JP2023161557A - Method of producing cobalt sulfate - Google Patents

Abstract

To provide a method of producing highly pure cobalt sulfate without using an electrolytic process.SOLUTION: Provided is a production method of obtaining cobalt sulfate by removing impurities from a cobalt chloride solution containing one or more impurities of copper, zinc, manganese, calcium, and magnesium, the production method including (1) in a preceding process, a copper removing step S1 of adding a sulfidizing agent to the cobalt chloride solution to form a precipitate of copper sulfide, and separating and removing the precipitate and a first solvent extraction step S2 of making the cobalt chloride solution contact with an organic solvent containing alkyl phosphate extractants and making zinc, manganese, and calcium to be extracted to separate and remove them, and (2) in a subsequent process, a second solvent extraction step S3 of adjusting the pH of the cobalt chloride solution that has passed through the preceding process to 4.0 to 7.0, and then making the cobalt chloride solution contact with an organic solvent containing carboxylic acid extractants that contain 0.05 weight% or more of a fat-soluble antioxidant, and then back-extracting the cobalt with sulfuric acid to obtain a cobalt sulfate solution.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for producing cobalt sulfate. More specifically, the present invention relates to a method for producing highly pure cobalt sulfate by removing impurity elements contained in a cobalt chloride solution.

Cobalt is a valuable metal that is widely used in industrial applications as a raw material for magnetic materials and lithium ion secondary batteries, as well as as an additive element for special alloys. In particular, recently, lithium-ion secondary batteries have been widely used as batteries for mobile devices and electric vehicles, and the demand for cobalt has increased rapidly. However, since most cobalt is produced as a byproduct of nickel and copper smelting, separation from impurities such as nickel and copper is an important elemental technology in the production of cobalt.

For example, when recovering cobalt as a by-product in nickel hydrometallurgy, the raw material is first leached or extracted into a solution using mineral acids or oxidizing agents, or subjected to dissolution treatment to obtain a solution containing nickel and cobalt. will be attached. Furthermore, nickel and cobalt contained in the obtained acidic solution are often separated and recovered by conventionally known methods such as solvent extraction using various organic extractants.
However, the obtained cobalt solution often contains various impurities derived from the raw materials to be treated.

Therefore, it is necessary to further remove impurity elements such as manganese, copper, zinc, calcium, and magnesium from the cobalt solution after nickel has been separated and recovered by the above solvent extraction method.
Moreover, in order to manufacture high-purity cobalt products with low impurity content, impurity elements in the cobalt solution separated and recovered from the cobalt-containing nickel solution must be removed in advance, and then cobalt can be added through an electrolytic process or crystallization. It was necessary to commercialize it.

As a method for removing impurity elements in a cobalt solution, there are conventional techniques described in Patent Documents 1 and 2.
Patent Document 1 discloses that (1) a sulfiding agent is added to a cobalt solution, the oxidation-reduction potential (ORP) (Ag/AgCl electrode reference) is adjusted to 50 mV or less and the pH is adjusted to 0.3 to 2.4, and sulfurization is carried out. Copper removal step to obtain copper precipitate and copper-removed purified liquid, (2) Add an oxidizing agent and a neutralizing agent to the copper-reduced purified liquid, and adjust the redox potential (Ag/AgCl electrode reference) to 950 to 1050 mV and pH. 2.4 to 3.0 to obtain a manganese precipitate and a purified demanganized liquid; (3) using an alkyl phosphoric acid as an extractant in the purified purified liquid demanganized; A method for purifying a cobalt solution is disclosed that includes a solvent extraction step to extract and separate zinc, calcium, and trace impurities.
Patent Document 2 discloses that a cobalt chloride solution with a hydrochloric acid concentration of 2 to 6 mol/L is brought into contact with an anion exchange resin to form a complex with a distribution coefficient of iron and zinc that is larger than that of the cobalt chloride complex with respect to the anion exchange resin. , a technique for adsorbing and separating metal impurities such as tin is described.

The solvent extraction method using alkyl phosphoric acid as an extractant described in Patent Document 1 has high separation performance for zinc and calcium. However, in the case of a cobalt chloride solution with a hydrochloric acid concentration of 2 to 6 mol/L, the ion exchange method using an anion exchange resin or the solvent extraction method using an amine extractant is better than the above solvent extraction method using alkyl phosphoric acid. It has higher zinc and cobalt separation performance.
Furthermore, when removing a very small amount of zinc from a cobalt chloride solution, the ion exchange method is more efficient and economical because the process and operation are simpler.

From this perspective, a method combining the purification method of Patent Document 1 and the separation technique of Patent Document 2 has been proposed as a method for removing these impurity elements from a cobalt chloride solution containing manganese, copper, and zinc. (For example, Patent Document 3).
The method for producing high-purity cobalt chloride described in paragraph 0022 of Patent Document 3 includes a solvent extraction step for separating nickel and cobalt, a demanganization step for removing manganese, a decoppering step for removing copper, and a dezincing step for removing zinc. and an electrolytic process.
In the dezincing step, the aqueous cobalt chloride solution obtained in the decoppering step is brought into contact with an anion exchange resin to adsorb and remove zinc. In the electrolytic process, metallic cobalt (also called electric cobalt) is produced using the high-purity cobalt chloride aqueous solution obtained in the dezincing process as an electrolytic supply liquid.

On the other hand, as mentioned above, the demand for cobalt as a raw material for lithium ion secondary batteries has recently increased, and cobalt sulfate solutions or cobalt sulfate crystals are desired.
In order to obtain cobalt sulfate crystals from metallic cobalt obtained by the conventional technique of Patent Document 3, metallic cobalt is dissolved in sulfuric acid to obtain a cobalt sulfate solution, and this solution is further crystallized to obtain cobalt sulfate crystals. Obtainable. However, when this manufacturing method is used, the manufacturing cost increases due to an increase in the number of steps and drug costs. In addition, plate-shaped metal cobalt has a slow dissolution rate in sulfuric acid, as is used in corrosion-resistant alloys, and in order to dissolve it in a short time, it is necessary to turn the plate-shaped metal cobalt into powder through atomization treatment, etc. .

