Purification method of impurity-containing nickel sulfate solution and preparation method of battery-grade nickel sulfate

Abstract

The invention discloses a purification method of an impurity-containing nickel sulfate solution and a preparation method of battery-grade nickel sulfate, and relates to the technical field of resource regeneration. The purification method comprises the following steps: adding sodium sulfide into a first part of impurity-containing nickel sulfate solution for reaction, and washing after solid-liquid separation to obtain nickel sulfide; adding nickel sulfide into the second part of the impurity-containing nickel sulfate solution to carry out an impurity removal reaction, and after the impurity removal reaction is finished, carrying out aging and solid-liquid separation to obtain impurity-removed slag and cobalt-removed solution; adding acid into the cobalt-removed liquid for high-temperature evaporative crystallization, and performing centrifugal separation to obtain evaporated crystals and evaporated mother liquor; and aging the evaporated crystal by using a saturated battery-grade nickel sulfate solution, and carrying out centrifugal separation to obtain an aged crystal and an aged mother solution. During high-temperature evaporation, silicon impurities entering the evaporation crystal are reduced by adding acid, then the crystal form of the evaporation crystal is improved by aging, the crystal form peak intensity of the obtained aged crystal is almost consistent with that of a standard sample, and the aged crystal can be used as a battery-grade nickel sulfate crystal.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of resource regeneration, in particular to a purification method of impurity-containing nickel sulfate solution and a preparation method of battery-grade nickel sulfate. BACKGROUND

[0002] Nickel resource is a non-renewable metal, mainly contained in minerals, which needs to be processed through mining, smelting and other steps to prepare nickel metal or nickel salt products. The current mainstream process for extracting nickel resources is to process nickel plate or nickel sulfate salt from laterite nickel ore by using fire or wet process, and then apply it to related industry fields.

[0003] With the development of new energy vehicles and energy storage power stations, the demand for lithium batteries has shown explosive growth, and ternary lithium batteries are one of the most important lithium batteries. The nickel content in ternary lithium batteries is the highest, which means the largest demand for nickel. Since nickel ore contains a high content of silicon element and other small amounts of impurity metals, although a series of smelting treatments can remove most of the silicon impurities, a small part of silicon and nickel will still be difficult to separate, and battery-grade nickel sulfate has a high requirement for impurity silicon, so the complete separation of nickel and silicon is still a challenge.

[0004] In view of this, the present application is proposed. SUMMARY

[0005] The purpose of the present application is to provide a purification method of impurity-containing nickel sulfate solution and a preparation method of battery-grade nickel sulfate.

[0006] The present application is implemented as follows: In a first aspect, the present application provides a purification method of impurity-containing nickel sulfate solution, comprising: S1, dividing the impurity-containing nickel sulfate solution into a first part and a second part; S2, adding the first part to sodium sulfide for reaction, and washing to obtain nickel sulfide after solid-liquid separation; S3, adding the nickel sulfide to the second part for impurity removal reaction, and obtaining impurity removal residue and cobalt-removed solution after first aging treatment and solid-liquid separation; S4, adding acid to the cobalt-removed solution for high-temperature evaporation crystallization, and centrifuging to obtain evaporation crystals and evaporation mother liquor; S5, using saturated battery-grade nickel sulfate solution for second aging treatment of the evaporation crystals, and obtaining battery-grade nickel sulfate crystals and aging mother liquor after centrifugation after the second aging treatment.

[0007] In an optional embodiment, the acid is added in an amount of 10-50 g / L, and the high-temperature evaporation crystallization is carried out at a temperature of 80-100℃; And / or, the content of silicon in the crystallization mother liquor is 0.3-0.5 g / L during the high-temperature evaporation crystallization.

[0008] In an alternative embodiment, the solid-liquid ratio of the evaporation crystals and the saturated battery-grade nickel sulfate solution is 1 g: 1-3 mL. And / or, the temperature of the second aging treatment is 30-60℃, and the time is 2-12 h.

[0009] In an alternative embodiment, the volume ratio of the first part and the second part is 1-10: 90-99.

[0010] In an alternative embodiment, the amount of added sodium sulfide is 1.0-1.5 times the theoretical reaction amount of nickel in the first part, the reaction temperature is 25-60℃, and the reaction time is 30-90 min.

[0011] In an alternative embodiment, the amount of added nickel sulfide is 2-2.5 times the theoretical reaction amount of cobalt in the second part. And / or, the reaction temperature of the impurity removal reaction is 70-90℃, and the reaction time is 1-3 h. And / or, the temperature of the first aging treatment is 80-100℃, and the aging time is 2-8 h.

