CN109852796B

CN109852796B - Method for extracting and separating nickel and sodium in nickel sulfate solution

Info

Publication number: CN109852796B
Application number: CN201910303428.6A
Authority: CN
Inventors: 钱有军; 裴晓东; 骆艳华; 王凡; 李涛; 刘晨; 佘世杰; 张倩倩
Original assignee: SINOSTEEL ANHUI TIANYUAN TECHNOLOGY CO LTD; Sinosteel Nanjing New Material Research Institute Co Ltd
Current assignee: Sinosteel Nanjing New Material Research Institute Co Ltd; Sinosteel New Materials Co Ltd
Priority date: 2019-04-16
Filing date: 2019-04-16
Publication date: 2020-06-26
Anticipated expiration: 2039-04-16
Also published as: CN109852796A

Abstract

The invention relates to the technical field of batteries, and discloses a method for extracting and separating nickel and sodium in a nickel sulfate solution, which is used for extracting and separating nickel and sodium in the nickel sulfate solution with the nickel content of 30-60 g/L and the sodium content of 3-7 g/L, and comprises the following steps: (1) extracting nickel; (2) washing sodium in one step; (3) washing sodium in the second step; (4) the invention has the advantages that the nickel is back extracted, the sodium is washed in one step to improve the processing capacity and reduce the cost, and the sodium is washed in the second step to effectively separate the nickel and the sodium; the method has the advantages of simple process flow, low cost, high comprehensive recovery rate of nickel and good product quality, wherein the nickel content in the pure nickel sulfate solution is 80-120 g/L, the sodium content is less than 0.08g/L, and the nickel sulfate product for the battery material can be obtained through the steps of oil removal, crystallization and the like.

Description

Method for extracting and separating nickel and sodium in nickel sulfate solution

Technical Field

The invention relates to the technical field of batteries, and relates to a method for extracting and separating nickel and sodium from a nickel sulfate solution, in particular to a method for extracting and separating nickel and sodium from a nickel sulfate solution with nickel content of 30-60 g/L and sodium content of 3-7 g/L after the steps of dissolving, chemically removing impurities, extracting and removing impurities and the like are carried out on crude nickel sulfate.

Background

Nickel sulfate is an important chemical product, and is mainly applied to the industrial fields of electroplating, batteries, chemical engineering, light industry, ceramics and the like. Driven by the driving action of the new energy automobile industry and related policies, the battery material industry develops rapidly, and the market demand for nickel sulfate is tightened for a long time.

The crude nickel sulfate mainly contains impurities such As Fe, As, Ca, Mg, Zn, Cu and the like, and can meet the requirements of the battery material industry only by removing the impurities. The impurity removing method of the crude nickel sulfate mainly comprises a chemical impurity removing method, an extraction method and a combination method of chemical impurity removing and extraction. When Fe and As are oxidized and precipitated and Ca and Mg are fluoridized and precipitated by a chemical impurity removal method, sodium hydroxide is adopted to adjust the pH value, a large amount of sodium ions are introduced, and the sodium content of the product is too high. The key of the nickel and other impurity ions separation by the extraction method is to control the pH value of the equilibrium water phase, and when acidic extracting agents such as P204, P507 and the like are adopted, saponification treatment is generally carried out before extraction, and a large amount of sodium ions are introduced.

At present, the separation of nickel and sodium in nickel sulfate solution is generally carried out by a precipitation-redissolution method and an extraction method. Application No. 201711402476.8 a method for comprehensively recovering valuable elements from crude nickel sulfate by precipitation-redissolution method, which realizes effective separation of nickel and sodium, i.e. using sodium carbonate to precipitate nickel ions, converting nickel into nickel carbonate precipitate, then using sulfuric acid to dissolve nickel carbonate, and converting nickel back into nickel sulfate.

