A method for preparing high-purity cobalt from crude cobalt hydroxide

Abstract

The present application belongs to the technical field of cobalt hydrometallurgy, and specifically relates to a method for preparing high-purity cobalt from crude cobalt hydroxide, which comprises the following steps: after the crude cobalt hydroxide is slurried, selective reduction leaching is performed on the slurry by using concentrated sulfuric acid and sulfur dioxide to obtain a cobalt leaching solution and a manganese residue; the pH of the cobalt leaching solution is adjusted by using sodium bicarbonate to perform staged precipitation and filtration, and after impurity removal, a nickel-containing cobalt sulfate solution is obtained; the solution is passed into a nickel-removing resin which has been pre-saturated with qualified cobalt sulfate to perform adsorption and elution separation, and high-purity cobalt sulfate is obtained by combining the cobalt-containing effluent; finally, the high-purity cobalt sulfate is used as an electrolyte solution to perform electrowinning to obtain high-purity cobalt plates; the present application adopts the processes of selective reduction leaching, sodium bicarbonate staged precipitation, cobalt pre-saturation, resin adsorption for nickel removal, and cobalt electrowinning, and has the advantages of a short process flow, simple operation, and low cost, and not only can high-purity cobalt plates be prepared, but also nickel sulfate can be recycled and utilized.

Description

Technical Field

[0001] This invention belongs to the field of cobalt hydrometallurgical technology, specifically a method for preparing high-purity cobalt from crude cobalt hydroxide. Background Technology

[0002] High-purity cobalt, due to its excellent physical, chemical, and electrical properties, has irreplaceable applications in multiple fields such as lithium-ion batteries, semiconductors, and aerospace. The traditional high-purity cobalt preparation process involves the following steps: crude cobalt hydroxide raw material undergoes multi-stage acid leaching, ensuring that cobalt and other metal elements are fully incorporated into the solution. The leaching solution then undergoes P204 extraction, P507 cobalt extraction, back-extraction, and oil removal processes to obtain a cobalt sulfate solution of a predetermined concentration. Finally, high-purity cobalt is produced through electrowinning. This method has a long process flow and consumes a large amount of auxiliary materials. Therefore, there is an urgent need to propose a more efficient and cost-effective method. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides a method for preparing high-purity cobalt from crude cobalt hydroxide, comprising the following steps: S1. Obtain crude cobalt hydroxide, wherein the crude cobalt hydroxide comprises Co 30wt%~40wt%, Ni 0.1wt%~0.2wt%, Fe 0.5wt%~0.8wt%, Al 0.1wt%~0.2wt%, Ca 0.5wt%~1.0wt%, Mg 4wt%~6wt%, Mn 2wt%~4wt%, Cu 0.5wt%~1.5wt%, and Zn 0.1wt%~0.2wt%; S2. Add deionized water to the crude cobalt hydroxide to obtain a crude cobalt hydroxide slurry. Add excess concentrated sulfuric acid to the crude cobalt hydroxide slurry and stir to react. Then, introduce sulfur dioxide into it for selective reduction leaching to obtain cobalt leachate and manganese slag. S3. The pH of the cobalt leaching solution is adjusted to 6.0~7.0 using sodium bicarbonate for the first precipitation. After filtration, the first precipitate and the first filtrate are obtained. Sodium bicarbonate is added to the first filtrate in stages to adjust the pH for the second precipitation. After filtration, the second precipitate and the second filtrate are obtained. The second precipitate is washed and the second filtrate is purified to obtain a nickel-containing cobalt sulfate solution. S4. Obtain nickel removal resin and saturate it with cobalt sulfate of a preset concentration. S5. Pass the nickel-containing cobalt sulfate solution into the nickel-removing resin after cobalt saturation treatment to obtain first cobalt sulfate, pass the cobalt sulfate of the preset concentration to obtain nickel-containing cobalt sulfate residue, pass the first sulfuric acid to obtain second cobalt sulfate, pass the second sulfuric acid to obtain nickel sulfate, pass deionized water to obtain washing water, and combine the first cobalt sulfate and the second cobalt sulfate to obtain high-purity cobalt sulfate. S6. Using titanium-coated lead dioxide as the anode and cobalt starting sheet as the cathode, high-purity cobalt sulfate is used as the electrolyte solution for electrowinning to obtain a high-purity cobalt plate.

