JP7673528B2 - 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 industrially as a raw material for magnetic materials and lithium-ion secondary batteries, in addition to its use as an additive element in special alloys. 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 still contains various impurities derived from the raw materials used in the process.

Therefore, after nickel has been separated and recovered by the above-mentioned solvent extraction method, it is necessary to further remove impurity elements such as manganese, copper, zinc, calcium and magnesium from the cobalt solution.
Furthermore, in order to produce a high-purity cobalt product with a low impurity content, it was necessary to remove impurity elements from a cobalt solution that had been separated and recovered from a nickel solution containing cobalt in advance, and then to commercialize the cobalt through an electrolysis process, crystallization, or the like.

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 2020-019664 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 decoppering step in which a sulfiding agent is added to a cobalt chloride solution containing one or more impurities of copper, zinc, manganese, calcium, and magnesium to precipitate copper sulfide and separate and remove it; a first solvent extraction step in which the cobalt chloride solution that has undergone the copper removal step is brought into contact with an organic solvent containing an alkylphosphate-based extractant to extract zinc, manganese, and calcium into the organic solvent for separation and removal; a second solvent extraction step in which the cobalt chloride solution that has undergone the first solvent extraction step is brought into contact with an organic solvent containing a carboxylic acid extractant to extract cobalt into the organic solvent, and then the cobalt is strip-extracted with sulfuric acid to obtain a cobalt sulfate solution; and a reduction stripping step in which the organic solvent obtained after the stripping step in which the cobalt that has undergone the second solvent extraction step is strip-extracted into a sulfuric acid solution is brought into contact with an acid and a reducing agent to reduce cobalt, manganese, and iron ions in the organic solvent and strip-extract them to obtain a reduced strip-extracted solution.
The method for producing cobalt sulfate according to the second aspect of the present invention is characterized in that in the reduction stripping step, the organic solvent used in the stripping step of stripping cobalt into a sulfuric acid solution is contacted with an acid and a reducing agent to adjust the pH to 4.5 or less and the oxidation-reduction potential to 500 mV vs. Ag/AgCl or less, thereby reducing cobalt, manganese and iron ions in the organic solvent and stripping them to obtain a reduction stripping solution.
The method for producing cobalt sulfate according to a third aspect of the present invention is characterized in that, in the method for producing cobalt sulfate according to the first aspect of the present invention, the reduction stripping solution obtained in the reduction stripping step is added to the extraction step in the second solvent extraction step and/or the extraction step in the first solvent extraction step.

According to the first invention, copper is removed in the copper removal step, zinc, manganese and calcium are removed in the first solvent extraction step, and magnesium is removed in the second solvent extraction step, so that a high-purity cobalt sulfate solution from which all of the above impurities have been removed can be obtained. Therefore, it is possible to directly produce high-purity cobalt sulfate by separating the impurities from the cobalt without using an electrolysis step. Furthermore, the reduction stripping step allows the metal ions to be stripped from the organic phase obtained in the second solvent extraction step, thereby regenerating the organic solvent. This organic solvent can be reused in the first solvent extraction step and the second solvent extraction step.
According to the second invention, by contacting the organic solvent in which cobalt has been stripped into a sulfuric acid solution with an acid and a reducing agent, metal ions such as cobalt, manganese, and iron that have accumulated in the organic solvent can be reduced and stripped.
According to the third invention , the reduced strip solution containing cobalt is added to the extraction step in the second solvent extraction step and/or the first solvent extraction step , whereby cobalt can be recovered and loss to the outside of the system can be reduced.

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 S2 shown in FIG. 2. FIG. 3 is a detailed process diagram of the second solvent extraction step S3 and the reduction stripping step S4 shown in FIG. 2.

Specific embodiments of the present invention are described in detail below. 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 copper removal step S1 in which a sulfiding agent is added to a cobalt chloride solution containing one or more impurities of copper, zinc, manganese, calcium, and magnesium to generate a precipitate of copper sulfide and separate and remove it;
(2) a first solvent extraction step S2 in which the cobalt chloride solution from which copper has been removed by the copper removal step S1 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;
(3) a second solvent extraction step S3 in which the cobalt chloride solution from which copper, zinc, manganese and calcium have been removed by the first solvent extraction step S2 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;
(4) A reduction stripping process S4 in which the extractant (organic solvent) used for stripping cobalt in the second solvent extraction process S3 is contacted with an acid and a reducing agent to reduce and strip-extract cobalt, manganese and iron ions accumulated in the organic solvent.

