Process for separating and removing impurities from a nickel sulfate solution

Abstract

This invention discloses a process for separating and removing impurities from a nickel sulfate solution. The process steps are as follows: 1) The extractant solution is mixed with cyclohexenoic acid and dithiophosphonic acid, and then reacted with liquid alkali for saponification to obtain a post-saponification organic phase; 2) The crude nickel sulfate solution and the post-saponification organic phase are subjected to a single-stage multi-stage countercurrent total extraction to obtain a raffinate aqueous phase and a fully extracted loaded organic phase; 3) The fully extracted loaded organic phase and the crude nickel sulfate solution are subjected to a two-stage multi-stage countercurrent extraction to remove impurities, resulting in a purified nickel sulfate solution and an organic phase loaded with impurities. This invention effectively reduces the oxidative degradation of the extractant during use by adding cyclohexenoic acid and dithiophosphonic acid as auxiliaries, thereby reducing the TOC and small molecule acid content in the raffinate / back-extraction solution from the source, lowering subsequent processing costs, and simultaneously improving the separation coefficient between impurity metals and nickel. This achieves the effect of efficiently separating impurity metals even when the extractant is already loaded with the target metal.

Description

Technical Field

[0001] This invention relates to a separation and impurity removal process, and more particularly to a nickel sulfate solution separation and impurity removal process, belonging to the field of hydrometallurgical technology. Background Technology

[0002] Nickel sulfate is a primary product resulting from the smelting and processing of nickel ore. Its main impurities include cobalt, iron, copper, zinc, calcium, magnesium, and manganese. After extraction to remove impurities, the purified nickel sulfate solution yields a crucial raw material for the production of ternary lithium-ion batteries, nickel plating, and nickel-metal hydride batteries. In recent years, benefiting from the rapid development of the new energy vehicle sector, the demand for nickel sulfate has surged. Intense competition among companies has led to a situation where reducing production costs while enhancing product competitiveness is the goal pursued by every nickel salt producer.

[0003] The traditional method for producing nickel sulfate in the hydrometallurgical industry involves removing impurities from the nickel sulfate solution using P204, extracting cobalt using P507, removing magnesium using C272, followed by nickel enrichment through P204 / P507 extraction, and then back-extraction to prepare a nickel sulfate solution with acceptable impurity levels. However, this method suffers from high consumption of liquid alkali and sulfuric acid, resulting in high production costs. Currently, the nickel sulfate production process uses sodium hydroxide to saponify the P204 extractant into nickel soap, followed by extraction to remove impurities and prepare high-purity nickel sulfate, thus reducing the sodium content. However, given the high purity requirements of electronic-grade products in the ternary lithium-ion battery industry, further reducing the overall content of other metallic impurities remains a problem that the industry is committed to solving.

[0004] Furthermore, during the research process, the inventors discovered that after the feed solution is extracted with an extractant or back-extracted with an acid, the raffinate or back-extract usually contains a high content of TOC. Moreover, elements such as zinc and iron in the feed solution can cause the extractant to oxidize and degrade during the back-extraction regeneration process, producing small molecule acids such as formic acid and acetic acid, which poses difficulties for the post-processing of the raffinate / back-extract. Therefore, solving the problem of extractant degradation and reducing the TOC content in the raffinate and back-extract from the source is also of great significance. Summary of the Invention

[0005] To address the above technical problems, this invention proposes a process for separating and removing impurities from nickel sulfate solution.

[0006] A process for separating and removing impurities from a nickel sulfate solution includes the following steps:

[0007] 1) The extractant solution is mixed with cyclohexenoic acid and dithiophosphonic acid, and then reacted with liquid alkali to saponify, yielding the saponified organic phase;

[0008] 2) The crude nickel sulfate solution was subjected to a multi-stage countercurrent total extraction with the post-soap organic phase to obtain the raffinate aqueous phase and the total extracted loaded organic phase;

[0009] 3) The whole-extracted loaded organic phase and crude nickel sulfate solution are subjected to two-stage multi-stage countercurrent extraction to remove impurities, resulting in purified nickel sulfate solution and organic phase loaded with impurities.

