Method for producing metal sulfate crystal and metal sulfate

Abstract

The present invention provides a method for producing a metal sulfate crystal, in which a metal sulfate crystal is crystallized and recovered from a metal sulfate solution that contains a metal sulfate and has a pH of less than 4.0. This method for producing a metal sulfate crystal is characterized by including: an alkaline metal compound addition step in which an alkaline metal compound of the metal that constitutes the metal sulfate is added to the metal sulfate solution that has a pH of less than 4.0 to so as to increase the pH to 4.5 or more; a crystallization step in which the metal sulfate crystal is crystallized from the metal sulfate solution that has a pH of 4.5 or more so as to obtain a metal sulfate crystal-containing slurry that contains the metal sulfate crystal; and a solid-liquid separation step in which the metal sulfate crystal-containing slurry is separated into the metal sulfate crystal and the residual liquid.

Description

Method for producing metal sulfate crystals and metal sulfate

[0001] The present invention relates to a method for producing metal sulfate crystals, which involves crystallizing and recovering metal sulfate crystals from a metal sulfate solution having a pH of less than 4.0. This application claims priority to Japanese Patent Application No. 2024-049695 filed on March 26, 2024, and Japanese Patent Application No. 2025-049896 filed on March 25, 2025, the contents of which are incorporated herein by reference.

[0002] In recent years, lithium has been recovered and reused from crushed lithium-ion batteries. When recovering lithium from lithium-ion batteries, it is common to use a recycled raw material called black mass, which is obtained by firing and crushing used lithium-ion batteries. The fired lithium-ion battery material contains valuable metals such as cobalt, nickel, and manganese in addition to lithium. Therefore, technologies have been proposed for recovering valuable metals such as cobalt, nickel, and manganese from the fired lithium-ion battery material.

[0003] For example, Patent Document 1 discloses a method for obtaining sulfates of cobalt, nickel, and manganese by adjusting the pH of an acidic solution obtained by wet treating lithium ion battery waste and dissolving at least cobalt, nickel, manganese, and aluminum, and then performing solid-liquid separation to remove aluminum, dissolving the resulting neutralized residue containing cobalt, nickel, and manganese in a sulfuric acidic solution, and heating and concentrating or cooling the sulfuric acidic solution and performing solid-liquid separation.

[0004] Furthermore, as a method for producing cobalt sulfate crystals used as a raw material for lithium-ion batteries, for example, Patent Document 2 discloses a method in which a cobalt chloride solution containing impurities is subjected to sulfide treatment and solvent extraction to remove the impurities, the cobalt is extracted into an organic solvent, and then a cobalt sulfate solution is obtained by back-extracting with sulfuric acid, and this cobalt sulfate solution is subjected to a crystallization step to obtain cobalt sulfate crystals.

[0005] Japanese Patent No. 7232119 Japanese Patent Application Laid-Open No. 2023-161557

[0006] In Patent Documents 1 and 2, a cobalt sulfate solution acidified with sulfuric acid (metal sulfate solution) is heated and concentrated or cooled to crystallize and recover cobalt sulfate crystals (metal sulfate crystals). ２ SO ４ The cobalt sulfate crystals (metal sulfate crystals) recovered from such a sulfuric acid cobalt sulfate solution (metal sulfate solution) have free H on the surface. ２ SO ４ When such highly acidic crystals are supplied as raw materials for other products, the amount of neutralizing agent such as alkali added is large if they are supplied to a wet manufacturing process, and the amount of free H attached to the crystals is large if they are supplied to a dry manufacturing process. ２ SO ４ There is a risk that the sulfur oxide gases produced may cause problems such as corrosion of equipment.

[0007] As a specific example of subjecting the recovered cobalt sulfate crystals (metal sulfate crystals) to a wet manufacturing process, the cobalt sulfate crystals (metal sulfate crystals) produced by crystallization are dissolved in water to form an aqueous cobalt sulfate solution (aqueous metal sulfate solution), and then various alkalis and other chemicals are added to produce solid cobalt particles (solid metal particles), for example, cobalt hydroxide Co(OH) ２ , cobalt oxyhydroxide CoOOH, cobalt oxide Co ３ O ４ After being recovered as a cathode active material, etc., the cobalt sulfate crystals (metal sulfate crystals) are further processed into cathode active materials. ２ SO ４If the cobalt sulfate aqueous solution (metal sulfate aqueous solution) containing dissolved cobalt becomes acidic, the amount of alkaline agent, such as sodium hydroxide (NaOH), added when producing solid cobalt particles (metal solid) will increase, resulting in high costs. Furthermore, if the amount of sodium hydroxide (NaOH) added increases, there is a concern that Na may migrate to the recovered cobalt solid (metal solid) and the content of Na impurities may increase.

[0008] In addition, free H ２ SO ４ In a process for recovering cobalt sulfate crystals (metal sulfate crystals) by subjecting a crystallization raw material solution containing a large amount of cobalt sulfate, i.e., a low-pH, sulfuric acid-acidic cobalt sulfate aqueous solution (metal sulfate aqueous solution), to a heating and concentration treatment, if the reaction vessel is made of metal, the metal parts may be corroded by heating. For example, SUS304 and SUS316, which are commonly used in industrial-scale chemical manufacturing process equipment, are known to be slightly corroded under sulfuric acid. Metal corrosion of the reaction vessel is synonymous with a reaction in which elements such as Cr and Fe dissolve into the solution, and there is also a concern that the recovered cobalt sulfate crystals may be contaminated by elements derived from the metal vessel. Naturally, corrosion can also lead to concerns about reduced equipment life, operational problems, reduced productivity, and increased processing costs. While there are methods for fabricating the reaction vessel from more corrosion-resistant metal materials, this approach entails high equipment costs.

[0009] In addition, free H ２ SO ４ The simplest method for increasing the pH of a cobalt sulfate solution (metal sulfate solution) that contains a lot of cobalt and has a low pH is to add an alkaline solution such as sodium hydroxide. However, this method increases the amount of Na in the solution during the neutralization process. ２ SO ４ (aq) is generated, resulting in a large amount of Na being dissolved in the cobalt sulfate solution (metal sulfate solution). ２ SO ４ (aq)+2NaOH(aq)→Na ２ SO ４ (aq)+H ２O(l) Cobalt sulfate crystals (metal sulfate crystals) produced from a cobalt sulfate solution (metal sulfate solution) with a large amount of dissolved Na, whose pH has been increased by this method, will contain a large amount of Na and have very low purity.

[0010] The present invention has been made in view of the above circumstances, and provides a method for producing a compound having free H ２ SO ４ From a metal sulfate solution containing ２ SO ４ The present invention aims to provide a method for producing metal sulfate crystals, which can produce high-quality metal sulfate crystals that are free from adhesion of impurities and have low amounts of impurities such as sodium, and a metal sulfate.

[0011] In order to solve the above problems, a method for producing metal sulfate crystals according to a first aspect of the present invention is a method for producing metal sulfate crystals by crystallizing and recovering metal sulfate crystals from a metal sulfate solution containing a metal sulfate and having a pH of less than 4.0, and is characterized by comprising: an alkaline metal compound addition step of adding an alkaline metal compound of a metal constituting the metal sulfate to the metal sulfate solution having a pH of less than 4.0 to adjust the pH to 4.5 or higher; a crystallization step of crystallizing the metal sulfate crystals from the metal sulfate solution with a pH of 4.5 or higher to obtain a metal sulfate crystal-containing slurry containing the metal sulfate crystals; and a solid-liquid separation step of separating the metal sulfate crystal-containing slurry into the metal sulfate crystals and a residual liquid.

[0012] According to the method for producing metal sulfate crystals of the first aspect of the present invention, an alkaline metal compound of a metal constituting a metal sulfate is added to a metal sulfate solution containing a metal sulfate and having a pH of less than 4.0 to adjust the pH to 4.5 or more. ２ SO ４ By reacting with an alkaline metal compound, free H ２ SO ４Furthermore, since the reaction produces metal sulfate, it is possible to prevent impurities such as sodium from being mixed into the metal sulfate solution. The method includes a crystallization step of crystallizing the metal sulfate crystals from the metal sulfate solution having a pH of 4.5 or higher to obtain a metal sulfate-containing slurry containing the metal sulfate, and a solid-liquid separation step of separating the metal sulfate-containing slurry into the metal sulfate and a residual liquid. ２ SO ４ Therefore, it is possible to obtain high-quality metal sulfates that are free from adhesion of impurities and have low amounts of impurities such as sodium.

[0013] A method for producing metal sulfate crystals according to Aspect 2 of the present invention is characterized in that, in the method for producing metal sulfate crystals according to Aspect 1 of the present invention, the pH after the addition of the alkaline metal compound is set in the range of 6 to 7. According to the method for producing metal sulfate crystals according to Aspect 2 of the present invention, the pH after the alkaline metal compound step is set in the range of 6 to 7, thereby removing impurity elements and producing high-purity metal sulfate crystals. Furthermore, since the metal ions and sulfate ions in the metal sulfate solution after the alkaline metal compound step are in a ratio of approximately 1:1, the metal ion concentration can be estimated from the electrical conductivity in the subsequent crystallization step, making it possible to easily confirm the concentration of the metal.