[0012] In an alternative embodiment, the crystallization mother liquor is returned to the second aging treatment step for recycling, and when the content of silicon in the crystallization mother liquor exceeds 0.1 g / L, the crystallization mother liquor is returned to the high-temperature evaporation crystallization step for recycling.

[0013] In an alternative embodiment, part of the evaporation mother liquor is returned to the high-temperature evaporation crystallization step for recycling, and another part is discharged, and the recycling rate of the evaporation mother liquor is 50%-80%.

[0014] In an alternative embodiment, the impurity removal residue is returned to the impurity removal reaction for recycling until the content of nickel in the impurity removal residue is less than 2%, and then the impurity removal residue is discharged.

[0015] In a second aspect, the application provides a preparation method of battery-grade nickel sulfate, which uses the purification method of impure nickel sulfate solution according to any one of the preceding embodiments to prepare battery-grade nickel sulfate from impure nickel sulfate solution.

[0016] The application has the following beneficial effects: The purification method of the impure nickel sulfate solution provided by the application can effectively precipitate cobalt in the impure nickel sulfate solution, and the above operation realizes internal circulation of materials, does not need to introduce other precipitants, has lower cost, and has better precipitation effect and purification effect on the impure nickel sulfate solution. During the impurity removal, the reaction conditions can be controlled to convert alpha-CoS into beta-CoS which is more difficult to dissolve, so that cobalt is removed, the content of Co impurities in the solution is lower, and the cobalt-removed solution with higher purity is obtained. In addition, in the application, the cobalt-removed solution is evaporated and crystallized at high temperature after being added with acid. The addition of acid can improve the solubility of silicon in the cobalt-removed solution, and the high-temperature evaporation and crystallization can make more silicon impurities remain in the evaporation mother liquor, so that the silicon impurities are reduced in the evaporation crystals. The evaporation crystals obtained by high-temperature evaporation and crystallization have poor crystallinity compared with the crystal form of battery-grade nickel sulfate, which causes the crystals to easily agglomerate. The evaporation crystals are then subjected to a second aging treatment with saturated battery-grade nickel sulfate solution. The saturated battery-grade nickel sulfate solution can wash the silicon and acid on the surface of the evaporation crystals, and can also improve the crystal form of the evaporation crystals. After low-temperature aging, the aged crystals are obtained. The crystal form peak intensity of the aged crystals is almost the same as that of the standard sample, so the aged crystals can be used as battery-grade nickel sulfate crystal products. The purification method of the impure nickel sulfate solution provided by the application is simple, has low cost, has high comprehensive benefits, and can prepare battery-grade nickel sulfate crystals from the impure nickel sulfate solution. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some of the embodiments of the application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0018] Figure 1 The process flow chart of the purification method of the impure nickel sulfate solution provided by the application; Figure 2 The XRD characterization chart of the evaporation crystals prepared in Example 1, the aged crystals (i.e. battery-grade nickel sulfate crystals) prepared in Examples 1-3, and the spray-washed crystals of Comparative Example 7. DETAILED DESCRIPTION

[0019] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below. If the specific conditions are not specified in the embodiments, the conventional conditions or the conditions recommended by the manufacturers are adopted. If the manufacturers of the reagents or instruments are not specified, the conventional products that can be purchased in the market are adopted.

[0020] Referring to Figure 1 The present application provides a purification method of impure nickel sulfate solution, comprising: dividing the impure nickel sulfate solution into a first part and a second part; adding the first part to sodium sulfide for reaction, washing after solid-liquid separation to obtain nickel sulfide; adding the nickel sulfide to the second part for impurity removal reaction, after the impurity removal reaction, performing first aging treatment, and performing solid-liquid separation to obtain impurity removal residue and cobalt-removed solution; adding acid to the cobalt-removed solution for high-temperature evaporation crystallization, and performing centrifugal separation to obtain evaporation crystals and evaporation mother liquor; and performing second aging treatment on the evaporation crystals with saturated battery-grade nickel sulfate solution, and performing centrifugal separation after the second aging treatment to obtain battery-grade nickel sulfate crystals and aging mother liquor.

