JP7600851B2 - How to make cobalt sulfate - Google Patents

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 for industrial purposes, not only as an additive element in special alloys, but also as a raw material for magnetic materials and lithium-ion secondary batteries. In particular, lithium-ion secondary batteries have recently come to be widely used as batteries for mobile devices and electric vehicles, and as a result, the demand for cobalt has expanded rapidly. However, since most cobalt is produced as a by-product of nickel and copper smelting, separation of cobalt from impurities such as nickel and copper is an important elemental technology in cobalt production.

For example, when recovering cobalt as a by-product in the hydrometallurgy of nickel, the raw material is first leached or extracted into a solution or subjected to a dissolution treatment using a mineral acid, an oxidizing agent, etc., to obtain a solution containing nickel and cobalt. Furthermore, the nickel and cobalt contained in the obtained acidic solution are often separated and recovered by a solvent extraction method using various organic extractants according to a conventionally known method.
However, the resulting cobalt solution often contains various impurities derived from the raw materials used in the process.

Therefore, it becomes 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-mentioned solvent extraction method.
Furthermore, in order to produce a high-purity cobalt product with a low impurity content, it was necessary to remove impurity elements from the cobalt solution that had been separated and recovered from the nickel solution containing cobalt, and then to commercialize the cobalt through an electrolysis process or crystallization, etc.

As a method for removing impurity elements from a cobalt solution, there are conventional techniques described in Patent Documents 1 and 2.
Patent Document 1 discloses a method for purifying a cobalt solution, including: (1) a copper removal step of adding a sulfiding agent to a cobalt solution and adjusting the oxidation-reduction potential (ORP) (based on Ag/AgCl electrode) to 50 mV or less and the pH to 0.3 to 2.4 to obtain a copper sulfide precipitate and a copper-depleted purified liquid; (2) a demanganization step of adding an oxidizing agent and a neutralizing agent to the copper-depleted purified liquid and adjusting the oxidation-reduction potential (based on Ag/AgCl electrode) to 950 to 1050 mV and the pH to 2.4 to 3.0 to obtain a manganese precipitate and a demanganized purified liquid; and (3) a solvent extraction step of extracting and separating zinc, calcium and trace impurities in the demanganized purified liquid using alkyl phosphoric acid as an extractant.
Patent Document 2 describes a technique in which a cobalt chloride solution having a hydrochloric acid concentration of 2 to 6 mol/L is brought into contact with an anion exchange resin, and metal impurities such as iron, zinc, and tin that form complexes with a distribution coefficient for the anion exchange resin that is larger than that of a cobalt chloride complex are adsorbed and separated.

The solvent extraction method using alkyl phosphoric acid as an extractant described in the above 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, an ion exchange method using an anion exchange resin and a solvent extraction method using an amine-based extractant have higher separation performance for zinc and cobalt than the above solvent extraction method using alkyl phosphoric acid.
Furthermore, when removing very small amounts 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 viewpoint, a method has been proposed in which the purification method of Patent Document 1 and the separation technique of Patent Document 2 are combined to remove 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 demanganese step for removing manganese, a decopper step for removing copper, a dezincification step for removing zinc, and an electrolysis step.
In the dezincification process, the aqueous cobalt chloride solution obtained in the decopperization process is brought into contact with an anion exchange resin to adsorb and remove zinc. In the electrolysis process, the high-purity aqueous cobalt chloride solution obtained in the dezincification process is used as an electrolytic feed solution to produce metallic cobalt (also called electrolytic cobalt).

On the other hand, as mentioned above, the demand for cobalt as a raw material for lithium ion secondary batteries has recently increased, and the form of a cobalt sulfate solution or cobalt sulfate crystals is desired.
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 then crystallized to obtain cobalt sulfate crystals. However, this manufacturing method increases the manufacturing cost due to an increase in the number of steps and chemical costs. Furthermore, plate-shaped metallic cobalt, which is used in corrosion-resistant alloys, dissolves slowly in sulfuric acid, and in order to dissolve it in a short time, it is necessary to turn the plate-shaped metallic cobalt into a powder by atomization or the like.
For this reason, a method for obtaining a cobalt sulfate solution directly from a cobalt chloride solution without going through metallic cobalt has been desired.

