Method for producing cobalt sulfate

Abstract

The present invention provides 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. The method sequentially implements the following steps: a decoppering step (S1), in which a sulfiding agent is added to a cobalt chloride solution containing one or more impurities selected from copper, zinc, manganese, calcium, and magnesium to form a copper sulfide precipitate, which is then separated and removed; a neutralization step (S2), in which a neutralizing agent or a carbonating agent is added to the cobalt chloride solution that has undergone the decoppering step (S1), to form cobalt hydroxide or alkaline cobalt carbonate, thereby separating the magnesium; a leaching step (S3), in which sulfuric acid is added to the cobalt hydroxide or alkaline cobalt carbonate to obtain a cobalt sulfate solution; and a solvent extraction step (S4), in which an organic solvent containing an alkylphosphoric acid-based extractant is brought into contact with the cobalt sulfate solution to extract zinc, manganese, and calcium into the organic solvent for separation and removal. The addition of the neutralizing agent or carbonating agent in the neutralization step (S2) is performed using a countercurrent multi-stage process.

Description

Technical Field

[0001] The present invention relates to a method for producing cobalt sulfate. More specifically, it relates to a method for producing high-purity cobalt sulfate by removing impurity elements contained in a cobalt chloride solution. Background Art

[0002] Cobalt is a valuable metal that, in addition to its use as an additive element in specialty alloys, is widely used industrially as a magnetic material and a raw material for lithium-ion secondary batteries. In particular, the recent rise in lithium-ion secondary batteries used as batteries for mobile devices and electric vehicles has led to a rapid increase in demand for cobalt. However, since the majority of cobalt is produced as a byproduct of nickel or copper smelting, separating it from impurities, such as nickel or copper, is a key technology in cobalt production.

[0003] For example, when recovering cobalt as a by-product in nickel wet smelting, the raw material is first leached or extracted into a solution using mineral acid or an oxidizing agent, or the raw material is dissolved to obtain a solution containing nickel and cobalt. The nickel and cobalt contained in the obtained acidic solution are then separated and recovered, in most cases, by solvent extraction using various organic extractants using conventional methods.

[0004] However, the obtained cobalt solution often contains various impurities derived from the processed raw materials.

[0005] 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-mentioned solvent extraction method.

[0006] Furthermore, in order to produce high-purity cobalt products with low impurity content, it is necessary to remove impurity elements from a cobalt solution separated and recovered from a nickel solution containing cobalt in advance, and then convert the cobalt into products through an electrolysis process or crystallization.

[0007] As methods for removing impurity elements from a cobalt solution, there are conventional technologies described in Patent Documents 1 and 2.

[0008] Patent Document 1 discloses a method for purifying a cobalt solution, which comprises the following steps: (1) a copper removal step, in which a sulfiding agent is added to the cobalt solution to adjust the oxidation-reduction potential (ORP) (based on an Ag / AgCl electrode) to 50 mV or less and the pH to 0.3 to 2.4, thereby obtaining a copper sulfide precipitate and a copper-depleted purified solution; (2) a manganese removal step, in which an oxidizing agent and a neutralizing agent are added to the copper-depleted purified solution to adjust the oxidation-reduction potential (based on an Ag / AgCl electrode) to 950 to 1050 mV and the pH to 2.4 to 3.0, thereby obtaining a manganese precipitate and a manganese-depleted purified solution; and (3) a solvent extraction step, in which alkylphosphoric acid is used as an extractant to extract and separate zinc, calcium, and trace impurities from the manganese-depleted purified solution.

[0009] 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 a complex having a distribution coefficient with respect to the anion exchange resin greater than the distribution coefficient of the cobalt chloride complex with respect to the anion exchange resin.

[0010] The solvent extraction method described in Patent Document 1, which uses an alkylphosphoric acid as an extractant, exhibits high separation performance for zinc and calcium. However, in the case of a cobalt chloride solution having a hydrochloric acid concentration of 2 to 6 mol / L, ion exchange using an anion exchange resin or solvent extraction using an amine-based extractant exhibits higher separation performance for zinc and cobalt than the solvent extraction method using the alkylphosphoric acid.

[0011] In addition, when removing extremely small amounts of zinc from a cobalt chloride solution, the ion exchange method is relatively simple in terms of process and operation, and is therefore both efficient and economical.

[0012] Based on this viewpoint, a method combining the purification method of Patent Document 1 and the separation technology of Patent Document 2 has been proposed as a method for removing these impurity elements from a cobalt chloride solution containing manganese, copper, and zinc (for example, Patent Document 3).

[0013] 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.

[0014] In the dezincification process, the aqueous cobalt chloride solution obtained in the copper removal process is brought into contact with an anion exchange resin to remove zinc by adsorption. In the electrolysis process, the high-purity aqueous cobalt chloride solution obtained in the dezincification process is used as the electrolysis feed solution to produce metallic cobalt (also known as electrolytic cobalt).

[0015] 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 cobalt sulfate solution or cobalt sulfate crystals is ideal.

[0016] To obtain cobalt sulfate crystals from the cobalt metal obtained in the prior art of Patent Document 3, the cobalt metal can be dissolved in sulfuric acid to obtain a cobalt sulfate solution, which is then crystallized to obtain cobalt sulfate crystals. However, this production method increases production costs due to increased process steps and reagent costs. Furthermore, plate-shaped cobalt metal dissolves slowly in sulfuric acid to be used in corrosion-resistant alloys. To achieve rapid dissolution, the plate-shaped cobalt metal must be powdered using atomization or other methods.

[0017] Therefore, a method for obtaining a cobalt sulfate solution directly from a cobalt chloride solution without using metallic cobalt is desired.

[0018] Prior art literature

[0019] Patent Literature

[0020] Patent Document 1: Japanese Patent Application Laid-Open No. 2004-285368.

[0021] Patent Document 2: Japanese Patent Application Laid-Open No. 2001-020021.

[0022] Patent document 3: Japanese Patent Application Laid-Open No. 2020-019664. Summary of the Invention

[0023] [Problems to be Solved by the Invention]

[0024] The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a method for producing high-purity cobalt sulfate by separating impurities from cobalt in a cobalt chloride solution containing impurities without using an electrolysis process.

[0025] [Means for solving the problem]

[0026] The method for producing cobalt sulfate of the first invention is characterized by sequentially carrying out the following steps: a decoppering step of adding a sulfiding agent to a cobalt chloride solution containing one or more impurities selected from the group consisting of copper, zinc, manganese, calcium, and magnesium to form a precipitate of copper sulfide, thereby separating and removing the copper; a neutralization step of adding a neutralizing agent or a carbonating agent to the cobalt chloride solution that has undergone the decoppering step to form cobalt hydroxide or alkaline cobalt carbonate, thereby separating the magnesium; a leaching step of adding sulfuric acid to the cobalt hydroxide or alkaline cobalt carbonate to obtain a cobalt sulfate solution; and a solvent extraction step of bringing an organic solvent containing an alkylphosphoric acid-based extractant into contact with the cobalt sulfate solution to extract zinc, manganese, and calcium into the organic solvent, thereby separating and removing them.

[0027] The method for producing cobalt sulfate according to the second invention is characterized in that, in the first invention, the addition of the neutralizing agent or the carbonating agent in the neutralization step is performed by a countercurrent multi-stage method.

[0028] The method for producing cobalt sulfate according to the third invention is characterized in that, in the first or second invention, the cobalt sulfate solution obtained through the solvent extraction step is subjected to a crystallization step to obtain cobalt sulfate crystals.

[0029] The method for producing cobalt sulfate according to the fourth invention is characterized in that, in the first or second invention, 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, and the redox 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.

[0030] The method for producing cobalt sulfate according to the fifth invention is characterized in that, in the first, second or fourth invention, the pH is adjusted to 6.5 to 7.0 in the neutralization step.

[0031] The method for producing cobalt sulfate according to the sixth invention is characterized in that, in the first, second, third or fourth invention, the pH is adjusted to 2.0 to 5.0 in the leaching step to obtain a cobalt sulfate solution.

[0032] The method for producing cobalt sulfate according to the seventh invention is characterized in that, in the first or second invention, in the solvent extraction step, the alkylphosphoric acid-based extractant is bis(2-ethylhexyl) hydrogenphosphate, the pH of the cobalt sulfate solution from which copper and magnesium have been removed is adjusted to 1.5 to 3.0, and solvent extraction using the extractant is carried out to extract the impurity elements into the organic solvent.

[0033] [Effects of the Invention]

[0034] According to the first invention, a copper sulfide is precipitated from a cobalt chloride solution containing impurities through a copper removal step, magnesium is separated and removed through a neutralization step, a cobalt sulfate solution is obtained through a leaching step, and zinc, manganese, and calcium are separated and removed through a solvent extraction step. Therefore, impurities can be separated from cobalt without using an electrolysis step, and high-purity cobalt sulfate can be directly produced.