[0004] In step S2, the concentration of the crude cobalt hydroxide slurry is 20wt%~35wt%; the temperature of the selective reduction leaching is 65~90℃, the pH is 1~3, and the redox potential is 200~400mV.

[0005] In step S3, the temperature of the first precipitation and the second precipitation is 65~85℃, the first precipitation includes calcium carbonate, and the second precipitation includes magnesium carbonate. The second precipitation is specifically achieved when the pH of the first filtrate is less than 7.2, and the sodium bicarbonate is added at a flow rate of 1.5~2.5 L / (min·m). 3 When the pH is greater than or equal to 7.2 and less than 8.0, the flow rate of sodium bicarbonate added is 0.75~1.5 L / (min·m). 3 When the pH is greater than or equal to 8.0 and less than 8.2, the flow rate of sodium bicarbonate added is 0.15~0.3 L / (min·m). 3 When the pH reaches 8.2, stop adding sodium bicarbonate, and continue to keep warm and stir to allow the precipitated crystals to grow and partially desorb the adsorbed cobalt ions.

[0006] In step S3, the removal of impurities from the second filtrate specifically involves extracting the second filtrate with P204 extractant and then removing the oil to obtain the nickel-containing cobalt sulfate solution.

[0007] In step S4, the nickel removal resin is Dow M4195 chelating resin, and the exchange capacity of the nickel removal resin is 20~30 g / L.

[0008] In step S4, the concentration of cobalt in the pre-concentrated cobalt sulfate is 80~120g / L, the flow rate of the pre-concentrated cobalt sulfate is 5.0~15.0BV / h, and the total introduced volume matches the exchange capacity of the nickel removal resin.

[0009] In step S5, the concentration of the first sulfuric acid is 0.35~0.65 mol / L, and the concentration of the second sulfuric acid is 1.25~1.75 mol / L.

[0010] In step S5, the flow rate of the nickel-containing cobalt sulfate is 1.0~5.0 BV / h, and the total flow volume matches the exchange capacity of the nickel removal resin; the flow rate of the cobalt sulfate of the preset concentration is 0.1~0.5 BV / h, and the total flow volume matches the exchange capacity of the nickel removal resin; the flow rate of the first sulfuric acid is 0.1~0.5 BV / h, and the total flow volume matches the exchange capacity of the nickel removal resin; the flow rate of the second sulfuric acid is 0.5~1.5 BV / h, and the total flow volume matches the exchange capacity of the nickel removal resin; and the flow rate of the deionized water is 1.0~2.0 BV / h, and the total flow volume matches the exchange capacity of the nickel removal resin.

[0011] In step S5, the residual nickel-containing cobalt sulfate is recovered and used as nickel-containing cobalt sulfate to be treated. The concentration of the nickel sulfate is 25~40g / L. The washing water is recovered and used to prepare sulfuric acid. In step S6, the electrowinning time is 120 hours.

[0012] In step S6, the high-purity cobalt plate has a cobalt content of 99.99 wt% or higher and a cobalt recovery rate of 96.5% or higher.

[0013] This invention employs selective reduction leaching and segmented sodium bicarbonate precipitation to effectively reduce the concentration of manganese, calcium, and magnesium impurities in the cobalt leaching solution, thereby reducing the pressure and cost for subsequent impurity removal. Pre-saturation treatment with a preset concentration of cobalt sulfate significantly enhances the selective adsorption capacity of the nickel removal resin, reducing cobalt loss. Continuous processing using multiple processes creates a stable processing flow and allows for the recovery of effluent from each process, resulting in high production efficiency, high resin utilization, good cobalt-nickel separation, and excellent resource recovery. Detailed Implementation

