How to make cobalt sulfate

Abstract

To provide a method for producing cobalt chloride having high purity, by separating impurities and cobalt from a cobalt chloride solution including impurities without using an electrolysis process.SOLUTION: A method for producing cobalt sulfate sequentially executes: a copper removal step S1 of adding a sulfating agent to a cobalt chloride solution including impurities, and separating and removing copper; a first solvent extraction step S2 of bringing an organic solvent including an alkyl phosphate-based extraction agent into contact with the cobalt chloride solution, and extracting zinc, manganese and calcium into the organic solvent, and separating and removing the zinc, manganese and calcium; a second solvent extraction step S3 of adding a sodium carbonate solution or sodium hydrogencarbonate solution to the cobalt chloride solution, thereby adjusting pH to 5.0-7.0, bringing an organic solvent including a carboxylic acid-extraction agent into contact with the cobalt chloride solution, extracting cobalt, then performing back extraction on the cobalt with a sulfuric acid, thereby obtaining a cobalt chloride solution; and a crystallization step S4 of crystallizing the cobalt chloride solution obtained through the second solvent extraction step S3. The method enables direct production of cobalt sulfate having high purity 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, comprising: (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 from 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 (for example, Patent Document 3). The method for producing high-purity cobalt chloride described in paragraph 0022 of Patent Document 3 includes a solvent extraction step for separating nickel and cobalt, a demanganese step for removing manganese, a decopper step for removing copper, a dezincification step for removing zinc, and an electrolysis step. In the dezincification process, the aqueous cobalt chloride solution obtained in the decopperization process is brought into contact with an anion exchange resin to adsorb and remove zinc. In the electrolysis process, the high-purity aqueous cobalt chloride solution obtained in the dezincification process is used as an electrolytic feed solution to produce metallic cobalt (also 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 powder the plate-shaped metallic cobalt 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 according to the first invention comprises adding a sulfiding agent to a cobalt chloride solution containing one or more impurities of copper, zinc, manganese, calcium, and magnesium. At the same time, an oxidizing agent and a neutralizing agent are added to the cobalt chloride solution to which the sulfiding agent has been added, 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, A copper removal process in which copper sulfide is precipitated and then separated and removed; a cobalt chloride solution that has undergone the copper removal process The pH of the solution is adjusted to 1.5-3.0. a first solvent extraction step in which zinc, manganese and calcium are extracted and separated and removed by contacting the cobalt chloride solution obtained in the first solvent extraction step with an organic solvent containing an alkyl phosphoric acid extractant, and a sodium carbonate solution or sodium bicarbonate solution is added to the cobalt chloride solution obtained in the first solvent extraction step to adjust the pH to 5.0 to 7.0, and the solution is contacted with an organic solvent containing a carboxylic acid extractant to extract cobalt into the organic solvent. Following the extraction step, a back-extraction step is carried out in which the organic solvent from 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. a second solvent extraction step, 。 Second The method for producing cobalt sulfate of the present invention is as follows: 1 shot In the above, the cobalt sulfate solution obtained through the second solvent extraction step is subjected to a crystallization step to obtain crystals of cobalt sulfate. 。 Effect of the Invention

[0012] According to the first invention, This has the following effects: a) In the copper removal process, a sulfurizing agent is added, and the oxidation-reduction potential is adjusted to -100 to 200 mV (based on an Ag / AgCl electrode) and the pH is adjusted to 1.3 to 3.0. 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. b) In the first solvent extraction process, the cobalt chloride solution that has been through the copper removal process is Alkyl phosphate extraction Contacting the agent with an organic solventThis makes it easier to separate the impurities zinc, manganese and calcium from the cobalt solution. In addition, by adjusting the pH to 1.5 to 3.0, it is possible to extract zinc, manganese and calcium and separate them from the cobalt, while leaving the cobalt in the aqueous phase. c) In the second solvent extraction step, the cobalt chloride solution obtained in the first solvent extraction step is contacted with an organic solvent containing a carboxylic acid extractant to leave magnesium in the aqueous phase, cobalt is extracted into the organic phase, and the cobalt extracted into the organic phase in the back extraction process is Contact with sulfuric acid solution 、 Cobalt can be back-extracted into sulfuric acid solution 。 d) In this way, From impure cobalt chloride solutions , non It is possible to obtain a high-purity cobalt sulfate solution without impurities. .child Therefore, high purity cobalt sulfate can be produced directly without using an electrolysis process. No. 2 According to the invention, by further carrying out a crystallization step, high purity cobalt sulfate crystals can be obtained 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 S2 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] Specific embodiments of the present invention will be described in detail below. Note that the present invention is not limited to the following embodiments, and various modifications are possible without departing from the gist of the present invention.