For this reason, a method of obtaining a cobalt sulfate solution directly from a cobalt chloride solution without going through metal cobalt has been desired.

Japanese Patent Application Publication No. 2004-285368 Japanese Patent Application Publication No. 2001-020021 Japanese Patent Application Publication No. 2020-19664

The present invention has been proposed in view of the above circumstances, and provides a method for producing highly pure cobalt sulfate by separating impurities and cobalt from a cobalt chloride solution containing impurities without using an electrolytic process. With the goal.

The method for producing cobalt sulfate of the first invention is a production method for obtaining cobalt sulfate by removing impurities from a cobalt chloride solution containing one or more impurities of copper, zinc, manganese, calcium, and magnesium, comprising: The method includes a copper removal step in which a sulfiding agent is added to the cobalt chloride solution to form a precipitate of copper sulfide and then separated and removed, and an organic solvent containing an alkyl phosphate extractant is brought into contact with the cobalt chloride solution. It includes a first solvent extraction step in which zinc, manganese and calcium are extracted and separated in an organic solvent, and the latter step is to adjust the pH of the cobalt chloride solution that has passed through the first step to 4.0 to 7.0. , and then brought into contact with an organic solvent containing a carboxylic acid extractant containing 0.05% by weight or more of a fat-soluble antioxidant, and after allowing the organic solvent to extract cobalt, the cobalt is back-extracted with sulfuric acid. It is characterized by comprising a second solvent extraction step to obtain a cobalt solution.
A method for producing cobalt sulfate according to a second aspect of the invention is characterized in that, in the first aspect, the first step is performed in the order of the copper removal step and the first solvent extraction step.
A method for producing cobalt sulfate according to a third aspect of the invention is characterized in that, in the first aspect, the first step is performed in the order of the first solvent extraction step and the copper removal step.
The method for producing cobalt sulfate according to the fourth invention is characterized in that, in the first invention, the cobalt sulfate solution obtained through the second solvent extraction step is subjected to a crystallization step to obtain crystals of cobalt sulfate.
A method for producing cobalt sulfate according to a fifth invention, in the first, second, third or fourth invention, includes adding an oxidizing agent and a neutralizing agent to a cobalt chloride solution to which a sulfiding agent has been added in the copper removal step. It is characterized by adjusting the redox potential to -100 to 200 mV (based on Ag/AgCl electrodes) and adjusting the pH to 1.3 to 3.0.
The method for producing cobalt sulfate according to the sixth invention is characterized in that in the first, second, third, or fourth invention, the alkyl phosphate extractant in the first solvent extraction step is bis(2-ethylhexyl hydrogen phosphate). The method is characterized in that the pH of the cobalt chloride solution from which copper has been removed is adjusted to 1.5 to 3.0 and subjected to solvent extraction using the extractant to extract impurity elements into an organic solvent. .
A method for producing cobalt sulfate according to a seventh aspect of the invention is, in the first, second, third, or fourth aspect, subsequent to the extraction step in the second solvent extraction step, a sulfuric acid solution is brought into contact with the organic solvent from which cobalt has been extracted. The method is characterized in that a back extraction step is performed in which the pH is adjusted to 2.0 to 4.5 and cobalt is back extracted into a sulfuric acid solution.
The method for producing cobalt sulfate according to the eighth invention is characterized in that in the first invention, the fat-soluble antioxidant is a phenolic antioxidant, an amine antioxidant, a sulfur-based antioxidant, a phosphorus-based antioxidant, a phenol-based antioxidant, or a phenolic antioxidant. It is characterized by being either a combination of a sulfur-based antioxidant and a sulfur-based antioxidant, or a combination of a phenol-based antioxidant and a phosphorus-based antioxidant.

According to the first invention, copper, zinc, manganese, and calcium can be removed from a cobalt chloride solution containing impurities through the decopper removal step and the first solvent extraction step included in the first step, and the second solvent extraction step included in the second step. Magnesium can be removed through the process. Therefore, high purity cobalt sulfate can be produced without using an electrolytic process. In addition, by containing 0.05% by weight or more of a fat-soluble antioxidant in the organic solvent in the extractant, it is possible to suppress the generation of oxidized trivalent cobalt ions, and the removal of cobalt during the back extraction process. Collection efficiency can be maintained at a high level.
According to the second invention, copper, zinc, manganese, and calcium can be separated and removed from a cobalt chloride solution containing impurities by performing the copper removal step and the first solvent extraction step in that order. By separating and removing magnesium in the process, a highly pure cobalt sulfate solution free of impurities can be obtained.
According to the third invention, copper, zinc, manganese, and calcium can be separated and removed by performing the first solvent extraction step and the copper removal step in that order from the cobalt chloride solution containing impurities. By separating and removing magnesium in the process, a highly pure cobalt sulfate solution free of impurities can be obtained.
According to the fourth invention, highly pure cobalt sulfate crystals can be obtained from the cobalt sulfate solution by further performing a crystallization step.
According to the fifth invention, by adjusting the redox potential and pH within appropriate ranges, copper sulfide can be precipitated and sufficiently removed from the cobalt chloride solution, and co-precipitation of cobalt can be suppressed.
According to the sixth invention, by adjusting the pH to 1.5 to 3.0, zinc, manganese, and calcium can be extracted and separated from cobalt while leaving cobalt in the aqueous phase.
According to the seventh invention, even if the pH is adjusted to a low pH side of 4.0 to 7.0, cobalt can be extracted by contacting with an organic solvent containing a carboxylic acid extractant. Furthermore, since extraction can be performed at a low pH, precipitates such as hydroxides are less likely to be generated, and as a result, crud is less likely to be formed, resulting in stable operation.
According to the eighth invention, the fat-soluble antioxidants used are phenolic antioxidants, amine antioxidants, sulfur-based antioxidants, phosphorus-based antioxidants, phenolic antioxidants, and sulfur-based antioxidants. By using one of the combinations of phenolic oxidizing agents and phosphorous antioxidants, the quality of wastewater can be improved, and the production cost of cobalt sulfate is also lowered due to its low market price and easy availability. do.