[0014] The technical solutions described below in conjunction with the embodiments will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0015] S1. Obtain crude cobalt hydroxide, wherein the crude cobalt hydroxide has the following composition: Co 30wt%~40wt%, Ni 0.1wt%~0.2wt%, Fe 0.5wt%~0.8wt%, Al 0.1wt%~0.2wt%, Ca 0.5wt%~1.0wt%, Mg 4wt%~6wt%, Mn 2wt%~4wt%, Cu 0.5wt%~1.5wt%, and Zn 0.1wt%~0.2wt%. S2. Add deionized water to the crude cobalt hydroxide to obtain a crude cobalt hydroxide slurry. Add concentrated sulfuric acid to the crude cobalt hydroxide slurry and stir to react for a first time. Then, introduce sulfur dioxide into it for selective reduction leaching to obtain cobalt leachate and manganese slag. This invention utilizes selective reduction leaching to maximize the leaching of cobalt while simultaneously inhibiting the dissolution of manganese. The trivalent cobalt in crude cobalt hydroxide is poorly soluble in dilute sulfuric acid, but can be reduced to easily soluble divalent cobalt by introducing sulfur dioxide as a reducing agent. The manganese in the material mainly exists in the form of manganese dioxide. Although sulfur dioxide can also reduce manganese dioxide, its reaction kinetics are very slow between pH 1.5 and 2.5, and the generated divalent manganese will also undergo a disproportionation reaction with manganese dioxide to generate insoluble manganese hydroxide.

[0016] S3. The pH of the cobalt leaching solution is adjusted to 6.0~7.0 using sodium bicarbonate for the first precipitation. After filtration, the first precipitate and the first filtrate are obtained. Sodium bicarbonate is added to the first filtrate in stages to adjust the pH for the second precipitation. After filtration, the second precipitate and the second filtrate are obtained. The second precipitate is washed and the second filtrate is purified to obtain a nickel-containing cobalt sulfate solution. Although calcium ions in the leachate can be completely removed by subsequent P204 extraction, this increases the consumption of saponifying agents such as alkali during extraction and can easily lead to calcium slag blockage in the extraction tubes. Magnesium ions, on the other hand, cannot be removed in subsequent stages. Currently, precipitation is the most economical and simplest method for removing calcium and magnesium. Sodium bicarbonate has a slow hydrolysis characteristic, making pH control easy and avoiding localized over-alkaliness that could cause massive nucleation and precipitation of cobalt carbonate. This is unmatched by strong alkaline precipitants such as alkali and sodium carbonate. Furthermore, sodium bicarbonate is more cost-effective. Since the pH ranges for calcium and magnesium ion precipitation differ, stepwise pH adjustment with varying speeds to remove calcium and magnesium is more advantageous than a one-step method. In addition, during the sodium bicarbonate pH adjustment precipitation process, magnesium ions combine with carbonate ions to form magnesium carbonate precipitate very quickly, requiring a large amount of sodium bicarbonate. In the reaction phase from pH 7.2 to 8.0, magnesium ions rapidly consume most of the precipitant in the solution. Although cobalt ions tend to precipitate at this pH, they form cobalt carbonate crystals very slowly, requiring an induction period. Before cobalt ions can form crystal nuclei, magnesium ions have already taken all the carbonate ions. Throughout the rapid precipitation of magnesium ions, cobalt ions remain in a supersaturated state. Although the cobalt concentration is high, because the carbonate ions are rapidly consumed by magnesium ions and cobalt carbonate nucleation is slow, they can only remain in the solution as cobalt ions, resulting in minimal cobalt loss. Continued heating and stirring can allow the crystals of the second precipitate to grow and partially release the adsorbed cobalt ions. Therefore, step S3 of this invention removes calcium through the first precipitation and removes magnesium through the second precipitation by controlling the flow rate of sodium bicarbonate at different pH values, thus achieving calcium and magnesium removal with minimal cobalt loss.

[0017] S4. Obtain nickel removal resin and saturate it with cobalt sulfate of a preset concentration. Step S4 of this invention has the following effects: 1. It significantly improves the selective adsorption capacity for trace nickel. Under high-concentration cobalt solution conditions, the active sites of the resin are first occupied by cobalt ions. When nickel-containing cobalt sulfate solution is introduced, because the affinity of the nickel-chelating resin for nickel ions is much greater than that for cobalt ions, nickel ions will selectively replace the cobalt ions already adsorbed on the resin; 2. It significantly reduces cobalt loss. In the direct adsorption method, nickel ions and cobalt ions compete for the limited vacancies in the resin. Although the resin prefers nickel ions, a large number of cobalt ions will still be adsorbed, especially in the early and late stages of resin adsorption, which leads to cobalt loss due to cobalt pre-saturation. The resin after the process is essentially free of vacancies, and the adsorption of nickel ions is mainly achieved by displacing cobalt ions. The displaced cobalt ions directly enter the effluent, with almost no additional cobalt loss. 3. It improves the effective working adsorption capacity of the resin because impurity ions need to diffuse through the entire resin bed to be adsorbed. Pre-saturation treatment makes the entire resin bed an effective working area, and nickel ions can undergo a displacement reaction from the inlet. 4. The effluent quality is more stable, and the displacement reaction is highly selective. Before the breakthrough point, the nickel concentration in the effluent can remain stable at a very low level for a long time. Once breakthrough occurs, the nickel concentration rises rapidly, and the breakthrough point is easier to predict and control.

[0018] S5. Pass the nickel-containing cobalt sulfate solution into the nickel-removing resin after cobalt saturation treatment to obtain first cobalt sulfate, then pass cobalt sulfate of the preset concentration to obtain nickel-containing cobalt sulfate residue, then pass first sulfuric acid to obtain second cobalt sulfate, then pass second sulfuric acid to obtain nickel sulfate, then pass deionized water to obtain washing water, and combine the first cobalt sulfate and the second cobalt sulfate to obtain high-purity cobalt sulfate.

[0019] In some embodiments of the present invention, step S5 can be performed by multiple nickel removal chelating resin columns connected in series, and a cycle can be formed.

[0020] S6. Using titanium-coated lead dioxide as the anode and cobalt starting sheet as the cathode, high-purity cobalt sulfate is used as the electrolyte solution for electrowinning to obtain a high-purity cobalt plate.

[0021] The crude cobalt hydroxide used in the embodiments and comparative examples of this invention comprises: Co 36.2wt%, Ni 0.15wt%, Fe 0.66wt%, Al 0.12wt%, Ca 0.8wt%, Mg 5.1wt%, Mn 2.9wt%, Cu 0.9%, and Zn 0.16wt%.

[0022] Example 1 A method for preparing high-purity cobalt from crude cobalt hydroxide includes the following steps: S1. Obtain crude cobalt hydroxide; S2. Add deionized water to the crude cobalt hydroxide to obtain a crude cobalt hydroxide slurry. Add concentrated sulfuric acid to the crude cobalt hydroxide slurry and stir for 2 hours. Then, introduce sulfur dioxide into it for selective reduction leaching to obtain cobalt leachate and manganese slag. The selective reduction leaching temperature is 65℃, the pH is 3.0, and the redox potential is 400mV. S3. The pH of the cobalt leaching solution is adjusted to 6 using sodium bicarbonate for the first precipitation and then filtered to obtain a first precipitate and a first filtrate. The pH of the first filtrate is further adjusted using sodium bicarbonate for a second precipitation. When the pH of the first filtrate is less than 7.2, the flow rate of sodium bicarbonate added is 2.5 L / (min·m). 3 When the pH is greater than or equal to 7.2 and less than 8.0, the sodium bicarbonate is added at a flow rate of 1.5 L / (min·m). 3 When the pH is greater than or equal to 8.0 and less than 8.2, the sodium bicarbonate addition rate is 0.3 L / (min·m). 3 When the pH reaches 8.2, stop adding sodium bicarbonate, continue to keep warm and stir, filter to obtain the second precipitate and the second filtrate, remove impurities from the second filtrate to obtain a nickel-containing cobalt sulfate solution, the temperature of the first precipitation and the second precipitation is 65℃; S4. Obtain nickel removal resin and saturate it with cobalt sulfate of a preset concentration of 80 g / L and a flow rate of 5.0 BV / h. The nickel removal resin is Dow M4195 chelating resin with an adsorption capacity of 20 g / L. S5. The nickel-containing cobalt sulfate solution is passed into the nickel-removing resin after cobalt saturation treatment at a flow rate of 5.0 BV / h to obtain the first cobalt sulfate. Then, cobalt sulfate of a preset concentration is passed into the solution at a flow rate of 0.1 BV / h to obtain the nickel-containing cobalt sulfate residue. Then, first sulfuric acid is passed into the solution at a flow rate of 0.1 BV / h to obtain the second cobalt sulfate. Then, second sulfuric acid is passed into the solution at a flow rate of 0.5 BV / h to obtain nickel sulfate. Then, deionized water is passed into the solution at a flow rate of 1.0 BV / h to obtain washing water. The first cobalt sulfate and the second cobalt sulfate are combined to obtain high-purity cobalt sulfate.

