Process and apparatus for removing impurities from crystallized metal sulfates

Abstract

A process for removing impurities from crystallized metal sulfate comprising contacting the crystallized metal sulfate with a metal sulfate-rich liquid. The metal may be cobalt, nickel or manganese and the impurity may be magnesium or calcium. The metal sulfate-rich liquid may be an overflow from the crystallization of the metal sulfate, and the overflow may be subjected to one or more impurity removal steps prior to contacting the crystallized metal sulfate such that the overflow contains a lower level of impurities than the crystallized metal sulfate being contacted. A countercurrent washing circuit for removing impurities from the crystallized metal sulfate may be used whereby a plurality of washing tanks are configured to receive the crystallized metal sulfate in sequence and to receive washing liquid in reverse of the sequence.

Description

[Technical field]

[0001] The present disclosure relates to processes and methods for producing and purifying crystallized metal sulfates, and in particular for removing impurities from crystallized metal sulfates. [Background technology]

[0002] Climate change is driving the electrification of transportation, resulting in an increased need for batteries such as lithium-ion batteries (LIBs). LIBs are already widespread in society, but their total annual consumption is small compared to the total annual consumption required for mass market adoption of electric vehicles. As the demand for LIBs increases, so does the demand for chemicals to manufacture LIBs, especially battery-grade metal sulfates.

[0003] Nickel and cobalt sulfate battery chemicals are typically produced by dissolving nickel and cobalt metals separately in sulfuric acid and refining before crystallization as battery grade sulfates. This metal dissolution process is carried out by both cathode manufacturers and mining companies who build sulfate production circuits into their refineries. The metal dissolution route from ore to battery requires expensive steps of either electrowinning or hydrogen reduction to produce London Metal Exchange (LME) grade metals before dissolution. This route is the main cause of the premium charged for battery grade sulfates, primarily nickel sulfate, over the price of the metal. The industry is moving towards more direct production routes from concentrates or intermediates to battery chemicals. For example, a more direct route has already been developed for cobalt chemicals as the chemistry of lithium cobalt oxide batteries used in mobile phones and electronics matures.

[0004] Additionally, current battery chemical production processes often include separation of cobalt and nickel by solvent extraction (SX), which allows for the production of individual battery grade sulfates that meet purity requirements. While SX can be very effective at separating metals, it is a relatively complex unit operation, requiring multiple stages of extraction, scrubbing and stripping, as well as systems for organic treatment of the aqueous effluent stream, crud removal, organic vapor recovery and fire suppression. These requirements result in significant capital costs associated with commercial-scale SX operations. Depending on the number of SX circuits required, direct costs associated with SX can exceed 30% of refinery costs. Summary of the Invention [Problem to be solved by the invention]

[0005] Processes and methods for obtaining high purity crystalline metal sulfates are desirable. [Means for solving the problem]

[0006] Embodiments of the present disclosure will now be described, by way of example only, with reference to the accompanying figures. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic diagram of a process for removing impurities from a crystallized metal sulfate according to one embodiment of the present disclosure. [Diagram 2] FIG. 1 is a schematic diagram of a process for crystallizing cobalt sulfate and removing magnesium and calcium impurities therefrom according to one embodiment of the present disclosure. [Diagram 3] FIG. 1 is a schematic diagram of a countercurrent washing circuit according to one embodiment of the present disclosure. [Figure 4] FIG. 1 is a flow diagram of a general process for producing crystallized metal sulfates. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Processes for producing crystallized metal sulfates, particularly crystallized metal sulfates of high purity, are desirable. Accordingly, the present disclosure provides processes and apparatus for reducing or removing at least a portion of the impurities from crystallized metal sulfates. The process may include contacting the crystallized metal sulfate with a solution that is rich in metal sulfate but low in impurities, thereby solubilizing impurities in the crystallized metal sulfate that may be distributed within the crystal lattice. The solution may be from an overflow stream of a metal sulfate crystallizer that has been treated to reduce or remove at least a portion of the impurities, such that the solution has a lower level of impurities than the crystallized metal sulfate, but is rich in metal sulfate. In such processes, the metal sulfate crystals do not materially redissolve upon contact with the solution, but may partially dissolve.

[0009] The processes and apparatus disclosed herein may be used to reduce or remove at least a portion of the impurities from the crystallized metal sulfate. The crystallized metal sulfate may be produced in the processes for producing crystallized metal sulfate described herein. It will be understood that the crystallized metal sulfate may be obtained from other suitable sources, including any process that produces crystallized metal sulfate using evaporative crystallization, or cooling crystallization, or heating crystallization.

[0010] FIG. 1 illustrates a process for removing impurities from crystallized metal sulfate according to one embodiment of the present disclosure. The metal sulfate may be cobalt sulfate, nickel sulfate, or manganese sulfate. The crystallized metal sulfate may be a metal sulfate hydrate or any suitable solvated metal sulfate. According to FIG. 1, a metal sulfate-rich feed solution containing a relatively high level of impurities may be fed to a crystallizer to obtain metal sulfate-rich crystals containing a relatively low level of impurities and an overflow solution rich in metal sulfate and impurities. The impurities in the metal sulfate-rich crystals may be distributed within the crystal lattice. The overflow solution may be fed to an impurity removal step. The impurities may include magnesium or calcium. The impurities may include trace metal cations in the +2 oxidation state. The removal of impurities may involve adding a precipitating agent, such as sodium fluoride, to induce precipitation of at least a portion of the impurities. The removal of impurities may include ion exchange (IX), such as nickel removal by IX from a cobalt solution or manganese removal by IX from a cobalt or nickel solution. The removal of impurities may occur before and / or after crystallization. Following the impurity removal step, as shown in FIG. 1, a liquid is formed that is rich in metal sulfate but relatively low in impurities, which can be used in the crystal leaching step. Because the metal sulfate concentration in the liquid of FIG. 1 is similar to that in the leaching step, the metal sulfate crystals do not redissolve. Furthermore, because the level of impurities in the liquid of FIG. 1 is lower than the level of impurities in the crystals, the impurities preferentially migrate from the crystals to the liquid.

[0011] Thus, the process of FIG. 1 produces crystals rich in metal sulfates containing relatively low levels of impurities and a liquid that can be reused as a recirculating wash elsewhere in this or a related process. The liquid wash can be used in the elutriation leg of the crystallizer, whereby the exiting crystals are washed with a purified liquid wash stream. In such a case, the liquid enters the crystallizer. Alternatively or additionally, a liquid wash can be used downstream of the crystallizer as an initial or subsequent washing step for the crystals to help achieve the target product composition. The liquid wash can be used to dissolve solid metal sulfates, such as to redissolve crude metal sulfates for further processing.

[0012] In one or more embodiments, the process includes crystallizing a metal sulfate-rich feed solution to form crystals enriched in the selected metal sulfate and an overflow solution containing the metal sulfate and impurities. Crystallizing the metal sulfate-rich feed solution may include preferentially crystallizing the selected metal sulfate from the metal sulfate-rich feed solution over alternative metal sulfates. Alternatively, or in addition, the metal sulfate-rich feed solution may be subjected to one or more pretreatment steps prior to crystallization of the selected metal sulfate hydrate.