[0010] As a preferred embodiment of the process of the present invention, it further includes step 4), which involves back-extracting and regenerating the organic phase loaded with impurities to obtain an impurity metal solution and a blank organic phase; the blank organic phase is mainly an extractant solution, and also includes unconsumed cycloenoic acid and dithiophosphonic acid, which can be recycled to step 1) to continue the saponification reaction, and the impurity metal solution can be sent to a subsequent impurity treatment system for further separation.

[0011] Preferably, the back-extraction regeneration is performed using inorganic acids, with hydrochloric acid or sulfuric acid having a hydrogen ion concentration of 4-6 mol / L being the preferred inorganic acid.

[0012] Preferably, the back-extraction regeneration ratio O:A = (5-20):1. In this invention, O:A represents the ratio of the volume of the organic phase to the volume of the aqueous phase.

[0013] As a preferred embodiment of the process of the present invention, in step 1), the total amount of cyclohexenoic acid and dithiophosphonic acid added is 0.05-0.1 times the volume of the extractant solution, based on the volume ratio.

[0014] Preferably, the volume ratio of the cyclohexenoic acid to the dithiophosphonic acid is (0.02-0.2):1.

[0015] As a preferred embodiment of the process of the present invention, the cyclohexene acid is 3-cyclohexene-1-carboxylic acid and / or (R)-3-cyclohexenecarboxylic acid;

[0016] Preferably, the dithiophosphonic acid is selected from one or more of dibutyldithiophosphonic acid, diisooctyldithiophosphonic acid, and diisobutyldithiophosphonic acid. The dithiophosphonic acid can be purchased directly from commercially available finished products, or it can be obtained by separating the aqueous phase from its inorganic salts after acid washing, or by mixing its inorganic salts with the extractant solution to form the oil phase, then separating the aqueous phase after acid washing and directly applying it to step 1) to obtain an extractant solution containing dithiophosphonic acid.

[0017] Through continuous research, the inventors have discovered that dithiophosphonic acid can improve the distribution ratio of impurity metals and nickel, thereby promoting metal separation and improving separation accuracy. However, it also causes a certain degree of phase miscibility, resulting in a longer phase separation time. The introduction of cycloenoic acid containing active double bonds can eliminate this problem and significantly reduce the amount of small molecule organic acids and TOC generated by the decomposition of the extractant. This has a synergistic effect on improving the separation effect of metallic nickel, while reducing the subsequent treatment cost of wastewater.

[0018] As a preferred embodiment of the process of the present invention, in step 1), the extractant solution is a mixture of extractant and solvent oil, wherein the volume content of extractant is 15-25%.

[0019] Preferably, the extractant is one or more of P204, P507, and C272;

[0020] Preferably, the solvent oil is one or more of light white oil, kerosene, and C12-C14 saturated alkanes.

[0021] As a preferred embodiment of the process of the present invention, in step 1), the liquid alkali is one or more of sodium hydroxide, potassium hydroxide, and ammonia solution;

[0022] Preferably, the concentration of the liquid alkali is 10-40 wt%.

[0023] Preferably, the saponification rate of the extractant solution reacting with the liquid alkali in step 1) is 30-60%. The saponification rate refers to the ratio of the amount of hydrogen ions reacting with the liquid alkali during the saponification process to the total amount of hydrogen ions in the extractant. It is generally used to indicate the amount of liquid alkali added or the degree of saponification of the extractant.

[0024] As a preferred embodiment of the process of the present invention, in step 2), the conditions for a multi-stage countercurrent total extraction are: 4-7 extraction stages, temperature 30-55℃, and extraction ratio O:A=(6-13):1.

[0025] As a preferred embodiment of the process of the present invention, in step 3), the conditions for two-stage multi-stage countercurrent extraction are: 12-14 extraction stages, 30-55℃ temperature, and an extraction ratio of O:A = (1.5-4):1.