[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 copper removal process S1 in which a sulfiding agent is added to a cobalt chloride solution containing one or more impurities of copper, zinc, manganese, calcium, and magnesium to generate a precipitate of copper sulfide, which is then separated and removed; (2) a first solvent extraction step S2 in which the cobalt chloride solution from which copper has been removed by the copper removal step S1 is contacted with an organic solvent containing an alkyl phosphoric acid-based extractant to extract and separate and remove zinc, manganese and calcium into the organic solvent; (3) A second solvent extraction step S3 is carried out in which a sodium carbonate solution or a sodium bicarbonate solution is added to the cobalt chloride solution from which copper, zinc, manganese and calcium have been removed by the first solvent extraction step S2 to adjust the pH to 5.0 to 7.0, an organic solvent containing a carboxylic acid extractant is brought into contact with the cobalt, the cobalt is extracted 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 S2 and / or after the second solvent extraction step S3, a step of subjecting the liquid to an oil-water separation device such as an activated carbon column 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 removing copper from a cobalt chloride solution by forming a precipitate of copper sulfide in a copper removal step S1, separating and removing zinc, manganese and calcium in a first solvent extraction 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 from 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] (Copper removal process S1) The copper removal step S1 will be described with reference to FIG. The copper removal step S1 is carried out by adding a sulfurizing agent to the cobalt chloride solution containing one or more impurities of copper, zinc, manganese, calcium, and magnesium as the starting material. The amount of sulfurizing agent added is adjusted, and an oxidizing agent and a neutralizing agent are added as necessary to adjust the redox potential of the cobalt chloride solution to -100 to 200 mV (Ag / AgCl electrode standard) and the pH to 1.3 to 3.0. 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 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)

[0023] In the copper removal step S1, if the redox potential of the cobalt chloride solution is adjusted to -100 to 200 mV (based on an Ag / AgCl electrode) and the pH is adjusted to 1.3 to 3.0, copper can be sufficiently removed as sulfide and coprecipitation of cobalt can be suppressed, thereby increasing the recovery rate of cobalt sulfate. 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 preferable. 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 preferable.

[0024] The oxidation-reduction potential can be adjusted by adjusting the amount of sulfurizing agent added. When the oxidation-reduction potential becomes lower than the desired value due to the addition of the sulfurizing agent, it can be adjusted by adding an oxidizing agent. For example, the oxidation-reduction potential can be adjusted by introducing air into the solution and stirring it, or by adding a hydrogen peroxide solution. The sulfurizing agent is not particularly limited, but hydrogen sulfide gas, sodium sulfide or sodium hydrosulfide crystals or aqueous solutions, etc., can be used. When hydrogen sulfide or sodium hydrosulfide is used as the sulfiding agent, the pH is adjusted by adjusting the amount of the sulfiding agent and adding a neutralizing agent. The neutralizing agent is not particularly limited, and alkali salts such as sodium hydroxide, calcium hydroxide, sodium carbonate, and cobalt carbonate can be used.

[0025] (First solvent extraction step S2) The first solvent extraction step S2 will be described with reference to FIGS. The first solvent extraction step S2 is a step in which the cobalt chloride solution that has been subjected to the copper removal step S1 is contacted with an organic solvent containing an alkyl phosphoric acid-based extractant, and zinc, manganese and calcium are extracted into the organic solvent and separated and removed.