[0014] The method for producing metal sulfate crystals according to Aspect 3 of the present invention is characterized in that, in the method for producing metal sulfate crystals according to Aspect 1 or Aspect 2 of the present invention, the crystallization step comprises heat-treating the metal sulfate solution adjusted to a pH of 4.5 or higher to crystallize the metal sulfate crystals. According to the method for producing metal sulfate crystals according to Aspect 3 of the present invention, the crystallization step involves heat-treating the metal sulfate solution adjusted to a pH of 4.5 or higher, thereby crystallizing the metal sulfate crystals. ２ SO ４ It is possible to obtain high-quality metal sulfate crystals free from adhesion of impurities and containing small amounts of impurities such as sodium. Furthermore, the metal sulfate crystals can be efficiently crystallized.

[0015] A method for producing metal sulfate crystals according to Aspect 4 of the present invention is characterized in that, in the method for producing metal sulfate crystals according to any one of Aspects 1 to 3 of the present invention, at least a portion of the alkaline metal compound added in the alkaline metal compound addition step is a metal hydroxide precipitate or a metal carbonate precipitate produced by adding sodium hydroxide, sodium carbonate, or sodium bicarbonate to a fractionated solution separated from a metal sulfate solution having a pH of less than 4.0. According to the method for producing metal sulfate crystals according to Aspect 4 of the present invention, at least a portion of the alkaline metal compound added in the alkaline metal compound addition step is a metal hydroxide precipitate or a metal carbonate precipitate produced by adding sodium hydroxide, sodium carbonate, or sodium bicarbonate to a fractionated solution separated from a metal sulfate solution having a pH of less than 4.0, thereby enabling efficient recovery of metal sulfate crystals from the metal sulfate solution.

[0016] A fifth aspect of the present invention relates to a method for producing metal sulfate crystals according to any one of the first to third aspects of the present invention, characterized in that at least a portion of the alkaline metal compound added in the alkaline metal compound addition step is a metal hydroxide precipitate or a metal carbonate precipitate produced by adding sodium hydroxide, sodium carbonate, or sodium bicarbonate to the residual liquid separated in the solid-liquid separation step. According to the method for producing metal sulfate crystals of the fifth aspect of the present invention, at least a portion of the alkaline metal compound added in the alkaline metal compound addition step is a metal hydroxide precipitate or a metal carbonate precipitate produced by adding sodium hydroxide, sodium carbonate, or sodium bicarbonate to the residual liquid separated in the solid-liquid separation step. This allows for efficient recovery of metal sulfate crystals from the metal sulfate solution.

[0017] A method for producing metal sulfate crystals according to Aspect 6 of the present invention is characterized in that, in the method for producing metal sulfate crystals according to Aspect 4 or Aspect 5 of the present invention, the metal hydroxide precipitate or the metal carbonate is washed with water. According to the method for producing metal sulfate crystals according to Aspect 6 of the present invention, the metal hydroxide precipitate or the metal carbonate is washed with water, so that sodium adhering to the metal hydroxide precipitate or the metal carbonate can be removed, further suppressing the incorporation of sodium as an impurity, and enabling the production of metal sulfate crystals of even higher purity.

[0018] A method for producing metal sulfate crystals according to Aspect 7 of the present invention is characterized in that, in the method for producing metal sulfate crystals according to any one of Aspects 1 to 6 of the present invention, the metal sulfate crystals are cobalt sulfate crystals. Since the method for producing metal sulfate crystals according to Aspect 7 of the present invention includes a metal compound addition step of adding at least one of cobalt hydroxide and cobalt carbonate to a cobalt sulfate solution having a pH of less than 4.0 to adjust the pH to 4.5 or higher, the free H ２ SO ４ with at least one or both of cobalt hydroxide and cobalt carbonate to produce free H ２ SO ４ Furthermore, since cobalt sulfate is produced by the reaction, it is possible to prevent impurities such as sodium from being mixed into the cobalt sulfate solution. The method includes a crystallization step of crystallizing the cobalt sulfate crystals from the cobalt sulfate solution having a pH of 4.5 or higher to obtain a cobalt sulfate crystal-containing slurry, and a solid-liquid separation step of separating the cobalt sulfate crystal-containing slurry into the cobalt sulfate crystals and a residual liquid. ２ SO ４ Therefore, high-quality cobalt sulfate crystals can be obtained that are free from adhesion of impurities and contain small amounts of impurities such as sodium.

[0019] The metal sulfate of embodiment 8 of the present invention is characterized in that when dissolved in water to a metal concentration of 1 mass %, the pH becomes 5.4 or higher.

[0020] The metal sulfate of Aspect 9 of the present invention is characterized in that when dissolved in water to give a metal concentration of 1 mass %, the pH becomes 6.0 or higher.

[0021] According to the present invention, free H ２ SO ４ From a metal sulfate solution containing a high concentration of H ２ SO ４ The present invention provides a method for producing metal sulfate crystals, which is capable of obtaining high-quality metal sulfate crystals free from adhesion of impurities and containing small amounts of impurities such as sodium, and a metal sulfate.

[0022] Fig. 1 is a flow chart showing a method for producing metal sulfate crystals (cobalt sulfate crystals) according to a first embodiment of the present invention; Fig. 2 is a flow chart showing a method for producing metal sulfate crystals (cobalt sulfate crystals) according to a second embodiment of the present invention; Fig. 3 is a graph showing the relationship between pH and dissolved cobalt concentration in examples; Fig. 4 is a graph showing the relationship between electrical conductivity and cobalt concentration in examples; Fig. 5 is a graph showing the relationship between electrical conductivity and nickel concentration in examples;

[0023] An example of an embodiment of the present invention will be described below.

[0024] The method for producing metal sulfate crystals according to this embodiment involves crystallizing and recovering metal sulfate from a metal sulfate solution having a pH of less than 4.0. In this embodiment, the target metal sulfate solution is a metal sulfate solution obtained by sulfuric acid treatment of lithium-ion battery slag (known as black mass) obtained by crushing used lithium-ion batteries or defective products (known as black powder) generated in the manufacturing process of cathode materials for secondary batteries. Examples of metals constituting the metal sulfate according to this embodiment include cobalt and nickel.

[0025] First Embodiment A method for producing metal sulfate crystals according to a first embodiment of the present invention will be described with reference to Fig. 1. In the method for producing metal sulfate crystals according to the first embodiment of the present invention, cobalt sulfate crystals (metal sulfate crystals) are recovered from a cobalt sulfate solution (metal sulfate solution). As shown in Fig. 1, the method for producing metal sulfate crystals according to this embodiment includes at least an alkaline metal compound addition step S01, a crystallization step S02, and a solid-liquid separation step S03.

[0026] (Alkaline Metal Compound Addition Step S01) In this alkaline metal compound addition step S01, an alkaline metal compound is added to a cobalt sulfate solution serving as a crystallization raw material liquid, the pH of which is less than 4.0 (for example, 0.5 or more and less than 4.0), to adjust the pH of the cobalt sulfate solution to 4.5 or more. As the alkaline metal compound, cobalt hydroxide (metal hydroxide) or cobalt carbonate (metal carbonate) can be used. In this embodiment, the pH of the cobalt sulfate solution after the alkaline metal compound addition step S01 is preferably 5.0 or more, more preferably 5.5 or more. It is even more preferable that the pH of the cobalt sulfate solution after the alkaline metal compound addition step S01 be within the range of 6.0 to 7.0.

[0027] Here, in a cobalt sulfate solution with a pH of less than 4.0, a large amount of free H ２ SO ４ By adding cobalt hydroxide to this cobalt sulfate solution with a pH of less than 4.0, free H is generated as follows: ２ SO ４ is consumed by reacting with cobalt hydroxide, causing the pH to rise. ２ SO ４ (aq)+Co(OH) ２ (s) → CoSO ４ (aq) + 2H ２ O(l)

[0028] In addition, by adding cobalt carbonate to a cobalt sulfate solution with a pH of less than 4.0, free H ２ SO ４is consumed by reacting with cobalt carbonate, causing the pH to rise. ２ SO ４ (aq) + CoCO ３ (s) → CoSO ４ (aq)+H ２ O(l) + CO ２ (g) The cobalt sulfate produced by the above reaction can also be used as a raw material for cobalt sulfate crystals.