At present, the nickel is extracted completely by adopting an acidic extractant, and the dilute sulfuric acid solution is used for washing sodium to realize the effective separation of the nickel and the sodium, and the principle is to utilize H⁺By substitution of Na in the organic phase⁺However, in actual production, H⁺In substitution for Na⁺While replacing part of Ni²⁺The nickel content in the washing liquid is high, the loss of nickel metal is large, and the method does not play a role in enriching nickel during extraction, and is increased inevitablyThe cost of continuing the nickel sulfate crystallization process. The application number 201210120102.8A method for refining nickel sulfate, which comprises washing organic phase loaded with nickel and sodium with pure nickel sulfate solution, wherein the concentration of nickel sulfate is better enriched from 52.08g/L Ni in raw material to 98.63g/L Ni in pure nickel sulfate solution, but in the process of sodium washing, the number of washing stages is small, the sodium content in refined nickel sulfate product is not up to standard, the number of washing stages is large, and Ni in pure nickel sulfate solution is in pure nickel sulfate solution²⁺The smaller the proportion of the organic phase entering, the higher the nickel content in the raffinate, and the greater the nickel loss, according to the parameters of nickel extraction and sodium washing in example 2 of the patent, because some parameters in the examples are not interchanged, 6400mL of raffinate with 8.73g/L nickel content is newly generated by processing 2000mL of nickel sulfate solution with 52.08g/L nickel content, which is directly discharged in the form of sodium sulfate solution, the nickel loss is at least 20% or more, and the actual nickel loss may be greater, therefore, the raffinate in the actual production must be returned to the nickel extraction system for purification treatment to reduce the loss of nickel metal, which inevitably increases the cost by 25% or more.

Disclosure of Invention

The invention aims to solve the problems in the prior art and provides a method for extracting and separating nickel and sodium from a nickel sulfate solution, which has the advantages of simple process flow, good nickel and sodium separation effect, high nickel yield and low cost.

In order to realize the purpose, the invention provides a method for extracting and separating nickel and sodium in a nickel sulfate solution, which adopts the technical scheme that:

a method for extracting and separating nickel and sodium in a nickel sulfate solution is used for the nickel sulfate solution with the nickel content of 30-60 g/L and the sodium content of 3-7 g/L, and adopts the following processes and steps:

(1) nickel extraction: firstly, adding a saponification extracting agent into a nickel sulfate solution to be treated, controlling the volume ratio (compared with O/A) of an organic phase to a water phase to be 1: 1-4: 1, carrying out 2-5-stage countercurrent extraction, then standing and separating to obtain an organic phase loaded with high Ni and high Na and a raffinate, and strictly controlling the nickel content of the raffinate to be less than 0.05 g/L;

the main component of the raffinate is sodium sulfate solution;

preferably, the saponification extractant used in step (1) is the sodium salt of bis (2-ethylhexyl) phosphinic acid (i.e., P204).

More preferably, the saponification method is to dilute the P204 to 20-30% by volume by using No. 260 sulfonated kerosene and extract 10-20% sodium hydroxide solution.

Preferably, the saponification rate of the di (2-ethylhexyl) phosphinic acid is 60-80%.

In this step, the saponification reaction equation of the extractant P204 is:

in this step, the chemical reaction equation for extracting nickel is:

(2) one-step sodium washing operation: adding a washing liquid a into the high-Ni high-Na loaded organic phase obtained in the step (1), controlling the ratio of O/A to be 3: 1-8: 1, carrying out 2-5-stage countercurrent washing, then standing and separating to obtain a high-Ni low-Na loaded organic phase and a raffinate a, and strictly controlling the nickel content of the raffinate a to be less than 0.05 g/L.

Preferably, the washing liquid a used in the step (2) is a nickel sulfate solution with a nickel content of 2.5-10 g/L and a sodium content of 0.2-1 g/L, which is prepared by diluting a nickel sulfate solution to be treated with pure water.

In the step, the separation of nickel and more than 95 percent of sodium is realized, namely 95 percent of sodium enters the raffinate a to obtain an organic phase loaded with high nickel and low sodium, wherein the residual sodium content accounts for less than 5 percent, the main component of the raffinate a is a sodium sulfate solution, the nickel content is less than 0.05g/L, and the nickel loss in the step is less than 0.5 percent.

In this step, the principle of sodium washing is to use Ni²⁺By substitution of Na in the organic phase⁺The chemical reaction equation is:

(3) and (3) two-step sodium washing operation: and (3) adding a washing liquid b into the organic phase loaded with high Ni and low Na obtained in the step (2), controlling the ratio of O/A to be 3: 1-8: 1, carrying out 2-5-stage countercurrent washing, and then standing and separating to obtain an organic phase loaded with Ni and a washing residual liquid b.

Preferably, the washing liquid b used in the step (3) is a nickel sulfate solution with a nickel content of 0.5-2.5 g/L diluted by pure nickel sulfate solution and pure water.

In the step, the principle of sodium washing is the same as that in the step (2), but if the sodium is washed by the washing liquid a in the second step, the sodium content in the final nickel sulfate product cannot meet the requirement of the battery material.

