Method for preparing high-purity nickel sulfate solution

Abstract

The present invention provides a process for preparing a high purity nickel sulfate solution, the process comprising the steps of: i. Forming a mixed metal sulfate aqueous solution by reacting sulfuric acid with a raw material feed comprising nickel, manganese, cobalt and magnesium in an aqueous medium; ii. Extracting manganese from the mixed aqueous metal sulfate solution, thereby obtaining a first aqueous raffinate comprising nickel, cobalt and magnesium, and a manganese-rich organic phase; iii. Extracting cobalt from the first aqueous raffinate, thereby obtaining a second aqueous raffinate comprising nickel and magnesium, and a cobalt-rich organic phase; and iv, extracting magnesium from the second aqueous raffinate to obtain a high-purity nickel sulfate solution and a magnesium-rich organic phase.

Description

Technical Field

[0001] The present invention relates to a novel process for producing a high purity aqueous nickel sulfate solution, the purity of which is sufficient for the electroless deposition of nickel metal layers or the production of battery materials. Background Art

[0002] The development of lithium-ion batteries, especially the use of nickel-manganese-cobalt and nickel-cobalt-aluminum cathode materials, has increased the demand for high-purity nickel sulfate as a solid or in solution. In fact, impurities in the cathode material can seriously affect the performance of the battery. Therefore, a lot of efforts have been made to produce high-purity nickel sulfate in an industrially feasible way.

[0003] In this regard, US 2014 322109 provides a method for obtaining high-purity nickel sulfate with low levels of impurities, particularly low levels of magnesium and chloride, by introducing a selective nickel sulfide precipitation step and redissolving the nickel sulfide in a nickel sulfate solution. The solution is further refined by solvent extraction to remove cobalt and magnesium impurities, adjusting the concentration and pH value or acid concentration of the acidic organic extractant during treatment. The described treatment strategy is cumbersome for concentrated nickel sulfate solutions because it requires intermediate precipitation and redissolution of the nickel body, followed by solvent extraction to remove impurities cobalt and magnesium. In particular, the nickel sulfide step is dangerous because there is a risk of producing hydrogen sulfide. In addition, solvent extraction is only used to remove cobalt and magnesium, but crude nickel raw materials generally contain more impurities.

[0004] CN 107 162 067 relates to the field of solid waste recycling and discloses in particular a method for recycling high-purity nickel sulfate from nickel-containing waste batteries. The method comprises the following steps: decomposing the nickel-containing waste batteries into battery powder, dissolving the battery powder with acid to obtain a metal-containing solution, adding alkali metal sulfate, removing iron by oxidation precipitation, further removing impurities by solvent extraction to obtain a magnesium-containing nickel liquid, passing the magnesium-containing nickel liquid through a chelating resin exchange column to selectively adsorb nickel ions and allowing a magnesium-rich solution to flow out for treatment, desorbing nickel ions to obtain a nickel sulfate solution, evaporating the nickel sulfate solution, cooling, crystallizing, filtering, and finally drying to obtain a purified nickel sulfate product. By this lengthy and complex method, it is ensured that the recycled nickel sulfate is a high-purity product with a nickel content of up to 99.5% and above, while the impurity (i.e. magnesium) content is less than 0.005%. However, it is proposed to use three different solvent extraction units to remove copper, manganese and cobalt in separate steps. In addition to the high investment cost, it is not even assumed that other impurities, such as calcium and magnesium, will be removed. Finally, the nickel is recovered by adsorption onto a resin, which requires a fourth separation step and the consumption of a neutralizing agent equal to the amount of metal ions adsorbed. In conclusion, the described process is considered to be neither simple nor efficient.

[0005] EP 1 252 345 B1 describes a method for extracting cobalt from a cobalt-nickel solution with a solvent loaded with nickel to obtain a purified nickel sulfate stream. However, it does not describe how to remove impurities such as calcium and magnesium to very low levels in order to produce a purified nickel sulfate solution for electroless nickel or battery applications. It seems more like a solvent extraction method has been developed in which the formation of insoluble ammonium / nickel sulfate double salts can be avoided.

[0006] EP 2 784 166 explains a method for producing a pure nickel sulfate solution by a plurality of process steps, including a sulfidation step, a redissolution step, a purification step by precipitation and a solvent extraction step. In particular, the sulfidation and redissolution steps are expensive operations, which use a sulfiding agent and produce nickel sulfide intermediates, both of which are toxic and which may lead to the formation of highly toxic gaseous hydrogen sulfide by contact and reaction with inorganic acids. Finally, the purified nickel sulfate solution still contains 50 mg / L of magnesium impurities, which is too much for battery-grade nickel sulfate and shows that the proposed method lacks selectivity.

[0007] EP 3 733 884 describes a solvent extraction process which allows the selective separation of magnesium from an acidic aqueous solution of sulfuric acid. The solvent extraction process consists in contacting an acidic aqueous solution of sulfuric acid containing nickel, cobalt and magnesium with an organic solvent to selectively extract magnesium into the organic solvent under very specific extraction conditions: either extracting the magnesium at a relatively low pH = 1.5 to 2 with a concentrated solvent (i.e. containing 40% to 60% of alkylphosphonic acid as extractant), or extracting the magnesium at a higher pH = 2.0 to 2.5 with a solvent having a lower extractant concentration (i.e. 20% to 50% of alkylphosphonic acid). The process is intended only to remove magnesium, without separating cobalt from the nickel solution. It is noteworthy that under the same extraction conditions, up to 46% of magnesium can be removed from a nickel sulfate solution, while also co-extracting about 9% of nickel. Under such conditions, a Mg / Ni separation factor of only 8 to 23 is obtained. When the extractant concentration in the used solvent is reduced to below 40 vol. %, higher Mg / Ni separation factors up to 35 are obtained, but at the same time the magnesium removal is much lower, i.e. below 28%.

[0008] EP 3 222 735 discloses a method for separating cobalt and magnesium from a nickel-containing feed solution by liquid-liquid extraction, wherein the organic solvent used contains alkylphosphinic acid as an extractant. Cobalt and magnesium are extracted together with some nickel. Nickel is first washed out of the loaded solvent with an acidic solution. Since the resulting nickel solution may contain some cobalt, it is returned to the feed solution. Then, magnesium is washed out of the solvent with an acidic solution. The obtained magnesium solution may contain some cobalt and is processed elsewhere. Cobalt is stripped from the solvent with a diluted acid aqueous solution to form a cobalt stripping solution. In addition to cobalt and magnesium, the patent does not involve how to remove other metal contaminants in the nickel sulfate solution, such as calcium, zinc, cadmium, copper, manganese and iron. In view of the release of acidic protons during extraction with an acidic extractant, the patent does not describe in detail how to achieve the required pH for extracting cobalt and magnesium from the nickel sulfate solution.

[0009] When EHEHPA (also known as PC88A) is used as an extractant, the extraction behavior for magnesium or calcium is similar to that for nickel. JP 10-310437 discloses an example of separating nickel and cobalt, which uses PC88A as an extractant to extract cobalt together with other impurities such as calcium, copper, zinc, iron and magnesium by solvent extraction. When a solution containing a high concentration of nickel is subjected to solvent extraction, the problem of reduced extraction efficiency of magnesium or calcium occurs. The difficulty of removing magnesium from nickel sulfate solution is mentioned. When containing 90g / L to 117g / L nickel, the final impurity output concentration in the purified nickel sulfate solution is still 3mg / L to 26mg / L cobalt, 2mg / L to 7mg / L calcium and 10mg / L to 27mg / L magnesium. The present invention solves the problem of insufficient calcium extraction by selecting operating conditions that are favorable for calcium extraction but at the same time reduce magnesium extraction. This situation can be offset by additional and separate solvent extraction of magnesium with a more favorable extractant and more favorable operating conditions.

