Method for producing cobalt sulfate

Abstract

To provide a method for separating impurities and cobalt without using a zinc electrowinning method, and producing a cobalt sulfate solution.SOLUTION: A method for producing cobalt sulfate executes: a copper removal step S1 of adding a sulfurizing agent to a cobalt chloride solution, and producing a precipitate of a sulfide of copper; a first solvent extraction step S2 of bringing an organic solvent containing an alkylphosphate-based extractant into contact with the cobalt chloride solution, and extracting zinc, manganese and calcium with the organic solvent and a second solvent extraction step S3 of bringing an organic solvent containing a carboxylic acid-based extractant into contact with the cobalt chloride solution and extracting cobalt with the organic solvent, and then back-extracting cobalt with a sulfuric acid and obtaining a cobalt sulfate solution; a solvent recovery step S5 of bringing the cobalt chloride solution after removal of the impurities into contact with the organic solvent containing the carboxylic acid extractant after back-extracting, and separating and recovering the carboxylic acid-based extractant contained in the cobalt chloride solution after the removal of the impurities; and a cobalt recovery step S6 of adding a carbonizing agent and / or a neutralizing agent to the cobalt chloride solution after the removal of the impurities, and precipitating and recovering cobalt.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for producing cobalt sulfate. More specifically, the present invention relates to a production method for removing impurity elements contained in a cobalt chloride solution to obtain cobalt sulfate with high purity.

Background Art

[0002] Cobalt is a valuable metal widely used in industrial applications 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, recently, lithium-ion secondary batteries are widely used as batteries for mobile devices and electric vehicles, and accordingly, the demand for cobalt is rapidly expanding. However, since most cobalt is produced as a by-product of nickel smelting and copper smelting, separation from impurities such as nickel and copper is an important key technology in cobalt production.

[0003] For example, when recovering cobalt as a by-product in the wet smelting of nickel, first, in order to obtain a solution containing nickel and cobalt, the raw material is subjected to leaching, extraction, or dissolution treatment using a mineral acid, an oxidizing agent, or the like. Further, nickel and cobalt contained in the obtained acidic solution are often separated and recovered by a solvent extraction method using various organic extractants by a conventionally known method. However, the obtained cobalt solution often contains various impurities derived from the treatment raw material.

[0004] Therefore, it is necessary to further remove impurity elements such as manganese, copper, zinc, calcium, and magnesium from the cobalt solution after nickel is separated and recovered by the above 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 in the cobalt solution separated and recovered from the nickel solution containing cobalt in advance, and then commercialize cobalt by an electrolysis process or crystallization.

[0005] As a method for removing impurity elements in a cobalt solution, there are conventional techniques described in Patent Documents 1 and 2. Patent Document 1 discloses a method for purifying a cobalt solution, including: (1) a copper removal step of adding a sulfiding agent to the cobalt solution, adjusting the oxidation-reduction potential (ORP) (Ag / AgCl electrode standard) to 50 mV or less and the pH to 0.3 to 2.4 to obtain a copper sulfide precipitate and a copper-removed purified solution; (2) a manganese removal step of adding an oxidizing agent and a neutralizing agent to the copper-removed purified solution, adjusting the oxidation-reduction potential (Ag / AgCl electrode standard) to 950 to 1050 mV and the pH to 2.4 to 3.0 to obtain a manganese precipitate and a manganese-removed purified solution; and (3) a solvent extraction step of using alkylphosphoric acid as an extractant to extract and separate zinc, calcium, and trace impurities in the manganese-removed purified solution. Patent Document 2 describes a technique in which a cobalt chloride solution with a hydrochloric acid concentration of 2 to 6 mol / L is brought into contact with an anion exchange resin to adsorb and separate metal impurities such as iron, zinc, and tin that form complexes with a distribution coefficient for the anion exchange resin larger than that of the cobalt chloride complex.

[0006] The solvent extraction method using alkylphosphoric acid as the extractant described in Patent Document 1 has high separation performance for zinc and calcium. However, in the case of a cobalt chloride solution with a hydrochloric acid concentration of 2 to 6 mol / L, the ion exchange method using an anion exchange resin or the solvent extraction method using an amine-based extractant has higher separation performance for zinc and cobalt than the solvent extraction method using the above alkylphosphoric acid. Also, when removing extremely trace amounts of zinc in a cobalt chloride solution, the ion exchange method is more efficient and economical because the process and operation are simpler.

[0007] From such a perspective, 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 technique 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 manganese removal step for removing manganese, a copper removal step for removing copper, a zinc removal step for removing zinc, and an electrolysis step. In the zinc removal step, an aqueous cobalt chloride solution obtained in the copper removal step is brought into contact with an anion exchange resin to adsorb and remove zinc. In the electrolysis step, the high-purity aqueous cobalt chloride solution obtained in the zinc removal step is used as an electrolysis feed solution to produce metallic cobalt (also referred to as electrolytic cobalt).