[0021] In the present application, sodium sulfide is reacted with the first part of the impure nickel sulfate solution to generate nickel sulfide, and the nickel sulfide is directly returned and added to the second part of the impure nickel sulfate solution for impurity removal reaction, and aging is performed after impurity removal, which can effectively reduce the cobalt in the impure nickel sulfate solution. Cobalt is fully precipitated during the aging process, thereby ensuring that the cobalt content in the nickel sulfide crystals is significantly reduced. Subsequently, acid is added for high-temperature evaporation crystallization. The addition of acid can increase the solubility of silicon in the solution, so that more silicon impurities remain in the evaporation mother liquor, thereby reducing the entry of silicon impurities into the evaporation crystals. The nickel sulfate crystals evaporated at high temperature have poor crystallinity compared to the crystal form of battery-grade nickel sulfate, which causes the crystals to easily clump. The evaporation crystals can be washed to remove the silicon and acid on the surface of the evaporation crystals during low-temperature aging, and the crystal form of the nickel sulfate crystals can also be improved, so that the aging crystals are obtained after low-temperature aging. The crystal form peak intensity of the aging crystals is almost the same as that of the standard sample, so the aging crystals can be used as battery-grade nickel sulfate crystal products. Specifically, the specific operations of each step are as follows: S1, dividing the impure nickel sulfate solution into a first part and a second part.

[0022] The impure nickel sulfate solution refers to a nickel sulfate solution containing impurity elements such as Co, Mn, Si, Na, Ca, Mg, Cu, Fe, and Zn. The impure nickel sulfate solution is processed by branch paths, and the volume ratio of the first part to the second part is adjusted to 1-10:90-99, so that the reaction amount in the subsequent steps S2 and S3 can be adjusted. Specifically, the amount of nickel sulfide required in step S3 can be used to determine the amount of nickel sulfide required in step S2, and the volume ratio of the first part to the second part in the present application is adjusted.

[0023] S2. Add sodium sulfide to the first part to react, and wash after solid-liquid separation to obtain nickel sulfide.

[0024] The amount of sodium sulfide added is 1.0 to 1.5 times the theoretical reaction amount of nickel in the first part, the reaction temperature is 25 to 60°C, and the reaction time is 30 to 90 minutes. The impure nickel sulfate solution reacts with sodium sulfide to form nickel sulfide. After solid-liquid separation, washing with pure water reduces impurities on the surface of the nickel sulfide, facilitating subsequent reactions and avoiding the introduction of impurities. In this invention, nickel sulfide is prepared directly using the impure nickel sulfate solution requiring purification, and the prepared nickel sulfide possesses the crystal form and specific Ksp required by this application, which is beneficial to ensuring the smooth progress of the impurity removal reaction in the subsequent step S3.

[0025] S3. Add nickel sulfide to the second part for impurity removal reaction. After the impurity removal reaction is completed, perform the first aging treatment and separate the solid and liquid to obtain impurity removal residue and cobalt removal liquid.

[0026] Nickel sulfide can react with cobalt impurities in nickel sulfate solutions because the Ksp values ​​of α-NiS, α-CoS, and β-CoS are 3.2 × 10⁻⁶. -19 4×10 -21 2×10 -25 Therefore, nickel sulfide can convert cobalt in the solution into a less soluble precipitate, thereby removing cobalt and resulting in a lower Co impurity content in the solution, yielding a cobalt-removed solution with higher purity. The amount of nickel sulfide added is 2 to 2.5 times the theoretical amount of cobalt reacted in the second part. The reaction temperature for the impurity removal reaction is 70–90°C, and the reaction time is 1–3 hours. In this invention, by directly preparing and utilizing the α-NiS (nascent nickel sulfide, amorphous or microcrystalline), NiS can be formed in the early stages of the reaction, exhibiting the strongest dissolving power (Ksp≈3.2×10⁻⁶). -19 .

[0027] The first aging treatment is carried out at a temperature of 80–100℃ for 2–8 hours. The purpose of aging is to convert α-CoS to β-CoS, because β-CoS has a smaller Ksp, which makes the precipitation of Co impurities in the solution more complete and the Co impurity content lower.

[0028] The slag is returned to the impurity removal reaction for recycling until the nickel content in the slag is less than 2%, at which point it is discharged for treatment.

[0029] S4. Add acid to the cobalt-removed liquid and evaporate it at high temperature to crystallize it. Separate the evaporated crystals and the mother liquor by centrifugation.