By carrying out the above steps S1 to S4 in order, a cobalt sulfate solution is obtained.
After each of the steps S1 to S4, if necessary, a crystallization step S5 is carried out to precipitate crystals from the cobalt sulfate solution, thereby obtaining cobalt sulfate crystals.

In the present invention, although not shown in FIG. 1, 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 to separate and remove organic components mixed in the liquid may be added.
The second solvent extraction step S3 may also include a solvent recovery treatment S32 (see FIG. 4).

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 the cobalt chloride solution obtained after nickel is separated and recovered from a cobalt-containing nickel solution using an alkyl phosphate extractant or an amine extractant in the solvent extraction process of nickel smelting.

According to the present invention, as shown in FIG. 2, a high-purity cobalt sulfate solution can be obtained by removing copper from a cobalt chloride solution by forming a copper sulfide precipitate in a copper removal process S1, separating and removing zinc, manganese and calcium in a first solvent extraction process S2, and separating and removing magnesium in a second solvent extraction process S3. Therefore, a high-purity cobalt sulfate solution can be produced directly by separating impurities and cobalt without using an electrolysis process.

Then, following the second solvent extraction step S3, the reduction stripping step S4 is carried out. The reduction stripping step S4 is a step in which the organic solvent in the second solvent extraction step S3, which has been subjected to the cobalt stripping step S33 in which cobalt is stripped into a sulfuric acid solution, is contacted with an acid and a reducing agent to reduce and strip-extract metal ions such as cobalt, manganese, and iron in the organic solvent.

The reduction stripping liquid containing cobalt, manganese, and iron obtained in the reduction stripping process S4 is added to the second solvent extraction process S3 and/or the first solvent extraction process S2, respectively, and is reused.

According to the present invention, the cobalt sulfate solution after the steps S1 to S4 is subjected to the crystallization step S5, whereby crystals are precipitated from the solution to 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. 5. Fig. 2 shows the details of steps S1 to S4 shown in Fig. 1.

(Copper removal step S1)
The copper removal step S1 will be described with reference to FIG.
The copper removal step S1 is carried out by adding a sulfurizing agent to a cobalt chloride solution containing one or more impurities selected from the group consisting of copper, zinc, manganese, calcium, and magnesium, which is the starting material. The amount of the sulfurizing agent added is adjusted, and a neutralizing agent is added as necessary, 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.
In step S1, a precipitate of copper sulfide is generated and separated from the cobalt chloride solution, thereby obtaining a cobalt chloride solution from which copper has been removed.

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 S1, by adjusting the redox potential of the cobalt chloride solution to −100 to 200 mV (based on an Ag/AgCl electrode, the same applies below) 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 removal of copper from the solution becomes insufficient, and if the redox potential 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 removal of copper from the solution becomes insufficient 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. When the oxidation-reduction potential becomes lower than the desired value due to the addition of the sulfurizing agent, it can be adjusted by adding an oxidizing agent. For example, the oxidation-reduction potential can be adjusted by introducing air into the solution and stirring it, or by adding a hydrogen peroxide solution. The sulfurizing agent is not particularly limited, but hydrogen sulfide gas, sodium sulfide or 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.

(First solvent extraction step S2)
The first solvent extraction step S2 will be described with reference to FIGS.
The first solvent extraction step S2 is a step in which the cobalt chloride solution that has been subjected to the copper removal step is contacted with an organic solvent containing an alkyl phosphoric acid-based extractant, and zinc, manganese and calcium are extracted into the organic solvent and separated and removed. Since the main purpose of the first solvent extraction step is to remove impurities, the first solvent extraction step can also be called a "cleaning solvent extraction step."

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) phosphonic acid (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, which has high separability from cobalt, as an alkyl phosphate extractant. This is because bis(2-ethylhexyl) hydrogen phosphate has good properties for separating the impurities zinc, manganese, and calcium from a cobalt solution.

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 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 that of cobalt, and it is possible to separate these impurity elements from cobalt by extracting them into the organic phase while leaving the 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.

(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 of carrying out a cobalt extraction step S31 in which the cobalt chloride solution that has been through the first solvent extraction step S2 is brought into contact with an organic solvent containing a carboxylic acid-based extractant to extract cobalt, and then carrying out a cobalt stripping step S33 in which the cobalt is stripped with sulfuric acid to obtain a cobalt sulfate solution. Since the main purpose of the second solvent extraction step S3 is to convert the cobalt chloride solution into a cobalt sulfate solution, the "second solvent extraction step" can also be called a "bath conversion solvent extraction step".