[0029] (Crystallization step S02) In this crystallization step S02, cobalt sulfate crystals are crystallized from the cobalt sulfate solution adjusted to a pH of 4.5 or higher by heating and concentrating, cooling, or the like, to obtain a cobalt sulfate crystal-containing slurry. In this embodiment, the cobalt sulfate solution adjusted to a pH of 4.5 or higher is heat-treated and concentrated under reduced pressure to crystallize the cobalt sulfate crystals, thereby producing a cobalt sulfate crystal-containing slurry.

[0030] Here, the heating temperature is preferably in the range of 30°C or higher and 40°C or lower. Furthermore, the holding time at the heating temperature is preferably in the range of 2 hours or higher and 24 hours or lower. Furthermore, the pressure during decompression is preferably 100 hPa or lower. By setting the heating temperature to 40°C or lower, the reduction of hydrated water of sulfate can be suppressed, and homogeneous cobalt sulfate crystals can be obtained. On the other hand, by setting the heating temperature to 30°C or higher, evaporation can be promoted, enabling efficient concentration. Furthermore, in a cobalt sulfate solution whose pH is set to 4.5 or higher during crystallization, free H ２ SO ４ Since there is almost no cobalt ion and the ratio of cobalt ions to sulfate ions is approximately 1:1, the cobalt ion concentration can be estimated from the electrical conductivity, and the concentration of the metal can also be confirmed from the measurement results of the electrical conductivity.

[0031] (Solid-liquid separation step S03) In this solid-liquid separation step S03, the cobalt sulfate crystals (solid components) produced in the above-mentioned crystallization step S02 are separated from the residual liquid (liquid component). As a method for separating the cobalt sulfate crystals (solid components) from the residual liquid (liquid component), an existing solid-liquid separation method such as gravity settling separation, centrifugation, or filter cloth filtration using a filter press or the like can be used.

[0032] In this way, cobalt sulfate crystals are produced from a cobalt sulfate solution having a pH of less than 4.0.

[0033] In this embodiment, as shown in FIG. 1 , at least a part of the alkaline metal compound added in the alkaline metal compound adding step S01 is a cobalt hydroxide precipitate or a cobalt carbonate precipitate obtained through the fractionating step S05, the carbonate source or hydroxide source adding step S06, the second solid-liquid separation step S07, and the washing step S08.

[0034] (Fracturing Step S05) In this fractionating step S05, a fraction of the cobalt sulfate solution having a pH of less than 4.0 to be used as the crystallization raw material liquid or the cobalt sulfate solution having a pH of 4.5 or higher obtained by subjecting the cobalt sulfate solution having a pH of less than 4.0 to the alkaline metal compound addition step is fractionated to obtain a fractionated solution. Here, the ratio of the fractionated solution to the cobalt sulfate solution having a pH of less than 4.0 to be used as the crystallization raw material liquid or the cobalt sulfate solution having a pH of less than 4.0 to be used as the crystallization raw material liquid and the alkaline metal compound addition step to obtain a fractionated solution is not particularly limited, but is preferably, for example, within a range of 1.0% to 20.0% by mass.

[0035] Furthermore, the cobalt concentration in the separated solution is preferably within the range of 40 g / L or more and 90 g / L or less. When adding the carbonate source or hydroxide source in the carbonate source or hydroxide source addition step S06 described below, if the cobalt concentration in the separated solution is 90 g / L or less, an increase in the viscosity of the resulting suspension slurry can be suppressed and uniform stirring can be achieved. This promotes the reaction between the cobalt in the solution and the carbonate source or hydroxide source, reduces the amount of carbonate source or hydroxide source added, and suppresses the incorporation of impurities. On the other hand, by setting the cobalt concentration in the separated solution to 40 g / L or more, the efficiency of the reaction with the carbonate source or hydroxide source is improved.

[0036] Furthermore, the electrical conductivity of the fractionated solution obtained by fractionating the cobalt sulfate solution having a pH of 4.5 or more obtained through the alkaline metal compound addition step S01 from the cobalt sulfate solution having a pH of less than 4.0 that serves as the crystallization raw material solution is preferably in the range of 3.7 S / m or more and 5.4 S / m or less. ２ SO ４ There is almost no cobalt ion, and the ratio of cobalt ions to sulfate ions is approximately 1:1. In the carbonate source or hydroxide source addition step S06 described below, the cobalt ion concentration can be estimated from the electrical conductivity. If the electrical conductivity of the separated solution is 3.7 S / m or more, it can be confirmed that the cobalt ion concentration in the separated solution is 40 g / L or more, and if the electrical conductivity of the separated solution is 5.4 S / m or less, it can be confirmed that the cobalt ion concentration in the separated solution is 90 g / L or less.

[0037] (Carbonate Source or Hydroxide Source Addition Step S06) In this carbonate source or hydroxide source addition step S06, any one of sodium hydroxide, sodium carbonate, sodium bicarbonate, and carbon dioxide gas is added to the separated solution as a carbonate source or hydroxide source, thereby obtaining a suspension slurry containing a cobalt hydroxide precipitate or a cobalt carbonate precipitate and dissolved sodium sulfate, or any one of added and unreacted sodium hydroxide, sodium carbonate, and sodium bicarbonate.

[0038] By adding sodium hydroxide to the separated solution (cobalt sulfate solution), a cobalt hydroxide precipitate is produced by the following neutralization reaction: ２ SO ４ (aq)+2NaOH(aq)→Na ２ SO ４ (aq)+H ２ O(l) CoSO ４ (aq)+2NaOH(aq)→Na ２ SO ４ (aq)+Co(OH) ２ (s)

[0039] The solution (cobalt sulfate solution) was diluted with sodium carbonate (Na ２ CO ３ By adding cobalt carbonate, a precipitate of cobalt carbonate is formed by the following neutralization reaction: ２ SO ４ (aq) + Na ２ CO ３ (aq) → Na ２ SO ４ (aq)+H ２ O(l) + CO ２ (g) CoSO ４ (aq) + Na ２ CO ３ (aq) → Na ２ SO ４ (aq) + CoCO ３ (s)

[0040] The separation solution (cobalt sulfate solution) was diluted with sodium bicarbonate (NaHCO ３ By adding cobalt carbonate, a precipitate of cobalt carbonate is formed by the following neutralization reaction: ２ SO ４ (aq)+2NaHCO ３ (aq) → Na ２ SO ４ (aq) + 2H ２ O(l) + 2CO ２ (g) CoSO ４ (aq)+2NaHCO ３ (aq) → Na ２ SO ４ (aq) + CoCO ３ (s) + H２ O(l) + CO ２ (g)

[0041] Here, it is preferable that the pH of the separated solution after the addition of the carbonate or hydroxide source (sodium hydroxide, sodium carbonate, sodium bicarbonate, carbon dioxide gas) be in the range of 6.5 or more and 11.0 or less. By adjusting the pH of the separated solution after the addition of the carbonate or hydroxide source to 6.5 or more, it is possible to sufficiently generate a cobalt hydroxide precipitate or a cobalt carbonate precipitate. On the other hand, by adjusting the pH of the separated solution after the addition of the carbonate or hydroxide source to 11.0 or less, it is possible to prevent the addition of an excessive amount of the carbonate source or hydroxide source. It is more preferable that the pH of the separated solution after the addition of the carbonate or hydroxide source be 6.5 or more. Furthermore, it is more preferable that the pH of the separated solution after the addition of the carbonate source or hydroxide source be 7.3 or less, and even more preferable that it be 7.0 or less.

[0042] The viscosity of the resulting suspension slurry is preferably in the range of 20 cP to 128 cP. By controlling the viscosity of the suspension slurry to fall within the above range, no large amount of energy is required during stirring, and problems such as blockage or breakage of pipes during transportation can be suppressed.

[0043] Here, when sodium carbonate or sodium bicarbonate is added to an acidic separated solution in the carbonate source or hydroxide source addition step S06, carbonate ions are liberated as carbon dioxide gas into the atmosphere in the early stage, accompanied by foaming. This may result in problems such as an increase in the amount of sodium carbonate or sodium bicarbonate used and splashing of the liquid due to foaming. Therefore, when sodium carbonate or sodium bicarbonate is added, it is preferable to add the separated solution to an aqueous sodium carbonate or sodium bicarbonate solution and mix them.

[0044] (Second solid-liquid separation step S07) In this second solid-liquid separation step S07, the cobalt hydroxide precipitate or cobalt carbonate precipitate (solid component) generated in the carbonate source or hydroxide source addition step S06 is separated from a liquid component. This second solid-liquid separation step S07 allows for separation and removal of most of the sodium component added in the carbonate source or hydroxide source addition step S06. As a method for separating the cobalt hydroxide precipitate or cobalt carbonate precipitate (solid component) from the liquid component, an existing solid-liquid separation method such as gravity settling, centrifugation, or filter cloth filtration using a filter press or the like can be used.