[0013] FIG. 2 shows an example of a process for removing magnesium and calcium impurities from cobalt sulfate heptahydrate (CoSO4.7H2O) crystals. Similar to the process in FIG. 1, FIG. 2 shows that a feed is fed to a crystallizer to provide cobalt sulfate heptahydrate crystals and an overflow liquid sent to Mg / Ca removal via precipitation induced by the addition of sodium fluoride. The crystallized cobalt sulfate in FIG. 2 is then fed to an elutriation leg that is fed with filtrate from Mg / Ca removal to displace a mother liquor stream from the crystallizer and wash some of the Mg from the crystals. This filtrate can be used because it has a low concentration of Mg and a high concentration of Co. Thus, by mixing this mother liquor stream with the crystals, some of the Mg from the crystals is washed without significantly dissolving the CoSO4.7H2O crystals. The premise for impurity removal is that the relative concentrations of the trace elements in the mother liquor and washed crystals with respect to CoSO4.7H2O define a uniform distribution coefficient. The uniform distribution coefficient depends on the time and the nature of the impurity (e.g., Cd, Fe, Mg, Ni, Zn, Mn, Cu or Ca). The same principle applies to the re-leaching tank 1 in FIG. 2, where the crystallized metal sulfate is fed after the elutriation leg. A residence time of 6 hours was selected in the re-leaching tank 1 to lower the Mg distribution coefficient and allow more Mg to be washed from the crystals. Any suitable residence time can be selected, for example, the residence time can be from about 30 minutes to about 10 hours. The slurry from the re-leaching tank 1 is then dewatered. The liquid enriched with CoSO4 is recycled to the crystallizer feed. The dewatered crystals are sent to a countercurrent washing (CCW) circuit for further washing of Mg.

[0014] FIG. 3 shows an embodiment of a countercurrent washing (CCW) circuit / apparatus 300 for removing impurities from crystallized metal sulfate 301, such as the cobalt sulfate heptahydrate crystals of FIG. 2. The countercurrent washing circuit / apparatus 300 can consist of multiple stages of washing to achieve a target impurity (e.g., Mg) concentration. The countercurrent washing circuit / apparatus 300 can include one or more inputs for wash water, such as countercurrent wash water 302 and wash water 303. In each stage 310, 320, 330, 340, 350, 360, 370, 380, 390, 400, the wash liquid and solids are mixed in a tank for a selected residence time, e.g., 6 hours (to achieve an optimal distribution coefficient for Mg). For example, in the first stage 310, the wash liquid 311 is mixed with the solids 301 in tank 312. The overflow from each stage is combined with the discharge slurry of the previous stage, and the combined flow is sent to a screen for dewatering. For example, the overflow 321 from the second stage 320 is combined with the discharge slurry 314 of the first stage 310 and the combined stream 315 is sent to a screen 316 for dewatering. The dewatered solids are passed to the next stage and the liquid is passed to the previous stage (i.e., the solids and water streams flow countercurrently in this circuit). For example, in the first stage 310, the dewatered solids 317 are passed to the second stage 320 and the liquid 311 is passed to the previous stage 310. The wash water 303 is used in the last stage 400 of the circuit to provide a final cake 305 of purified crystallized metal sulfates. The wash liquor 304 from the first stage 310, concentrated with CoSO4, is sent to a crystallizer. For the CCW circuit 300 of FIG. 3, the final concentration of Mg in the wash liquor 304 is based on the distribution coefficient and the final concentration of Co is based on the solubility limit of CoSO4. Countercurrent flow allows for more efficient mass transfer between the crystals and the wash liquid (compared to cocurrent flow). The number of stages or the flow of the wash water can be adjusted accordingly to achieve higher / lower Mg concentration in the final crystals. In the embodiment of Figure 3, approximately 50% of the Mg is removed from the crystals approximately every two stages.

[0015] In a CCW circuit such as that of Figure 3, the wash liquid from the first tank may be recycled to the metal sulfate crystallizer. The recycled wash liquid may be subjected to one or more further processing steps such as thickening or other enrichment. The wash liquid of the last wash tank in the sequence is preferably substantially free of impurities and may be water or substantially pure metal sulfate brine. The solid / liquid separation device used in the CCW circuit may be any suitable means for separating solids from liquids such as a centrifuge, thickener or screen.

[0016] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0017] As used in this specification and claims, the singular forms "a," "an," and "the" include the plural forms unless the context clearly indicates otherwise.

[0018] As used herein, the term "comprising" will be understood to mean that the list that follows is not exhaustive but may or may not include any other additional suitable items as appropriate, such as one or more further features, components and / or ingredients.

[0019] As used herein, "impurities" refer to components of a feedstock that are not metal sulfates as described herein or that do not contribute to the formation of a metal sulfate or a crystallized metal sulfate as described herein. As used herein, an "impurity" may be a useful, valuable, or desirable substance when isolated from a feedstock. In one or more embodiments, an impurity may be a sulfate other than the sulfate of interest. For example, a process may produce two or more sulfates, such as magnesium sulfate, cobalt sulfate, and / or nickel sulfate. Any one of these sulfates may be considered an impurity in the production of any of the sulfates.

[0020] As used herein, "crystallization," "crystallize," or "crystallized" refers to the process of selectively and slowly forming a crystalline network from a metal sulfate in an aqueous solution, such as a leached solution (or PLS), resulting in a more purified crystalline compound. In contrast, as used herein, "precipitation" refers to a process characterized by the addition of a precipitating or basifying reagent and the formation of a crystalline or amorphous solid from solution. As used herein, "co-crystallize" or "co-crystallizing" refers to the crystallization of two or more components (e.g., metal sulfate, impurities, etc.) together (e.g., simultaneously) from a solution. As used herein, when referring to "selectively crystallizing" or "selectively co-crystallizing" a metal sulfate, "selective" refers to crystallizing the metal sulfate from most, if not all, impurities or other components, or in other words, "selective" refers to forming a purer crystallized metal sulfate.

[0021] As used herein, "feedstock" or "pre-leached feedstock" refers to a solid material that contains at least some material that is desired to be extracted / isolated from said solid for further processing and / or use in an end product, such as a metal that is desired for making battery materials.

[0022] As used herein, "treatment process" refers to a process that may include a pretreatment step (e.g., pre-leaching), a purification step in which the leached solution is treated to remove impurities (e.g., fluoride precipitation, direct lithium extraction), or a combination of both.

[0023] As used herein, "NMC" refers to nickel, manganese, and / or cobalt. For example, NMC sulfate refers to nickel sulfate, manganese sulfate, and / or cobalt sulfate. As used herein, "metal sulfate" refers to any one or combination of nickel sulfate, cobalt sulfate, and / or manganese sulfate. Additionally, "metal hydroxide" refers to any one or combination of nickel hydroxide, cobalt hydroxide, and / or manganese hydroxide. As used herein, the term "metal hydroxide" can refer to any one or combination of sodium hydroxide, potassium hydroxide, and / or lithium hydroxide.

[0024] Process for producing metal sulfates In one aspect, a process for producing a metal sulfate is provided that includes crystallizing a metal sulfate from an aqueous solution to form a crystallized metal sulfate in a mother liquor that includes uncrystallized metal sulfate. The process may further include separating the crystallized metal sulfate from the mother liquor. The crystallized metal sulfate produced in such a process may be further purified using a process for removing impurities from the crystallized metal sulfate according to one or more embodiments of the present disclosure.

