Method for recovering valuable metals

Abstract

To provide a method for recovering valuable metals by which the valuable metals composed of cobalt and nickel can efficiently and stably be recovered from a raw solution containing cobalt and nickel.SOLUTION: A method for recovering a valuable metal comprising at least one of cobalt and nickel from a raw solution containing at least one of cobalt and nickel, the method comprising: The method includes a sulfide generation step S01 of forming at least one of cobalt sulfide and nickel sulfide to obtain a sulfide-containing liquid, a solid-liquid separation step S02 of subjecting the sulfide-containing liquid to solid-liquid separation to obtain a sulfide-cake containing at least one of the cobalt sulfide and the nickel sulfide, and a sulfide dissolution step S04 of adding a mineral acid to the sulfide-cake to dissolve the sulfide-cake in a non-oxidizing atmosphere.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for recovering valuable metals, comprising recovering valuable metals comprising at least one of cobalt and nickel from a raw solution containing at least one of cobalt and nickel. [Background technology]

[0002] Valuable metals such as cobalt and nickel are contained in the leachate of nickel laterite ore, the copper raffinate solution obtained after copper is extracted from the leachate of copper ore, and wastewater generated during the treatment of waste batteries, etc. Note that these leachates, copper raffinate solutions, and wastewater also contain impurities such as iron, copper, and zinc in addition to cobalt and nickel. As a method for recovering cobalt and nickel from the above-mentioned leachate and waste liquid, a method for separating cobalt and nickel as sulfides has been proposed.

[0003] For example, in Patent Document 1, cobalt and nickel are leached from a battery sintered product (so-called black mass) obtained by sintering and crushing used lithium ion batteries, and S is added to the leachate. 2- A method has been proposed to separate cobalt and nickel by adding sulfide containing compounds and stirring them to precipitate them as water-insoluble cobalt sulfide and nickel sulfide. Furthermore, Non-Patent Document 1 discloses the mechanism by which cobalt and nickel sulfides are re-dissolved in sulfuric acid while generating hydrogen sulfide. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-042982 [Non-patent literature]

[0005] [Non-Patent Document 1] "Selective Leaching of Nickel from Nickel-Cobalt Mixed Sulfides with Sulfuric Acid", Journal of the Japan Institute of Metals, Vol. 81, No. 6 (2017) 320-326 Summary of the Invention [Problem to be solved by the invention]

[0006] The cobalt and nickel separation method disclosed in Patent Document 1 makes it possible to selectively concentrate and recover target metals such as cobalt and nickel without incorporating impurities such as aluminum, iron, and manganese contained in the battery calcined product (black mass). However, the cost of sulfiding agents such as sodium hydrosulfide, sodium sulfide, and hydrogen sulfide, which convert only the cobalt and nickel contained in the leachate into sulfides and precipitate them, is high, which poses a problem in that the separation of cobalt and nickel is expensive.

[0007] Furthermore, according to Non-Patent Document 1, when cobalt and nickel sulfides are re-dissolved in sulfuric acid while generating hydrogen sulfide, compounds such as nickel disulfide (NiS2) are generated and cover the surface of the sulfide particles, causing the dissolution reaction in sulfuric acid to stop midway, resulting in a drawback in that only a small amount of hydrogen sulfide is generated. Furthermore, in order to dissolve compounds such as nickel disulfide that have already been generated and recover cobalt and nickel, it is necessary to completely decompose the compounds such as nickel disulfide using some kind of oxidizing agent, which raises concerns about additional chemical costs.

[0008] The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a method for recovering valuable metals that can efficiently and stably recover valuable metals consisting of cobalt and nickel from a raw solution containing cobalt and nickel. [Means for solving the problem]

[0009] As a result of intensive research by the present inventors to solve the above problems, they have found that when cobalt sulfide and nickel sulfide are dissolved using an inorganic acid, in the presence of oxygen, elemental sulfur is produced instead of hydrogen sulfide, and this elemental sulfur reacts with cobalt sulfide and nickel sulfide to produce poorly soluble cobalt disulfide and nickel disulfide.