[0035] According to the second invention, by supplying the product produced by neutralization or carbonation to the front stage of the countercurrent multi-stage process, the cobalt remaining in the solution can be reduced, preventing cobalt loss. At the same time, the loss of the neutralizing agent or carbonating agent remaining due to unreacted reaction can be reduced, thereby cutting costs.

[0036] According to the third invention, by further carrying out the crystallization step, high-purity cobalt sulfate crystals can be obtained from the cobalt sulfate solution.

[0037] According to the fourth invention, since the oxidation-reduction potential and pH range are appropriate, copper sulfide can be precipitated from the cobalt chloride solution and sufficiently removed, and coprecipitation of cobalt can be suppressed.

[0038] According to the fifth invention, by adjusting the pH in the neutralization step to 6.5 to 7.0, cobalt is precipitated and magnesium remains in the liquid, thereby separating the two substances.

[0039] According to the sixth invention, by adjusting the pH to 2.0 to 5.0, it is possible to prevent the incorporation of iron and aluminum as impurities and convert the cobalt chloride solution into a cobalt sulfate solution.

[0040] According to the seventh invention, the alkylphosphoric acid-based extractant is bis(2-ethylhexyl) hydrogen phosphate, and the pH of the cobalt sulfate solution is adjusted to 1.5 to 3.0 and solvent extraction is performed. This allows the impurity elements to be extracted into the organic solvent, leaving the cobalt in the aqueous phase for separation. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a process diagram showing the method for producing cobalt sulfate of the present invention.

[0042] Figure 2 It is a graph showing the pH, and the precipitation rates of cobalt and magnesium in the neutralization step.

[0043] Figure 3 This is a graph showing the relationship between the temperature in the neutralization step and the magnesium / cobalt ratio of the filtrate. DETAILED DESCRIPTION

[0044] 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 can be made without departing from the spirit of the present invention.

[0045] (Basic Principle of the Invention)

[0046] based on Figure 1 The method for producing cobalt sulfate of the present invention will be described.

[0047] This production method is characterized by carrying out the following steps in order.

[0048] The following steps are carried out in sequence: (1) a copper removal step S1, in which a sulfiding agent is added to a cobalt chloride solution containing one or more impurities selected from copper, zinc, manganese, calcium, and magnesium to generate a precipitate of copper sulfide, thereby separating and removing the copper; (2) a neutralization step S2, in which a neutralizing agent or a carbonating agent is added to the cobalt chloride solution from which copper has been removed in the copper removal step S1, thereby generating cobalt hydroxide or alkaline cobalt carbonate, thereby separating the magnesium; (3) a leaching step S3, in which sulfuric acid is added to the cobalt hydroxide or alkaline cobalt carbonate obtained in the neutralization step S2 to obtain a cobalt sulfate solution; and (4) a solvent extraction step S4, in which an organic solvent containing an alkylphosphoric acid-based extractant is brought into contact with the cobalt sulfate solution obtained in the leaching step S3, thereby extracting zinc, manganese, and calcium into the organic solvent and separating them.

[0049] In the present invention, after each of the above steps S1 to S4, a crystallization step S5 of precipitating crystals from the cobalt sulfate solution is carried out as needed.

[0050] Furthermore, although Figure 1 Although not shown in the figure, the following step may be added after the solvent extraction step S4: supplying the liquid to an oil-water separation device such as an activated carbon column to separate and remove organic components mixed in the liquid.

[0051] In the present invention, the cobalt chloride solution used as the starting material contains one or more of copper, zinc, manganese, calcium, and magnesium as impurity elements. The present invention is not limited to any application of the cobalt chloride solution as long as it contains such impurities. However, the cobalt chloride solution is particularly suitable for use as a cobalt chloride solution after nickel is separated and recovered from a cobalt-containing nickel solution using an alkylphosphoric acid-based extractant or an amine-based extractant in the solvent extraction process of nickel smelting.

[0052] 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 copper sulfide precipitate in a copper removal step S1, removing copper in a neutralization step S2, obtaining a cobalt sulfate solution in a leaching step S3, and separating zinc, manganese, and calcium in a solvent extraction step S4. Therefore, impurities can be separated from cobalt without using an electrolysis step, allowing the production of a high-purity cobalt sulfate solution.