[0010] In JP 2021031729 A2, a method for treating a crude nickel sulfate solution in a solvent extraction process is shown, wherein the method attempts to remove all cobalt, magnesium and calcium from the nickel sulfate solution at once. The ratio of the amount of nickel loaded on the solvent to the cobalt concentration in the nickel sulfate solution must vary depending on the amount of impurity removal required. However, as can be seen from the example, it is not possible to remove all contaminants, since the purified nickel sulfate solution still contains 1 mg / L to 60 mg / L cobalt, 1 mg / L to 20 mg / L magnesium and 1 mg / L to 15 mg / L calcium. In addition, the removal of magnesium seems to be negligible, since the input concentration of magnesium in the crude nickel sulfate solution is very low, only 19 mg / L to 31 mg / L magnesium, compared to the very high cobalt concentration of 8 g / L to 12 g / L cobalt. This proof of principle of co-extracting trace amounts of magnesium (even incompletely extracted) with large amounts of cobalt requires the use of large amounts of nickel on the solvent. It can only be assumed that better magnesium removal can be achieved when the amount of nickel loaded on the solvent is increased compared to the concentration of cobalt in the crude nickel sulfate solution. In a similar patent, JP 2021031730 A, it is assumed that the amount of magnesium reported in the cobalt eluate will be affected by the amount of nickel on the chosen solvent (compared to the cobalt concentration present in the crude nickel sulfate solution) by co-extraction into the solvent. The same example is given in JP2021031729 A2. The purified nickel sulfate solution may still contain impurities of up to 1 mg / L to 60 mg / L cobalt, 1 mg / L to 20 mg / L magnesium, and 1 mg / L to 15 mg / L calcium. And the amount of magnesium reported co-extracted into the cobalt eluate will obviously also be different.

[0011] In US 6149885 A, a method is explained in which impurities such as cobalt, calcium, copper and zinc are removed from a crude nickel sulfate solution by solvent extraction. A method is disclosed on how nickel is loaded onto a solvent, which can then be used to remove impurities from a crude nickel sulfate solution. However, magnesium is only removed in small amounts. In one example, there are still 34 mg / L magnesium left in the purified nickel sulfate solution, which is generally considered too impure for battery-grade nickel sulfate quality. In another example, there are even 354 ppm magnesium left in the purified nickel sulfate solution relative to 100% nickel. It is not even considered to remove other metals such as cadmium and manganese from the crude nickel sulfate solution.

[0012] CN 111 334 664 describes a ternary lithium battery positive electrode material containing nickel, cobalt, manganese and lithium, the recovery of valuable metals, and the use of a sulfuric acid oxygen-free roasting-overflow-acid leaching-extraction process. The extraction process has the following steps:

[0013] Extraction of manganese: P204 concentration is 20%, saponification degree is 50%, extraction section, after extraction stage 10, a loaded organic phase containing Ni, Co, Mn and Mg raffinate is obtained.

[0014] Extraction of cobalt: P507 with a concentration of 20%, a saponification degree of 60%, and an extraction stage level of 8 was used to obtain a loaded organic phase rich in cobalt and a raffinate rich in Ni and Mg.

[0015] Extraction of magnesium: P507 concentration was 25%, saponification degree was 40%, extraction stage 5, and a loaded organic phase rich in Mg and a raffinate rich in Ni were obtained.

[0016] Nickel extraction: Use P507 to extract nickel. The specific conditions are: P507 concentration is 20% and saponification degree is 70%.

[0017] CN 113 444 885 describes a method for preferentially extracting metallic lithium from spent ternary lithium-ion batteries and simultaneously obtaining battery-grade metal salts, wherein the method for extracting manganese, cobalt and nickel comprises the following steps:

[0018] -Extraction of high-purity manganese salt: Mix the raffinate collected after leaching out impurities with the organic extractant P204, extract using countercurrent extraction, and collect the raffinate. Mix the organic extractant P204 with 260# solvent oil at a ratio of 25%.

[0019] - Extraction of cobalt salts: Mix the raffinate with the organic extractant P507 and extract the raffinate using a countercurrent extraction method; mix the organic extractant with 260# solvent oil, of which P507 accounts for 25%.

[0020] - Extraction of nickel salts: The raffinate is mixed with an organic extractant Cyanex 272 mixed with 260# solvent oil and extracted using a countercurrent extraction method. In the extraction process, all magnesium ions in the aqueous phase are extracted into the organic phase to obtain a high-purity nickel sulfate solution. The high-purity nickel sulfate solution is subsequently treated to obtain battery-grade nickel sulfate.

[0021] WO 20 / 220559 describes a method for recovering valuable metals from waste nickel-cobalt-manganese ternary lithium batteries, comprising the following steps:

[0022] (1) crushing and carbonizing the waste nickel-cobalt-manganese ternary lithium batteries, and separating the powder and metal particles by air separation;

[0023] (2) leaching the powder separated in step (1) with sulfuric acid to obtain a leachate;

[0024] (3) Removal of Fe from the leachate 2+ 、Al 3+ , Ca 2+ Mg 2+ , as a pre-extraction liquid;

[0025] (4) extracting the pre-extracted solution with P204 to remove impurities, and performing stripping to obtain a stripping solution containing manganese sulfate and a stripping solution containing Co 2+ 、Ni 2+ and Li + After removing copper from the stripping solution, evaporation, concentration and crystallization are performed to obtain manganese sulfate;

[0026] (5) extracting cobalt from the raffinate obtained in step (4) with P507. When extracting cobalt with P507, the ratio of oil to water is controlled at 0.8 to 0.9:1, saponification is performed with alkali solution, and the saponification rate is controlled at 55% to 60%; Ni 2+ and Li + The cobalt stripping solution and the raffinate are obtained; the stripping solution is evaporated, concentrated and crystallized to obtain cobalt sulfate;

[0027] (6) extracting the raffinate obtained in step (5) with C272 to remove impurities, thereby obtaining a Mg-free 2+ The C272 raffinate after

[0028] (7) Using P507 to extract nickel from the C272 raffinate, and performing stripping to obtain a stripping solution containing nickel sulfate and a stripping solution containing Li + the raffinate solution; and evaporating and concentrating the stripping solution to obtain nickel sulfate.

[0029] The general limitation of the methods according to the prior art is that they need to feed a very specific nickel-containing material source into the method to obtain a nickel sulfate solution of the desired purity. More commonly, such methods focus on recycling battery waste. What is needed is a method that allows raw materials of various quality grades and nickel contents to be processed into battery-grade, high-purity nickel sulfate solutions. In addition, such new methods should also be highly economical in terms of the number of process steps, and have high efficiency in the recovery of nickel and other valuable materials such as cobalt.

[0030] In summary, a simple, efficient and practical method is needed by which high-purity nickel sulfate with low levels of cobalt, manganese, magnesium and other impurities is obtained, and the nickel sulfate obtained by the method can be used for applications with high purity requirements, such as electroless deposition of nickel metal layers, or as a precursor of battery positive electrode materials. An object of the present invention is to provide a new method for producing a high-purity nickel sulfate solution from a nickel aqueous solution containing cobalt, magnesium and manganese and optional impurities such as iron, zinc, copper, cadmium and calcium. In addition, an object of the present invention is to easily produce nickel sulfate with stable quality. Finally, an object of the present invention is to provide a method that allows the production of a cobalt-rich aqueous solution suitable for further processing from a crude nickel raw material. Summary of the invention

[0031] The present invention provides a solution to at least one of the above problems by providing a method for preparing a high-purity nickel sulfate solution as claimed in claim 1.

[0032] An advantage of the present invention is that the elements cobalt, zinc, manganese, cadmium, aluminum, copper, calcium and magnesium (if any are present) are completely separated from the nickel.