JP 2004-285368 A JP 2001-020021 A JP 2020-19664 A

The present invention has been proposed in view of the above-mentioned circumstances, and aims to provide a method for producing highly pure cobalt sulfate by separating impurities and cobalt from a cobalt chloride solution containing impurities without using an electrolysis process.

The method for producing cobalt sulfate of the first invention is characterized by sequentially carrying out the following steps: a first solvent extraction step in which a cobalt chloride solution containing one or more impurities of copper, zinc, manganese, calcium, and magnesium is contacted with an organic solvent containing an alkylphosphate-based extractant, and zinc, manganese, and calcium are extracted into the organic solvent for separation and removal; a decoppering step in which a sulfiding agent is added to the cobalt chloride solution that has been subjected to the first solvent extraction step to produce a precipitate of copper sulfide, which is then separated and removed; a dephosphorization step in which an iron-containing solution is added to the cobalt chloride solution that has been subjected to the decoppering step to precipitate phosphorus, thereby separating and removing it; and a second solvent extraction step in which the cobalt chloride solution that has been subjected to the dephosphorization step is contacted with an organic solvent containing a carboxylic acid-based extractant, cobalt is extracted into the organic solvent, and then the cobalt is stripped with sulfuric acid to obtain a cobalt sulfate solution.
The method for producing cobalt sulfate according to the second invention is characterized in that, in the first invention, the alkyl phosphate extractant in the first solvent extraction step is bis(2-ethylhexyl) hydrogen phosphate, and the pH of the cobalt chloride solution is adjusted to 1.5 to 3.0 and subjected to solvent extraction using the bis(2-ethylhexyl) hydrogen phosphate, thereby extracting impurity elements into an organic solvent.
A third invention relates to a method for producing cobalt sulfate according to the first or second invention, and is characterized in that in the copper removal step, an oxidizing agent and a neutralizing agent are added to the cobalt chloride solution to which a sulfiding agent has been added, thereby adjusting the redox potential to −100 to 200 mV (Ag/AgCl electrode standard) and the pH to 1.3 to 3.0.
A fourth invention is a method for producing cobalt sulfate according to the first, second or third invention, characterized in that in the dephosphorization step, an alkaline solution is added to the cobalt chloride solution to adjust the pH to 4 to 5.
A fifth aspect of the present invention is a method for producing cobalt sulfate according to any one of the first, second, third and fourth aspects of the present invention, characterized in that the second solvent extraction step includes an extraction step of adding an alkaline solution to a cobalt chloride solution from which copper, zinc, manganese and calcium have been removed, adjusting the pH to 5.0 to 7.0, and extracting cobalt into an organic solvent using a carboxylic acid- based extractant.
A sixth aspect of the present invention is a method for producing cobalt sulfate according to the fifth aspect of the present invention, characterized in that the second solvent extraction step includes , subsequent to the extraction step, a stripping step of contacting the organic solvent from which cobalt has been extracted with a sulfuric acid solution, adjusting the pH to 2.0 to 4.5, and stripping the cobalt into the sulfuric acid solution.
The seventh aspect of the present invention is a method for producing cobalt sulfate according to the first aspect of the present invention, characterized in that the cobalt sulfate solution obtained through the second solvent extraction step is subjected to a crystallization step to obtain cobalt sulfate crystals.

