Continuous process and production plant for recovering metal salts from acidic aqueous metal solution

Abstract

The present disclosure relates to a continuous process and a production plant for recovering metal salts from an acidic aqueous solution comprising nickel, cobalt, manganese, and lithium cations.

Description

[0001] Continuous process and production plant for recovering metal salts from acidic aqueous metal solution

[0002] The project leading to this application has received funding from Bundesministerium fur Wirtschaft und Klimaschutz and State of Brandenburg (DE; FKZ:16BZF101A / B); the applicant bears responsibility for all disclosures herein.

[0003] Field of the invention

[0004] The present disclosure relates to a continuous process and a production plant for recovering metal salts from an acidic aqueous solution comprising nickel, cobalt, manganese, and lithium cations.

[0005] Background

[0006] Lithium ion battery materials are complex mixtures of various elements and compounds. For example, many lithium ion battery materials contain valuable metals such as lithium, aluminum, copper, nickel, cobalt, and / or manganese. It may be desirable to recover various elements and compounds from lithium ion battery materials. For example, it may be advantageous to recover lithium, aluminum, copper, nickel, cobalt, and / or manganese. Accordingly, there is a need for devices and processes for recycling lithium ion battery materials.

[0007] WO 20231054621 A1 discloses a method for recovering valuable metals from waste lithium ion batteries comprising a dissolution step for dissolving an active material powder obtained by pre-treating the waste lithium-ion batteries in a mineral acid to obtain an acid solution; and a solvent extraction step for separating manganese, cobalt, and nickel, among metals contained in the active material powder, from the acid solution through solvent extraction to obtain a first lithium salt aqueous solution as a residual liquid of the solvent extraction. WO 2020 / 124130 A1 discloses a method for the recovery of metals from a feed stream containing one or more value metals and lithium. The method comprises subjecting the feed stream to a sulfuric acid leach to form a slurry comprising a pregnant leach solution of soluble metal salts and a solid residue; separating the pregnant leach solution and the solid residue; subjecting the pregnant leach solution to one or more separate solvent extraction steps, wherein each solvent extraction step recovers one or more value metals from the pregnant leach solution, the remaining pregnant leach solution comprising lithium; and recovery of lithium from the pregnant leach solution.

[0008] US 2022 / 205064 A1 discloses hydrometallurgical solvent extraction processes for recovering value metal ion species such as any of manganese, cobalt, nickel, and / or lithium from solutions derived from recycled electronics and / or batteries and containing mixed-metal ions by separating the value metal ions using selective stripping techniques.

[0009] CN 109 921 120 A discloses a method for recycling a waste refractory material in a preparation process of a ternary positive electrode material. The waste refractory material contains silicon, aluminum and magnesium impurities, and the method comprises the following steps: 1 ) mixing the waste refractory material, an acid solution and an additive, carrying out a leaching reaction, and then separating to obtain a purified refractory material and a leachate; 2) adjusting the pH value of the leachate to 2-5, and separating to obtain solid slag and a separation solution; 3) adding an aluminum removal agent into the separation solution, crystallizing, and separating to obtain solid slag and aluminum removal liquid; 4) adjusting the pH value of the aluminum removal liquid to be greater than or equal to 9, and separating to obtain a ternary mixture and a coprecipitation separation liquid; 5) adding a magnesium removal agent into the coprecipitation separation liquid, adjusting the pH value to be more than or equal to 12, and separating to obtain solid slag and a magnesium removal liquid, and 6) adding a precipitant into the magnesium removal liquid, and carrying out a reaction and separation to obtain a lithium-containing substance and a lithium precipitation liquid.

[0010] It is an object of the present disclosure to provide an improved recycling plant for lithium ion battery materials and an improved recycling process for lithium ion battery materials.

[0011] Summary of the invention

[0012] The present disclosure provides a continuous process for recovering value metals from an acidic aqueous solution comprising nickel, cobalt, manganese, and lithium cations. The process involves removing impurity cations of the group consisting of Al and Fe cations and impurity anions comprising P, F, Al and / or Si present in the solution from the solution by precipitation, followed by solvent extraction of manganese and impurity cations of the group consisting of Ca, Cu, Zn, and Cd cations, solvent extraction of cobalt cations, precipitating and recovering a mixed metal hydroxide and / or carbonate from the aqueous solution depleted of cobalt cations, precipitating and removing magnesium hydroxide from the solution, and removing lithium cations from the solution by solvent extraction.

[0013] The present disclosure also provides a production plant suitable for performing the continuous process of the present disclosure.

[0014] Brief description of the drawings

[0015] Fig. 1 is a schematic diagram of an exemplary production plant of the present disclosure.

[0016] Detailed description

[0017] The present disclosure provides a continuous process for recovering value metals from an acidic aqueous solution comprising nickel, cobalt, manganese, and lithium cations. In some embodiments, the acidic aqueous solution comprising nickel, cobalt, manganese, and lithium cations has been obtained by leaching lithium ion battery materials with sulfuric acid. Examples of suitable lithium ion battery materials for preparing the acidic aqueous solution comprising nickel, cobalt, manganese, and lithium cations include black mass, cathode active materials, and mixed metal hydroxides (MHP). The acidic aqueous solution comprising nickel, cobalt, manganese, and lithium cations may additionally contain cations of other metals like copper, manganese, iron, aluminum, magnesium, calcium, and / or titanium; as well as anions like fluoride and / or phosphate.

[0018] The continuous process of the present disclosure comprises the steps of a) optionally, adjusting the pH of the solution to a value in the range of from 1 .5 to 2.5 and recovering copper from the solution by solvent extraction, or by precipitation of copper sulfide, followed by solid / liquid separation, b) adjusting the pH of the acidic aqueous solution comprising nickel, cobalt, manganese, and lithium cations to be in the range of from 3.0 to 4.0 by addition of sodium carbonate, and subsequently precipitating impurity cations of the group consisting of Al and Fe cations and impurity anions comprising P, F, Al, and / or Si present in the solution from the solution, c) removing solids from the mixture obtained in step b), d) adjusting the pH of the acidic aqueous solution obtained in step c) to be in the range of from 4.5 to 5.0 by addition of sodium carbonate, and subsequently precipitating impurity cations of the group consisting of Al and Fe cations and impurity anions comprising P, F, Al and / or Si present in the solution from the solution, e) removing solids from the mixture obtained in step d), f) adjusting the pH of the acidic aqueous solution obtained in step e) to be in the range of from 2 to 4, and subsequently removing manganese cations and any residual impurity cations of the group consisting of Ca, Cu, Zn, and Cd cations present in the solution by solvent extraction to obtain an aqueous solution depleted of manganese cations and impurity cations and a solvent comprising manganese cations and impurity cations; and scrubbing and stripping the solvent comprising manganese cations and impurity cations with sulfuric acid to obtain an acidic aqueous solution comprising manganese cations and impurity cations, g) adjusting the pH of the acidic aqueous solution depleted of manganese cations and impurity cations obtained in step f) to be in the range of from 3 to 6; and subsequently removing cobalt cations from the solution by solvent extraction to obtain an aqueous solution depleted of cobalt cations and an organic solvent comprising cobalt cations, and scrubbing and stripping the organic solvent comprising cobalt cations with sulfuric acid to obtain an acidic aqueous solution comprising cobalt cations, h) adjusting the pH of the aqueous solution depleted of cobalt cations obtained in step f) to be in the range of from 7 to 8.5, and precipitating a mixed metal hydroxide and / or carbonate from the solution, i) performing a solid / liquid separation of the mixture obtained in step h) to obtain solid mixed metal hydroxide and / or carbonate and a mother liquor, j) adding sodium hydroxide to the mother liquor obtained in step i), adjusting the pH of the mother liquor to be in the range of from 10 to 12.5, and precipitating magnesium hydroxide from the mother liquor, k) removing solids from the mixture obtained in step j), l) adjusting the pH of the aqueous solution obtained in step k) to be in the range of from 8 to 12, e.g., from 8 to 10, for instance, from 8 to 9; and subsequently removing lithium cations from the solution by solvent extraction to obtain an aqueous solution depleted of lithium cations and an organic solvent comprising lithium cations; and scrubbing and stripping the organic solvent comprising lithium cations with sulfuric acid to obtain an acidic aqueous solution comprising lithium cations.

[0019] In an optional first step a), copper is recovered by a first solvent extraction from the acidic aqueous solution comprising nickel, cobalt, manganese, and lithium cations.

[0020] Solvent extraction is a useful method for separating and purifying metal ions from an aqueous solution or leachate. This can be difficult when purifying metal ions present in a hydrated form in an aqueous solution, since it is difficult to move the ions to an organic solvent layer having a low polarity. In order to move hydrated metal ions to the organic phase, the metal ions should be in a form of an uncharged complex and the metal ions should be able to remove water molecules from the hydrated complex.

[0021] A solvent extracting agent allows the metal ions to form a non-charged complex and remove water molecules. The extraction efficiency depends on, e.g., the type of solvent extracting agent, the equilibrium pH, and the metal ions in the aqueous solution. The extraction efficiency may also be affected by, e.g., the concentration of the solvent extracting agent, the ratio of the solvent extracting agent to the aqueous solution, and the composition and concentration of the stripping solution. In some embodiments of the process, the solvent extracting agent is LIX984N, a 1 :1 mixture of 5-nonyl salicylaldoxime and 2-hydroxy-5- nonyl acetophenone.

[0022] In some embodiments, the first solvent extraction comprises

[0023] • adding an alkaline solution to the acidic aqueous solution comprising nickel, cobalt, manganese, and lithium cations to adjust the pH of the solution to a value in the range of from 1 .5 to 2.5,

[0024] • adding a solvent extracting agent to the acidic aqueous solution,

[0025] • homogenizing the mixture of acidic aqueous solution and solvent extracting agent,

[0026] • allowing the mixture to separate into a layer of an acidic aqueous solution depleted of Cu and a layer of solvent extracting agent comprising Cu,

[0027] • separating the layer of solvent extracting agent comprising Cu from the layer of acidic aqueous solution depleted of Cu,

[0028] • mixing the separated solvent extracting agent comprising Cu with a second aqueous acidic solution,

[0029] • homogenizing the mixture,

[0030] • allowing the mixture to separate into a layer of a second aqueous solution comprising copper and a layer of solvent extracting agent, and

[0031] • separating the aqueous solution comprising Cu from the layer of solvent extracting agent. In some embodiments, the first solvent extraction is a two-step process (or even a three-step process if impurities need to be scrubbed before the stripping). The optional step of scrubbing (step 2), if necessary, is carried out in-between the extraction of the target species into the organic phase (step 1 ) and the stripping (step 3).

[0032] In a first step, a solvent extracting agent (a non-polar weak acid) is dissolved in an organic liquid (diluent), such as kerosene. This mixture forms the extracting agent solution. This solution is brought into contact / mixed with the acidic aqueous solution, from which the extracting agent selectively extracts copper cations.

[0033] In a second optional step, impurities are removed from the organic phase (the extracting agent solution) by scrubbing.

[0034] Subsequently, the extracting agent solution, which now comprises copper cations, is brought into contact with an acid solution (strong acid), which causes the copper cations to be replaced by H+. In return, the copper cations transfer into the acidic aqueous solution. This solution is then called loaded stripping solution. The process of transferring the copper cations back into an aqueous phase is called stripping.

[0035] In some embodiments, copper is recovered by precipitation followed by solid / liquid separation. In some embodiments, the copper ions are removed by precipitation of copper sulfide. To precipitate copper sulfide, sulfide, hydrogen sulfide, or thiosulfate ions are added to the solution. In some embodiments, Na2SO3 is added to the solution to precipitate copper sulfide. The precipitate is separated from the aqueous solution depleted of copper cations by solid / liquid separation, for instance, by filtration.

[0036] The acidic aqueous solution depleted of Cu obtained after the first solvent extraction, or after precipitation of copper sulfide, followed by solid / liquid separation, is further processed in step b). In step b) of the process of the present disclosure, impurities are precipitated from the acidic aqueous solution comprising nickel, cobalt, manganese, and lithium cations. The precipitation involves the addition of sodium carbonate.

[0037] The impurities comprise one or more selected from iron, aluminum, magnesium, calcium, titanium, residual copper, fluoride, and phosphate. The precipitation involves the addition of a sodium carbonate solution to the acidic aqueous solution comprising nickel, cobalt, manganese, and lithium cations, thereby adjusting the pH value of the solution to a value in the range of from 3.0 to 4.0. In some embodiments of the process, air is injected into the solution to oxidize any Fe(ll) present to Fe(lll). Iron, aluminum, and titanium precipitate from the solution as hydroxides and / or oxide-hydroxides and / or carbonates, fluorides and / or phosphates, and are removed from the mother liquor in a subsequent step c) by solid-liquid separation, e.g., filtration.