[0023] S6. Using titanium-coated lead dioxide as the anode and cobalt starting sheet as the cathode, high-purity cobalt sulfate is used as the electrolyte solution for electrowinning for 120 hours to obtain a high-purity cobalt plate.

[0024] Example 2 Unlike Example 1, in step S2, the concentrated sulfuric acid stirring reaction time is 3 hours, the selective reduction leaching temperature is 90°C, the pH is 1.0, and the redox potential is 200 mV. In step S3, the pH of the first precipitation is 7.0. During the second precipitation, when the pH of the first filtrate is less than 7.2, the sodium bicarbonate is added at a flow rate of 1.5 L / (min·m). 3 When the pH is greater than or equal to 7.2 and less than 8.0, the sodium bicarbonate addition rate is 0.75 L / (min·m). 3 When the pH is greater than or equal to 8.0 and less than 8.2, the sodium bicarbonate addition rate is 0.15 L / (min·m). 3 The temperatures for both the first and second precipitation were 85℃. In step S4, the concentration of cobalt sulfate is preset to be 120 g / L, and the flow rate is 15.0 BV / h; In step S5, the flow rate of nickel-containing cobalt sulfate is 1.0 BV / h, the flow rate of cobalt sulfate with a preset concentration is 0.5 BV / h, the flow rate of the first sulfuric acid is 0.5 BV / h, the flow rate of the second sulfuric acid is 1.5 BV / h, and the flow rate of deionized water is 2.0 BV / h.

[0025] Example 3 Unlike Example 2, in step S2, the concentrated sulfuric acid stirring reaction time is 2.5 h, the selective reduction leaching temperature is 80 °C, the pH is 1.5, and the redox potential is 300 mV.

[0026] Example 4 Unlike Example 3, in step S3, the pH of the first precipitation is 6.8, and during the second precipitation, when the pH of the first filtrate is less than 7.2, the sodium bicarbonate is added at a flow rate of 2.0 L / (min·m). 3 When the pH rises to 7.2-8.0, sodium bicarbonate is added at a flow rate of 1.0 L / (min·m). 3 When the pH rises to 8.0~8.2, sodium bicarbonate is added at a flow rate of 0.2 L / (min·m). 3 The temperatures for both the first and second precipitation were 80℃.

[0027] Comparative Example 1 Unlike Example 1, in step S2, the selective reduction leaching temperature is 60°C, the pH is 4, and the redox potential is 500mV.

[0028] Comparative Example 2 Unlike Example 1, in step S2, the selective reduction leaching temperature is 100°C, the pH is 0.5, and the redox potential is 100mV.

[0029] Comparative Example 3 Unlike Example 1, in step S3, the pH of the first precipitation is 4, and the second precipitation does not involve stepwise variable-rate addition of sodium bicarbonate, but is directly added at a rate of 2.5 L / (min·m). 3 Adjust the pH of the first filtrate to 8.2 by adjusting the flow rate. The temperature for both the first and second precipitation is 60°C.