According to the first invention, zinc, manganese and calcium are separated and removed from a cobalt chloride solution containing impurities in the first solvent extraction step, copper is removed in the copper removal step, phosphorus is separated and removed in the phosphorus removal step, and magnesium is separated and removed in the second solvent extraction step, so that a high-purity cobalt sulfate solution free of impurities can be obtained. Therefore, high-purity cobalt sulfate can be directly produced by separating the impurities and cobalt without using an electrolysis step.
According to the second invention, bis(2-ethylhexyl) hydrogen phosphate is used as an alkyl phosphate extractant, which makes it easier to separate the impurities zinc, manganese and calcium from the cobalt solution. In addition, by adjusting the pH to 1.5 to 3.0, zinc, manganese and calcium can be extracted and separated from cobalt, leaving cobalt in the aqueous phase.
According to the third invention, copper sulfide can be precipitated and sufficiently removed from the cobalt chloride solution, and coprecipitation of cobalt can be suppressed, thereby increasing the recovery rate of cobalt sulfate.
According to the fourth invention, when the pH of the cobalt chloride solution is 4 to 5, the solubility of iron phosphate is low, so that a large amount of phosphorus is precipitated as iron phosphate, and dephosphorization is carried out efficiently.
According to the fifth invention, in the extraction step included in the second solvent extraction step, the pH is adjusted to 5.0 to 7.0, and cobalt can be extracted into the organic phase by contacting with an organic solvent containing a carboxylic acid extractant.
According to the sixth aspect of the present invention, in the stripping step included in the second solvent extraction step, the cobalt extracted into the organic phase is brought into contact with a sulfuric acid solution and the pH is adjusted to 2.0 to 4.5, whereby the cobalt can be stripped into the sulfuric acid solution, thereby obtaining a high-purity cobalt sulfate solution.
According to the seventh aspect of the present invention, by further carrying out a crystallization step, it is possible to obtain high-purity cobalt sulfate crystals from the cobalt sulfate solution.

FIG. 1 is a process diagram showing a method for producing cobalt sulfate according to the present invention. FIG. 1 is a process diagram showing a method for producing cobalt sulfate according to one embodiment of the present invention. FIG. 3 is a detailed process diagram of the first solvent extraction step S1 shown in FIG. 2. FIG. 3 is a detailed process diagram of the second solvent extraction step S3 shown in FIG. 2. FIG. 3 is a detailed process diagram of the dephosphorization step S5 shown in FIG. 2.

Next, an embodiment of the present invention will be described with reference to the drawings.
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 modifications are possible without departing from the gist of the present invention.

(Basic principle of the present invention)
The method for producing cobalt sulfate according to the present invention will be described with reference to FIG.
This manufacturing method is characterized by carrying out the following steps in order.
(1) a first solvent extraction step S1 in which a cobalt chloride solution containing one or more impurities of copper, zinc, manganese, calcium, and magnesium is contacted with an organic solvent containing an alkyl phosphoric acid-based extractant, and zinc, manganese, and calcium are extracted into the organic solvent to be separated and removed;
(2) a copper removal step S2 in which a sulfiding agent is added to the cobalt chloride solution from which zinc, manganese, and calcium have been removed by the first solvent extraction step S1 to generate a precipitate of copper sulfide, which is then separated and removed;
(3) a dephosphorization step S5 in which an iron-containing solution is added to the cobalt chloride solution from which copper, zinc, manganese and calcium have been removed through the copper removal step S2, to precipitate phosphorus as iron phosphate, which is then separated and removed;
(4) A second solvent extraction step S3 is carried out in which the cobalt chloride solution from which phosphorus has been removed by the dephosphorization step is contacted with an organic solvent containing a carboxylic acid to extract cobalt into the organic solvent, and then the cobalt is stripped with sulfuric acid to obtain a cobalt sulfate solution.

In the present invention, after each of the steps S1, S2, S5, and S3, a crystallization step S4 of precipitating crystals from the cobalt sulfate solution is carried out as necessary.
Although not shown in FIG. 1, after the first solvent extraction step S1 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 to separate and remove organic components that have become mixed in the liquid may be added.

The cobalt chloride solution used as the starting material in the present invention contains one or more of the impurity elements copper, zinc, manganese, calcium, and magnesium. The application of the present invention is not limited to any cobalt chloride solution containing such impurities, but it is particularly suitable for use in cobalt chloride solutions obtained after nickel is separated and recovered from a cobalt-containing nickel solution using an alkyl phosphoric acid extractant or an amine extractant in the solvent extraction process of nickel smelting.

According to the present invention, a high-purity cobalt sulfate solution can be obtained by separating and removing zinc, manganese, and calcium from a cobalt chloride solution containing impurities in a first solvent extraction step S1, removing copper by forming a copper sulfide precipitate in a copper removal step S2, separating and removing phosphorus in a phosphorus removal step S5, and separating and removing magnesium in a second solvent extraction step S3. Therefore, a high-purity cobalt sulfate solution can be produced directly by separating impurities and cobalt without using an electrolysis step.

Furthermore, according to the present invention, the cobalt sulfate solution after the steps S1, S2, S5, and S3 can be subjected to the crystallization step S4 to precipitate crystals from the solution and obtain cobalt sulfate crystals.

(Embodiment)
Hereinafter, an embodiment of the method for producing cobalt sulfate will be described with reference to Fig. 2 to Fig. 4. Fig. 2 shows the details of steps S1, S2, S5 and S3 shown in Fig. 1 .

(First solvent extraction step S1)
The first solvent extraction step S1 will be described with reference to FIGS. 2 and 3.
The first solvent extraction step S1 is a step in which an organic solvent containing an alkyl phosphoric acid-based extractant is brought into contact with a cobalt chloride solution containing one or more impurities of copper, zinc, manganese, calcium, and magnesium, which is the starting material, to extract and separate and remove zinc, manganese, and calcium into the organic solvent. Note that a part of the copper can also be extracted and separated and removed.

As the organic solvent, an alkyl phosphate extractant diluted with a diluent is used. Examples of alkyl phosphate extractants include bis(2-ethylhexyl) hydrogen phosphate (trade name D2EHPA), 2-ethylhexyl (2-ethylhexyl)phosphonate (trade name PC-88A), and di(2,4,4-trimethylpentyl)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 the extractant, as it has high separability from cobalt.

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

An acidic extractant such as an alkyl phosphate extractant is an extractant that extracts metal ions by forming a metal salt through the substitution of the -H of the extractant with a cation in the aqueous phase, as shown in formula 4. In general, as the pH increases, metal ions are more easily extracted into the organic phase, and as the pH decreases, the reaction of formula 4 proceeds in the opposite direction, and the metal ions extracted into the organic phase are more easily back-extracted into the aqueous phase.
Since the pH at which metal ions are extracted varies depending on the type of metal ion, the target element is separated from impurity elements by controlling the pH in the solvent extraction process using an acidic extractant.
nRH _org + M ⁿ⁺ _aq → MR _norg + nH ⁺ _aq ... (Formula 4)
In the formula, RH represents an acidic extractant, Mn ⁺ represents an n-valent metal ion, org represents an organic phase, and aq represents an aqueous phase.

Therefore, in the first solvent extraction step S1, 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 that of cobalt, and it is possible to separate these impurity elements from cobalt by extracting them into an organic phase while leaving cobalt in the aqueous phase.
If the pH is less than 1.5, the extraction rate of these impurities is low and separation from cobalt becomes difficult, and if the pH exceeds 3.0, the extraction rate of cobalt also increases and the separability from the impurities decreases. When the pH is adjusted to 1.5 to 3.0, some of the cobalt may be extracted, but it is also possible to contact the organic phase after extraction with a hydrochloric acid solution with a lower pH than that used during extraction to recover the cobalt by back-extraction, thereby reducing the loss of cobalt.
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.

(Copper removal process S2)
The copper removal step S2 will be described with reference to FIG.
The copper removal step S2 is carried out by adding a sulfurizing agent to the cobalt chloride solution that has been subjected to the first solvent extraction step S1. An oxidizing agent and a neutralizing agent are also added to adjust the redox potential of the cobalt chloride solution to −100 to 200 mV (Ag/AgCl electrode standard) and the pH to 1.3 to 3.0.
By this step, a precipitate of copper sulfide is generated and separated from the cobalt chloride solution, and a cobalt chloride solution from which copper has been removed can be obtained.