[0008] On the other hand, as described above, recently, the demand for cobalt as a raw material for lithium-ion secondary batteries has been expanding, and the form of cobalt sulfate solution or cobalt sulfate crystals is desired. If one attempts to obtain cobalt sulfate crystals from the metallic cobalt obtained by the prior art of Patent Document 3, the metallic cobalt can be dissolved in sulfuric acid to obtain a cobalt sulfate solution, and further, this solution can be crystallized to obtain cobalt sulfate crystals. However, when using this manufacturing method, the manufacturing cost increases due to an increase in the number of steps and an increase in chemical costs. In addition, plate-shaped metallic cobalt has a slow dissolution rate in sulfuric acid as used in corrosion-resistant alloys, and in order to dissolve it in a short time, it is necessary to make the plate-shaped metallic cobalt into a powder by an atomization process or the like. For this reason, a method for directly obtaining a cobalt sulfate solution from a cobalt chloride solution without going through metallic cobalt has been desired.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0010] The present invention has been proposed in view of the above circumstances, and an object thereof is to provide a method for producing cobalt sulfate with high purity by separating impurities and cobalt from a cobalt chloride solution containing impurities without using an electrolysis step.

Means for Solving the Problems

[0011] A method for producing a cobalt sulfate solution according to a first invention is a production method for obtaining cobalt sulfate by removing one or more impurities of copper, zinc, manganese, calcium, and magnesium from a cobalt chloride solution containing the impurities, A front-end process, a back-end process, and a recovery process are executed. In the Previous step above, is a copper removal process and a first solvent extraction process are included. The back-end process consists of a second solvent extraction process including a cobalt extraction process and a stripping process. The recovery process includes a solvent recovery process and a cobalt recovery process. In the copper removal process, adding a sulfiding agent to the cobalt chloride solution , the redox potential of the cobalt chloride solution is adjusted to -100 to 200 mV (Ag / AgCl electrode standard) and the pH is adjusted to 1.3 to 3.0 to generating and separating a precipitate of copper sulfide make , In the first solvent extraction process, the after passing through the copper removal process, contacting an organic solvent containing an alkyl phosphoric acid extractant with the cobalt chloride solution, the pH is adjusted to 1.5 to 3.0, extracting zinc, manganese, and calcium into the organic solvent , leaving cobalt in the aqueous phase and separating making , In the cobalt extraction process, the the first solvent extraction contacting an organic solvent containing a carboxylic acid extractant with the cobalt chloride solution that has undergone the above steps, the pH is adjusted to 5.0 to 7.0, organic phase extracting cobalt into the so that magnesium remains in the aqueous phase. In the stripping process, the cobalt extracted into the organic phase in the cobalt extraction process is brought into contact with a sulfuric acid solution, and the pH is adjusted to 2.0 to 4.5, cobalt with sulfuric acid into the solution performing back extraction to obtain a cobalt sulfate solution to make it so. In the solvent recovery process, the cobalt contacting the cobalt chloride solution after impurity removal obtained by the extraction step with the cobalt in the stripping process the back extraction is made organic solvent containing a carboxylic acid extractant after to adjusting the pH to 4.0 or less to separate the carboxylic acid extractant contained in the cobalt chloride solution after impurity removal and recovered. In the cobalt recovery process, the cobalt chloride solution after impurity removal after recovering the carboxylic acid extractant the pH is adjusted to 7.0 to 12.0 to recovering cobalt by precipitation make it It is characterized by the above. The method for producing a cobalt sulfate solution according to the second invention is characterized in that, in the first invention, the previous stage process is executed in the order of the copper removal process and the first solvent extraction process. The method for producing a cobalt sulfate solution according to the third invention is characterized in that, in the first invention, the previous stage process is executed in the order of the first solvent extraction process and the copper removal process. 。 Fourth The method for producing a cobalt sulfate solution of the invention is the first 1 In the invention, the cobalt precipitate is added in the first solvent extraction process and used as a neutralizing agent. The first 5 The method for producing a cobalt sulfate solution of the invention is the first 1 In the invention, the cobalt precipitate is added to the cobalt extraction process in the second solvent extraction process and used as a neutralizing agent.

