JP2023067663A - Production method of cobalt sulfate - Google Patents

Abstract

To provide a production method of a highly pure cobalt sulfate without using an electrolysis process.SOLUTION: A production method of obtaining cobalt sulfate by removing impurities from a cobalt chloride solution containing one or more kinds of impurities of copper, zinc, manganese, calcium, and magnesium includes: (1) a prestage step including a copper removal step S1 of adding a sulfating agent to a cobalt chloride solution to generate, separate and remove a precipitation of a sulfide of copper, and a first solvent extraction step S2 of bringing a cobalt chloride solution into contact with an organic solvent containing alkylphosphoric acid-based extractant to extract into the organic solvent, thereby, separating and removing zinc, manganese, and calcium; and (2) a poststage step including a second solvent extraction step S3 of adjusting a pH of the cobalt chloride solution after the prestage step, to 4.0-7.0, bringing the cobalt chloride solution into contact with an organic solvent containing a carboxylic acid-based extractant containing 1 vol.% or more of strait-chain carboxylic acid, and thereafter subjecting to back-extraction 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 particularly, it relates to a production method for obtaining high-purity 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, in addition to being used as an additive element in special alloys. In particular, recently, lithium ion secondary batteries have been widely used as batteries for mobile devices and electric vehicles, and along with this, the demand for cobalt is rapidly expanding. However, most of cobalt is produced as a by-product of nickel smelting and copper smelting, so 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, first, in order to obtain a solution containing nickel and cobalt, the raw material is leached or extracted into a solution using a mineral acid or an oxidizing agent, or is subjected to a dissolution treatment. attached. Furthermore, nickel and cobalt contained in the obtained acidic solution are often separated and recovered by a conventionally known method by solvent extraction using various organic extractants.
However, the obtained cobalt solution often contains various impurities derived from the processing raw material.

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 solvent extraction method.
Moreover, in order to produce a high-purity cobalt product with a low impurity content, it is necessary to remove the impurity elements from the cobalt solution that has been separated and recovered from the cobalt-containing nickel solution in advance, and then remove the cobalt by electrolysis or crystallization. It had to be produced.

Patent Documents 1 and 2 disclose conventional techniques for removing impurity elements in a cobalt solution.
Patent Document 1 describes (1) adding a sulfiding agent to a cobalt solution, adjusting the oxidation-reduction potential (ORP) (based on Ag/AgCl electrode) to 50 mV or less and pH to 0.3 to 2.4, and sulfiding (2) adding an oxidizing agent and a neutralizing agent to the copper-removing purification solution, and increasing the oxidation-reduction potential (based on Ag/AgCl electrode) to 950 to 1050 mV and the pH; 2.4 to 3.0 to obtain a manganese precipitate and a demanganized purified liquid; A method for purifying a cobalt solution is disclosed that includes a solvent extraction step to extract zinc, calcium and trace impurities.
In Patent Document 2, a cobalt chloride solution with a hydrochloric acid concentration of 2 to 6 mol/L is brought into contact with an anion exchange resin, and iron and zinc that form a complex having a partition coefficient with respect to the anion exchange resin greater than that of the cobalt chloride complex. , a technique of adsorbing and separating metal impurities such as tin.

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 and the solvent extraction method using an amine-based extractant are better than the solvent extraction method using the above-mentioned alkyl phosphoric acid. It has higher zinc and cobalt separation performance.
Further, when removing a very small amount of zinc in a cobalt chloride solution, the ion exchange method is more efficient and economical because the steps and operations are simpler.

From this point of view, as a method for removing these impurity elements from a cobalt chloride solution containing manganese, copper, and zinc, a method combining the purification method of Patent Document 1 and the separation technology of Patent Document 2 has been proposed. (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 electrolysis steps.
In the dezincification step, the cobalt chloride aqueous solution obtained in the decopperization step is brought into contact with an anion exchange resin to adsorb and remove zinc. In the electrolysis step, the high-purity cobalt chloride aqueous solution obtained in the dezincification step is used as an electrolysis supply liquid to produce metallic cobalt (also called electrolytic cobalt).