[0025] FIG. 4 shows a flow diagram of a general process for producing a crystallized metal sulfate, which may include basifying a portion of the mother liquor with, for example, a metal hydroxide to convert the uncrystallized metal sulfate to a basic metal salt. The basic metal salt may be used upstream of the crystallization of the metal sulfate. The crystallization process may include one or more processes for removing impurities from the crystallized metal sulfate according to the present disclosure. The crystallizing process may further include bleeding the mother liquor and controlling the bleeding rate to selectively inhibit crystallization of impurities when crystallizing the metal sulfate. The crystallizing process may further include controlling the amount of free water in the crystallizer to selectively inhibit crystallization of impurities when crystallizing the metal sulfate. Controlling the amount of free water may include controlling the evaporation rate of water from the crystallizer or controlling the addition of water to the crystallizer. The step of basifying a portion of the mother liquor to convert the uncrystallized metal sulfate to a basic metal salt further includes bleeding the mother liquor and controlling a bleeding rate to produce an amount of basic metal salt at least approximately equal to the amount of acid neutralized upstream of the crystallization of the metal sulfate. The crystallized metal sulfate can be a battery grade crystallized metal sulfate.

[0026] In one or more embodiments of the process for producing metal sulfates described herein, the process further comprises leaching the feedstock and forming an aqueous solution comprising metal sulfates. In one or more embodiments, the feedstock comprises any one or combination of mixed hydroxide precipitate, mixed sulfide precipitate, nickel sulfide concentrate, cobalt sulfide concentrate, nickel laterite, nickel matte, ferronickel, materials from recycled lithium ion batteries or lithium ion battery manufacturing scrap, or spent cathode materials. In one or more embodiments, the feedstock comprises pre-formed and / or pre-crystallized metal sulfates. The feedstock may comprise metal sulfates containing impurities, such as pre-formed nickel sulfate or cobalt sulfate crystals. The feedstock may comprise a solution comprising metal sulfates. The process for producing metal sulfates may include solubilizing the metal sulfates in the feedstock prior to further processing the feedstock. In one embodiment, the crystallized metal sulfates are produced at a first location, transported to a second location, and dissolved in a solution used to facilitate removal of impurities from the crystallized metal sulfates at the second location. The solution can then be recrystallized at a second location to recover the metal sulfate. In one or more embodiments of the processes described herein, the process further comprises isolating the basic metal salt from the mother liquor. In one or more embodiments, isolating the basic metal salt comprises selectively precipitating the basic metal salt using a one or two stage precipitation circuit. In one or more embodiments of the processes described herein, the metal sulfate is any one or combination of nickel sulfate, cobalt sulfate, or manganese sulfate. In one or more embodiments of the processes described herein, the basic metal salt comprises a metal hydroxide. In one or more embodiments, the metal hydroxide comprises any one or combination of nickel hydroxide, cobalt hydroxide, or manganese hydroxide.

[0027] In one or more embodiments of the processes for producing metal sulfates described herein, the step of crystallizing the metal sulfate comprises selectively crystallizing any one or two of nickel sulfate, manganese sulfate, and cobalt sulfate from an aqueous solution. In one or more embodiments of the processes described herein, the step of crystallizing the metal sulfate comprises selectively crystallizing any combination of nickel sulfate, manganese sulfate, and cobalt sulfate from an aqueous solution. In one or more embodiments of the processes described herein, the crystallized metal sulfate is a battery grade crystallized metal sulfate or an electroplating grade crystallized metal sulfate.

[0028] In one or more embodiments, the process for producing metal sulfates described herein includes further purifying the aqueous solution containing the metal sulfates (e.g., sulfate matrix, pregnant leach solution (PLS)), where the PLS is subjected to any one or combination of purification steps (also referred to herein as impurity or component removal steps) to remove certain impurities or components such as Cu (e.g., via sulfidation, solvent extraction, cementation, ion exchange, etc.), Fe and Al (e.g., via precipitation, ion exchange, etc.), Zn (e.g., via sulfidation, solvent extraction, ion exchange, etc.), Co (e.g., via solvent extraction, ion exchange, precipitation, etc.), Ca (e.g., via solvent extraction, ion exchange, etc.), Mg (e.g., via solvent extraction, ion exchange, etc.), F (e.g., via calcium / lime addition), or graphite (e.g., via filtration). The purified PLS may be purified by filtration or by filtration. The feedstock may be introduced into a crystallizer under conditions sufficient to selectively crystallize any one or combination of nickel sulfate (NiSO4), cobalt sulfate (CoSO4), manganese sulfate (MnSO4), and lithium sulfate (Li2SO4) from the feedstock to produce crystallized metal sulfates in the mother liquor (e.g., via a forced circulation crystallizer under vacuum, etc., for lithium, magnesium, sodium, or potassium, depending on the feedstock). These crystallized metal sulfates are then isolated from the mother liquor (e.g., discharged from the crystallizer). If one crystallization cycle (e.g., using one crystallizer) is insufficient to produce crystallized metal sulfates (which may occur, for example, with feedstocks containing high concentrations of impurities), the crystals discharged from the crystallizer may be dissolved in pure water to form an aqueous sulfate solution before being introduced into a second crystallization cycle (e.g., using a second crystallizer) to be recrystallized.

[0029] After crystallization, the mother liquor may contain impurities including undesired salts / metals (e.g., Li2SO4, MgSO4, Na2SO4, etc.) and metal sulfates that did not crystallize out of solution (also referred to herein as uncrystallized metal sulfates). In one embodiment, to selectively recover these uncrystallized metal sulfates from the undesired materials remaining in solution, the mother liquor can be bled from the crystallizer and basified to convert the uncrystallized metal sulfates to basic metal salts such as metal hydroxides (e.g., Ni(OH)2, Co(OH)2, Mn(OH)2, etc.). These metal hydroxides can be used upstream to neutralize acids introduced during the leaching and / or purification stages of the process that formed the PLS, thereby converting the metal hydroxides back to metal sulfates, which can then be isolated by crystallization. Prior to upstream use, the metal hydroxides can be isolated and washed from the mother liquor and reslurried with water for transfer, which can limit exposure to air and therefore oxidation of the hydroxides. In another embodiment, after crystallization, some or all of the mother liquor (overflow solution) may be used to facilitate removal of impurities from the crystallized metal sulfate. In this embodiment, the overflow solution is first treated to remove at least a portion of the impurities to provide a liquid rich in metal sulfate and lean in impurities. The crystallized metal sulfate is then contacted with the liquid to facilitate migration of at least a portion of the impurities from the crystals. The liquid remaining after this step may contain even more impurities. The liquid may be basified to convert any remaining uncrystallized metal sulfate to a basic metal salt. The basic metal salt may be used upstream as disclosed herein. In addition to using metal hydroxide as a neutralizing agent, the process may also use an external source of neutralizing agent (e.g., added oxide, hydroxide) to basify the mother liquor leaving the crystallizer, optionally to neutralize acids introduced during the leaching and / or purification steps.These external neutralizing agents are selected for their ability to be regenerated (e.g., via electrolysis, etc.) from waste materials to minimize or avoid the formation of waste streams (e.g., CaO / CaCO3 as agent, CaSO4.2H2O as waste material, NaOH as agent, Na2SO4 as waste material) or to generate more valuable by-products (e.g., KOH as agent, K2SO4 as by-product). In one or more embodiments, NaOH is used as the neutralizing agent and a sodium sulfate stream is formed in the basification step.