[0026] As a preferred embodiment of the process of the present invention, the metal components in the crude nickel sulfate solution, in terms of metal ion concentration, are: Ni 75-100 g / L, Co 2-15 g / L, Mg 0.5-5 g / L, Cu 0.1-3 g / L, Mn 0.1-7 g / L, Zn 0-3 g / L, Ca 0-0.5 g / L, Fe 0-0.2 g / L, Na 0-0.2 g / L.

[0027] This invention effectively reduces the oxidative degradation of the extractant during use by adding cyclohexenoic acid and dithiophosphonic acid as adjuvants, thereby reducing the TOC and small molecule acid content in the raffinate / back-extraction solution from the source, lowering subsequent processing costs, and improving the separation coefficient between impurity metals and nickel, achieving the effect of efficiently separating impurity metals even when the extractant is loaded with the target metal. Attached Figure Description

[0028] Figure 1This is a flowchart of the overall separation process of the present invention. Detailed Implementation

[0029] The present invention will be further illustrated below with specific embodiments. These embodiments are merely illustrative and do not limit the scope of the invention.

[0030] Unless otherwise specified, all raw materials and reagents used in this invention can be purchased commercially. The main metallic components of the crude nickel sulfate solution are: Ni 85 g / L, Co 12 g / L, Mg 2.02 g / L, Cu 0.52 g / L, Mn 1.08 g / L, Zn 0.46 g / L, Ca 0.45 g / L, Fe 0.13 g / L, and Na 0.11 g / L.

[0031] Naphthenic acid: CAS1388-24-5, Shandong Guohua Chemical

[0032] (R)-3-Cyclohexenic acid: CAS 5709-98-8, Aladdin

[0033] 3-Cyclohexene-1-carboxylic acid: CAS 4771-80-6, Sigma-Aldrich

[0034] Diisooctyl dithiophosphonic acid: CAS 107667-02-7, Shandong Xiya Chemical

[0035] Dibutyldithiophosphonic acid: It can be synthesized according to the method in patent CN112745348A. The specific synthesis route of this invention is as follows:

[0036] In a 500ml three-necked flask equipped with a reflux condenser and a constant-pressure dropping funnel, add 4.32g of magnesium shavings and 100ml of anhydrous THF (tetrahydrofuran). Then, add 40ml of 1-iodobutane solution (containing 30g of 1-iodobutane, with anhydrous THF as the solvent) to the constant-pressure dropping funnel. First, add a small amount and heat to initiate the reaction, then start stirring and add the remaining 1-iodobutane solution dropwise. After the addition is complete, heat under reflux for 4.5h until no bubbles are generated to obtain the Grignard reagent.

[0037] Cool the Grignard reagent to room temperature, add 9g of phosphorus pentasulfide under stirring, react at room temperature for 1 hour, then heat to reflux at 70°C until all phosphorus pentoxide disappears, and continue the reaction for 2.5 hours until the reaction is complete.

[0038] After adjusting the pH to 2 with dilute hydrochloric acid and stirring for 30 min, the mixture was extracted 6 times with ethyl acetate. The organic phases were combined, dried with anhydrous sodium sulfate to remove water, and the ethyl acetate was removed by vacuum distillation to obtain the product dibutyldithiophosphonic acid.

[0039]

Example 1

[0040] A process for separating and removing impurities from a nickel sulfate solution (overall process flow is as follows) Figure 1 (As shown), including the following steps:

[0041] 1) Extractant P204 and light white oil were mixed at a volume ratio of 25:75 to obtain an extractant solution. Then, (R)-3-cyclohexenic acid and diisooctyl dithiophosphonic acid were added, with the total amount added being 0.08 times the volume of the extractant solution, and the volume ratio of (R)-3-cyclohexenic acid to diisooctyl dithiophosphonic acid being 0.05:1. 32wt% sodium hydroxide was added to the mixture to carry out a saponification reaction, controlling the saponification rate at 60%, to obtain the post-saponification organic phase.