Advantages of the Invention

[0012] According to the first invention, The following effects are achieved. a) From a cobalt chloride solution containing impurities, copper, zinc, manganese, and calcium can be removed by the copper removal process and the first solvent extraction process included in the previous stage process, and magnesium can be removed by the second solvent extraction process included in the subsequent stage process. Therefore, high-purity cobalt sulfate can be produced without using an electrolysis process. b) In the copper removal process, by adjusting 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, copper can be sufficiently removed as a sulfide, and moreover, coprecipitation of cobalt can be suppressed. c) In the first solvent extraction process, by adjusting the pH to 1.3 to 3.0, the extraction rates of zinc, manganese, and calcium can be made higher than the extraction rate of cobalt, enabling separation from cobalt. d) In the extraction process of the second solvent extraction process, by adjusting the pH to 5.0 to 7.0, magnesium can be left in the aqueous phase and cobalt can be extracted into the organic phase. In the stripping process, by adjusting the pH to 2.0 to 4.5 and stripping cobalt into the sulfuric acid solution, a high-purity cobalt sulfate solution can be obtained. e) In the solvent recovery process in the recovery process, by adjusting the pH to 4.0 or less, the carboxylic acid-based extractant contained in the cobalt chloride solution can be separated and recovered into the organic phase, so this carboxylic acid-based extractant can be used as the organic phase in the extraction process. Also, in the cobalt recovery process, by adjusting the pH to 7.0 to 12.0, the precipitation rate of cobalt can be increased, and the ratio of cobalt recoverable within the system can be increased. According to the second invention, by performing the copper removal process and the first solvent extraction process in that order from a cobalt chloride solution containing impurities, copper, zinc, manganese, and calcium can be separated and removed. Therefore, if magnesium is separated and removed in the second solvent extraction process, a high-purity cobalt sulfate solution with impurities removed can be obtained. According to the third invention, by performing the first solvent extraction step and the copper removal step in that order from a cobalt chloride solution containing impurities, copper, zinc, manganese, and calcium can be separated and removed. Therefore, if magnesium is separated and removed in the second solvent extraction step, a high-purity cobalt sulfate solution with impurities removed can be obtained. 。 Fourth According to the invention, by using the cobalt precipitate as a neutralizing agent in the first solvent extraction step, the off-system loss of cobalt can be reduced. Article 5 According to the invention, by using the cobalt precipitate as a neutralizing agent in the cobalt extraction step of the second solvent extraction step, the off-system loss of cobalt can be reduced.

Brief Description of the Drawings

[0013]

Figure 1

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Modes for Carrying Out the Invention

[0014] Hereinafter, specific embodiments of the present invention will be described in detail. It should be noted that the present invention is not limited to the following embodiments, and various modifications are possible without changing the gist of the present invention. In this specification, the notation "X to Y" (where X and Y are arbitrary numerical values) means "X or more and Y or less".

[0015] (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. 1. The present invention is a production method for obtaining cobalt sulfate by removing one or more impurities of copper, zinc, manganese, calcium, and magnesium from a cobalt chloride solution containing the impurities, (1) The previous stage process includes a copper removal step S1 in which a sulfiding agent is added to the cobalt chloride solution to form a precipitate of copper sulfide and separate and remove it, and an organic solvent containing an alkylphosphoric acid-based extractant is brought into contact with the cobalt chloride solution, and zinc, manganese, and calcium are extracted into the organic solvent and separated and removed in a first solvent extraction step S2. (2) The subsequent stage process consists of a second solvent extraction step S3 in which an organic solvent containing a linear carboxylic acid-based extractant is brought into contact with the cobalt chloride solution that has undergone the previous stage process, cobalt is extracted into the organic solvent, and then cobalt is back-extracted with sulfuric acid to obtain a cobalt sulfate solution. (3) As a recovery step, the cobalt chloride solution after impurity removal obtained by the second solvent extraction step is brought into contact with the organic solvent containing the carboxylic acid extractant after back-extraction, the pH is adjusted to 4.0 or less, and the carboxylic acid-based extractant contained in the cobalt chloride solution after impurity removal is separated and recovered in a solvent recovery step, and a carbonating agent and / or a neutralizing agent are added to the cobalt chloride solution after impurity removal from which the carboxylic acid-based extractant has been recovered, and a cobalt recovery step of precipitating and recovering cobalt is performed.

[0016] In the present invention, the previous stage process may be carried out in the order of the copper removal step S1 and the first solvent extraction step S2, or may be carried out 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 subsequent stage process is carried out after the previous stage process. Among the recovery steps, the solvent recovery step S5 may be carried out in parallel with the back-extraction step S32 in the second solvent extraction step S3, or may be carried out as a subsequent step to the back-extraction step S32. The cobalt recovery step S6 is executed after the solvent recovery step S5.

[0017] In the present invention, after the first solvent extraction step S2 and / or after the second solvent extraction step S3, a step of subjecting 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.

[0018] The cobalt chloride solution used as a starting material in the present invention contains at least one of copper, zinc, manganese, calcium, and magnesium as impurity elements. The cobalt chloride solution containing such impurities is not particularly limited to the application of the present invention, but is particularly suitable for a cobalt chloride solution in which nickel is separated and recovered from a nickel solution containing cobalt by an alkylphosphoric acid-based extractant or an amine-based extractant in the solvent extraction step of nickel smelting.

[0019] According to the present invention, from the cobalt chloride solution, copper sulfide precipitate is generated by the copper removal step S1 to remove copper, zinc, manganese, and calcium are separated and removed by the first solvent extraction step S2, and magnesium is separated and removed by the second solvent extraction step S3, so that a high-purity cobalt sulfate solution can be obtained. Therefore, impurities and cobalt can be separated without using an electrolysis step, and a high-purity cobalt sulfate solution can be directly produced. In addition, the carboxylic acid-based extractant obtained in the solvent recovery step S5 can be used as the organic phase in the extraction step S31, and cobalt can be recovered at a high precipitation rate in the cobalt recovery step S6, so that a high-purity cobalt sulfate solution can be produced with less loss outside the system.

