium carbonate solids at a temperature of at least 50 °C. The washed lithium carbonate solids are discharged via conduit 162 out of the solids-liquid separationunit 160. A washing discharge is also produced from the solids-liquid separation unit 160 and is directed via conduit 173 to the washing-water heat exchanger 170. The heat in the washing discharge is transferred into the washing water by flowing the washing water through a first portion of the washing-water heat exchanger 170 and by flowing the washing discharge through the second portion of the washing-water heat exchanger 170. The washing discharge is directed via conduit 174 out of the washing-water heat exchanger 170.

[0050] FIG. 2 illustrates, according to another example embodiment, a system 200 for preparing lithium carbonate. The system 200 comprises: i) a direct lithium extraction unit 110 configured to extract lithium from a saltwater received through conduit 201 to produce a lithium recovery solution and a lithium-depleted brine; ii) a membrane concentrator 120 fluidly coupled to the direct lithium extraction unit 110 and configured to concentrate the lithium recovery solution to produce a concentrated lithium recovery solution; iii) a concentrated lithium recovery solution heat exchanger 230 fluidly coupled to the membrane concentrator 120 and the direct lithium extraction unit 110 and configured to heat the concentrated lithium recovery solution received from the membrane concentrator 120 using heat from the lithium recovery solution received from the direct lithium extraction unit 110 to produce a heated lithium recovery solution; iv) a chelating ion exchange unit 140 fluidly coupled to the concentrated lithium recovery solution heat exchanger 230 and configured to remove multivalent cations and / or boron from the heated lithium recovery solution to produce a purified lithium recovery solution; v) a reactor unit 150 fluidly coupled to the chelating ion exchange unit 140 for reacting the purified lithium recovery solution with sodium carbonate at a temperature of at least 70 °C to produce a lithium carbonate slurry; and vi) a solids-liquid separation unit 160 fluidly coupled to the reactor unit 150 and configured to receive and separate the lithium carbonate slurry into lithium carbonate solids and a mother liquor.

[0051] The membrane concentrator 120 is thermally coupled through the concentrated lithium recovery solution heat exchanger 230 to the direct lithium extraction unit 110 so that the concentrated lithium recovery solution heat exchanger 230 heats the concentrated lithium recoverysolution by flowing the concentrated lithium recovery solution received through conduit 233 through a first portion of the concentrated lithium recovery solution heat exchanger 230 and the lithium recovery solution received through conduit 231 through the second portion of the concentrated lithium recovery solution heat exchanger 230. In at least some embodiments, the concentrated lithium recovery solution may be heated to at least 40 °C.

[0052] The system 200 further comprises a washing-water heat exchanger 170 that is coupled to the solids-liquid separator 160 by conduits 172 and 173. The direct lithium extraction unit 110, the membrane concentrator 120, the chelating ion exchange unit 140, the reactor unit 150, the solids-liquid separation unit 160, and the washing-water heat exchanger 170 in the system 200 of FIG. 2 are same as those described above in the system 100 of FIG. 1, and are connected in the same manner as in the system 100.

[0053] According to at least some embodiments and with reference to FIG. 2, an example process for preparing lithium carbonate comprises: i) extracting lithium from a saltwater through applying direct lithium extraction to produce a lithium recovery solution and a lithium-depleted brine; ii) concentrating the lithium recovery solution using the membrane concentrator 120 to produce a concentrated lithium recovery solution; iii) heating the concentrated lithium recovery solution to produce a heated lithium recovery solution; iv) removing through chelating ion exchange at least one of multivalent cations or boron from the heated lithium recovery solution to form a purified lithium recovery solution; v) reacting the purified lithium recovery solution with sodium carbonate at a temperature of at least 70 °C to produce a lithium carbonate slurry; and vi) separating the lithium carbonate slurry into lithium carbonate solids and a mother liquor.

[0054] Heating of the concentrated lithium recovery solution comprises flowing the concentrated lithium recovery solution through a first portion of the concentrated lithium recovery solution heat exchanger 230 and the lithium recovery solution from the direct lithium extraction through a second portion of the concentrated lithium recovery solution heat exchanger 230. In atleast some embodiments, the concentrated lithium recovery solution may be heated to at least 40 °C.

