How to make cobalt sulfate

Abstract

To provide a method for manufacturing a cobalt sulfate of high purity through separating contaminants and cobalt from a cobalt chloride solution containing the contaminants without using an electrolysis process.SOLUTION: A method for manufacturing a cobalt sulfate sequentially executes: a first solvent extraction step S1 of making a cobalt chloride solution containing contaminants have contact with an organic solvent containing an alkylphosphate-based extractant to extract to the organic solvent and separate / remove zinc, manganese and calcium; a copper removal step S2 of adding a sulfating agent to the cobalt chloride solution having undergone the first solvent extraction step S1 to generate and separate / remove copper sulfide precipitation; a second solvent extraction process S3 of adding a sodium carbonate solution or a sodium hydrogencarbonate solution to the cobalt chloride solution having undergone the copper removal step S2 to adjust pH to 5.0 to 7.0 and making contact with an organic solvent containing a carboxylic acid-based extractant to extract cobalt then back-extracting the cobalt by a sulfuric acid to obtain a cobalt sulfate solution; and a crystallization process S4 of the cobalt sulfate solution. Thus, a cobalt sulfate of high purity can be manufactured directly without using an electrolysis process.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing cobalt sulfate, and more particularly to a method for producing high-purity cobalt sulfate by removing impurity elements contained in a cobalt chloride solution. [Background technology]

[0002] 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 its use as an additive element in special alloys. In particular, lithium-ion secondary batteries have recently come to be widely used as batteries for mobile devices and electric vehicles, and the demand for cobalt has been expanding rapidly accordingly. However, most cobalt is produced as a by-product of nickel and copper smelting, so separation of impurities, including nickel and copper, is an important elemental technology in the production of cobalt.

[0003] For example, when recovering cobalt as a by-product in the hydrometallurgy of nickel, the raw material is first leached or extracted into a solution or subjected to a dissolution treatment using a mineral acid, an oxidizing agent, etc., to obtain a solution containing nickel and cobalt. Furthermore, the nickel and cobalt contained in the obtained acidic solution are often separated and recovered by a solvent extraction method using various organic extractants according to a conventionally known method. However, the resulting cobalt solution often contains various impurities derived from the raw materials used in the process.

[0004] Therefore, it becomes necessary to further remove impurity elements such as manganese, copper, zinc, calcium and magnesium from the cobalt solution after nickel has been separated and recovered by the above-mentioned solvent extraction method. Furthermore, in order to produce a high-purity cobalt product with a low impurity content, it was necessary to remove impurity elements from the cobalt solution that had been separated and recovered from the nickel solution containing cobalt, and then to commercialize the cobalt through an electrolysis process or crystallization, etc.

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

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

[0007] From this perspective, a method has been proposed in which the purification method of Patent Document 1 and the separation technique of Patent Document 2 are combined to remove these impurity elements from a cobalt chloride solution containing manganese, copper, and zinc (e.g., Patent Document 3). The method for producing high-purity cobalt chloride described in paragraph 0022 of Patent Document 3 includes a solvent extraction step for separating nickel and cobalt, a demanganese step for removing manganese, a decopper step for removing copper, a dezincification step for removing zinc, and an electrolysis step. In the dezincification process, the aqueous cobalt chloride solution obtained in the decopperization process is brought into contact with an anion exchange resin to adsorb and remove zinc. In the electrolysis process, the high-purity aqueous cobalt chloride solution obtained in the dezincification process is used as an electrolytic feed solution to produce metallic cobalt (also known as electrolytic cobalt).

[0008] On the other hand, as mentioned above, the demand for cobalt as a raw material for lithium ion secondary batteries has recently increased, and the form of a cobalt sulfate solution or cobalt sulfate crystals is desired. To obtain cobalt sulfate crystals from metallic cobalt obtained by the conventional technique of Patent Document 3, metallic cobalt is dissolved in sulfuric acid to obtain a cobalt sulfate solution, and this solution is then crystallized to obtain cobalt sulfate crystals. However, this manufacturing method increases the manufacturing cost due to an increase in the number of steps and chemical costs. In addition, plate-shaped metallic cobalt, which is used in corrosion-resistant alloys, dissolves slowly in sulfuric acid, and in order to dissolve it in a short time, it is necessary to turn the plate-shaped metallic cobalt into a powder by atomization or the like. For this reason, a method for obtaining a cobalt sulfate solution directly from a cobalt chloride solution without going through metallic cobalt has been desired. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] JP 2004-285368 A [Patent Document 2] JP 2001-020021 A [Patent Document 3] JP 2020-19664 A Summary of the Invention [Problem to be solved by the invention]

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

[0011] The method for producing cobalt sulfate of the first invention is characterized by sequentially carrying out the following steps: a first solvent extraction step in which a cobalt chloride solution containing one or more impurities of copper, zinc, manganese, calcium, and magnesium is contacted with an organic solvent containing an alkylphosphate extractant, and zinc, manganese, and calcium are extracted into the organic solvent for separation and removal; a copper removal step in which a sulfiding agent is added to the cobalt chloride solution that has been through the first solvent extraction step to produce a copper sulfide precipitate, which is then separated and removed; and a second solvent extraction step in which a sodium carbonate solution or sodium hydrogen carbonate solution is added to the cobalt chloride solution that has been through the copper removal step to adjust the pH to 5.0 to 7.0, the solution is contacted with an organic solvent containing a carboxylic acid extractant, cobalt is extracted into the organic solvent, and the cobalt is then stripped with sulfuric acid to obtain a cobalt sulfate solution. The method for producing cobalt sulfate according to the second invention is the same as that according to the first invention, except that the alkyl phosphate extractant in the first solvent extraction step is bis(2-ethylhexyl) hydrogen phosphate, and the pH of the cobalt chloride solution is adjusted to 1.5 to 3.0. Bis(2-ethylhexyl) hydrogen phosphate The method is characterized in that an extraction step is carried out in which the impurity elements are extracted into an organic solvent by subjecting the material to solvent extraction using an organic solvent. The method for producing cobalt sulfate according to the third invention is the method according to the first or second invention, further comprising the step of adding a sulfurizing agent to cobalt chloride in the copper removal step. to The method is characterized in that an oxidizing agent and a neutralizing agent are added to the solution to adjust the redox potential to -100 to 200 mV (based on an Ag / AgCl electrode) and the pH to 1.3 to 3.0. The method for producing cobalt sulfate according to the fourth aspect of the present invention is the method for producing cobalt sulfate according to the first aspect of the present invention, further comprising the step of: teethThen, an alkaline solution is added to the cobalt chloride solution from which copper, zinc, manganese and calcium have been removed to adjust the pH to 5.0 to 7.0, and the cobalt is extracted into an organic solvent using a carboxylic acid extractant. include It is characterized by: The method for producing cobalt sulfate according to the fifth aspect of the present invention is as follows: 4 In the present invention, the second solvent extraction step teeth, Following the extraction process Execute a back-extraction step in which the organic solvent in which the cobalt has been extracted is contacted 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; include It is characterized by: The method for producing cobalt sulfate according to the sixth aspect of the present invention is characterized in that, in the first aspect of the present invention, the cobalt sulfate solution obtained through the second solvent extraction step is subjected to a crystallization step to obtain cobalt sulfate crystals. Effect of the Invention

[0012] According to the first invention, zinc, manganese, and calcium are separated and removed from a cobalt chloride solution containing impurities in the first solvent extraction step, copper is removed in the copper removal step, and magnesium is separated and removed in the second solvent extraction step, so that a high-purity cobalt sulfate solution free of impurities can be obtained. Moreover, the stripping step of the second solvent extraction step can be easily performed. Therefore, high-purity cobalt sulfate can be directly produced without using an electrolysis step. According to the second invention, bis(2-ethylhexyl) hydrogen phosphate is used as an alkyl phosphate extractant, which makes it easier to separate zinc, manganese, and calcium, which are impurities, from the cobalt solution. In addition, by adjusting the pH to 1.5 to 3.0, zinc, manganese, and calcium can be extracted and separated from cobalt, leaving cobalt in the aqueous phase. According to the third invention, copper sulfide can be precipitated and sufficiently removed from the cobalt chloride solution, and coprecipitation of cobalt can be suppressed, thereby increasing the recovery rate of cobalt sulfate. According to the fourth invention, the cobalt extracted into the organic phase can be back-extracted into the sulfuric acid solution by contacting the cobalt with the sulfuric acid solution and adjusting the pH to 2.0 to 4.5. In this way, a high-purity cobalt sulfate solution can be obtained. According to the fifth invention, the cobalt extracted into the organic phase is brought into contact with a sulfuric acid solution and the pH is adjusted to 2.0 to 4.5, whereby the cobalt can be back-extracted into the sulfuric acid solution, thus obtaining a high-purity cobalt sulfate solution. According to the sixth aspect of the present invention, by further carrying out a crystallization step, it is possible to obtain high-purity cobalt sulfate crystals from the cobalt sulfate solution. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a process diagram showing a method for producing cobalt sulfate according to the present invention. [Diagram 2] FIG. 1 is a process diagram showing a method for producing cobalt sulfate according to one embodiment of the present invention. [Diagram 3] FIG. 3 is a detailed process diagram of the first solvent extraction step S1 shown in FIG. 2. [Figure 4] FIG. 3 is a detailed process diagram of the second solvent extraction step S3 shown in FIG. 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, specific embodiments of the present invention will be described in detail. Note that the present invention is not limited to the following embodiments, and various modifications are possible without departing from the gist of the present invention.

[0015] (Basic principle of the present invention) The method for producing cobalt sulfate according to the present invention will be described with reference to FIG. This manufacturing method is characterized by carrying out the following steps in order. (1) a first solvent extraction step S1 in which a cobalt chloride solution containing one or more impurities of copper, zinc, manganese, calcium, and magnesium is contacted with an organic solvent containing an alkyl phosphoric acid-based extractant, and zinc, manganese, and calcium are extracted into the organic solvent to be separated and removed; (2) a copper removal step S2 in which a sulfiding agent is added to the cobalt chloride solution from which zinc, manganese, and calcium have been removed by the first solvent extraction step S1 to generate a precipitate of copper sulfide, which is then separated and removed; (3) A second solvent extraction step S3 is carried out in which the cobalt chloride solution from which copper, zinc, manganese and calcium have been removed by the copper removal step S2 is contacted with an organic solvent containing a carboxylic acid extractant to extract the cobalt into the organic solvent, and the cobalt is then stripped with sulfuric acid to obtain a cobalt sulfate solution.

[0016] In the present invention, after each of the steps S1 to S3, a crystallization step S4 of precipitating crystals from the cobalt sulfate solution is carried out as necessary. Although not shown in FIG. 1, after the first solvent extraction step S1 and / or after the second solvent extraction step S3, a step of subjecting the liquid to an oil-water separation device such as an activated carbon column may be added to separate and remove organic components that have become mixed in the liquid.

[0017] The cobalt chloride solution used as the 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 to any cobalt chloride solution containing such impurities, but it is particularly suitable for use in a cobalt chloride solution obtained after nickel is separated and recovered from a cobalt-containing nickel solution using an alkyl phosphoric acid extractant or an amine extractant in the solvent extraction process of nickel smelting.

[0018] According to the present invention, a high-purity cobalt sulfate solution can be obtained by separating and removing zinc, manganese, and calcium from a cobalt chloride solution containing impurities in a first solvent extraction step S1, removing copper by forming a copper sulfide precipitate in a copper removal step S2, and separating and removing magnesium in a second solvent extraction step S3. Therefore, a high-purity cobalt sulfate solution can be directly produced by separating impurities and cobalt without using an electrolysis step.

[0019] Furthermore, according to the present invention, the cobalt sulfate solution that has been subjected to the steps S1 to S3 can be subjected to the crystallization step S4 to precipitate crystals from the solution, thereby obtaining cobalt sulfate crystals.

[0020] (Embodiment) Hereinafter, an embodiment of the method for producing cobalt sulfate will be described with reference to Fig. 2 to Fig. 4. Fig. 2 shows the details of steps S1 to S3 shown in Fig. 1.

[0021] (First solvent extraction step S1) The first solvent extraction step S1 will be described with reference to FIGS. The first solvent extraction step S1 is a step in which the cobalt chloride solution containing one or more impurities of copper, zinc, manganese, calcium and magnesium as the starting material is contacted with an organic solvent containing an alkyl phosphoric acid extractant, and zinc, manganese and calcium are extracted into the organic solvent and separated and removed. Note that a part of the copper can also be extracted and separated and removed.