[0030] Adding acid (e.g., sulfuric acid) to the cobalt-removed solution at a concentration of 10–50 g / L increases the solubility of silicon in the solution. This is followed by high-temperature evaporation and crystallization at 80–100°C. This high-temperature evaporation and crystallization allows more silicon impurities to remain in the mother liquor, thus reducing the amount of silicon impurities entering the crystals. During the high-temperature evaporation and crystallization process, centrifugation is performed when the silicon content in the mother liquor reaches 0.3–0.5 g / L.

[0031] A portion of the mother liquor is returned to the high-temperature evaporation and crystallization step for recycling, while the other portion is discharged. The recycling rate of the mother liquor is 50% to 80%.

[0032] S5. The evaporated crystals are subjected to a second aging treatment with saturated battery-grade nickel sulfate solution. After the second aging treatment, they are separated by centrifugation to obtain battery-grade nickel sulfate crystals and aging mother liquor.

[0033] The solid-liquid ratio of the evaporated crystals to the saturated battery-grade nickel sulfate solution was 1 g: 1–3 mL; the second aging treatment was carried out at a temperature of 30–60 °C for 2–12 h. Low-temperature aging of the evaporated crystals after high-temperature evaporation washes away the silicon and acid inclusions on the surface of the crystals and improves the crystal structure, resulting in aged crystals with lower impurity content and peak intensities almost identical to the standard sample. These aged crystals can be used as battery-grade nickel sulfate crystals.

[0034] The mother liquor from the aging process is returned to the second aging process for recycling. When the silicon content in the mother liquor exceeds 0.1 g / L, it is returned to the high-temperature evaporation and crystallization process for recycling.

[0035] In addition, the present invention provides a method for preparing battery-grade nickel sulfate, which uses the above-mentioned purification method for impure nickel sulfate solution to prepare battery-grade nickel sulfate from impure nickel sulfate solution.

[0036] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0037] Example 1 This embodiment provides a method for purifying nickel sulfate solution containing impurities, including the following specific steps: (1) Please refer to Table 1 for the composition content of the impure nickel sulfate solution in this embodiment. The impure nickel sulfate solution is divided into a first part and a second part according to a volume ratio of 5:95.

[0038] (2) Add sodium sulfide, which is 1.0 times the theoretical amount of nickel, to the first part of the nickel sulfate solution containing impurities and react at 25°C for 90 min. After the reaction is complete, separate the solid and liquid to obtain crude nickel sulfide. Wash the crude nickel sulfide with pure water to obtain washed nickel sulfide.

[0039] (3) The nickel sulfide obtained in step (2) is added to the second part of the impurity-containing nickel sulfate solution for impurity removal reaction. The amount of nickel sulfide added is 2.0 times the theoretical amount of cobalt reaction. The reaction is carried out at 70°C for 3 hours. After the reaction is completed, the first aging treatment is carried out at 80°C for 8 hours. After solid-liquid separation, impurity-removed slag and cobalt-removed liquid are obtained. The impurity-removed slag is returned to the impurity removal reaction for recycling. After the nickel content in the slag is less than 2%, it is discharged for treatment.

[0040] (4) Add 30 g / L of sulfuric acid to the impurity removal solution from step (3), and evaporate and crystallize it using a rotary evaporator at a temperature of 95°C. When the silicon content in the crystallization mother liquor reaches 0.3 g / L or more, centrifuge to separate the crystals and the mother liquor. Part of the mother liquor is returned to the high-temperature evaporation and crystallization step for recycling, and the other part is discharged. The recycling rate of the mother liquor is 80%.

[0041] (5) The evaporated crystals obtained in step (4) are subjected to a second aging treatment using saturated battery-grade nickel sulfate solution. The solid-liquid ratio of nickel sulfate crystals to saturated battery-grade nickel sulfate solution is 1 g: 1.5 mL. The second aging treatment lasts for 5 hours and is carried out at a temperature of 45°C. After the second aging treatment, the crystals are separated by centrifugation to obtain aged crystals as battery-grade nickel sulfate crystals and aging mother liquor. The aging mother liquor is returned to the second aging treatment step in step S5 for recycling. When the silicon content in the aging mother liquor exceeds 0.1 g / L, it is returned to the high-temperature evaporation crystallization step in step S4 for recycling.

[0042] Example 2 (1) Please refer to Table 1 for the composition content of the impure nickel sulfate solution in this embodiment. The impure nickel sulfate solution is divided into the first part and the second part according to the volume ratio of 2:98.

[0043] (2) Add the first part of the nickel sulfate solution containing impurities to sodium sulfide with a theoretical amount of 1.2 times that of nickel and react at 40°C for 60 min. After the reaction is complete, separate the solid and liquid to obtain nickel sulfide. Wash the nickel sulfide with pure water to obtain washed nickel sulfide.