(4) And (3) nickel stripping operation: and (4) adding a stripping agent into the Ni-loaded organic phase obtained in the step (3), controlling the ratio of O/A to be 7: 1-2: 1, performing 1-2-stage counter-current stripping, and then standing and separating to obtain a pure nickel sulfate solution and an organic phase.

Preferably, the stripping agent used in the step (4) is a sulfuric acid solution with the concentration of 100-400 g/L; the nickel content of the pure nickel sulfate solution is 80-120 g/L, the sodium content is less than 0.08g/L, and a nickel sulfate product for a battery material can be obtained through the steps of oil removal, crystallization and the like.

Preferably, the organic phase in step (4) is recycled after regeneration treatment.

The concrete values of the parameters such as saponification rate of the extracting agent, nickel extraction series, one-step sodium washing series, two-step sodium washing series, nickel content in the washing liquid a, nickel content in the washing liquid b, concentration of back extraction sulfuric acid, series and the like can be determined through laboratory test results according to the nickel and sodium contents in the nickel sulfate solution to be treated.

Compared with the prior art, the method for extracting and separating nickel and sodium from the nickel sulfate solution has the following advantages:

(1) in the prior art, no matter dilute sulfuric acid or pure nickel sulfate solution is adopted for sodium washing, although the sodium content of a nickel sulfate product meets the requirement, the nickel content in the remaining liquid is higher, and the nickel sulfate solution which is polluted by sodium and has 20-50% of nickel content basically consistent with that of the raw material is generated while the raw material is treated; the invention adopts the methods of nickel extraction, one-step sodium washing, two-step sodium washing and nickel back extraction, and the nickel extraction operation loads more than 99.9 percent of nickel into an organic phase; the organic phase loaded with high Ni and high Na is subjected to step-by-step sodium washing, and the diluted nickel sulfate solution to be treated is adopted as a washing solution in the one-step sodium washing operation, so that more than 95 percent of sodium in the organic phase can be washed, and the content of nickel in the organic phase can be enriched by about one time; the sodium content in the two-step sodium washing operation is only within 5 percent of the sodium content in the organic phase loaded with Ni and Na, and the sodium content after washing by adopting a pure nickel sulfate solution with low concentration can meet the requirement of the battery material industry.

(2) The invention is based on Ni in the sodium washing process²⁺And Na⁺In the flow direction rule of the organic phase and the water phase, namely the process of washing sodium, Ni in the water phase at the early stage²⁺By substitution of Na in the organic phase⁺The method for washing sodium by two steps is developed according to the law of high efficiency and low efficiency in the later period. The one-step sodium washing improves the processing capacity by about one time and reduces the cost, the nickel content in the one-step raffinate is less than 0.05g/L, the one-step sodium washing is recycled in the form of sodium sulfate, and the loss of nickel in the one-step sodium washing is less than 0.5 percent; the nickel content in the two-step sodium washing raffinate is 0.5-1 g/L and only accounts for 3% of the nickel content in the whole process, the two-step sodium washing raffinate and the nickel sulfate solution to be treated can be prepared into a washing liquid for one-step sodium washing together, and the comprehensive recovery rate of nickel is more than 99%.

(3) The method has the advantages of simple process flow, low cost and high nickel recovery rate. The nickel content in the pure nickel sulfate solution is 80-120 g/L, the sodium content is less than 0.08g/L, the product quality is good, and the nickel sulfate product for the battery material can be obtained after the steps of oil removal, crystallization and the like.

Drawings

The invention is further described below with reference to the accompanying drawings.

FIG. 1 is a schematic process flow diagram of an embodiment of the present invention.

Detailed Description

Example 1

(1) The results of chemical composition analysis of the nickel sulfate solution to be treated used in this example are shown in table 1:

TABLE 1 chemical composition (g/L) of nickel sulfate solution to be treated

Element(s)

Ni

Na

Fe

Ca

Mg

Cu

Zn

Co

Content (wt.)