[0033] The whole process according to the invention is effective in the following sense: it can provide a high purity nickel solution, i.e. at least 99.8 atomic % nickel relative to the metal content of the solution, while avoiding material losses due to minimal co-extraction of the matrix element nickel; this avoids the formation of complex nickel-containing mixtures. Therefore, the process according to the invention is environmentally friendly. Using this processing strategy, the presence of unwanted ions in the final solution, which originate from reagents used during the nickel refining process in the nickel sulfate final solution, such as calcium from calcium alkali, sodium from sodium alkali and chloride from hydrochloric acid, can be avoided. In this way, the nickel sulfate solution obtained from the process of the invention is easy to further process by crystallization or spray drying to form nickel sulfate crystals or particles that are easy to transport, respectively. Advantageously, the present invention also allows the production of cobalt-rich eluents and manganese-rich eluents, which can be further processed, for example, for the production of high purity cobalt salts (such as cobalt chloride, cobalt sulfate, etc.) and for the production of high purity manganese salts (such as manganese chloride, manganese sulfate, etc.), respectively. The process of the invention is simple, environmentally friendly and provides high purity nickel sulfate.

[0034] Furthermore, the present invention provides a process in which raw material feeds such as battery waste, mixed hydroxide precipitate (MHP) and cobalt hydroxide intermediate precipitate (CHIP) or mixtures thereof can be converted from complex, impure feeds to battery-grade nickel sulfate solution using only three solvent extraction steps and, if applicable, a precipitation step prior to the solvent extraction step for removing iron, aluminum, etc. The battery-grade nickel sulfate solution obtained by this process can be used directly for the production of battery precursor materials, i.e., without the need for further purification by ion exchange, extraction or other means. DETAILED DESCRIPTION

[0035] Unless otherwise defined, all terms (including technical and scientific terms) used to disclose the present invention have the meaning commonly understood by one of ordinary skill in the art to which the present invention belongs. By further guidance, term definitions are included to better understand the teachings of the present invention.

[0036] As used herein, the following terms have the following meanings:

[0037] As used herein, "a", "an", and "the" refer to both singular and plural references unless the context clearly indicates otherwise. For example, "a compartment" refers to one or more than one compartment.

[0038] As used herein, "about" with respect to a measurable value (such as a parameter, amount, transient duration, etc.) is intended to encompass the specified value and variations of + / -20% or less, preferably + / -10% or less, more preferably + / -5% or less, even more preferably + / -1% or less, and still more preferably + / -0.1% or less from the specified value, as long as such variations are suitable for making in the disclosed invention. However, it is to be understood that the value to which the modifier "about" refers is itself also specifically disclosed.

[0039] As used herein, "comprising" and "consisting of" are synonymous with "including" or "containing", and are inclusive or open-ended terms that specify at least the presence of what follows and do not exclude or preclude the presence of additional, unrecited components, features, elements, components or steps known in the art or disclosed herein.

[0040] Numerical ranges recited by endpoints include all values ​​and fractions contained within the range, as well as the recited endpoints. All percentages are understood to be weight percentages (abbreviated as "wt %) or volume percentages (abbreviated as "vol %) or atomic percentages (abbreviated as "atomic %), unless otherwise defined or unless a different meaning is apparent to one skilled in the art from its use and the context in which it is used.

[0041] With respect to the organic phase, the following terms are used to identify its components or as a whole:

[0042] i. In the context of the present invention, the term "organic phase" is understood to be synonymous with the term "solvent" or "solvent mixture" and means a liquid composition comprising one or more extractants, a diluent and optionally one or more modifiers.

[0043] ii. "Extractant" or extraction reagent is the active component in the organic phase that extracts metal species into the organic phase by chemically combining with the metal species and forming a metal-extractant complex that is more soluble in the organic phase than in the aqueous phase.

[0044] iii. A "diluent" is an organic molecule or a mixture of usually different organic molecules added to the organic phase to dilute the extractant and allow the metal complex to dissolve, improve the physical properties of the organic phase (particularly the phase separation phenomenon) and reduce its cost, since the diluent is usually cheaper than the extractant. The diluent is usually a kerosene fraction and can be an aliphatic or aromatic hydrocarbon, a cycloalkane, etc., or a mixture thereof. The diluent is preferably a kerosene-based petroleum fraction, such as Escaid, Elixore, Shellsol, Isopar, etc.

[0045] iv. The organic phase may also contain "modifiers". Modifiers are sometimes added to improve the solubility of metal complexes in the organic phase, to change the physical properties of the solvent, and thus to avoid fouling or the formation of third phases, which are undesirable in solvent extraction. Modifiers may also be added to prevent chemical degradation of the extractant or diluent. However, modifiers may impair the selectivity of the organic phase, as these modifiers may participate in the formation of complexes between the metal and the extractant.

[0046] The "selectivity" S of an extractant for one metal relative to another can be expressed as the ratio of the distribution coefficients D of the two metals:

[0047] S Mg / Ni =D Mg / D Ni

[0048] The "partition coefficient" of a metal is understood to be the ratio of the equilibrium concentration of the metal in the organic phase to the equilibrium concentration of the metal in the aqueous phase:

[0049] D M =[M] O / [M] A

[0050] wherein M is a metal, such as nickel or magnesium, O refers to the organic phase, and A refers to the aqueous phase.

[0051] In the context of the present invention, the term "raw material feed" refers to one or more raw materials comprising any one or a combination of nickel, cobalt, manganese or lithium. The metal may exist as is or may exist as a compound of the aforementioned metal or as a mixture of compounds. In some embodiments, the raw material feed may include any one or a combination of raw materials and recycled materials. Examples of raw materials include, but are not limited to, mixed hydroxide precipitates (MHP), mixed sulfide precipitates (MSP), nickel sulfide concentrates, cobalt sulfide concentrates, nickel laterite, nickel matte or nickel iron. Examples of recycled materials include, but are not limited to, spent positive electrode materials and materials derived from recycled lithium-ion batteries or lithium-ion battery manufacturing waste, collectively referred to herein as "black matter".

[0052] In the context of the present invention, the term "MHP" is considered to be an abbreviation of the term "mixed hydroxide precipitate". Mixed hydroxide precipitate (MHP) is an intermediate product of nickel metallurgy, which originates from the processing of laterite ores containing mainly nickel and a small amount of cobalt. MHP is a solid product, usually prepared by extracting nickel and cobalt from laterite ores. Alternatively or additionally, MHP can be obtained from nickel-containing and / or cobalt-containing materials generated as production waste during the preparation of positive electrode materials, or from battery recycling processes.

[0053] In the context of the present invention, the term "CHIP" is considered to be an abbreviation of the term "cobalt hydroxide intermediate precipitate". The cobalt hydroxide intermediate consists mainly of cobalt and generally has a cobalt content of 25% to 40% by weight relative to the total weight of the intermediate product. Typically, the CHIP contains a large amount of nickel. CHIPs are known to have a very low impurity content, which makes them attractive for the process according to the present invention.

[0054] The "raw material feed" may refer to a solid feed comprising an MHP product, a CHIP product, or a mixture of two or more MHP products, two or more CHIP products, or a mixture of one or more MHP products and one or more CHIP products. Preferably, the raw material feed comprises at least one nickel compound and at least one cobalt compound. Preferably, the nickel compound and the cobalt compound are contained as a nickel (II) compound and a cobalt (II) compound, respectively. However, the nickel compound and the cobalt compound may also be contained in a higher oxidation state such as 3+ or 4+, or the metal-containing feed may contain a mixture of nickel and / or cobalt compounds in oxidation state 2+ and oxidation state 3+ and / or 4+. In addition, the raw material feed may contain an alloy of nickel (0) and cobalt (0), and / or the raw material feed may contain one or more nickel- and cobalt-containing ores.

[0055] In the context of the present invention, the term "continuous process" will be considered to be such a process, wherein the solution produced has a substantially constant outflow and composition. Specifically, a continuous process is such a process, wherein the solution produced has a constant composition within the range considered to be normal process variation. More specifically, the solution produced has a composition, wherein the concentration of each component is within the range of + / -20% or less, preferably + / -10% or less, more preferably + / -5% or less, even more preferably + / -3% or less of its average concentration. In a preferred embodiment, the invention provides a continuous process operated under steady state conditions.

[0056] In the context of the present invention, the term "aqueous medium" is used for water-based solutions. The aqueous medium facilitates the handling of the reactor contents, such as mixing or pumping. The aqueous medium may already contain some other ingredients that participate in the reaction, or those ingredients may be added later. The aqueous medium may particularly contain an inorganic acid.