[0030] In general, the metal sulfate production process is largely feedstock independent, accepting and handling raw feedstocks (e.g., concentrates, mixed hydroxide / sulfide precipitates, other Ni-based feedstocks) and recycled feedstocks (e.g., spent battery materials). The process may also include leaching the feedstock under conditions (e.g., pressure leaching, pressure oxidation) to form an aqueous solution (e.g., sulfate matrix, pregnant leach solution (PLS)) containing the metal sulfate. The process may produce any one or combination of crystallized nickel sulfate (NiSO4), cobalt sulfate (CoSO4), manganese sulfate (MnSO4), and lithium sulfate (Li2SO4). The process may produce any one or two of crystallized nickel sulfate (NiSO4), cobalt sulfate (Co-SO4), and manganese sulfate (MnSO4). The process may produce all three of crystallized nickel sulfate (NiSO4), cobalt sulfate (CoSO4), and manganese sulfate (MnSO4). Some of the crystallized metal sulfates isolated from the process may be battery grade. Some of the crystallized metal sulfates isolated from the process may be suitable for use in electroplating. Some of the crystallized metal sulfates isolated from the process may be metal sulfate hydrates (e.g., crystallized metal sulfates and water molecules combined in various ratios as an integral part of the crystal, such as ratios of one water molecule per metal sulfate, or six water molecules per metal sulfate, or seven water molecules per metal sulfate).

[0031] In one or more embodiments of the process described herein, the process includes leaching a feedstock and forming an aqueous solution including metal sulfates. For example, the process may begin with an input of one or more feedstocks. Suitable feedstocks include any feedstock including any one or combination of nickel (Ni), cobalt (Co), manganese (Mn), or lithium (Li). In some embodiments, the feedstock may include any one or combination of raw feedstocks and recycled material feedstocks. Examples of raw feedstocks include, but are not limited to, mixed hydroxide precipitate (MHP), mixed sulfide precipitate (MSP), nickel sulfide concentrate, cobalt sulfide concentrate, nickel laterite, nickel matte, or ferronickel. Examples of recycled material feedstocks include, but are not limited to, spent cathode material and materials derived from recycled lithium ion batteries or lithium ion battery manufacturing scrap (collectively referred to herein as black mass).

[0032] The feedstock may be leached under conditions to form an aqueous solution containing metal sulfates (PLS), e.g., a sulfate matrix, a pregnant leach solution, etc. Generally, the leaching conditions include reacting the feedstock with an acid leach stream, which may include: an acid stream, an acid stream and hydrogen peroxide, an acid stream and sulfur dioxide, or an acid stream and another reducing agent, such as sucrose. The leaching conditions may also include solubilizing the feedstock by oxidizing it in a pressure vessel using oxygen or air. In forming the sulfate matrix PLS, the acid stream may act as a sulfate source, e.g., may include sulfuric acid, or the acid stream and / or the feedstock may act as the sulfate source.

[0033] There are many leaching conditions that may be suitable for the formation of PLS. A person skilled in the art will know which leaching conditions to select and test to determine the specific conditions, confirming the selection based on the type or source of the feedstock being processed. For example, leaching may occur at ambient temperature and / or pressure or above ambient temperature and / or pressure. For feedstocks containing MHP or black mass, leaching may occur at a temperature of about 65° C. and atmospheric pressure, for example, with the addition of an acid and a reducing agent. For feedstocks containing MSP or nickel matte, leaching may occur by pressure leaching and / or pressure oxidation at temperatures between 150 and 220° C.

[0034] Leaching conditions may be selected to minimize the use of acid or base reagents. For example, leaching conditions may include countercurrent leaching, which involves contacting and flowing the feedstock with an acid leach stream in opposite directions. The use of such countercurrent flow can improve leaching efficiency and reduce the use of acid reagents in the leaching stage. Countercurrent leaching can also reduce the use of base reagents, as less acid passes downstream in the process that must then be neutralized with a base. In some embodiments, leaching conditions may include pressure leaching, which produces sulfates by oxidation of sulfides in the feedstock, thus eliminating the need to use additional acid reagents to solubilize metals in the feedstock.

[0035] In one or more embodiments, the process for producing metal sulfates described herein includes purifying an aqueous solution (e.g., a sulfate matrix, pregnant leach solution (PLS)) containing a metal sulfate, where the PLS is subjected to any one or combination of purification steps (also referred to herein as impurity or component removal steps) to remove certain impurities or components.

[0036] Following leaching, the PLS may undergo one or more purification steps to purify the PLS by removing one or more impurities or components. The type and amount of impurities or components removed will depend at least in part on the type of feedstock from which the PLS is formed and the specifications of the final product produced by the process (e.g., purity, grade, if only one or two of nickel sulfate (NiSO4), cobalt sulfate (CoSO4), and manganese sulfate (MnSO4) are required, etc.). Examples of impurities or components that may be removed include, but are not limited to, sodium (Na), aluminum (Al), iron (Fe), copper (Cu), zinc (Zn), lithium (Li), cobalt (Co), and manganese (Mn). Components that may need to be removed may include any one or two of nickel, cobalt, and manganese, so that only one or two of the crystallized nickel sulfate (NiSO4), cobalt sulfate (CoSO4), and manganese sulfate (MnSO4) are isolated from the crystallizer when used as an end product, such as battery grade metal sulfate. In other cases, all three of nickel sulfate (NiSO4), cobalt sulfate (CoSO4) and manganese sulfate (MnSO4) are isolated from the crystallizer. When battery grade metal sulfates are required, there are specific product specifications (e.g., limits) for such impurities that are permitted, such as in battery grade nickel sulfate, and any such impurities present in the process feeds, water or reagents in amounts above the product specifications must be reduced in concentration.

[0037] There are many suitable methods for removing impurities or components from PLS. Such methods include, but are not limited to, precipitation, atmospheric or pressure leaching, sulfidation, solvent extraction, ion exchange, and cementation. The selection of an appropriate method (and its operating conditions) depends at least in part on the type and amount of impurities or components to be removed and the specifications of the end product produced by the process. For example, copper can be removed by precipitation, solvent extraction, sulfidation, cementation, or ion exchange, etc.; iron and aluminum can be removed by precipitation or ion exchange, etc.; zinc can be removed by sulfidation, solvent extraction, or ion exchange, etc.; cobalt can be removed by solvent extraction, ion exchange, or oxidative precipitation, etc. The conditions and operating parameters for each method are generally known and can be selected depending on the type and amount of impurities or components to be removed.

[0038] For example, cementation is a process involving a redox reaction between a first metal ion and a first solid metal, whereby the first metal ion is reduced to a second solid metal by the first solid metal, and then the first solid metal is oxidized to the second metal ion. Cementation may be chosen for the removal of, for example, copper, because it allows for the addition of valuable metals to the process without the use of other reagents (e.g., by adding Ni if nickel powder is used as the first solid metal), and / or allows for the removal of impurities (e.g., by reduction) without the need to add acid or base reagents to the process.