[0042] 2) The crude nickel sulfate solution and the post-soap organic phase were subjected to a multi-stage countercurrent total extraction with 7 extraction stages at a temperature of 30°C and an extraction ratio of O:A = 6:1, resulting in the raffinate aqueous phase and the total extracted loaded organic phase.

[0043] 3) The whole-extracted loaded organic phase and crude nickel sulfate solution were subjected to two-stage multi-stage countercurrent extraction to remove impurities. The number of extraction stages was 12, the temperature was 45℃, and the extraction ratio was O:A = 2:1, to obtain a purified nickel sulfate solution and an organic phase loaded with impurities.

[0044] 4) The organic phase loaded with impurities was back-extracted and regenerated using hydrochloric acid with a hydrogen ion concentration of 4 mol / L. The back-extraction ratio was O:A = 15:1, resulting in an impurity metal solution and a blank organic phase.

[0045]

Example 2

[0046] A process for separating and removing impurities from a nickel sulfate solution includes the following steps:

[0047] 1) Extractant P507 and light white oil were mixed at a volume ratio of 20:80 to obtain an extractant solution. Then, (R)-3-cyclohexenic acid and diisooctyl dithiophosphonic acid were added, with the total amount of the two added being 0.1 times the volume of the extractant solution, and the volume ratio of 3-cyclohexenic acid and sodium diisobutyl dithiophosphonate being 0.2:1. Ammonia water with a concentration of 10wt% was added to the mixture to carry out a saponification reaction, controlling the saponification rate to 50%, to obtain the post-saponification organic phase.

[0048] 2) The crude nickel sulfate solution and the post-soap organic phase were subjected to a multi-stage countercurrent total extraction with 4 extraction stages at a temperature of 38°C and an extraction ratio of O:A = 8.7:1, resulting in raffinate aqueous phase and total extracted loaded organic phase.

[0049] 3) The whole-extracted loaded organic phase and crude nickel sulfate solution were subjected to two-stage multi-stage countercurrent extraction to remove impurities. The number of extraction stages was 13, the temperature was 30℃, and the extraction ratio was O:A = 1.5:1, resulting in purified nickel sulfate solution and organic phase loaded with impurities.

[0050] 4) The organic phase loaded with impurities was back-extracted and regenerated using hydrochloric acid with a hydrogen ion concentration of 6 mol / L. The back-extraction ratio was O:A = 17:1, resulting in an impurity metal solution and a blank organic phase.

[0051]

Example 3

[0052] A process for separating and removing impurities from a nickel sulfate solution includes the following steps:

[0053] 1) Extractant P507 and light white oil were mixed at a volume ratio of 15:85 to obtain an extractant solution. Then, 3-cyclohexene-1-carboxylic acid and dibutyldithiophosphonic acid were added, with the total amount added being 0.05 times the volume of the extractant solution, and the volume ratio of 3-cyclohexene-1-carboxylic acid to dibutyldithiophosphonic acid being 0.07:1. A 40wt% potassium hydroxide solution was added to the mixture to carry out a saponification reaction, controlling the saponification rate at 30%, to obtain the post-saponification organic phase.

[0054] 2) The crude nickel sulfate solution and the post-soap organic phase were subjected to a multi-stage countercurrent total extraction with 6 extraction stages at a temperature of 55°C and an extraction ratio of O:A = 13:1, resulting in the raffinate aqueous phase and the total extracted loaded organic phase.

[0055] 3) The whole-extracted loaded organic phase and crude nickel sulfate solution were subjected to two-stage multi-stage countercurrent extraction to remove impurities. The number of extraction stages was 14, the temperature was 55℃, and the extraction ratio was O:A = 2.8:1, resulting in purified nickel sulfate solution and organic phase loaded with impurities.

[0056] 4) The organic phase loaded with impurities was back-extracted and regenerated using sulfuric acid with a hydrogen ion concentration of 5 mol / L. The back-extraction ratio was O:A = 6.5:1, resulting in an impurity metal solution and a blank organic phase.