[0044] (3) The nickel sulfide obtained in step (2) is added to the second part of the impurity-containing nickel sulfate solution for impurity removal reaction. The amount of nickel sulfide added is 2.5 times the theoretical amount of cobalt reaction. The reaction is carried out at 80°C for 2 hours. After the reaction is completed, the first aging treatment is carried out at 85°C for 5 hours. After solid-liquid separation, impurity-removed slag and cobalt-removed liquid are obtained. The impurity-removed slag is recycled until the nickel content in the slag is less than 2% before being discharged for treatment.

[0045] (4) Add 10 g / L of sulfuric acid to the impurity removal solution from step (3), and evaporate and crystallize it using a rotary evaporator at a temperature of 95°C. When the silicon content in the crystallization mother liquor reaches 0.3 g / L or more, centrifuge to separate the evaporated crystals and the evaporation mother liquor.

[0046] (5) The crystals obtained from the high-temperature evaporation in step (4) are subjected to a second aging treatment using saturated battery-grade nickel sulfate solution. The solid-liquid ratio of the crystals to the saturated battery-grade nickel sulfate solution is 1 g: 2 mL. The second aging treatment lasts for 3 hours and is carried out at a temperature of 60°C. After the second aging treatment, the crystals are separated by centrifugation to obtain the aged crystals as battery-grade nickel sulfate crystals and the aging mother liquor. The aging mother liquor is recycled. When the impurity silicon is enriched to 0.1 g / L, it is sent to the high-temperature evaporation crystallization process for further processing.

[0047] Example 3 (1) Please refer to Table 1 for the content of impure nickel sulfate solution in this embodiment. The impure nickel sulfate solution is divided into a first part and a second part according to a volume ratio of 10:90.

[0048] (2) Add a portion of the nickel sulfate solution containing impurities to sodium sulfide with a theoretical amount of 1.5 times that reacts with nickel and react at 60°C for 30 min. After the reaction is complete, separate the solid and liquid to obtain nickel sulfide. Wash the nickel sulfide with pure water to obtain washed nickel sulfide.

[0049] (3) The nickel sulfide obtained in step (2) is added to the nickel sulfate solution containing impurities for impurity removal reaction. The amount of nickel sulfide added is 2.5 times the theoretical amount for cobalt reaction. The reaction is carried out at 90°C for 1 hour. After the reaction is completed, the first aging treatment is carried out at 90°C for 3 hours. After solid-liquid separation, impurity-removed slag and cobalt-removed liquid are obtained. The impurity-removed slag is recycled until the nickel content in the slag is less than 2% before being discharged for treatment.

[0050] (4) Add 50 g / L of sulfuric acid to the impurity removal solution from step (3), and evaporate and crystallize it using a rotary evaporator at a temperature of 80°C. When the silicon content in the crystallization mother liquor reaches 0.3 g / L or more, centrifuge to separate the evaporated crystals and the evaporation mother liquor.

[0051] (5) The crystals obtained from the high-temperature evaporation in step (4) are subjected to a second aging treatment using saturated battery-grade nickel sulfate solution. The solid-liquid ratio of the crystals to the saturated battery-grade nickel sulfate solution is 1 g: 3 mL. The second aging treatment lasts for 5 hours and is carried out at a temperature of 45°C. After the second aging treatment, the crystals are separated by centrifugation to obtain aged crystals as battery-grade nickel sulfate crystals and aging mother liquor. The aging mother liquor is recycled. When the impurity silicon is enriched to 0.1 g / L, it is sent to the high-temperature evaporation crystallization process for further processing.

[0052] Comparative Example 1 This comparative example is basically the same as Example 1, except that the cobalt removal step of adding nickel sulfide is not included in this comparative example. Specifically, it includes the following steps: (1) Add 30 g / L of sulfuric acid to the nickel sulfate solution containing impurities, and evaporate and crystallize it using a rotary evaporator at 95°C. When the silicon content in the mother liquor reaches 0.3 g / L or more, centrifuge to separate the crystals and the mother liquor. Part of the mother liquor is returned to the high-temperature evaporation and crystallization step for recycling, and the other part is discharged. The recycling rate of the mother liquor is 80%.