[0038] The mother liquor is further processed in a second precipitation step d). The precipitation involves the addition of a sodium carbonate solution to the mother liquor obtained in step c), thereby adjusting the pH value of the solution to a value in the range of from 4.5 to 5.0. Iron, aluminum, and titanium precipitate from the solution as hydroxides and / or oxide-hydroxides and / or carbonates, fluorides and / or phosphates, and are removed from the mother liquor in a subsequent step e) by solid-liquid separation, e.g., filtration. In some embodiments of the process, some manganese also is precipitated as manganese carbonate. As the precipitate obtained in step e) may contain significant amounts of value metals, in particular, nickel, it can be recycled into a leaching step and used for generating an acidic aqueous solution comprising nickel, cobalt, manganese, and lithium cations.

[0039] Using the two-stage precipitation and separation process of steps b) through e) maximizes precipitation of Al, Fe, F and thus the removal of impurities from the acidic aqueous solution comprising nickel, cobalt, manganese, and lithium cations, and it minimizes co-precipitation of value metals, and thus minimizes losses of nickel, cobalt, manganese, and lithium.

[0040] The process further comprises f) adjusting the pH of the acidic aqueous solution comprising nickel, cobalt, manganese, and lithium cations to be in the range of from 2 to 4 by addition of sodium hydroxide, and subsequently removing manganese cations and any impurity cations of the group consisting of Ca, Cu, Zn, and Cd present in the solution from the solution by solvent extraction to obtain an aqueous solution depleted of manganese cations and impurity cations and an organic solvent comprising manganese cations and impurity cations, and scrubbing and stripping the organic solvent comprising manganese cations and impurity cations with sulfuric acid to obtain an acidic aqueous solution comprising manganese cations and impurity cations,

[0041] Solvent extraction is performed in step f) using an organic solvent suitable for extracting manganese cations from an aqueous solution. Examples of suitable organic solvents include bis(2-ethylhexyl)phosphate (D2EHPA). In some embodiments, the solvent used in step f) is a solution of 40 vol% bis(2- ethylhexyl)phosphate (D2EHPA) in dearomatized hydrocarbon fluid (Escaid™ 110).

[0042] The process further comprises g) adjusting the pH of the acidic aqueous solution depleted of manganese cations and impurity cations obtained in step j) to be in the range of from 3 to 6, e.g., from 4.3 to 5.8, and subsequently removing cobalt cations from the solution by solvent extraction to obtain an aqueous solution depleted of cobalt cations and an organic solvent comprising cobalt cations, and scrubbing and stripping the organic solvent comprising cobalt cations with sulfuric acid to obtain an acidic aqueous solution comprising cobalt cations.

[0043] Solvent extraction is performed in step g) using an organic solvent suitable for extracting cobalt cations from an aqueous solution. Examples of suitable organic solvents include phosphinic acid derivatives, e.g., bis-(2,4,4-trimethyl- pentyl) phosphinic acid (Cyanex® 272). In some embodiments, the solvent used in step d) is a solution of 20 vol% bis-(2,4,4-trimethylpentyl) phosphinic acid (Cyanex® 272) in dearomatized hydrocarbon fluid (Escaid™ 110) containing 1 g / L butylhydroxytoluene (BHT).

[0044] The process further comprises h) adjusting the pH of the aqueous solution depleted of cobalt cations obtained in step g) to be in the range of from 7 to 8.5, and precipitating a mixed metal hydroxide and / or carbonate from the solution.

[0045] The process further comprises i) performing a solid / liquid separation of the mixture obtained in step h) to obtain solid mixed metal hydroxide and / or carbonate and a mother liquor. The mixed metal hydroxide and / or carbonate mainly comprises nickel hydroxide and / or carbonate. The precipitation step yields a solid with low sodium sulfate content that can be re-dissolved and used as feed for cathode material precursor synthesis. The mixed metal hydroxide and / or carbonate can be used without further purification for the production of cathode active materials (CAM) for lithium ion batteries. As bases like NaOH or Na2CO3 are used for pH adjustment in all process steps after acid leaching, Na2SO4 is formed. Due to the high concentration of Na, a NiNa(SO4)2double salt is formed upon evaporation of a recycling feed, so that recovery of Ni from the solution usually requires an additional solvent extraction step.

[0046] The process further comprises j) adding sodium hydroxide to the mother liquor obtained in step i), adjusting the pH of the mother liquor to be in the range of from 10 to 12.5, and precipitating magnesium hydroxide from the mother liquor. This step is essential for the subsequent recovery of lithium cations by solvent extraction. It has been found that magnesium cations hamper the phase separation of the organic phase from the aqueous phase in solvent extraction of lithium-containing solutions. Without prior removal of magnesium cations from the solution, solvent extraction of lithium cations does not work properly.

[0047] The process further comprises k) removing solids from the mixture obtained in step j). The process further comprises I) adjusting the pH of the aqueous solution obtained in step k) to be in the range of from 8 to 12, e.g., from 8 to 10, for instance, from 8 to 9; and subsequently removing lithium cations from the solution by solvent extraction to obtain an aqueous solution depleted of lithium cations and an organic solvent comprising lithium cations; and scrubbing and stripping the organic solvent comprising lithium cations with sulfuric acid to obtain an acidic aqueous solution comprising lithium cations. As the aqueous solution obtained in step k) also contains high concentrations of sodium cations, recovery of lithium cations from the solution by solvent extraction offers advantages over the precipitation of lithium salts like lithium carbonate, as contamination of the acidic aqueous solution comprising lithium cations by sodium cations, and consequently, the sodium content of lithium salts recovered from the acidic aqueous solution comprising lithium cations is minimized.

[0048] Solvent extraction is performed in step I) using an organic solvent suitable for extracting lithium cations from an aqueous solution. Examples of suitable organic solvents include synergistic extractant mixtures comprising a betadiketone and a neutral extractant, e.g. an organic phosphate, as disclosed in J Chem Technol Biotechnol 2016; 91 : 2549-2562 (table 3); Hydrometallurgy 154 (2015) 33-39; and Hydrometallurgy 175 (2018) 35-42. Further examples of suitable organic solvents include organic solutions comprising an organic diluent, at least one phosphine oxide and at least one proton donating agent, as disclosed in WO 2013 / 065050 A1 . In some embodiments, the phosphine oxide corresponds to the general formula O=PRI R2R3, wherein each of Ri, R2and R3is independently selected from straight or branched C1-C10 alkyl, straight or branched C2-C10 alkenyl, straight or branched C2-C10 alkynyl, optionally substituted C5-C12 aryl, optionally substituted C4 -C12 heteroaryl; the at least one proton donating agent is selected from the group consisting of straight or branched C1-C10 alcohol, C1-C10 ketone, C1-C10 aldehyde, C3-C20 fatty acid, and any combination thereof; and the molar ratio between said phosphine oxide and an organic acid in said extracting organic solution is in the range of between about 5:1 to about 1 :5. In some embodiments, the solvent used in step I) comprises benzoyltrifluoroacetone (HBTA) and tri-n-octylphosphine oxide (TOPO). In some embodiments, the solvent used in step I) comprises thenoyltrifluoroacetone (TTA) and tri-n-octylphosphine oxide (TOPO). In some embodiments, the solvent used in step I) is a solution of 27 vol% Cyanex® 936P in in dearomatized hydrocarbon fluid (Escaid™ 110).