[0030] Comparative Example 4 Unlike Example 1, step S3 involves a single-step precipitation instead of a fractional precipitation, with sodium bicarbonate used to adjust the pH to 8.2.

[0031] Comparative Example 5 Unlike Example 1, in step S3, sodium hydroxide is used to adjust the pH.

[0032] Comparative Example 6 Unlike Example 1, in step S4, the concentration of cobalt sulfate at the preset concentration is 70 g / L and the flow rate is 4 BV / h.

[0033] Comparative Example 7 Unlike Example 1, in step S4, cobalt saturation treatment with a preset concentration of cobalt sulfate is not used.

[0034] Comparative Example 8 Unlike Example 1, in step S5, the nickel-containing cobalt sulfate solution is passed into the nickel-removing resin after cobalt saturation treatment at a flow rate of 6.0 BV / h to obtain the first cobalt sulfate. Then, cobalt sulfate of a preset concentration is passed into the solution at a flow rate of 0.7 BV / h to obtain the nickel-containing cobalt sulfate residue. Then, first sulfuric acid is passed into the solution at a flow rate of 0.7 BV / h to obtain the second cobalt sulfate. Then, second sulfuric acid is passed into the solution at a flow rate of 0.1 BV / h to obtain nickel sulfate. Then, deionized water is passed into the solution at a flow rate of 0.5 BV / h to obtain washing water. The first cobalt sulfate and the second cobalt sulfate are combined to obtain high-purity cobalt sulfate.

[0035] The test results of the cobalt plates prepared in the examples and comparative examples are shown in Table 1; Table 1. Test results of cobalt plates prepared in the examples and comparative examples. This invention employs selective reduction leaching and segmented sodium bicarbonate precipitation to effectively reduce the concentration of manganese, calcium, and magnesium impurities in the cobalt leaching solution, thereby reducing the pressure and cost for subsequent impurity removal. Pre-saturation treatment with a preset concentration of cobalt sulfate significantly enhances the selective adsorption capacity of the nickel removal resin, reducing cobalt loss. Continuous processing using multiple processes creates a stable processing flow and allows for the recovery of effluent from each process, resulting in high production efficiency, high resin utilization, good cobalt-nickel separation, and excellent resource recovery.

[0036] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for preparing high-purity cobalt from crude cobalt hydroxide, characterized in that, Includes the following steps: S1. Obtain crude cobalt hydroxide, wherein the crude cobalt hydroxide comprises Co 30wt%~40wt%, Ni 0.1wt%~0.2wt%, Fe 0.5wt%~0.8wt%, Al 0.1wt%~0.2wt%, Ca 0.5wt%~1.0wt%, Mg 4wt%~6wt%, Mn 2wt%~4wt%, Cu 0.5wt%~1.5wt%, and Zn 0.1wt%~0.2wt%; S2. Add deionized water to the crude cobalt hydroxide to obtain a crude cobalt hydroxide slurry. Add excess concentrated sulfuric acid to the crude cobalt hydroxide slurry and stir to react. Then, introduce sulfur dioxide into it for selective reduction leaching to obtain cobalt leachate and manganese slag. S3. The pH of the cobalt leaching solution is adjusted to 6.0~7.0 using sodium bicarbonate for the first precipitation. After filtration, the first precipitate and the first filtrate are obtained. Sodium bicarbonate is added to the first filtrate in stages to adjust the pH for the second precipitation. After filtration, the second precipitate and the second filtrate are obtained. The second precipitate is washed and the second filtrate is purified to obtain a nickel-containing cobalt sulfate solution. S4. Obtain nickel removal resin and saturate it with cobalt sulfate of a preset concentration. S5. Pass the nickel-containing cobalt sulfate solution into the nickel-removing resin after cobalt saturation treatment to obtain first cobalt sulfate, pass the cobalt sulfate of the preset concentration to obtain nickel-containing cobalt sulfate residue, pass the first sulfuric acid to obtain second cobalt sulfate, pass the second sulfuric acid to obtain nickel sulfate, pass deionized water to obtain washing water, and combine the first cobalt sulfate and the second cobalt sulfate to obtain high-purity cobalt sulfate. S6. Using titanium-coated lead dioxide as the anode and cobalt starting sheet as the cathode, high-purity cobalt sulfate is used as the electrolyte solution for electrowinning to obtain a high-purity cobalt plate.