[0053] (2) The evaporated crystals obtained in step (1) are aged in saturated battery-grade nickel sulfate solution with a solid-liquid ratio of 1g:1.5mL. The aging time is 5h and the aging temperature is 45℃. After aging, the crystals are separated by centrifugation to obtain aged crystals and aging mother liquor. The aging mother liquor is returned to the second aging process for recycling. When the silicon content in the aging mother liquor exceeds 0.1g / L, it is returned to the high-temperature evaporation crystallization process for recycling.

[0054] Comparative Example 2 This comparative example is basically the same as Example 1, except that the first aging treatment is not performed in step (3) of this comparative example. Specifically, it includes the following steps: (1) Same as Example 1.

[0055] (2) Same as in Example 1.

[0056] (3) Add the nickel sulfide obtained in step (2) to the second part of the impurity-containing nickel sulfate solution for impurity removal reaction. The amount of nickel sulfide added is 2.0 times the theoretical amount of cobalt reaction. The reaction is carried out at 70°C for 3 hours. After the reaction is completed, the first aging treatment is not carried out. The solid and liquid are directly separated to obtain the impurity-removed residue and the cobalt-removed liquid.

[0057] (4) Same as in Example 1.

[0058] (5) Same as in Example 1.

[0059] Comparative Example 3 This comparative example is basically the same as Example 1, except that sulfuric acid is not added in step (4) of this comparative example. Specifically, it includes the following steps: (1) Same as Example 1.

[0060] (2) Same as in Example 1.

[0061] (3) Same as in Example 1.

[0062] (4) The impurity removal liquid from step (3) is evaporated and crystallized at 95°C using a rotary evaporator. When the crystallization rate is controlled to be the same as that in step (4) of Example 1, centrifugation is performed to obtain evaporated crystals and evaporated mother liquor.

[0063] (5) Same as in Example 1.

[0064] Comparative Example 4 This comparative example is basically the same as Example 1, except that in this comparative example, after high-temperature evaporation and crystallization in step (4), it is not centrifuged, but then aged at low temperature of 45°C for 5 hours, and then centrifuged to obtain nickel sulfate crystals. Specifically, it includes the following steps: (1) Same as Example 1.

[0065] (2) Same as in Example 1.

[0066] (3) Same as in Example 1.

[0067] (4) Add 30 g / L of sulfuric acid to the impurity removal solution from step (3), and evaporate and crystallize it at 95°C using a rotary evaporator. When the silicon content in the crystallization mother liquor reaches 0.3 g / L or more, it is aged at 45°C for 5 hours.

[0068] Comparative Example 5 This comparative example is basically the same as Example 1, except that the evaporation and crystallization parameters are changed. Specifically, it includes the following steps: (1) Same as Example 1.

[0069] (2) Same as in Example 1.

[0070] (3) Same as in Example 1.

[0071] (4) Add 30 g / L of sulfuric acid to the impurity removal solution from step (3), and evaporate and crystallize it using a rotary evaporator at a temperature of 60°C. When the crystallization rate is controlled to be the same as that in Example 1, centrifuge separation is performed to obtain evaporated crystals and mother liquor.

[0072] (5) Same as in Example 1.

[0073] Comparative Example 6 This comparative example is basically the same as Example 1, except that steps (1) and (2) of Example 1 are omitted in this comparative example. Commercially available nickel sulfide is directly used to remove impurities from the nickel sulfate solution containing impurities. The specific operation is as follows: (1) Nickel sulfide (purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., Ksp is 1.0×10) -24The impurity removal reaction was carried out by adding nickel sulfate solution containing impurities. The amount of nickel sulfide added was 2.0 times the theoretical amount for the cobalt reaction. The reaction was carried out at 70℃ for 3 hours. After the reaction was completed, a first aging treatment was carried out at 80℃ for 8 hours. After solid-liquid separation, impurity-removed slag and cobalt-removed liquid were obtained. The impurity-removed slag was returned to the impurity removal reaction for recycling until the nickel content in the slag was less than 2%, after which it was discharged for disposal.

[0074] (2)-(3): Same as (4)-(5) of Example 1.

[0075] Comparative Example 7 This comparative example is basically the same as Example 1, except that step (5) of this comparative example is different, and the second aging step is omitted.

[0076] Specifically, the evaporated crystals obtained in step (4) are sprayed and washed with saturated battery-grade nickel sulfate solution, and the solid-liquid mixture after washing is centrifuged to obtain the sprayed and washed crystals and the washed liquid.

