Preparation method of nickel sulfate

Abstract

The method for preparing nickel sulfate according to an exemplary embodiment may prepare a nickel-containing raw material. Nickel may be selectively leached from a nickel-containing feedstock using an oxidant to produce a first leachate. Residual metals may be separated from the first leachate to produce a second leachate. Nickel sulfate may then be obtained from the second leachate. Therefore, a separate nickel extraction step can be omitted, thereby reducing unnecessary by-products.

Description

Technical Field

[0001] The present invention relates to a method for preparing nickel sulfate. More specifically, the present invention relates to a method for preparing nickel sulfate from a nickel-containing raw material. Background Art

[0002] Nickel is used in various fields, for example, alloys for magnets, filaments, etc., plating for corrosion prevention, catalysts, bonded carbides, positive electrode materials for secondary batteries, etc. In particular, nickel is widely used as a transition metal contained in a positive electrode active material for lithium secondary batteries.

[0003] Since the cathode active material uses expensive valuable metals including nickel, more than 20% of the manufacturing cost is required in the preparation of the cathode material. In addition, as environmental issues have become increasingly prominent in recent years, research is being conducted on recycling methods for cathode active materials.

[0004] For example, the spent positive electrode active material may be leached in a strong acid and nickel may be recovered in the form of nickel sulfate, and the recovered nickel sulfate may be used to prepare the positive electrode active material again.

[0005] However, the recovered nickel sulfate may contain other transition metals such as manganese and iron as impurities. In addition, the amount of unnecessary by-products may increase due to the sodium hydroxide used when extracting nickel.

[0006] Therefore, there is a need for a method for preparing a high-purity nickel compound that can reduce the amount of by-products generated and increase the nickel yield.

[0007] For example, Korean Patent No. 10-1623930 discloses a process for leaching Ni, Co and Mn from the cathode material of spent lithium-ion batteries. Summary of the invention

[0008] 1. Technical issues to be resolved

[0009] A technical problem of the present invention relates to a method for preparing nickel sulfate with improved productivity and purity.

[0010] (II) Technical solution

[0011] In the method for preparing nickel sulfate according to an exemplary embodiment of the present invention, a nickel-containing raw material may be prepared. An oxidant may be used to selectively leach nickel from the nickel-containing raw material to generate a first leachate. Residual metals may be separated from the first leachate to generate a second leachate. Nickel sulfate may be obtained from the second leachate.

[0012] In some embodiments, the nickel-containing raw material may include nickel (Ni)-mixed hydroxide precipitate (MHP).

[0013] In some embodiments, the Ni-MHP may also contain cobalt and manganese.

[0014] In some embodiments, in the step of generating the first leachate, only nickel may be leached from nickel, cobalt, and manganese contained in the Ni-MHP.

[0015] In some embodiments, the oxidizing agent may comprise a metal persulfate.

[0016] In some embodiments, the step of generating the first leachate may be performed using an acidic solution containing an oxidant and at a pH of 2 or above.

[0017] In some embodiments, in the step of separating the residual metals to generate the second leachate, a fluoride precipitation agent may be used to precipitate at least one of calcium and magnesium.

[0018] In some embodiments, in the step of separating the residual metals to generate the second leachate, zinc may be precipitated or extracted.

[0019] In some embodiments, precipitation of zinc may be performed by using a sulfide precipitation agent.

[0020] In some embodiments, extraction of zinc may be performed using a phosphate-based extractant.

[0021] In some embodiments, the nickel-containing raw material may be washed before generating the first leachate.

[0022] In some embodiments, calcium or magnesium contained in the nickel-containing raw material may be partially removed by washing the nickel-containing raw material.

[0023] In some embodiments, washing the nickel-containing raw material may be performed by using water at 40°C to 100°C.

[0024] In some embodiments, the nickel sulfate may be obtained by crystallizing into nickel sulfate hydrate.

[0025] (III) Beneficial effects

[0026] According to an exemplary embodiment of the present invention, nickel can be selectively extracted by adding an acid solution and a metal salt oxidant to a nickel-containing mixed hydroxide precipitate. Thus, cobalt, manganese, etc. can be removed as residues, and the amount of acid solution and hydroxide used to extract cobalt and manganese separately can be reduced.

[0027] In some embodiments, residual metals such as magnesium, calcium, and zinc can be removed or reduced from the first leachate for leaching nickel to form a second leachate. Thereafter, high-purity nickel sulfate can be obtained from the second leachate by crystallization. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a schematic flow chart for explaining a method for preparing high-purity nickel sulfate according to an exemplary embodiment.

[0029] Figure 2 is a schematic flow chart for explaining a method for preparing nickel sulfate according to a comparative example. DETAILED DESCRIPTION

[0030] An exemplary embodiment of the present invention provides a method for preparing nickel sulfate from a nickel-containing raw material. For example, an exemplary embodiment of the present invention may include a method for refining nickel from a nickel-containing product.

[0031] The following is a more detailed description of the embodiments of the present invention with reference to the accompanying drawings, but this is merely exemplary and the present invention is not limited to the specific embodiments described exemplarily.

[0032] Figure 1 is a schematic flow chart for explaining a method for preparing nickel sulfate according to an exemplary embodiment.

[0033] Reference Figure 1 , a nickel (Ni)-containing raw material can be prepared (e.g., S10 process).

[0034] In some embodiments, the nickel-containing raw material may be a nickel (Ni)-mixed hydroxide precipitate (MHP) derived from an ore. For example, the nickel-containing raw material may include a hydrorefining byproduct of a Ni oxide ore. In addition to nickel, the Ni-MHP may further include additional metals such as calcium (Ca), magnesium (Mg), cobalt (Co), manganese (Mn), aluminum (Al), iron (Fe), and zinc (Zn).

[0035] In some embodiments, the nickel-containing raw materials can also be collected from electronic products / chemical products containing nickel, such as waste batteries.

[0036] In some embodiments, the nickel-containing raw material may be washed (e.g., S15 process). For example, the nickel-containing raw material may be washed with water.

[0037] For example, the washing may be performed using water at 40°C or above (eg, 40°C to 100°C) or 60°C or above (eg, 60°C to 100°C). In one embodiment, the washing may be performed using water at 60°C to 80°C.

[0038] By washing the nickel-containing raw material with high temperature water in the above temperature range, Ca and / or Mg can be partially removed from the nickel-containing raw material. As described above, by using high temperature water having a temperature of 40° C. or above or 60° C. or above, Mg components (e.g., MgSO 4 ) and Ca components (e.g., CaSO 4 ) can be washed and removed with sufficient solubility.

[0039] In some embodiments, the ratio of the weight of water used in the washing process to the weight of the nickel-containing raw material may be 2 to 5 or 2.5 to 5. Within the above ratio range, it is easy to prepare a slurry-state nickel-containing raw material for subsequent processes, and partial removal of Ca and Mg can be substantially achieved.

[0040] For example, in the S20 process, nickel can be leached from the nickel-containing raw material using an extraction selective oxidant that is selective for nickel.

[0041] According to an exemplary embodiment, the oxidant may include a metal persulfate. For example, the oxidant may include sodium persulfate (Na2S2O8). The oxidant may be supplied to the nickel-containing raw material together with a sulfuric acid solution, thereby selectively leaching nickel to obtain a first leachate.

[0042] In some embodiments, a residue in the form of a solid may be generated by the leaching process, for example. The residue may contain Co, Mn, Al, Fe, etc.

[0043] For example, the residue can be removed or separated by a first solid-liquid separation (e.g., S25 process) to generate the first leachate from which Co, Mn, Al, and Fe are at least partially removed. In some embodiments, the first solid-liquid separation can be performed by a filter press or centrifugal separation.

[0044] In some embodiments, the amount of the oxidant used in the Ni leaching process may be 1.5 wt % to 7 wt % relative to the weight of the nickel-containing raw material (e.g., washed nickel-containing raw material). For example, 1.5 g to 7 g of the oxidant may be used relative to 100 g of the nickel-containing raw material.

[0045] Within the above range, the leaching rate of Ni can be increased while the separation efficiency of Co, Mn, Al and Fe can be improved.

[0046] In one embodiment, the amount of the oxidant may be 2 wt % to 7 wt % or 4 wt % to 6 wt % relative to the weight of the nickel-containing raw material.