[0057]

Example 4

[0058] A process for separating and removing impurities from a nickel sulfate solution includes the following steps:

[0059] 1) Extractant P204 and light white oil were mixed at a volume ratio of 15:85 to obtain an extractant solution. Then, (R)-3-cyclohexenic acid and diisooctyl dithiophosphonic acid were added, with the total amount of the two added being 0.05 times the volume of the extractant solution, and the volume ratio of 3-cyclohexenic acid to sodium diisobutyl dithiophosphonate being 0.02:1. Sodium hydroxide with a concentration of 32wt% was added to the mixture to carry out a saponification reaction, controlling the saponification rate at 60%, to obtain the post-saponification organic phase.

[0060] 2) The crude nickel sulfate solution and the post-soap organic phase were subjected to a multi-stage countercurrent total extraction with 7 extraction stages at a temperature of 30°C and an extraction ratio of O:A = 6:1, resulting in the raffinate aqueous phase and the total extracted loaded organic phase.

[0061] 3) The whole-extracted loaded organic phase and crude nickel sulfate solution were subjected to two-stage multi-stage countercurrent extraction to remove impurities. The number of extraction stages was 12, the temperature was 45℃, and the extraction ratio was O:A = 4:1, to obtain a purified nickel sulfate solution and an organic phase loaded with impurities.

[0062] 4) The organic phase loaded with impurities was back-extracted and regenerated using hydrochloric acid with a hydrogen ion concentration of 4 mol / L. The back-extraction ratio was O:A = 12:1, resulting in an impurity metal solution and a blank organic phase.

[0063]

Example 5

[0064] A process for separating and removing impurities from a nickel sulfate solution includes the following steps:

[0065] 1) Extractant P204 and light white oil were mixed at a volume ratio of 25:75 to obtain an extractant solution. Then, (R)-3-cyclohexenic acid and diisooctyl dithiophosphonic acid were added, with the total amount added being 0.08 times the volume of the extractant solution, and the volume ratio of 3-cyclohexenic acid to diisooctyl dithiophosphonic acid being 0.2:1. Sodium hydroxide with a concentration of 32wt% was added to the mixture to carry out a saponification reaction, controlling the saponification rate at 55%, to obtain the post-saponification organic phase.

[0066] 2) The crude nickel sulfate solution and the post-soap organic phase were subjected to a multi-stage countercurrent total extraction with 5 extraction stages at a temperature of 30°C and an extraction ratio of O:A = 7:1, resulting in raffinate aqueous phase and total extracted loaded organic phase.

[0067] 3) The whole-extracted loaded organic phase and crude nickel sulfate solution were subjected to two-stage multi-stage countercurrent extraction to remove impurities. The number of extraction stages was 11, the temperature was 30℃, and the extraction ratio was O:A = 2:1, to obtain a purified nickel sulfate solution and an organic phase loaded with impurities.

[0068] 4) The organic phase loaded with impurities was back-extracted and regenerated using hydrochloric acid with a hydrogen ion concentration of 4 mol / L. The back-extraction ratio was O:A = 8.3:1, resulting in an impurity metal solution and a blank organic phase.

[0069]

Example 6

[0070] A process for separating and removing impurities from a nickel sulfate solution includes the following steps:

[0071] 1) Extractant C272 and light white oil were mixed at a volume ratio of 20:80 to obtain an extractant solution. Then, 3-cyclohexen-1-carboxylic acid and diisooctyl dithiophosphonic acid were added, with the total amount added being 0.08 times the volume of the extractant solution, and the volume ratio of 3-cyclohexenic acid to diisooctyl dithiophosphonic acid being 0.2:1. Sodium hydroxide with a concentration of 20 wt% was added to the mixture to carry out a saponification reaction, controlling the saponification rate at 40%, to obtain the post-saponification organic phase.