[0077] Experimental Example In this experimental example, the composition of the products (raw material impure nickel sulfate solution, cobalt-removed solution, evaporation mother liquor, evaporation crystals, and aged crystals, wherein the aged crystals are the final product battery-grade nickel sulfate crystals) from each step of Examples 1-3 and Comparative Examples 1-7 was determined by ICP. The test results are shown in Tables 1-5. Table 1. Composition content of nickel sulfate solution containing impurities / g·L -1

[0078] Table 2. Composition of the liquid after cobalt removal / g·L -1

[0079] Table 3. Composition of Evaporated Mother Liquor / g·L -1

[0080] Table 4. Evaporated crystal composition content / %

[0081] Table 5. Composition content of aged crystals (i.e., battery-grade nickel sulfate crystals) / %

[0082] As can be seen from Tables 1-5 above, compared with battery-grade indicators, the aged crystals prepared in Examples 1-3 all meet battery-grade standards and can be used as battery-grade nickel sulfate crystals. Compared with Example 1, Comparative Example 1, due to the absence of nickel sulfide for cobalt removal, resulted in a cobalt content of 25 ppm in the aged crystals after the second aging treatment, significantly higher than the cobalt content in the aged crystals of Example 1. Although Comparative Example 2 added nickel sulfide for cobalt removal, the lack of a first aging treatment during cobalt removal led to incomplete cobalt precipitation in the liquid after removal, resulting in a cobalt content of 16 ppm in the aged crystals obtained after the second aging treatment. In Comparative Example 3, due to the absence of sulfuric acid during high-temperature evaporation crystallization, the silicon content in the mother liquor only increased to 0.18 g / L, while the silicon content in the high-temperature crystals reached as high as 256 ppm, indicating that a large amount of silicon entered the evaporated crystals. In contrast, in Example 1, due to the addition of sulfuric acid during high-temperature evaporation crystallization, the silicon content in the mother liquor increased to 0.45 g / L, while the silicon content in the high-temperature crystals was only 76 ppm, with most of the silicon remaining in the mother liquor. Comparative Example 4 used a traditional high-temperature evaporation and cooling crystallization method. Due to the lack of centrifugal separation, a large amount of silicon from the mother liquor entered the aged crystals, resulting in a silicon content as high as 123 ppm. In Comparative Example 5, the high-temperature evaporation temperature was only 60°C, leading to a silicon concentration in the mother liquor of only 0.28 g / L, while the silicon content in the high-temperature crystals reached 135 ppm. After the second aging treatment, the silicon content was still 26 ppm, far exceeding the silicon content in the aged crystals of Example 1. This is because the lower temperature reduces the solubility of silicon, resulting in a relatively low silicon concentration in the mother liquor and a greater amount of silicon impurities mixed in with the aged crystals. In Comparative Example 6, the purchased nickel sulfide had a low ksp, resulting in poor cobalt removal; after cobalt removal, 0.112 g / L of cobalt remained in the liquid. In Comparative Example 7, the high-temperature crystals were washed by spraying. The impurity content in the spray-washed crystals was higher than that in the aged crystals after the second aging in Example 1.

[0083] In addition, please see Figure 2 The characterization results show that the evaporated crystals obtained from high-temperature evaporation in Example 1 have poorer crystallinity compared to the battery-grade nickel sulfate standard. The crystal form peak intensity of the aged crystals (i.e., the final product, battery-grade nickel sulfate crystals) obtained after the second aging treatment is almost identical to that of the standard. The crystal form peak intensities of the aged crystals in Examples 2 and 3 are also almost identical to those of the standard. However, the high-temperature crystals in Comparative Example 7, after being spray-washed, have a higher impurity content than the aged crystals in Example 1, and the crystallinity is significantly worse after spray-washing.