[0047] In some embodiments, the molar ratio of sulfuric acid (H2SO4) to the molar number of Ni contained in the nickel-containing raw material can be 0.5 to 1. Within the above range, the amount of Co, Mn, Al and Fe can be fully removed from the nickel-containing raw material. In one embodiment, the molar ratio of sulfuric acid to the molar number of Ni contained in the nickel-containing raw material can be 0.7 to 0.9 or 0.7 to 0.8.

[0048] In some embodiments, no other oxidant (eg, hydrogen peroxide) other than the metal persulfate may be used in the Ni leaching process, thereby increasing the selectivity of Ni.

[0049] In the Ni leaching process, the addition amount of sulfuric acid and the oxidant (metal persulfate) may be adjusted so that the pH of the first leachate is greater than 2, greater than 2.5, or greater than 3. In one embodiment, the addition amount of sulfuric acid and the oxidant may be adjusted so that the pH of the first leachate is greater than 4.

[0050] In the above pH range, the selective extraction of Ni can be promoted. In some embodiments, the pH of the first leachate can be adjusted to not more than 6. In one embodiment, the pH of the first leachate can be adjusted to not more than 5. For example, the pH of the first leachate can be 2 to 6, 3 to 6, 4 to 6, or 4 to 5.

[0051] Afterwards, the residual metals other than Ni contained in the first leaching solution may be further separated or removed.

[0052] For example, in the S30 process, Ca and / or Mg may be at least partially removed from the first leachate through a first precipitation process.

[0053] According to an exemplary embodiment, a first precipitant may be added to the first leachate to precipitate Ca and / or Mg. In some embodiments, the first precipitant may include a metal fluoride. For example, the metal fluoride may include an alkali metal fluoride (e.g., NaF).

[0054] Therefore, Ca and Mg can be precipitated in the form of calcium fluoride (CaF2) and magnesium fluoride (MgF2) from the first leachate. The precipitated calcium fluoride and magnesium fluoride can be separated or removed by a second solid-liquid separation (e.g., S35 process). The second solid-liquid separation can be performed by a filter press or centrifugal separation.

[0055] The second solid-liquid separation can be used to obtain a second leachate from which the amount of Ca and / or Mg is reduced or removed from the first leachate. For example, the first leachate from which Ca and / or Mg is partially removed by the washing process can be used to obtain a second leachate from which Ca and / or Mg is substantially removed.

[0056] According to an exemplary embodiment, the additional residual metals in the second leachate may be further subjected to a reduction / removal process. For example, a separation process of zinc (Zn) contained in the second leachate may be further subjected to.

[0057] In some embodiments, in the S40-1 process, Zn may be at least partially removed from the first leachate by a second precipitation process.

[0058] According to an exemplary embodiment, Zn can be precipitated by adding a second precipitant to the first leachate. In some embodiments, the second precipitant can include a metal sulfide and / or a non-metal sulfide. For example, the metal sulfide can include an alkali metal sulfide (e.g., Na2S), and the non-metal sulfide can include hydrogen sulfide (H2S).

[0059] Therefore, Zn can be precipitated in the form of zinc sulfide (ZnS) from the first leachate. The precipitated zinc sulfide can be separated or removed by the third solid-liquid separation (e.g., S45-1 process). The third solid-liquid separation can be performed by a filter press or centrifugal separation.

[0060] The third solid-liquid separation can be used to obtain a second leachate in which the amount of Zn is reduced or removed from the first leachate.

[0061] In some embodiments, in the S40-2 process, Zn may be at least partially removed from the first leachate by an extraction process.

[0062] According to an exemplary embodiment, Zn can be extracted by adding an extractant to the first leachate. In some embodiments, the extractant may include a phosphate-based extractant. For example, the phosphate-based extractant may include di-2-ethylhexyl phosphate (Di-2-ethylhexyl phosphoric acid), 2-ethylhexyl phosphoric acid mono-2-ethylhexyl ester (2-Ethylhexyl phosphoric acid mono-2-ethylhexyl ester).

[0063] Therefore, Zn can be extracted from the first leachate in the form of zinc sulfate (ZnSO4). The extracted zinc sulfate can be separated or removed by liquid-liquid separation (e.g., S45-2). The liquid-liquid separation can be performed by mixed sedimentation or centrifugal extraction.

[0064] Through the liquid-liquid separation, a second leachate in which the amount of Zn is reduced or removed can be obtained from the first leachate.

[0065] Thereafter, for example, in process S50, nickel sulfate hydrate may be obtained from the second leachate through a concentration and / or crystallization process.