[0010] The present invention has been made based on the above-mentioned findings, and a method for recovering valuable metals according to a first aspect of the present invention is a method for recovering valuable metals comprising at least one of cobalt and nickel from a raw solution containing at least one of cobalt and nickel, and is characterized by comprising: a sulfide production step of adding a sulfiding agent to the raw solution to form at least one of cobalt sulfide and nickel sulfide to obtain a sulfide-containing solution; a solid-liquid separation step of performing solid-liquid separation of the sulfide-containing solution to obtain a sulfide cake containing at least one of cobalt sulfide and nickel sulfide; and a sulfide dissolution step of adding an inorganic acid to the sulfide cake in a non-oxidizing atmosphere to dissolve the sulfide cake.

[0011] The valuable metal recovery method of the first aspect of the present invention includes a sulfide dissolution step of adding an inorganic acid to a sulfide cake containing at least one of the cobalt sulfide and the nickel sulfide in a non-oxidizing atmosphere to dissolve the sulfide cake, thereby preventing oxygen from being present when the cobalt sulfide and the nickel sulfide react with the inorganic acid, thereby suppressing the generation of elemental sulfur. This makes it possible to suppress the generation of poorly soluble cobalt disulfide and nickel disulfide. Therefore, cobalt sulfide and nickel sulfide can be dissolved well, and valuable metals such as cobalt and nickel can be recovered efficiently and stably.

[0012] A valuable metal recovery method according to a second aspect of the present invention is characterized in that, in the valuable metal recovery method according to the first aspect of the present invention, the time from the solid-liquid separation step to the sulfide dissolution step is 2.0 hours or less. According to the method for recovering valuable metals of aspect 2 of the present invention, the time from the solid-liquid separation step to the sulfide dissolving step is set to 2.0 hours or less. This makes it possible to suppress oxidation of the sulfide cake obtained in the solid-liquid separation step before the sulfide dissolving step, further suppress the presence of oxygen when cobalt sulfide and nickel sulfide react with inorganic acid, and enable more stable dissolution of cobalt sulfide and nickel sulfide.

[0013] A method for recovering valuable metals according to a third aspect of the present invention is the method for recovering valuable metals according to the first or second aspect of the present invention, further comprising, after the solid-liquid separation step, a cake washing step of washing the sulfide cake with a washing liquid, and in the cake washing step, adjusting the mass ratio L / S of the liquid (L) to the solid (S) in the sulfide cake to a range of 4 or more and 9 or less. According to the method for recovering valuable metals of Aspect 3 of the present invention, in the cake washing step, the mass ratio L / S of the liquid (L) to the solid (S) in the sulfide cake is set to a range of 4 or more and 9 or less. Therefore, the inclusion of a liquid in the sulfide cake can suppress oxidation of the sulfide cake, and the shape of the sulfide cake is maintained, making it easy to handle.

[0014] A method for recovering valuable metals according to a fourth aspect of the present invention is the method for recovering valuable metals according to the third aspect of the present invention, characterized in that in the cake washing step, the sulfide cake is washed with wash water having a dissolved oxygen content of 4.0 massppm or less. According to the method for recovering valuable metals of the fourth aspect of the present invention, in the cake washing step, the sulfide cake is washed with wash water having a dissolved oxygen content of 4.0 massppm or less. This makes it possible to further reduce the amount of oxygen contained in the sulfide cake after washing, further inhibit the presence of oxygen during the reaction between cobalt sulfide and nickel sulfide and inorganic acid, and more stably dissolve cobalt sulfide and nickel sulfide.

[0015] A method for recovering valuable metals according to a fifth aspect of the present invention is the method for recovering valuable metals according to any one of the first to third aspects of the present invention, characterized in that hydrogen sulfide generated in the sulfide dissolution step is used as at least a part of the sulfiding agent in the sulfide production step. According to the method for recovering valuable metals of the fifth aspect of the present invention, the hydrogen sulfide generated in the sulfide dissolving step is used as at least a part of the sulfiding agent in the sulfide production step, so that the cost of using the sulfiding agent in the sulfide dissolving step can be reduced, and valuable metals such as cobalt and nickel can be recovered at low cost from a raw solution containing cobalt and nickel. [Effects of the Invention]