[0020] (First Embodiment) The first embodiment of the method for manufacturing cobalt sulfate will be described with reference to FIGS. 2 to 6. FIG. 2 is a diagram showing all the steps in the first embodiment, and FIG. 3 is a diagram summarizing the details of each of the steps S1 to S3 shown in FIG. 2. As shown in FIG. 2, in the first embodiment, in the previous step, the copper removal step S1 is first performed, and then the first solvent extraction step S2 is performed in this order.

[0021] (Copper removal step S1) The copper removal step S1 will be described with reference to FIG. 3. The copper removal step S1 is performed by adding a sulfiding agent to a cobalt chloride solution containing one or more impurities of copper, zinc, manganese, calcium, and magnesium as starting materials. An oxidizing agent and a neutralizing agent are also added to adjust the oxidation-reduction potential of the cobalt chloride solution to -100 to 200 mV (Ag / AgCl electrode standard) and the pH to 1.3 to 3.0. By this step, a precipitate of copper sulfide is generated and separated from the cobalt chloride solution, and a cobalt chloride solution from which copper has been removed can be obtained.

[0022] Copper in the cobalt chloride solution forms a precipitate of copper sulfide according to the following formula 1, formula 2, or formula 3 and is removed from the solution. CuCl2 + H2S → CuS↓ + 2HCl ··· (Formula 1) CuCl2 + Na2S → CuS↓ + 2NaCl ··· (Formula 2) CuCl2 + NaHS → CuS↓ + NaCl + HCl ··· (Formula 3)

[0023] In the above copper removal step S1, when the oxidation-reduction potential of the cobalt chloride solution is adjusted to -100 to 200 mV (Ag / AgCl electrode standard) and the pH is adjusted to 1.3 to 3.0, copper can be sufficiently removed as a sulfide, and coprecipitation of cobalt can be suppressed. If the redox potential exceeds 200 mV, the removal of copper in the solution will be insufficient. If the redox potential is less than -100 mV, the amount of coprecipitation of cobalt will increase, which is not preferable. Also, if the pH is less than 1.3, the removal of copper in the solution will be insufficient and the filterability of the sulfide precipitate formed will deteriorate. If the pH exceeds 3.0, the amount of cobalt coprecipitation accompanying the removal of copper will increase, which is not preferable.

[0024] The adjustment of the above redox potential can be carried out by adjusting the addition amount of the sulfurizing agent. The sulfurizing agent is not particularly limited, and hydrogen sulfide gas, sodium sulfide, crystals or aqueous solutions of sodium hydrosulfide, etc. can be used.

[0025] Also, when hydrogen sulfide or sodium hydrosulfide is used as the sulfurizing agent, the adjustment of the above pH is carried out by adjusting the addition amount of the sulfurizing agent and adding a pH adjuster. The pH adjuster is not particularly limited, and alkali salts such as sodium hydroxide, calcium hydroxide, sodium carbonate, cobalt carbonate, etc. can be used. Further, when the redox potential becomes lower than the desired value due to the introduction of the sulfurizing agent, it can be adjusted by adding an oxidizing agent. For example, it can be adjusted by introducing air into the solution and stirring, or by adding a hydrogen peroxide solution.

[0026] (First solvent extraction step S2) The first solvent extraction step S2 will be described based on FIGS. 3 and 4. The first solvent extraction step S2 is a step of bringing an organic solvent containing an alkylphosphoric acid-based extractant into contact with the cobalt chloride solution that has undergone the copper removal step S1, and extracting and separating zinc, manganese, and calcium into the organic solvent.

[0027] An alkyl phosphate extractant diluted with a diluent is used as the organic solvent. Examples of the alkyl phosphate extractant include bis(2-ethylhexyl) hydrogen phosphate (D2EHPA), 2-ethylhexyl 2-ethylhexylphosphonate (PC-88A), and di(2,4,4-trimethylpentyl)phosphinic acid (CYANEX272). Among these, bis(2-ethylhexyl) hydrogen phosphate is preferably used as the extractant for separating and removing zinc, manganese, and calcium from a cobalt chloride solution from which copper has been removed.

[0028] 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 desirably to 20 to 50% by volume. If the concentration of the extractant is less than 10%, impurity elements with high concentrations and impurity elements with low distribution ratios (element concentration in the organic phase / element concentration in the solution) 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 property after the extraction operation of the organic solvent (organic phase) and the cobalt chloride solution (aqueous phase) deteriorates.