1 is a principle diagram of a method for producing cobalt sulfate according to the present invention. 1 is a process diagram showing a method for producing cobalt sulfate according to a first embodiment of the present invention. FIG. 3 is a detailed process diagram showing a method for producing cobalt sulfate shown in FIG. 2. FIG. 4 is a detailed process diagram of the first solvent extraction step S2 shown in FIG. 3. FIG. 4 is a detailed process diagram of the second solvent extraction step S3 shown in FIG. 3. FIG. FIG. 6 is a process diagram showing a method for producing cobalt sulfate according to a second embodiment of the present invention. 7 is a detailed process diagram showing the method for producing cobalt sulfate shown in FIG. 6. FIG. 8 is a detailed process diagram of the first solvent extraction step S2 shown in FIG. 7. FIG. 8 is a detailed process diagram of the second solvent extraction step S3 shown in FIG. 7. FIG.

Hereinafter, specific embodiments of the present invention will be described in detail. Note that the present invention is not limited to the following embodiments, and various changes can be made without departing from the gist of the present invention.

(Basic principle of the present invention)
The basic principle of the method for producing cobalt sulfate according to the present invention will be explained based on FIG.
The present invention is a production method for obtaining cobalt sulfate by removing impurities from a cobalt chloride solution containing one or more impurities of copper, zinc, manganese, calcium, and magnesium, comprising:
(1) The first step includes a copper removal step S1 in which a sulfiding agent is added to the cobalt chloride solution to form a precipitate of copper sulfide and then separated and removed, and an organic compound containing an alkyl phosphate extractant in the cobalt chloride solution A first solvent extraction step S2 of contacting a solvent and extracting and separating zinc, manganese and calcium with the organic solvent,
(2) In the second step, the pH of the cobalt chloride solution that has passed through the first step is adjusted to 4.0 to 7.0, and then an organic compound containing a carboxylic acid extractant containing 0.05% by weight or more of an antioxidant is It is characterized by comprising a second solvent extraction step S3 of contacting with a solvent, causing the organic solvent to extract cobalt, and then back-extracting the cobalt with sulfuric acid to obtain a cobalt sulfate solution.
The first step may be performed in the order of the copper removal step S1 and the first solvent extraction step S2, or may be performed in the order of the first solvent extraction step S2 and the copper removal step S1. . The second solvent extraction step S3 included in the latter step is executed after the first step.

In the present invention, after each of the steps S1 to S3, a crystallization step S4 is performed to precipitate crystals from a cobalt sulfate solution, if necessary. By performing the crystallization step S4, cobalt sulfate crystals can be obtained by precipitating crystals from the solution.

In the present invention, after the first solvent extraction step S2 and/or after the second solvent extraction step S3, a step of subjecting the liquid to an oil-water separation device such as an activated carbon column in order to separate and remove organic components mixed into the liquid. may be added.

The cobalt chloride solution used as a starting material in the present invention contains one or more of copper, zinc, manganese, calcium, and magnesium as impurity elements. Application of the present invention is not limited to any cobalt chloride solution containing such impurities, but in particular, in the solvent extraction process of nickel smelting, a nickel solution containing cobalt is extracted with an alkyl phosphate extractant or It is suitably applied to a cobalt chloride solution after nickel has been separated and recovered using an amine extractant.

According to the present invention, from a cobalt chloride solution, copper is removed by producing a copper sulfide precipitate in the copper removal step S1, zinc, manganese and calcium are separated and removed in the first solvent extraction step S2, and the second solvent In the extraction step S3, magnesium can be separated and removed to obtain a highly pure cobalt sulfate solution. Therefore, a high purity cobalt sulfate solution can be directly produced by separating impurities and cobalt without using an electrolytic process.

(First embodiment)
A first embodiment of the method for producing cobalt sulfate will be described based on FIGS. 2 to 5. FIG. 2 is a diagram showing all steps in the first embodiment, and FIG. 3 shows details of each step S1 to S3 shown in FIG. 2.
In the first embodiment, as shown in FIG. 2, in the first step, the copper removal step S1 is first performed, and then the first solvent extraction step S2 is performed in this order.

(Copper removal process S1)
The copper removal step S1 will be explained based on FIG. 3.
The copper removal step S1 is performed by adding a sulfiding agent to a cobalt chloride solution containing one or more impurities of copper, zinc, manganese, calcium, and magnesium as a starting material. Further, an oxidizing agent and a neutralizing agent are added to adjust the redox potential of the cobalt chloride solution to -100 to 200 mV (based on Ag/AgCl electrode) and the pH to 1.3 to 3.0.
Through this step, a copper sulfide precipitate is generated and separated from the cobalt chloride solution, and a cobalt chloride solution from which copper is removed can be obtained.

Copper in the cobalt chloride solution is removed from the solution by forming a copper sulfide precipitate according to Formula 1, Formula 2, or Formula 3 below.
CuCl ₂ +H ₂ S→CuS↓+2HCl... (Formula 1)
CuCl ₂ +Na ₂ S→CuS↓+2NaCl... (Formula 2)
CuCl ₂ +NaHS→CuS↓+NaCl+HCl...(Formula 3)

In the copper removal step S1, if the redox potential of the cobalt chloride solution is adjusted to -100 to 200 mV (Ag/AgCl electrode reference) and the pH is adjusted to 1.3 to 3.0, copper is removed as sulfide. Co-precipitation of cobalt can be sufficiently removed and co-precipitation of cobalt can be suppressed.
If the redox potential exceeds 200 mV, copper in the solution will not be removed sufficiently, and if the redox potential is less than -100 mV, the amount of coprecipitated cobalt will increase, which is not preferable. Furthermore, if the pH is less than 1.3, copper in the solution will not be removed sufficiently and the filterability of the generated sulfide precipitate will deteriorate. If the pH exceeds 3.0, the amount of cobalt co-precipitation increases as copper is removed, which is not preferable.