[0045] (Washing Step S08) In this washing step S08, the cobalt hydroxide precipitate or cobalt carbonate precipitate is washed with water. This removes sodium components adhering to the surface of the cobalt hydroxide precipitate or cobalt carbonate precipitate. Because the cobalt hydroxide precipitate or cobalt carbonate precipitate is almost insoluble in water, sodium sulfate adhering to the surface of the cobalt hydroxide precipitate or cobalt carbonate precipitate can be selectively washed and removed. Here, in the washing step S08, washing with pure water is preferably performed until the electrical conductivity of the washing liquid after washing is 200 mS / m or less. By washing until the electrical conductivity of the washing liquid after washing is 200 mS / m or less, the sodium components adhering to the surface of the cobalt hydroxide precipitate or cobalt carbonate precipitate can be sufficiently removed.

[0046] In this embodiment, the cobalt hydroxide precipitate or the cobalt carbonate precipitate obtained as described above is added in the alkaline metal compound adding step S01.

[0047] According to the method for producing metal sulfate crystals of this embodiment configured as described above, an alkaline metal compound addition step S01 is provided in which an alkaline metal compound (cobalt hydroxide or cobalt carbonate) is added to a cobalt sulfate solution having a pH of less than 4.0 to adjust the pH to 4.5 or more. ２ SO ４ By reacting with an alkaline metal compound, free H ２ SO ４Furthermore, since cobalt sulfate is produced by the reaction, it is possible to prevent impurities such as sodium from being mixed into the cobalt sulfate solution.

[0048] The method includes a crystallization step S02 in which cobalt sulfate crystals are crystallized from a cobalt sulfate solution having a pH of 4.5 or higher to obtain a cobalt sulfate crystal-containing slurry, and a solid-liquid separation step S03 in which the cobalt sulfate crystal-containing slurry is separated into cobalt sulfate crystals (solid components) and a residual liquid (liquid component). ２ SO ４ This allows the production of high-quality cobalt sulfate crystals that are free from adhesion of cobalt and have a low content of impurities such as sodium. Furthermore, when the cobalt sulfate crystals thus obtained are dissolved in pure water (pH 6.5 to 7.0) to a cobalt concentration of 1% by mass or more, the pH of the solution is 5.4 to 7.0, or 6.0 to 6.5.

[0049] In the method for producing metal sulfate crystals according to this embodiment, when the pH of the cobalt sulfate solution after the alkaline metal compound addition step S01 is set to a range of 6.0 to 7.0, impurity elements such as Al, Fe, Cu, and Zn can be sufficiently removed. Furthermore, by setting the pH of the cobalt sulfate solution after the alkaline metal compound addition step S01 to a range of 4.5 or higher, particularly 6.0 to 7.0, the ratio of cobalt ions to sulfate ions becomes approximately 1:1, which makes it possible to estimate the cobalt concentration from the electrical conductivity in the crystallization step S02.

[0050] In the method for producing metal sulfate crystals according to the present embodiment, when cobalt sulfate crystals are crystallized in the crystallization step S02 by heating a cobalt sulfate solution adjusted to a pH of 4.5 or higher and concentrating it under reduced pressure, it becomes possible to efficiently crystallize the cobalt sulfate crystals from the cobalt sulfate solution.

[0051] In the method for producing metal sulfate crystals of this embodiment, when at least a portion of the alkaline metal compound added in the alkaline metal compound adding step S01 is converted into a cobalt hydroxide precipitate or a cobalt carbonate precipitate obtained through the fractionating step S05, the carbonate source or hydroxide source adding step S06, the second solid-liquid separation step S07, and the washing step S08, cobalt sulfate crystals can be produced with high recovery efficiency from a cobalt sulfate solution having a pH of less than 4.0.

[0052] Furthermore, the second solid-liquid separation step S07 makes it possible to sufficiently remove sodium present in the liquid component. Furthermore, when the cobalt hydroxide precipitate or the cobalt carbonate precipitate is washed with water in the washing step S08, the sodium content adhering to the cobalt hydroxide precipitate can be further removed, further suppressing the incorporation of sodium as an impurity, and enabling the production of cobalt sulfate crystals of even higher purity.

[0053] Second Embodiment A method for producing metal sulfate crystals according to a second embodiment of the present invention will be described with reference to FIG. 2. The method for producing metal sulfate crystals according to the first embodiment of the present invention involves recovering cobalt sulfate crystals (metal sulfate crystals) from a cobalt sulfate solution (metal sulfate solution). Note that the same components as those in the first embodiment are designated by the same reference numerals, and detailed description thereof will be omitted. As shown in FIG. 2, the method for producing metal sulfate crystals according to this embodiment includes at least an alkaline metal compound addition step S01, a crystallization step S02, and a solid-liquid separation step S03.

[0054] In the second embodiment, as shown in FIG. 2 , at least a part of the alkaline metal compound added in the alkaline metal compound adding step S01 is a cobalt hydroxide precipitate or a cobalt carbonate precipitate obtained through the residual liquid recovering step S15, the carbonate source or hydroxide source adding step S16, the second solid-liquid separation step S17, and the washing step S18.

[0055] (Residual Liquid Recovery Step S15) In this residual liquid recovery step S15, the residual liquid (liquid component) separated in the solid-liquid separation step S03 is recovered. This residual liquid contains a portion of unrecovered cobalt sulfate dissolved as cobalt sulfate crystals. Furthermore, the cobalt concentration in the residual liquid is preferably in the range of 40 g / L to 90 g / L. When adding a carbonate source or hydroxide source in the carbonate or hydroxide source addition step S16 described below, if the cobalt concentration in the residual liquid is 90 g / L or less, an increase in the viscosity of the resulting suspension slurry can be suppressed and uniform stirring can be achieved. Therefore, the reaction between the cobalt in the liquid and the carbonate source or hydroxide source is promoted, the amount of carbonate source or hydroxide source added can be reduced, and the incorporation of impurities can be suppressed. On the other hand, by increasing the cobalt concentration in the residual liquid to 40 g / L or more, the reaction efficiency with the carbonate source or hydroxide source is improved. The residual liquid may have a cobalt concentration of 150 g / L or more. In this case, the residual liquid is mixed with pure water to adjust the cobalt concentration to fall within a desired range.

[0056] Furthermore, the electrical conductivity of the residual liquid is preferably in the range of 3.7 S / m to 5.4 S / m. The pH of this residual liquid is 4.5 or more, and the free H ２ SO ４ There is almost no cobalt ion, and the ratio of cobalt ions to sulfate ions is approximately 1:1. In the carbonate source or hydroxide source addition step S16 described below, the cobalt ion concentration can be estimated from the electrical conductivity. If the electrical conductivity of the fractionated solution is 3.7 S / m or higher, it can be confirmed that the cobalt ion concentration in the fractionated solution is 40 g / L or higher, and if the electrical conductivity of the residual liquid is 5.4 S / m or lower, it can be confirmed that the cobalt ion concentration in the residual liquid is 90 g / L or lower.

[0057] (Carbonate Source or Hydroxide Source Addition Step S16) In this carbonate source or hydroxide source addition step S16, any one of sodium hydroxide, sodium carbonate, sodium bicarbonate, and carbon dioxide gas is added as a carbonate source or hydroxide source to the residual liquid recovered in the residual liquid recovery step S15, thereby obtaining a suspension slurry containing a cobalt hydroxide precipitate or a cobalt carbonate precipitate and dissolved sodium sulfate, or any one of added and unreacted sodium hydroxide, sodium carbonate, and sodium bicarbonate. Addition of sodium hydroxide, sodium carbonate, or sodium bicarbonate to the residual liquid results in the production of a cobalt hydroxide precipitate or a cobalt carbonate precipitate.

[0058] Here, it is preferable that the pH of the residual liquid after the addition of the carbonate source or hydroxide source (sodium hydroxide or sodium carbonate, sodium bicarbonate, carbon dioxide gas) is within the range of 6.5 to 11.0. By adjusting the pH of the residual liquid after the addition of the carbonate source or hydroxide source to 6.5 or higher, it is possible to sufficiently generate a cobalt hydroxide precipitate or a cobalt carbonate precipitate. On the other hand, by adjusting the pH of the residual liquid after the addition of the carbonate source or hydroxide source to 11.0 or lower, it is possible to prevent the addition of an excessive amount of the carbonate source or hydroxide source. It is more preferable that the pH of the residual liquid after the addition of the carbonate source or hydroxide source is 6.5 or higher. Furthermore, it is more preferable that the pH of the residual liquid after the addition of the carbonate source or hydroxide source is 7.3 or lower, and even more preferably 7.0 or lower.

[0059] The viscosity of the resulting suspension slurry is preferably in the range of 20 cP to 128 cP. By controlling the viscosity of the suspension slurry to fall within the above range, no large amount of energy is required during stirring, and problems such as blockage or breakage of pipes during transportation can be suppressed.