[0029] An acidic extractant such as an alkyl phosphate extractant is an extractant that extracts metal ions by substituting the -H of the extractant with a cation in the aqueous phase to form a metal salt, as shown in Formula 4. Generally, as the pH increases, metal ions are more likely to be extracted into the organic phase, and when the pH is lowered, the reaction of Formula 4 proceeds in the reverse direction, and the metal ions extracted into the organic phase are likely to be back-extracted into the aqueous phase. Since the extraction pH varies depending on the type of metal ion, in the solvent extraction process using an acidic extractant, the separation of the target element and impurity elements is performed by controlling the pH. nRH org + M n+ aq → MR norg + nH + aq ···(Formula 4) Here, RH in the formula is an acidic extractant, M n+n-valent metal ion, org represents the organic phase, and aq represents the aqueous phase.

[0030] 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. By leaving cobalt in the aqueous phase and extracting these impurity elements into the organic phase, separation from cobalt is possible. When the pH is less than 1.5, the extraction rates of these impurities are low, making it difficult to separate from cobalt. When the pH exceeds 3.0, the extraction rate of cobalt also increases, and the separability from impurities decreases. When the pH is adjusted to 1.5 to 3.0, although a part of cobalt may be extracted, the extracted organic phase can be contacted with a hydrochloric acid solution having a lower pH than that during extraction to back-extract and recover cobalt, thereby reducing the loss of cobalt. Furthermore, when this organic phase is contacted 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.

[0031] (Second solvent extraction step S3) The second solvent extraction step S3 will be described based on FIGS. 3 and 5. The second solvent extraction step S3 performs a cobalt extraction step S31 in which an organic solvent containing a carboxylic acid extractant is brought into contact with the cobalt chloride solution that has undergone the first solvent extraction step to extract cobalt, and then a cobalt back-extraction step S33 in which cobalt is back-extracted with sulfuric acid, to obtain a cobalt sulfate solution.

[0032] As the organic solvent, a carboxylic acid extractant diluted with a diluent is used. Many carboxylic acids form dimers and trimers with each other by hydrogen bonding in a non-polar solvent. Also, when extracting metal ions, a carboxylic acid that has not dissociated acid to remove the water of hydration coordinated to the metal ion may coordinate. For example, the reaction in which a 6-coordinate divalent metal ion M 2+ is extracted by a dimer carboxylic acid extractant R2H2 is represented by the following formula 5. [M(H2O)6]2+ aq +3(R2H2) org → (MR2·4RH) org +2H + aq +6H2O aq ···(Formula 5) Here, org in the formula indicates the organic phase, and aq indicates the aqueous phase.

[0033] As the carboxylic acid extractant, either a branched - structured one or a linear - structured one can be used. Examples of the branched - structured extractants include versatic acid and naphthenic acid, etc., and examples of the linear - structured extractants include heptanoic acid, octanoic acid, decanoic acid, and dodecanoic acid, etc. If a linear - structured carboxylic acid is included in a part of the carboxylic acid extractant, the oxidation of cobalt can be suppressed. In addition, carboxylic acids with a linear structure can extract cobalt at a lower pH compared to branched - structured versatic acid, etc. Therefore, even if the pH rises during operation, the formation of hydroxides and other unfavorable situations such as clad generation associated with it can be avoided. For this reason, there is an advantage that the operation is stable.

[0034] (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, the pH is adjusted to 5.0 - 7.0, and it is brought into contact with an organic solvent containing a carboxylic acid extractant to extract cobalt into the organic phase. At this time, magnesium is not extracted and remains in the aqueous phase. If the pH is less than 5, the extraction of cobalt is difficult. On the other hand, if the pH exceeds 7, the solubility of cobalt decreases and precipitation may occur. At this time, the carboxylic acid extractant dissolves partially into the cobalt chloride solution by setting the pH to 5.0 - 7.0.

[0035] (Back - extraction step S33) After the cobalt extraction step S31, the cobalt extracted into the organic phase is brought into contact with a sulfuric acid solution to adjust the pH to 2.0 to 4.5, and the cobalt is back-extracted into the sulfuric acid solution, thereby obtaining a high-purity cobalt sulfate solution. Although back-extraction is possible even when the pH is less than 2, it is not preferable because the amount of back-extracted trace impurities extracted at a pH lower than that of cobalt increases. On the other hand, when the pH exceeds 4.5, the back-extraction rate of cobalt decreases, and the recovery amount of cobalt decreases.

[0036] Note that since a fine aqueous phase is mixed in the organic phase even after phase separation after extraction, a washing step for removing this aqueous phase may be added before back-extraction. For example, a cobalt sulfate solution can be used for the aqueous phase in the washing step. Further, the organic phase after back-extraction can be reused as the organic phase in the extraction step.

[0037] (Recovery step) The solvent recovery step S5 and the cobalt recovery step S6 in the recovery step will be described. As shown in FIG. 6, the solvent recovery step S5 is a step of bringing the cobalt chloride solution after impurity removal obtained in the cobalt extraction step S31 in the second solvent extraction step S3 into contact with an organic solvent containing a carboxylic acid extractant after back-extracting cobalt in the back-extraction step S33, adjusting the pH to 4.0 or less, and separating and recovering the carboxylic acid extractant contained in the cobalt chloride solution after impurity removal. In this step S5, by adjusting the pH to 4.0 or less, the carboxylic acid extractant dissolved in the cobalt chloride solution is separated and can be recovered into the organic phase. The organic phase to which the carboxylic acid extractant has been returned can be reused as the organic phase in the cobalt extraction step S31 as shown in FIG. 5. This solvent recovery step S5 may be carried out in parallel with the back-extraction step S32 in the second solvent extraction step S3 as shown by the dotted line in FIG. 5.

[0038] As shown in FIG. 6, the cobalt recovery step S6 is a step of adding a carbonating agent and / or a neutralizing agent to the cobalt chloride solution after impurity removal after recovering the carboxylic acid extractant and recovering cobalt by precipitation. That is, in the solvent recovery step S5, the carboxylic acid extractant dissolved from the cobalt chloride solution is recovered, and a carbonating agent and a neutralizing agent are added to the residual liquid after the solvent is recovered, or a carbonating agent or a neutralizing agent is added to obtain cobalt carbonate or cobalt hydroxide.

[0039] In this step, by adjusting the pH to 7.0 - 12.0, the precipitation rate of cobalt can be increased, and the ratio of cobalt recoverable in the system can be increased. When the pH is less than 7.0, the recovery rate decreases, and when the pH exceeds 12.0, an excessive amount of carbonating agent or neutralizing agent will be used. Therefore, a pH of 7.0 - 12.0 is appropriate. In particular, a pH range of 7.0 - 8.0 is more preferable because it can maintain a high cobalt recovery ratio while reducing the usage amount of the carbonating agent and the neutralizing agent. Thereby, the loss of cobalt outside the system can be reduced, and a high-purity cobalt sulfate solution can be produced.

[0040] As shown in Fig. 6, the cobalt precipitate obtained in the cobalt recovery step S6 can be added as a neutralizing agent in the first solvent extraction step S2. It can also be added to the cobalt extraction step S31 in the second solvent extraction step S3 and used as a neutralizing agent. By using the cobalt precipitate as a neutralizing agent in this way, the loss of cobalt outside the system can be reduced.

[0041] (Crystallization of Cobalt Sulfate Solution) When it is desired to obtain cobalt sulfate crystals from the cobalt sulfate solution obtained in the second solvent extraction step, it may be subjected to a crystallization step. The crystallization method is not particularly limited and can be carried out using a general crystallization method. For example, there is a method of obtaining crystals by storing the cobalt sulfate solution in a crystallization tank and crystallizing it in the crystallization tank. The crystallization tank is one that precipitates crystals by evaporating the water in the cobalt sulfate solution under a predetermined pressure. For example, a rotary evaporator or a double propeller type crystallization tank is used. The pressure inside is reduced by a vacuum pump or the like, and in the case of a rotary evaporator, crystallization proceeds while rotating the flask, and in the case of a double propeller, while stirring. Note that in the crystallization tank, it is a slurry in which cobalt sulfate crystals are mixed in the cobalt sulfate solution.

[0042] The slurry discharged from the crystallization tank is solid-liquid separated into cobalt sulfate crystals and mother liquor by a filter, a centrifuge, or the like. Thereafter, the cobalt sulfate crystals are dried with a dryer to remove moisture. High-purity cobalt sulfate crystals with few impurities can be produced by the above method.

[0043] (Second Embodiment) A second embodiment of the method for producing cobalt sulfate will be described based on FIGS. 7 to 9. FIG. 7 is a diagram showing all the steps in the second embodiment, and FIG. 8 is a diagram summarizing the details of each of the steps S2, S1, and S3 shown in FIG. 7. As shown in FIG. 7, in the second embodiment, in the previous step, first, the first solvent extraction step S2 and then the copper removal step S1 are executed in this order.

[0044] (First Solvent Extraction Step S2) The first solvent extraction step S2 will be described based on FIGS. 8 and 9. In the first solvent extraction step S2, an organic solvent containing an alkyl phosphoric acid extractant is brought into contact with a cobalt chloride solution containing one or more impurities of copper, zinc, manganese, calcium, and magnesium as starting materials, and zinc, manganese, and calcium are extracted and separated and removed by this organic solvent. Note that a part of copper can also be extracted and separated and removed.

[0045] The alkyl phosphoric acid 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 that in the first embodiment. Further, including the adjustment range of pH, this step S2 is carried out in the same manner as in the first embodiment.

[0046] 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 rate of cobalt. By leaving cobalt in the aqueous phase and extracting these impurity elements into the organic phase, it is possible to separate them from cobalt. When the pH is adjusted to 1.5 to 3.0, a part of cobalt may be extracted. However, by bringing the organic phase after extraction into contact with a hydrochloric acid solution having a lower pH than at the time of extraction and back-extracting and recovering cobalt, the loss of cobalt can also be reduced.