The above-mentioned redox potential can be adjusted by adjusting the amount of the sulfiding agent added. The sulfurizing agent is not particularly limited, but hydrogen sulfide gas, sodium sulfide, sodium hydrosulfide crystals, aqueous solutions, and the like can be used.
Further, when hydrogen sulfide or sodium hydrogen sulfide is used as the sulfurizing agent, the above pH adjustment is performed by adjusting the amount of the sulfurizing agent and adding a neutralizing agent. The neutralizing agent is not particularly limited, and alkali salts such as sodium hydroxide, calcium hydroxide, sodium carbonate, and cobalt carbonate can be used. Furthermore, if the redox potential becomes lower than a desired value due to the addition of the sulfurizing agent, it can be adjusted by adding an oxidizing agent. For example, it can be adjusted by introducing air into the solution and stirring it, or by adding a hydrogen peroxide solution.

(First solvent extraction step S2)
The first solvent extraction step S2 will be explained based on FIGS. 3 and 4.
The first solvent extraction step S2 is a step of bringing an organic solvent containing an alkyl phosphate extractant into contact with the cobalt chloride solution that has passed through the copper removal step S1, and extracting and separating zinc, manganese, and calcium with the organic solvent. It is.

As the organic solvent, an alkyl phosphate extractant diluted with a diluent is used. As alkyl phosphate extractants, bis(2-ethylhexyl) hydrogen phosphate (trade name D2EHPA), 2-ethylhexyl (2-ethylhexyl)phosphonate (trade name PC-88A), di(2,4,4-trimethyl (pentyl) phosphinic acid (trade name: CYANEX272). Among these, when separating zinc, manganese and calcium from a cobalt chloride solution from which copper has been removed, it is preferable to use bis(2-ethylhexyl) hydrogen phosphate as an extractant, as it has high separability from cobalt.

The diluent is not particularly limited as long as it can dissolve the extractant. As the diluent, for example, a naphthenic solvent or an aromatic solvent can be used. The concentration of the extractant is preferably adjusted to 10 to 60% by volume, more preferably 20 to 50% by volume. When the concentration of the extractant is within this range, both impurity elements with a high concentration and impurity elements with a low distribution ratio (element concentration in organic/element concentration in solution) can be sufficiently extracted. On the other hand, if the concentration of the extractant is less than 10%, impurity elements with a high concentration or impurity elements with a low distribution ratio cannot be sufficiently extracted and tend to remain in the cobalt chloride solution. Moreover, when the concentration of the extractant exceeds 60%, the viscosity of the organic solvent increases, and the phase separation property of the organic solvent (organic phase) and cobalt chloride solution (aqueous phase) after the extraction operation deteriorates.

Acidic extractants such as alkyl phosphate extractants extract metal ions by replacing -H in the extractant with cations in the aqueous phase to form metal salts, as shown in formula 4. It is an extractant that In general, as the pH increases, metal ions are more likely to be extracted into the organic phase, and as the pH is lowered, the reaction in equation 4 proceeds in the opposite direction, making it easier for metal ions extracted into the organic phase to be back-extracted into the aqueous phase. .
Since the extracted pH differs depending on the type of metal ion, the target element and impurity elements are separated by controlling the pH in the solvent extraction step using an acidic extractant.
nRH _org + M ⁿ⁺ _aq → MR _norg + nH ⁺ _aq ... (Formula 4)
Here, RH in the formula represents an acidic extractant, M ⁿ⁺ represents an n-valent metal ion, org represents an organic phase, and aq represents an aqueous phase.

Therefore, in the first solvent extraction step S2, it is desirable to adjust the pH of the cobalt chloride solution from which copper has been removed to 1.5 to 3.0. In this pH range, the extraction rates of zinc, manganese, and calcium tend to be higher than those of cobalt, and they can be separated from cobalt by leaving cobalt in the aqueous phase and extracting these impurity elements into the organic phase. It is possible.
When the pH is less than 1.5, the extraction rate of these impurities is low, making it difficult to separate them from cobalt, and when the pH exceeds 3.0, the extraction rate of cobalt also increases and the separation from impurities decreases. . When the pH is adjusted to 1.5 to 3.0, some cobalt may be extracted, but the organic phase after extraction is brought into contact with a hydrochloric acid solution with a pH lower than that during extraction to back-extract the cobalt. Cobalt can also be recovered to reduce cobalt loss.
Furthermore, when this organic phase is brought into contact with an acidic solution having a pH of 1 or less, most of the extracted metal ions can be back-extracted into the aqueous phase, and the organic phase after back-extraction can be reused.

Note that cobalt loss does not necessarily mean that it cannot be recovered and is disposed of. For example, if cobalt cannot be recovered from the extractant and cobalt remains in the extractant, the extraction capacity of the extractant will decrease the next time it is subjected to cobalt extraction, and cobalt may not be efficiently recovered. be. In the present invention, even when production costs increase due to a decrease in production efficiency, it is included in the amount that cannot be optimally recovered and is treated as a "loss."

(Second solvent extraction step S3)
The second solvent extraction step S3 will be explained based on FIGS. 3 and 5.
In the second solvent extraction step S3, the pH of the cobalt chloride solution that has passed through the first solvent extraction step S2 is adjusted to 4.0 to 7.0, and then the cobalt chloride solution containing 0.05% by weight or more of a fat-soluble antioxidant is added. This is a step in which cobalt is extracted by bringing it into contact with an organic solvent containing a carboxylic acid extractant, and then back-extracting the cobalt with sulfuric acid to obtain a cobalt sulfate solution.

As the organic solvent, a carboxylic acid extractant diluted with a diluent is used. Examples of carboxylic acid extractants include versatic acid and naphthenic acid. These are acidic extractants with a branched structure having COOH groups. Furthermore, by including a fat-soluble antioxidant in a part of the organic solvent, oxidation of cobalt can be suppressed as described later.