[0016] According to the present invention, it is possible to provide a method for recovering valuable metals that can efficiently and stably recover valuable metals such as cobalt and nickel from a raw solution containing cobalt and nickel. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a flow chart showing a method for recovering valuable metals according to an embodiment of the present invention. [Figure 2] 1 is a graph showing the relationship between the atmospheric gas in the sulfide dissolving step and the Ni dissolution rate, the Co dissolution rate, and the H2S recovery rate in Example 1. [Figure 3] 10 is a graph showing the relationship between the time elapsed from the solid-liquid separation step to the sulfide dissolution step, and the Ni dissolution rate, Co dissolution rate, and H2S recovery rate in Example 2. [Figure 4] 10 is a graph showing the relationship between the liquid-solid ratio (L / S) of the sulfide cake and the Ni dissolution rate, Co dissolution rate, and H2S recovery rate in Example 3. [Figure 5] 10 is a graph showing the relationship between the type of washing water for the sulfide cake and the Ni dissolution rate, Co dissolution rate, and H2S recovery rate in Example 4. DETAILED DESCRIPTION OF THE INVENTION

[0018] An example of an embodiment of the present invention will be described below.

[0019] The method for recovering valuable metals according to this embodiment recovers valuable metals consisting of at least one of cobalt and nickel from a raw solution containing at least one of cobalt and nickel, such as a leachate of nickel laterite ore, a copper raffinate solution obtained after copper is extracted from a leachate of copper ore, a leachate obtained by leaching cobalt and nickel from a battery calcined product (so-called black mass) obtained by calcining and / or crushing used lithium ion batteries, or a defective product (so-called black powder) generated in the manufacturing process of a positive electrode material for secondary batteries or the like. In this embodiment, the raw solution is a leachate obtained by leaching at least one of cobalt and nickel from a battery sintered product (so-called black mass) obtained by sintering and crushing used lithium ion batteries.

[0020] Here, the method for recovering valuable metals according to this embodiment will be described with reference to the flow chart of FIG. As shown in FIG. 1, the method for recovering valuable metals according to this embodiment includes a sulfide production step S01, a solid-liquid separation step S02, a cake washing step S03, and a sulfide dissolution step S04.

[0021] (Sulfide generation step S01) First, a sulfiding agent is added to a raw solution containing at least one of cobalt and nickel to form cobalt sulfide and nickel sulfide, which precipitate as solid components, to obtain a sulfide-containing solution. The sulfiding agent may be, for example, sodium sulfide, sodium hydrosulfide, hydrogen sulfide, etc. In this embodiment, an aqueous solution of sodium hydrogen sulfide is used as the sulfiding agent. The sulfurizing agent is preferably added until the oxidation-reduction potential (vs. Ag / AgCl) reaches -300 mV or less, and more preferably -400 mV or less. By adding the sulfurizing agent until the oxidation-reduction potential reaches -300 mV or less, the cobalt and nickel contained in the original solution can be sufficiently sulfurized and precipitated.

[0022] The pH of the original solution from the start to the end of the addition of the sulfiding agent is preferably maintained within the range of 2.0 to 5.0, more preferably within the range of 2.0 to 3.5. By adjusting the pH of the raw solution to 2.0 or higher, it is possible to promote the sulfurization reaction, and by adjusting the pH of the raw solution to 5.0 or lower, it is possible to suppress the formation of precipitates of other metals. As mentioned above, it is preferable to add a pH adjuster such as sulfuric acid as needed to maintain the pH of the original solution.

[0023] (Solid-liquid separation process S02) The sulfide-containing solution obtained in the sulfide production step S01 is subjected to solid-liquid separation treatment to obtain a sulfide cake containing at least one of cobalt sulfide and nickel sulfide as a solid phase. The means for the solid-liquid separation treatment is not particularly limited, but for example, by filtering the sulfide-containing solution using a pressure filtration device, a solid phase (sulfide cake) containing at least one of cobalt sulfide and nickel sulfide and a liquid phase containing almost no valuable metals can be obtained. The liquid phase obtained by the solid-liquid separation step S02 can be treated as a metal recovery effluent, and remaining impurities, etc. can be treated in a wastewater treatment facility. The solid-liquid separation step S02 can also be performed by, for example, suction filtration under reduced pressure or natural filtration under normal pressure, in addition to the above-mentioned pressure filtration.

[0024] (Cake washing process S03) Next, the sulfide cake obtained in the solid-liquid separation step S02 is preferably washed with a washing liquid, which makes it possible to further reduce impurities other than cobalt and nickel. In this cake washing step S03, washing is preferably performed so that the mass ratio L / S of the liquid (L) to the solid (S) in the sulfide cake after washing is within the range of 4 or more and 9 or less.