[0047] (Copper removal step S1) The copper removal step S1 will be described based on FIG. 8. The copper removal step S1 is carried out by adding a sulfurizing agent to the cobalt chloride solution that has passed through the first solvent extraction step S2. Further, 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 (Ag / AgCl electrode standard) 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.

[0048] 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 sulfurizing agent may also be the one used in the first embodiment. By carrying out this process, 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.

[0049] (Second solvent extraction step S3) The second solvent extraction step S3 will be described with reference to FIG. 8. In the second solvent extraction step S3, an organic solvent containing a carboxylic acid extractant is brought into contact with a cobalt chloride solution that has passed through the first solvent extraction step S2 and the copper removal step S1. After extracting cobalt into this organic solvent, cobalt is back-extracted with sulfuric acid to obtain a cobalt sulfate solution.

[0050] As the carboxylic acid extractant as the organic solvent, branched and / or linear carboxylic acids are used as the extractant, similar to the first embodiment.

[0051] The implementation details such as the addition of the alkali solution and the pH adjustment range in the cobalt extraction step S31 in the second solvent extraction step S3 may be the same as those in the first embodiment. Also, the implementation details such as the contact with the sulfuric acid solution and the pH adjustment range in the cobalt back-extraction step S33 may be the same as those in the first embodiment. By performing the above steps, magnesium can be left in the aqueous phase, and a high-purity cobalt sulfate solution with fewer impurities can be obtained.

[0052] The solvent recovery step S5 and the cobalt recovery step S6 in the recovery process are carried out as shown in FIG. 6, similar to the first embodiment. The pH adjustment value in the solvent recovery step S5 and the pH adjustment value in the cobalt recovery step S6 are also the same as those in the first embodiment.

[0053] By the above method, a high-purity cobalt sulfate solution with fewer impurities can be produced. Also, by using the cobalt precipitate, the off-system loss of cobalt can be reduced.

Example

[0054] Hereinafter, embodiments of the present invention will be shown for more specific description, but the present invention is not limited to the following embodiments. Note that the following Example 1 is included in the manufacturing method of the first embodiment.

[0055] (Example 1) (Copper removal step S1) A sodium hydrosulfide solution was added to 2 L of a cobalt chloride solution having the composition shown in A of Table 1 adjusted to pH 2.5 to adjust the redox potential to -50 mV (Ag / AgCl electrode standard), thereby generating a precipitate of copper sulfide. The precipitate was separated and removed with a filter to obtain a filtrate having the composition shown in B of Table 1. The concentration of copper in the filtrate was less than 0.001 g / L, and copper was successfully separated and removed.

[0056] (First solvent extraction step S2) An organic phase was prepared by diluting di-(2-ethylhexyl) phosphoric acid (D2EHPA, manufactured by Daihachi Chemical Industry Co., Ltd.), an alkylphosphoric acid-based extractant, to a concentration of 40% by volume with TECREEN N20 (manufactured by JX Nippon Mining & Metals Co., Ltd.). 0.9 L of an aqueous phase composed of the cobalt chloride solution obtained in the copper removal step and 1.8 L of the organic phase were mixed, and the pH was adjusted by adding a sodium hydroxide solution to 1.7 to extract impurities. 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, for a total of 3 extraction operations. As a result, a cobalt chloride solution having the composition shown in C of Table 1 was obtained. The concentrations of zinc, manganese, and calcium were all less than 0.001 g / L, and these impurities were successfully separated and removed.

[0057] (Second solvent extraction step S3) An organic phase was prepared by diluting Versatic Acid 10 (manufactured by Oxalis Chemicals), a carboxylic acid extractant, with TECLEAN N20 to a concentration of 30% by volume. 0.44 L of the aqueous phase consisting of the cobalt chloride solution obtained in the first solvent extraction step and 1 L of the organic phase were mixed, and an alkaline solution was added and adjusted to a pH of 6.5 to extract cobalt into the organic phase. 0.6 L of the extracted organic phase and 0.6 L of a cobalt chloride solution with a cobalt concentration of 10 g / L were mixed to wash the aqueous phase mixed in the organic phase after extraction. Subsequently, this organic phase was mixed with 0.09 L of pure water, sulfuric acid was added to adjust the pH to 4, and cobalt was back-extracted. As a result, a cobalt sulfate solution having the composition shown in D of Table 1 was obtained. The magnesium concentration was less than 0.001 g / L, and magnesium could be separated and removed. A high-purity cobalt sulfate solution was obtained by the above method.

[0058]

Table 1

[0059] (Solvent recovery step S5) Sulfuric acid was added to the cobalt chloride solution showing a pH of 6.5 after cobalt was extracted in the second solvent extraction step S3 to adjust the pH to 2 - 4. The total organic carbon (TOC) concentration in the adjusted cobalt chloride solution is shown in Table 2. As shown in Table 2, TOC decreased from 260 mg / l before adjustment to 98 - 106 mg / l with the adjustment of pH to 2 - 4, confirming that the carboxylic acid extractant remaining in the cobalt chloride solution could be separated. As a result, loss of the extractant could be suppressed, and the environmental load when discharging the cobalt chloride solution after extraction to wastewater treatment and discharging it into the sea area or the like could be reduced.

[0060]

Table 2

[0061] (Cobalt recovery step S6) Next, 100 ml of the cobalt chloride solution after separating the carboxylic acid extractant in the solvent recovery step S5 was taken for each sample, and while maintaining the temperature at 40°C, an aqueous sodium carbonate solution of 150 g / l was added to adjust the pH to 6.9 to 7.6 shown in Table 3. The obtained slurry was filtered, and the cobalt concentration in the filtrate was analyzed. Table 3 shows the relationship between the pH and the cobalt precipitation rate, and it was found that cobalt can be precipitated and recovered as cobalt carbonate at 90% or more when the pH is 7.1 or higher.

[0062]

Table 3

[0063] Also, 100 ml of the solution after recovering the same organic solvent as above was taken for each sample, and while maintaining the temperature at 40°C, an aqueous sodium hydroxide solution of 200 g / l was added to adjust the pH to the range of 6.7 to 8.8 shown in Table 4. The obtained slurry was filtered, and the cobalt concentration of the filtrate was analyzed. As shown in Table 4, cobalt could be recovered as cobalt hydroxide at 60% when the pH was 6.9 or higher and exceeding 99% at pH 7.6 or higher.

[0064]

Table 4

[0065] The cobalt carbonate and cobalt hydroxide recovered above can be used as neutralizing agents for adjusting the pH of the cobalt chloride solution when subjected to the first solvent extraction step S2 and the second solvent extraction step S3, and at the same time, cobalt can be recovered while preventing loss to the outside of the system.

Industrial Applicability

[0066] The highly pure cobalt sulfate crystals obtained by the present invention can be used as raw materials for lithium-ion secondary batteries and can also be used in various applications.

Explanation of Symbols

[0067] S1 Copper Stripping Process S2 First Solvent Extraction Process S3 Second Solvent Extraction Process S5 Solvent Recovery Process S6 Cobalt Recovery Process

Claims

1. A production method for obtaining cobalt sulfate by removing one or more impurities of copper, zinc, manganese, calcium, and magnesium from a cobalt chloride solution containing the same, wherein a pre-stage process, a post-stage process, and a recovery process are executed, the pre-stage process includes a copper removal process and a first solvent extraction process, the post-stage process consists of a second solvent extraction process including a cobalt extraction process and a back-extraction process, the recovery process includes a solvent recovery process and a cobalt recovery process, in the copper removal process, a sulfiding agent is added to the cobalt chloride solution, and the oxidation-reduction potential of the cobalt chloride solution is adjusted to -100 to 200 mV (Ag / AgCl electrode reference) and the pH is adjusted to 1.3 to 3.0 to form and separate a precipitate of copper sulfide, in the first solvent extraction process, an organic solvent containing an alkyl phosphoric acid-based extractant is brought into contact with the cobalt chloride solution that has undergone the copper removal process, the pH is adjusted to 1.5 to 3.0, zinc, manganese, and calcium are extracted into the organic solvent, and cobalt remains in the aqueous phase and is separated, in the cobalt extraction process, an organic solvent containing a carboxylic acid-based extractant is brought into contact with the cobalt chloride solution that has undergone the first solvent extraction process, the pH is adjusted to 5.0 to 7.0, cobalt is extracted into the organic phase, and magnesium remains in the aqueous phase, in the back-extraction process, the cobalt extracted into the organic phase in the cobalt extraction process is brought into contact with a sulfuric acid solution, the pH is adjusted to 2.0 to 4.5, and cobalt is back-extracted into the sulfuric acid solution to obtain a cobalt sulfate solution, in the solvent recovery process, the cobalt chloride solution after impurity removal obtained by the cobalt extraction process is brought into contact with the organic solvent containing the carboxylic acid extractant after cobalt is back-extracted in the back-extraction process, the pH is adjusted to 4.0 or less, and the carboxylic acid-based extractant contained in the cobalt chloride solution after impurity removal is separated and recovered, in the cobalt recovery process, the pH of the cobalt chloride solution after impurity removal after recovering the carboxylic acid-based extractant is adjusted to 7.0 to 12.0 to precipitate and recover cobalt A method for producing a cobalt sulfate solution, characterized by the above.

2. The pre-stage process is executed in the order of the copper removal process and the first solvent extraction process A method for producing cobalt sulfate according to Claim 1, characterized by the above.

3. The pre-stage process is executed in the order of the first solvent extraction process and the copper removal process A method for producing cobalt sulfate according to Claim 1, characterized by the above.

4. Add the cobalt precipitate in the first solvent extraction step and use it as a neutralizing agent. The method for producing a cobalt sulfate solution according to claim 1, characterized in that.

5. Add the cobalt precipitate to the cobalt extraction step in the second solvent extraction step and use it as a neutralizing agent. The method for producing a cobalt sulfate solution according to claim 1, characterized in that.

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