[0057] In the context of the present invention, the term "positive electrode precursor material" consists of a mixed metal hydroxide, carbonate, oxyhydroxide and / or oxide, and comprises nickel and at least one metal selected from cobalt, manganese and aluminum. Preferably, the positive electrode precursor material comprises at least 30 mol%, or even at least 50 mol% of Ni, preferably 60 mol% to 95 mol% and all values ​​therebetween, relative to the total content of nickel, cobalt, manganese and aluminum in the positive electrode precursor material. The positive electrode precursor material may also comprise one or more metals selected from Ba, Al, Ti, Zr, W, Fe, Cr, Mo, Nb, Mg and V, more preferably selected from Al, Ti, Zr, W and Mg. In a preferred embodiment, the positive electrode precursor material comprises Ni, Co and Al. In another preferred embodiment, the positive electrode precursor material comprises Ni, Co and Mn.

[0058] In a first aspect, the present invention provides a method for preparing a high purity nickel sulfate solution, the method comprising the following steps:

[0059] i. forming a mixed metal sulfate aqueous solution by reacting sulfuric acid with a raw material feed comprising nickel, manganese, cobalt and magnesium in an aqueous medium;

[0060] ii. extracting manganese from the mixed metal sulfate aqueous solution using a first organic phase comprising a first alkylphosphorus-based extractant (I) and a first diluent, thereby obtaining a first aqueous raffinate comprising nickel, cobalt and magnesium content and a manganese-rich organic phase;

[0061] iii. extracting cobalt from the first aqueous raffinate using a second organic phase comprising a second alkylphosphorus-based extractant (II) and a second diluent, thereby obtaining a second aqueous raffinate comprising nickel and residual magnesium content and a cobalt-rich organic phase; and

[0062] iv. extracting magnesium from the aqueous raffinate using a third organic phase comprising a third alkylphosphorus-based extractant (III) and a third diluent, thereby obtaining a high-purity nickel sulfate solution and a magnesium-rich organic phase.

[0063] In a preferred embodiment, the present invention provides a method according to the first aspect of the present invention, wherein:

[0064] a) the first alkylphosphorus-based extractant (I) comprises alkylphosphoric acid, and / or nickel and / or cobalt salts of alkylphosphoric acid,

[0065] b) the second alkylphosphorus-based extractant (II) comprises an alkylphosphinic acid and / or a nickel salt of an alkylphosphinic acid, and

[0066] c) The third alkylphosphorus-based extractant (III) comprises an alkylphosphinic acid and / or a nickel salt of an alkylphosphinic acid.

[0067] In a preferred embodiment, the present invention provides a method according to the first aspect of the present invention, wherein the extraction in step ii. is carried out at a temperature of 20°C to 45°C, preferably at a temperature of 20°C to 40°C, more preferably at a temperature of 25°C to 35°C, most preferably at a temperature of about 20°C, 25°C, 30°C, 35°C or 40°C, or any value therebetween. It has been found that lower temperatures provide better selectivity for Mn extraction, and thus better separation of Mn from Co. Preferably, the temperature is above 20°C, or even above 25°C, so as to facilitate setting the operating temperature when the ambient temperature is high.

[0068] In a preferred embodiment, the present invention provides a method according to the first aspect of the present invention, wherein the extraction in step iii. is carried out at a temperature between 40°C and 60°C, preferably at a temperature of about 50°C. It has been found that a sufficiently low temperature in step ii., combined with a higher temperature in step iii., helps to separate manganese and cobalt from the aqueous stream, which is obtained as an aqueous raffinate in step iii. Advantageously, the setting of the method of the present invention allows a battery-grade, high-purity nickel sulfate solution to be obtained in three solvent extraction steps, avoiding the need to extract Ni from the aqueous stream. Therefore, the present invention also provides a method according to the first aspect of the present invention, wherein the high-purity nickel sulfate solution obtained in step iv. is not subjected to solvent extraction for extracting nickel from an aqueous nickel sulfate solution.

[0069] The solvent extraction steps ii., iii. and iv. can be carried out in any suitable device and are not particularly limited. The solvent extraction equipment generally comprises at least one or more devices consisting of a mixer-settler, a column contactor, a centrifugal contactor or any other type of contactor. Preferably, the extraction is carried out in a countercurrent configuration.

[0070] The first aqueous raffinate obtained in step ii. comprises (i) nickel sulfate, (ii) cobalt sulfate, and (iii) magnesium in a concentration between 20 mg / L and 20 g / L, preferably in a concentration between 20 mg / L and 2 g / L, and more preferably in a concentration between 20 mg / L and 500 mg / L. Typically, the residual impurity content in the first aqueous raffinate (A1) obtained is too high for high purity applications, so a second solvent extraction step is required.

[0071] The second aqueous raffinate obtained in step iii. comprises (i) nickel sulfate, (ii) and (iii) magnesium in a concentration between 20 mg / L and 20 g / L, preferably between 20 mg / L and 2 g / L, and more preferably between 20 mg / L and 500 mg / L. Typically, the residual magnesium content in the obtained second aqueous raffinate (A2) is too high for high purity applications, so a third solvent extraction step is required to extract the magnesium.

[0072] In a preferred embodiment, the present invention provides a method according to the first aspect of the present invention, wherein the mixed metal sulfate aqueous solution contains at least nickel, manganese, cobalt and magnesium, and also contains one or more impurities selected from zinc, calcium, cadmium, iron, aluminum and copper. Other impurities may also be present. The advantage of the present invention is that the elemental cobalt, magnesium and manganese and (if present) zinc, calcium, cadmium, iron, aluminum and copper can be completely separated from nickel in a series of simple solvent extraction processes. It provides a high-purity nickel sulfate aqueous solution, which contains nickel at a concentration between 40g / L and 200g / L and a magnesium concentration of up to 10mg / L, and three loaded organic phases, namely a manganese-rich organic phase containing manganese, magnesium, cobalt and nickel and (if present) zinc, copper, cadmium and calcium; a cobalt-rich organic phase containing nickel and a portion of the residual content of magnesium; and a magnesium-rich organic phase containing nickel and magnesium. Preferably, the high-purity nickel sulfate aqueous solution contains up to 5mg / L magnesium, and even more preferably up to 1mg / L magnesium. The first organic phase, the second organic phase and / or the third organic phase may contain a modifier.

[0073] In a preferred embodiment, the present invention provides a method according to the first aspect of the present invention, wherein the mixed metal sulfate aqueous solution entering step ii. has a pH between 1.0 and 4.0 before contacting with the solvent containing the extractant I, producing a chemical equilibrium between the nickel aqueous solution and the solvent, more preferably the pH is between 1.5 and 3.5, and most preferably the pH is between 2.0 and 3.0.

[0074] In a preferred embodiment, the present invention provides a method according to the first aspect of the present invention, wherein the first aqueous raffinate entering step iii. has a pH between 2.5 and 5.5 before contacting with the solvent comprising the extractant II, producing a chemical equilibrium between the nickel aqueous solution and the solvent, more preferably a pH between 3.0 and 5.0, and most preferably a pH between 3.5 and 4.5.

[0075] In a preferred embodiment, the present invention provides a method according to the first aspect of the present invention, wherein the second aqueous raffinate entering step iv. has a pH between 4.0 and 6.5 before contacting with the solvent comprising the extractant III, producing a chemical equilibrium between the nickel aqueous solution and the solvent, more preferably a pH between 4.5 and 6.0, and most preferably a pH between 5.0 and 5.5.

[0076] In a preferred embodiment, the present invention provides a method according to the first aspect of the present invention, wherein said extraction in step iv. is carried out at a temperature between 45°C and 65°C, preferably at a temperature of about 55°C.