[0026] As the organic solvent, an alkyl phosphate extractant diluted with a diluent is used. Examples of alkyl phosphate extractants include bis(2-ethylhexyl) hydrogen phosphate (trade name D2EHPA), 2-ethylhexyl (2-ethylhexyl) phosphonic acid (trade name PC-88A), and di(2,4,4-trimethylpentyl) phosphinic acid (trade name CYANEX272). Among these, when separating zinc, manganese, and calcium from a cobalt chloride solution from which copper has been removed, it is preferable to use bis(2-ethylhexyl) hydrogen phosphate, which has high separability from cobalt, as an alkyl phosphate extractant. This is because bis(2-ethylhexyl) hydrogen phosphate has good properties for separating zinc, manganese, and calcium, which are impurities, from a cobalt solution.

[0027] 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.

[0028] 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.

[0029] Therefore, in the first solvent extraction step S2, it is desirable to adjust the pH of the cobalt chloride solution from which copper has been removed to 1.5 to 3.0. In this pH range, the extraction rates of zinc, manganese, and calcium tend to be higher than that of cobalt, and it is possible to separate these impurity elements from cobalt by extracting them into the organic phase while leaving 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.

[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 subjected to the first solvent extraction 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 second solvent extraction step S3, a sodium carbonate (Na2CO3) solution or a sodium bicarbonate (NaHCO3) solution is added as a neutralizing agent to the cobalt chloride solution from which copper, zinc, manganese, and calcium have been removed, to adjust the pH to 5.0 to 7.0. When the pH is in this range, the cobalt can be extracted into the organic phase by contacting the solution with an organic solvent containing a carboxylic acid-based extractant. At this time, magnesium is not extracted and remains in the aqueous phase. If the pH is less than 5, it is difficult to extract cobalt, while if the pH exceeds 7, the solubility of cobalt decreases and precipitation may occur. In addition, because magnesium remaining in the aqueous phase has high solubility, there is almost no risk of it precipitating as crystals of magnesium sulfate, etc., which could block pipes and cause equipment trouble. Furthermore, there is no impact on the environment, and after the wastewater treatment process to separate other remaining metal ions, etc., it can be discharged into the sea, etc.

[0033] To adjust the pH in the second solvent extraction step S3, a neutralizing agent such as sodium carbonate or sodium bicarbonate is used. 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 reduce the concentration of dissolved oxygen in the cobalt chloride solution. This reduces the oxidation of cobalt ions extracted into the organic phase, making it easier to back-extract cobalt in the subsequent process.

[0034] Furthermore, even when a neutralizing agent having a carbonate radical as described above is not used as the neutralizing agent, a non-oxidizing gas such as nitrogen gas, carbon dioxide gas, or argon gas may be blown into the cobalt chloride solution prior to the solvent extraction step to reduce the dissolved oxygen, or the extraction apparatus itself may be placed in an inert atmosphere such as nitrogen, thereby preventing the oxidation of cobalt ions during extraction. The dissolved oxygen concentration can be measured using a commercially available device. However, it is not easy to industrially measure and control the concentration in the organic phase. Therefore, it is preferable to measure the dissolved oxygen by separating the cobalt chloride solution before subjecting it to solvent extraction or the aqueous phase after separation by solvent extraction.

[0035] (reverse extraction process) After the extraction step, the cobalt extracted into the organic phase is brought into contact with a sulfuric acid solution, and the pH is adjusted to 2.0 to 4.5. This allows the cobalt to be back-extracted into the sulfuric acid solution. Thus, 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 is not preferred because the rate of stripping cobalt decreases and the amount of cobalt recovered decreases.

[0036] 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.

[0037] (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.

[0038] 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.

[0039] 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

[0040] 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.

[0041] Example 1 (Copper removal process S1) A sodium hydrosulfide solution was added as a sulfiding agent to 2 L of a cobalt chloride solution having the composition shown in original solution A in Table 1, which had been adjusted to pH 2.5, and the oxidation-reduction potential was adjusted to -50 mV (Ag / AgCl electrode standard) to generate a precipitate of copper sulfide. The precipitate was separated and removed using a filter, and a filtrate having the composition shown in post-sulfidation B in Table 1 was obtained. The copper concentration was less than 0.001 g / L, and copper was successfully separated and removed.