[0060] Here, when sodium carbonate or sodium bicarbonate is added to an acidic residual liquid in the carbonate source or hydroxide source addition step S16, carbonate ions are liberated as carbon dioxide gas into the atmosphere while generating bubbles in the early stage. This may result in problems such as an increase in the amount of sodium carbonate or sodium bicarbonate used and splashing of the liquid due to the bubbles. Therefore, when adding sodium carbonate or sodium bicarbonate, it is preferable to add the residual liquid to an aqueous sodium carbonate solution or an aqueous sodium bicarbonate solution and mix them.

[0061] (Second solid-liquid separation step S17) In this second solid-liquid separation step S17, the cobalt hydroxide precipitate or cobalt carbonate precipitate (solid component) generated in the carbonate source or hydroxide source addition step S16 is separated from a liquid component. This second solid-liquid separation step S17 makes it possible to separate and remove most of the sodium component added in the carbonate source or hydroxide source addition step S16. As a method for separating the cobalt hydroxide precipitate or cobalt carbonate precipitate (solid component) from the liquid component, an existing solid-liquid separation method such as gravity settling, centrifugal separation, or filter cloth filtration using a filter press or the like can be used.

[0062] (Washing Step S18) In this washing step S18, the cobalt hydroxide precipitate or cobalt carbonate precipitate is washed with water. This removes sodium components adhering to the surface of the cobalt hydroxide precipitate or cobalt carbonate precipitate. Because the cobalt hydroxide precipitate or cobalt carbonate precipitate is almost insoluble in water, sodium sulfate adhering to the surface of the cobalt hydroxide precipitate or cobalt carbonate precipitate can be selectively washed and removed. Here, in the washing step S18, washing with pure water is preferably performed until the electrical conductivity of the washing liquid after washing is 200 mS / m or less. By washing until the electrical conductivity of the washing liquid after washing is 200 mS / m or less, the sodium components adhering to the surface of the cobalt hydroxide precipitate or cobalt carbonate precipitate can be sufficiently removed.

[0063] In this embodiment, the cobalt hydroxide precipitate or the cobalt carbonate precipitate obtained as described above is added in the alkaline metal compound adding step S01.

[0064] According to the method for producing metal sulfate crystals of this embodiment configured as described above, as in the first embodiment, free H ２ SO ４ This allows the production of high-quality cobalt sulfate crystals that are free from adhesion of cobalt and have a low content of impurities such as sodium. Furthermore, when the cobalt sulfate crystals thus obtained are dissolved in pure water (pH 6.5 to 7.0) to a cobalt concentration of 1% by mass or more, the pH of the solution is 5.4 to 7.0, or 6.0 to 6.5.

[0065] In the method for producing metal sulfate crystals of this embodiment, when at least a portion of the alkaline metal compound added in the alkaline metal compound adding step S01 is converted into a cobalt hydroxide precipitate or a cobalt carbonate precipitate obtained through the residual liquid recovering step S15, the carbonate source or hydroxide source adding step S16, the second solid-liquid separation step S17, and the washing step S18, cobalt sulfate crystals can be produced with high recovery efficiency from a cobalt sulfate solution having a pH of less than 4.0.

[0066] Furthermore, sodium present in the liquid component can be sufficiently removed by the second solid-liquid separation step S17. Furthermore, when the cobalt hydroxide precipitate or cobalt carbonate precipitate is washed with water in the washing step S18, sodium adhering to the cobalt hydroxide precipitate or cobalt carbonate precipitate can be further removed, further suppressing the incorporation of sodium as an impurity, and enabling the production of cobalt sulfate crystals of even higher purity.

[0067] Although the embodiment of the present invention has been described above, the present invention is not limited to this and can be modified as appropriate within the scope of the technical idea of ​​the invention.

[0068] In this embodiment, the metal sulfate is described using cobalt sulfate as an example, but the present invention is not limited thereto and may be applied to other metal sulfates. For example, when the metal sulfate is nickel sulfate, the above-described steps make it possible to crystallize and recover nickel sulfate crystals from a nickel sulfate solution having a pH of less than 4.0. When the nickel sulfate crystals thus obtained are dissolved in pure water (pH 6.5 to 7.0) so that the nickel concentration is 1% by mass or more, the pH of the solution is 5.4 to 7.0, or 6.0 to 6.5.

[0069] When nickel hydroxide is added as an alkaline metal compound to a nickel sulfate solution having a pH of less than 4.0, the free H ２ SO ４ is consumed by reacting with nickel hydroxide, causing the pH to rise. ２ SO ４ (aq)+Ni(OH) ２ (s) → NiSO ４ (aq) + 2H ２ O(l)

[0070] In addition, when nickel carbonate is added as an alkaline metal compound to a nickel sulfate solution having a pH of less than 4.0, the free H ２ SO ４ is consumed by reacting with nickel carbonate, causing the pH to rise. ２ SO ４ (aq) + NiCO ３ (s) → NiSO ４ (aq)+H ２ O(l) + CO ２ (g) The nickel sulfate produced by the above reaction can also be used as a raw material for nickel sulfate crystals.

[0071] Furthermore, by adding sodium hydroxide to the separated solution (nickel sulfate solution) in the first embodiment or the residual solution (nickel sulfate solution) in the second embodiment, a nickel hydroxide precipitate is produced by the following neutralization reaction: ２ SO ４(aq)+2NaOH(aq)→Na ２ SO ４ (aq)+H ２ O(l) NiSO ４ (aq)+2NaOH(aq)→Na ２ SO ４ (aq)+Ni(OH) ２ (s)

[0072] The separated solution (nickel sulfate solution) or the remaining solution (nickel sulfate solution) was diluted with sodium carbonate (Na ２ CO ３ By adding H, nickel carbonate precipitate is formed by the following neutralization reaction: ２ SO ４ (aq) + Na ２ CO ３ (aq) → Na ２ SO ４ (aq)+H ２ O(l) + CO ２ (g) NiSO ４ (aq) + Na ２ CO ３ (aq) → Na ２ SO ４ (aq) + NiCO ３ (s)

[0073] The separated solution (nickel sulfate solution) or the remaining solution (nickel sulfate solution) was treated with sodium bicarbonate (NaHCO ３ By adding H, nickel carbonate precipitate is formed by the following neutralization reaction: ２ SO ４ (aq)+2NaHCO ３ (aq) → Na ２ SO ４ (aq) + 2H ２ O(l) + 2CO ２ (g) NiSO ４ (aq)+2NaHCO ３ (aq) → Na ２ SO ４ (aq) + NiCO ３ (s) + H ２ O(l) + CO ２ (g)

[0074] The viscosity of the suspension slurry obtained by adding sodium hydroxide, sodium carbonate, sodium bicarbonate, or carbon dioxide as a carbonate or hydroxide source to the fractionated solution or residual liquid is preferably in the range of 20 cP to 128 cP. The electrical conductivity of the fractionated solution and residual liquid is preferably in the range of 3.7 S / m to 5.4 S / m. Furthermore, the pH of the residual liquid after adding the carbonate or hydroxide source (sodium hydroxide, sodium carbonate, sodium bicarbonate, or carbon dioxide) is preferably in the range of 6.5 to 7.3.

[0075] Furthermore, in this embodiment, as at least a part of the alkaline metal compound added in the alkaline metal compound adding step S01, a cobalt hydroxide precipitate or a cobalt carbonate precipitate obtained by using a fractionated solution fractionated from a cobalt sulfate solution having a pH of less than 4.0 or a cobalt sulfate solution having a pH of 4.5 or higher obtained through the alkaline metal compound adding step S01 or a residual liquid separated in the solid-liquid separation step S03 is used in place of a cobalt sulfate solution having a pH of less than 4.0. However, the present invention is not limited to this, and there is no particular limitation on the method for producing the alkaline metal compound to be added.

[0076] In addition, in the present embodiment, the crystallization step S02 is described as being configured to crystallize cobalt sulfate crystals by heating a cobalt sulfate solution adjusted to a pH of 4.5 or higher and concentrating it under reduced pressure. However, the method for crystallizing the cobalt sulfate crystals is not limited, and for example, the cobalt sulfate crystals may be crystallized by cooling a cobalt sulfate solution adjusted to a pH of 4.5 or higher.

[0077] The results of confirmation experiments conducted to confirm the effectiveness of the present invention will be described below.

[0078] Example 1: A predetermined amount of cobalt sulfate heptahydrate (special grade reagent) was weighed and dissolved in pure water to obtain a cobalt concentration of 1 mol / L. Furthermore, before the volumetric adjustment, 47% by mass sulfuric acid was added to the solution to adjust the pH of the entire solution after volumetric adjustment to 1.0 (initial pH). This solution was used as a crystallization raw material solution (cobalt sulfate solution). The concentration analysis values ​​of this crystallization raw material solution (cobalt sulfate solution) by ICP atomic emission spectroscopy were Co: 59 g / L and Na: 12 mg / L.