[0077] In a preferred embodiment, the present invention provides a method according to the first aspect of the present invention, further comprising the step of at least partially removing lithium from the mixed metal sulfate aqueous solution before step ii. The lithium may be removed by washing from the raw material before step i. before step ii. Alternatively, lithium may be removed from the obtained high purity nickel sulfate solution after step iv. Therefore, in an alternative or supplementary embodiment, the method further comprises the step of at least partially removing lithium from the mixed metal sulfate aqueous solution after step iv.

[0078] In a preferred embodiment, the present invention provides a method according to the first aspect of the invention, wherein nickel is washed out from the manganese-rich organic phase, from the cobalt-rich organic phase and / or from the magnesium-rich organic phase.

[0079] In a preferred embodiment, the present invention provides a method according to the first aspect of the present invention, wherein the magnesium-depleted high-purity nickel sulfate aqueous solution contains nickel at a concentration of 40 g / L to 180 g / L and magnesium at a concentration of up to 5 mg / L.

[0080] In a preferred embodiment, the present invention provides a method according to the first aspect of the present invention, wherein the mixed metal sulfate aqueous solution comprises nickel and cobalt in an amount of at least 30 atomic %, preferably at least 50 atomic %, more preferably at least 70 atomic % and most preferably at least 85 atomic % relative to the total metal content of the mixed metal sulfate aqueous solution formed in step i. Preferably, the present invention provides a method according to the first aspect of the present invention, wherein the mixed metal sulfate aqueous solution comprises nickel and cobalt in an amount of at least 30 atomic %, preferably at least 60 atomic % relative to the total metal content of the mixed metal sulfate aqueous solution formed in step i., and wherein the mixed metal sulfate aqueous solution comprises magnesium, manganese, zinc, copper and cadmium in an amount of up to 40 atomic % relative to the total metal content of the mixed metal sulfate aqueous solution formed in step i. Preferably, the mixed metal sulfate aqueous solution comprises nickel and cobalt in an amount of at least 75 atomic %, more preferably, the mixed metal sulfate aqueous solution comprises nickel and cobalt in an amount of at least 90 atomic %, and most preferably, the mixed metal sulfate aqueous solution comprises nickel and cobalt in an amount of at least 95 atomic %. In a preferred embodiment, the present invention provides a method according to the first aspect of the present invention, wherein the mixed metal sulfate aqueous solution further comprises calcium, zinc, copper and cadmium in a total amount of up to 25 atomic % relative to the total metal content of the mixed metal sulfate aqueous solution formed in step i. Preferably, the mixed metal sulfate aqueous solution also comprises calcium, zinc, copper and cadmium in a total amount of up to 10 atomic % and even more preferably up to 5 atomic %. Therefore, the mixed metal sulfate aqueous solution can be derived from all kinds of resources, such as mixed hydroxide precipitates, crude nickel sulfate or any other type of suitable resources, which are suitable in themselves or have been optionally processed into suitable feed solutions. Such processing may include leaching, selective leaching, dissolution, precipitation steps and / or any other type of pretreatment steps. It can also be a combination of them. For example, if at least leaching and final pre-lithium removal are included in the pretreatment, pretreated battery recycling materials containing nickel, cobalt, manganese and lithium can be treated in this process to produce pure nickel sulfate solution and pure cobalt salt solution. Alternatively, lithium is removed by, for example, a lithium ion exchange column at the end of step vi.

[0081] In a preferred embodiment, the present invention provides a method according to the first aspect of the present invention, wherein the first organic phase, the second organic phase and the third organic phase provided in steps ii., iii. and iv. respectively contain the first extractant, the second extractant and the third extractant in an amount of 5 volume % to 50 volume % relative to the total volume of the solvent, and the diluent in an amount of 50 volume % to 95 volume % relative to the total volume of the solvent.

[0082] In a preferred embodiment, the present invention provides a method according to the first aspect of the present invention, wherein the first organic phase used in step ii. comprises 5% to 50% by volume of the first extractant (I) relative to the total volume of the first organic phase, and 50% to 95% by volume of the first diluent relative to the total volume of the first organic phase. More preferably, the first organic phase comprises 30% to 40% by volume of the first extractant (I) and 60% to 70% by volume of the first diluent.

[0083] In a preferred embodiment, the present invention provides a method according to the first aspect of the present invention, wherein the second organic phase used in step iii. comprises the second extractant (II) in an amount of 5% to 50% by volume relative to the total volume of the second organic phase, and the second diluent in an amount of 50% to 95% by volume relative to the total volume of the second organic phase. More preferably, the second organic phase comprises the second extractant (II) in an amount of 10% to 25% by volume and the diluent in an amount of 75% to 90% by volume. It was found that the concentration of extractant in the organic phase allows for optimal extraction of cobalt without loss of processability of the solvent.

[0084] In a preferred embodiment, the present invention provides a method according to the first aspect of the present invention, wherein the third organic phase used in step iv. comprises the third extractant (III) in an amount of 5% to 50% by volume relative to the total volume of the third organic phase, and the third diluent in an amount of 50% to 95% by volume relative to the total volume of the third organic phase. More preferably, the third organic phase comprises the third extractant (III) in an amount of 10% to 25% by volume and the diluent in an amount of 75% to 90% by volume. It was found that the concentration of the extractant in the organic phase allows for optimal extraction of magnesium without loss of processability of the solvent.

[0085] In a preferred embodiment, the present invention provides a method according to the first aspect of the present invention, wherein the first diluent, the second diluent and / or the third diluent are hydrocarbons. More generally, any organic, water-immiscible solvent capable of dissolving the extractant may be used. Therefore, there is no particular restriction on the diluent. As an example of a diluent, a kerosene-based compound may be used, which may be aliphatic, cycloalkane, aromatic or even a mixture thereof.

[0086] In a preferred embodiment, the present invention provides a method according to the first aspect of the present invention, wherein the first extractant is preloaded with nickel and / or cobalt (preferably nickel), i.e. converted into their nickel and / or cobalt salts (preferably their nickel salts), to a concentration of at least 20% of the available extractant capacity. Preferably, the second extractant and the third extractant are preloaded with nickel, i.e. converted into their nickel salts, to a concentration of at least 20% of the available extractant capacity. Preferably, the first organic phase, the second organic phase and the third organic phase contain less than 2 g / L of sodium after preloading.

[0087] In a preferred embodiment, the present invention provides a method according to the first aspect of the present invention, wherein the extractant used in step ii. comprises an alkyl phosphorus-based acid and / or its nickel salt and / or cobalt salt, preferably its nickel salt. Preferably, the extractant used in step iii. and step iv., respectively, comprises an alkyl phosphorus-based acid and / or its nickel salt. Suitable alkyl phosphorus-based acids include bis(2-ethylhexyl)phosphoric acid (D2EHPA), (2-ethylhexyl)phosphonic acid mono(2-ethylhexyl) ester (EHEHPA, PC88A), bis-(2,4,4-trimethylpentyl)phosphinic acid (CYANEX272 or IONQUEST 290) and diisooctylphosphinic acid (DOPA). Alkyl phosphorus-based acids can act as chelating extractants because of the presence of coordinated phosphorus and oxygen atoms in these molecules. Among the elements in aqueous solution, elements that form corresponding chelated compounds have higher stability and are more conducive to improving extraction efficiency than elements that are less likely to form chelated compounds. Alkyl phosphorus-based extractants can be selected from but are not limited to the following options:

[0088] -phosphoric acid, such as di-(2-ethylhexyl)phosphoric acid (also known as D2EHPA, DEHPA, HDEHP, P204), an organophosphorus compound with the formula (C8H 17 O)2PO2H.

[0089] -phosphonic acid, such as 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (also known as EHEHPA, HEHEHP, P507, PC88A), an organophosphorus compound with the formula R1=(C8H 17 )(C8H 17 O)PO2H.

[0090] -phosphinic acid, such as bis-(2,4,4-trimethylpentyl)phosphinic acid (also known as Cyanex 272, Ionquest 290), an organophosphorus compound with the formula (C 16 H 34 )PO2H.