The organic solvent used in the second solvent extraction step S3 is a carboxylic acid extractant diluted with a diluent. Examples of carboxylic acid extractants include versatic acid and naphthenic acid. These are acidic extractants that contain 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.

(Cobalt extraction step S31)
In the cobalt extraction step S31, 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-based 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, while if the pH is more than 7, the solubility of cobalt decreases and precipitation may occur.

The alkaline solution used as the neutralizing agent may be a solution of sodium hydroxide or potassium hydroxide.
In order to prevent oxidation of cobalt during extraction, bubbling with an inert gas such as nitrogen gas, argon gas, or carbon dioxide gas may be performed.
The residual liquid containing residual magnesium is discarded together with the residual liquid after the completion of the solvent recovery process S32 described below. Note that there is no environmental problem even if the magnesium is discharged.

(Solvent recovery process S32 and cobalt stripping process S33)
As shown in Fig. 2, a cobalt stripping step S33 is carried out after the cobalt extraction step S31. Also, as shown in Fig. 4, a solvent recovery process S32 may be carried out in parallel with the cobalt stripping step S33.

(Solvent recovery process S32)
In the cobalt chloride solution (aqueous phase) after the cobalt extraction step S31, the carboxylic acid extractant may be partially dissolved. This is not preferable because it results in a loss of the extractant and also affects the environment due to TOC (total organic carbon) caused by the extractant when the aqueous phase is subjected to wastewater treatment and discharged into the sea, etc. For this reason, it is advisable to carry out a solvent recovery process S32 shown in FIG. 4.

(Cobalt stripping step S33)
As shown in Fig. 4, in the cobalt stripping step S33, the cobalt extracted with the carboxylic acid extractant obtained in the cobalt extraction step S31 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 stripped into the sulfuric acid solution. In this way, a high-purity cobalt sulfate solution is obtained.
Although back extraction is possible even at a pH of less than 2, lowering the pH too much does not change the recovery amount much and the effect obtained is small. On the other hand, it is not preferable because the back extraction amount of trace impurities extracted at a pH lower than cobalt increases. In addition, there are problems such as high chemical costs, so it is preferable to set the pH at 2.0 or more. On the other hand, if the pH exceeds 4.5, the back extraction rate of cobalt decreases and the recovery amount of cobalt decreases, which is not preferable.

Since the organic phase after extraction obtained in the cobalt extraction step S31 contains fine aqueous phase even after phase separation, a washing step may be added to remove this aqueous phase before stripping. For the aqueous phase in the washing step, for example, a cobalt sulfate solution may be used. In addition, the organic phase after stripping obtained in the cobalt stripping step S33 can be reused as the organic phase used in the solvent recovery process S32.

(Reduction back extraction step S4)
The organic phase after stripping in the cobalt stripping step S33 can be reused as the organic phase (organic solvent) in the extraction step, but some metal ions are not stripped and remain extracted in the organic phase. If the amount of extracted metal ions increases, the number of organic molecules capable of newly extracting metal ions decreases relatively, so that it may become increasingly difficult to reuse the organic phase in the extraction step.

In the present invention, therefore, a reduction stripping step S4 is provided for stripping metal ions. In this reduction stripping step S4, an acid and a reducing agent are added to the organic phase in which some metal ions have not been stripped and remain extracted, and the pH is adjusted to 4.5 or less and the oxidation-reduction potential is adjusted to 500 mV vs. Ag/AgCl or less, thereby stripping metal ions.
By this reduction stripping step S4, metal ions such as cobalt, manganese, and iron accumulated in the organic solvent can be stripped at a high stripping rate.
In this way, the organic phase can be regenerated into an organic solvent more suitable for reuse in the extraction step, which can be reused as a carboxylic acid-based extractant in the second solvent extraction step S3, as shown in FIG.

The organic phase to be subjected to this reduction stripping step S4 does not need to be treated all at once after the cobalt has been stripped. For example, the accumulation status can be monitored and the organic phase can be subjected to the reduction stripping step only after it has reached a certain level.

In addition, in the reduction stripping step S4, a reduction stripping solution containing cobalt is obtained through reduction and stripping. By adding this to the cobalt extraction step S31 of the second solvent extraction step S3, it is recovered as cobalt sulfate by stripping, and the amount of cobalt loss outside the system can also be reduced.

Furthermore, by adding the reduction stripping solution to the first solvent extraction step S2, cobalt can also be recovered and the amount of cobalt loss outside the system can be reduced. When the method of adding the solution to the first solvent extraction step S2 is used, impurities such as manganese and iron are extracted with the solvent in the first solvent extraction step S2, and can be discharged outside the system, preventing the accumulation of impurities within the system.