[0053] (Implementation Method)

[0054] The following is based on Figure 1 An embodiment of the method for producing cobalt sulfate will be described.

[0055] (Decoppering Step S1)

[0056] The copper removal step S1 is performed by adding a sulfiding agent to a cobalt chloride solution containing one or more impurities selected from copper, zinc, manganese, calcium, and magnesium as a starting material. Furthermore, an oxidizing agent and a neutralizing agent are added to adjust the redox potential of the cobalt chloride solution to -100 to 200 mV (Ag / AgCl electrode reference) and the pH to 1.3 to 3.0.

[0057] Through this step, a precipitate of copper sulfide is generated from the cobalt chloride solution and separated, thereby obtaining a cobalt chloride solution from which copper has been removed.

[0058] The copper in the cobalt chloride solution is removed from the solution by forming a copper sulfide precipitate according to the following formula 1, formula 2 or formula 3.

[0059] CuCl2+H2S→CuS↓+2HCl (Formula 1)

[0060] CuCl2+Na2S→CuS↓+2NaCl (Formula 2)

[0061] CuCl2+NaHS→CuS↓+NaCl+HCl (Formula 3)

[0062] In the copper removal step S1, if the redox 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 in advance, copper can be precipitated as sulfide and fully removed, and coprecipitation of cobalt can be suppressed.

[0063] If the redox potential exceeds 200 mV, copper removal from the solution is insufficient. If the redox potential is less than -100 mV, the amount of cobalt coprecipitated increases, which is not preferred. Furthermore, if the pH is less than 1.3, copper removal from the solution is insufficient, and the filterability of the resulting sulfide precipitate deteriorates. If the pH exceeds 3.0, the amount of cobalt coprecipitated accompanying copper removal increases, which is also not preferred.

[0064] The above-mentioned redox potential can be adjusted by adjusting the amount of the sulfiding agent added. The sulfiding agent is not particularly limited, and hydrogen sulfide gas, sodium sulfide, or sodium hydrosulfide crystals or aqueous solutions can be used.

[0065] When hydrogen sulfide or sodium hydrosulfide is used as the sulfiding agent, the pH can be 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.

[0066] (Neutralization Step S2)

[0067] Neutralization step S2 is described below. Neutralization step S2 is a step of adding a neutralizing agent or a carbonating agent to the cobalt chloride solution that has undergone the copper removal step S1 to generate cobalt hydroxide or basic cobalt carbonate, and to separate the cobalt from the magnesium remaining in the solution.

[0068] In the neutralization step S2, the pH is maintained in the range of 6.5 to 7.0. When the pH is in the range of 6.5 to 7.0, cobalt is precipitated and magnesium remains in the liquid, thereby separating the two substances.

[0069] If the pH is lower than 6.5, the precipitation rate of cobalt decreases, which is not preferred. On the other hand, if the pH exceeds 7, the precipitation rate of magnesium also increases, and the separation efficiency from cobalt decreases, which is not preferred.

[0070] By adjusting the temperature to a range exceeding 40° C. and 60° C., magnesium can be separated more efficiently.

[0071] In the neutralization step S2 of the present invention, it is more preferable to use a countercurrent multi-stage method for adding the neutralizing agent or carbonating agent.

[0072] Neutralization or carbonation is performed by adding a neutralizing agent or carbonating agent to the solution to obtain a neutralized product or carbonate precipitate. In this case, during a single neutralization or carbonation step, some of the cobalt in the solution may remain unreacted.

[0073] Furthermore, when the cobalt grade of the starting solution supplied to the neutralization step S2 is low, the cobalt grade of the obtained precipitate is also relatively low, which reduces the efficiency of the subsequent steps of purifying cobalt.

[0074] Furthermore, some of the added neutralizing agent or carbonating agent may be mixed into the precipitate in an unreacted state, which is also undesirable in terms of cost.

[0075] Therefore, in the present invention, in order to completely neutralize or carbonate the cobalt, the solution is neutralized or carbonated again, that is, the neutralization or carbonated is performed in two or more stages.

[0076] In this case, all or part of the cobalt hydroxide or basic cobalt carbonate obtained by the second-stage neutralization or carbonation is added as a neutralizing agent or carbonating agent in the first-stage neutralization or carbonation.