[0039] Purification steps for removing impurities or components from PLS can be selected to minimize the use of acid or base reagents. For example, Cu can be removed by cementation with nickel powder, which requires little or no acid or base, and generates no acid; in contrast, removal of Cu by solvent extraction (SX) requires one mole of sulfuric acid per mole of Cu removed, and all added acid must be neutralized by a downstream base. Other impurities such as Fe and Al can be removed via precipitation by raising the pH (e.g., to about 5.5), which requires the addition of a base but not an acid, which can be introduced as an external neutralizer or a basic metal salt generated downstream in the process. In contrast, removal of Fe and Al by ion exchange (IX) requires the addition of a base to load Fe and Al onto the exchange column, and the addition of an acid to remove Fe and Al from the exchange column, and requires additional reagents or processes to convert these impurities into easily disposable forms.

[0040] The processes described herein may include a step of crystallizing a metal sulfate from an aqueous solution to form a crystallized metal sulfate. The purified PLS may be introduced into a crystallizer under conditions sufficient to selectively crystallize or co-crystallize any one or combination of nickel sulfate, cobalt sulfate, manganese sulfate, and / or lithium sulfate from solution. Such selective crystallization may be performed on components remaining in the purified PLS, such as lithium, sodium, potassium, magnesium, etc. (depending on the feedstock), to provide one or more crystallized metal sulfates (e.g., NMC sulfate and / or lithium sulfate) in the mother liquor.

[0041] Different types of crystallizers may be suitable to affect the selective crystallization or co-crystallization of NMC sulfate and / or lithium sulfate. Such crystallizers include, but are not limited to, evaporative crystallizers, forced circulation (FC) crystallizers, indirect force circulation (IFC) crystallizers, and draft tube baffle (DTB) crystallizers. The conditions and operating parameters of such crystallizers may be selected depending on the type and purity of the metal sulfate to be crystallized and / or the type and concentration of impurities in the PLS. For example, when an IFC or DTB crystallizer is used, coarser crystals may be formed when crystallizing NMC sulfate, thereby suppressing the entrainment of impurities during said crystallization, such as lithium, sodium, magnesium, and / or potassium. When a forced circulation crystallizer is used, the PLS may be operated under vacuum to rapidly cool to ambient temperature (e.g., about 25° C.), which may facilitate the evaporation of water and the crystallization of NMC sulfate and / or lithium sulfate. In such cases, the amount of free water evaporated may be less than the amount required to reach the saturation point of a particular impurity, such as lithium or sodium. When using a crystallizer to crystallize nickel sulfate, cobalt sulfate, and manganese sulfate together selectively to impurities such as lithium and sodium, the crystallizer can be operated at a pH level of 1 to 5 or 1.5 to 2.5. In some embodiments, pH levels below 0, below 1.5, or 0.5 to 1.5 are effective.

[0042] Additionally, the crystallizer conditions and operating parameters can be selected to selectively crystallize one metal sulfate or combination of metal sulfates over other sulfates and components (e.g., impurities) in the solution. For example, if the concentration of one or two metal sulfates in the PLS is very low and the concentration of a third metal sulfate is very high, then careful selection of the crystallizer bleed rate (e.g., a sufficiently high bleed rate) can allow the third metal sulfate to be selectively crystallized over the one or two metal sulfates.

[0043] The crystallizer conditions and operating parameters may be selected to control the purity of the crystallized metal sulfate. Bleeding of the mother liquor from the crystallizer during crystallization and the rate at which the bleed occurs may affect the purity of the crystallized metal sulfate, for example, by selectively suppressing the crystallization of an impurity. As used herein, selecting a bleed rate to selectively suppress the crystallization of a particular impurity means setting a crystallizer bleed rate that, within a range of possible bleed rates, suppresses the crystallization of a particular impurity more than another impurity. The bleed rate may be selected to maximally suppress the crystallization of a particular impurity. The impurities may be sodium, potassium, magnesium, etc. Using a higher bleed rate of the mother liquor facilitates maintaining lower concentrations of impurities and other components in the mother liquor that may affect the purity of the crystallized metal sulfate.

[0044] Furthermore, the solubility of impurities may be temperature dependent, and therefore, selecting the temperature of the crystallizer may be effective in controlling the purity of the crystallized metal sulfate. For example, the solubility of lithium sulfate decreases with increasing temperature, so operating the crystallizer at a high temperature may cause any lithium sulfate remaining in the PLS to precipitate and affect the purity of the crystallized metal sulfate. However, operating the crystallizer at a low temperature may prevent the lithium sulfate from remaining in solution and coming out of solution with the crystallizing metal sulfate. Instead, operating the crystallizer at different temperature conditions while maintaining the same bleed rate may result in different levels of impurity contamination. In contrast, the solubility of sodium increases with increasing temperature. Therefore, operating the crystallizer at a higher temperature may cause sodium to remain in solution, and increasing the bleed rate of the crystallizer may remove the sodium from the crystallizer before it can come out of solution with the crystallizing metal sulfate. However, when the crystallizer is operated at lower temperatures, the sodium remaining in the mother liquor may precipitate due to its low solubility or may react with the nickel to form double salts that may affect the purity of the crystallized metal sulfate.

[0045] The solubility of impurities may also depend on the amount of free water present in the PLS and / or mother liquor, and therefore controlling the water level in the crystallizer may be an effective means of controlling the purity of the crystallized metal sulfate. For example, in some cases, metal sulfates may crystallize out of solution as metal sulfate hydrates (i.e., crystallized metal sulfates and water molecules combined in a certain ratio as an integral part of the crystal), thereby reducing the water concentration in the mother liquor. With the concentration of free water reduced, the concentration of impurities (such as lithium, sodium, potassium, magnesium, etc.) in the mother liquor may also increase to the point where they crystallize out of solution and affect the purity of the crystallized metal sulfate. However, if a sufficient amount of water is added to the PLS and / or mother liquor when in the crystallizer, or if an excess amount of water remains in the PLS after upstream processing (e.g., at least as much water as would be expected to be lost due to hydrate formation), the presence of free water may inhibit the crystallization of impurities from solution.

[0046] The crystallized metal sulfate can be isolated from the mother liquor by discharging it from the crystallizer. For example, the crystallized metal sulfate can be discharged as a slurry that is passed through a filter or centrifuge to separate the crystals from the mother liquor. The filtrate or centrifuged liquid (i.e., mother liquor) can then be returned to the crystallizer or a portion of it can be bled off, and the isolated crystals can be washed in a filter or centrifuge and dried. In some cases, such as when the PLS is formed from a dirtier feedstock, the use of only one crystallizer is insufficient to produce a crystallized metal sulfate of adequate purity. The crystals discharged from the first crystallizer can then be dissolved in water (e.g., pure water), recrystallized, and further purified before being introduced into a second crystallizer.

[0047] The processes for producing metal sulfate described herein may include basifying a portion of the mother liquor to convert the uncrystallized metal sulfate to a basic metal salt. In one or more embodiments of the processes described herein, the process includes basifying a portion of the mother liquor using a second neutralizing agent to convert the uncrystallized metal sulfate to a basic metal salt. In one or more embodiments, converting the basic metal salt back to the uncrystallized metal sulfate includes using the basic metal salt as a first neutralizing agent to neutralize an acid upstream of the crystallization of the metal sulfate.