[0066] For example, the water of the second leachate is partially evaporated to be concentrated and then cooled, so that the nickel sulfate in the second leachate can be crystallized and precipitated in the form of nickel sulfate hydrate (for example, NiSO4·6H2O). The precipitated nickel sulfate hydrate can be separated by the fourth solid-liquid separation while leaving Na. The fourth solid-liquid separation can be performed by a filter press or a centrifugal separator.

[0067] Crystallized nickel sulfate hydrate can be obtained from the second leachate through the fourth solid-liquid separation.

[0068] Figure 2 : is a schematic flow chart for explaining a method for preparing nickel sulfate according to a comparative example. Figure 2 The following comparative example is to illustrate in more detail Figure 1 The effects of the process concept are provided and are not intended to be excluded from the scope of the present invention. For example, Figure 2 The steps / processes included in may also be included in the exemplary embodiments of the present invention.

[0069] Reference Figure 2 , a raw material containing nickel (Ni) can be prepared.

[0070] The nickel-containing raw material may be leached with metal using sulfuric acid to obtain a leachate.

[0071] Sodium hydroxide (NaOH) is added to the leachate to precipitate Al and / or Fe. Thus, Al and Fe can be precipitated from the leachate in the form of aluminum hydroxide (Al(OH)3) and iron hydroxide (Fe(OH)3). The precipitated aluminum hydroxide and iron hydroxide can be separated or removed by solid-liquid separation, thereby obtaining a first solution in which the amount of Al and / or Fe is reduced or removed.

[0072] Alkali metal fluoride (e.g., NaF) is added to the first solution, so that Ca and / or Mg can be precipitated. Therefore, Ca and Mg can be precipitated in the form of calcium fluoride (CaF2) and magnesium fluoride (MgF2) from the first solution. The precipitated calcium fluoride and magnesium fluoride can be separated or removed by solid-liquid separation, so that a second solution in which the amount of Ca and / or Mg is reduced or removed can be obtained.

[0073] The second solution may be used to extract Zn, Mn and / or Ca using a phosphoric acid-based extractant. For saponification of the phosphoric acid-based extractant, an alkaline compound such as sodium hydroxide may be used together, and sulfuric acid may be used together, so that Zn, Mn and Ca may be extracted from the second solution in the form of zinc sulfate (ZnSO4), manganese sulfate (MnSO4) and calcium sulfate (CaSO4).

[0074] The extracted zinc sulfate, manganese sulfate and calcium sulfate are separated or removed by liquid-liquid separation, thereby obtaining a third solution in which the amount of Zn, Mn and / or Ca is reduced or removed.

[0075] The above-mentioned phosphoric acid-based extractant, sodium hydroxide and sulfuric acid are added to the third solution, so that Co can be extracted.

[0076] Therefore, Co can be extracted from the leaching solution in the form of cobalt sulfate (CoSO4). The extracted cobalt sulfate is separated or removed by liquid-liquid separation, thereby obtaining a fourth solution in which the amount of Co is reduced or removed.

[0077] Ni can be extracted by adding an acidic extractant, sodium hydroxide and sulfuric acid to the fourth solution. The acidic extractant may include a phosphoric acid-based extractant or a carboxylic acid-based extractant.

[0078] Therefore, Ni can be extracted from the leaching solution in the form of nickel sulfate (NiSO4). The extracted nickel sulfate is separated by liquid-liquid separation, thereby obtaining a nickel sulfate aqueous solution containing nickel sulfate.

[0079] By partially concentrating and crystallizing the nickel sulfate aqueous solution, nickel sulfate can be obtained in the form of nickel sulfate hydrate.

[0080] As described above, according to the comparative example, in order to prevent the reduction of pH, sodium hydroxide is used. Therefore, the sodium derived from the sodium hydroxide is concentrated. Therefore, the generation of unnecessary by-products (e.g., Na2SO4) is caused. In addition, for the continuous / sequential extraction of different metals, different types of acidic extractants are used, and multiple extraction processes for separating different metals such as Mn, Co, Ni, etc. are included.

[0081] However, according to the reference Figure 1In the illustrated exemplary embodiment, Co, Mn, etc. can be removed or separated as residues in the leaching process (e.g., S20 process). Therefore, for example, the sodium from sodium hydroxide is reduced, so that further Ni extraction processes can be deleted. In addition, the generation of unnecessary by-products (e.g., Na2SO4) can be reduced.