[0079] Using this crystallization raw material solution (cobalt sulfate solution) with a pH of 1.0, several solutions were separated and, while thoroughly stirring, an 8 mol / L sodium hydroxide solution was added dropwise to adjust the pH of each solution to between 4.0 and 11.0, followed by stirring for one hour. After pH adjustment and stirring, the slurry and solution, which may contain precipitates, were recovered and all were filtered through a 1.0 μm membrane, after which the cobalt concentration in the filtrate was measured. The dissolved cobalt concentration in the solution at each pH is shown in Figure 3.

[0080] As shown in Figure 3, at pH levels below 7.0, the formation of cobalt hydroxide is insufficient and dissolved cobalt is detected in the solution, whereas at pH levels above 7.0, dissolved cobalt is barely detected, confirming that the formation of cobalt hydroxide precipitates is sufficient.

[0081] Example 2 Similar to Example 1, a crystallization raw material solution (cobalt sulfate solution) with a pH of 1.0 was prepared. A portion of the crystallization raw material solution (cobalt sulfate solution) with a pH of 1.0 was taken and, while thoroughly stirring, an 8 mol / L sodium hydroxide solution was added dropwise to adjust the pH of the solution to 11.0, producing a cobalt hydroxide precipitate, forming a cobalt hydroxide slurry. After stirring and maintaining this slurry for 1 hour, it was filtered through a 1.0 μm membrane. The cobalt hydroxide precipitate remaining on the membrane was thoroughly washed with pure water and filtered, and the solution adhering to the surface was washed away. After thorough washing with pure water and filtration, the cobalt hydroxide precipitate was allowed to stand and dry at 25°C, and recovered. The Na concentration in the recovered cobalt hydroxide precipitate was less than 0.1% by mass.

[0082] The recovered cobalt hydroxide precipitate was added to a crystallization raw material solution (cobalt sulfate solution) with an initial pH of 1.0, and dissolved while stirring and mixing, and the pH was adjusted to 4.5. ２ SO ４ (aq)+Co(OH) ２ (s) → CoSO ４ (aq) + 2H ２ O(l) (When the cobalt hydroxide precipitate was added to the crystallization stock solution at 15 g / L, the Co concentration in the crystallization stock solution increased by 8 g / L and the Na concentration increased by 15 mg / L.) The crystallization stock solution (cobalt sulfate solution) after being adjusted to pH 4.5 was subjected to a heat treatment and concentrated under reduced pressure until the cobalt concentration in the solution reached 200 g / L, thereby crystallizing cobalt sulfate heptahydrate.

[0083] The concentrated cobalt sulfate crystal-containing slurry containing the precipitated crystals was filtered, centrifuged, and then recovered. The slurry was then left to dry at 25°C to recover cobalt sulfate heptahydrate crystals. The Co and Na contents of the recovered cobalt sulfate heptahydrate crystals were analyzed. The analysis results are shown in Table 1. As shown in Table 1, the Co content was 20.9 mass% and the Na content was less than 5 mass ppm, indicating that the crystals were of sufficiently high purity. Approximately 10 g of the cobalt sulfate heptahydrate crystals recovered by leaving to dry were further weighed and dissolved in pure water (pH 6.5 to 7) to give a cobalt concentration of 1.00 mass%, and the pH was measured. The results are shown in Table 1. The pH of the solution was 6.0, and the free H ２ SO ４ It was confirmed that crystals with low adhesion could be recovered.

[0084] Example 3 A crystallization raw material solution (cobalt sulfate solution) was prepared using the same procedure as in Example 1, except that the pH (initial pH) of the crystallization raw material solution (cobalt sulfate solution) was set to 2.0. A portion of the crystallization raw material solution (cobalt sulfate solution) with pH 2.0 was taken and, while thoroughly stirring, 8 mol / L sodium hydroxide solution was added dropwise to adjust the solution's pH to 11.0, producing a cobalt hydroxide precipitate, forming a cobalt hydroxide slurry. This slurry was stirred for 1 hour and then filtered through a 1.0 μm membrane. The cobalt hydroxide precipitate remaining on the membrane was thoroughly filtered by adding pure water dropwise to wash away any solution adhering to the surface. After thorough washing with pure water and filtration, the precipitate was allowed to stand at 25°C and dried, and the cobalt hydroxide precipitate was recovered. The Na concentration in the recovered cobalt hydroxide precipitate was less than 0.1% by mass.

[0085] The recovered cobalt hydroxide precipitate was added to a crystallization raw material solution (cobalt sulfate solution) with a pH of 2.0, and dissolved while stirring and mixing, and the pH was adjusted to 5.0. ２ SO ４ (aq)+Co(OH) ２ (s) → CoSO ４ (aq) + 2H ２ O(l) (When cobalt hydroxide precipitate was added to the crystallization stock solution at 6 g / L, the Co concentration in the crystallization stock solution increased by 3 g / L and the Na concentration increased by 6 mg / L.) The crystallization stock solution (cobalt sulfate solution) after being adjusted to pH 5.0 was subjected to a heat treatment and concentrated under reduced pressure until the cobalt concentration in the solution reached 200 g / L, thereby crystallizing cobalt sulfate heptahydrate.

[0086] The concentrated cobalt sulfate crystal-containing slurry containing the precipitated crystals was filtered, centrifuged, and then recovered. The slurry was then allowed to stand and dried at 25°C to recover cobalt sulfate heptahydrate crystals. The Co and Na contents of the recovered cobalt sulfate heptahydrate crystals were analyzed. The analysis results are shown in Table 1. As shown in Table 1, the Co content was 21.0 mass% and the Na content was less than 5 mass ppm, indicating that the crystals were of sufficiently high purity. Approximately 10 g of the cobalt sulfate heptahydrate crystals recovered by standing and drying were further weighed and dissolved in pure water (pH 6.5 to 7) to give a cobalt concentration of 1.00 mass%, and the pH was measured. The results are shown in Table 1. The pH of the solution was 6.1, and the free H ２ SO ４ It was confirmed that crystals with low adhesion could be recovered.

[0087] Example 4 A crystallization raw material solution (cobalt sulfate solution) was prepared using the same procedure as in Example 1, except that the pH (initial pH) of the crystallization raw material solution (cobalt sulfate solution) was set to 3.0. A portion of the crystallization raw material solution (cobalt sulfate solution) with pH 3.0 was taken and, while thoroughly stirring, 8 mol / L sodium hydroxide solution was added dropwise to adjust the pH of the solution to 7.0, producing a cobalt hydroxide precipitate, forming a cobalt hydroxide slurry. This slurry was stirred for 1 hour and then filtered through a 1.0 μm membrane. The cobalt hydroxide precipitate remaining on the membrane was thoroughly filtered by adding pure water dropwise to wash away any solution adhering to the surface. After thorough washing with pure water and filtration, the cobalt hydroxide precipitate was allowed to stand and dry at 25°C, and recovered. The Na concentration in the recovered cobalt hydroxide precipitate was less than 0.1% by mass.

[0088] The recovered cobalt hydroxide precipitate was added to a crystallization raw material solution (cobalt sulfate solution) with a pH of 3.0, and dissolved while stirring and mixing, and the pH was adjusted to 5.5. ２ SO ４ (aq)+Co(OH) ２ (s) → CoSO ４ (aq) + 2H ２O(l) (When cobalt hydroxide precipitate was added to the crystallization stock solution at 1 g / L, the Co concentration in the crystallization stock solution increased by 0.5 g / L and the Na concentration increased by 1 mg / L.) The crystallization stock solution (cobalt sulfate solution) after being adjusted to pH 5.5 was subjected to a heat treatment and concentrated under reduced pressure until the cobalt concentration in the solution reached 200 g / L, thereby crystallizing cobalt sulfate heptahydrate.

[0089] The concentrated cobalt sulfate crystal-containing slurry containing the precipitated crystals was filtered, centrifuged, and then recovered. The slurry was then allowed to stand and dried at 25°C to recover cobalt sulfate heptahydrate crystals. The Co and Na contents of the recovered cobalt sulfate heptahydrate crystals were analyzed. The analysis results are shown in Table 1. As shown in Table 1, the Co content was 21.0 mass% and the Na content was less than 5 mass ppm, indicating that the crystals were of sufficiently high purity. Approximately 10 g of the cobalt sulfate heptahydrate crystals recovered by standing and drying were further weighed and dissolved in pure water (pH 6.5 to 7) to give a cobalt concentration of 1.00 mass%, and the pH was measured. The results are shown in Table 1. The pH of the solution was 6.2, and the free H ２ SO ４ It was confirmed that crystals with low adhesion could be recovered.