[0048] The crystallization mother liquor may contain uncrystallized metal sulfates in addition to other impurities and components such as salts and metals such as Li2SO4, Na2SO4, etc. To selectively recover these uncrystallized metal sulfates and form basic metal salts for use upstream as neutralizing agents (also referred to herein as first neutralizing agents), the mother liquor may be bled from the crystallizer and basified to convert the uncrystallized metal sulfates remaining in the mother liquor to said basic metal salts, e.g., metal hydroxides (e.g., Ni(OH)2, Co(OH)2, Mn(OH)2, etc.). When basifying the mother liquor, sufficient base may be added to increase the pH level to 7.5-10 or 7.5-9.5. The resulting metal hydroxides may precipitate from the mother liquor, be isolated from the mother liquor via filtration, washed to form a cake, and repulped to form a slurry. For example, the metal hydroxides may be recovered by filtration, concentration and filtration or centrifugation, and then washed in a filter or centrifuge to form a cake. At least a portion of the cake may be passed to a repulping tank for slurrying with water or a process solution. The metal hydroxide may be selectively precipitated from the mother liquor, for example, via a one or two stage precipitation circuit. The precipitation circuit may be used to selectively precipitate the metal hydroxide from impurities in the metal hydroxide due to the presence of that metal hydroxide in the mother liquor.

[0049] The metal hydroxide can be introduced upstream in the process and used as a neutralizing agent to neutralize the acid introduced in the leaching and / or purification stages. For example, about 0%-40% of the metal hydroxide (e.g., as a cake) can be introduced in the leaching stage and about 60%-100% of the metal hydroxide (e.g., as a cake) can be introduced in the purification stage. The use of the metal hydroxide as a neutralizing agent reduces and / or eliminates the need to introduce an external neutralizing agent, thereby reducing reagent usage (and associated costs) and reduces the amount of impurities that may affect the purity of the product (e.g., the cation Na from the external neutralizing agent). + , K + , Ca 2+ , Mg 2+ ) are reduced and / or eliminated, and the crystallizer bleed rate may need to be increased to avoid co-precipitation of impurities and contamination of the crystallized metal sulfate. In some cases, to ensure sufficient amounts of basic metal salts, e.g., metal hydroxides, that can be used as neutralizing agents, the rate at which the mother liquor is bled from the crystallizer and basified to form metal hydroxides may be controlled so that the amount of metal hydroxide formed is at least about equal to or approximately equal to the amount of acid introduced in the leaching and / or purification steps. For example, if the purified PLS is of high purity, the crystallizer bleed rate may not need to be as high (e.g., as described above) to control the purity of the crystallized metal sulfate, however, the crystallizer bleed rate may nevertheless need to be increased to ensure sufficient amounts of metal hydroxide are formed for upstream use. In other cases, the rate at which the mother liquor is bled from the crystallizer and basified to form metal hydroxides may be controlled such that the amount of metal hydroxide formed in combination with the amount of external neutralizing agent added is at least approximately equal to or approximately equal to the amount of acid introduced in the leaching and / or purification steps, but the amount of external neutralizing agent added may be controlled such that the use of the external neutralizing agent does not introduce impurities (e.g., cations, Na) at concentrations that affect the purity of the crystallized metal sulfate. + , K + , Li + , Mg 2+The pH of the metal hydroxide is kept low enough so as not to introduce an external neutralizing agent into the upstream process (e.g., leaching, purification, etc.). In such cases, the use of an external neutralizing agent in combination with the formed metal hydroxide can control capital and / or operating costs. Additionally, the rate at which the metal hydroxide is metered into the upstream process can be controlled by the pH setpoint of said process (e.g., leaching, purification, etc.).

[0050] Additionally, the use of a basic metal salt (e.g., metal hydroxide) as a neutralizing agent converts the basic metal salt back to metal sulfate within the purified PLS. The purified PLS containing the converted metal sulfate can then proceed to a crystallizer where the converted metal sulfate can be crystallized and isolated from the mother liquor. The mother liquor can be isolated and basified to convert the uncrystallized metal sulfate in solution to a basic metal salt, which can then be used as a neutralizing agent to convert the basic metal salt back to metal sulfate, which can then be isolated by crystallization. This loop can improve the yield of isolated crystallized metal sulfate from a particular feedstock.

[0051] In addition to using basic metal salts, e.g., metal hydroxides, as neutralizing agents, the process can use an external source of neutralizing agent (e.g., added oxides, hydroxides, etc.) in the purification step to neutralize the acid and / or basify the mother liquor bleed from the crystallizer (also referred to herein as a second neutralizing agent). Selecting the type and amount of external neutralizing agent can depend, at least in part, on the nature of the purification step and the type of metal sulfates and other components in the mother liquor. As one skilled in the art will recognize, there are various types of external neutralizing agents suitable for use in the purification step and / or for use in basifying the mother liquor. Suitable external neutralizing agents include, but are not limited to, potassium hydroxide (KOH), calcium hydroxide (Ca(OH)2), sodium hydroxide (NaOH), lithium hydroxide (LiOH), or magnesium oxide (MgO). For example, any one or combination of potassium hydroxide (KOH), calcium hydroxide (Ca(OH)2), sodium hydroxide (NaOH), lithium hydroxide (LiOH) and magnesium oxide (MgO) may be used as an external neutralizing agent. One skilled in the art will also recognize that there are types of external neutralizing agents that are less suitable for use in the purification step and / or for use in basifying the mother liquor. For example, the use of ammonia as an external neutralizing agent may result in the formation of double salts such as nickel sulfate-ammonium salts or metal complexes such as Ni and / or Co complexes. Such cations, salts or complexes may render the process infeasible and / or increase the operating and capital costs due to the required solvent extraction circuit.

[0052] The amount of external neutralizing agent can be selected depending on the nature of the refining step. For example, if there is a high concentration of Cu that needs to be removed in the refining step, a high concentration / volume of neutralizing agent may be required to neutralize any acid generated in the copper solvent extraction step. Additionally, if there is a high concentration of Fe that needs to be removed in the refining step, a high concentration / volume of neutralizing agent will be required to raise the pH and remove the Fe by hydrolysis.

[0053] The type of external neutralizer can be selected to produce and recover specific by-products, such as by-products that have commercial value, through the salt recovery process. For example, if an external neutralizer is selected to be potassium hydroxide, its use produces potassium sulfate (K2SO4), which is a fertilizer. If an external neutralizer is selected to be calcium hydroxide, its use produces gypsum (CaSO4.2H2O), which is a product that can be disposed of as waste or used in drywall and construction. If an external neutralizer is selected to be magnesium oxide (MgO), its use produces magnesium sulfate. If an external neutralizer is selected to be lithium hydroxide (LiOH), its use produces lithium sulfate.