[0049] In some embodiments, the process further comprises m) adjusting the pH of the acidic aqueous solution comprising manganese cations and impurity cations obtained in step f) to be in the range of from 6.8 to 8.5, for instance, from 7.3 to 8, and precipitating manganese carbonate and / or manganese hydroxide from the solution, n) removing solids from the mixture obtained in step m), o) optionally, adjusting the pH of the solution obtained in step m) to be in the range of from 10 to 12.5, and precipitating metal hydroxides from the solution, and p) optionally, removing solids from the mixture obtained in step o). In some embodiments, manganese carbonate is precipitated from the solution in step m).

[0050] In some embodiments, the process further comprises q) crystalizing cobalt sulfate from the acidic aqueous solution comprising cobalt cations obtained in step g).

[0051] In some embodiments, the process further comprises r) crystalizing lithium sulfate from the acidic aqueous solution comprising lithium cations obtained in step I).

[0052] The present disclosure also provides a production plant suitable for performing the process of the present disclosure. In some embodiments, the production plant comprises a first solvent extraction (SX) unit configured to receive an acidic aqueous solution comprising nickel, cobalt, manganese, and lithium cations. The first SX unit comprises an extraction module and a scrubbing and stripping module. In the extraction module of the SX unit, an aqueous solution is extracted with an organic solvent, an aqueous phase and an organic phase being formed in the process. The organic phase is separated from the aqueous phase and transferred to the scrubbing and stripping module, where it is extracted with an aqueous acid. After scrubbing and stripping, the organic phase is cycled back to the extraction module. Suitable solvent extraction (SX) units are known in the art.

[0053] The production plant comprises at least one first continuous stirred-tank reactor (CSTR) configured to receive an aqueous effluent of the extraction module of the first SX unit, if a first SX unit is present, or, in the alternative, to receive an acidic aqueous solution comprising nickel, cobalt, manganese, and lithium cations. If a first SX unit is present, the first CSTR is located downstream of the first SX unit. The at least one first CSTR comprises a dosing device for liquids, heating / cooling means, and gas injection means. Suitable continuous stirred- tank reactors are known in the art.

[0054] The production plant further comprises at least one first solid / liquid separation device configured to receive an effluent of the first CSTR. The at least one first solid / liquid separation device thus is located downstream of the first CSTR. In some embodiments, the first solid / liquid separation device comprises a filter press.

[0055] The production plant also comprises at least one second continuous stirred-tank reactor (CSTR) configured to receive an aqueous effluent of the at least one first solid / liquid separation device. The second CSTR thus is located downstream of the first solid / liquid separation device. The first CSTR comprises a dosing device for liquids and heating / cooling means. Suitable continuous stirred-tank reactors are known in the art.

[0056] The production plant further comprises at least one second solid / liquid separation device configured to receive an effluent of the second CSTR. The at least one second solid / liquid separation device thus is located downstream of the second CSTR. In some embodiments, the first solid / liquid separation device comprises a filter press. The production plant further comprises a second solvent extraction (SX) unit configured to receive an aqueous effluent of the at least one second solid / liquid separation device. The second SX unit comprises an extraction module and a scrubbing and stripping module. In the extraction module of the SX unit, an aqueous solution is extracted with an organic solvent, an aqueous phase and an organic phase being formed in the process. The organic phase is separated from the aqueous phase and transferred to the scrubbing and stripping module, where it is extracted with an aqueous acid. After scrubbing and stripping, the organic phase is cycled back to the extraction module. Suitable solvent extraction (SX) units are known in the art.

[0057] The production plant further comprises a third solvent extraction (SX) unit configured to receive an aqueous effluent of the extraction module of the second SX unit. The third SX unit comprises an extraction module and a scrubbing and stripping module. In the extraction module of the SX unit, an aqueous solution is extracted with an organic solvent, an aqueous phase and an organic phase being formed in the process. The organic phase is separated from the aqueous phase and transferred to the scrubbing and stripping module, where it is extracted with an aqueous acid. After scrubbing and stripping, the organic phase is cycled back to the extraction module. Suitable solvent extraction (SX) units are known in the art.

[0058] The production plant further comprises a first crystallizer configured to receive an aqueous effluent of the scrubbing and stripping module of the third SX unit and to produce crystals of a first metal salt. Suitable crystallizers are known in the art.

[0059] The production plant also comprises at least one third continuously stirred tank reactor (CSTR) configured to receive an aqueous effluent of the extraction module of the third SX unit. The third CSTR thus is located downstream of the third SX unit. The third CSTR comprises a dosing device for liquids and heating / cooling means. Suitable continuously stirred tank reactors are known in the art. The production plant further comprises at least one third solid / liquid separation device configured to receive an effluent of the third CSTR. The at least one third solid / liquid separation device thus is located downstream of the third CSTR. In some embodiments, the third solid / liquid separation device comprises a filter press.

[0060] The production plant further comprises at least one fourth continuously stirred tank reactor (CSTR) configured to receive an aqueous effluent from the third solid / liquid separation device. The fourth CSTR thus is located downstream of the third solid / liquid separation device. The fourth CSTR comprises a dosing device for liquids and heating / cooling means. Suitable continuously stirred tank reactors are known in the art.

[0061] The production plant further comprises at least one fourth solid / liquid separation device configured to receive an effluent of the fourth CSTR. The at least one fourth solid / liquid separation device thus is located downstream of the fourth CSTR. In some embodiments, the fourth solid / liquid separation device comprises a filter press.

[0062] The production plant further comprises a fourth solvent extraction (SX) unit configured to receive an aqueous effluent of the fourth solid / liquid separation device. The fourth SX unit comprises an extraction module and a scrubbing and stripping module. In the extraction module of the SX unit, an aqueous solution is extracted with an organic solvent, an aqueous phase and an organic phase being formed in the process. The organic phase is separated from the aqueous phase and transferred to the scrubbing and stripping module, where it is extracted with an aqueous acid. After scrubbing and stripping, the organic phase is cycled back to the extraction module. Suitable solvent extraction (SX) units are known in the art.