[0082] Below, specific experimental examples are proposed to help understand the present invention, but this is only used to illustrate the present invention and is not used to limit the scope of rights. Various changes and modifications can be made to the embodiments within the scope of the scope of the present invention and the technical idea, which is obvious to those skilled in the art, and such changes and modifications also fall within the scope of rights.

[0083] Example 1

[0084] 150 g of water at 80° C. was added to 50 g of Ni-MHP and washed for 4 hours, thereby obtaining a nickel-containing mixed hydroxide precipitate containing metals in the contents shown in Table 1 below.

[0085] 15 g of 2M sulfuric acid and 2.9 g of sodium persulfate (Na2S2O8) as an oxidant were added to the washed nickel-containing mixed hydroxide precipitate, and leached at 80°C for 6 hours to obtain a first leachate.

[0086] Example 2

[0087] The first leachate was obtained by the same process as in Example 1, except that the amount of the oxidant used was adjusted as shown in Table 2.

[0088] Example 3

[0089] The first leachate was obtained by the same process as in Example 1, except that the amount of sulfuric acid used was adjusted as shown in Table 2.

[0090] Example 4

[0091] The first leachate was obtained by the same process as in Example 1, except that the amount of sulfuric acid used was adjusted as shown in Table 2.

[0092] Example 5

[0093] The first leachate was obtained by the same process as in Example 1, except that the amount of sulfuric acid used was adjusted as shown in Table 2.

[0094] Example 6

[0095] The first leachate was obtained by the same process as in Example 1, except that the amount of sulfuric acid and the amount of oxidant used were adjusted as shown in Table 2.

[0096] Comparative Example 1

[0097] The first leachate was obtained by the same process as in Example 1, except that the amount of sulfuric acid used was adjusted as shown in Table 2, and no oxidant was added.

[0098] Comparative Example 2

[0099] The first leachate was obtained by the same process as in Example 1, except that the amount of sulfuric acid used was adjusted as shown in Table 2, no oxidant (sodium persulfate) was added, and 2.25 g of hydrogen peroxide (H2O2) was added.

[0100] [Table 1]

[0101]

[0102] [Table 2]

[0103]

[0104] Experimental Example 1

[0105] (1) Measurement of calcium and magnesium content after washing process

[0106] The results of confirming the contents of Ca and Mg in the liquid product after the washing process by inductively coupled plasma (ICP) analysis showed that the contents of Ca and Mg were 280 wtppm and 780 wtppm, respectively, which were 46 wt% for Ca and 23 wt% for Mg in the nickel-containing mixed hydroxide precipitate before the washing process.

[0107] (2) Measurement of impurity extraction rate in leachate

[0108] The weights of Co, Mn, Mg, Fe, Zn, Ca and Al of the nickel-containing mixed hydroxide precipitate and the weights of Co, Mn, Mg, Fe, Zn, Ca and Al of the first leachate were measured, and the metal weight of the first leachate relative to the metal weight of the nickel-containing mixed hydroxide precipitate was calculated in weight %.

[0109] (3) Measurement of metal concentration and pH in the first leachate

[0110] The concentrations of Co, Mn, Mg, Fe, Zn, Ca, Al and Na in the first leachate are calculated as % by weight of the metal in the first leachate relative to the weight of the first leachate.

[0111] In addition, the pH of the first leachate was measured.

[0112] The measurement results are recorded in Tables 3 and 4 below.

[0113] [Table 3]

[0114]

[0115] [Table 4]

[0116]

[0117] Referring to Tables 3 and 4, in the case of leaching a nickel-containing hydroxide precipitate, when an oxidant is used, a first leachate in which the leaching rate of each of Co, Mn, Fe and Al is reduced can be obtained. According to an embodiment, when the pH of the first leachate is adjusted to be greater than 3 and less than 5, the leaching rate of each of Co, Mn, Fe and Al in the first leachate is less than 3 wt %. Therefore, nickel can be selectively leached without an additional process for removing cobalt and manganese.

[0118] In Example 3 where the pH of the first leaching solution was less than 3, the leaching rate of Al was relatively increased.