On the other hand, as described above, the demand for cobalt as a raw material for lithium ion secondary batteries has increased recently, and cobalt sulfate solutions or cobalt sulfate crystals are desired.
In order to obtain cobalt sulfate crystals from metallic cobalt obtained by the prior art of Patent Document 3, the 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, manufacturing costs increase due to an increase in the number of steps and an increase in the cost of chemicals. In addition, plate-like metallic cobalt has a slow dissolution rate in sulfuric acid as it is used in corrosion-resistant alloys, and in order to dissolve it in a short time, it is necessary to powderize the plate-like metallic cobalt by atomizing treatment or the like. .
Therefore, there has been a demand for a method of directly obtaining a cobalt sulfate solution from a cobalt chloride solution without going through metallic cobalt.

JP-A-2004-285368 Japanese Patent Application Laid-Open No. 2001-020021 JP 2020-19664 A

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

A method for producing cobalt sulfate according to a first aspect of the present invention is 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, comprising: is a decoppering step in which a sulfiding agent is added to the cobalt chloride solution to form a precipitate of copper sulfide to be separated and removed; It includes a first solvent extraction step in which zinc, manganese and calcium are extracted into an organic solvent and separated and removed. Then, it is brought into contact with an organic solvent containing a carboxylic acid-based extractant containing 1% by volume or more of a straight-chain carboxylic acid, and after cobalt is extracted with the organic solvent, the cobalt is back-extracted with sulfuric acid to obtain a cobalt sulfate solution. It is characterized by comprising a two-solvent extraction process.
A method for producing cobalt sulfate according to a second aspect of the invention is characterized in that, in the first aspect of the invention, the preceding step is performed in the order of the decoppering 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 of the invention, the first stage step is performed in the order of the first solvent extraction step and the copper removal step.
A fourth aspect of the invention is a method for producing cobalt sulfate in the first aspect, wherein 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 aspect of the invention is the method according to the first, second, third or fourth aspect, wherein in the decoppering step, an oxidizing agent and a neutralizing agent are added to a cobalt chloride solution to which a sulfiding agent has been added. It is characterized by adjusting the oxidation-reduction potential to −100 to 200 mV (based on Ag/AgCl electrode) and the pH to 1.3 to 3.0.
A method for producing cobalt sulfate according to a sixth invention is characterized in that, in the first, second, third or fourth invention, the alkyl phosphate-based extractant in the first solvent extraction step is bis(2-ethylhexyl) hydrogen phosphate. 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 the impurity elements into the organic solvent. .
A method for producing cobalt sulfate according to a seventh invention is characterized in that, in the first, second, third or fourth invention, 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. and adjusting the pH to 2.0 to 4.5, and performing a back-extraction step of back-extracting cobalt into a sulfuric acid solution.

According to the first invention, copper, zinc, manganese, and calcium can be removed from the cobalt chloride solution containing impurities by the decoppering step and the first solvent extraction step included in the former step, and the second solvent extraction included in the latter step. Magnesium can be removed by the process. Therefore, high-purity cobalt sulfate can be produced without using an electrolytic process. In addition, by containing 1% by volume or more of the straight-chain carboxylic acid in the extractant, the generation of oxidized trivalent cobalt ions can be suppressed, and the recovery efficiency of cobalt in the back extraction step can be maintained at a high level.
According to the second invention, copper, zinc, manganese, and calcium can be separated and removed from the cobalt chloride solution containing impurities by performing the decoppering step and the first solvent extraction step in that order, so that the second solvent extraction can be performed. A high-purity cobalt sulfate solution from which impurities are removed can be obtained by separating and removing magnesium in the process.
According to the third invention, copper, zinc, manganese, and calcium can be separated and removed from the cobalt chloride solution containing impurities by performing the first solvent extraction step and the copper removal step in that order, so that the second solvent extraction can be performed. A high-purity cobalt sulfate solution from which impurities are removed can be obtained by separating and removing magnesium in the process.
According to the fourth invention, high-purity cobalt sulfate crystals can be obtained from the cobalt sulfate solution by further performing the crystallization step.
According to the fifth invention, by adjusting the oxidation-reduction potential and pH to 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 cobalt remains in the aqueous phase.
According to the seventh invention, even if the pH is adjusted to the low pH side of 4.0 to 7.0, cobalt can be extracted by bringing it into contact with an organic solvent containing a carboxylic acid-based extractant. In addition, since extraction can be performed at a low pH, precipitates such as hydroxides are less likely to occur, and as a result, crud is less likely to form, resulting in stable operation.