[0063] The production plant further comprises a second crystallizer configured to receive an aqueous effluent of the scrubbing and stripping module of the fourth SX unit and to produce crystals of a third metal salt. Suitable crystallizers are known in the art.

[0064] The production plant further comprises at least one fifth continuously stirred tank reactor (CSTR) configured to receive an aqueous effluent of the scrubbing and stripping module of the second SX unit. The fifth CSTR thus is located downstream of the second SX unit. The fifth CSTR comprises dosing devices for liquids and heating / cooling means. Suitable continuously stirred tank reactors are known in the art.

[0065] The production plant further comprises at least one fifth solid / liquid separation device configured to receive an effluent of the fifth CSTR. The at least one second fifth / liquid separation device thus is located downstream of the fifth CSTR. In some embodiments, the fifth solid / liquid separation device comprises a filter press.

[0066] The production plant further comprises at least one sixth continuously stirred tank reactor (CSTR) configured to receive an aqueous effluent of the fifth solid / liquid separation device. The sixth CSTR thus is located downstream of the fifth solid / liquid separation device. The sixth CSTR comprises a dosing device for liquids, and heating / cooling means. Suitable continuously stirred tank reactors are known in the art.

[0067] The production plant further comprises at least one sixth solid / liquid separation device configured to receive an effluent of the sixth CSTR. The at least one sixth solid / liquid separation device thus is located downstream of the sixth CSTR. In some embodiments, the sixth solid / liquid separation device comprises a filter press.

[0068] In some embodiments of the production plant, the first solid / liquid separation device, the second solid / liquid separation device, the third solid / liquid separation device, the fourth solid / liquid separation device, the fifth solid / liquid separation device, and the sixth solid / liquid separation device each comprise a filter press.

[0069] Detailed description of the drawing

[0070] A schematic diagram of an exemplary production plant of the present disclosure is shown in Fig. 1 .

[0071] The production plant comprises a first solvent extraction (SX) unit 10 which is configured to receive an acidic aqueous solution comprising nickel, cobalt, manganese, and lithium cations 1000. The first SX unit 10 comprises an extraction module 11 and a scrubbing and stripping module 12. The acidic aqueous solution comprising nickel, cobalt, manganese, and lithium cations entering the first SX unit 10 is extracted with an organic solvent in the extraction module 11 . The extracted aqueous phase leaves the extraction module 11 as an aqueous effluent 1001. The loaded organic phase is transferred to the scrubbing and stripping module 12, where it is scrubbed and stripped of metal cations with sulfuric acid to produce an acidic aqueous solution comprising the metal cations from the organic phase. The organic phase is recycled to the extraction module 11 , and the acidic aqueous solution comprising the metal cations from the organic phase leaves the scrubbing and stripping module 12 as an aqueous effluent 1002.

[0072] The production plant further comprises at least one first continuously stirred tank reactor (CSTR) 50 which is configured to receive an aqueous effluent 1001 of the extraction module 11 of the first SX unit 10. The CSTR 50 comprises a dosing device for liquids, heating / cooling means, and gas injection means. In the CSTR 50, a solution comprising sodium carbonate is added to precipitate impurities from the solution. The impurities comprise one or more selected from iron, aluminum, magnesium, calcium, titanium, residual copper, fluoride, and phosphate. Air is injected into the solution to oxidize any Fe(ll) present to Fe(lll). Iron, aluminum, and titanium precipitate from the solution as hydroxides and / or oxide-hydroxides and / or carbonates, fluorides and / or phosphates, The production plant further comprises at least one first solid / liquid separation device 110 which is configured to receive an effluent 5001 of the first CSTR 50. In the at least one first solid / liquid separation device 110, the precipitated impurities 11002 are removed from the effluent of the first CSTR 50 by solid / liquid separation, e.g., filtration.

[0073] The production plant further comprises at least one second CSTR 60 which is configured to receive an aqueous effluent 11001 from the first solid / liquid separation device 100. The second CSTR 60 comprises a dosing device for liquids and heating / cooling means. In the second CSTR 60, a solution comprising sodium carbonate is added to precipitate residual impurities from the solution.

[0074] The production plant further comprises at least one second solid / liquid separation device 120 which is configured to receive an effluent 6001 of the second CSTR 60. In the at least one second solid / liquid separation device 120, solids 1202 are recovered from the effluent 6001 of the second CSTR 60 by solid / liquid separation, e.g., filtration.

[0075] The production plant further comprises a second SX unit 20 which is configured to receive an aqueous effluent 12001 of the at least one second solid / liquid separation device 110. The second SX unit 20 comprises an extraction module 21 and a scrubbing and stripping module 22. The aqueous effluent 12001 of the at least one second solid / liquid separation device 120 is extracted with an organic solvent in the extraction module 21. The extracted aqueous phase leaves the extraction module 21 as an aqueous effluent 2001. The loaded organic phase is transferred to the scrubbing and stripping module 22, where it is scrubbed and stripped of metal cations with sulfuric acid to produce an acidic aqueous solution comprising the metal cations from the organic phase. The organic phase is recycled to the extraction module 21 , and the acidic aqueous solution comprising the metal cations from the organic phase leaves the scrubbing and stripping module 22 as an aqueous effluent 2002. The production plant further comprises a third SX unit 30 which is configured to receive an aqueous effluent 2001 of the extraction module 21 of the second SX unit 20. The third SX unit 30 comprises an extraction module 31 and a scrubbing and stripping module 32. The aqueous effluent 2001 of the extraction module 21 of the second SX unit 20 is extracted with an organic solvent in the extraction module 31. The extracted aqueous phase leaves the extraction module 31 as an aqueous effluent 3001. The loaded organic phase is transferred to the scrubbing and stripping module 32, where it is scrubbed and stripped of metal cations with sulfuric acid to produce an acidic aqueous solution comprising the metal cations from the organic phase. The organic phase is recycled to the extraction module 31 , and the acidic aqueous solution comprising the metal cations from the organic phase leaves the scrubbing and stripping module 32 as an aqueous effluent 3002.

[0076] The production plant further comprises a first crystallizer 170 configured to receive an aqueous effluent 3002 of the scrubbing and stripping module 32 of the third SX unit 30 and to produce crystals of a first metal salt, e.g., cobalt sulfate.