[0090] Example 5 A crystallization raw material solution (cobalt sulfate solution) was prepared using the same procedure as in Example 1, except that the pH (initial pH) of the crystallization raw material solution (cobalt sulfate solution) was set to 3.5. A portion of the crystallization raw material solution (cobalt sulfate solution) with pH 3.5 was taken and, while thoroughly stirring, 8 mol / L sodium hydroxide solution was added dropwise to adjust the pH of the solution to 7.0, producing a cobalt hydroxide precipitate, forming a cobalt hydroxide slurry. This slurry was stirred and held for 1 hour, then filtered through a 1.0 μm membrane. The cobalt hydroxide precipitate remaining on the membrane was thoroughly filtered by adding pure water dropwise to wash away any solution adhering to the surface. After thorough washing with pure water and filtration, the precipitate was allowed to stand at 25°C and dried, and the cobalt hydroxide precipitate was recovered. The Na concentration in the recovered cobalt hydroxide precipitate was less than 0.1% by mass.

[0091] The recovered cobalt hydroxide precipitate was added to a crystallization raw material solution (cobalt sulfate solution) with a pH of 3.5, and dissolved while stirring and mixing, and the pH was adjusted to 6.0.２ SO ４ (aq)+Co(OH) ２ (s) → CoSO ４ (aq) + 2H ２ O(l) (When cobalt hydroxide precipitate was added to the crystallization stock solution at 1 g / L, the Co concentration in the crystallization stock solution increased by 0.5 g / L and the Na concentration increased by 1 mg / L.) The crystallization stock solution (cobalt sulfate solution) after being adjusted to pH 6.0 was subjected to a heat treatment and concentrated under reduced pressure until the cobalt concentration in the solution reached 200 g / L, thereby crystallizing cobalt sulfate heptahydrate.

[0092] The concentrated cobalt sulfate crystal-containing slurry containing the precipitated crystals was filtered, centrifuged, and then recovered. The slurry was then allowed to stand and dried at 25°C to recover cobalt sulfate heptahydrate crystals. The Co and Na contents of the recovered cobalt sulfate heptahydrate crystals were analyzed. The analysis results are shown in Table 1. As shown in Table 1, the Co content was 20.9 mass% and the Na content was less than 5 mass ppm, indicating that the crystals were of sufficiently high purity. Approximately 10 g of the cobalt sulfate heptahydrate crystals recovered by standing and drying were further weighed and dissolved in pure water (pH 6.5 to 7) to give a cobalt concentration of 1.00 mass%, and the pH was measured. The results are shown in Table 1. The pH of the solution was 6.2, and the free H ２ SO ４ It was confirmed that crystals with low adhesion could be recovered.

[0093] Comparative Examples 1 to 4 Cobalt sulfate heptahydrate was crystallized and recovered from the crystallization raw material solution (cobalt sulfate solution) of pH 1.0 to 3.5 used in Examples 2 to 5 under the same conditions as in Examples 2 to 5, without adjusting the pH by adding cobalt hydroxide, at a pH of 1.0 to 3.5. The Co content and Na content of the recovered cobalt sulfate heptahydrate crystals were measured in the same manner as in Examples 2 to 5. Approximately 10 g of the recovered cobalt sulfate heptahydrate crystals were further weighed and dissolved in pure water (pH 6.5 to 7) to give a cobalt concentration of 1.00% by mass, and the pH was measured. The evaluation results are shown in Table 1.

[0094] As a result, the Co content and Na content of the cobalt sulfate heptahydrate crystals were of the same quality as those in Examples 2 to 5, but the pH of the aqueous solution with a cobalt concentration of 1.00 mass % was significantly lower than those in Examples 1 to 5, and the free H ２ SO ４ When the crystallization raw material solution (cobalt sulfate solution) is subjected to the crystallization treatment without adjusting the pH and while it is acidic with sulfuric acid, the free H ２ SO ４ It was found that it was difficult to recover the cobalt sulfate heptahydrate without the cobalt sulfate attached.

[0095] Comparative Examples 5 to 8 The crystallization raw material solution (cobalt sulfate solution) having a pH of 1.0 to 3.5 used in Examples 2 to 5 was adjusted to a pH of 4.5 to 6.0 by adding an aqueous sodium hydroxide solution instead of adjusting the pH by adding cobalt hydroxide, as in Examples 2 to 5, and cobalt sulfate heptahydrate was crystallized and recovered under the same conditions as in Examples 2 to 5.

[0096] The Co content and Na content of the recovered cobalt sulfate heptahydrate crystals were measured in the same manner as in Examples 2 to 5. Approximately 10 g of the recovered cobalt sulfate heptahydrate crystals were further weighed and dissolved in pure water (pH 6.5 to 7) to give a cobalt concentration of 1.00 mass%, and the pH was measured. The evaluation results are shown in Table 1. Note that in the comparative example, cobalt hydroxide was not prepared, so the "pH adjustment" item in Table 1 is entered as "-".

[0097] As a result, the Co content and the pH of the aqueous solution with a cobalt concentration of 1.00% by mass were of equivalent quality to those in Examples, but the Na content was significantly higher than that in Examples, resulting in the recovery of cobalt sulfate heptahydrate with a high sodium impurity. Although pH adjustment by adding an aqueous sodium hydroxide solution is a simple method, it excessively increased the sodium concentration in the crystallization raw material solution (cobalt sulfate solution), increasing sodium contamination in the cobalt sulfate heptahydrate, confirming that this method is unsuitable for recovering high-purity cobalt sulfate heptahydrate.

[0098]

[0099] (Comparative Example 11, Examples 11 to 16) Next, sodium carbonate was added to a cobalt sulfate solution having the composition shown in Table 3 to adjust the pH to 8.69, thereby obtaining a cobalt carbonate precipitate. The cobalt carbonate precipitate obtained as described above was then added to a crystallization raw material liquid (cobalt sulfate solution) having the composition shown in Table 2 and a pH of 2.0, and the pH was adjusted to the pH during crystallization shown in Table 4, thereby crystallizing cobalt sulfate crystals. The composition of the obtained cobalt sulfate crystals and the results of dissolving them in pure water (pH 6.5 to 7) to give a cobalt concentration of 1.00 mass% and measuring the pH are shown in Table 4.

[0100]

[0101]

[0102]

[0103] As shown in Table 4, in Examples 11 to 16, in which the pH during crystallization was 4.5 or higher, the contents of Al, Fe, Mn, and Zn in the crystals were reduced compared to Comparative Example 11, in which the pH during crystallization was less than 4.5. Furthermore, in Examples 11 to 16, crystals with lower acidity than Comparative Example 11 were obtained.

[0104] (Examples 21 to 25) Sodium carbonate was added to a cobalt sulfate solution having the composition shown in Table 3, and the pH was adjusted to the pH shown in Table 5, to obtain a suspension slurry containing a cobalt carbonate precipitate and dissolved sodium sulfate or added, unreacted sodium carbonate. The cobalt concentration, electrical conductivity, and viscosity of this suspension slurry were measured. The measurement results are shown in Table 5. The obtained suspension slurry was subjected to solid-liquid separation (gravity settling method) to obtain a cobalt carbonate precipitate. The composition of this cobalt carbonate precipitate is shown in Table 5.

[0105]

[0106] It was confirmed that the contents of Mn, Mg, and Ca in the cobalt carbonate precipitate were reduced in Examples 21 to 23, in which the pH was 7.0 or less, compared to Examples 24 and 25, in which the pH was 7.5 or more.

[0107] Example 31 Next, pure water was added to a cobalt sulfate solution (simulating a fractionated solution or residual solution) with a pH of 4.72 after neutralization of free sulfuric acid with the composition shown in Table 6. The Co concentration was adjusted as shown in Table 7, and the electrical conductivity was measured (using a portable electrical conductivity meter, D-210C, manufactured by HORIBA, Ltd.) to confirm the relationship between Co concentration and electrical conductivity. The evaluation results are shown in Table 7 and Figure 4. When the Co concentration was in the range of 40 g / L or more and 90 g / L or less, the electrical conductivity was in the range of 3.7 S / m or more and 5.4 S / m or less, and it was confirmed that the Co concentration and electrical conductivity were proportional to each other and that the Co concentration could be estimated by measuring the electrical conductivity.

[0108]

[0109]

[0110] Example 41: Pure water was added to a cobalt sulfate solution (simulating a preparative solution or residual solution) with a pH of 3.0 and the composition shown in Table 8 to adjust the Co concentration as shown in Table 8. Sodium carbonate was then added to the cobalt sulfate solution to obtain a suspension slurry containing cobalt carbonate precipitate and dissolved sodium sulfate or unreacted sodium carbonate. This suspension slurry was placed in a glass beaker, and the viscosity was measured using a digital viscometer (manufactured by Eiko Seiki Co., Ltd., Brookfield, LVDV-E). The measurement results are shown in Table 8.

[0111]

[0112] From Table 8, it was confirmed that stirring was easy when the slurry viscosity corresponded to a Co concentration of 40 g / L or more and 90 g / L or less.