[0025] By setting the mass ratio L / S of the liquid (L) to the solid (S) in the sulfide cake to 4 or more, it becomes possible to suppress the oxidation of the solid components, cobalt sulfide and nickel sulfide, by the liquid component. On the other hand, by setting the mass ratio L / S of the liquid (L) to the solid (S) in the sulfide cake to 9 or less, the shape retention of the sulfide cake is ensured, making it easy to handle. The mass ratio L / S of the liquid (L) to the solid (S) in the sulfide cake is more preferably 5 or more, and even more preferably 5.5 or more. The mass ratio L / S of the liquid (L) to the solid (S) in the sulfide cake is more preferably 7 or less, and even more preferably 6.5 or less.

[0026] Furthermore, in the present embodiment, in the cake washing step S03, it is preferable to wash the sulfide cake using wash water having a dissolved oxygen content of 4.0 mass ppm or less. By washing using wash water having a low dissolved oxygen content in this way, the amount of oxygen contained in the sulfide cake after washing can be reduced. The amount of dissolved oxygen in the washing water is more preferably 2.0 massppm or less, and even more preferably 1.0 massppm or less. The amount of dissolved oxygen in the cleaning water can be reduced by degassing the cleaning water with an inert gas (for example, nitrogen gas).

[0027] (Sulfide dissolution process S04) Then, an inorganic acid is added to the sulfide cake containing at least one of cobalt sulfide and nickel sulfide obtained as described above, and at least one of cobalt sulfide and nickel sulfide is redissolved while generating hydrogen sulfide, thereby obtaining a valuable metal solution in which at least one of cobalt and nickel is dissolved. In this embodiment, the elapsed time from the solid-liquid separation step S02 for obtaining a sulfide cake to the sulfide dissolving step S04 is preferably 2.0 hours or less, and more preferably 1.0 hour or less.

[0028] As the inorganic acid used in this sulfide dissolution step S04, sulfuric acid is available industrially at low cost. Furthermore, hydrochloric acid has a better ability to dissolve cobalt sulfide and nickel sulfide than sulfuric acid, but the inorganic acid is not limited to sulfuric acid or hydrochloric acid. Furthermore, iron powder, nickel powder, or the like may be added as a reaction accelerator. In this embodiment, sulfuric acid is used as the inorganic acid.

[0029] When sulfuric acid is added to cobalt sulfide and nickel sulfide, the cobalt sulfide and nickel sulfide dissolve and hydrogen sulfide is generated through the reactions of the following formulas (1) and (2). (1) Formula: CoS+H2SO4→CoSO4+H2S (2) Formula: NiS+H2SO4→NiSO4+H2S

[0030] If oxygen is present in the system, the reactions of equations (3) and (4) proceed, producing elemental sulfur. (3) Formula: CoS+H2SO4+1 / 2O2→CoSO4+H2O+S (4) Formula: NiS+H2SO4+1 / 2O2→NiSO4+H2O+S

[0031] The elemental sulfur generated in equations (3) and (4) reacts with cobalt sulfide and nickel sulfide in the reactions of equations (5) and (6), producing insoluble cobalt disulfide and nickel disulfide. (5) Formula: CoS+S→CoS2 (6) Formula: NiS+S→NiS2

[0032] Here, the free energy of the reactions of the formulas (3), (4), (5), and (6) is lower than that of the reactions of the formulas (1) and (2). Therefore, if oxygen is present in the system in the sulfide dissolution step S04, the reactions of the formulas (3), (4), (5), and (6) will proceed, and the dissolution of cobalt and nickel will be inhibited.

[0033] For this reason, in the sulfide dissolving step S04, inorganic acid is added to the sulfide cake in a non-oxidizing atmosphere to dissolve the sulfide. Examples of the non-oxidizing atmosphere include an inert gas atmosphere, a vacuum atmosphere, a reducing atmosphere, etc. In this embodiment, it is preferable to carry out the treatment in an atmosphere in which the oxygen concentration is 10 mass ppm or less.