[0091] In a preferred embodiment, the present invention provides a method according to the first aspect of the present invention, wherein the first extractant (I) has a higher selectivity for calcium (higher than nickel) than the second extractant (II). In other words, the first extractant (I) has a higher affinity for calcium (higher than nickel) than the second extractant (II) has a higher affinity for calcium (higher than nickel). In addition, the first extractant (I) has a higher selectivity for calcium than for nickel. Most preferably, the first extractant (I) comprises an alkylphosphoric acid, such as D2EHPA. Preferably, the first alkylphosphorus-based extractant (I) comprises an alkylphosphoric acid and / or a nickel salt and / or a cobalt salt thereof, and the second alkylphosphorus-based extractant (II) comprises an alkylphosphonic acid and / or a nickel salt thereof.

[0092] In a preferred embodiment, the present invention provides a method according to the first aspect of the present invention, wherein the third extractant (III) has a higher selectivity for magnesium than the first (I) and the second extractant (II). In other words, the affinity of the third extractant (III) for magnesium is higher than the affinity of the first extractant (I) and the second extractant (II). In addition, the selectivity of the third extractant (III) for magnesium is higher than the selectivity for nickel. Most preferably, the third extractant (III) comprises an alkylphosphinic acid, such as IONQUEST 290.

[0093] In a preferred embodiment, the extractant used in steps ii., iii. and iv. is neutralized with an alkali metal hydroxide and preloaded with nickel at a high pH and then used for the extraction in steps ii. to iv., wherein the organic phase preloaded with nickel is contacted with an aqueous nickel sulfate solution containing metal impurities. In such cases, an exchange reaction occurs, by which elements that are more likely to be extracted than nickel are transferred to the solvent, while the nickel in the organic phase is transferred to the aqueous phase. As a result, impurities in the mixed metal sulfate aqueous solution are removed, while the nickel concentration in the resulting raffinate solution is increased, thereby largely avoiding the entry of alkali metals from the neutralizer into the main process (raffinate) stream. As alkali metal hydroxides, sodium hydroxide, potassium hydroxide, ammonium hydroxide, etc. can be used. In addition, preferably, sodium hydroxide is used as the alkali metal hydroxide. Alternatively, the extractant used in step ii. may be preloaded with cobalt or a mixture of nickel and cobalt.

[0094] It has been found that preloading the extractant used in steps ii. to iv. with nickel allows for optimal and improved extraction without loss of processability of the extractant. During this preloading step, the partially neutralized extractant (i.e. in alkali metal converted form) exchanges the alkali metal (usually sodium) on the extractant with nickel or cobalt in the aqueous nickel sulfate solution. Preferably, the residual amount of alkali metal on the preloading solvent is as low as possible in order to limit the transfer of residual alkali metal from the preloading solvent to the mixed metal sulfate aqueous solution when the impurities are extracted from this solution.

[0095] Part of the nickel can be replaced by another harmless metal that will exchange with the impurities to be extracted from the aqueous nickel sulfate solution to be purified. This can be an alkali metal, such as sodium or potassium, or similar substances such as ammonium. However, these other metals may result in the need to extract these metals present in the aqueous nickel sulfate solution to be purified, or even contaminate the nickel sulfate solution by exchanging with the impurities to be extracted.

[0096] In a preferred embodiment, the present invention provides a method according to the first aspect of the invention, wherein before extraction, the extractant is converted into their nickel and / or cobalt salts, preferably into nickel salts corresponding to the appropriate conversion of the extractant, thus containing nickel in an amount of 20% to 70% of the available extractant capacity and residual sodium at a concentration of up to 2 g / L, preferably up to 0.5 g / L and more preferably up to 0.1 g / L. Preferably, nickel is preloaded to an amount between 25% and 60% of the available extractant capacity, and preferably greater than 30% of the available extractant capacity, and the concentration of residual sodium is up to 0.5 g / L. More preferably, nickel is preloaded to an amount between 30% and 50% of the available extractant capacity, and the concentration of residual sodium is up to 0.1 g / L. For step ii., cobalt salts of the same specifications as the above-mentioned nickel or combined nickel-cobalt salts are also possible.

[0097] Therefore, the preferred nickel concentration on the preload solvent depends on the extractant concentration and the degree of conversion. Both are determined by the target pH in the mixed metal sulfate aqueous solution and are therefore a function of the total amount of impurities to be removed. A higher degree of conversion of the extractant results in a higher pH during extraction, thereby allowing more impurities (and nickel) to be extracted from the nickel-containing feed solution, while a lower degree of conversion of the extractant results in a lower pH during extraction, thereby allowing selectivity for impurities over nickel.

[0098] In a preferred embodiment, the preloaded solvent containing nickel and possibly some other metals such as sodium, potassium or other metals, or other cations such as ammonium, can be contacted again with a pure nickel-containing solution such as nickel sulfate or nickel chloride solution in order to further exchange the metallic sodium, potassium, ammonium or other metal on the solvent with the nickel from the pure nickel-containing solution. The nickel preloading, cobalt preloading or nickel-cobalt preloading operation can be carried out in two or more stages, preferably in countercurrent operation, using at least a pure nickel sulfate solution, so that the alkali metals that may be co-extracted from the base used are washed out of the solvent. As a result, a nickel preloaded solvent containing significantly less other metals is obtained, which can be used for extraction steps ii. to iv., which in this way avoids contamination of the nickel aqueous solution with unwanted metals to the greatest extent.

[0099] In a preferred embodiment, the present invention provides a method according to the first aspect of the present invention, comprising step v., step v. comprising stripping the manganese-rich organic phase obtained in step ii. with an aqueous solution comprising an inorganic acid. This effectively results in manganese, calcium and zinc, copper and cadmium (if present) eluting from the first solvent. Preferably, the inorganic acid is one or more selected from the group comprising the following: hydrofluoric acid, hydrochloric acid, hydrobromic acid, hydroiodic acid, nitric acid, phosphoric acid, sulfuric acid, boric acid and perchloric acid. More preferably, the inorganic acid is one or more selected from the group comprising the following: hydrochloric acid, hydrobromic acid, nitric acid, phosphoric acid and perchloric acid. In another embodiment, the inorganic acid is sulfuric acid. Considering the presence of calcium in the stripping solution obtained, hydrochloric acid is most preferably used. This allows a concentrated elution solution to be obtained from the first solvent, which contains manganese and calcium and (if present) zinc, copper, cadmium and a residual amount of nickel and a residual amount of cobalt. Therefore, the extractant is regenerated to produce a metal-free solvent that can be reused for extraction or preloading. In view of the presence of calcium in the stripping solution obtained, hydrochloric acid is preferably used. By stripping with hydrochloric acid, calcium chloride, which is soluble in water, is formed. In this way, the metal content can be concentrated from the solvent into the aqueous solution. In view of the low solubility of calcium sulfate, the use of sulfuric acid can induce the formation of solid precipitates, thereby destroying the solvent extraction process. In a preferred embodiment, the hydrochloric acid solution has a concentration of at least 50g / L, and more preferably a concentration of 100g / L to 300g / L.

[0100] In a preferred embodiment, the invention provides a method according to the first aspect of the invention, comprising step vi., step vi. comprising stripping the cobalt-rich organic phase obtained in step iii. with an aqueous solution comprising a mineral acid. This effectively causes cobalt to be eluted from the second solvent. Preferably, the mineral acid is one or more selected from the group comprising the following: hydrofluoric acid, hydrochloric acid, hydrobromic acid, hydroiodic acid, nitric acid, phosphoric acid, sulfuric acid, boric acid and perchloric acid. More preferably, the mineral acid is one or more selected from the group comprising the following: hydrochloric acid, hydrobromic acid, nitric acid, sulfuric acid, phosphoric acid and perchloric acid. Most preferably, the mineral acid is sulfuric acid or hydrochloric acid. This allows a concentrated elution solution comprising cobalt to be obtained.