[0113] Example 101: A predetermined amount of nickel sulfate hexahydrate (special grade reagent) was weighed and dissolved in pure water to obtain a nickel concentration of 1 mol / L. Furthermore, before the volumetric adjustment, 47% by mass sulfuric acid was added to the solution to adjust the pH of the entire solution to 2.0 after volumetric adjustment. This solution was used as a crystallization raw material solution (nickel sulfate solution). The concentration analysis values ​​of this crystallization raw material solution (nickel sulfate solution) by ICP atomic emission spectroscopy were Ni: 63 g / L and Na: 10 mg / L.

[0114] A portion of the crystallization raw material solution (nickel sulfate solution) with a pH of 2.0 (initial pH) was taken and, while thoroughly stirring, a 1.0 mol / L sodium carbonate solution was added dropwise to adjust the pH of the solution to 11.0, producing a nickel carbonate precipitate, forming a nickel carbonate slurry. After stirring and maintaining this slurry for 1 hour, it was filtered through a 1.0 μm membrane, and the nickel carbonate precipitate remaining on the membrane was thoroughly filtered by adding pure water dropwise to wash away any solution adhering to the surface. After thorough washing with pure water and filtration, the solution was allowed to stand at 25°C and dried, and the nickel carbonate precipitate was recovered. The Na concentration in the recovered nickel carbonate precipitate was less than 0.1% by mass.

[0115] The recovered nickel carbonate precipitate was added to a crystallization raw material solution (nickel sulfate solution) of pH 2.0 and dissolved under stirring to cause the following reaction, and the pH was adjusted to 4.5. ２ SO ４ (aq) + NiCO ３ (s) → NiSO ４ (aq)+H ２ O(l) + CO ２ (g) The crystallization raw material liquid (nickel sulfate solution) after being adjusted to pH 4.5 was subjected to a heat treatment and concentrated under reduced pressure until the nickel concentration in the solution reached 250 g / L, thereby crystallizing nickel sulfate hexahydrate.

[0116] The concentrated nickel sulfate crystal-containing slurry containing the precipitated crystals was filtered, centrifuged, and then recovered. The recovered nickel sulfate hexahydrate crystals were dried at 25°C to recover nickel sulfate hexahydrate crystals. The Ni and Na contents of the recovered nickel sulfate hexahydrate crystals were analyzed. The analysis results are shown in Table 9. As shown in Table 9, the Ni content was 22.3 mass% and the Na content was less than 5 mass ppm, indicating that the crystals were of sufficiently high purity.

[0117] Approximately 10 g of the recovered nickel sulfate hexahydrate crystals were weighed and dissolved in pure water (pH 6.5 to 7.0) to a nickel concentration of 1.00% by mass, and the pH was measured. The results are shown in Table 9. The pH of the solution was 5.4, and sufficient free H ２ SO ４It was confirmed that crystals with low adhesion could be recovered.

[0118] (Examples 102 to 104) The pH of the crystallization raw material solution (initial pH), the pH during preparation of nickel carbonate precipitate (preparation pH), and the pH during nickel sulfate crystallization (crystallization pH) were changed as shown in Table 9, and the other conditions were the same as those in Example 101. The evaluation results are shown in Table 9.

[0119]

[0120] (Comparative Example 111, Examples 111 to 115) Next, sodium carbonate was added to a nickel sulfate solution having the composition shown in Table 11 to adjust the pH to 8.77, thereby obtaining a nickel carbonate precipitate. Then, the nickel carbonate precipitate obtained as described above was added to a crystallization raw material liquid (nickel sulfate solution) having the composition shown in Table 10 and a pH of 2.5, and the pH was adjusted to the pH shown in Table 12, thereby crystallizing nickel sulfate crystals. The composition of the obtained nickel sulfate crystals is shown in Table 12.

[0121]

[0122]

[0123]

[0124] As shown in Table 12, in Examples 111 to 115, in which the pH during crystallization was 4.5 or higher, the contents of Al, Fe, Mn, and Zn in the crystals were reduced compared to Comparative Example 111, in which the pH during crystallization was less than 4.5. Furthermore, in Examples 111 to 115, crystals with lower acidity than Comparative Example 111 were obtained.

[0125] (Examples 121 to 125) Sodium carbonate was added to a nickel sulfate solution having the composition shown in Table 11, and the pH was adjusted to the pH shown in Table 13, to obtain a suspension slurry containing a nickel carbonate precipitate and dissolved sodium sulfate or added, unreacted sodium carbonate. The nickel concentration, electrical conductivity, and viscosity of this suspension slurry were measured. The measurement results are shown in Table 13. The obtained suspension slurry was subjected to solid-liquid separation (gravity settling method) to obtain a nickel carbonate precipitate. The composition of this nickel carbonate precipitate is shown in Table 13.

[0126]

[0127] It was confirmed that the contents of Mn, Mg, and Ca in the nickel carbonate precipitate were reduced in Examples 121 to 123, in which the pH was 7.0 or less, compared to Examples 124 and 125, in which the pH was 7.5 or more.

[0128] Example 131 Next, pure water was added to a nickel sulfate solution (simulating a preparative solution or residual solution) with a pH of 4.9 after neutralization of free sulfuric acid with the composition shown in Table 14, and the Ni concentration was adjusted as shown in Table 15. The electrical conductivity was measured (using a portable electrical conductivity meter, D-210C, manufactured by HORIBA, Ltd.) to confirm the relationship between Ni concentration and electrical conductivity. The evaluation results are shown in Table 15 and FIG. 5. When the Ni concentration was in the range of 40 g / L or more and 90 g / L or less, the electrical conductivity was in the range of 3.7 S / m or more and 5.4 S / m or less, and it was confirmed that the Ni concentration and electrical conductivity were proportional to each other and that the Ni concentration could be estimated by measuring the electrical conductivity.

[0129]

[0130]

[0131] Example 141: Pure water was added to a pH 3.5 nickel sulfate solution (simulating a preparative solution or residual solution) with the composition shown in Table 16 to adjust the Ni concentration as shown in Table 16. Sodium carbonate was then added to the nickel sulfate solution to obtain a suspension slurry containing nickel carbonate precipitate and dissolved sodium sulfate or unreacted sodium carbonate. This suspension slurry was placed in a glass beaker, and the viscosity was measured using a digital viscometer (manufactured by Eiko Seiki Co., Ltd., Brookfield, LVDV-E). The measurement results are shown in Table 16.

[0132]

[0133] From Table 16, it was confirmed that stirring was easy when the slurry viscosity corresponded to a Ni concentration of 40 g / L or more and 90 g / L or less.

[0134] As a result of the above confirmation experiments, according to the present invention, free H ２ SO４ From a metal sulfate solution containing a large amount of H ２ SO ４ It has been confirmed that it is possible to provide a method for producing metal sulfate crystals and a metal sulfate that can produce high-quality metal sulfate crystals that are free from adhesion of impurities and have low amounts of impurities such as sodium.

Claims

1. A method for producing metal sulfate crystals, comprising crystallizing and recovering metal sulfate crystals from a metal sulfate solution containing a metal sulfate and having a pH of less than 4.0, the method comprising: an alkaline metal compound addition step of adding an alkaline metal compound of a metal constituting the metal sulfate to the metal sulfate solution having a pH of less than 4.0 to adjust the pH to 4.5 or higher; a crystallization step of crystallizing the metal sulfate crystals from the metal sulfate solution with a pH of 4.5 or higher to obtain a metal sulfate crystal-containing slurry; and a solid-liquid separation step of separating the metal sulfate crystal-containing slurry into the metal sulfate crystals and a residual liquid.

2. A method for producing metal sulfate crystals, characterized in that the pH after the alkaline metal compound addition step is set within the range of 6 to 7.

3. The method for producing metal sulfate crystals according to claim 1, characterized in that the crystallization step involves heat-treating the metal sulfate solution with a pH of 4.5 or higher to crystallize the metal sulfate crystals.

4. The method for producing metal sulfate crystals according to claim 1, characterized in that at least a portion of the alkaline metal compound added in the alkaline metal compound addition step is a metal hydroxide precipitate or a metal carbonate precipitate produced by adding sodium hydroxide, sodium carbonate, or sodium bicarbonate to a solution separated from a metal sulfate solution having a pH of less than 4.

0.

5. The method for producing metal sulfate crystals described in claim 1, characterized in that at least a portion of the alkaline metal compound added in the alkaline metal compound addition step is a metal hydroxide precipitate or a metal carbonate precipitate produced by adding sodium hydroxide, sodium carbonate, or sodium bicarbonate to the residual liquid separated in the solid-liquid separation step.

6. The method for producing metal sulfate crystals according to claim 4 or 5, characterized in that the metal hydroxide precipitate or the metal carbonate precipitate is washed with water.

7. The method for producing metal sulfate crystals according to claim 1, wherein the metal sulfate crystals are cobalt sulfate crystals.

8. A metal sulfate characterized by having a pH of 5.4 or higher when dissolved in water to give a metal concentration of 1% by mass.

9. A metal sulfate characterized by having a pH of 6.0 or higher when dissolved in water to give a metal concentration of 1% by mass.

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