Copper in the cobalt chloride solution forms a precipitate of copper sulfide according to the following formula 1, 2 or 3, and is removed from the solution.
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 S2, by adjusting the redox potential of the cobalt chloride solution to −100 to 200 mV (based on an Ag/AgCl electrode) and the pH to 1.3 to 3.0, copper can be sufficiently removed as sulfide and coprecipitation of cobalt can be suppressed.
If the redox potential exceeds 200 mV, the copper in the solution is not sufficiently removed, and if it is less than -100 mV, the amount of cobalt co-precipitated increases, which is not preferred. If the pH is less than 1.3, the copper in the solution is not sufficiently removed and the filterability of the resulting sulfide precipitate deteriorates. If the pH exceeds 3.0, the amount of cobalt co-precipitated increases with the removal of copper, which is not preferred.

The oxidation-reduction potential can be adjusted by adjusting the amount of sulfurizing agent added. The sulfurizing agent is not particularly limited, but hydrogen sulfide gas, sodium sulfide, sodium hydrosulfide crystals or aqueous solutions, etc. can be used.
When hydrogen sulfide or sodium hydrosulfide is used as the sulfiding agent, the pH is adjusted by adjusting the amount of the sulfiding 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. When the oxidation-reduction potential becomes lower than the desired value due to the addition of the sulfiding agent, the pH can be adjusted by adding an oxidizing agent. For example, the pH can be adjusted by introducing air into the solution and stirring it, or by adding a hydrogen peroxide solution.

(Dephosphorization step S5)
The dephosphorization step S5 will be described with reference to Figs.
The phosphorus removal step S5 is a step of precipitating phosphorus by adding an iron-containing solution to the cobalt chloride solution that has been subjected to the copper removal step S2. As the iron-containing solution, a ferric chloride solution or a ferric sulfate solution can be used.

In the alkyl phosphate extractant used in the first solvent extraction step S1, an amount of alkyl phosphate corresponding to the solubility is distributed to the aqueous phase. In particular, a new extractant contains phosphoric acid remaining at the time of production, and this phosphoric acid is distributed to the aqueous phase. In the phosphorus removal step S5 of the present invention, in order to remove the phosphorus, an iron-containing solution is added to the cobalt chloride solution, and the contained phosphorus is precipitated as iron phosphate as shown in formula 6.
Fe3 ^{+ +} _PO43- → FePO4 _↓ ... (Equation 6)

Iron ions come in divalent and trivalent forms, but trivalent iron ions are preferred when carrying out the dephosphorization step S5. This is because trivalent iron ions are less basic and precipitate at a lower pH. In addition, the solubility of iron phosphate is low at a pH of around 4 to 5, so it is desirable to adjust the pH to within this range.

The iron concentration of the cobalt chloride solution after the iron-containing solution is added is preferably approximately 0.1 to 2.0 g/L, depending on the phosphorus concentration. If the iron concentration is less than 0.1, phosphorus may not be removed. Even when a new extractant is used, an iron concentration of 2.0 g/L is sufficient, and excess iron is uneconomical as it increases chemical costs and lengthens the filtration time of the precipitate. In the dephosphorization step S5, if the iron concentration in the cobalt chloride solution after the iron-containing solution is added is 0.1 to 2.0 g/L, the phosphorus contained in the cobalt chloride solution and the added iron can be sufficiently recovered as precipitate, and a cobalt chloride solution free of phosphorus and iron can be obtained.

(Second solvent extraction step S3)
The second solvent extraction step S3 will be described with reference to FIGS.
The second solvent extraction step S3 is a step in which the cobalt chloride solution that has been subjected to the dephosphorization step S5 is contacted with an organic solvent containing a carboxylic acid extractant, cobalt is extracted into the organic solvent, and then the cobalt is stripped with sulfuric acid to obtain a cobalt sulfate solution.
The organic solvent used is a carboxylic acid extractant diluted with a diluent. Examples of the carboxylic acid extractant include versatic acid and naphthenic acid. These are acidic extractants having COOH groups.