[0022] As the organic solvent, an alkyl phosphate extractant diluted with a diluent is used. Examples of alkyl phosphate extractants include bis(2-ethylhexyl) hydrogen phosphate (trade name D2EHPA), 2-ethylhexyl (2-ethylhexyl) phosphonic acid (trade name PC-88A), and di(2,4,4-trimethylpentyl) phosphinic acid (trade name CYANEX272). Among these, when separating zinc, manganese, and calcium from a cobalt chloride solution from which copper has been removed, it is preferable to use bis(2-ethylhexyl) hydrogen phosphate, which has high separability from cobalt, as the extractant.

[0023] 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, more preferably 20 to 50% by volume. When the concentration of the extractant is within this range, impurity elements with high concentrations and impurity elements with low distribution ratios (element concentration in organic solvent / element concentration in solution) can be sufficiently extracted. On the other hand, when the concentration of the extractant is less than 10%, impurity elements with high concentrations and impurity elements with low distribution ratios cannot be sufficiently extracted, and tend to remain in the cobalt chloride solution. In addition, when the concentration of the extractant exceeds 60%, the viscosity of the organic solvent increases, and the phase separation property after the extraction operation of the organic solvent (organic phase) and the cobalt chloride solution (aqueous phase) deteriorates.

[0024] Acidic extractants such as alkyl phosphate extractants extract metal ions by forming metal salts by replacing the -H of the extractant with cations in the aqueous phase, as shown in formula 4. Generally, as the pH increases, metal ions are more easily extracted into the organic phase, and as the pH decreases, the reaction in formula 4 proceeds in the opposite direction, making it easier for metal ions extracted into the organic phase to be back-extracted into the aqueous phase. Since the pH at which metal ions are extracted varies depending on the type of metal ion, the target element is separated from impurity elements by controlling the pH in the solvent extraction process using an acidic extractant. nRH org + M n+ aq → MR norg + nH + aq ...(Formula 4) where RH is the acid extractant, M n+ indicates an n-valent metal ion, org indicates the organic phase, and aq indicates the aqueous phase.

[0025] Therefore, in the first solvent extraction step S1, it is desirable to adjust the pH of the cobalt chloride solution to 1.5 to 3.0. In this pH range, the extraction rates of zinc, manganese, and calcium tend to be higher than that of cobalt, and it is possible to separate these impurity elements from cobalt by extracting them into the organic phase while leaving cobalt in the aqueous phase. If the pH is less than 1.5, the extraction rate of these impurities is low and separation from cobalt becomes difficult, and if the pH exceeds 3.0, the extraction rate of cobalt also increases and separation from impurities decreases. If the pH is adjusted to 1.5 to 3.0, some of the cobalt may be extracted, but it is also possible to reduce the loss of cobalt by contacting the organic phase after extraction with a hydrochloric acid solution with a lower pH than that used during extraction to recover the cobalt by back-extraction. Furthermore, when this organic phase is brought into contact with an acidic solution of pH 1 or less, most of the extracted metal ions can be back-extracted into the aqueous phase, allowing the organic phase after back-extraction to be reused.

[0026] (Copper removal process S2) The copper removal step S2 will be described with reference to FIG. The copper removal step S2 is carried out by adding a sulfiding agent to the cobalt chloride solution that has been subjected to the first solvent extraction step S1, and by adding an oxidizing agent and a neutralizing agent, 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. 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.

[0027] Copper in the cobalt chloride solution is removed from the solution by forming a copper sulfide precipitate according to Equation 1, Equation 2, or Equation 3 below. CuCl2+H2S→CuS↓+2HCl...(Formula 1) CuCl2+Na2S→CuS↓+2NaCl···(Formula 2) CuCl2+NaHS→CuS↓+NaCl+HCl···(Formula 3)

[0028] In the copper removal step S2, by adjusting the redox potential of the cobalt chloride solution to −100 to 200 mV (based on an Ag / AgCl electrode) and the pH to 1.3 to 3.0, copper can be sufficiently removed as sulfide and coprecipitation of cobalt can be suppressed. If the redox potential exceeds 200 mV, the copper in the solution is not sufficiently removed, and if it is less than -100 mV, the amount of cobalt co-precipitated increases, which is not preferred. If the pH is less than 1.3, the copper in the solution is not sufficiently removed and the filterability of the resulting sulfide precipitate deteriorates. If the pH exceeds 3.0, the amount of cobalt co-precipitated increases with the removal of copper, which is not preferred.