[0034] As described above, in this embodiment, by dissolving cobalt sulfide and nickel sulfide using an inorganic acid (sulfuric acid) in a non-oxidizing atmosphere with a reduced amount of oxygen in the system, the reactions of the formulas (3), (4), (5), and (6) are suppressed and the reactions of the formulas (1) and (2) are promoted, thereby enabling efficient dissolution of cobalt and nickel. The generated hydrogen sulfide can be used as at least a part of the sulfiding agent in the sulfide generation step S01. The generated hydrogen sulfide may be recovered as a gas and used as the sulfiding agent, or hydrogen sulfide may be absorbed in an alkaline solution such as an aqueous sodium hydroxide solution and used as the sulfiding agent.

[0035] The above-described process makes it possible to efficiently and stably recover valuable metals such as cobalt and nickel from a raw solution containing impurities such as iron, copper, and zinc in addition to cobalt and nickel. The metal solution thus obtained, in which either cobalt or nickel has been dissolved, contains almost no other components (copper, iron, aluminum, lithium, calcium, etc.) other than cobalt and nickel, and can be used as a recycled raw material for cobalt and nickel.

[0036] Furthermore, the cobalt and nickel in the insoluble residue that remains undissolved in the sulfide dissolution step S04 may be dissolved using an oxidizing agent such as hydrogen peroxide after solid-liquid separation, and recovered as a valuable metal solution containing cobalt and nickel. In this case, the amount of hydrogen peroxide added can be reduced by aerating the solution in air instead of just adding hydrogen peroxide.

[0037] The valuable metal recovery method of this embodiment configured as described above includes the sulfide dissolution step S04 of adding an inorganic acid to a sulfide cake containing at least one of cobalt sulfide and nickel sulfide in a non-oxidizing atmosphere to dissolve the sulfide cake. This prevents oxygen from being present when the cobalt sulfide and nickel sulfide react with the inorganic acid, thereby suppressing the generation of elemental sulfur. This makes it possible to suppress the generation of poorly soluble cobalt disulfide and nickel disulfide. Therefore, cobalt sulfide and nickel sulfide can be dissolved well, and hydrogen sulfide gas that can be reused as a sulfiding agent can be efficiently generated, while valuable metals such as cobalt and nickel can be efficiently and stably recovered.

[0038] In this embodiment, when the time from the solid-liquid separation step S02 to the sulfide dissolving step S04 is 2.0 hours or less, oxidation of the sulfide cake obtained in the solid-liquid separation step S02 can be suppressed before the sulfide dissolving step S04. This further suppresses the presence of oxygen when cobalt sulfide and nickel sulfide react with inorganic acid in the sulfide dissolving step S04, thereby suppressing the generation of elemental sulfur. This suppresses the generation of sparingly soluble cobalt disulfide and nickel disulfide. Therefore, cobalt sulfide and nickel sulfide can be more stably dissolved while efficiently generating hydrogen sulfide that can be reused as a sulfiding agent.

[0039] In this embodiment, the solid-liquid separation step S02 is followed by a cake washing step S03 in which the sulfide cake is washed with a washing liquid. In the cake washing step S03, if the mass ratio L / S of the liquid (L) to the solid (S) in the sulfide cake is set to 4 or more, the sulfide cake contains a sufficient amount of liquid, which can suppress oxidation of the sulfide cake. This can further suppress the presence of oxygen when cobalt sulfide and nickel sulfide react with inorganic acid in the subsequent sulfide dissolution step S04. This allows the cobalt sulfide and nickel sulfide to be dissolved more stably. On the other hand, when the mass ratio L / S of the liquid (L) to the solid (S) in the sulfide cake is set to 9 or less, the shape retention of the sulfide cake is ensured, the sulfide cake becomes easy to handle, and subsequent operations can be carried out efficiently.

[0040] In the present embodiment, if the cake washing step S03 is configured to wash the sulfide cake using wash water with a dissolved oxygen content of XX massppm or less, the amount of oxygen contained in the sulfide cake after washing can be further reduced, and the presence of oxygen during the reaction between cobalt sulfide and nickel sulfide and inorganic acid in the subsequent sulfide dissolving step S04 can be further suppressed. This allows for efficient generation of hydrogen sulfide that can be reused as a sulfiding agent, while more stably dissolving cobalt sulfide and nickel sulfide.

[0041] In the present embodiment, when the hydrogen sulfide generated in the sulfide dissolving step S04 is used as at least a part of the sulfiding agent in the sulfide generating step S01, the cost of using the sulfiding agent in the sulfide generating step S01 can be reduced, and valuable metals such as cobalt and nickel can be recovered at low cost from a raw solution containing cobalt and nickel.

[0042] 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. In this embodiment, the raw solution is a leachate obtained by leaching at least one of cobalt and nickel from a battery calcined product (so-called black mass) obtained by calcining and pulverizing used lithium-ion batteries, but the raw solution is not limited to this and may be any raw solution containing at least one of cobalt and nickel. Furthermore, although the sulfide cake has been described as being dissolved using sulfuric acid, this is not limiting and other inorganic acids may be used. [Example]

[0043] The results of confirmation experiments conducted to confirm the effectiveness of the present invention will be described below.

[0044] Example 1 150 mL of a stock solution was prepared, which consisted of a leachate obtained by leaching cobalt and nickel from the fired battery material (so-called black mass) obtained by firing and crushing used lithium-ion batteries. A sulfiding agent (NaSH solution: 250 g / L) was added to 150 mL of this original solution until the oxidation-reduction potential (vs. Ag / AgCl) reached -400 mV or less. At this time, 47 vol% sulfuric acid was added appropriately to adjust the pH to 2.0-3.5. This resulted in a sulfide-containing solution containing precipitates of cobalt sulfide and nickel sulfide.

[0045] Next, the sulfide-containing solution was filtered using a vacuum filtration device to obtain a sulfide cake containing at least one of cobalt sulfide and nickel sulfide as a solid phase. The obtained sulfide cake was washed with wash water, and the amount of wash water remaining on the sulfide cake after washing was adjusted by controlling the filtration time of the wash water, and the liquid-solid ratio (L / S) of the sulfide cake after washing was adjusted to 5.7. The liquid-solid ratio can be calculated using the following equation. Liquid-solid ratio (L / S) = {Wet weight of sulfide cake after washing (g) - Dry weight of cobalt sulfide and nickel sulfide in the sulfide cake (g)} / {Dry weight of cobalt sulfide and nickel sulfide in the sulfide cake (g)} The dry weights (g) of cobalt sulfide and nickel sulfide in the sulfide cake were calculated on the assumption that 100% of the cobalt and nickel in the raw material solution in the sulfurization step were sulfurized.

[0046] Then, sulfuric acid was added to the sulfide cake obtained in the separable flask, and cobalt sulfide and nickel sulfide were redissolved while generating hydrogen sulfide. The time from obtaining the sulfide cake by solid-liquid separation to dissolving with sulfuric acid was 0.5 hours. The generated hydrogen sulfide gas was absorbed and collected by passing it through 1000 mL of a 4.0 mass% sodium hydroxide aqueous solution. Here, to adjust the atmosphere in the separable flask during dissolution of the sulfide cake, N gas: 0.5 L / min and air: 0.5 L / min were blown in as atmospheric gases, and the Ni dissolution rate, Co dissolution rate, and H2S recovery rate for each are shown in Figure 2. The literature values ​​described in Non-Patent Document 1 are also shown.

[0047] The Ni dissolution rate, Co dissolution rate, and H2S recovery rate were measured as follows. After dissolving the sulfide cake, solid-liquid separation was performed using a filter, and the cobalt and nickel concentrations of the resulting liquid phase (valuable metal solution) were measured using an ICP-AES (Thermo, model number iCAP7000). The solid phase (residue) remaining on the filter was dried overnight in a vacuum dryer, after which its weight was measured and quantitative analysis of cobalt, nickel, and sulfur was performed using a powder XRF (Rigaku, model number EDXL300). The sulfur concentration in the recovered hydrogen sulfide solution was determined by neutralization titration with 0.5 M hydrochloric acid, and the weight of sulfur was calculated from the amount of sodium hydrosulfide equivalent to the titration amount.

[0048] Using the various concentrations thus obtained, the volume of the liquid phase, and the weight of the solid phase, the Ni dissolution rate, Co dissolution rate, and H2S recovery rate were calculated using the following formulas. (Ni dissolution rate (%)) = (amount of nickel in valuable metal solution (g)) / {(amount of nickel in valuable metal solution (g)) + (amount of nickel in residue (g))} × 100 (Co dissolution rate (%)) = (amount of cobalt in valuable metal solution (g)) / {(amount of cobalt in valuable metal solution (g)) + (amount of cobalt in residue (g))} × 100 (H2S recovery rate (%)) = (amount of sulfur in recovered hydrogen sulfide solution (g)) / {(amount of sulfur in recovered hydrogen sulfide solution (g) + (amount of sulfur in residue (g))) × 100

[0049] As shown in Figure 2, when dissolution of sulfide cake with sulfuric acid is carried out in an inert N2 gas atmosphere (non-oxidizing atmosphere), it is confirmed that the Ni dissolution rate, Co dissolution rate, and H2S recovery rate are all improved compared to dissolution in an air atmosphere. It is presumed that the reduction in the amount of oxygen during dissolution in a non-oxidizing atmosphere suppressed the reactions of the above-mentioned formulas (3), (4), (5), and (6), and promoted the reactions of the formulas (1) and (2).

[0050] Example 2 As in Example 1, 150 mL of a raw solution consisting of a leachate obtained by leaching cobalt and nickel was prepared. A sulfiding agent (NaSH solution: 250 g / L) was added to 150 mL of this original solution until the oxidation-reduction potential (vs. Ag / AgCl) reached -400 mV or less. At this time, 47 vol% sulfuric acid was added appropriately to adjust the pH to 2.0-3.5. This resulted in a sulfide-containing solution containing precipitates of cobalt sulfide and nickel sulfide.

[0051] Next, the sulfide-containing solution was filtered using a vacuum filtration device to obtain a sulfide cake containing at least one of cobalt sulfide and nickel sulfide as a solid phase. The obtained sulfide cake was washed with wash water, and the liquid-solid ratio (L / S) of the sulfide cake after washing was adjusted to 5.7.

[0052] Then, sulfuric acid was added to the sulfide cake obtained as described above, and cobalt sulfide and nickel sulfide were redissolved while generating hydrogen sulfide. Note that N gas: 0.5 L / min was used as the atmospheric gas during dissolution of the sulfide cake. The relationship between the time from obtaining a sulfide cake by solid-liquid separation to dissolution with sulfuric acid (cake standing time) and the Ni dissolution rate, Co dissolution rate, and HS recovery rate is shown in Figure 3. The liquid-solid ratio, Ni dissolution rate, Co dissolution rate, and HS recovery rate were evaluated in the same manner as in Example 1.

[0053] As shown in Figure 3, it was confirmed that the Ni dissolution rate, Co dissolution rate, and HS recovery rate could be improved by shortening the time (cake standing time) from obtaining the sulfide cake by solid-liquid separation until dissolution with sulfuric acid. This is presumably because the oxidation of the sulfide cake can be suppressed by shortening the time from obtaining the sulfide cake through solid-liquid separation to dissolution with sulfuric acid. This suppresses the reactions of the above-described formulas (3), (4), (5), and (6) during dissolution with sulfuric acid, and promotes the reactions of the formulas (1) and (2).

[0054] Example 3 As in Example 1, 150 mL of a raw solution consisting of a leachate obtained by leaching cobalt and nickel was prepared. A sulfiding agent (NaSH solution: 250 g / L) was added to 150 mL of this original solution until the oxidation-reduction potential (vs. Ag / AgCl) reached -400 mV or less. At this time, 47 vol% sulfuric acid was added appropriately to adjust the pH to 2.0-3.5. This resulted in a sulfide-containing solution containing precipitates of cobalt sulfide and nickel sulfide.

[0055] Next, the sulfide-containing solution was filtered using a vacuum filtration device to obtain a sulfide cake containing at least one of cobalt sulfide and nickel sulfide as a solid phase. The obtained sulfide cake was then washed with wash water, and the liquid-solid ratio (L / S) of the washed sulfide cake was adjusted.

[0056] Sulfuric acid was added to the sulfide cake obtained as described above, and cobalt sulfide and nickel sulfide were redissolved while generating hydrogen sulfide. The time from obtaining the sulfide cake by solid-liquid separation to dissolution with sulfuric acid was 0.5 hours. N gas: 0.5 L / min was used as the atmospheric gas during dissolution of the sulfide cake.

[0057] The relationship between the liquid-solid ratio (L / S) of the sulfide cake after washing and the Ni dissolution rate, Co dissolution rate, and H2S recovery rate is shown in Figure 4. The liquid-solid ratio, Ni dissolution rate, Co dissolution rate, and H2S recovery rate were evaluated in the same manner as in Example 1.

[0058] As shown in Figure 4, it was confirmed that increasing the liquid-solid ratio (L / S) of the sulfide cake after washing slightly improved the Ni dissolution rate, Co dissolution rate, and H2S recovery rate. It is presumed that by increasing the liquid-solid ratio (L / S) of the sulfide cake after washing and suppressing oxidation of the sulfide cake, the reactions of equations (3), (4), (5), and (6) described above can be suppressed during dissolution in sulfuric acid, and the reactions of equations (1) and (2) can be promoted.

[0059] Example 4 As in Example 1, 150 mL of a raw solution consisting of a leachate obtained by leaching cobalt and nickel was prepared. A sulfiding agent (NaSH solution: 250 g / L) was added to 150 mL of this original solution until the oxidation-reduction potential (vs. Ag / AgCl) reached -400 mV or less. At this time, 47 vol% sulfuric acid was added appropriately to adjust the pH to 2.0-3.5. This resulted in a sulfide-containing solution containing precipitates of cobalt sulfide and nickel sulfide.

[0060] Next, the sulfide-containing solution was filtered using a vacuum filtration device to obtain a sulfide cake containing at least one of cobalt sulfide and nickel sulfide as a solid phase. The obtained sulfide cake was then washed with a washing liquid, and the liquid-solid ratio (L / S) of the washed sulfide cake was adjusted to 4.5.

[0061] Sulfuric acid was added to the sulfide cake obtained as described above, and cobalt sulfide and nickel sulfide were redissolved while generating hydrogen sulfide. The time from obtaining the sulfide cake by solid-liquid separation to dissolution with sulfuric acid was 0.5 hours. N gas: 0.5 L / min was used as the atmospheric gas during dissolution of the sulfide cake.

[0062] Here, the washing liquid used to wash the sulfide cake was N2-degassed washing water (dissolved oxygen content: 0.0 mass ppm) and distilled water (dissolved oxygen content: 8.0 mass ppm), and the Ni dissolution rate, Co dissolution rate, and HS recovery rate were measured. The measurement results are shown in Figure 5. The liquid-solid ratio, Ni dissolution rate, Co dissolution rate, and HS recovery rate were evaluated in the same manner as in Example 1.

[0063] As shown in Figure 5, it was confirmed that the Ni dissolution rate, Co dissolution rate, and H2S recovery rate were slightly improved by using N2-degassed washing water. It is presumed that the use of N2-degassed wash water to reduce the amount of oxygen contained in the sulfide cake suppresses the reactions of equations (3), (4), (5), and (6) described above during dissolution in sulfuric acid, and promotes the reactions of equations (1) and (2).

[0064] As a result of the above confirmatory experiments, it was confirmed that the present invention can provide a method for recovering valuable metals that can efficiently and stably recover valuable metals consisting of cobalt and nickel from a raw solution containing cobalt and nickel.

Claims

1. A method for recovering valuable metals comprising at least one of cobalt and nickel from a raw solution containing at least one of cobalt and nickel, comprising: a sulfide generation step of adding a sulfiding agent to the raw solution to form at least one of cobalt sulfide and nickel sulfide to obtain a sulfide-containing solution; a solid-liquid separation step of subjecting the sulfide-containing solution to solid-liquid separation to obtain a sulfide cake containing at least one of the cobalt sulfide and the nickel sulfide; a sulfide dissolving step of adding an inorganic acid to the sulfide cake in a non-oxidizing atmosphere to dissolve the sulfide; A method for recovering valuable metals, comprising:

2. 2. The method for recovering valuable metals according to claim 1, wherein the time from the solid-liquid separation step to the sulfide dissolution step is 2.0 hours or less.

3. a cake washing step of washing the sulfide cake with a washing liquid after the solid-liquid separation step, 3. The method for recovering valuable metals according to claim 1, wherein in the cake washing step, a mass ratio L / S of a liquid (L) to a solid (S) in the sulfide cake is set within a range of 4 or more and 9 or less.

4. 4. The method for recovering valuable metals according to claim 3, wherein in the cake washing step, the sulfide cake is washed with wash water having a dissolved oxygen content of 4.0 mass ppm or less.

5. 3. The method for recovering valuable metals according to claim 1, wherein hydrogen sulfide generated in the sulfide dissolving step is used as the sulfiding agent in the sulfide producing step.

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