When extracting metal ions, the carboxylic acid extractant releases protons corresponding to the valence of the metal into the aqueous phase, and the metal ion coordinates to the carbonyl oxygen. Many carboxylic acids form dimers and trimers by hydrogen bonding with each other in non-polar solvents. In addition, when extracting metal ions, carboxylic acids that are not acid-dissociated may coordinate to remove the hydration water coordinated to the metal ion. For example, the reaction in which a hexacoordinated divalent metal ion M2 ⁺ is extracted by _a dimeric carboxylic acid extractant _R2H2 is represented by 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)
In the formula, org represents an organic phase, and aq represents an aqueous phase.

(Extraction process)
In the extraction step 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 5.0 to 7.0. When the pH is in this range, the cobalt can be extracted into the organic phase by contacting the solution with an organic solvent containing a carboxylic acid extractant.
In this case, magnesium is not extracted and remains in the aqueous phase. If the pH is less than 5, it is difficult to extract cobalt, whereas if the pH is more than 7, the solubility of cobalt decreases and precipitation may occur.

When hydroxides and other precipitates are formed in this way, crud may be formed. Crud is an emulsion stabilized by solid particles that flow into or are generated in the solvent extraction process. When a third phase containing crud is formed at the interface between the aqueous phase and the organic phase, oil-water separation deteriorates, which is a major problem in terms of production efficiency.
If phosphorus remains in the cobalt chloride solution, cobalt phosphate or cobalt hydrogen phosphate will be formed. These compounds have low solubility and form precipitates even at a pH of around 5, which is thought to be a cause of crud formation. For this reason, in the present invention, a dephosphorization step S5 is provided to remove phosphorus in advance.

(Back extraction process)
In the back-extraction step in the second solvent extraction step S3, after the extraction step, the cobalt extracted into the organic phase is brought into contact with a sulfuric acid solution to adjust the pH to 2.0 to 4.5. This allows the cobalt to be back-extracted into the sulfuric acid solution. In this way, a high-purity cobalt sulfate solution is obtained.
Although stripping is possible even at a pH of less than 2, this is not preferred because the amount of the trace impurities extracted at a lower pH than cobalt increases, whereas a pH of more than 4.5 is not preferred because the rate of stripping cobalt decreases and the amount of cobalt recovered decreases.

Since the organic phase after extraction still contains fine aqueous phase even after phase separation, a washing step may be added to remove the aqueous phase before stripping. For example, a cobalt sulfate solution can be used as the aqueous phase in the washing step. The organic phase after stripping can be reused as the organic phase in the extraction step.
By the above method, a high-purity cobalt sulfate solution with few impurities can be produced.

(Crystallization step S4)
The crystallization step S4 will be described with reference to FIG.
In the crystallization step S4, crystals of cobalt sulfate are precipitated from the cobalt sulfate solution obtained in the second solvent extraction step S3. The crystallization method is not particularly limited, and can be performed using a general crystallization method.

For example, one method is to obtain crystals by placing a cobalt sulfate solution in a crystallizer and crystallizing it within the crystallizer. The crystallizer is used to precipitate crystals by evaporating the water in the cobalt sulfate solution under a certain pressure, and for example, a rotary evaporator or a double propeller type crystallizer is used. The internal pressure is reduced using a vacuum pump or the like, and in the rotary evaporator, crystallization proceeds while the flask is rotated and stirred with a double propeller. Note that in the crystallizer, a slurry is formed in which the cobalt sulfate solution is mixed with cobalt sulfate crystals.

