Solvent extraction method for selectively extracting cobalt

Abstract

A solvent extraction method for selectively extracting cobalt from a leach liquor obtained by subjecting discarded lithium ion batteries to wet processing and containing at least cobalt and nickel, the solvent extraction method comprising: step A in which a halide salt having an amine chelate skeleton is added to the leach liquor; and step B in which neodecanoic acid is used as an extractant to thereby selectively extract cobalt from the leach liquor.

Description

Solvent extraction method for selectively extracting cobalt

[0001] The present invention relates to a solvent extraction method for selectively extracting cobalt from lithium ion battery waste.

[0002] From the perspective of the SDGs, the recovery and reuse of valuable metals such as cobalt and nickel from lithium-ion battery waste is being widely considered.

[0003] To recover valuable metals such as cobalt and nickel from lithium-ion battery waste, the lithium-ion battery waste is roasted, crushed, and other processes. The resulting lithium-ion battery powder is added to an acidic solution to obtain a leachate containing dissolved lithium, copper, cobalt, nickel, iron, aluminum, manganese, and other metals. Next, solid-liquid separation and solvent extraction are repeatedly performed to obtain a solution containing the desired valuable metals, such as cobalt and nickel. Finally, nickel and cobalt are recovered from each solution by electrolysis or other methods.

[0004] For example, Patent Document 1 listed below describes a method for separating nickel and cobalt, which is characterized in that when a phosphonic acid or phosphinic acid or an ester thereof containing nickel and cobalt is back-extracted with an aqueous mineral acid solution, the aqueous mineral acid solution contains magnesium ions.

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 9-209054

[0006] As a result of extensive research by the present inventors into the separation method described in Patent Document 1, it was found that it is difficult to separate cobalt from nickel and copper in particular, and that there is room for further improvement in order to selectively separate only cobalt.

[0007] In view of the above, an object of the present invention is to provide a solvent extraction method that ultimately extracts cobalt selectively from lithium ion battery waste with a high extraction rate.

[0008] The above-mentioned problems can be solved by the following configuration: The present invention relates to a solvent extraction method (1) for selectively extracting cobalt from a leachate containing at least cobalt and nickel, which is obtained by wet processing of lithium-ion battery waste, the method comprising: a step A of adding a halide salt having an amine chelate skeleton to the leachate; and a step B of selectively extracting the cobalt from the leachate by using neodecanoic acid as an extractant.

[0009] In the solvent extraction method (1), the step A is a pretreatment step of adding the halide salt to the leachate to obtain a pretreated leachate, and the step B is an extraction step of selectively extracting the cobalt from the pretreated leachate by using the neodecanoic acid as an extractant, and the solvent extraction method (2) is preferred, in which the pretreatment step is carried out before the extraction step.

[0010] In the solvent extraction method (1), the step B is an extraction step in which an extract is obtained from the leaching solution by using the neodecanoic acid as an extractant, the step A is a scrubbing step in which the halide salt is added to the extract, and the solvent extraction method (3) is preferred, in which the extraction step is carried out before the scrubbing step.

[0011] In any of the above solvent extraction methods (1) to (3), solvent extraction method (4) is preferred in which the halide salt is a hydrochloride salt.

[0012] In any of the above solvent extraction methods (1) to (4), the leachate contains copper, and in the extraction step, a solvent extraction method (5) is preferred in which at least a portion of the copper is removed.

[0013] In any of the above solvent extraction methods (1) to (5), a solvent extraction method (6) is preferred in which the pH of the leaching solution is adjusted to 7.0 to 9.0 in the pretreatment step.

[0014] In any of the above solvent extraction methods (1) to (6), solvent extraction method (7) is preferred, in which the concentration of halide ions derived from the halide salt is 1.5 M or more.

[0015] The present invention relates to a solvent extraction method for selectively extracting cobalt from lithium-ion battery waste, which can ultimately extract cobalt selectively at a high extraction rate from a leachate containing at least cobalt and nickel. Furthermore, even when the leachate further contains copper, the present invention can also selectively extract cobalt at a high extraction rate.

[0016] The present invention relates to a solvent extraction method for selectively extracting cobalt from a leachate containing at least cobalt and nickel, which is obtained by wet processing of lithium ion battery waste.

[0017] Lithium-ion battery waste is waste from lithium-ion batteries used in various devices such as electric vehicles, mobile phones, and personal computers. Lithium-ion batteries typically consist of a positive electrode with lithium cobalt oxide as the main active material, a negative electrode with special carbon as the main active material, a separator, and other components stacked or spirally wound together while containing an electrolyte, and then placed inside an exterior material such as aluminum.

[0018] Lithium-ion battery waste is usually subjected to pretreatment such as roasting and crushing before the wet treatment step. In the roasting step, the lithium-ion batteries are heated and held at a temperature in the range of 500 to 1000°C for several hours. The heating and holding may be carried out in a furnace or in the air. In the crushing step, a crusher such as a sample mill, hammer mill, or hammer crusher is used. In the present invention, pretreatment other than roasting and crushing may be carried out before the wet treatment step, as necessary. For example, lithium-ion battery waste may be converted into finely powdered lithium-ion battery powder through pretreatment such as roasting and crushing, and then the lithium-ion battery powder may be contacted with, for example, ion-exchanged water to recover a certain amount of lithium from the lithium-ion battery powder.

[0019] Lithium-ion battery waste contains lithium, copper, cobalt, nickel, iron, aluminum, manganese, and other metals. The concentrations of each metal contained in lithium-ion battery waste can be measured, for example, by the following method. Specifically, lithium-ion battery waste is subjected to pretreatment such as roasting and pulverization to produce a finely powdered lithium-ion battery powder. The lithium-ion battery powder is then added to, for example, aqua regia (a solution of hydrochloric acid and nitric acid in a ratio of 3:1) to obtain a leachate containing dissolved lithium, copper, cobalt, nickel, iron, aluminum, manganese, and other metals. The leachate is preferably prepared by leaching lithium-ion battery powder with an acidic solution such as aqua regia. The pH of the leachate after the addition of aqua regia is preferably 0.0 to 1.0. Examples of conditions for obtaining the leachate include adding 1.0 to 10.0 g of lithium-ion battery powder per 50.0 to 500.0 ml of aqua regia, and leaching at 25 to 80°C for 1 to 72 hours with a stirring speed of 250 to 1500 rpm. After leaching, solid-liquid separation is performed using a suction filter or the like, and the concentration of each metal in the resulting filtrate is measured. The concentration of each metal in the leaching solution can be measured using, for example, an inductively coupled plasma optical emission spectrometer (ICP-OES).

[0020] In the present invention, the conditions for obtaining the leachate are not particularly limited, and the leachate can be obtained, for example, by the following wet treatment method.

[0021] (Wet Treatment Method) The wet treatment method may include, for example, the following wet treatment step and solid-liquid separation step.

[0022] (Wet Treatment Step) In the wet treatment step, at least one compound (1) selected from the group consisting of ammonia and its salts, and amine compounds and their salts is added to and mixed with lithium ion battery waste to obtain a leachate in which at least cobalt and nickel are dissolved.

[0023] Compound (1) is at least one compound selected from the group consisting of ammonia and its salts, and amine compounds and their salts. Examples of ammonia salts (ammonium salts) include ammonium chloride. Examples of amine compounds include ethylenediamine, tris(2-ethylamino)amine, imidazole, 2-piperazine, triethanolamine, L-lysine, and aminoguanidine. Examples of amine compound salts include ethylenediamine dihydrochloride, 2-piperazine hydrochloride, 2-piperazine hydrochloride monohydrate, cysteamine hydrochloride, triethanolamine hydrochloride, L-lysine hydrochloride, and aminoguanidine hydrochloride. Ammonia and its salts, and amine compounds and their salts may be used alone or in combination. For example, an ammonium salt may be combined with ammonia, or an amine compound salt may be combined with ammonia. More specifically, for example, a combination of ammonium chloride and ammonia may be used, a combination of 2-piperazine hydrochloride monohydrate and ammonia may be used, a combination of cysteamine hydrochloride and ammonia may be used, a combination of ethylenediamine dihydrochloride and ammonia may be used, a combination of triethanolamine hydrochloride and ammonia may be used, a combination of L-lysine hydrochloride and ammonia may be used, or a combination of aminoguanidine hydrochloride and ammonia may be used.

[0024] Among the compounds (1), at least one compound selected from the group consisting of amine compounds having an amino group and salts thereof is preferred, and at least one compound selected from the group consisting of chelating amine compounds having two or more amino groups and salts thereof is more preferred.Specific examples of compounds (1) that can be used include ethylenediamine, tris(2-ethylamino)amine, 2-piperazine hydrochloride monohydrate, ethylenediamine dihydrochloride, and L-lysine hydrochloride, which are preferred because they can further increase the recovery rate of desired valuable metals such as nickel and cobalt.

[0025] To increase the recovery rate of desired valuable metals such as nickel and cobalt, the wet treatment step preferably involves adding an acid to the lithium-ion battery waste in addition to compound (1) and mixing the mixture to remove at least a portion of the metals other than cobalt and nickel. It is even more preferable to add at least one compound (2) selected from the group consisting of monocarboxylic organic acids and inorganic acids as the acid and mix the mixture to remove at least a portion of the metals other than cobalt and nickel. