Method for recovering cobalt

Abstract

Provided is a cobalt recovery method for recovering cobalt from a cobalt sulfate solution. The method is characterized by comprising: adding, to the cobalt sulfate solution, an additive of which the solubility becomes lower at a pH of at most 2.0; and electrolytically recovering cobalt from the cobalt sulfate solution to which the additive has been added. The additive preferably has a pH-buffering effect in a pH range of 2.0-4.5.

Description

Technical Field

[0001] The present invention relates to a method for recovering cobalt from a sulfuric acid solution (cobalt sulfate solution) in which cobalt is dissolved. This application claims priority based on Japanese Patent Application No. 2023-082354 filed in Japan on May 18, 2023, and incorporates its content herein by reference.

Background Art

[0002] Conventionally, an electrolytic deposition method has been used as a method for recovering cobalt from a solution (cobalt sulfate solution) in which cobalt is dissolved. In the electrolytic deposition of cobalt, a solution in which cobalt is dissolved is used as an electrolyte, an insoluble anode and a cathode are immersed in this electrolyte, and a predetermined voltage is applied between this anode and cathode to electrolytically reduce cobalt and deposit it on the surface of the cathode, thereby recovering cobalt.

[0003] Here, in the electrolytic deposition of cobalt, since the pH decreases during electrolysis, reactions other than the reaction in which cobalt is deposited on the cathode surface (for example, hydrogen generation reaction, etc.) are likely to occur, which has been a factor in reducing the current efficiency. In addition, when the pH of the electrolyte is low, the adhesion between the deposited cobalt and the cathode becomes high, and there has been a problem that it becomes difficult to peel off and recover the deposited cobalt. On the other hand, although the current efficiency is improved by maintaining the pH of the electrolyte at a high level, since the adhesion between the deposited cobalt and the cathode is poor, there has been a risk that the cobalt will naturally peel off and the anode and cathode will short-circuit.

[0004] Therefore, for example, Patent Document 1 proposes a technique for controlling the surface roughness of an electrode plate (cathode plate) and ensuring the peelability of the metal deposited on the electrode plate.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] By the way, in the method disclosed in Patent Document 1, there is a problem that the processing cost becomes high. In addition, it is difficult to control the peelability of cobalt deposited only on the surface shape of the electrode plate.

[0007] The present invention has been made in view of the above circumstances, and an object thereof is to provide a method for recovering cobalt that can efficiently and stably recover cobalt from a cobalt sulfate solution.

Means for Solving the Problems

[0008] In order to solve the above problems, the cobalt recovery method according to Aspect 1 of the present invention is a cobalt recovery method for recovering cobalt from a cobalt sulfate solution, and an additive whose solubility decreases at a pH of 2.0 or less Potassium hydrogen phthalate is used as is added to the cobalt sulfate solution, the addition amount of the potassium hydrogen phthalate is in the range of 15 g / L or more and 25 g / L or less. and cobalt is electrolytically deposited from the cobalt sulfate solution to which the additive has been added.

[0009] According to the cobalt recovery method of Aspect 1 of the present invention, since the solubility of the additive decreases at a pH of 2.0 or less, when the pH of the electrolytic solution decreases to 2.0 or less, the additive is deposited on the cathode surface, so that the adhesion between the cobalt deposited on the cathode surface and the cathode can be appropriately controlled, the deposited cobalt can be easily peeled off, and the natural peeling of cobalt can be suppressed to suppress the occurrence of short circuits. Since potassium hydrogen phthalate is used as the additive, when the pH of the electrolyte solution drops to 2.0 or less, potassium hydrogen phthalate precipitates on the cathode surface, making it possible to appropriately control the adhesion between the cobalt deposited on the cathode surface and the cathode. Since the addition amount of the potassium hydrogen phthalate is in the range of 15 g / L or more and 25 g / L or less, it is possible to sufficiently exhibit the pH buffering effect and appropriately control the adhesion between the cobalt deposited on the cathode surface and the cathode.

[0010] The cobalt recovery method of Embodiment 2 of the present invention is characterized in that, in the cobalt recovery method of Embodiment 1, the additive has a pH buffering effect in the range where the pH is 2.0 or more and 4.5 or less. According to the cobalt recovery method of Embodiment 2 of the present invention, since an additive having a pH buffering effect in the range where the pH is 2.0 or more and 4.5 or less is added to the cobalt sulfate solution, it is possible to suppress a sharp decrease in pH even when electrolysis proceeds, and it is possible to suppress a decrease in current efficiency.

[0013] The cobalt recovery method of Embodiment 5 of the present invention is characterized in that, in the cobalt recovery method of any one of Embodiments 1 to 4, the cobalt sulfate solution is obtained by separating cobalt from crushed lithium ion batteries. According to the cobalt recovery method of Embodiment 5 of the present invention, since the cobalt sulfate solution is obtained by separating cobalt from crushed lithium ion batteries, it is possible to efficiently recover cobalt, which is a valuable metal, from discarded lithium ion batteries.

Effects of the Invention

[0014] According to the present invention, it is possible to provide a cobalt recovery method capable of efficiently and stably recovering cobalt from a cobalt sulfate solution.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3A

Figure 3B

Figure 3C

Figure 3D

Figure 4

Mode for Carrying Out the Invention

[0016] Hereinafter, an example of an embodiment of the present invention will be described.

[0017] The cobalt recovery method of this embodiment is, for example, to recover cobalt from a sulfuric acid solution (cobalt sulfate solution) in which cobalt is dissolved.

[0018] The cobalt recovery method of this embodiment is, for example, like the electrolysis apparatus 10 shown in FIG. 1, using a sulfuric acid solution (cobalt sulfate solution) in which cobalt is dissolved as the electrolytic solution 3, immersing an insoluble anode electrode 12 and a cathode electrode 13 in the electrolytic solution 3 stored in the electrolytic cell 11, and applying a predetermined voltage between this anode electrode 12 and the cathode electrode 13 to electrolytically reduce cobalt and deposit it on the surface of the cathode electrode 13, thereby collecting cobalt.

[0019] In this embodiment, an additive whose solubility decreases when the pH is 2.0 or less is added to the cobalt sulfate solution that becomes the electrolytic solution 3, and electrolytic collection is carried out. It is preferable that the additive has a pH buffering effect in the range where the pH is 2.0 or more and 4.5 or less.

[0020] When the pH of the electrolytic solution 3 decreases during electrolysis, the adhesion between the deposited cobalt and the cathode electrode 13 increases, and when the pH becomes 2.0 or less, it becomes difficult to peel off the cobalt. Here, when an additive whose solubility decreases when the pH is 2.0 or less is added, and the electrolytic collection progresses and the pH of the electrolytic solution becomes 2.0 or less, the additive in the electrolytic solution deposits on the surface of the cathode electrode 13, and it is possible to suppress the strong adhesion between the cathode electrode 13 and cobalt, and it becomes possible to easily peel off the cobalt deposited from the cathode electrode 13.

[0021] In addition, when an additive having a pH buffering effect in the range of pH 2.0 or more and 4.5 or less is added, by setting the pH of the electrolytic solution 3 to 2.0 or more, the occurrence of the hydrogen generation reaction can be preferentially suppressed, and it becomes possible to improve the current efficiency. On the other hand, by setting the pH of the electrolytic solution 3 to 4.5 or less, the precipitation of cobalt as a hydroxide can be suppressed, and it becomes possible to efficiently recover cobalt. Therefore, it is preferable to add an additive having a pH buffering effect in the range of pH 2.0 or more and 4.5 or less.

[0022] As described above, specific examples of the additive whose solubility decreases when the pH is 2.0 or less include potassium hydrogen phthalate (KHP). Note that potassium hydrogen phthalate (KHP) has a pH buffering effect in the range of pH 2.0 or more and 4.5 or less. Here, when adding potassium hydrogen phthalate as an additive, it is preferable that the addition amount is in the range of 15 g / L or more and 25 g / L or less.

[0023] By setting the addition amount of potassium hydrogen phthalate to the electrolytic solution 3 to 15 g / L or more, it becomes possible to sufficiently achieve the above-described pH buffering effect and the effect of controlling the adhesion between cobalt and the cathode electrode 13. Note that "setting the addition amount of potassium hydrogen phthalate to the electrolytic solution 3 to 15 g / L or more" means adding potassium hydrogen phthalate to the electrolytic solution 3 so that the concentration of potassium hydrogen phthalate in the electrolytic solution 3 becomes 15 g / L or more. On the other hand, by setting the addition amount of potassium hydrogen phthalate to the electrolytic solution 3 to 25 g / L or less, the precipitation of potassium hydrogen phthalate before the start of electrolysis can be suppressed, and the spontaneous peeling of the precipitated cobalt can be suppressed.

[0024] Here, the temperature of the electrolytic solution 3 during electrolytic collection is preferably maintained within the range of 50°C or more and 55°C or less. By setting the temperature of the electrolytic solution 3 to 50 °C or higher, the reaction rate can be ensured. On the other hand, by setting the temperature of the electrolytic solution 3 to 55 °C or lower, evaporation of the electrolytic solution 3 can be suppressed, and precipitation of cobalt sulfate can be inhibited.

[0025] Also, the current density during electrolytic extraction is preferably in the range of 0.026 A / cm 2 or more and 0.040 A / cm 2 or less. By performing electrolytic extraction with the current density in the range of 0.026 A / cm 2 or more and 0.040 A / cm 2 or less, it is possible to suppress a decrease in current efficiency and efficiently perform electrolytic extraction of cobalt.

[0026] Furthermore, the cobalt concentration in the electrolytic solution 3 is preferably in the range of 50 g / L or more and 100 g / L or less. By setting the cobalt concentration in the electrolytic solution 3 to 50 g / L or more, a decrease in current efficiency can be suppressed, and electrolytic extraction of cobalt can be efficiently performed. On the other hand, by setting the cobalt concentration in the electrolytic solution 3 to 100 g / L or less, precipitation of cobalt sulfate is suppressed.

[0027] Also, the pH of the electrolytic solution 3 at the start of electrolytic extraction is preferably in the range of 4.0 or more and 4.5 or less. By setting the pH of the electrolytic solution 3 at the start of electrolytic extraction to 4.5 or less, precipitation of cobalt as a hydroxide can be suppressed, and cobalt can be efficiently recovered. By setting the pH of the electrolytic solution 3 at the start of electrolytic extraction to 4.0 or more, it is possible to ensure the time until the pH of the electrolytic solution 3 decreases to 2.0 or less when electrolytic extraction is started, and electrolytic extraction can be efficiently performed.

[0028] In this embodiment, it is preferable that the cobalt sulfate solution serving as the electrolytic solution 3 is obtained by separating cobalt from lithium-ion battery crushed materials obtained by crushing waste lithium-ion batteries. Regarding the specific means for obtaining a cobalt sulfate solution from a lithium-ion battery, the method described in Japanese Patent No. 7121885 can be applied.

[0029] That is, as shown in the flowchart of FIG. 2, a heat treatment step S1 for heat-treating the discarded lithium-ion battery, a pulverization and separation step S2 for pulverizing the heat-treated lithium-ion battery and separating the electrode material, and a step of immersing the separated electrode material in a treatment liquid obtained by mixing sulfuric acid and hydrogen peroxide to leach cobalt and nickel. An extraction step S3, a copper separation step S4 in which a hydrogen sulfide compound is added to the obtained leachate to separate copper as copper sulfide (solid matter), and after adjusting the pH of the eluate obtained in the copper separation step S4, a hydrogen sulfide compound is added to obtain a precipitate containing cobalt sulfide and nickel sulfide. A cobalt-nickel separation step S5, a redissolution step S6 for dissolving the above precipitate in a redissolution liquid containing sulfuric acid, and a solvent extraction step S7 for adding an extractant solution to the cobalt-nickel solution obtained in the redissolution step S6 to obtain a cobalt sulfate solution and a nickel sulfate solution. Thus, a cobalt sulfate solution is obtained. By applying the cobalt recovery method according to the present embodiment to the cobalt sulfate solution thus obtained, it is possible to recover cobalt, which is a valuable metal, from the discarded lithium-ion battery.

[0030] According to the cobalt recovery method of the present embodiment configured as described above, since an additive whose solubility decreases at a pH of 2.0 or less is added to the electrolytic solution 3 composed of a cobalt sulfate solution, when the pH of the electrolytic solution 3 drops to 2.0 or less, the additive is deposited on the surface of the cathode electrode 13, so that the adhesion between the deposited cobalt and the cathode electrode 13 can be appropriately controlled, and the deposited cobalt can be easily peeled off, and natural peeling of cobalt can be suppressed, thereby suppressing the occurrence of a short circuit.

[0031] In the cobalt recovery method of the present embodiment, when an additive having a pH buffering effect in the range of pH 2.0 or more and 4.5 or less is added as the additive, it is possible to suppress a rapid decrease in pH even when electrolysis proceeds, and to suppress a decrease in current efficiency.

[0032] In the cobalt recovery method of the present embodiment, when potassium hydrogen phthalate is used as an additive, when the pH of the electrolytic solution 3 drops to 2.0 or less, potassium hydrogen phthalate precipitates on the surface of the cathode electrode 13, so that the adhesion between the precipitated cobalt and the cathode electrode 13 can be appropriately controlled. In addition, a sufficient pH buffering effect can be obtained in the range where the pH is 2.0 or more and 4.5 or less, and it is possible to suppress a sharp drop in pH even when electrolysis proceeds, and to suppress a decrease in current efficiency.

[0033] In the cobalt recovery method of the present embodiment, when the addition amount of potassium hydrogen phthalate added as an additive is in the range of 15 g / L or more and 25 g / L or less, the pH adjustment effect can be sufficiently achieved, and the adhesion between the precipitated cobalt and the cathode electrode 13 can be appropriately controlled.

[0034] In the cobalt recovery method of the present embodiment, when the cobalt sulfate solution used as the electrolytic solution 3 is obtained by separating cobalt from the crushed lithium ion battery, it is possible to efficiently and highly purely recover cobalt, which is a valuable metal, from the discarded lithium ion battery.

[0035] As described above, the embodiments of the present invention have been described, but the present invention is not limited thereto, and can be appropriately changed without departing from the technical idea of the invention.

Example

[0036] The results of the confirmation experiments conducted to confirm the effectiveness of the present invention will be described below.

[0037] (Example 1-3 of the present invention) A cobalt sulfate solution with a cobalt concentration of 50 g / L was prepared. In the examples of the present invention, potassium hydrogen phthalate was added as an additive to the cobalt sulfate solution. The addition amounts of potassium hydrogen phthalate were 20 g / L in Example 1 of the present invention, 10 g / L in Example 2 of the present invention, and 30 g / L in Example 3 of the present invention. Using the cobalt sulfate solution with the additive as the electrolyte, electrolysis was carried out under the conditions of a pH of 4.0 at the start of electrolysis, an electrolyte temperature of 55 °C, and a current density of 0.026 A / cm 2 .

[0038] (Comparative Example) A cobalt sulfate solution with a cobalt concentration of 50 g / L was prepared. In the comparative example, no additive was added to the cobalt sulfate solution. Using this cobalt sulfate solution as the electrolyte, electrolysis was carried out under the conditions of a pH of 4.0 at the start of electrolysis, an electrolyte temperature of 55 °C, and a current density of 0.026 A / cm 2 .

[0039] In the examples and comparative example of the present invention, the state of cobalt produced on the surface of the cathode electrode is shown in Figure 3. Also, in the examples and comparative example of the present invention, the cobalt obtained by electrolytic collection was acid-dissolved and quantitatively analyzed by ICP-AES to evaluate the purity of cobalt. The evaluation results are shown in Table 1. Furthermore, Figure 4 shows the results of confirming the change in the pH of the electrolyte with the elapsed time from the start of electrolytic collection in Examples 1-3 and the comparative example of the present invention.

[0040]

Table 1

[0041] In Comparative Example 1, no additive was added to the electrolyte (cobalt sulfate solution). As shown in Figure 3A, cobalt was strongly adhered to the surface of the cathode electrode plate, and it was difficult to peel off the cobalt by the commonly used method. The commonly used method includes physically separating the cobalt on the surface from the surface of the cathode electrode plate using tools such as a spatula. Also, as shown in Fig. 4, when the electrolytic extraction progresses, the pH of the electrolyte solution rapidly decreases, and the current efficiency was 83.7%.

[0042] In contrast, in Invention Example 1, 20 g / L of potassium hydrogen phthalate was added as an additive to the electrolyte solution (cobalt sulfate solution). As shown in Fig. 3B, cobalt was not strongly adhered to the surface of the cathode electrode plate, and it was easy to peel off cobalt by the commonly used method. Also, even when the additive was added, no significant difference was observed in the purity of the obtained cobalt. Also, as shown in Fig. 4, even when the electrolytic extraction progressed, the pH of the electrolyte solution did not rapidly decrease, and the current efficiency was 85.5%.

[0043] In Invention Example 2, 10 g / L of potassium hydrogen phthalate was added as an additive to the electrolyte solution (cobalt sulfate solution). As shown in Fig. 3C, cobalt was not strongly adhered to the surface of the cathode electrode plate, and it was easy to peel off cobalt by the commonly used method. Also, even when the additive was added, no significant difference was observed in the purity of the obtained cobalt. On the other hand, as shown in Fig. 4, even when the electrolytic extraction progressed, the pH of the electrolyte solution did not rapidly decrease, but the current efficiency was 54.6%.

[0044] In Invention Example 3, 30 g / L of potassium hydrogen phthalate was added as an additive to the electrolyte solution (cobalt sulfate solution). As shown in Fig. 3(d), cobalt was not strongly adhered to the surface of the cathode electrode plate, and it was easy to peel off cobalt by the commonly used method. Also, even when the additive was added, no significant difference was observed in the purity of the obtained cobalt. On the other hand, as shown in Fig. 4, even when the electrolytic extraction progressed, the pH of the electrolyte solution did not rapidly decrease, but the current efficiency was 68.5%. It is presumed that this is because a large amount of the additive precipitated and coated the electrode.

[0045] As a result of the above confirmation experiments, it was confirmed that according to the present invention, it is possible to provide a method for recovering cobalt that can efficiently and stably recover cobalt from a cobalt sulfate solution.

Industrial Applicability

[0046] According to the present invention, it becomes possible to provide a method for recovering cobalt that can efficiently and stably recover cobalt from a cobalt sulfate solution.

Claims

1. 1. A method for recovering cobalt from a cobalt sulfate solution, comprising the steps of: Add potassium hydrogen phthalate to the cobalt sulfate solution as an additive whose solubility decreases at a pH of 2.0 or less, and set the amount of potassium hydrogen phthalate added to the cobalt sulfate solution to be within a range of 15 g / L or more and 25 g / L or less; A method for recovering cobalt, comprising electrolytically recovering cobalt from the cobalt sulfate solution to which the additive has been added.

2. 2. The method for recovering cobalt according to claim 1, wherein the additive has a pH buffering effect in the range of pH 2.0 to 4.

5.

3. 3. The method for recovering cobalt according to claim 1, wherein the cobalt sulfate solution is obtained by separating cobalt from crushed lithium ion batteries.

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