52.45

6.25

＜0.001

0.011

0.029

＜0.001

0.34

As can be seen from the data in Table 1, except that the content of sodium in the nickel sulfate solution exceeds the standard, the content of other impurities can meet the requirements of nickel sulfate products for battery materials, and an effective method for separating nickel and sodium in the nickel sulfate solution is an extraction method;

(2) taking 1000mL of the nickel sulfate solution, adding a saponification P204 extraction agent into the nickel sulfate solution, wherein the volume fraction of P204 is 25%, the saponification rate is 80%, the control ratio of O/A is 2:1, performing three-stage countercurrent extraction, then standing and separating to obtain an organic phase loaded with high Ni and high Na and a raffinate, wherein the volume of the raffinate is 1000mL, the nickel concentration of the raffinate is less than 0.05g/L, and directly discharging the raffinate for treatment;

(3) adding a washing liquid a into the organic phase loaded with high Ni and high Na obtained by extracting the nickel, diluting the washing liquid a into a nickel sulfate solution with the nickel content of 7.5g/L and the sodium content of 0.89g/L by adding pure water into the nickel sulfate solution to be treated, controlling the ratio of O/A to be 4:1, carrying out four-stage countercurrent washing, then standing and separating to obtain an organic phase loaded with high Ni and low Na and a washing residual liquid a, wherein the volume of the washing residual liquid a is 6000mL, the nickel concentration of the washing residual liquid a is less than 0.05g/L, and the nickel loss rate of the step (3) is less than 0.5%;

(4) adding a washing solution b into the organic phase loaded with high Ni and low Na obtained by one-step sodium washing, diluting the washing solution b into a nickel sulfate solution with the nickel concentration of 2g/L by using a pure nickel sulfate solution, controlling the ratio of O/A to be 4:1, carrying out four-stage countercurrent washing, then standing and separating to obtain an organic phase loaded with Ni and a raffinate b, wherein the volume of the raffinate a is 6000mL, the nickel content of the raffinate a is 0.57g/L, and preparing the raffinate b and the nickel sulfate solution to be treated together to be used as a washing solution for the next one-step sodium washing;

(5) adding a sulfuric acid solution with the concentration of 400g/L into the Ni-loaded organic phase obtained by sodium washing in the two steps, controlling the ratio of O/A to be 6:1, performing primary back extraction, standing and separating to obtain 1000mL of pure nickel sulfate solution and an organic phase, performing regeneration treatment on the organic phase, and recycling, wherein the chemical components of the pure nickel sulfate solution are shown in Table 2;

TABLE 2 pure nickel sulfate solution chemistry (g/L)

Element(s)	Ni	Na	Fe	Ca	Mg	Cu	Zn	Co
									Content (wt.)	105.21	0.065	0.001	0.021	0.057	0.002	0.002	0.51

(6) The comprehensive recovery rate of nickel in the embodiment is 99.25%, and the raffinate b can be prepared into a washing solution for sodium washing in the next step, so that the nickel content in the raffinate b is not calculated as nickel loss;

(7) table 3 shows the quality of nickel sulfate product and the national industry standard HG/T2824-2009.

TABLE 3 quality of nickel sulfate product and national industry Standard HG/T2824-

By combining the data in tables 2 and 3, the pure nickel sulfate solution obtained by the nickel and sodium extraction separation method of the nickel sulfate solution can reach the standard of class II (battery grade) high-class products after simple steps of oil removal, crystallization and the like.

Example 2

(1) The results of chemical composition analysis of the nickel sulfate solution to be treated used in this example are shown in table 4:

TABLE 4 chemical composition (g/L) of nickel sulfate solution to be treated

Element(s)

Ni

Na

Fe

Ca

Mg

Cu

Zn

Co

Content (wt.)

43.28

3.51

＜0.001

0.007

0.023

＜0.001

0.21

(2) Taking 1000mL of the nickel sulfate solution, adding a saponification P204 extraction agent into the nickel sulfate solution, wherein the volume fraction of P204 is 25%, the saponification rate is 65%, the control ratio of O/A is 3:2, performing two-stage countercurrent extraction, and then standing and separating to obtain an organic phase loaded with high Ni and high Na and a raffinate, wherein the volume of the raffinate is 1000mL, and the nickel content of the raffinate is less than 0.05 g/L;

(3) adding a washing liquid a into the organic phase loaded with high Ni and high Na obtained by extracting the nickel, diluting the washing liquid a into a nickel sulfate solution with the nickel content of 10g/L and the sodium content of 0.81g/L by adding pure water into the nickel sulfate solution to be treated, controlling the ratio of O/A to be 3:1, carrying out three-stage countercurrent washing, then standing and separating to obtain an organic phase loaded with high Ni and low Na and a washing liquid a, wherein the volume of the washing liquid a is 3000mL, the nickel content of the washing liquid a is less than 0.05g/L, and the nickel loss rate in the step (3) is less than 0.5%;