[0055] In at least some example embodiments, during operation of the system 200 for preparing lithium carbonate, a lithium-containing saltwater at a temperature of above 70 °C is directed via conduit 201 to the direct lithium extraction unit 110. Lithium in the saltwater is selectively extracted through adsorption onto lithium alumina intercalate resins within the direct lithium extraction unit 110 at a temperature of above 70 °C and the saltwater after the DLE unit 110 becomes a lithium-depleted brine with a temperature above 60 °C. An elution water is fed via conduit 206 to the elution water heat exchanger 202, which heats the elution water. The heated elution water, which is directed via conduit 203 to the direct lithium extraction unit 110, may be heated by other heat sources (not shown in FIG. 2) to a temperature of at least 40 °C, and in some example embodiments to around 70 °C. The heated elution water elutes lithium from the lithium alumina intercalate resins to produce a lithium recovery solution having a temperature of above 60 °C. To improve energy efficiency, the lithium-depleted brine is used to heat the elution water and is directed via conduit 204 to the elution water heat exchanger 202. Heat in the lithium- depleted brine is transferred through the elution water heat exchanger 202 into the elution water by flowing the elution water through a first portion of an elution-water heat exchanger 202 and the lithium-depleted brine through a second portion of the elution-water heat exchanger 202. The lithium-depleted brine is directed via conduit 205 out of the elution-water heat exchanger 202 after being used to heat the elution water.

[0056] The temperature of the lithium recovery solution from the direct lithium extraction unit 110 of the system 200 is above 60 °C and may be cooled to below 40 °C in at least some embodiments before being delivered to the membrane concentrator 120 to avoid membrane damage. The lithium recovery solution with a temperature above 60 °C is directed via conduit 231 to the concentrated lithium recovery solution heat exchanger 230, which cools the lithium recovery solution to a temperature below 40 °C. The cooled lithium recovery solution is directed via conduit 232 to the membrane concentrator 120, which concentrates the lithium recovery solution into a concentrated lithium recovery solution. The concentrated lithium recovery solution is used to cool the lithium recovery solution from the direct lithium extraction 110 and is directed via conduit 233 to the concentrated lithium recovery solution heat exchanger 230 to recover heat from the lithiumrecovery solution. Heat from the lithium recovery solution is transferred through the concentrated lithium recovery solution heat exchanger 230 into the concentrated lithium recovery solution by flowing the concentrated lithium recovery solution through a first portion of the concentrated lithium recovery solution heat exchanger 230 and the lithium recovery solution from the direct lithium extraction unit 110 through a second portion of the concentrated lithium recovery solution heat exchanger 230. The heated lithium recovery solution from the concentrated lithium recovery solution heat exchanger 230 is directed via conduit 141 to the ion exchange unit 140 for purification. Lithium carbonate is produced and washed respectively in the reactor unit 150 and the solids-liquid separation unit 160 of the system 200 in same processes as those described above for the system 100 of FIG. 1. The mother liquor produced from the solids-liquid separation unit 160 of the system 200 is discharged via conduit 163. Washed lithium carbonate solids are discharged via conduit 162 out of the solids-liquid separation unit 160. Washing water used in the solids-liquid heat separator may be heated through operation of the washing-water heat exchanger as in system 100.

[0057] FIG. 3 illustrates, according to another example embodiment, a system 300 for preparing lithium carbonate. The example system 300 of FIG. 3 is identical to that shown in FIG. 2, except the concentrated lithium recovery solution heat exchanger 230 of FIG. 2 acts as a first concentrated lithium recovery solution heat exchanger 230, and is fluidly coupled in series with a second concentrated lithium recovery solution heat exchanger 330. Conduit 141 fluidly couples the second concentrated lithium recovery solution heat exchanger 330 to the chelating ion exchange unit 140, and conduits 161 and 131 are used to transport the mother liquor from the solids-liquid separator 160 to the second concentrated lithium recovery solution heat exchanger 330 in a manner analogous to that described in respect of FIG. 1. In the embodiment of FIG. 3, both the lithium recovery solution and the mother liquor can accordingly be used to sequentially heat the concentrated lithium recovery solution to produce the heated lithium recovery solution. Accordingly, in the embodiment of FIG. 3, the heating of the concentrated lithium recovery solution is performed by sequentially transferring heat from the lithium recovery solution (via the first concentrated lithium recovery solution heat exchanger 230) and then the mother liquor (via the second concentrated lithium recovery solution heat exchanger 330) to the concentrated lithium recovery solution. In alternative embodiments (not shown), the heat exchangers 230, 330 may beswapped such that heat is sequentially transferred from the mother liquor and then from the lithium recovery solution into the concentrated lithium recovery solution.

[0058] 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 clearly indicates 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 “couple” and variants of it such as “coupled”, “couples”, and “coupling” as used in this description are intended to include indirect and direct connections unless otherwise indicated. For example, if a first device is coupled to a second device, that coupling may be through a direct connection or through an indirect connection via other devices and connections.

[0059] 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.

[0060] 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.

[0061] 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 embodimentdiscussed in this specification, so long as such implementation or combination is not performed using mutually exclusive parts.

[0062] 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 art that a number of variations and modifications can be made without departing from the scope of the claims.

Claims

CLAIMS1. A process for preparing lithium carbonate, the process comprising: i) extracting lithium from a saltwater through applying direct lithium extraction to produce a lithium recovery solution and a lithium-depleted brine; ii) concentrating the lithium recovery solution using a membrane concentrator to produce a concentrated lithium recovery solution; iii) heating the concentrated lithium recovery solution to produce a heated lithium recovery solution; iv) removing, through chelating ion exchange, multivalent cations and / or boron from the heated lithium recovery solution to form a purified lithium recovery solution; v) reacting the purified lithium recovery solution with sodium carbonate at a temperature of at least 70 °C to produce a lithium carbonate slurry; and vi) separating the lithium carbonate slurry into lithium carbonate solids and a mother liquor, wherein the heating of the concentrated lithium recovery solution is performed by transferring heat from at least one of the lithium recovery solution or the mother liquor to the concentrated lithium recovery solution.

2. The process of claim 1, further comprising washing the separated lithium carbonate solids with a washing water at a temperature of at least 50 °C to produce washed lithium carbonate solids and a washing discharge.

3. The process of claim 2, further comprising heating the washing water before the washing of the separated lithium carbonate solids.

4. The process of claim 3, wherein the heating of the washing water comprises flowing the washing water through a first portion of a washing-water heat exchanger and the washing discharge through a second portion of the washing-water heat exchanger.

5. The process of any one of claims 1 to 4, further comprising cooling the saltwater to less than 70 °C before extracting the lithium through applying the direct lithium extraction.

6. The process of claim 5, wherein the cooling comprises flowing the saltwater through a first portion of a feeding-saltwater heat exchanger and the lithium-depleted brine through a second portion of the feeding-saltwater heat exchanger.

7. The process of claim 2, wherein the separating and the washing of the lithium carbonate solids is performed with a peeler centrifuge and / or a pusher centrifuge.

8. The process of any one of claims 1 to 7, wherein the direct lithium extraction comprises contacting the saltwater with a lithium alumina intercalate resin to extract the lithium from the saltwater and onto the lithium alumina intercalate resin.

9. The process of claim 8, wherein the direct lithium extraction comprises eluting the extracted lithium from the lithium alumina intercalate resin using an elution water to produce the lithium recovery solution.

10. The process of claim 9, further comprising heating the elution water to at least 40 °C before eluting the extracted lithium.

11. The process of claim 10, wherein the elution water is heated to about 70 °C before eluting the extracted lithium.

12. The process of claim 10, wherein the heating of the elution water comprises flowing the elution water through a first portion of an elution water heat exchanger and the lithium-depleted brine through a second portion of the elution water heat exchanger.

13. The process of any one of claims 1 to 12, wherein the heating comprises transferring heat from only one of the lithium recovery solution or the mother liquor to the concentrated lithium recovery solution.

14. The process of any one of claims 1 to 13, wherein the concentrated lithium recovery solution is heated to at least 40 °C.

15. A system for preparing lithium carbonate, the system comprising: i) a direct lithium extraction unit configured to extract lithium from a saltwater to produce a lithium recovery solution and a lithium-depleted brine;ii) a membrane concentrator fluidly coupled to the direct lithium extraction unit and configured to concentrate the lithium recovery solution to produce a concentrated lithium recovery solution; iii) at least one concentrated lithium recovery solution heat exchanger fluidly coupled to the membrane concentrator and configured to heat the concentrated lithium recovery solution to produce a heated lithium recovery solution; iv) a chelating ion exchange unit fluidly coupled to the concentrated lithium recovery solution heat exchanger and configured to remove multivalent cations and / or boron from the heated lithium recovery solution to produce a purified lithium recovery solution; v) a reactor unit fluidly coupled to the chelating ion exchange unit for reacting the purified lithium recovery solution with sodium carbonate at a temperature of at least 70 °C to produce a lithium carbonate slurry; and vi) a solids-liquid separation unit fluidly coupled to the reactor unit and configured to receive and separate the lithium carbonate slurry into lithium carbonate solids and a mother liquor, wherein the membrane concentrator is thermally coupled through the at least one concentrated lithium recovery solution heat exchanger to at least one of the direct lithium extraction unit or the solids-liquid separation unit so that heat is transferred from at least one of the lithium recovery solution or the mother liquor to the concentrated lithium recovery solution through the at least one concentrated lithium recovery solution heat exchanger.

16. The system of claim 15, further comprising a washing-water heat exchanger fluidly coupled to the solids-liquid separation unit to receive and heat a washing water that is used to wash lithium carbonate solids within the solids-liquid separation unit to produce a washing discharge, wherein the washing-water heat exchanger has first and second portions configured to receive the washing water through the first portion and the washing discharge through the second portion so that heat in the washing discharge is transferred to the washing water through the washing-water heat exchanger.

17. The system of claim 15 or 16, further comprising a feeding-saltwater heat exchanger fluidly coupled to the direct lithium extraction unit to cool the saltwater directed to the direct lithium extraction unit, wherein the feeding-saltwater heat exchanger has first and second portions configured to receive the saltwater through the first portion and the lithium-depleted brinethrough the second portion so that heat in the saltwater is transferred to the lithium-depleted brine through the feeding-saltwater heat exchanger.

18. The system of any one of claims 15 to 17, further comprising an elution water heat exchanger fluidly coupled to the direct lithium extraction unit to heat an elution water that is used to elute lithium from the direct lithium extraction unit, wherein the elution-water heat exchanger has first and second portions configured to receive the elution water through the first portion and the lithium-depleted brine through the second portion so that heat in the lithium-depleted brine is transferred to the elution water.

19. The system of any one of claims 15 to 18, wherein the direct lithium extraction unit comprises lithium alumina intercalate resin.

20. The system of any one of claims 15 to 19, wherein the solids-liquid separation unit comprises a peeler centrifuge and / or a pusher centrifuge.

21. The system of any one of claims 15 to 20, wherein the membrane concentrator is thermally coupled through the at least one concentrated lithium recovery solution heat exchanger to either of the direct lithium extraction unit or the solids-liquid separation unit such that heat is transferred from either the lithium recovery solution or the mother liquor to the concentrated lithium recovery solution.

22. The system of any one of claims 15 to 20, wherein the membrane concentrator is thermally coupled through the at least one concentrated lithium recovery solution heat exchanger to both of the direct lithium extraction unit and the solids-liquid separation unit such that heat is sequentially transferred from both of the lithium recovery solution and the mother liquor to the concentrated lithium recovery solution.

23. The system of any one of claims 15 to 21, wherein the concentrated lithium recovery solution heat exchanger is configured to heat the concentrated lithium recovery solution to at least

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