Antioxidants are additives that prevent the oxidation of other substances by oxidizing themselves, and can be broadly classified into water-soluble and fat-soluble.
In the present invention, a fat-soluble antioxidant is used. In addition to phenolic antioxidants, these include amine antioxidants, sulfur-based antioxidants, phosphorus-based antioxidants, combinations of phenolic antioxidants and sulfur-based antioxidants, and combinations of phenolic and phosphorus-based antioxidants. Any combination of antioxidants may be used and may be selected arbitrarily.
Phenolic antioxidants include the product name "Butylated Hydroxytoluene" manufactured by Tokyo Chemical Industry Co., Ltd., the product name "ADEKA STAB AO-20" and "ADEKA STAB AO-30" manufactured by ADEKA Co., Ltd., and the product name manufactured by Kawaguchi Chemical Industry Co., Ltd. Product names include ``ANTAGE BHT'' and ``ANTAGE DAH.''
Examples of amine-based antioxidants include the product name "N-isopropyl-N'-phenyl-p-phenylenediamine" manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.
Examples of sulfur-based antioxidants include the trade name "3,3'-didodecyl thiodipropionate" manufactured by Tokyo Chemical Industry Co., Ltd.
Examples of phosphorus-based antioxidants include the trade name "tris(2,4-di-tert-butylphenyl) phosphite" manufactured by Tokyo Chemical Industry Co., Ltd.

The content of the fat-soluble antioxidant in the organic solvent is 0.05% by weight or more. When adding an antioxidant to an organic solvent to obtain a desired content, the addition ratio means the ratio of the antioxidant to the organic solvent. Specifically, it means adding 0.05% by weight or more of an antioxidant to an organic solvent mixed with 30% by volume of an extractant and 70% by volume of a diluent. If the fat-soluble antioxidant is added in an amount of 0.05% by weight or more, oxidation of cobalt can be suppressed as described later.

Generally, when a carboxylic acid extractant extracts metal ions, it releases protons into the aqueous phase according to the valence of the metal, and the metal ions are coordinated to carbonyl oxygen. Many carboxylic acids form dimers and trimers through hydrogen bonding with each other in nonpolar solvents. Further, when extracting metal ions, a carboxylic acid that has not been acid-dissociated may coordinate to remove water of hydration that is coordinated to the metal ions. For example, a reaction in which a hexacoordinated divalent metal ion M ²⁺ is extracted by a dimeric carboxylic acid extractant R ₂ H ₂ is expressed as shown in Formula 5.
[M(H ₂ O) ₆ ] ²⁺ _aq +3(R ₂ H ₂ ) _org
→ (MR ₂・4RH) _org +2H ⁺ _aq +6H ₂ O _aq ... (Formula 5)
Here, org in the formula represents an organic phase, and aq represents an aqueous phase.

(Extraction process)
In the second solvent extraction step S3, an alkaline solution is added as a neutralizing agent to the cobalt chloride solution from which copper, zinc, manganese, and calcium have been removed to adjust the pH to 4.0 to 7.0.

In the present invention, since the pH is adjusted to the above range, cobalt can be extracted into the organic phase by contacting with an organic solvent containing a fat-soluble antioxidant. At this time, magnesium is not extracted and remains in the aqueous phase. If the pH is less than 4, it is difficult to extract cobalt, while if the pH exceeds 7, the solubility of cobalt may decrease and precipitation may occur.
Note that as the alkaline solution used for pH adjustment, specifically, a solution of sodium hydroxide or potassium hydroxide can be used.
Furthermore, in order to prevent oxidation during extraction, bubbling may be performed using an inert gas such as nitrogen gas, argon gas, or carbon dioxide gas.

In the above extraction process, if an antioxidant is not used, cobalt is likely to oxidize and become trivalent cobalt ions, but if an antioxidant is used, the oxidation of cobalt is suppressed and the generation of hydroxide crud is suppressed. Operations can be stabilized. Therefore, as will be described later, the cobalt recovery efficiency in the back extraction process can be maintained at a high level.

In addition to fat-soluble antioxidants, for example, linear carboxylic acids are known as antioxidants. Although this linear carboxylic acid has an antioxidant effect when the number of carbon atoms in the linear chain is small, there is a problem in that it dissolves in the aqueous phase. When organic components such as antioxidants are dissolved in the aqueous phase, the total organic carbon (TOC) in the wastewater is ) could not be lowered sufficiently, and there were concerns that the environmental burden on the sea area due to wastewater would increase in terms of water quality.
On the other hand, the fat-soluble antioxidant used in the present invention is not substantially dissolved in the aqueous phase, so it can be obtained after further recovering cobalt sulfate from the back extract obtained by back extracting cobalt from an organic solvent. It is possible to prevent an increase in the total organic carbon component (TOC) value in the residual liquid (hereinafter collectively referred to as back extraction liquid). Therefore, there is also a great environmental advantage in that it can prevent deterioration in the quality of wastewater. Furthermore, since the market price is low and it is easily available, the manufacturing cost of cobalt sulfate can be reduced.

(Reverse extraction process)
After the extraction process, the extracted cobalt is brought into contact with a sulfuric acid solution to adjust the pH to 2.0 to 4.5. This allows cobalt to be back-extracted into the sulfuric acid solution. In this way, a highly purified cobalt sulfate solution is obtained.
Although back extraction is possible even when the pH is less than 2, it is not preferable because the amount of back extraction of trace impurities extracted at a pH lower than that of cobalt increases. On the other hand, if the pH exceeds 4.5, the cobalt back extraction rate will decrease and the amount of cobalt recovered will decrease, which is not preferable.

Furthermore, if cobalt is oxidized into trivalent cobalt ions in the extraction process, it will be stable in the organic phase and cannot be recovered unless it is reduced once, requiring extra operations for recovery.
In contrast, in the present invention, as described above, the oxidation of cobalt is suppressed, so trivalent cobalt ions do not accumulate in the organic phase, and cobalt is reliably extracted in the extraction step. Therefore, cobalt recovery efficiency can be maintained at a high level.