[0072] 2) The crude nickel sulfate solution and the post-soap organic phase were subjected to a multi-stage countercurrent total extraction with 5 extraction stages at a temperature of 45°C and an extraction ratio of O:A = 7:1, resulting in the raffinate aqueous phase and the total extracted loaded organic phase.

[0073] 3) The whole-extracted loaded organic phase and crude nickel sulfate solution were subjected to two-stage multi-stage countercurrent extraction to remove impurities. The number of extraction stages was 12, the temperature was 45℃, and the extraction ratio was O:A = 1.8:1, resulting in purified nickel sulfate solution and organic phase loaded with impurities.

[0074] 4) The organic phase loaded with impurities was back-extracted and regenerated using sulfuric acid with a hydrogen ion concentration of 5 mol / L. The back-extraction ratio was O:A = 18:1, resulting in an impurity metal solution and a blank organic phase.

[0075] Comparative Example 1

[0076] The nickel sulfate solution was separated and impurities removed using a process essentially the same as in Example 1, except that diisooctyl dithiophosphonic acid was not added.

[0077] Comparative Example 2

[0078] The nickel sulfate solution was separated and purified using a process essentially the same as in Example 1, except that diisooctyl dithiophosphonic acid was not added, and (R)-3-cyclohexenic acid was replaced with cycloalkanoic acid.

[0079] Comparative Example 3

[0080] The nickel sulfate solution was separated and impurities removed using a process essentially the same as in Example 1, except that (R)-3-cyclohexenecarboxylic acid was not added.

[0081] Comparative Example 4

[0082] The nickel sulfate solution was separated and purified using a process essentially the same as in Example 1, except that (R)-3-cyclohexenecarboxylic acid and diisooctyl dithiophosphonic acid were not added.

[0083] The TOC and small molecule organic acids (formic acid, acetic acid) of the raffinate obtained from the first extraction in Examples 1-6 and Comparative Examples 1-4 were measured, and the average phase separation time of the first extraction was recorded in Table 1.

[0084] Table 1

[0085] Grouping TOC / ppm Small molecule organic acids / ppm Average phase separation time / s Example 1 53 4.6 90 Example 2 48 3.8 87 Example 3 53 5.2 89 Example 4 47 4.1 95 Example 5 42 3.9 87 Example 6 55 4.9 91 Comparative Example 1 60 5.2 98 Comparative Example 2 702 73 92 Comparative Example 3 698 79 520 Comparative Example 4 756 82 106

[0086] The nickel sulfate solutions obtained from the two-stage extraction in Examples 1-6 and Comparative Examples 1-4 were tested for metal content and TOC, and the average phase separation time of the two-stage extraction was recorded in Table 2.

[0087] Table 2

[0088]

[0089]

[0090] The TOC and small molecule organic acids (formic acid, acetic acid) of the impurity metal solutions obtained by back-extraction and regeneration in Examples 1-6 and Comparative Examples 1-4 were detected, and the average phase separation time of back-extraction was recorded in Table 3.

[0091] Table 3

[0092] Grouping TOC / ppm Small molecule organic acids / ppm Average phase separation time / s Example 1 282 40 88 Example 2 335 44 82 Example 3 227 31 86 Example 4 302 38 97 Example 5 206 29 78 Example 6 270 36 92 Comparative Example 1 268 37 90 Comparative Example 2 1080 412 90 Comparative Example 3 1140 398 395 Comparative Example 4 1189 402 86

[0093] The comparison of Example 1 and Comparative Examples 1-4 in Tables 1, 2, and 3 shows that the addition of cyclohexenoic acid and dithiophosphonic acid to the extractant solution significantly reduced the content of TOC and small molecule organic acids in the raffinate / back-extract, and significantly improved the separation accuracy of nickel from other impurity metals.

[0094] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and additions without departing from the method of the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention.