As described above, the solution containing cobalt and the like obtained in the reduction stripping step S4 can be added to either the first solvent extraction step S2 or the second solvent extraction step S3, or to both extraction steps. When added to both steps, the amount of each added can be adjusted depending on the amount of impurities contained.
Furthermore, by subjecting the reduction stripping solution to a treatment such as neutralization, cobalt, manganese, iron, etc. can be recovered as neutralized precipitate.

The above method makes it possible to produce a high-purity cobalt sulfate solution with few impurities.

(Crystallization step S5)
The crystallization step S5 will be described with reference to FIG.
In the crystallization step S5, crystals of cobalt sulfate are precipitated from the cobalt sulfate solution obtained through the above steps. 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. A crystallizer is a device that precipitates 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 a rotary evaporator, crystallization proceeds while the flask is rotated and stirred with a double propeller. Inside 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, cobalt sulfate crystals can be produced from the cobalt sulfate solution. Of course, since the cobalt sulfate solution is relatively high purity 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]
(Copper removal step S1)
A sodium hydrosulfide solution was added as a sulfiding agent to 2 L of a cobalt chloride solution having the composition shown in original solution A in Table 1 and adjusted to pH 2.5, and the oxidation-reduction potential was adjusted to -50 mV (Ag/AgCl electrode standard) to generate a precipitate of copper sulfide. The precipitate was separated and removed using a filter, and a filtrate having the composition shown in post-sulfidation B in Table 1 was obtained. The copper concentration was less than 0.001 g/L, and copper was successfully separated and removed.

(First solvent extraction step S2)
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 the aqueous phase consisting of the cobalt chloride solution obtained in the copper removal step S1 and 1.8 L of the 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 C in Table 1 was obtained. The concentrations of zinc, manganese, and calcium were all less than 0.001 g/L, and these impurities were able to 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. 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, and a sodium hydroxide solution was added to adjust the pH to 6.5, and cobalt was extracted into the organic phase (cobalt extraction step S31).
0.6L of the extracted organic phase was mixed with 0.6L of a cobalt chloride solution with a cobalt concentration of 10g/L, and the aqueous phase mixed in the organic phase after extraction was washed. Then, this organic phase was mixed with 0.09L of pure water, and sulfuric acid was added to adjust the pH to 4, and cobalt was stripped (cobalt stripping step S33). As a result, a cobalt sulfate solution with the composition shown in 2SX after D in Table 1 was obtained. The magnesium concentration in the cobalt sulfate solution was less than 0.001g/L, and magnesium was sufficiently separated and removed.
By the above method, a high purity cobalt sulfate solution was obtained.

(Reduction back extraction step S4)
Next, 0.1 L of pure water was mixed with 0.1 L of the organic solvent from which most of the cobalt had been stripped, and the redox potential was gradually lowered while adjusting the pH to 1.0 using 35 wt % hydrochloric acid and 100 g/L aqueous sodium sulfite solution. As a result, the following cobalt stripping rates were obtained at each redox potential, and the organic solvent was regenerated to a state where it could be used again for cobalt extraction. Table 2 shows the relationship between the redox potential (mV vs. Ag/AgCl) and the cobalt stripping rate (%).

As shown in Table 2, by adjusting the redox potential to a reducing atmosphere of 500 mV vs. Ag/AgCl or less, cobalt could be recovered at a high back-extraction rate of 90% or more, preventing the loss of cobalt and at the same time obtaining an organic solvent with low cobalt accumulation suitable for reuse in the extraction process.

(Crystallization step S5)
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 3 were obtained.

[Example 2]
A cobalt sulfate solution was obtained in the same manner as in Example 1, except that in the copper removal step S1, the oxidation-reduction potential was adjusted to 150 mV (Ag/AgCl electrode standard), in the second solvent extraction step S3, 0.44 L of an aqueous phase obtained by diluting the cobalt chloride solution obtained in the first solvent extraction step S2 by two with pure water was mixed with the organic phase (cobalt extraction step S31), 0.6 L of the extracted organic phase was mixed with 0.6 L of a cobalt chloride solution having a cobalt concentration of 10 g/L to wash the aqueous phase that had been mixed in the organic phase after extraction, and this organic phase was mixed with 0.08 L of pure water, and sulfuric acid was added to adjust the pH to 4 to strip-extract cobalt (cobalt strip-extraction step S33).
The composition in this case is shown in Table 4. As shown in Table 4, after 2SX D, a high purity cobalt sulfate solution was obtained.