(4) adding a washing solution b into the organic phase loaded with high Ni and low Na obtained by one-step sodium washing, diluting the washing solution b into a nickel sulfate solution with the nickel content of 0.5g/L by adding pure water into a pure nickel sulfate solution, controlling the ratio of O/A to be 3:1, carrying out five-stage countercurrent washing, then standing and separating to obtain an organic phase loaded with Ni and a raffinate b, wherein the volume of the raffinate a is 5000mL, the nickel content of the raffinate a is 0.21g/L, and preparing the raffinate b and the nickel sulfate solution to be treated together to be used as a washing solution for next one-step sodium washing;

(5) adding a sulfuric acid solution with the concentration of 200g/L into the Ni-loaded organic phase obtained by sodium washing in the two steps, controlling the ratio of O/A to be 10:3, performing primary back extraction, standing and separating to obtain 900mL of pure nickel sulfate solution and an organic phase, performing regeneration treatment on the organic phase, and recycling, wherein the chemical components of the pure nickel sulfate solution are shown in Table 5;

TABLE 5 pure Nickel sulfate solution chemistry composition (g/L)

Element(s)	Ni	Na	Fe	Ca	Mg	Cu	Zn	Co
									Content (wt.)	82.51	0.049	0.001	0.015	0.045	0.002	0.002	0.37

(6) The comprehensive recovery rate of nickel in the embodiment is 99.36%, and the raffinate b can be prepared into a washing solution for sodium washing in the next step, so that the nickel content in the raffinate b is not calculated as nickel loss;

(7) the quality of the nickel sulfate product is the same as that of the national industry standard HG/T2824-containing 2009 in Table 3, and the data in Table 3 and Table 5 are synthesized, so that the quality of the obtained nickel sulfate product can reach the standard of class II (battery grade) first-class products after the pure nickel sulfate solution obtained by the nickel sulfate solution nickel and sodium extraction separation method is subjected to simple steps of oil removal, crystallization and the like.

Example 3

(1) The results of chemical composition analysis of the nickel sulfate solution to be treated used in this example are shown in table 6:

TABLE 6 chemical composition (g/L) of nickel sulfate solution to be treated

Element(s)

Ni

Na

Fe

Ca

Mg

Cu

Zn

Co

Content (wt.)

31.75

4.78

＜0.001

0.006

0.018

＜0.001

0.14

(2) Taking 1000mL of the nickel sulfate solution, adding a saponification P204 extraction agent into the nickel sulfate solution, carrying out five-stage countercurrent extraction on the P204 volume fraction of 30% and the saponification rate of 60% in a control ratio of O/A to 3:2, then standing and separating to obtain an organic phase loaded with high Ni and high Na and a raffinate, wherein the volume of the raffinate is 1000mL, and the nickel content of the raffinate is less than 0.05 g/L;

(3) adding a washing liquid a into the organic phase loaded with high Ni and high Na obtained by extracting the nickel, diluting the washing liquid a into a nickel sulfate solution with the nickel content of 10g/L and the sodium content of 0.60g/L by adding pure water into the nickel sulfate solution to be treated, controlling the ratio of O/A to be 8:1, carrying out five-stage countercurrent washing, then standing and separating to obtain an organic phase loaded with high Ni and low Na and a washing liquid a, wherein the volume of the washing liquid a is 4687.5mL, the nickel content of the washing liquid a is less than 0.05g/L, and the nickel loss rate in the step (3) is less than 0.5%;

(4) adding a washing solution b into the organic phase loaded with high Ni and low Na obtained by one-step sodium washing, diluting the washing solution b into a nickel sulfate solution with the nickel content of 2g/L by adding pure water into a pure nickel sulfate solution, controlling the ratio of O/A to be 8:1, carrying out five-stage countercurrent washing, then standing and separating to obtain an organic phase loaded with Ni and a raffinate b, wherein the volume of the raffinate a is 4687.5mL, the nickel content of the raffinate a is 0.25g/L, and preparing the raffinate b and the nickel sulfate solution to be treated together to be used as a washing solution for next one-step sodium washing;

(5) adding a sulfuric acid solution with the concentration of 400g/L into the Ni-loaded organic phase obtained by sodium washing in the two steps, controlling the ratio of O/A to be 7:1, performing primary back extraction, standing and separating to obtain 1071.5mL of pure nickel sulfate solution and an organic phase, wherein the organic phase is recycled after regeneration treatment, and the chemical components of the pure nickel sulfate solution are shown in Table 7;

TABLE 7 pure Nickel sulfate solution chemistry composition (g/L)