Claims

1. A process for separating and removing impurities from a nickel sulfate solution, characterized in that, Includes the following steps: 1) The extractant solution is mixed with cyclohexenoic acid and dithiophosphonic acid, and then reacted with liquid alkali to undergo saponification, yielding the saponified organic phase; 2) The crude nickel sulfate solution and the post-soap organic phase are subjected to a single-stage countercurrent total extraction to obtain the raffinate aqueous phase and the total extracted supported organic phase; the metal components in the crude nickel sulfate solution, in terms of metal ion concentration, are: Ni 75-100 g / L, Co 2-15 g / L, Mg 0.5-5 g / L, Cu 0.1-3 g / L, Mn 0.1-7 g / L, Zn 0-3 g / L, Ca 0-0.5 g / L, Fe 0-0.2 g / L, Na 0-0.2 g / L; 3) The whole-extracted loaded organic phase and crude nickel sulfate solution are subjected to two-stage multi-stage countercurrent extraction to remove impurities, resulting in purified nickel sulfate solution and organic phase loaded with impurities.

2. The nickel sulfate solution separation and impurity removal process according to claim 1, characterized in that, It also includes step 4), which involves back-extraction and regeneration of the impurity-loaded organic phase to obtain an impurity metal solution and a blank organic phase.

3. The nickel sulfate solution separation and impurity removal process according to claim 2, characterized in that, In step 4), the back-extraction regeneration is performed using inorganic acids.

4. The nickel sulfate solution separation and impurity removal process according to claim 3, characterized in that, The inorganic acid is hydrochloric acid or sulfuric acid with a hydrogen ion concentration of 4-6 mol / L.

5. The nickel sulfate solution separation and impurity removal process according to claim 1, characterized in that, In step 1), the total amount of cyclohexenoic acid and dithiophosphonic acid added is 0.05-0.1 times the volume of the extractant solution, based on the volume ratio.

6. The nickel sulfate solution separation and impurity removal process according to claim 5, characterized in that, The volume ratio of the cyclohexenoic acid to the dithiophosphonic acid is (0.02-0.2):

1.

7. The nickel sulfate solution separation and impurity removal process according to any one of claims 1-6, characterized in that, The cyclohexenoic acid is 3-cyclohexene-1-carboxylic acid and / or (R)-3-cyclohexenecarboxylic acid.

8. The nickel sulfate solution separation and impurity removal process according to claim 7, characterized in that, The dithiophosphonic acid is selected from one or more of dibutyl dithiophosphonic acid, diisooctyl dithiophosphonic acid, and diisobutyl dithiophosphonic acid.

9. The nickel sulfate solution separation and impurity removal process according to any one of claims 1-6, characterized in that, In step 1), the extractant solution is a mixture of extractant and solvent oil, wherein the volume content of extractant is 15-25%.

10. The nickel sulfate solution separation and impurity removal process according to claim 9, characterized in that, The extractant is one or more of P204, P507, and C272.

11. The nickel sulfate solution separation and impurity removal process according to claim 9, characterized in that, The solvent oil is one or more of light white oil, kerosene, and C12-C14 saturated alkanes.

12. The nickel sulfate solution separation and impurity removal process according to any one of claims 1-6, characterized in that, In step 1), the liquid alkali is one or more of sodium hydroxide, potassium hydroxide, and ammonia solution.

13. The nickel sulfate solution separation and impurity removal process according to claim 12, characterized in that, The concentration of the liquid alkali is 10-40 wt%.

14. The nickel sulfate solution separation and impurity removal process according to claim 12, characterized in that, In step 1), the saponification rate of the extractant solution reacting with liquid alkali is 30-60%.

15. The nickel sulfate solution separation and impurity removal process according to any one of claims 1-6, characterized in that, In step 2), the conditions for a single-stage countercurrent total extraction are: 4-7 extraction stages, temperature 30-55℃, and extraction ratio O:A = (6-13):

1.

16. The nickel sulfate solution separation and impurity removal process according to any one of claims 1-6, characterized in that, In step 3), the conditions for two-stage countercurrent extraction are: 12-14 extraction stages, temperature 30-55℃, and extraction ratio O:A = (1.5-4):1.

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