Subsequently, crystallization was carried out in the same manner as in Example 1, and high purity cobalt sulfate crystals as shown in Table 5 were obtained.

[Example 3]
The same operations as in the copper removal step S1 and the first solvent extraction step S2 of Example 1 were carried out to prepare 24 liters of the first SX post-liquid C. Using this liquid, the second solvent extraction step S3 and the reduction stripping step S4 were carried out to prepare 5 liters of the reduction stripping post-liquid.
The copper removal step S1 and the first solvent extraction step S2 of Example 1 were carried out again to prepare 24 liters of the first SX post-liquid C, to which 5 liters of the reduction stripping post-liquid C that had been prepared in advance was added and thoroughly stirred. The second solvent extraction step S3 was carried out using the liquid.

In the copper removal step S1, the cobalt contained in the sulfide precipitate is lost to the outside of the system, in the first solvent extraction step S2, the cobalt contained in the stripping liquid is lost to the outside of the system, and in the second solvent extraction step S3, the cobalt contained in the raffinate is lost to the outside of the system. In the reduction stripping step S4, a post-reduction stripping liquid is also generated, and there was a possibility that the cobalt contained therein would be lost to the outside of the system, but by repeating the second solvent extraction step S3, it was possible to recover it in the system. Table 6 shows the cobalt loss in each step when the amount of cobalt contained in the liquid before the copper removal step S1 is taken as 100%. When the process was not repeated, 2.7% of cobalt was lost, but by repeating the process, it was possible to suppress this to 0.7%.

[Example 4]
The same operations as in the copper removal step S1 and the first solvent extraction step S2 in Example 1 were carried out to prepare 720 L of the first SX post-liquid. Using this liquid, the second solvent extraction step S3 and the reduction stripping step S4 were carried out, and of the 150 L generated as the reduction stripping post-liquid, the first 145 L was not used, and only the 5 L generated near the end point was prepared.
The copper removal step S1 of Example 1 was repeated to prepare 35 L of sulfurization solution, to which 5 L of reduction stripping solution was added and stirred. The solution was used to carry out the first solvent extraction step S2 to obtain a first SX solution and a first SX stripping solution.

The sulfurization liquid and the reduction stripping liquid, which are the starting liquids of the first solvent extraction step S2, and the first SX liquid and the first SX stripping liquid, which are the final liquids of the first solvent extraction step S2, were analyzed by an ICP emission spectrometer, and the concentrations were calculated. Table 7 shows the cobalt, manganese, and iron concentrations of each liquid.
It was found that the manganese and iron contained in the post-sulfurization solution and the post-reduction stripping solution were distributed to the first SX stripping solution and could be discharged outside the system.

The results of Examples 1 to 4 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 copper removal step S2 first solvent extraction step S3 second solvent extraction step S4 reduction stripping step S5 crystallization step S31 cobalt extraction step S33 cobalt stripping step

Claims (3)

A copper removal process in which a sulfiding agent is added to a cobalt chloride solution containing one or more impurities selected from the group consisting of copper, zinc, manganese, calcium, and magnesium, to generate copper sulfide precipitates, which are then separated and removed;
a first solvent extraction step in which an organic solvent containing an alkylphosphoric acid extractant is contacted with the cobalt chloride solution that has been subjected to the copper removal step, and zinc, manganese and calcium are extracted into the organic solvent to be separated and removed;
a second solvent extraction step in which the cobalt chloride solution obtained in the first solvent extraction 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 reduction stripping step in which the organic solvent obtained after the second solvent extraction step is stripped into a sulfuric acid solution is contacted with an acid and a reducing agent to reduce and strip-extract the cobalt, manganese and iron ions in the organic solvent, and obtain a reduced stripping solution;
A method for producing cobalt sulfate, comprising the steps of: 2. The method for producing cobalt sulfate according to claim 1, wherein in the reduction stripping step, the organic solvent used in the stripping step of stripping cobalt into a sulfuric acid solution is contacted with an acid and a reducing agent to adjust the pH to 4.5 or less and the oxidation-reduction potential to 500 mV vs. Ag/AgCl or less, thereby reducing and stripping cobalt, manganese and iron ions in the organic solvent to obtain a reduction stripped solution. 2. The method for producing cobalt sulfate according to claim 1, wherein the reduction stripping solution obtained in the reduction stripping step is added to the extraction step in the second solvent extraction step and/or the extraction step in the first solvent extraction step.