1 is a principle diagram of a method for producing cobalt sulfate according to the present invention; FIG. BRIEF DESCRIPTION OF THE DRAWINGS It is process drawing which shows the manufacturing method of cobalt sulfate which concerns on 1st Embodiment of this invention. 3 is a detailed process diagram showing a method for producing cobalt sulfate shown in FIG. 2. FIG. FIG. 4 is a detailed process diagram of a first solvent extraction step S2 shown in FIG. 3; FIG. 4 is a detailed process diagram of a second solvent extraction step S3 shown in FIG. 3; It is process drawing which shows the manufacturing method of the cobalt sulfate which concerns on 2nd Embodiment of this invention. 7 is a detailed process diagram showing a method for producing cobalt sulfate shown in FIG. 6. FIG. FIG. 8 is a detailed process diagram of a first solvent extraction step S2 shown in FIG. 7; FIG. 8 is a detailed process diagram of a second solvent extraction step S3 shown in FIG. 7;

Specific embodiments of the present invention will be described in detail below. In addition, the present invention is not limited to the following embodiments, and various modifications are possible without changing 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 described with reference to FIG.
The present invention provides 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 former step includes a decoppering step S1 in which a sulfiding agent is added to the cobalt chloride solution to form a precipitate of copper sulfide to separate and remove it, and an organic A first solvent extraction step S2 of contacting a solvent and extracting zinc, manganese and calcium into the organic solvent to separate and remove them,
(2) In the latter step, the pH of the cobalt chloride solution that has undergone the previous step is adjusted to 4.0 to 7.0, and then the solution is added to an organic solvent containing a carboxylic acid-based extractant containing 1% by volume or more of a straight-chain carboxylic acid. It is characterized by comprising a second solvent extraction step S3 for obtaining a cobalt sulfate solution by contacting and extracting cobalt with the organic solvent and then back-extracting the cobalt with sulfuric acid.
The preceding 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 performed after the former step.

In the present invention, a crystallization step S4 of precipitating crystals from a cobalt sulfate solution is carried out as necessary after each of the steps S1 to S3. By performing the crystallization step S4, crystals can be precipitated from the solution to obtain cobalt sulfate crystals.

In the present invention, after the first solvent extraction step S2 and/or after the second solvent extraction step S3, the step of subjecting the liquid to an oil-water separator such as an activated carbon column in order to separate and remove organic components mixed in 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. The application of the present invention is not limited at all as long as the cobalt chloride solution contains such impurities. It is preferably applied to a cobalt chloride solution after nickel has been separated and recovered by an amine-based extractant.

According to the present invention, copper is removed from the cobalt chloride solution by producing copper sulfide precipitates in the decoppering step S1, zinc, manganese and calcium are separated and removed in the first solvent extraction step S2, and the second solvent is A high-purity cobalt sulfate solution can be obtained by separating and removing magnesium in the extraction step S3. 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 a method for producing cobalt sulfate will be described with reference to FIGS. 2 to 5. FIG. FIG. 2 is a diagram showing all the steps in the first embodiment, and FIG. 3 shows details of each step S1 to S3 shown in FIG.
In the first embodiment, as shown in FIG. 2, the copper removal step S1 and then the first solvent extraction step S2 are performed in the order of the former steps.