[0077] By recycling the cobalt hydroxide or cobalt carbonate obtained by the neutralization or carbonation in the second stage, there is the following advantage: during the neutralization or carbonation in the first stage, the cobalt concentration in the reaction vessel increases, and accordingly, the cobalt grade of the precipitate obtained in the first stage is improved, thereby enabling efficient treatment in subsequent steps. In addition, the costs of the neutralizing agent and the carbonating agent can be reduced.

[0078] Furthermore, similarly, neutralization or carbonation may be performed in the third and subsequent stages, and the cobalt hydroxide or basic cobalt carbonate obtained by the neutralization or carbonation in the third stage may be added as the neutralizing agent or carbonating agent in the second stage.

[0079] In this way, by using a countercurrent multi-stage method, neutralization or carbonation is carried out in multiple stages, and the product produced by neutralization or carbonation is supplied to the front stage, that is, circulated in the opposite direction (countercurrent) to the flow of the liquid, thereby preventing cobalt loss and reducing the loss of neutralizing agent or carbonating agent remaining due to unreacted, which also helps to reduce costs.

[0080] The number of neutralization or carbonation stages is not particularly limited as long as it is two or more. However, too many stages will increase the cost of equipment, so it is preferably within 10 stages.

[0081] In addition, when the process is started, there will naturally be no precipitate of cobalt hydroxide or cobalt carbonate to be circulated, so the addition of cobalt precipitate can be omitted in the initial neutralization or carbonation of the first stage, or a method such as using a substance obtained elsewhere can be adopted.

[0082] By implementing this countercurrent multi-stage neutralization step, it is possible to achieve both the reduction of residual cobalt in the solution and the separation of magnesium.

[0083] (Leaching Step S3)

[0084] The leaching step S3 is a step of adding sulfuric acid to the cobalt hydroxide or basic cobalt carbonate obtained in the neutralization step S2 to perform leaching (dissolution) to obtain a cobalt sulfate solution.

[0085] During leaching, by adjusting the pH to a range of 2.0 to 5.0, the incorporation of iron and aluminum as impurities can be prevented, and the amount of neutralizing agent used in the next step, the solvent extraction step S4, can be reduced.

[0086] If the pH is set below 2.0, excessive acid addition will increase the amount of neutralizer used in the next step. Furthermore, if the pH is above 5.0, the cobalt leaching rate decreases. Therefore, a pH range of 2.0 to 5.0 is ideal.

[0087] Through the neutralization step S2 and the leaching step S3 of the present invention, the form of cobalt chloride can be converted into cobalt sulfate.

[0088] (Solvent Extraction Step S4)

[0089] The solvent extraction step S4 is a step of bringing an organic solvent containing an alkylphosphoric acid-based extractant into contact with the cobalt sulfate solution to extract zinc, manganese, and calcium into the organic solvent, thereby separating and removing these impurities.

[0090] As the organic solvent, an alkyl phosphate-based extractant diluted with a diluent can be used. Examples of alkyl phosphate-based extractants include bis(2-ethylhexyl) hydrogen phosphate (trade name: D2EHPA), 2-ethylhexyl (2-ethylhexyl)phosphonate (trade name: PC-88A), and di(2,4,4-trimethylpentyl)phosphinic acid (trade name: CYANEX272). When separating zinc, manganese, and calcium from a cobalt sulfate solution from which copper has been removed, bis(2-ethylhexyl) hydrogen phosphate is preferably used as the extractant due to its high separability from cobalt.

[0091] The diluent is not particularly limited as long as it is a substance that can dissolve the extractant. As the diluent, for example, cycloparaffinic solvents and aromatic solvents can be used. The concentration of the extractant is preferably adjusted to 10 to 60% by volume, more preferably to 20 to 50% by volume. If the concentration of the extractant is within this range, both impurity elements with high concentrations and impurity elements with low distribution ratios (element concentration in the organic solvent / element concentration in the solution) can be fully extracted. On the other hand, if the concentration of the extractant is less than 10%, impurity elements with high concentrations or impurity elements with low distribution ratios cannot be fully extracted and are likely to remain in the cobalt sulfate solution. In addition, if the concentration of the extractant exceeds 60%, the viscosity of the organic solvent becomes high, and the phase separation between the organic solvent (organic phase) and the cobalt sulfate solution (aqueous phase) after the extraction operation becomes poor.