[0029] The oxidation-reduction potential can be adjusted by adjusting the amount of sulfurizing agent added. The sulfurizing agent is not particularly limited, but hydrogen sulfide gas, sodium sulfide, sodium hydrosulfide crystals or aqueous solutions, etc. can be used. When hydrogen sulfide or sodium hydrosulfide is used as the sulfiding agent, the pH is adjusted by adjusting the amount of the sulfiding agent and adding a neutralizing agent. The neutralizing agent is not particularly limited, and alkali salts such as sodium hydroxide, calcium hydroxide, sodium carbonate, and cobalt carbonate can be used. When the oxidation-reduction potential becomes lower than the desired value due to the addition of the sulfiding agent, the pH can be adjusted by adding an oxidizing agent. For example, the pH can be adjusted by introducing air into the solution and stirring it, or by adding a hydrogen peroxide solution.

[0030] (Second solvent extraction step S3) The second solvent extraction step S3 will be described with reference to FIGS. The second solvent extraction step S3 is a step in which the cobalt chloride solution that has been through the copper removal step S2 is contacted with an organic solvent containing a carboxylic acid extractant, the cobalt is extracted into the organic solvent, and then the cobalt is stripped with sulfuric acid to obtain a cobalt sulfate solution. The organic solvent used is a carboxylic acid extractant diluted with a diluent. Examples of carboxylic acid extractants include versatic acid and naphthenic acid. These are acidic extractants that contain COOH groups.

[0031] When extracting metal ions, carboxylic acid extractants release protons into the aqueous phase according to the valence of the metal, and the metal ion coordinates to the carbonyl oxygen. Many carboxylic acids form dimers and trimers through hydrogen bonds with each other in non-polar solvents. In addition, when extracting metal ions, carboxylic acids that have not been acid-dissociated may coordinate to remove the water of hydration coordinated to the metal ion. For example, in the case of a 6-coordinate divalent metal ion M 2+ The reaction in which is extracted by the dimeric carboxylic acid extractant R2H2 is represented as shown in Equation 5. [M(H2O)6] 2+ aq +3(R2H2) org → (MR2 4RH) org +2H + aq +6H2O aq ...(Formula 5) In the formula, org represents an organic phase and aq represents an aqueous phase.

[0032] (extraction process) In the extraction step in the second solvent extraction step S3, a sodium carbonate solution or a sodium bicarbonate solution is added as a neutralizing agent to the cobalt chloride solution from which copper, zinc, manganese, and calcium have been removed, to adjust the pH to 5.0 to 7.0. When the pH is in this range, the cobalt can be extracted into the organic phase by contacting the solution with an organic solvent containing a carboxylic acid extractant. In this case, magnesium is not extracted and remains in the aqueous phase. At a pH below 5, it is difficult to extract cobalt, while at a pH above 7, the solubility of cobalt decreases and precipitation may occur.

[0033] A sodium carbonate solution or a sodium bicarbonate solution is used to adjust the pH in the second solvent extraction step S3. If a common neutralizing agent such as sodium hydroxide is used, the cobalt extracted into the organic phase may be oxidized from divalent to trivalent by oxygen. Trivalent cobalt ions tend to bond strongly with carboxylic acid complex ions, making back extraction difficult. However, if a neutralizing agent having a carbonate radical, such as a sodium carbonate solution or a sodium bicarbonate solution, is used as the neutralizing agent, the carbon dioxide gas generated by the neutralization reaction can suppress contact with oxygen caused by air entrainment during stirring, and can also lower the dissolved oxygen concentration. This reduces the oxidation of cobalt ions extracted into the organic phase, and facilitates back-extraction in the subsequent process.

[0034] (reverse extraction process) In the back-extraction step in the second solvent extraction step S3, after the extraction step, the cobalt extracted into the organic phase is brought into contact with a sulfuric acid solution to adjust the pH to 2.0 to 4.5. This allows the cobalt to be back-extracted into the sulfuric acid solution. In this way, a high-purity cobalt sulfate solution is obtained. Although stripping is possible at a pH of less than 2, this is not preferred because the amount of trace impurities extracted at a lower pH than cobalt increases, while a pH of more than 4.5 reduces the rate of stripping cobalt and reduces the amount of cobalt recovered, which is not preferred.

[0035] Since the organic phase after extraction still contains fine aqueous phase even after phase separation, a washing step may be added to remove the aqueous phase before stripping. For example, a cobalt sulfate solution can be used as the aqueous phase in the washing step. The organic phase after stripping can be reused as the organic phase in the extraction step. By the above method, a high-purity cobalt sulfate solution with few impurities can be produced.