(Decopper step S1)
The copper removal step S1 will be explained based on FIG.
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, which are starting materials. Also, an oxidizing agent and a neutralizing agent are added to adjust the oxidation-reduction 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.
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 is removed from the solution by forming a precipitate of copper sulfide according to Equation 1, Equation 2 or Equation 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 decoppering step S1, the oxidation-reduction potential of the cobalt chloride solution is adjusted to −100 to 200 mV (based on Ag/AgCl electrode) and the pH is adjusted to 1.3 to 3.0. It can be sufficiently removed and, moreover, the co-precipitation of cobalt can be suppressed.
If the oxidation-reduction potential exceeds 200 mV, the removal of copper in the solution becomes insufficient, and if the oxidation-reduction potential is less than -100 mV, the amount of co-precipitation of cobalt increases, which is not preferable. On the other hand, if the pH is less than 1.3, the removal of copper in the solution becomes insufficient, and the filterability of the sulfide precipitate that forms deteriorates. If the pH exceeds 3.0, the amount of cobalt co-precipitation increases due to the removal of copper, which is not preferable.

The oxidation-reduction potential can be adjusted by adjusting the amount of the sulfiding agent added. The sulfiding agent is not particularly limited, but hydrogen sulfide gas, crystals or aqueous solutions of sodium sulfide or sodium hydrosulfide can be used.
When hydrogen sulfide or sodium hydrosulfide is used as the sulfiding agent, the pH is adjusted by adjusting the addition 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. Moreover, when the oxidation-reduction potential becomes lower than the desired value due to the introduction of the sulfurizing agent, it can be adjusted by adding the 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)
1st solvent extraction process S2 is demonstrated based on FIG.3 and FIG.4.
In the first solvent extraction step S2, the cobalt chloride solution that has undergone the copper removal step S1 is brought into contact with an organic solvent containing an alkyl phosphate-based extractant, and zinc, manganese, and calcium are extracted from the organic solvent and separated and removed. is.

As the organic solvent, an alkyl phosphate-based extractant diluted with a diluent is used. As alkyl phosphate-based 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, bis(2-ethylhexyl) hydrogen phosphate is preferably used as an extractant because it is highly separable from cobalt when zinc, manganese and calcium are separated from a cobalt chloride solution from which copper has been removed.

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

An acidic extractant such as an alkyl phosphate-based extractant extracts metal ions by replacing the -H of the extractant with cations in the aqueous phase to form a metal salt, as shown in Equation 4. It is an extractant that In general, the higher the pH, the easier it is for metal ions to be extracted into the organic phase, and the lower the pH, the more the reaction of formula 4 proceeds in the opposite direction, and the more likely it is that the metal ions extracted into the organic phase will be back-extracted into the aqueous phase. .
Since the extracted pH differs depending on the type of metal ion, the target element and the impurity element are separated by controlling the pH in the solvent extraction step using an acidic extractant.
nRH _org + M ^{n +} _aq → MR _norg + nH ⁺ _aq (equation 4)
In the formula, RH is an acidic extractant, Mn ⁺ is an n-valent metal ion, org is an organic phase, and aq is 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 extractability of zinc, manganese and calcium tends to be higher than that of cobalt, leaving cobalt in the aqueous phase and extracting these impurity elements into the organic phase to separate them from cobalt. It is possible.
If the pH is less than 1.5, the extraction rate of these impurities is low, making it difficult to separate them from cobalt. . When the pH is adjusted to 1.5 to 3.0, some of the cobalt may be extracted, but the organic phase after the extraction is brought into contact with a hydrochloric acid solution having a pH lower than that of the extraction to back-extract the cobalt. Cobalt loss can also be reduced.
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 the loss of cobalt is not limited to the case where 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 when the extractant is subjected to the next cobalt extraction, and the cobalt cannot be efficiently recovered. A loss of efficiency may occur, which may result in increased production costs. In the present invention, the term "loss" is used as a general term for the fact that these and others cannot be recovered optimally.