[0054] The type of external neutralizer can be selected based on its ability to be recovered and regenerated via a salt recovery step, so that the external neutralizer can be used in the process and then regenerated for reuse. For example, if the external neutralizer is selected to be sodium hydroxide, its use produces sodium sulfate as a by-product. Sodium hydroxide can be regenerated from sodium sulfate by electrolysis. Generally, electrolysis can directly convert the by-product sodium sulfate back to sodium hydroxide for reuse in the process, producing sulfuric acid during the conversion. More specifically, electrolysis is performed using an electrochemical cell that uses an applied potential and one or more ion selective membranes to regenerate acids and bases from the salt solution, and can include two or more compartments separated by selective membranes. For example, electrolysis can be performed at 1500-3000 A / m 2The present invention may involve a three-compartment cell operating at a potential of 6 V at a current density of 0.1 to 1.0 V, producing from sodium sulfate about 20% by weight sodium hydroxide solution along with about 10% by weight sulfuric acid solution, both of which may be recycled for use upstream in the process. If the external neutralizing agent is selected to be LiOH, its use produces lithium sulfate, which may be converted back to LiOH using downstream recovery steps such as basification and crystallization or electrolysis, or may be converted to lithium carbonate as a saleable product. In one or more embodiments, the external neutralizing agent is sodium hydroxide, and its use produces sodium sulfate as a by-product.

[0055] In one or more embodiments of the present disclosure, the process for producing metal sulfates described herein provides selective crystallization or co-crystallization of any one or combination of nickel sulfate (NiSO4), cobalt sulfate (CoSO4), manganese sulfate (MnSO4), and lithium sulfate (Li2SO4). In one or more embodiments, the process described herein provides selective crystallization or co-crystallization of one or two of crystallized nickel sulfate (NiSO4), cobalt sulfate (CoSO4), and manganese sulfate (MnSO4). In one or more embodiments, the process described herein provides selective co-crystallization of all three of crystallized nickel sulfate (NiSO4), cobalt sulfate (CoSO4), and manganese sulfate (MnSO4). In one or more embodiments, the process described herein provides battery grade crystallized metal sulfates. In one or more embodiments, the process provides electroplating grade crystallized metal sulfates. In one or more embodiments, the process described herein does not use a solvent extraction circuit to isolate the battery grade crystallized metal sulfates. In one or more embodiments, the processes described herein reduce capital and operating costs, increase the yield of crystallized metal sulfates, and / or reduce or eliminate sodium sulfate as a solid waste product (when sodium hydroxide is used as an external neutralizing agent and sodium sulfate is converted back to sodium hydroxide by electrolysis or when the amount of external neutralizing agent required is reduced).

[0056] In some embodiments, the processes described herein reduce capital and operating costs because a crystallizer is used to isolate crystallized metal sulfate salts instead of a solvent extraction circuit. Although crystallization requires an energy input, no additional reagents need to be used, thereby reducing operating costs. Furthermore, the capital costs associated with crystallization are lower than those associated with a solvent extraction circuit.

[0057] In other embodiments, the processes described herein reduce capital and operating costs by reducing the use of reagents. For example, a nickel solvent extraction circuit to form nickel sulfate requires the consumption of one mole of sulfuric acid and two moles of sodium hydroxide per mole of nickel sulfate produced. In contrast, crystallization does not require the use of any additional reagents. Even when a solvent extraction step is used as part of a purification stage, the processes described herein can reduce reagent usage because the solvent extraction is typically subjected to a smaller load (i.e., lower concentrations of impurities) and therefore requires less acid and base. In some embodiments, the processes described herein reduce capital and operating costs by reducing the number of process steps. Reducing the number of process steps not only reduces capital and operating costs, but also reduces the complexity of the process and therefore the complexity of the infrastructure and skill sets required to run the process. For example, solvent extraction is a relatively complex unit operation requiring multiple stages of extraction, scrubbing and stripping, and requires systems for treating aqueous effluent streams, removing crud, recovering organic vapors and fire protection. Instead of a solvent extraction circuit, the complexities (and associated costs) of such processes can be avoided by using a crystallizer to isolate the crystallized metal sulfate.

[0058] In other embodiments, the processes described herein increase the yield of crystallized metal sulfate by reducing or preventing the addition of certain impurities or components in the leaching and / or purification stages of the process, such as lithium, sodium, potassium, or magnesium. For example, as the single-pass yield of crystallized metal sulfate increases in the crystallizer, the concentration of impurities such as lithium, sodium, etc. in the mother liquor also increases. As a result, the bleed rate of the crystallizer must also be increased to manage the purity of the crystallized metal sulfate (e.g., by inhibiting or preventing the impurities from approaching saturation concentrations in the mother liquor). However, increasing the bleed rate of the crystallizer can be inefficient as the bled uncrystallized metal sulfate basifies, precipitates, and consumes reagents. Thus, reducing or preventing the addition of these impurities in the leaching and / or purification stages of the process means that the crystallizer can be operated at a lower bleed rate while avoiding co-crystallization of the impurities and the metal sulfate, thereby increasing the single-pass yield of crystallized metal sulfate while also reducing operating costs. In one or more embodiments of the disclosed process, the addition of certain impurities (e.g., lithium, sodium, magnesium, etc.) is reduced or prevented by using basic metal salts (e.g., metal hydroxides Ni(OH)2, Co(OH)2, Mn(OH)2, etc.) precipitated from the mother liquor bled from the crystallizer. In some embodiments, the precipitation and washing of the basic metal salts is carefully controlled (e.g., by selection of pH levels, use of a two-stage precipitation circuit, etc.) to reduce or prevent precipitation of impurities (e.g., lithium, sodium, magnesium, etc.) into the basic metal salts.

[0059] In some embodiments, the processes described herein increase the yield of crystallized metal sulfate by using a loop that isolates and basifies the crystallization mother liquor to convert the uncrystallized metal sulfate in solution to a basic metal salt (e.g., metal hydroxide), and uses those basic metal salts as neutralizing agents to convert the salt back to the metal sulfate for crystallization. The repetitive nature of the loop ensures very good recovery of the crystallized metal sulfate.

[0060] The crystallized metal sulfate, whether produced by a process for producing a metal sulfate according to the present disclosure or otherwise, may be subjected to one or more embodiments or a process for removing impurities from the crystallized metal sulfate according to the present disclosure. Similarly, a countercurrent washing circuit for removing impurities from a crystallized metal sulfate according to the present disclosure may be used to remove impurities from any suitable source of crystallized metal sulfate, including, but not limited to, the processes for producing metal sulfate disclosed herein.

[0061] The embodiments described herein are intended to be merely examples. Changes, modifications, and variations to the specific embodiments may be implemented by those skilled in the art. The claims should not be limited by the specific embodiments described herein, but should be interpreted in a manner consistent with the specification as a whole.

[0062] All publications, patents, and patent applications mentioned in this specification are indicative of the level of skill of those skilled in the art to which this invention pertains, and each individual published patent or patent application is herein incorporated by reference to the same extent as if specifically and individually indicated to be incorporated by reference.

[0063] The present invention being thus described, it will be apparent that the same may be varied in many ways. Such variations should not be regarded as a departure from the spirit and scope of the invention, and all such variations that are obvious to those skilled in the art are intended to be included within the scope of the following claims.

Claims

1. 1. A process for removing impurities from a crystallized metal sulfate comprising contacting the crystallized metal sulfate with a liquid rich in the metal sulfate.

2. 2. The process of claim 1, wherein the metal sulfate is cobalt sulfate, nickel sulfate or manganese sulfate.

3. 3. The process of claim 1 or 2, wherein the crystallized metal sulfate is in the form of a crystal lattice and the impurities are distributed within the crystal lattice.