Note that since the organic phase after extraction still contains a fine aqueous phase even after phase separation, a washing step for removing this aqueous phase may be added before back extraction. For example, a cobalt sulfate solution can be used as the aqueous phase in the washing step. Moreover, the organic phase after back extraction can be reused as an organic phase for the extraction step.
By the above method, a highly purified cobalt sulfate solution containing few impurities can be produced.

(Crystallization step S4)
The crystallization step S4 will be explained based on FIG. 2.
In the crystallization step S4, cobalt sulfate crystals are precipitated from the cobalt sulfate solution obtained in the second solvent extraction step S3. The crystallization method is not particularly limited, and a general crystallization method can be used.

For example, there is a method of obtaining crystals by storing a cobalt sulfate solution in a crystallizer and crystallizing it within the crystallizer. The crystallizer is used to precipitate crystals by evaporating water in the cobalt sulfate solution under a predetermined pressure, and for example, a rotary evaporator or a double propeller type crystallizer is used. The internal pressure is reduced using a vacuum pump, etc., and crystallization proceeds while rotating the flask in a rotary evaporator and stirring with a double propeller. Note that in the crystallizer, a slurry is formed in which cobalt sulfate crystals are mixed with a cobalt sulfate solution.

The slurry discharged from the crystallizer is separated into solid and liquid into cobalt sulfate crystals and a mother liquor using a filter, a centrifuge, or the like. Thereafter, the cobalt sulfate crystals are dried in a dryer to remove moisture.
Cobalt sulfate crystals can be produced from a cobalt sulfate solution using the above method. Of course, since the cobalt sulfate solution is highly pure with little impurities, the obtained cobalt sulfate crystals are also highly pure with little impurities.

(Second embodiment)
A second embodiment of the method for producing cobalt sulfate will be described based on FIGS. 6 to 9.
FIG. 6 is a diagram showing all steps in the second embodiment, and FIG. 7 shows details of each step S2, S1, and S3 shown in FIG. 6.
In the second embodiment, as shown in FIG. 6, the first solvent extraction step S2 is first performed in the first step, and then the copper removal step S1 is performed in this order.

(First solvent extraction step S2)
The first solvent extraction step S2 will be explained based on FIGS. 7 and 8.
In the first solvent extraction step S2, an organic solvent containing an alkyl phosphate extractant is brought into contact with a cobalt chloride solution containing one or more impurities of copper, zinc, manganese, calcium, and magnesium as a starting material. This is a process in which zinc, manganese and calcium are extracted and separated. Note that a portion of the copper can also be extracted and separated and removed.

The alkyl phosphate extractant as the organic solvent may be the same as that used in the first embodiment, and the diluent may also be the same as in the first embodiment. In addition, this step S2 is performed in the same manner as in the first embodiment, including the pH adjustment range.

In this first solvent extraction step S2, when the pH of the cobalt chloride solution is adjusted to 1.5 to 3.0, the extraction rate of zinc, manganese and calcium tends to be higher than that of cobalt, and cobalt is extracted from the aqueous phase. It is possible to separate these impurity elements from cobalt by extracting them into the organic phase. When the pH is adjusted to 1.5 to 3.0, some cobalt may be extracted, but the organic phase after extraction is brought into contact with a hydrochloric acid solution with a pH lower than that during extraction to back-extract the cobalt. Cobalt can also be recovered to reduce cobalt loss.

(Copper removal process S1)
The copper removal step S1 will be explained based on FIG. 7.
The copper removal step S1 is performed by adding a sulfiding agent to the cobalt chloride solution that has undergone the first solvent extraction step S2. Further, an oxidizing agent and a neutralizing agent are added to adjust the redox potential of the cobalt chloride solution to -100 to 200 mV (based on Ag/AgCl electrode) and the pH to 1.3 to 3.0.
Through this step S1, a copper sulfide precipitate is generated and separated from the cobalt chloride solution, and a cobalt chloride solution from which copper is removed can be obtained.

The method of adjusting the oxidation-reduction potential and the method of adjusting the pH may be the same as in the first embodiment, and the sulfurizing agent used in the first embodiment may also be used.
By performing this step, a copper sulfide precipitate can be obtained according to formula (1), formula (2), or formula (3) shown in the first embodiment, and copper can be removed from the solution.

(Second solvent extraction step S3)
The second solvent extraction step S3 will be explained based on FIGS. 7 and 9.
In the second solvent extraction step S3, the pH of the cobalt chloride solution that has passed through the first solvent extraction step S2 and the copper removal step S1 is adjusted to 4.0 to 7.0, and then a fat-soluble antioxidant is added to 0.0 to 7.0. In this process, an organic solvent containing a carboxylic acid extractant containing 0.5% by weight or more is brought into contact, cobalt is extracted with this organic solvent, and then cobalt is back-extracted with sulfuric acid to obtain a cobalt sulfate solution.

As in the first embodiment, an organic solvent containing a carboxylic acid extractant containing 0.05% by weight or more of a fat-soluble antioxidant is used as the organic solvent. In addition, by adding a fat-soluble antioxidant to a part of the organic solvent, it is possible to suppress the oxidation of cobalt. It is possible to prevent an increase in the total organic carbon content (TOC) value in the extract. Therefore, the advantages of being able to prevent deterioration of water quality and reducing the manufacturing cost of cobalt sulfate are the same as in the first embodiment.
As in the first embodiment, generation of hydroxide crud can be suppressed and operations can be stabilized.
As in the first embodiment, fat-soluble antioxidants include, in addition to phenolic antioxidants, amine antioxidants, sulfur-based antioxidants, phosphorus-based antioxidants, phenolic antioxidants, and sulfur-based antioxidants. Any combination of phenolic oxidants and phosphorus antioxidants can be used.