(Second solvent extraction step S3)
The second solvent extraction step S3 will be described based on FIGS. 3 and 5. FIG.
In the second solvent extraction step S3, the pH of the cobalt chloride solution that has undergone the first solvent extraction step is adjusted to 4.0 to 7.0, and then a carboxylic acid-based extractant containing 1% by volume or more of linear carboxylic acid is added. It is a step of contacting with an organic solvent to extract cobalt from the organic solvent, and then back-extracting the cobalt with sulfuric acid to obtain a cobalt sulfate solution.

As the organic solvent, a carboxylic acid-based extractant diluted with a diluent is used. Examples of carboxylic acid-based extractants include versatic acid and naphthenic acid. These are acidic extractants with a branched structure with COOH groups. Furthermore, a carboxylic acid having a straight-chain structure (straight-chain carboxylic acid) is included in a part of the carboxylic acid-based extractant. Examples of linear carboxylic acids include heptanoic acid, octanoic acid, decanoic acid, and dodecanoic acid. By including a straight-chain carboxylic acid, oxidation of cobalt can be suppressed as described later.

The content of the linear carboxylic acid in the carboxylic acid-based extractant is 1% by volume or more. When the linear carboxylic acid is added to the carboxylic acid-based extractant to obtain a desired content, the addition ratio means the ratio of the linear carboxylic acid to the organic solvent. As a specific example, when adding 1 vol.% of a linear carboxylic acid using an organic solvent of 30 vol.% of extractant mixed with 70 vol. This means mixing 29% by volume of the carboxylic acid with 70% by volume of the diluent.

In general, when extracting metal ions, a carboxylic acid-based extractant releases protons corresponding to the valence of the metal into the aqueous phase, and the metal ions are coordinated to carbonyl oxygen. Many carboxylic acids form dimers and trimers with each other through hydrogen bonding in nonpolar solvents. In addition, when extracting metal ions, carboxylic acids that are not acid-dissociated may be coordinated so as 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-based extractant R ₂ H ₂ is represented by Equation 5.
[M _{( H2O} ) ₆ ] ²⁺ _aq +3( _R2H2 ) _org
→ (MR ₂ ·4RH) _org +2H ⁺ _aq +6H ₂ O _aq (Formula 5)
Here, org in the formula indicates an organic phase and aq indicates an aqueous phase.

In the present invention, only part of the carboxylic acid-based extractant is linear carboxylic acid. Extraction using straight-chain carboxylic acid alone is technically possible, and there are advantages such as efficient extraction even at a lower pH. On the other hand, linear carboxylic acids have the disadvantage of being slightly more soluble in the aqueous phase than carboxylic acids with non-linear structures. be. Specifically, when octanoic acid is 1% by volume, the TOC is 5 mg/L, but when it is 30% by volume, it increases to 150 mg/L. load increases. Therefore, in the present invention, the linear carboxylic acid is contained in a composition that prevents oxidation of cobalt at a minimum ratio.

(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 case of the extractant of the present invention, as described above, there is an advantage that extraction can be performed at a pH lower than that of the conventional one. On the other hand, since the solubility is slightly high, there is also a demerit that the concentration of TOC (total organic carbon) in the aqueous phase obtained by solvent extraction increases. Specifically, when octanoic acid is 1%, TOC increases by 5 mg/L, and when 30%, the TOC increases by 150 mg/L, so the load on COD (Chemical Oxygen Demand) treatment in wastewater treatment increases accordingly. However, even with the above disadvantages, extraction at a low pH has the great advantage of avoiding crud formation and stabilizing the operation.

In the present invention, since the pH is adjusted to the above range, the cobalt can be extracted into the organic phase by bringing it into contact with an organic solvent containing a straight-chain carboxylic acid-based extractant. At this time, magnesium is not extracted and remains in the aqueous phase. If the pH is less than 4, extraction of cobalt is difficult, while if the pH exceeds 7, the solubility of cobalt decreases and precipitation may occur.
In addition, as an alkaline solution used for pH adjustment, specifically, a solution of sodium hydroxide or potassium hydroxide can be used.
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 step, if only a carboxylic acid with a low carbon number is used as an extractant, cobalt is likely to be oxidized into trivalent cobalt ions, but if an extractant containing a straight-chain carboxylic acid with a high carbon number is used, , the oxidation of cobalt is suppressed.
Therefore, as will be described later, the cobalt recovery efficiency in the back extraction process can be maintained at a high level.