[0092] As shown in Formula 4, acidic extractants, such as alkylphosphonic acid-based extractants, extract metal ions by replacing the -H groups of the extractant with cations in the aqueous phase to form metal salts. Generally, increasing the pH facilitates the extraction of metal ions into the organic phase. Lowering the pH reverses the reaction in Formula 4, and metal ions already extracted into the organic phase are readily back-extracted into the aqueous phase.

[0093] The pH at which extraction is performed varies depending on the type of metal ions. Therefore, in the solvent extraction process using an acidic extractant, the target element and impurity elements are separated by controlling the pH.

[0094] nRH org +M n+ aq →MR norg +nH + aq (Formula 4)

[0095] Here, RH in the formula represents an acidic extractant, M n+ represents an n-valent metal ion, org represents an organic phase, and aq represents an aqueous phase.

[0096] Therefore, in the solvent extraction step S4, the pH of the cobalt sulfate solution is preferably adjusted to 1.5 to 3.0. Within this pH range, 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, these impurity elements can be separated from the cobalt.

[0097] If the pH is less than 1.5, the extraction rate of these impurities is low, making it difficult to separate them from the cobalt. If the pH exceeds 3.0, the extraction rate of cobalt also increases, and the separation efficiency from the impurities decreases. When the pH is adjusted to 1.5-3.0, some cobalt may be extracted. However, the loss of cobalt can be reduced by contacting the organic phase after extraction with a sulfuric acid solution with a lower pH than that during extraction to strip and recover the cobalt.

[0098] Furthermore, by bringing the organic phase into contact with an acidic solution having a pH of 1 or less, most of the extracted metal ions can be stripped back into the aqueous phase, and the stripped organic phase can be reused.

[0099] (Crystallization Step S5)

[0100] In the crystallization step S5, cobalt sulfate crystals are precipitated from the cobalt sulfate solution obtained in the solvent extraction step S4. The crystallization method is not particularly limited, and a conventional crystallization method can be used.

[0101] For example, a method for obtaining crystals by placing a cobalt sulfate solution in a crystallization tank and performing crystallization in the crystallization tank can be cited. The crystallization tank is a tank that evaporates the water in the cobalt sulfate solution under a specific pressure to separate out crystals. For example, a rotary evaporator or a twin-screw crystallization tank can be used. The internal pressure is reduced by a vacuum pump or the like. In the case of a rotary evaporator, crystallization is performed while the flask is rotated. In the case of a twin-screw crystallization tank, crystallization is performed while stirring. Furthermore, a slurry of cobalt sulfate crystals mixed with the cobalt sulfate solution is formed in the crystallization tank.

[0102] The slurry discharged from the crystallization tank is separated into cobalt sulfate crystals and mother liquor by passing through a filter or centrifuge. The cobalt sulfate crystals are then dried in a dryer to remove moisture.

[0103] The above method can 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 cobalt sulfate crystals obtained are also high-purity crystals with few impurities.

[0104] [Example]

[0105] Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples at all.

[0106] (Example 1)

[0107] (Decoppering Step S1)

[0108] To 2 L of a cobalt chloride solution having the composition shown in stock solution A, which had been adjusted to a pH of 2.5 as shown in Table 1, a sodium bisulfide solution was added as a sulfiding agent, and the redox potential was adjusted to -50 mV (Ag / AgCl electrode reference) to precipitate copper sulfide. The precipitate was separated and removed using a filter, yielding a filtrate having the composition shown in Table 1 (after sulfidation B). The copper concentration was less than 0.001 g / L, indicating successful separation and removal of copper.

[0109] [Table 1]

[0110] element Co Cu Zn Mn Ca Mg Stock Solution A 83 0.01 0.07 0.11 4 0.093 After vulcanization B 76 ＜0.001 0.066 0.09 3.9 0.083 1stSX Post C 56 ＜0.001 ＜0.001 ＜0.001 ＜0.001 0.028 No. 2SX rear D 110 ＜0.001 ＜0.001 ＜0.001 ＜0.001 ＜0.001

[0111] (Unit: g / L)

[0112] (Neutralization Step S2)

[0113] Next, the influence of pH and temperature in the neutralization step was confirmed.

[0114] The cobalt chloride solution having the composition shown in Table 1 after sulfidation B was taken in 100 ml portions, and while maintaining the temperatures at 20° C., 40° C., and 60° C., 100 g / l of calcium hydroxide slurry was added while stirring to adjust the pH to a specific pH value within the range of 5.7 to 8 to prepare a neutralized slurry, which was then filtered.