[0119] In Example 4 in which the pH of the first leaching solution was 5 or more, the leaching rates of Ni and Zn were relatively reduced.

[0120] In Example 5 where the pH of the first leaching solution was less than 2, the leaching rates of Co, Fe, and Al were relatively increased.

[0121] In Example 6, in which the pH of the first leaching solution was less than 3 and the amount of the oxidant added was reduced, the leaching rates of Co, Mn, and Al were relatively increased.

[0122] In Comparative Example 1 in which the pH of the first leachate was less than 1 and no oxidant was added, the leaching rates of Co, Mn, Fe, and Al were all increased compared to the examples.

[0123] In Comparative Example 2 in which sodium persulfate was not added but hydrogen peroxide (H2O2) was added while the pH of the first leachate was less than 1, the leaching rates of Co, Mn, Fe and Al were all increased compared with those of the examples.

[0124] Experimental Example 2: Measurement of Ca and Mg concentrations and pH in the leachate

[0125] Example 7

[0126] 15 g of 2M sulfuric acid and 2.9 g of sodium persulfate (Na2S2O8) as an oxidant were added to 50 g of the unwashed nickel hydroxide precipitate (Ni-MHP), and leached at 80°C for 6 hours to obtain a first leachate.

[0127] The first leachate was precipitated using 1.15 g of sodium fluoride (NaF) as a precipitant for 4 hours to obtain a second leachate.

[0128] Example 8

[0129] The second leachate was obtained by the same process as in Example 7, except that 1.4 g of sodium fluoride was used.

[0130] The concentrations of Mg and Ca in the second leachates of Example 7 and Example 8 were calculated in ppm by weight. In addition, the pH in the leachate was measured.

[0131] The measurement results are recorded in Table 5 below.

[0132] [Table 5]

[0133]

[0134] Referring to Table 5, when sodium fluoride (NaF) is used to precipitate Ca and Mg in the first leachate for selectively leaching nickel-containing hydroxide precipitate, a second leachate is formed in which 90 wt % or more of Ca and Mg are removed compared with the first leachate.

Claims

1. A method for preparing nickel sulfate, comprising the following steps: preparing nickel-containing raw materials; selectively leaching nickel from the nickel-containing raw material using an oxidant to generate a first leachate; separating residual metals from the first leachate to produce a second leachate; and Nickel sulfate is obtained from the second leaching solution.

2. The method for preparing nickel sulfate according to claim 1, wherein: The nickel-containing raw material includes nickel (Ni)-mixed hydroxide precipitate (MHP).

3. The method for preparing nickel sulfate according to claim 2, wherein: The Ni-MHP also contains cobalt and manganese.

4. The method for preparing nickel sulfate according to claim 3, wherein: The step of generating the first leachate includes leaching only nickel from nickel, cobalt and manganese contained in the Ni-MHP.

5. The method for preparing nickel sulfate according to claim 1, wherein: The oxidizing agent comprises a metal persulfate.

6. The method for preparing nickel sulfate according to claim 1, wherein: The step of generating the first leachate is performed using an acidic solution containing the oxidant at a pH of 2 or higher.

7. The method for preparing nickel sulfate according to claim 1, wherein: The step of separating the residual metals to produce the second leachate includes precipitating at least one of calcium and magnesium using a fluoride precipitation agent.

8. The method for preparing nickel sulfate according to claim 7, wherein: The step of separating the residual metals to generate the second leachate further comprises precipitating zinc or extracting zinc.

9. The method for preparing nickel sulfate according to claim 8, wherein: The zinc precipitation is carried out using a sulfide precipitation agent.

10. The method for preparing nickel sulfate according to claim 8, wherein: The extraction of zinc is carried out using a phosphoric acid-based extractant.

11. The method for preparing nickel sulfate according to claim 1, wherein: The method further comprises the step of washing the nickel-containing raw material before the step of generating the first leachate.

12. The method for preparing nickel sulfate according to claim 11, wherein: The step of washing the nickel-containing raw material includes partially removing calcium or magnesium contained in the nickel-containing raw material.

13. The method for preparing nickel sulfate according to claim 11, wherein: The step of washing the nickel-containing raw material is performed by using water at 40° C. to 100° C.

14. The method for preparing nickel sulfate according to claim 1, wherein: The step of obtaining the nickel sulfate includes crystallization into nickel sulfate hydrate.

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