[0042] (First solvent extraction step S2) An organic phase was prepared by diluting an alkyl phosphoric acid extractant (trade name D2EHPA, manufactured by Daihachi Chemical Industry Co., Ltd.) with a diluent (trade name Teclean N20, manufactured by JX Nippon Oil & Energy Corporation) so that the concentration was 40% by volume. 0.9 L of the aqueous phase consisting of the cobalt chloride solution obtained in the copper removal step S1 and 1.8 L of the organic phase were mixed, and a sodium hydroxide solution was added to adjust the pH to 1.7, and impurities were extracted. The same extraction operation was repeated with 0.9 L of the aqueous phase after extraction and 1.8 L of new organic phase, for a total of three extraction operations. As a result, a cobalt chloride solution with the composition shown in Table 1, 1SX after C was obtained. The concentrations of zinc, manganese, and calcium were all less than 0.001 g / L, and these impurities were able to be separated and removed.

[0043] (Second solvent extraction step S3) An organic phase was prepared by diluting a carboxylic acid extractant (product name: Versatic Acid 10, manufactured by Oxalis Chemicals) with a diluent (Teclean N20) so that the concentration was 30% by volume. 0.44 L of the aqueous phase consisting of the cobalt chloride solution obtained in the first solvent extraction step S2 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.

[0044] [Table 1]

[0045] (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]

[0046] Example 2 A cobalt sulfate solution was obtained in the same manner as in Example 1, except that in the copper removal step S1, the oxidation-reduction potential was adjusted to 150 mV (Ag / AgCl electrode standard), in the second solvent extraction step S3, 0.44 L of an aqueous phase obtained by adding pure water to the cobalt chloride solution obtained in the first solvent extraction step S2 to adjust the cobalt concentration to 40 g / L was mixed with an 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]

[0047] 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]

[0048] Example 3 A cobalt sulfate solution was obtained in the same manner as in Example 1, except that in the second solvent extraction step S3, sodium bicarbonate was added to adjust the pH to 6.6. The composition in this case is shown in Table 3. As shown in Table 5, after 2SX, D, a high purity cobalt sulfate solution was obtained. [Table 5]

[0049] Subsequently, crystallization was carried out in the same manner as in Example 1, and high-purity cobalt sulfate crystals as shown in Table 6 were obtained. [Table 6]

[0050] From the results of Examples 1, 2 and 3 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]

[0051] 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]

[0052] S1 Copper removal process S2 1st solvent extraction step S3 Second solvent extraction process S4 Crystallization Engineering

Claims

1. a copper removal process in which a sulfiding agent is added to a cobalt chloride solution containing one or more impurities of copper, zinc, manganese, calcium, and magnesium, and an oxidizing agent and a neutralizing agent are added to the cobalt chloride solution to which the sulfiding agent has been added, thereby adjusting the redox potential to −100 to 200 mV (based on an Ag / AgCl electrode) and the pH to 1.3 to 3.0, thereby generating a precipitate of copper sulfide, which is then separated and removed; a first solvent extraction step in which the pH of the cobalt chloride solution that has been subjected to the copper removal step is adjusted to 1.5 to 3.0 and an organic solvent containing an alkyl phosphoric acid-based extractant is contacted with the solution to extract zinc, manganese and calcium into the organic solvent for separation and removal; 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 first solvent extraction step to adjust the pH to 5.0 to 7.0, and an extraction step is carried out in which an organic solvent containing a carboxylic acid extractant is contacted with the solution to extract cobalt into the organic solvent, and following the extraction step, a stripping step is carried out in which a sulfuric acid solution is contacted with the organic solvent from which cobalt has been extracted to adjust the pH to 2.0 to 4.5 and the cobalt is stripped into the sulfuric acid solution; Execute in order A method for producing cobalt sulfate comprising the steps of:

2. 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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