The slurry discharged from the crystallizer is separated into cobalt sulfate crystals and mother liquor by a filter, a centrifuge, etc. The cobalt sulfate crystals are then dried in a dryer to remove moisture.
By the above method, it is possible to produce cobalt sulfate crystals from a cobalt sulfate solution. Of course, since the cobalt sulfate solution is a high-purity solution with few impurities, the obtained cobalt sulfate crystals are also high-purity with few impurities.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

Example 1
(First solvent extraction step S1)
An organic phase was prepared by diluting an alkyl phosphoric acid extractant (trade name D2EHPA, manufactured by Daihachi Chemical Industry Co., Ltd.) with a diluent (trade name Teclain N20, manufactured by JX Nippon Oil & Energy Corporation) so that the concentration was 40% by volume. 0.9 L of an aqueous phase consisting of a cobalt chloride solution having the composition shown in the original liquid A in Table 1 and 1.8 L of an organic phase were mixed, and a sodium hydroxide solution was added to adjust the pH to 1.7, and impurities were extracted. The same extraction operation was repeated with 0.9 L of the aqueous phase after extraction and 1.8 L of a new organic phase, and a total of three extraction operations were performed. As a result, a cobalt chloride solution having the composition shown in 1SX after B in Table 1 was obtained. The concentrations of zinc, manganese, and calcium were all 0.001 g/L or less, and these impurities were able to be separated and removed.

(Copper removal process S2)
0.9 L of the cobalt chloride solution obtained in the first solvent extraction step S1 was adjusted to pH 2.5 by adding sodium hydroxide solution, and then sodium hydrosulfide solution was added as a sulfiding agent to adjust the redox potential to -50 mV (Ag/AgCl electrode standard) to generate a precipitate of copper sulfide. The precipitate was separated and removed using a filter to obtain a filtrate having the composition shown in Post-sulfidation C in Table 1. The copper concentration was less than 0.001 g/L, and copper could be separated and removed.

(Dephosphorization step S5)
A ferric chloride solution with an iron concentration of 100 g/L was prepared and added to 0.5 L of the cobalt chloride solution obtained in the first solvent extraction step S1 so that the iron concentration was 2 g/L. Sodium hydroxide solution was then added to adjust the pH to 5, and a precipitate was obtained. The precipitate was separated and removed using a filter to obtain the composition shown in D after the second SX in Table 1. The phosphorus concentration was less than 0.001 g/L, and phosphorus could be separated and removed.

(Second solvent extraction step S3)
An organic phase was prepared by diluting a carboxylic acid extractant (product name Versatic Acid 10, manufactured by Oxalis Chemicals) with a diluent (Teclean N20) so that the concentration was 30% by volume. The cobalt chloride solution obtained in the dephosphorization step S5 was diluted with pure water to prepare an aqueous phase consisting of a cobalt chloride solution with a cobalt concentration of 20 g/L. Next, 0.44 L of the aqueous phase and 1 L of the organic phase were mixed, and a sodium hydroxide solution was added to adjust the pH to 6.0, and cobalt was extracted into the organic phase. At this time, a third phase containing a crud was not formed at the interface between the aqueous phase and the organic phase.
0.6 L of the extracted organic phase was mixed with 0.6 L of a cobalt chloride solution with a cobalt concentration of 10 g/L, and the aqueous phase mixed in the organic phase after extraction was washed. Then, this organic phase was mixed with 0.09 L of pure water, and sulfuric acid was added to adjust the pH to 4, and cobalt was back-extracted. As a result, a cobalt sulfate solution with the composition shown in 2nd SX D in Table 1 was obtained. The magnesium concentration was less than 0.001 g/L, and magnesium was separated and removed.
By the above method, a high purity cobalt sulfate solution was obtained.

(Crystallization step S4)
The cobalt sulfate solution was placed in a rotary evaporator, and the inside of the rotary evaporator was decompressed with a vacuum pump while the flask was rotated at a temperature of 40° C. to evaporate water and precipitate cobalt sulfate crystals. After solid-liquid separation, the obtained cobalt sulfate crystals were dried in a dryer. As a result, high-purity cobalt sulfate crystals as shown in Table 2 were obtained.