[0036] (Crystallization step S4) The crystallization step S4 will be described with reference to FIG. In the crystallization step S4, crystals of cobalt sulfate are precipitated from the cobalt sulfate solution obtained in the second solvent extraction step S3. The crystallization method is not particularly limited, and can be performed using a general crystallization method.

[0037] For example, a method of obtaining crystals by placing a cobalt sulfate solution in a crystallizer and crystallizing in the crystallizer can be mentioned. The crystallizer is a device for precipitating crystals by evaporating water in the cobalt sulfate solution under a predetermined pressure, and for example, a rotary evaporator or a double propeller type crystallizer is used. The internal pressure is reduced by a vacuum pump or the like, and in the rotary evaporator, crystallization proceeds while rotating the flask and stirring with a double propeller. In the crystallizer, the cobalt sulfate solution is mixed with cobalt sulfate crystals to form a slurry.

[0038] The slurry discharged from the crystallizer is separated into cobalt sulfate crystals and mother liquor by a filter, a centrifuge, etc. The cobalt sulfate crystals are then dried in a dryer to remove moisture. By the above method, it is possible to produce cobalt sulfate crystals from a cobalt sulfate solution. Of course, since the cobalt sulfate solution is a high-purity solution with few impurities, the obtained cobalt sulfate crystals are also high-purity with few impurities. EXAMPLES

[0039] 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 in any way.

[0040] Example 1 (First solvent extraction step S1) An organic phase was prepared by diluting an alkyl phosphoric acid extractant (trade name D2EHPA, manufactured by Daihachi Chemical Industry Co., Ltd.) with a diluent (trade name Teclean N20, manufactured by JX Nippon Oil & Energy Corporation) to a concentration of 40% by volume. 0.9 L of the aqueous phase consisting of a cobalt chloride solution with the composition shown in the original solution A in Table 1 and 1.8 L of the organic phase were mixed, and the pH was adjusted to 1.7 by adding sodium hydroxide solution to extract impurities. The same extraction operation was repeated with 0.9 L of the aqueous phase after extraction and 1.8 L of new organic phase, for a total of three extraction operations. As a result, a cobalt chloride solution with the composition shown in 1SX after B in Table 1 was obtained. The concentrations of zinc, manganese, and calcium were all 0.001 g / L or less, and these impurities were able to be separated and removed.

[0041] (Copper removal process S2) 0.9 L of the cobalt chloride solution obtained in the first solvent extraction step S1 was adjusted to pH 2.5 by adding sodium hydroxide solution, and then sodium hydrosulfide solution was added as a sulfiding agent to adjust the oxidation-reduction potential to -50 mV (Ag / AgCl electrode standard) to generate a precipitate of copper sulfide. The precipitate was separated and removed using a filter to obtain a filtrate having the composition shown in Table 1 after sulfidation C. The copper concentration was less than 0.001 g / L, and copper was successfully separated and removed.

[0042] (Second solvent extraction step S3) An organic phase was prepared by diluting a carboxylic acid extractant (product name: Versatic Acid 10, manufactured by Oxalis Chemicals) with a diluent (Teclean N20) so that the concentration was 30% by volume. 0.44 L of the aqueous phase consisting of the cobalt chloride solution obtained in the copper removal step S2 was mixed with 1 L of the organic phase, and a sodium carbonate solution was added to adjust the pH to 6.5, and the cobalt was extracted into the organic phase. 0.6L of the extracted organic phase was mixed with 0.6L of a cobalt chloride solution with a cobalt concentration of 10g / L, and the aqueous phase that had been mixed into the organic phase after extraction was washed. Next, this organic phase was mixed with 0.09L of pure water, and sulfuric acid was added to adjust the pH to 4, and cobalt was back-extracted. As a result, a cobalt sulfate solution with the composition shown in Table 1, 2SX-D, was obtained. The magnesium concentration was less than 0.001g / L, and magnesium was successfully separated and removed. By the above method, a high purity cobalt sulfate solution was obtained.