[0077] The production plant further comprises at least one third continuously stirred tank reactor (CSTR) 70 which is configured to receive an aqueous effluent 3001 of the extraction module 31 of the third SX unit 30. The CSTR 70 comprises a dosing device for liquids, and heating / cooling means. In the CSTR 70, a solution comprising hydroxide or carbonate anions is added to precipitate a mixed metal hydroxide and / or carbonate from the solution.

[0078] The production plant further comprises at least one third solid / liquid separation device 130 which is configured to receive an effluent 7001 of the third CSTR 70. In the at least one third solid / liquid separation device 130, a mixed metal hydroxide and / or carbonate 13002 is recovered from the effluent 7001 of the third CSTR 70 by solid / liquid separation, e.g., filtration. The production plant further comprises at least one fourth CSTR 80 which is configured to receive an aqueous effluent 13001 of the third solid / liquid separation device 130. The fourth CSTR 80 comprises a dosing device for liquids and heating / cooling means. In the fourth CSTR 80, sodium hydroxide solution is added to precipitate magnesium hydroxide.

[0079] The production plant further comprises at least one fourth solid / liquid separation device 140 which is configured to receive an effluent 8001 of the fourth CSTR 80. In the at least one fourth solid / liquid separation device 130, magnesium hydroxide 14002 is removed from the effluent 8001 of the fourth CSTR 80 by solid / liquid separation, e.g., filtration.

[0080] The production plant further comprises a forth SX unit 40 which is configured to receive an aqueous effluent 14001 of the at least one fourth solid / liquid separation device 140. The fourth SX unit 40 comprises an extraction module 41 and a scrubbing and stripping module 42. The aqueous effluent 14001 from the fourth solid / liquid separation device 130 is extracted with an organic solvent in the extraction module 41 . The extracted aqueous phase leaves the extraction module 41 as an aqueous effluent 4001. The loaded organic phase is transferred to the scrubbing and stripping module 42, where it is scrubbed and stripped of metal cations with sulfuric acid to produce an acidic aqueous solution comprising the metal cations from the organic phase. The organic phase is recycled to the extraction module 41 , and the acidic aqueous solution comprising the metal cations from the organic phase leaves the scrubbing and stripping module 42 as an aqueous effluent 4002.

[0081] The production plant further comprises a second crystallizer 180 configured to receive an aqueous effluent 4002 of the scrubbing and stripping module 42 of the fourth SX unit 40 and to produce crystals of a second metal salt, e.g., lithium sulfate.

[0082] The production plant further comprises at least one fifth CSTR 90 which is configured to receive an aqueous effluent 2002 of the scrubbing and stripping module 22 of the second SX unit 20. The fifth CSTR 90 comprises a dosing device for liquids, gas injection means, and heating / cooling means. In the fifth CSTR 90, alkaline solution is added to precipitate manganese carbonate and / or hydroxide.

[0083] The production plant further comprises at least one fifth solid / liquid separation device 150 which is configured to receive an effluent 9001 of the fifth CSTR 90. In the at least one fifth solid / liquid separation device 150, manganese carbonate and / or hydroxide 15002 is recovered from the effluent 9001 of the fifth CSTR 90 by solid / liquid separation, e.g., filtration.

[0084] The production plant further comprises at least one sixth CSTR 100 which is configured to receive an aqueous effluent 15001 of the at least one fifth solid / liquid separation device 140. The sixth CSTR 100 comprises a dosing device for liquids and heating / cooling means. In the sixth CSTR 100, alkaline solution is added to precipitate metal hydroxides.

[0085] The production plant further comprises at least one sixth solid / liquid separation device 160 which is configured to receive an effluent 10001 of the sixth CSTR 100. In the at least one sixth solid / liquid separation device 150, metal hydroxides 16002 are recovered from the effluent 10001 of the seventh CSTR 100 by solid / liquid separation, e.g., filtration.

[0086] Examples

[0087] Residual moisture

[0088] Residual moisture was determined by a gravimetric method. The initial weight mtot of the sample was measured, then the sample was completely dried overnight in an oven at 70°C and 110 mbar pressure and subsequently the dry weight mdry was determined. Residual moisture was calculated as 1 -(mdry / mtot).

[0089] Metal content

[0090] Elemental analysis of solids was performed using a combination of acid dissolution and alkaline-borate fusion digestion with analysis by inductively coupled plasma optical emission spectrometry (ICP-OES) on an inductively coupled plasma optical emission spectrometer (e.g., Agilent 5110 ICP-OES, Agilent Technologies Germany GmbH & Co. KG, 76337 Waldbronn, Germany).

[0091] An aliquot (e.g., about 0.2 g) of the sample material was weighed into a volumetric flask and dissolved under slight heating with 30 ml HCI. After cooling down, the insoluble residue was filtered out and incinerated together with the filter paper in a Pt crucible above an open flame. Subsequently, the residue was calcinated at about 600 °C in a muffle furnace and then mixed with 1.0 g of a K2CO3-Na2CO3 / Na2B4O7 flux mixture (4:1 ) and melted above an open flame until a clear melt was obtained. After cooling down, the melt cake was dissolved in deionized (DI) water under slight heating and 12 ml of HCI were added. Finally, the solution was joined to the initial filtered solution in the volumetric flask and topped up to its final volume with DI water. Each sample was prepared in triplicate. A blank sample was prepared in an analogous manner.

[0092] The digestion solution was analyzed by inductively coupled plasma-optical emission spectrometry (ICP-OES), using external calibration. For some samples, the digestion solution may be diluted before analysis, e.g., adapted to the concentration and calibration range of the respective analyte.

[0093] Calculations

[0094] The following calculations were used for determining the metal yields in the solids in example 1 m(Es)=EICP-S * F * T ( 2 ) wherein

[0095] E denotes a given element,

[0096] S denotes the dry solid,

[0097] EICP-S is the determined percentage-based content in the dry solid, m(Es) is the weight content of the element in the dry solid, m(EMax) is the total weight of an element based on the feed solution,

[0098] F is the flow rate of the continuous process,

[0099] T is a time span during steady state, and

[0100] YEis the leaching efficiency of the respective element.

[0101] Feeds

[0102] Comparative Example

[0103] Feed I containing Li, Ni and Co was subjected to a continuous operation to precipitate MHP at a temperature of 60 °C. The mixture was treated with Na2CO3-solution until a first pH of 7.3 was reached and a first MHP precipitate was separated. Through the addition of flocculation agents, sedimentation rate and particle size of the MHP was improved. From this operation a dry solid residue (1a) was obtained. The liquid fraction was treated with Na2COs until a second and final pH of 8.3 was reached. Through the addition of flocculation agents, sedimentation rate and particle size of the MHP was improved. From this operation a dry solid residue (1b) and overflow (1c) was obtained. Constitution of fractions and yields are found in the tables below.

[0104] Table 1 Composition of the fractions as determined by ICP-OES analysis

[0105] Fraction Co Li Mn Ni

[0106] 1a 14.2 wt.% 0.2 wt.% 0.2 wt.% 28.2 wt.%

[0107] 1b 10.9 wt.% 0.5 wt.% 0.8 wt.% 22.3 wt.%

[0108] 1c 32 m g / L 0.34 g / L 0 mg / L 63 m g / L Table 2 Final yields of selected elements in the precipitate

[0109] Co Li Mn Ni

[0110] 99.1 % 2.3% 94.4% 99.2%

[0111] Example 1 Performing analogous process steps on a Co-depleted feed (II) containing Li and Ni like described in the Comparative Example, the following constitution of the first dry solid (2a), second dry solid (2b) and the overflow (2c) and metal yields was obtained: Table 3 Composition of the fractions

[0112] Fraction Co Li Mn Ni

[0113] 2a 0.0 wt.% 0.2 wt.% 0.0 wt.% 37.0 wt.%

[0114] 2b 0.0 wt.% 0.5 wt.% 0.0 wt.% 27.7 wt.%

[0115] 2c 0 mg / L 0.34 g / L 0 mg / L 63 mg / L

[0116] Table 4 Final yields of selected elements in the precipitate

[0117] Co Li Mn Ni

[0118] 0.0% 2.3% 0.0% 99.5%

[0119] List of reference numerals

[0120] 10 First SX unit

[0121] 11 Extraction module of first SX unit

[0122] 12 Scrubbing and stripping module of first SX unit

[0123] 20 Second SX unit

[0124] 21 Extraction module of second SX unit

[0125] 22 Scrubbing and stripping module of second SX unit

[0126] 30 Third SX unit

[0127] 31 Extraction module of third SX unit

[0128] 32 Scrubbing and stripping module of third SX unit

[0129] 40 Fourth SX unit

[0130] 41 Extraction module of fourth SX unit

[0131] 42 Scrubbing and stripping module of fourth SX unit

[0132] 50 First CSTR

[0133] 60 Second CSTR

[0134] 70 Third CSTR

[0135] 80 Fourth CSTR

[0136] 90 Fifth CSTR

[0137] 100 Sixth CSTR

[0138] 110 First solid / liquid separation unit

[0139] 120 Second solid / liquid separation unit

[0140] 130 Third solid / liquid separation unit

[0141] 140 Fourth solid / liquid separation unit

[0142] 150 Fifth solid / liquid separation unit

[0143] 160 Sixth solid / liquid separation unit

[0144] 170 First crystallizer

[0145] 180 Second crystallizer

[0146] 1000 Acidic aqueous solution comprising Ni, Co, Mn, and Li cations

[0147] 1001 Aqueous effluent of extraction module of first SX unit

[0148] 1002 Aqueous effluent of scrubbing and stripping module of first SX unit

[0149] 2001 Aqueous effluent of extraction module of second SX unit

[0150] 2002 Aqueous effluent of scrubbing and stripping module of second SX unit 3001 Aqueous effluent of extraction module of third SX unit

[0151] 3002 Aqueous effluent of scrubbing and stripping module of third SX unit

[0152] 4001 Aqueous effluent of extraction module of fourth SX unit

[0153] 4002 Aqueous effluent of scrubbing and stripping module of fourth SX unit

[0154] 5001 Effluent of first CSTR

[0155] 6001 Effluent of second CSTR

[0156] 7001 Effluent of third CSTR

[0157] 8001 Effluent of fourth CSTR

[0158] 9001 Effluent of fifth CSTR

[0159] 10001 Effluent of sixth CSTR

[0160] 11001 Aqueous effluent of first solid / liquid separation unit

[0161] 11002 Solids (First impurity precipitate)

[0162] 12001 Aqueous effluent of second solid / liquid separation unit

[0163] 12002 Solids (Second impurity precipitate)

[0164] 13001 Aqueous effluent of third solid / liquid separation unit

[0165] 13002 Solids (mixed metal hydroxide and / or carbonate precipitate)

[0166] 14001 Aqueous effluent of fourth solid / liquid separation unit

[0167] 14002 Solids (Magnesium hydroxide)

[0168] 15001 Aqueous effluent of fifth solid / liquid separation unit

[0169] 15002 Solids (Manganese hydroxide and / or carbonate)

[0170] 16001 Aqueous effluent of sixth solid / liquid separation unit

[0171] 16002 Solids (Metal hydroxides)

Claims

Claims1 . A continuous process for recovering metal salts from an acidic aqueous solution comprising nickel, cobalt, manganese, and lithium cations, the process comprising a) optionally, adjusting the pH value of the solution to a value in the range of from 1.5 to 2.5 and recovering copper from the solution by solvent extraction, or by precipitation of copper sulfide, followed by solid / liquid separation, b) adjusting the pH of the acidic aqueous solution comprising nickel, cobalt, manganese, and lithium cations to be in the range of from 3.0 to 4.0 by addition of sodium carbonate, and subsequently precipitating impurity cations of the group consisting of Al and Fe cations and impurity anions comprising P, F, Al and / or Si present in the solution from the solution, c) removing solids from the mixture obtained in step b), d) adjusting the pH of the acidic aqueous solution obtained in step c) to be in the range of from 4.5 to 5.0 by addition of sodium carbonate, and subsequently precipitating impurity cations of the group consisting of Al and Fe cations and impurity anions comprising P, F, Al and / or Si present in the solution from the solution, e) removing solids from the mixture obtained in step d), f) adjusting the pH of the acidic aqueous solution obtained in step e) to be in the range of from 2 to 4, and subsequently removing manganese cations and any residual impurity cations of the group consisting of Ca, Cu, Zn, and Cd cations present in the solution by solvent extraction to obtain an aqueous solution depleted of manganese cations and impurity cations and a solvent comprising manganese cations and impurity cations; and scrubbing andstripping the solvent comprising manganese cations and impurity cations with sulfuric acid to obtain an acidic aqueous solution comprising manganese cations and impurity cations, g) adjusting the pH of the acidic aqueous solution depleted of manganese cations and impurity cations obtained in step f) to be in the range of from 3 to 6; and subsequently removing cobalt cations from the solution by solvent extraction to obtain an aqueous solution depleted of cobalt cations and an organic solvent comprising cobalt cations, and scrubbing and stripping the organic solvent comprising cobalt cations with sulfuric acid to obtain an acidic aqueous solution comprising cobalt cations, h) adjusting the pH of the aqueous solution depleted of cobalt cations obtained in step f) to be in the range of from 7 to 8.5, and precipitating a mixed metal hydroxide and / or carbonate from the solution, i) performing a solid / liquid separation of the mixture obtained in step h) to obtain solid mixed metal hydroxide and / or carbonate and a mother liquor, j) adding sodium hydroxide to the mother liquor obtained in step i), adjusting the pH of the mother liquor to be in the range of from 10 to 12.5, and precipitating magnesium hydroxide from the mother liquor, k) removing solids from the mixture obtained in step j), l) adjusting the pH of the aqueous solution obtained in step k) to be in the range of from 8 to 12; and subsequently removing lithium cations from the solution by solvent extraction to obtain an aqueous solution depleted of lithium cations and an organic solvent comprising lithium cations; and scrubbing and stripping the organic solvent comprising lithium cations with sulfuric acid to obtain an acidic aqueous solution comprising lithium cations.