Element(s)	Ni	Na	Fe	Ca	Mg	Cu	Zn	Co
									Content (wt.)	81.75	0.035	0.001	0.013	0.037	0.001	0.001	0.28

(6) The comprehensive recovery rate of nickel in the embodiment is 99.54%, and the raffinate b can be prepared into a washing solution for sodium washing in the next step, so that the nickel content in the raffinate b is not calculated as nickel loss;

(7) the quality of the nickel sulfate product is the same as that of the national industry standard HG/T2824-containing 2009 in Table 3, and the data in Table 3 and Table 7 are synthesized, so that the quality of the obtained nickel sulfate product can reach the standard of class II (battery grade) first-class products after the pure nickel sulfate solution obtained by the nickel sulfate solution nickel and sodium extraction separation method is subjected to simple steps of oil removal, crystallization and the like.

The foregoing is illustrative and explanatory only and is not intended to be exhaustive or to limit the invention to the precise embodiments described, and various modifications and additions may be made thereto by those skilled in the art without departing from the spirit of the invention or exceeding the scope defined by the claims.

Claims

1. A method for extracting and separating nickel and sodium in a nickel sulfate solution is used for extracting and separating the nickel and the sodium in the nickel sulfate solution with the nickel content of 30-60 g/L and the sodium content of 3-7 g/L, and is characterized by comprising the following steps:

(1) nickel extraction: firstly, adding a saponification extracting agent into a nickel sulfate solution to be treated, controlling the volume ratio of an organic phase to a water phase to be 1: 1-4: 1, carrying out 2-5-stage countercurrent extraction, then standing and separating to obtain an organic phase loaded with high Ni and high Na and raffinate, and strictly controlling the nickel concentration of the raffinate to be less than 0.05 g/L;

(2) one-step sodium washing operation: adding a washing liquid a into the organic phase loaded with high Ni and high Na obtained in the step (1), controlling the volume ratio of the organic phase to the water phase to be 3: 1-8: 1, carrying out 2-5-stage countercurrent washing, then standing and separating to obtain the organic phase loaded with high Ni and low Na and a raffinate a, and strictly controlling the nickel concentration of the raffinate a to be less than 0.05 g/L;

(3) and (3) two-step sodium washing operation: adding a washing solution b into the organic phase loaded with high Ni and low Na obtained in the step (2), controlling the volume ratio of the organic phase to the water phase to be 3: 1-8: 1, carrying out 2-5-stage countercurrent washing, and then standing and separating to obtain an organic phase loaded with Ni and a washing residual solution b;

(4) and (3) nickel stripping operation: adding a stripping agent into the Ni-loaded organic phase obtained in the step (3), controlling the volume ratio of the organic phase to the water phase to be 7: 1-2: 1, performing 1-2-stage counter-current stripping, and then standing and separating to obtain a pure nickel sulfate solution and an organic phase;

the washing liquid a used in the step (2) is a nickel sulfate solution with the nickel content of 2.5-10 g/L and the sodium content of 0.2-1 g/L, which is prepared by diluting a nickel sulfate solution to be treated with pure water;

and (4) diluting the washing liquid b used in the step (3) by adding pure water into the pure nickel sulfate solution to prepare a nickel sulfate solution with the nickel content of 0.5-2.5 g/L.

2. The process of claim 1, wherein the saponified extractant of step (1) is the sodium salt of di (2-ethylhexyl) phosphinic acid.

3. The method of claim 2, wherein the sodium salt of bis (2-ethylhexyl) phosphinic acid is prepared by diluting bis (2-ethylhexyl) phosphinic acid to 20-30% by volume with 260# sulfonated kerosene and extracting a sodium hydroxide solution having a mass concentration of 10-20%.

4. The method according to claim 3, wherein the saponification rate of bis (2-ethylhexyl) phosphinic acid is 60 to 80%.

5. The method according to claim 1, wherein the stripping agent used in step (4) is a sulfuric acid solution with a concentration of 100-400 g/L.

6. The process according to claim 1, wherein the raffinate of step (1) and the raffinate a of step (2) each comprise a sodium sulfate solution and each have a nickel content of less than 0.05 g/L.

7. The method as claimed in claim 1, wherein the pure nickel sulfate solution in the step (4) has a nickel content of 80-120 g/L and a sodium content of less than 0.08g/L, and a nickel sulfate product for battery materials can be obtained after oil removal and crystallization.

8. The method of claim 1, wherein the organic phase of step (4) is recycled after regeneration.