[0043] [Table 1]

[0044] (Crystallization step S4) The cobalt sulfate solution was placed in a rotary evaporator, and the inside of the rotary evaporator was decompressed with a vacuum pump while the temperature was maintained at 40°C. The water was evaporated while rotating the flask, and cobalt sulfate crystals were precipitated. After solid-liquid separation, the obtained cobalt sulfate crystals were dried in a dryer. As a result, high-purity cobalt sulfate crystals as shown in Table 2 were obtained. [Table 2]

[0045] Example 2 A cobalt sulfate solution was obtained in the same manner as in Example 1, except that in the copper removal step S2, the oxidation-reduction potential was adjusted to 150 mV (Ag / AgCl electrode standard), in the second solvent extraction step S3, 0.44 L of an aqueous phase obtained by adding pure water to the cobalt chloride solution obtained in the copper removal step S2 to adjust the cobalt concentration to 40 g / L was mixed with the organic phase, 0.6 L of the extracted organic phase was mixed with 0.6 L of a cobalt chloride solution with a cobalt concentration of 10 g / L to wash the aqueous phase that had been mixed into the organic phase after extraction, and this organic phase was mixed with 0.08 L of pure water, and sulfuric acid was added to adjust the pH to 4 to strip the cobalt. The composition in this case is shown in Table 3. As shown in Table 3, after 2SX, D, a high purity cobalt sulfate solution was obtained. [Table 3]

[0046] Subsequently, crystallization was carried out in the same manner as in Example 1, and high-purity cobalt sulfate crystals as shown in Table 4 were obtained. [Table 4]

[0047] From the results of Examples 1 and 2 above, it is clear that according to the present invention, it is possible to obtain cobalt sulfate with high purity from which impurities have been sufficiently removed. [Industrial Applicability]

[0048] The highly pure cobalt sulfate crystals obtained by the present invention can be used as a raw material for lithium ion secondary batteries and can also be used for a variety of other purposes. [Explanation of symbols]

[0049] S1 First solvent extraction step S2 Copper removal process S3 Second solvent extraction process S4 Crystallization process

Claims

1. a first solvent extraction step in which an organic solvent containing an alkylphosphoric acid-based extractant is contacted with a cobalt chloride solution containing one or more impurities of copper, zinc, manganese, calcium, and magnesium, and zinc, manganese, and calcium are extracted into the organic solvent to be separated and removed; a copper removal step of adding a sulfiding agent to the cobalt chloride solution that has been subjected to the first solvent extraction step to generate a precipitate of copper sulfide, which is then separated and removed; a second solvent extraction step in which a sodium carbonate solution or a sodium hydrogen carbonate solution is added to the cobalt chloride solution that has been subjected to the copper removal step to adjust the pH to 5.0 to 7.0, and an organic solvent containing a carboxylic acid extractant is contacted with the solution to extract cobalt into the organic solvent, and then the cobalt is stripped with sulfuric acid to obtain a cobalt sulfate solution; Execute in order A method for producing cobalt sulfate comprising the steps of:

2. The alkyl phosphate extractant in the first solvent extraction step is bis(2-ethylhexyl) hydrogen phosphate; The pH of the cobalt chloride solution is adjusted to 1.5 to 3.0, and the solution is subjected to solvent extraction using the bis(2-ethylhexyl) hydrogen phosphate to extract impurity elements into an organic solvent.

2. The method for producing cobalt sulfate according to claim 1 .

3. In the copper removal step, an oxidizing agent and a neutralizing agent are added to the cobalt chloride solution to which a sulfiding agent has been added, so as to adjust the redox potential to −100 to 200 mV (based on an Ag / AgCl electrode) and the pH to 1.3 to 3.

0.

3. The method for producing cobalt sulfate according to claim 1 or 2.

4. The second solvent extraction step includes an extraction step of adding an alkaline solution to the cobalt chloride solution from which copper, zinc, manganese and calcium have been removed, adjusting the pH to 5.0 to 7.0, and extracting cobalt into an organic solvent using a carboxylic acid extractant.

2. The method for producing cobalt sulfate according to claim 1 .

5. The second solvent extraction step includes a back-extraction step, which is carried out following the extraction step, in which the organic solvent from which the cobalt has been extracted is contacted with a sulfuric acid solution, the pH is adjusted to 2.0 to 4.5, and the cobalt is back-extracted into the sulfuric acid solution. The method for producing cobalt sulfate according to claim 4.

6. The cobalt sulfate solution obtained through the second solvent extraction step is subjected to a crystallization step to obtain cobalt sulfate crystals.

2. The method for producing cobalt sulfate according to claim 1 .

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