2. The method for preparing high-purity cobalt from crude cobalt hydroxide according to claim 1, characterized in that, In step S2, the concentration of the crude cobalt hydroxide slurry is 20wt%~35wt%; the temperature of the selective reduction leaching is 65~90℃, the pH is 1~3, and the redox potential is 200~400mV.

3. The method for preparing high-purity cobalt from crude cobalt hydroxide according to claim 1, characterized in that, In step S3, the temperature of the first precipitation and the second precipitation is 65~85℃, the first precipitation includes calcium carbonate, and the second precipitation includes magnesium carbonate. The second precipitation is specifically achieved when the pH of the first filtrate is less than 7.2, and the sodium bicarbonate is added at a flow rate of 1.5~2.5 L / (min·m). 3 When the pH is greater than or equal to 7.2 and less than 8.0, the flow rate of sodium bicarbonate added is 0.75~1.5 L / (min·m). 3 When the pH is greater than or equal to 8.0 and less than 8.2, the flow rate of sodium bicarbonate added is 0.15~0.3 L / (min·m). 3 Once the pH reaches 8.2, stop adding sodium bicarbonate and continue stirring while maintaining the temperature.

4. The method for preparing high-purity cobalt from crude cobalt hydroxide according to claim 1, characterized in that, In step S3, the removal of impurities from the second filtrate specifically involves extracting the second filtrate with P204 extractant to remove impurities, and then removing oil to obtain the nickel-containing cobalt sulfate solution.

5. The method for preparing high-purity cobalt from crude cobalt hydroxide according to claim 1, characterized in that, In step S4, the nickel removal resin is Dow M4195 chelating resin, and the exchange capacity of the nickel removal resin is 20~30g / L.

6. The method for preparing high-purity cobalt from crude cobalt hydroxide according to claim 1, characterized in that, In step S4, the concentration of cobalt in the preset concentration of cobalt sulfate is 80~120g / L, the flow rate of the preset concentration of cobalt sulfate is 5.0~15.0BV / h, and the total introduced volume matches the exchange capacity of the nickel removal resin.

7. The method for preparing high-purity cobalt from crude cobalt hydroxide according to claim 1, characterized in that, In step S5, the concentration of the first sulfuric acid is 0.35~0.65 mol / L, and the concentration of the second sulfuric acid is 1.25~1.75 mol / L.

8. The method for preparing high-purity cobalt from crude cobalt hydroxide according to claim 6, characterized in that, In step S5, the flow rate of the nickel-containing cobalt sulfate is 1.0~5.0 BV / h, and the total flow volume matches the exchange capacity of the nickel removal resin. The flow rate of the cobalt sulfate with the preset concentration is 0.1~0.5 BV / h, and the total flow volume matches the exchange capacity of the nickel removal resin. The flow rate of the first sulfuric acid is 0.1~0.5 BV / h, and the total flow volume matches the exchange capacity of the nickel removal resin. The flow rate of the second sulfuric acid is 0.5~1.5 BV / h, and the total flow volume matches the exchange capacity of the nickel removal resin. The flow rate of the deionized water is 1.0~2.0 BV / h, and the total flow volume matches the exchange capacity of the nickel removal resin.

9. The method for preparing high-purity cobalt from crude cobalt hydroxide according to claim 1, characterized in that, In step S5, the residual nickel-containing cobalt sulfate is recovered and used as nickel-containing cobalt sulfate to be treated. The concentration of the nickel sulfate is 25~40g / L. The washing water is recovered and used to prepare sulfuric acid. In step S6, the electrowinning time is 120 hours.

10. The method for preparing high-purity cobalt from crude cobalt hydroxide according to claim 1, characterized in that, In step S6, the high-purity cobalt plate has a cobalt content of 99.99 wt% or higher and a cobalt recovery rate of 96.5% or higher.

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