2. The process of claim 1 , further comprising m) adjusting the pH of the acidic aqueous solution comprising manganese cations and impurity cations obtained in step f) to be in the range of from 6.8 to 8.5, and precipitating manganese carbonate and / or manganese hydroxide from the solution, n) removing solids from the mixture obtained in step m), o) optionally, adjusting the pH of the solution obtained in step n) to be in the range of from 10 to 12.5, and precipitating metal hydroxides from the solution, p) optionally, removing solids from the mixture obtained in step o).

3. The process of claim 1 or 2, further comprising q) crystalizing cobalt sulfate from the acidic aqueous solution comprising cobalt cations obtained in step g).

4. The process of any one of claims 1 to 3, further comprising r) crystalizing lithium sulfate from the aqueous solution depleted of cobalt cations obtained in step I).

5. The process of any one of claims 1 to 4, wherein copper is recovered from the solution by solvent extraction in step a) and the organic solvent used is a solution of a 1 :1 mixture of 5-nonyl salicylaldoxime and 2-hydroxy-5- nonyl acetophenone.

6. The process of any one of claims 1 to 4, wherein copper is recovered from the solution in step a) by precipitation of copper sulfide, followed by solid / liquid separation.

7. The process of claim 6, wherein sodium thiosulfate is added in step a) to precipitate copper sulfide.

8. The process of any one of claims 1 to 7, wherein the organic solvent used in step f) is a solution of 40 vol% bis(2-ethylhexyl)phosphate in dearomatized hydrocarbon fluid.

9. The process of any one of claims 1 to 8, wherein the organic solvent used in step g) is a solution of 20 vol% bis-(2,4,4-trimethylpentyl) phosphinic acid in dearomatized hydrocarbon fluid containing 1 g / L butylhydroxytoluene.

10. A production plant comprising(1 ) a first solvent extraction (SX) unit (10) configured to receive an acidic aqueous solution comprising nickel, cobalt, manganese, and lithium cations (1000), the first SX unit (10) comprising i. an extraction module (11 ), ii. a scrubbing and stripping module (12),(2) at least one first continuous stirred-tank reactor (CSTR) (50) configured to receive an aqueous effluent (1001 ) of the extraction module (11 ) of the first SX unit (10), the first CSTR (50) comprising i. a dosing device for liquids, ii. heating / cooling means, iii. gas injection means,(3) at least one first solid / liquid separation device (110) configured to receive an effluent (5001) of the first CSTR (50),(4) at least one second continuous stirred-tank reactor (CSTR) (60) configured to receive an effluent (11001) of the first solid / liquid separation device (110), the second CSTR (60) comprising i. a dosing device for liquids, ii. heating / cooling means,(5) at least one second solid / liquid separation device (120) configured to receive an effluent (6001) of the second CSTR (60),(6) a second solvent extraction (SX) unit (20) configured to receive an aqueous effluent (12001) of the second solid / liquid separation device (120), the second SX unit (20) comprisingi. an extraction module (21 ), ii. a scrubbing and stripping module (22),(7) a third solvent extraction (SX) unit (30) configured to receive an aqueous effluent (2001 ) of the scrubbing and stripping module (22) of the second SX unit (20), the third SX unit (30) comprising i. an extraction module (31 ), ii. a scrubbing and stripping module (32),(8) a first crystallizer (170) configured to receive an aqueous effluent (3002) of the scrubbing and stripping module (32) of the third SX unit (30) and to produce crystals of a first metal salt,(9) at least one third continuous stirred-tank reactor (CSTR) (70) configured to receive an aqueous effluent (3001 ) of the extraction module (31 ) of the third SX unit (30), the third CSTR (70) comprising i. a dosing device for liquids, ii. heating / cooling means,(10) at least one third solid / liquid separation device (130) configured to receive an effluent (7001) of the third CSTR (70),(11 ) at least one fourth continuous stirred-tank reactor (CSTR) (80) configured to receive an aqueous effluent (13001 ) of the at least one third solid / liquid separation device (130), the fourth CSTR (80) comprising i. a dosing device for liquids, ii. heating / cooling means,(12) at least one fourth solid / liquid separation device (140) configured to receive an effluent (8001 ) of the fourth CSTR (80),(13) a fourth solvent extraction (SX) unit (40) configured to receive an aqueous effluent (14001) of the at least one fourth solid / liquid separation device (140), the fourth SX unit (40) comprising i. an extraction module (41 ), ii. a scrubbing and stripping module (42),(14) a second crystallizer (180) configured to receive an aqueous effluent (4002) of the scrubbing and stripping module (42) of the fourth SX unit (40) and to produce crystals of a second metal salt,(15) at least one fifth continuous stirred-tank reactor (CSTR) (90) configured to receive an effluent (2002) of the scrubbing and stripping module (22) of the second SX unit (20), the fifth CSTR (90) comprising i. a dosing device for liquids, ii. heating / cooling means,(16) at least one fifth solid / liquid separation device (150) configured to receive an effluent (9001 ) of the fifth CSTR (90),(17) at least one sixth continuous stirred-tank reactor (CSTR) (100) configured to receive an effluent (15001) of the fifth solid / liquid separation device (150, the sixth CSTR (100) comprising i. a dosing device for liquids, ii. heating / cooling means,(18) at least one sixth solid / liquid separation device (160) configured to receive an effluent (10001) of the sixth CSTR (100).

11. The production plant of claim 10, wherein the first solid / liquid separation device (110), the second solid / liquid separation device (120), the third solid / liquid separation device (130), the fourth solid / liquid separation device (140), the fifth solid / liquid separation device (150), and the sixth solid / liquid separation device (160) each comprise a filter press.

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