[0101] In a preferred embodiment, the invention provides a method according to the first aspect of the invention, comprising the step of stripping the magnesium-rich organic phase obtained in step iv. with an aqueous solution comprising an inorganic acid. Preferably, the inorganic acid is one or more selected from the group comprising the following: hydrofluoric acid, hydrochloric acid, hydrobromic acid, hydroiodic acid, nitric acid, phosphoric acid, sulfuric acid, boric acid and perchloric acid. More preferably, the inorganic acid is one or more selected from the group comprising the following: hydrochloric acid, hydrobromic acid, nitric acid, sulfuric acid, phosphoric acid and perchloric acid. Most preferably, the inorganic acid is sulfuric acid. This allows obtaining a concentrated elution solution comprising magnesium and regenerating the solvent.

[0102] The stripping step can be carried out in any suitable device and is not particularly limited. The stripping equipment generally includes at least one or more devices consisting of a mixer-settler, a column contactor, a centrifugal contactor or any other type of contactor. Preferably, the stripping is carried out in a countercurrent configuration.

[0103] In a preferred embodiment, the present invention provides a method according to the first aspect of the invention, wherein the stripping steps v. and / or vi. are carried out at a temperature between 40°C and 60°C, preferably between 40°C and 50°C and more preferably about 45°C.

[0104] In a preferred embodiment, the present invention provides a post-treatment step according to the first aspect of the invention, wherein the manganese-rich organic phase is additionally washed with sulfuric acid after being stripped with hydrochloric acid in step v. Washing with sulfuric acid allows the removal of chloride ions and possible residual metals, such as iron or aluminum, from the solvent. In this way, the solvent is regenerated and can be used again for extraction after it has been preloaded.

[0105] In a preferred embodiment, the present invention provides a post-treatment step according to the first aspect of the present invention, wherein the high-purity nickel sulfate aqueous solution obtained in step iv. contains nickel at a concentration of 40 g / L to 180 g / L and magnesium at a concentration of up to 5 mg / L, preferably up to 1 mg / L. Preferably, the content of calcium, iron, aluminum, zinc, copper, manganese, cobalt, magnesium and / or cadmium in the high-purity nickel sulfate aqueous solution is each individually up to 10 mg / L, preferably up to 5 mg / L, or even up to 1 mg / L.

[0106] In a preferred embodiment, the present invention provides a method according to the first aspect of the present invention, wherein at least a portion of the high purity nickel sulfate solution obtained in step iv. is crystallized without further purification, and wherein the formed nickel sulfate crystals are used to prepare a positive electrode precursor material for a lithium ion battery.

[0107] In a preferred embodiment, the present invention provides a method according to the first aspect of the present invention, wherein at least a portion of the high purity nickel sulfate solution obtained in step iv. is used for preparing a positive electrode precursor material for a lithium ion battery without further purification.

[0108] The present invention is particularly suitable for processing raw material feeds containing nickel and cobalt compounds, such as but not limited to MHP, CHIP, etc. Advantageously, no further extraction of the high purity nickel sulfate solution obtained in step iv. is required.

[0109] In a preferred embodiment, the present invention provides a method according to the first aspect of the invention, wherein at least a portion of the high purity nickel sulfate solution obtained in step iv. is subjected to crystallization, wherein at least a portion of the mother liquor formed during crystallization is discharged, and wherein at least a portion of the crystallizer discharge is used for preloading of one or more organic phases used in steps ii., iii. and iv. The crystallizer discharge generally has a relatively high sodium content. The crystallizer discharge is recycled to any of the solvent extraction steps ii., iii. and / or iv., which allows the nickel sulfate present in the crystallizer discharge to be recovered while allowing the sodium present in the discharge to be discharged from the process via the raffinate of the preloading step.

[0110] In a preferred embodiment, the present invention provides a method according to the first aspect of the present invention, wherein the high purity nickel sulfate aqueous solution obtained after removing residual magnesium in step iv. is subjected to crystallization or granulation. Preferably, the nickel sulfate in the nickel sulfate solution is crystallized, thereby allowing an additional purification step. In the case of granulation, any granulation technique known to the skilled person is suitable, such as spray drying. In a preferred embodiment, the present invention provides a method according to the first aspect of the present invention, wherein at least a portion of the mother liquor formed from the crystallization unit is recycled upstream. Preferably, the crystallizer discharge comprising a saturated nickel sulfate solution is used to preload nickel onto one or more extractants, in particular for preloading nickel onto one or more extractants used in one or more of steps ii., iii. and / or iv.

[0111] In a preferred embodiment, the present invention provides a method according to the first aspect of the invention, wherein nickel is washed out from the manganese-rich organic phase, from the cobalt-rich organic phase and / or from the magnesium-rich organic phase. In order to recover this co-extracted nickel from the loaded organic phase before entering the elution stage, it is first washed with an acidic solution (such as aqueous sulfuric acid) to selectively wash it out of these solvents. The nickel is selectively washed by adopting optimal pH conditions, especially the acidity of the final washing solution, and the amount of acid added is suitable to achieve the required pH.

[0112] In a preferred embodiment, the present invention provides a method according to the first aspect of the present invention, wherein the first organic phase, the second organic phase and / or the third organic phase, after washing or stripping with sulfuric acid, is loaded with nickel using an alkali metal hydroxide and a solution containing a nickel salt and / or a cobalt salt such as a nickel sulfate and / or cobalt sulfate solution or a nickel chloride and / or cobalt chloride solution, and is subsequently recycled in step ii., step iii. and / or step iv., thereby achieving a closed loop of the method.

[0113] In a preferred embodiment, the present invention provides a method according to the first aspect of the present invention, wherein the mixed metal sulfate aqueous solution is obtained by removing iron and / or aluminum from a mixed metal sulfate aqueous solution comprising nickel, cobalt, manganese, magnesium and (if present) zinc, copper, cadmium and / or calcium, respectively, and also comprising iron and / or aluminum. The iron and / or aluminum can be advantageously removed by adding an alkaline agent such as a hydroxide or other substance to the aqueous solution, thereby forming an iron hydroxide and / or aluminum hydroxide precipitate. Possibly, the addition of an oxidant, such as oxygen or hydrogen peroxide, may be included in the iron and / or aluminum removal step.

[0114] In a preferred embodiment, the iron and / or aluminum are removed by precipitation using a calcium base such as calcium hydroxide, calcium oxide, calcium carbonate, calcium bicarbonate or any other calcium-containing alkaline reagent. The use of a calcium base is advantageous because calcium forms low water-soluble calcium sulfate, also known as gypsum, in this step of the method. Therefore, the use of an excess of calcium base has no adverse effect on the purity of the nickel sulfate solution obtained. Only a limited amount of calcium will be retained in the nickel solution sent to the solvent extraction step ii. The latter method is designed to be able to completely remove calcium from the nickel solution. The formation of calcium sulfate during the precipitation of iron and / or aluminum can enhance the filterability of the iron and / or aluminum precipitate. Therefore, a stoichiometric excess of calcium base can be preferably used relative to the amount of iron and / or aluminum impurities in the mixed metal sulfate aqueous solution containing nickel, cobalt, magnesium and iron and / or aluminum.

[0115] In another preferred embodiment, the base used can be nickel hydroxide or carbonate or any other nickel-containing alkaline agent, thereby introducing beneficial nickel ions into the nickel sulfate solution. Other preferred nickel bases are nickel bicarbonate and nickel hydroxysulfate.

[0116] In another preferred embodiment, the base used may be a hydroxide or carbonate of cobalt or any other cobalt-containing alkaline agent, thereby introducing cobalt ions in the nickel sulfate solution to be removed in step iii. Other preferred cobalt bases are cobalt bicarbonate and cobalt hydroxysulfate.

[0117] In another preferred embodiment, the base used may be magnesium hydroxide or carbonate or any other magnesium-containing alkaline agent, since magnesium is efficiently and effectively removed in the subsequent steps of the process of the present invention. Other preferred magnesium bases are magnesium bicarbonate and magnesium hydroxysulfate.

[0118] In another preferred embodiment, impurities such as iron and / or aluminum may be separated by precipitation using a combination of two or more precipitants selected from calcium bases, magnesium bases, cobalt bases, and nickel bases.