Example 2
A cobalt sulfate solution was obtained in the same manner as in Example 1, except that the organic phase to be subjected to the first solvent extraction step S1 was the organic phase used in Example 1, which had been subjected to stripping to separate and remove impurity elements with hydrochloric acid adjusted to a pH of 0.5 and was reused, and that in the dephosphorization step S5, a second ferric chloride solution was added to 0.5 L of the cobalt chloride solution obtained in the first solvent extraction step S1 so that the iron concentration was 1 g/L.
The composition in this case is shown in Table 3. As shown in D after the second SX in Table 3, a high-purity cobalt sulfate solution was obtained. In addition, in the second solvent extraction step S3, no third phase containing crud was generated at the interface between the aqueous phase and the organic phase.

Subsequently, crystallization was carried out in the same manner as in Example 1, and high purity cobalt sulfate crystals as shown in Table 4 were obtained.

(Comparative Example 1)
The second solvent extraction step S3 was carried out in the same manner as in Example 1, except that the dephosphorization step S5 was not carried out. As a result, a third phase containing crud was formed at the interface between the aqueous phase and the organic phase.

The results of Examples 1 and 2 and Comparative Example 1 above show that the present invention makes it possible to obtain highly pure cobalt sulfate from which impurities have been sufficiently removed.

The highly pure cobalt sulfate crystals obtained by this invention can be used as a raw material for lithium-ion secondary batteries and for a variety of other purposes.

S1 First solvent extraction step S2 Decopper removal step S3 Second solvent extraction step S4 Crystallization step S5 Dephosphorization step

Claims (7)

a first solvent extraction step in which an organic solvent containing an alkylphosphoric acid-based extractant is contacted with a cobalt chloride solution containing one or more impurities of copper, zinc, manganese, calcium, and magnesium, and zinc, manganese, and calcium are extracted into the organic solvent to be separated and removed;
a copper removal step of adding a sulfiding agent to the cobalt chloride solution that has been subjected to the first solvent extraction step to generate a precipitate of copper sulfide, which is then separated and removed;
a dephosphorization step in which an iron-containing solution is added to the cobalt chloride solution that has been subjected to the copper removal step to separate and remove phosphorus by precipitating the phosphorus;
a second solvent extraction step in which the cobalt chloride solution that has been subjected to the dephosphorization step is contacted with an organic solvent containing a carboxylic acid extractant to extract the cobalt into the organic solvent, and then the cobalt is stripped with sulfuric acid to obtain a cobalt sulfate solution;
A method for producing cobalt sulfate, comprising the steps of: The alkyl phosphate extractant in the first solvent extraction step is bis(2-ethylhexyl) hydrogen phosphate;
2. The method for producing cobalt sulfate according to claim 1, wherein the pH of the cobalt chloride solution is adjusted to 1.5 to 3.0, and the solution is subjected to solvent extraction using the bis(2-ethylhexyl) hydrogen phosphate , thereby extracting impurity elements into the organic solvent. 3. The method for producing cobalt sulfate according to claim 1 or 2, characterized in that in the copper removal step, an oxidizing agent and a neutralizing agent are added to the cobalt chloride solution to which the sulfiding agent has been added, thereby adjusting the redox potential to −100 to 200 mV (Ag/AgCl electrode standard) and the pH to 1.3 to 3.0. 4. The method for producing cobalt sulfate according to claim 1, 2 or 3, wherein in the dephosphorization step, an alkaline solution is added to the cobalt chloride solution to adjust the pH to 4 to 5. The second solvent extraction step includes an extraction step of adding an alkaline solution to the cobalt chloride solution from which copper, zinc, manganese and calcium have been removed, adjusting the pH to 5.0 to 7.0, and extracting cobalt into an organic solvent using a carboxylic acid extractant.
5. The method for producing cobalt sulfate according to claim 1, 2, 3 or 4. The second solvent extraction step includes a stripping step of contacting the organic solvent from which the cobalt has been extracted with a sulfuric acid solution, adjusting the pH to 2.0 to 4.5, and stripping the cobalt into the sulfuric acid solution, subsequent to the extraction step.
The method for producing cobalt sulfate according to claim 5 . 2. The method for producing cobalt sulfate according to claim 1, further comprising subjecting the cobalt sulfate solution obtained through the second solvent extraction step to a crystallization step to obtain crystals of cobalt sulfate.