[0084] In summary, the purification method for impure nickel sulfate solution provided by this invention involves reacting the impure nickel sulfate solution to be purified with sodium sulfide to prepare nickel sulfide, and then directly using the prepared nickel sulfide as a precipitant to precipitate cobalt from the impure nickel sulfate solution. This method effectively precipitates cobalt from the impure nickel sulfate solution. Furthermore, the above operation achieves internal material circulation, eliminating the need to introduce other precipitants, resulting in lower costs and better precipitation and purification effects on the impure nickel sulfate solution. During impurity removal, by adjusting the reaction conditions, α-CoS can be converted into the less soluble β-CoS, thereby removing cobalt and resulting in a lower Co impurity content in the solution, yielding a cobalt-removed solution with higher purity. In addition, this invention involves adding acid to the cobalt-removed solution followed by high-temperature evaporation and crystallization. Adding acid increases the solubility of silicon in the cobalt-removed solution, and high-temperature evaporation and crystallization allows more silicon impurities to remain in the evaporation mother liquor, thereby reducing the amount of silicon impurities entering the evaporated crystals obtained from high-temperature evaporation. Because the crystallinity of evaporated crystals obtained from high-temperature evaporation is inferior to that of battery-grade nickel sulfate, the crystals are prone to agglomeration. Therefore, this invention subsequently performs a second aging treatment on the evaporated crystals using a saturated battery-grade nickel sulfate solution. This saturated solution can wash away silicon and acid inclusions on the surface of the evaporated crystals and improve their crystal structure. The resulting aged crystals after the second aging treatment have peak intensities almost identical to the standard sample. Therefore, the aged crystals can be used as battery-grade nickel sulfate crystal products. The purification method for impure nickel sulfate solutions provided by this invention is simple, low-cost, and yields high overall benefits, enabling the preparation of battery-grade nickel sulfate crystals from impure nickel sulfate solutions.

[0085] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for purifying nickel sulfate solution containing impurities, characterized in that, include: S1. Divide the nickel sulfate solution containing impurities into a first part and a second part; S2. Add sodium sulfide to the first part to react, and wash after solid-liquid separation to obtain nickel sulfide. S3. The nickel sulfide is added to the second part to carry out a purification reaction. After the purification reaction is completed, a first aging treatment is performed, and solid-liquid separation is carried out to obtain the purification residue and the cobalt-removed liquid. S4. Add acid to the cobalt-removed liquid and evaporate and crystallize it at high temperature. Separate the evaporated crystals and the mother liquor by centrifugation. S5. The evaporated crystals are subjected to a second aging treatment with saturated battery-grade nickel sulfate solution. After the second aging treatment is completed, the crystals are separated by centrifugation to obtain battery-grade nickel sulfate crystals and aging mother liquor.

2. The purification method for nickel sulfate solution containing impurities according to claim 1, characterized in that, The amount of acid added is 10-50 g / L, and the temperature of the high-temperature evaporation crystallization is 80-100℃; And / or, during the high-temperature evaporation crystallization process, the silicon content in the crystallization mother liquor is 0.3 to 0.5 g / L, and centrifugation is performed.

3. The purification method for nickel sulfate solution containing impurities according to claim 1, characterized in that, The solid-liquid ratio of the evaporated crystals to the saturated battery-grade nickel sulfate solution is 1g:1-3mL; And / or, the temperature of the second aging treatment is 30-60°C, and the time is 2-12 hours.

4. The purification method for nickel sulfate solution containing impurities according to claim 1, characterized in that, The volume ratio of the first part to the second part is 1-10:90-99.

5. The purification method for nickel sulfate solution containing impurities according to claim 1, characterized in that, The amount of sodium sulfide added is 1.0 to 1.5 times the theoretical amount of nickel reacted in the first part, the reaction temperature is 25 to 60°C, and the reaction time is 30 to 90 min.

6. The purification method for nickel sulfate solution containing impurities according to claim 1, characterized in that, The amount of nickel sulfide added is 2 to 2.5 times the theoretical amount of cobalt reacted in the second part; And / or, the reaction temperature of the impurity removal reaction is 70–90°C, and the reaction time is 1–3 h; And / or, the temperature of the first aging treatment is 80-100℃, and the aging time is 2-8h.

7. The purification method for nickel sulfate solution containing impurities according to any one of claims 1 to 6, characterized in that, The aging mother liquor is returned to the second aging treatment step for recycling. When the silicon content in the aging mother liquor exceeds 0.1 g / L, it is returned to the high-temperature evaporation and crystallization step for recycling.

8. The purification method for nickel sulfate solution containing impurities according to any one of claims 1 to 6, characterized in that, A portion of the mother liquor is returned to the high-temperature evaporation and crystallization step for recycling, while the other portion is discharged. The recycling rate of the mother liquor is 50% to 80%.

9. The purification method for nickel sulfate solution containing impurities according to any one of claims 1 to 6, characterized in that, The impurity removal residue is returned to the impurity removal reaction for recycling until the nickel content in the residue is less than 2%, at which point it is discharged for treatment.

10. A method for preparing battery-grade nickel sulfate, characterized in that, It uses the purification method of impure nickel sulfate solution as described in any one of claims 1 to 9 to prepare battery-grade nickel sulfate from impure nickel sulfate solution.

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