Implementation procedures such as the addition of an alkaline solution and the pH adjustment range in the extraction step in the second solvent extraction step S3 may be the same as in the first embodiment.
In addition, the implementation procedures such as contact with the sulfuric acid solution and pH adjustment range in the back extraction step may be the same as in the first embodiment.
By performing each of the above steps, it is possible to obtain a highly pure cobalt sulfate solution with reduced impurities by allowing magnesium to remain in the aqueous phase. In the second solvent extraction step S3, it is possible to avoid unfavorable situations such as the pH rising during operation and the production of hydroxide, and the generation of crud due to this, thereby stabilizing the operation. can take advantage of this. Moreover, as in the first embodiment, cobalt recovery efficiency can be maintained at a high level.

(Crystallization step S4)
The crystallization step S4 will be explained based on FIG. 6.
In the crystallization step S4, cobalt sulfate crystals are precipitated from the cobalt sulfate solution obtained in the second solvent extraction step S3. The crystallization method is not particularly limited, and a general crystallization method can be used. Therefore, similar to the first embodiment, a crystallization method using a crystallizer can be used.

Cobalt sulfate crystals can be produced from a cobalt sulfate solution using the above method. Of course, since the cobalt sulfate solution is highly pure with little impurities, the obtained cobalt sulfate crystals are also highly pure with little impurities.

EXAMPLES Hereinafter, the present invention will be described in more detail by showing examples, but the present invention is not limited to the following examples. Note that Example 1 below is included in the manufacturing method of the first embodiment.

[Example 1]
(Copper removal process S1)
A sodium hydrogen sulfide solution was added as a sulfiding agent to 2 L of a cobalt chloride solution having the composition shown in base solution A in Table 1, which was adjusted to pH 2.5, and the redox potential was adjusted to -50 mV (Ag/AgCl electrode reference). This produced a copper sulfide precipitate. The precipitate was separated and removed using a filter to obtain a filtrate having the composition shown in B after sulfurization in Table 1. The concentration of copper was less than 0.001 g/L, and copper could be separated and removed.

(First solvent extraction step S2)
An alkyl phosphate extractant (trade name D2EHPA, manufactured by Daihachi Chemical Industries, Ltd.) was diluted with a diluent (trade name Techclean N20, manufactured by JX Nippon Oil & Energy Corporation) so that the concentration was 40% by volume. I prepared the phase. 0.9 L of the aqueous phase consisting of the cobalt chloride solution obtained in the copper removal step S1 and 1.8 L of the organic phase are mixed, and the pH is adjusted to 1.7 by adding sodium hydroxide solution to remove impurities. Extracted. The same extraction operation was repeated using 0.9 L of the aqueous phase after extraction and 1.8 L of a new organic phase, for a total of three extraction operations. As a result, a cobalt chloride solution having the composition shown in C after the first SX in Table 1 was obtained. The concentrations of zinc, manganese, and calcium were all less than 0.001 g/L, and these impurities could be separated and removed.
Note that SX means "solvent extraction".

(Second solvent extraction step S3)
An organic phase was prepared by diluting a carboxylic acid extractant (trade name: Versatic Acid 10, manufactured by Oxalis Chemicals) with a diluent (TECLEAN N20) so that the concentration was 30% by volume. In addition, butylated hydroxytoluene (manufactured by Tokyo Kasei Kogyo Co., Ltd., abbreviated as BHT), which is a phenolic antioxidant, was used as a fat-soluble antioxidant in the organic phase, and as shown in Table 1, as a comparative example, a sample without addition was used. Including, as an example, it was changed under five conditions: 0.01% by weight addition, 0.05% by weight addition, 2% by weight addition, and 4% by weight addition.

Next, 0.44 L of the aqueous phase consisting of the cobalt chloride solution obtained in the first solvent extraction step S2 and 1 L of the organic phase were mixed into each sample, and a sodium hydroxide solution was added so that the pH became 6.5. Cobalt was extracted into the organic phase.
At the same time, the organic phase was separated immediately after mixing the organic phase and the cobalt chloride solution and after 164 hours, and subjected to back extraction. Cobalt that could not be back extracted from the organic phase was determined to have been oxidized, and its ratio was confirmed.

Next, 0.06 L of the extracted organic phase was mixed with 0.06 L of a cobalt chloride solution having a cobalt concentration of 10 g/L, and the aqueous phase mixed in the extracted organic phase was washed. Subsequently, this organic phase and 0.009 L of pure water were mixed, sulfuric acid was added to adjust the pH to 4, and cobalt was back extracted. The results are shown in Table 2. The copper, zinc, manganese, calcium, and magnesium concentrations shown in D after the second SX in Table 2 were all less than 0.001 g/L, and impurities could be effectively separated and removed.

As shown in Table 1, as the amount of phenolic antioxidant, which is a fat-soluble antioxidant, was increased, especially when 0.05% by weight or more of phenolic antioxidant was added, 164 hours elapsed. It was found that cobalt oxidation can be suppressed even after the extraction process, and cobalt loss during the back extraction process can be suppressed.

(Crystallization step S4)
A cobalt sulfate solution was inserted into a rotary evaporator, and the pressure inside the rotary evaporator was reduced using a vacuum pump, and the temperature was maintained at 40° C. while the flask was rotated to evaporate water and precipitate cobalt sulfate crystals. After solid-liquid separation, the obtained cobalt sulfate crystals were dried in a drier. As a result, highly purified cobalt sulfate crystals as shown in Table 3 were obtained.

[Example 2]
In the second solvent extraction step S3, the fat-soluble antioxidant added to the organic phase is an amine antioxidant, N-isopropyl-N'-phenyl-p-phenylenediamine (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., A cobalt sulfate solution was obtained in the same manner as in Example 1, except that the abbreviation was changed to IPPD). Note that a reagent manufactured by Fuji Film Wako Pure Chemical Industries, Ltd. was used as the amine antioxidant.

As shown in Table 4, as the amount of N-isopropyl-N'-phenyl-p-phenylenediamine added, which is an amine antioxidant, increases, especially 0.05 wt% or more of N-isopropyl-N'- It was found that when phenyl-p-phenylenediamine was added, cobalt oxidation could be suppressed even after 168 hours, and cobalt loss in the back extraction process could be suppressed.