[0119] In addition, impurities such as iron and / or aluminum can be removed by precipitation in two or more precipitation steps, wherein a different precipitation agent can be used in each precipitation step. In a preferred embodiment, a nickel base is used in the first precipitation step and a calcium base is used in the subsequent precipitation step.

[0120] Alternatively, impurities such as iron and / or aluminum may be separated by other methods such as neutralization. However, the use of a strong alkaline base such as sodium hydroxide or potassium hydroxide introduces metallic impurities into the mixed metal sulfate aqueous solution which cannot be extracted by the subsequent solvent extraction process and thus may complicate potential crystallization or granulation at the end of the process.

[0121] In another embodiment, calcium is already present in the nickel feed solution entering the solvent extraction step ii., because calcium has been introduced from the raw materials or by using a calcium-containing reagent (such as a calcium base, e.g. calcium hydroxide, calcium oxide, calcium carbonate, calcium bicarbonate or another calcium-containing alkaline reagent) prior to entering the solvent extraction step ii.

[0122] Example

[0123] For each method step, examples are provided to further illustrate the present invention. These examples are based on experimentally obtained data and are not intended to limit the scope of the present invention.

[0124] Extraction of manganese from mixed metal sulfate solutions

[0125] The first organic phase consisted of 25 vol% D2EHPA with Escaid 110 as diluent. The extractant was 49% saponified with 400 g / L NaOH.

[0126] The extraction was performed on a feed solution having the following composition:

[0127]

[0128] The extraction of manganese was carried out in batch mode in four steps at O / A = 0.25 and a temperature of 30°C. The raffinate composition is also reported in the table above. Manganese, calcium and zinc were removed from the raffinate to less than 1 mg / L.

[0129] Extraction of cobalt from mixed metal sulfate solutions

[0130] A first organic phase consisting of 35 volume % Cyanex 272 with as diluent Escaid 110 was used. The extractant was first saponified 58% with 400 g / L NaOH and then preloaded with nickel to 12.9 g / L nickel and 120 mg / L sodium from a preload solution consisting of 110 g / L nickel and 960 mg / L sodium.

[0131] Extraction was performed on a feed solution having the following composition :

[0132]

[0133] The extraction of cobalt was carried out in batch mode in four steps at O / A = 1.0 and a temperature of 55°C. The raffinate composition is also reported in the table above. The cobalt in the raffinate was removed to less than 1 mg / L.

[0134] Extraction of Magnesium from Mixed Metal Sulfate Solutions

[0135] A first organic phase consisting of 15 volume % Ionquest 290 with Escaid 110 as diluent was used. The extractant was preloaded from a solution containing 130 g / L nickel to 6.2 g / L nickel on the solvent with injection of 125 g / L sodium hydroxide solution.

[0136] Extraction was performed on a feed solution having the following composition :

[0137]

[0138] The extraction of magnesium was carried out in batch mode in five steps at O / A = 0.5 and a temperature of 55°C. The raffinate composition is also reported in the table above. The magnesium in the raffinate was removed to less than 1 mg / L.

Claims

1. A method for preparing a high-purity nickel sulfate solution, the method comprising the following steps: i. forming a mixed metal sulfate aqueous solution by reacting sulfuric acid with a raw material feed comprising nickel, manganese, cobalt and magnesium in an aqueous medium; ii. extracting manganese from the mixed metal sulfate aqueous solution using a first organic phase comprising a first alkylphosphorus-based extractant (I) and a first diluent at a temperature between 20°C and 45°C, wherein the first alkylphosphorus-based extractant (I) comprises alkylphosphoric acid and / or a nickel salt of alkylphosphoric acid, thereby obtaining a first aqueous raffinate comprising nickel, cobalt and magnesium content and a manganese-rich organic phase; iii. extracting cobalt from the first aqueous raffinate using a second organic phase comprising a second alkylphosphorus-based extractant (II) and a second diluent at a temperature between 45°C and 65°C, wherein the second alkylphosphorus-based extractant (II) comprises an alkylphosphinic acid and / or a nickel salt of an alkylphosphinic acid, thereby obtaining a second aqueous raffinate comprising nickel and residual magnesium content and a cobalt-rich organic phase; and iv. extracting magnesium from the second aqueous raffinate using a third organic phase comprising a third alkylphosphorus-based extractant (III) and a third diluent, wherein the third alkylphosphorus-based extractant (III) comprises an alkylphosphinic acid and / or a nickel salt of an alkylphosphinic acid, thereby obtaining a high-purity nickel sulfate solution and a magnesium-rich organic phase.

2. The process according to claim 1, wherein the raw material feed further comprises iron and / or aluminum, and wherein prior to step ii., a base is added to the mixed metal sulfate aqueous solution formed in step i., thereby forming a precipitate comprising iron and / or aluminum, respectively, and wherein the precipitate is filtered off.

3. The method of claim 2, wherein the base comprises a calcium base, a magnesium base, a cobalt base, a nickel base, or a combination of two or more of the foregoing bases.

4. The method according to any one of claims 1 to 3, wherein at least a portion of the high-purity nickel sulfate solution obtained in step iv. is crystallized without further purification, and wherein the formed nickel sulfate crystals are used to prepare a positive electrode precursor material for a lithium-ion battery.

5. The method according to any one of claims 1 to 4, wherein at least a portion of the high-purity nickel sulfate solution obtained in step iv. is used directly for preparing a positive electrode precursor material for a lithium-ion battery without further purification.

6. The process according to any one of claims 1 to 5, comprising the step of back-extracting the magnesium-rich organic phase obtained in step iv. with an aqueous solution comprising a mineral acid.

7. The process according to any one of claims 1 to 6, wherein the extraction in step iv. is carried out at a temperature between 45°C and 65°C.

8. The process according to any one of claims 1 to 7, wherein the first, second and third extractants are preloaded with nickel, i.e. converted into their nickel salts, to a concentration of at least 20% of the available extractant capacity.

9. The process according to any one of claims 1 to 8, wherein at least a portion of the high purity nickel sulfate solution obtained in step iv. is subjected to crystallization, wherein at least a portion of the mother liquor formed during the crystallization is discharged, and wherein at least a portion of the crystallizer discharge is used for preloading of one or more of the organic phases used in steps i., ii. and iii.

10. The method according to any one of claims 1 to 9, further comprising the step of at least partially removing lithium from the mixed metal sulfate aqueous solution prior to step ii.

11. The process according to any one of claims 1 to 10, comprising a step v. comprising back-extracting the manganese-rich organic phase obtained in step ii. with an aqueous solution comprising a mineral acid.

12. The process according to any one of claims 1 to 11, comprising a step vi. comprising back-extracting the cobalt-rich organic phase obtained in step iii. with an aqueous solution comprising a mineral acid.

13. The method according to any one of claims 1 to 12, wherein the first organic phase, the second organic phase and the third organic phase provided in steps ii., iii. and iv. respectively contain the first extractant, the second extractant and the third extractant in an amount of 5 to 50 volume % relative to the total volume of the solvent, and the diluent in an amount of 50 to 95 volume % relative to the total volume of the solvent.

14. The process according to any one of claims 1 to 13, wherein nickel is washed out from the manganese-rich organic phase, from the cobalt-rich organic phase and / or from the magnesium-rich organic phase.

15. A process according to any one of claims 1 to 14, wherein cobalt is washed out of the manganese-rich organic phase.

16. The process according to any one of claims 1 to 15, wherein the mixed metal sulfate aqueous solution formed in step i. comprises nickel and / or cobalt in an amount of at least 60 atomic % relative to the total metal content of the mixed metal sulfate aqueous solution formed, and wherein the mixed metal sulfate aqueous solution comprises calcium, magnesium, zinc, copper and cadmium in an amount of at most 40 atomic % relative to the total metal content of the mixed metal sulfate aqueous solution formed in step i.

17. The process according to any one of claims 11 to 16, wherein after stripping with the mineral acid, the first organic phase and / or the second organic phase is washed with sulfuric acid.

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