(Reverse extraction process)
After the extraction step, the extracted cobalt and sulfuric acid solution are brought into contact with the organic phase to adjust the pH to 2.0-4.5. This allows the cobalt to be back-extracted into the sulfuric acid solution. A high-purity cobalt sulfate solution is thus obtained.
Back-extraction is possible even if the pH is less than 2, but this 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 reverse extraction rate of cobalt decreases, and the recovery amount of cobalt decreases, which is not preferable.

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

Since fine water phases are mixed in the organic phase after extraction even after phase separation, a washing step may be added to remove the water phases before back extraction. For example, a cobalt sulfate solution can be used for the aqueous phase of the washing step. In addition, the organic phase after back extraction can be reused as the organic phase in the extraction process.
A high-purity cobalt sulfate solution containing few impurities can be produced by the above method.

(Crystallization step S4)
The crystallization step S4 will be explained based on 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. A crystallization method is not particularly limited, and a general crystallization method can be used.

For example, a method of obtaining crystals by placing a cobalt sulfate solution in a crystallizer and crystallizing in the crystallizer can be used. The crystallizer deposits crystals by evaporating water in the cobalt sulfate solution under a predetermined pressure. For example, a rotary evaporator or a double propeller type crystallizer is used. The internal pressure is reduced by a vacuum pump or the like, and crystallization proceeds while rotating the flask with a rotary evaporator and stirring with a double propeller. In the crystallizer, the cobalt sulfate solution is mixed with cobalt sulfate crystals to form a slurry.

The slurry discharged from the crystallizer is subjected to solid-liquid separation into cobalt sulfate crystals and a mother liquor by a filter, a centrifugal separator, or the like. After that, the cobalt sulfate crystals are dried in a dryer to remove water.
Cobalt sulfate crystals can be produced from a cobalt sulfate solution in the manner described above. Of course, since the cobalt sulfate solution contains few impurities and is of high purity, the obtained cobalt sulfate crystals are also of high purity with few impurities.

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

(First solvent extraction step S2)
1st solvent extraction process S2 is demonstrated based on FIG.7 and FIG.8.
In the first solvent extraction step S2, a cobalt chloride solution containing one or more impurities of copper, zinc, manganese, calcium and magnesium, which is a starting material, is brought into contact with an organic solvent containing an alkyl phosphate-based extractant, and the organic solvent is This is the process of extracting and separating and removing zinc, manganese and calcium. Note that part of the copper can also be extracted and separated and removed.

The alkyl phosphate-based 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, including the adjustment range of pH, the execution of this step S2 is performed in the same manner as in the first embodiment.

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 rates of zinc, manganese and calcium tend to be higher than the extraction rates of cobalt, and cobalt is extracted from the aqueous phase. These impurity elements can be separated from cobalt by leaving them in the organic phase and extracting them into the organic phase. When the pH is adjusted to 1.5 to 3.0, some of the cobalt may be extracted, but the organic phase after the extraction is brought into contact with a hydrochloric acid solution having a pH lower than that of the extraction to back-extract the cobalt. Cobalt loss can also be reduced.

(Decopper step S1)
The copper removal step S1 will be described with reference to FIG.
The copper removal step S1 is performed by adding a sulfiding agent to the cobalt chloride solution that has passed through the first solvent extraction step S2. Also, an oxidizing agent and a neutralizing agent are added to adjust the oxidation-reduction 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.
By this step S1, 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.

The method for adjusting the oxidation-reduction potential and the method for adjusting the pH may be the same as in the first embodiment, and the sulfiding agent used in the first embodiment may be used.
By carrying out this step, copper sulfide precipitates 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. FIG.
In the second solvent extraction step S3, the pH of the cobalt chloride solution that has undergone the first solvent extraction step S2 and the copper removal step S1 is adjusted to 4.0 to 7.0, and then linear carboxylic acid is added at 1% by volume or more. It is a step of bringing into contact with an organic solvent containing a carboxylic acid extractant, extracting cobalt with this organic solvent, and then back-extracting the cobalt with sulfuric acid to obtain a cobalt sulfate solution.

As the carboxylic acid-based extractant as the organic solvent, a carboxylic acid-based extractant containing 1% by volume or more of carboxylic acid having a linear structure is used as in the first embodiment. In addition, oxidation of cobalt can be suppressed by using a linear carboxylic acid as a part of the carboxylic acid-based extractant.
Then, similarly to the first embodiment, generation of hydroxide crud can be suppressed and operation can be stabilized.

The addition of the alkaline solution in the extraction step in the second solvent extraction step S3 and the adjustment range of the pH may be the same as in the first embodiment.
In addition, the contact with the sulfuric acid solution in the back extraction step and the operation procedure such as the adjustment range of pH may be the same as in the first embodiment.
By performing each of the above steps, magnesium can be left in the aqueous phase, and a high-purity cobalt sulfate solution with reduced impurities can be obtained. Then, in the second solvent extraction step S3, it is possible to avoid situations unfavorable to the operation such as the generation of hydroxide due to the increase in pH during operation and the accompanying crud generation, so that the operation is stable. can be played. Moreover, the high cobalt recovery efficiency can be maintained as in the first embodiment.

(Crystallization step S4)
The crystallization step S4 will be explained based on 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. A crystallization method is not particularly limited, and a general crystallization method can be used. Therefore, a crystallization method using a crystallization can can be used as in the first embodiment.

Cobalt sulfate crystals can be produced from a cobalt sulfate solution in the manner described above. Of course, since the cobalt sulfate solution contains few impurities and is of high purity, the obtained cobalt sulfate crystals are also of high purity with few impurities.

EXAMPLES 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. Examples 1 to 3 below are included in the manufacturing method of the first embodiment.

[Example 1]
(Decopper step S1)
A sodium hydrosulfide solution was added as a sulfiding agent to 2 L of the cobalt chloride solution having the composition shown in the original solution A in Table 1 adjusted to pH 2.5 to adjust the oxidation-reduction potential to −50 mV (based on Ag/AgCl electrode). to form copper sulfide precipitates. The precipitate was separated and removed with a filter to obtain a filtrate having the composition shown in B after sulfurization in Table 1. The copper concentration was less than 0.001 g/L, and the copper could be separated and removed.

(First solvent extraction step S2)
Organic diluted with a diluent (trade name Teclean N20, JX Nikko Nisseki Energy Co., Ltd.) so that the concentration of alkyl phosphate-based extractant (trade name D2EHPA, manufactured by Daihachi Chemical Co., Ltd.) is 40% by volume Prepare the phases. 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 a sodium hydroxide solution is added to adjust the pH to 1.7, and impurities are removed. Extracted. The same extraction operation was repeated with 0.9 L of the aqueous phase after extraction and 1.8 L of the new organic phase, and a total of three extraction operations were carried out. As a result, a cobalt chloride solution having the composition shown in Table 1 after the first SX 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.

(Second solvent extraction step S3)
The organic phase was diluted with a diluent (Techleen N20) so that the concentration of the carboxylic acid-based extractant (trade name: Versatic Acid 10, manufactured by Oxalis Chemicals), together with the amount of octanoic acid described later, was 30% by volume. Got ready. In addition, octanoic acid (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd. under the trade name of octanoic acid) was used as a straight-chain carboxylic acid-based extractant in the organic phase. Five conditions of 0.5 volume % addition, 1 volume % addition, and 10 volume % addition were changed.

Next, each sample was mixed with 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, and a sodium hydroxide solution was added to adjust the pH to 6.5. to extract the cobalt 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 had passed, and subjected to back extraction.

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 to wash the aqueous phase mixed in the extracted organic phase. Subsequently, this organic phase was mixed with 0.009 L of pure water, sulfuric acid was added to adjust the pH to 4, and cobalt was back-extracted. Table 2 shows the results. The concentrations of copper, zinc, manganese, calcium and magnesium 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 added amount of octanoic acid, which is a straight-chain carboxylic acid, is increased, the oxidation of cobalt can be suppressed even after 164 hours, especially when 1% by volume or more of octanoic acid is added. It can be seen that the cobalt loss in the back extraction process can be suppressed.

(Crystallization step S4)
The cobalt sulfate solution was put into a rotary evaporator, the pressure inside was reduced by a vacuum pump, and the temperature was maintained at 40° C., and water was evaporated while rotating the flask portion to precipitate crystals of cobalt sulfate. After the solid-liquid separation, the cobalt sulfate crystals obtained were dried with 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 decanoic acid was used as the linear carboxylic acid-based extractant added to the organic phase in the second solvent extraction step S3. A reagent manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd. (trade name: decanoic acid) was used as the extractant.
As shown in Table 4, when 1 vol% of decanoic acid was added to the organic solvent, oxidation of cobalt after 164 hours could be suppressed, and cobalt loss in the back extraction process could be suppressed. .

[Example 3]
In the second solvent extraction step S3, cobalt sulfate was extracted in the same manner as in Example 1, except that the straight-chain carboxylic acid-based extractant added to the organic phase was changed to dodecanoic acid (lauric acid is another name for dodecanoic acid). A solution was obtained. As the extractant, a reagent manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd. (trade name: lauric acid) was heated to 50° C. and liquefied.
As shown in Table 5, when 1 vol% of dodecanoic acid was added to the organic solvent, oxidation of cobalt after 164 hours could be suppressed, and cobalt loss in the back extraction step could be suppressed. .

According to the results of Examples 1 to 3 belonging to the method for producing cobalt sulfate according to the first embodiment described above, it is possible to obtain high-purity cobalt sulfate in which impurities are sufficiently removed while the recovery efficiency of cobalt is maintained high. I found out. Regarding the method for producing cobalt sulfate according to the second embodiment, experiments according to Examples 1 to 3 were not conducted. Since the order of the solvent extraction step S2 is different but there is no essential difference, similar results can be obtained by experiments.

The high-purity cobalt sulfate crystals obtained by the present invention can be used as raw materials for lithium-ion secondary batteries, as well as for various other purposes.

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

Claims (7)

A manufacturing 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 former step includes a decoppering step of adding a sulfiding agent to the cobalt chloride solution to form a precipitate of copper sulfide to separate and remove the copper sulfide, and bringing the cobalt chloride solution into contact with an organic solvent containing an alkyl phosphate-based extractant. , a first solvent extraction step of extracting zinc, manganese and calcium into the organic solvent to separate and remove;
In the latter step, the pH of the cobalt chloride solution that has undergone the previous step is adjusted to 4.0 to 7.0, and then contacted with an organic solvent containing a carboxylic acid-based extractant containing 1% by volume or more of a straight-chain carboxylic acid, A method for producing cobalt sulfate, comprising a second solvent extraction step of 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 stage 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 cobalt sulfate crystals. In the decoppering step, an oxidizing agent and a neutralizing agent are added to a cobalt chloride solution containing a sulfiding agent to adjust the redox potential to −100 to 200 mV (based on Ag/AgCl electrode) and pH to 1.3 to 3. 5. The method for producing cobalt sulfate according to claim 1, 2, 3 or 4, wherein the adjustment is made to 0.0. The alkyl phosphate-based extractant in the first solvent extraction step is bis(2-ethylhexyl) hydrogen phosphate,
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 the cobalt is back extracted into the sulfuric acid solution. 5. The method for producing cobalt sulfate according to claim 1, 2, 3 or 4, wherein an extraction step is performed.

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