[0115] 20 ml of pure water was added to each of the cobalt hydroxide precipitates obtained by filtration, and the mixture was stirred. The solution adhering to the precipitate was removed by filtration again to obtain washed cobalt hydroxide, and the cobalt and magnesium contained therein were analyzed.

[0116] The ratio of cobalt or magnesium distributed to the precipitate by neutralization was calculated as the precipitation rate based on the amount of cobalt or magnesium contained in the washed cobalt hydroxide obtained under each neutralization condition and the amount of cobalt or magnesium contained in the sulfided solution B used for neutralization.

[0117] Figure 2 The relationship between the precipitation rates of cobalt and magnesium obtained by neutralization at various temperatures and pH values ​​is shown in FIG.

[0118] The precipitation rate of cobalt shows a tendency that the higher the temperature, the higher the precipitation rate even at a lower pH.

[0119] For example, at 20°C, cobalt cannot be completely precipitated unless the pH is 7.5 to 8.0. However, at 40°C, cobalt can be precipitated at a pH of about 7 to 7.5, and at 60°C, cobalt can be completely precipitated at a pH of 6.5.

[0120] On the other hand, while the precipitation rate of magnesium is not temperature-dependent, it tends to increase with increasing pH. For example, at a pH of 6.5, the precipitation rate is approximately 20-25%, increasing to approximately 40% at a pH of 7, and reaching approximately 70% at a pH of 8.

[0121] In addition, Figure 3 The graph in Figure 2 shows the analysis values ​​of cobalt and magnesium in the filtrate produced by neutralization, expressed as the Mg / Co ratio. Since this represents the Mg / Co concentration ratio in the filtrate, a larger number indicates a lower ratio of cobalt to magnesium in the filtrate. Conversely, a higher ratio of cobalt to magnesium in the precipitate indicates superior selectivity.

[0122] The pH of the sulfided solution B shown in Table 1 before neutralization was approximately 0.8. The cobalt concentration was 76 g / l and the magnesium concentration was 0.083 g / l, so the Mg / Co ratio was 0.001.

[0123] Compared with 20°C, the selectivity of cobalt at each pH tends to be better at a temperature of 40°C or 60°C.

[0124] Therefore, in order to improve the recovery rate of cobalt, it is preferable to perform neutralization at a temperature of about 60° C. and a pH range of 6.5 to 7.0, which gives the best selectivity.

[0125] Furthermore, although it can be expected that the separability from magnesium will be further improved at a temperature exceeding 60°C, from the perspectives of the heat resistance of the materials used in the equipment, the increase in energy required for heating, and the safety of handling high-temperature objects, it is industrially preferred to set the temperature to around 60°C.

[0126] Then, neutralization is performed using a countercurrent multi-stage method.

[0127] The solution obtained from the liquid of the sulfurized B obtained in the copper removal step S1 by performing the same operation as in the neutralization step S2 was aliquoted in 100 ml portions, and while adjusting the temperature to a specific temperature, 100 g / l of calcium hydroxide slurry was added, and the pH was adjusted to a specific value to prepare a neutralized slurry, which was then filtered.

[0128] While the obtained filtrate was adjusted to a specific temperature, 100 g / l of calcium hydroxide slurry was added, and the pH was adjusted to a specific value, followed by filtration.

[0129] The obtained precipitate is added to a 100 ml solution obtained by performing the same operation, and while adjusting to a specific temperature, 100 g / l of calcium hydroxide slurry is added, adjusted to a specific pH, and filtered. 20 ml of pure water is added to the filtered cobalt hydroxide precipitate, and filtered again to remove the attached solution and obtain cobalt hydroxide. Thus, cobalt hydroxide obtained by the neutralization reaction of the countercurrent two sections is obtained.

[0130] Table 2 shows the neutralization pH conditions, the composition of the resulting cobalt sulfate solution, the yield of cobalt obtained as cobalt sulfate, and the magnesium removal rate. The yield and removal rate were calculated based on the total amount of the cobalt sulfate solution and the second neutralization filtrate as 100%.

[0131] and Figure 2 Compared to the case of neutralization in one stage as shown in the figure, the cobalt recovery rate (precipitation rate) at the same pH is significantly increased. Furthermore, if the pH in the second neutralization stage is 9 or higher, the magnesium removal rate (the same value as that obtained by subtracting the precipitation rate from 100%) is significantly reduced due to the increase in magnesium precipitation.

[0132] (Leaching Step S3)

[0133] 64 wt % sulfuric acid was added to the cobalt hydroxide obtained in Example 1, and the pH was adjusted to 2.0 for leaching to obtain a cobalt sulfate solution.

[0134] (Solvent Extraction Step S4)

[0135] An organic phase was prepared by diluting an alkylphosphoric acid-based extractant (trade name: D2EHPA, manufactured by Daihachi Chemical Industry Co., Ltd.) with a diluent (trade name: Teclean N20, manufactured by JX Nippon Mining and Energy Co., Ltd.) to a concentration of 40% by volume. 0.9 L of an aqueous phase consisting of the cobalt sulfate solution obtained in the copper removal step S1 was mixed with 1.8 L of the organic phase, and the pH was adjusted to 1.7 by adding sodium hydroxide solution to extract impurities. The same extraction procedure was repeated using the extracted aqueous phase (0.9 L) and the fresh organic phase (1.8 L), for a total of three extractions. The result was a cobalt sulfate solution with the composition shown in Table 1 (Section 1SX, C). The concentrations of zinc, manganese, and calcium were all less than 0.001 g / L, indicating successful separation and removal of these impurities.

[0136] [Table 2]

[0137] Neutralization 1 pH Neutralization 2-stage pH Temperature [℃] Cobalt yield [%] Magnesium removal rate [%] 5.8 8.0 60 ＞99.9 72 6.0 8.0 60 ＞99.9 68 6.2 8.0 60 ＞99.9 58 6.0 9.0 60 ＞99.9 28

[0138] (Crystallization Step S5)

[0139] The cobalt sulfate solution was placed in a rotary evaporator, and the interior was depressurized using a vacuum pump. While maintaining the temperature at 40°C, the flask was rotated to evaporate the water, thereby precipitating cobalt sulfate crystals. After solid-liquid separation, the resulting cobalt sulfate crystals were dried in a dryer. The results were high-purity cobalt sulfate crystals as shown in Table 3.

[0140] [Table 3]

[0141] element Co Cu Zn Mn Ca Mg concentration 22 ＜1 ＜1 ＜5 ＜10 ＜1

[0142] (Unit: Cobalt is %, other elements are ppm)

[0143] As can be seen from the results of the above examples, according to the present invention, high-purity cobalt sulfate from which impurities are sufficiently removed is obtained.

[0144] Industrial applicability

[0145] The high-purity cobalt sulfate crystals obtained by the present invention can be used for various purposes in addition to being a raw material for lithium-ion secondary batteries.

[0146] Description of Reference Signs

[0147] S1: copper removal process.

[0148] S2: Neutralization process.

[0149] S3: Leaching process.

[0150] S4: solvent extraction process.

[0151] S5: crystallization step.

Claims

1. A method for producing cobalt sulfate, wherein the method comprises: The method for producing cobalt sulfate sequentially implements the following steps: a copper removal step, in which a sulfiding agent is added to the cobalt chloride solution, and an oxidizing agent and a neutralizing agent are 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, thereby generating a precipitate of copper sulfide and separating and removing the copper; A neutralization step, in which a neutralizing agent or a carbonating agent is added to the cobalt chloride solution after the copper removal step to adjust the pH to 6.5-7.0, thereby generating cobalt hydroxide or basic cobalt carbonate and separating magnesium; a leaching step of adding sulfuric acid to the cobalt hydroxide or basic cobalt carbonate to adjust the pH to 2.0 to 5.0 to obtain a cobalt sulfate solution; A solvent extraction step is a step of bringing an organic solvent containing an alkylphosphoric acid-based extractant into contact with the cobalt sulfate solution to extract zinc, manganese, and calcium into the organic solvent for separation and removal.

2. The method for producing cobalt sulfate according to claim 1, wherein: In the solvent extraction step, the alkylphosphoric acid-based extractant is bis(2-ethylhexyl) hydrogen phosphate. The pH of the cobalt sulfate solution from which copper and magnesium have been removed is adjusted to 1.5 to 3.0, and solvent extraction is performed using the extractant to extract the impurity elements into the organic solvent.

3. The method for producing cobalt sulfate according to claim 1, wherein: The addition of the neutralizing agent or carbonating agent in the neutralization step is performed by a countercurrent multi-stage method.

4. The method for producing cobalt sulfate according to claim 1 or 2, wherein: The cobalt sulfate solution obtained through the solvent extraction step is subjected to a crystallization step to obtain cobalt sulfate crystals.

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