4. The impurities are trace metal cations in the +2 oxidation state; and / or The process of any one of claims 1 to 3, comprising magnesium, calcium, sodium or lithium, or a combination thereof.

5. 5. The process of claim 1, further comprising providing said liquid enriched in metal sulfate containing a level of impurities lower than the level of impurities in said crystallized metal sulfate.

6. 6. The process of any one of claims 1 to 5, wherein the metal sulphate rich liquid is a crystallisation liquid containing a concentration of metal sulphate similar to the metal sulphate concentration in the crystallisation liquid from which the crystallised metal sulphate was crystallised.

7. mixing a portion of the metal sulfate crystals with water; and / or Washing the metal sulfate crystals with water; 7. The process of any one of claims 1 to 6, further comprising forming the metal sulfate enriched liquid by dissolving at least a portion of the metal sulfate crystals in the water to form the metal sulfate enriched liquid.

8. 1. A process for crystallizing a selected metal sulfate comprising the steps of: crystallizing a metal sulfate from an aqueous solution to form crystals enriched in the selected metal sulfate and an overflow solution containing the metal sulfate and impurities; contacting the crystals enriched in the selected metal sulfate with a liquid enriched in a metal sulfate, thereby displacing at least a portion of the impurities from the crystals enriched in the selected metal sulfate; A process including.

9. 9. The process of claim 8, further comprising removing at least a portion of said impurities from said overflow solution to provide said liquid enriched in metal sulfates.

10. 10. The process of claim 8 or 9, wherein crystallizing the metal sulfate-rich feed solution comprises preferentially crystallizing the selected metal sulfate from the metal sulfate-rich feed solution over alternative metal sulfates.

11. A process according to any one of claims 8 to 10, further comprising the step of reusing the liquid elsewhere in the process or a related process.

12. 12. The process of claim 11, wherein reusing the liquid comprises adding at least a portion of the liquid to the aqueous metal sulfate solution for crystallization.

13. The process of any one of claims 8 to 12, wherein removing at least a portion of the impurities from the overflow solution comprises precipitation or ion exchange.

14. 14. The process of any one of claims 8 to 13, wherein contacting the metal sulfate-enriched crystals comprises treating the metal sulfate-enriched crystals in a countercurrent washing circuit.

15. A process according to any one of claims 8 to 14, wherein the selected metal sulphate is cobalt sulphate, nickel sulphate or manganese sulphate.

16. 16. The process of any one of claims 8 to 15, wherein the metal sulfate enriched crystals define a crystal lattice and the impurities are distributed within the crystal lattice.

17. The impurities are trace metal cations in the +2 oxidation state; and / or The process of any one of claims 8 to 16, further comprising magnesium, calcium or sodium, or a combination thereof.

18. the metal sulfate-rich liquid has a lower level of impurities than the level of impurities in the metal sulfate-rich crystals; and / or 18. The process of any one of claims 8 to 17, comprising a concentration of metal sulfate similar to that in the metal sulfate-rich feed solution.

19. 1. A countercurrent washing circuit for removing impurities from crystallized metal sulfate, the countercurrent washing circuit comprising a plurality of washing tanks configured to receive crystallized metal sulfate in a sequence and to receive a washing solution in a reverse of the selected sequence, each washing tank being coupled to a solid / liquid separation device for separating the crystallized metal sulfate from the washing solution, the crystallized metal sulfate in a given washing tank being advanced to a next washing tank in the sequence, and the washing solution from the given washing tank being advanced to a previous washing tank in the sequence.

20. 20. The countercurrent washing circuit of claim 19, wherein each washing tank is configured to contact the crystallized metal sulfate with the washing solution for a designated residence time.

21. 21. The countercurrent washing circuit of claim 20, wherein the residence time is about 6 hours.

22. A countercurrent washing circuit according to any one of claims 19 to 21, wherein the washing liquid in the last washing tank in the sequence is substantially free of impurities.

23. the cleaning liquid of the last cleaning tank in the sequence is water; and / or A countercurrent washing circuit as claimed in any one of claims 19 to 22, wherein the washing liquid of the first washing tank in the sequence is recycled to the metal sulphate crystallizer.

24. The countercurrent washing circuit according to any one of claims 19 to 23, wherein the solid / liquid separation device is a centrifuge, a thickener or a screen.

25. A countercurrent washing circuit according to any one of claims 19 to 24, wherein the metal sulphate is cobalt sulphate, nickel sulphate or manganese sulphate.

26. 26. The countercurrent washing circuit of any one of claims 19 to 25, wherein the crystallized metal sulfate defines a crystal lattice and the impurities are distributed within the crystal lattice.

27. The impurities are trace metal cations in the +2 oxidation state; and / or 27. The countercurrent washing circuit according to any one of claims 1 to 26, comprising magnesium, calcium or sodium, or a combination thereof.

28. crystallizing the metal sulfate from the aqueous solution to form said crystallized metal sulfate in a mother liquor containing uncrystallized metal sulfate; separating the crystallized metal sulfate from the mother liquor; basifying a portion of the mother liquor to convert the uncrystallized metal sulfate to a basic metal salt; using said basic metal salt upstream of crystallization of said metal sulfate salt; The process of any one of claims 1 to 27, further comprising:

29. basifying at least a portion of the overflow solution to convert uncrystallized metal sulfates to basic metal salts; using said basic metal salt upstream of crystallization of said metal sulfate salt; The process of any one of claims 1 to 28, further comprising:

30. 1. A process for producing metal sulfates, comprising the steps of: crystallizing the metal sulfate from the aqueous solution to form a crystallized metal sulfate in a mother liquor containing uncrystallized metal sulfate; separating the crystallized metal sulfate from the mother liquor; contacting the crystallized metal sulfate with a metal sulfate-rich liquid to remove impurities from the crystallized metal sulfate; basifying a portion of the mother liquor to convert the uncrystallized metal sulfate to a basic metal salt; using said basic metal salt upstream of crystallization of said metal sulfate salt; A process including.

31. 31. The process of claim 30, further comprising purifying the mother liquor to form the liquid enriched in metal sulfates.

32. 32. The process of claim 30 or 31, wherein contacting the crystallized metal sulfate with a metal sulfate-rich liquid thereby forms a liquid containing metal sulfate and impurities, and the process further comprises basifying a portion of the liquid containing metal sulfate and impurities to convert the metal sulfate to a basic metal salt.

33. The process of any one of claims 28 to 32, wherein the step of crystallizing the metal sulfate further comprises the steps of bleeding the mother liquor and controlling the bleeding rate to selectively suppress crystallization of impurities when crystallizing the metal sulfate, the impurities optionally comprising lithium, sodium, potassium or magnesium, or a combination thereof.

34. The process of any one of claims 28 to 33, wherein the step of crystallizing the metal sulfate further comprises the steps of bleeding the mother liquor when crystallizing the metal sulfate, controlling the bleeding rate, and controlling the amount of free water in the crystallization apparatus to selectively suppress crystallization of impurities, the impurities optionally comprising lithium, sodium, potassium or magnesium, or a combination thereof.

35. The process of claim 28, wherein using the basic metal salt upstream of the crystallization of the metal sulfate comprises using at least a portion of the basic metal salt to remove one or more impurities upstream of the crystallization of the metal sulfate in a purification stage.

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