[Example 3]
In the second solvent extraction step S3, the fat-soluble antioxidant added to the organic phase is changed to didodecyl 3,3'-thiodipropionate (manufactured by Tokyo Chemical Industry Co., Ltd., abbreviated as DLTDP), which is a sulfur-based antioxidant. A cobalt sulfate solution was obtained in the same manner as in Example 1 except for the above.
As shown in Table 5, as the amount of didodecyl 3,3'-thiodipropionate added, which is a sulfur-based antioxidant, was increased, the oxidation of cobalt after 168 hours could be suppressed, and the back extraction It was found that cobalt loss in the process can be suppressed.

[Example 4]
In the second solvent extraction step S3, the fat-soluble antioxidant added to the organic phase is replaced with the phosphorus-based antioxidant tris(2,4-di-tert-butylphenyl) phosphite (manufactured by Tokyo Kasei Kogyo Co., Ltd.). A cobalt sulfate solution was obtained in the same manner as in Example 1 except for the following changes.
As shown in Table 6, when tris(2,4-di-tert-butylphenyl) phosphite is added to the organic solvent, the oxidation of cobalt after 168 hours can be suppressed, and the back extraction process We were able to suppress Cobalt Loss.

[Example 5]
In the second solvent extraction step S3, the fat-soluble antioxidant added to the organic phase is mixed with the phenolic antioxidant dibutylhydroxytoluene, which is a primary antioxidant, and the sulfur-based antioxidant 3,3, which is a secondary antioxidant. A cobalt sulfate solution was obtained in the same manner as in Example 1 except that the combination was changed to didodecyl '-thiodipropionate.
As shown in Table 7, when a combination of antioxidants was added to the organic solvent, oxidation of cobalt after 168 hours could be suppressed, and cobalt loss during the back extraction process could be suppressed. .

[Example 6]
In the second solvent extraction step S3, the fat-soluble antioxidant added to the organic phase is mixed with the phenolic antioxidant dibutylhydroxytoluene, which is a primary antioxidant, and the phosphorous antioxidant, phosphorous acid, which is a secondary antioxidant. A cobalt sulfate solution was obtained in the same manner as in Example 1, except that the combination was changed to tris(2,4-di-tert-butylphenyl).
As shown in Table 8, when a combination of antioxidants was added to the organic solvent, oxidation of cobalt after 168 hours could be suppressed, and cobalt loss during the back extraction process could be suppressed. .

According to the results of Examples 1 to 6 belonging to the method for producing cobalt sulfate according to the first embodiment described above, highly pure cobalt sulfate in which impurities were sufficiently removed while maintaining high cobalt recovery efficiency was obtained. That's what I found out.
It was also confirmed that the total organic carbon component (TOC) value in the back extract did not increase, and that the quality of the wastewater did not deteriorate.

The highly purified cobalt sulfate crystals obtained by the present invention can be used as a raw material for lithium ion secondary batteries, as well as for various other uses.

S1 Copper removal process S2 First solvent extraction process S3 Second solvent extraction process S4 Crystallization process

Claims (8)

A method for producing cobalt sulfate by removing impurities from a cobalt chloride solution containing one or more impurities of copper, zinc, manganese, calcium and magnesium, the method comprising:
The first step includes a decopper removal step in which a sulfurizing agent is added to the cobalt chloride solution to form a precipitate of copper sulfide and then separated and removed, and an organic solvent containing an alkyl phosphate extractant is brought into contact with the cobalt chloride solution. , including a first solvent extraction step of extracting and separating zinc, manganese and calcium into the organic solvent,
In the second step, the pH of the cobalt chloride solution that has passed through the first step is adjusted to 4.0 to 7.0, and then an organic extractant containing a carboxylic acid extractant containing 0.05% by weight or more of a fat-soluble antioxidant is added. A method for producing cobalt sulfate, comprising a second solvent extraction step of contacting with a solvent and extracting cobalt with the organic solvent, and then back-extracting the cobalt with sulfuric acid to obtain a cobalt sulfate solution. 2. The method for producing cobalt sulfate according to claim 1, wherein the first step is performed in the order of the copper removal step and the first solvent extraction step. 2. The method for producing cobalt sulfate according to claim 1, wherein the first step is performed in the order of the first solvent extraction step and the copper removal step. 2. The method for producing cobalt sulfate according to claim 1, wherein the cobalt sulfate solution obtained through the second solvent extraction step is subjected to a crystallization step to obtain crystals of cobalt sulfate. In the copper removal step, an oxidizing agent and a neutralizing agent are added to the cobald chloride solution to which a sulfurizing agent has been added to adjust the redox potential to -100 to 200 mV (based on Ag/AgCl electrodes) and to adjust the pH to 1.3 to 3. 5. The method for producing cobalt sulfate according to claim 1, wherein the cobalt sulfate content is adjusted to .0. The alkyl phosphate extractant in the first solvent extraction step is bis(2-ethylhexyl) hydrogen phosphate,
A claim characterized in that the pH of the cobalt chloride solution from which copper has been removed is adjusted to 1.5 to 3.0 and subjected to solvent extraction using the extractant to extract impurity elements into an organic solvent. 5. The method for producing cobalt sulfate according to 1, 2, 3 or 4. Following the extraction step in the second solvent extraction step, a sulfuric acid solution is brought into contact with the organic solvent from which cobalt has been extracted, the pH is adjusted to 2.0 to 4.5, and cobalt is back extracted into the sulfuric acid solution. The method for producing cobalt sulfate according to claim 1, 2, 3 or 4, characterized in that an extraction step is performed. The fat-soluble antioxidant may be a phenolic antioxidant, an amine antioxidant, a sulfur-based antioxidant, a phosphorus-based antioxidant, a combination of a phenolic antioxidant and a sulfur-based antioxidant, or a phenolic antioxidant. The method for producing cobalt sulfate according to claim 1, characterized in that it is a combination of: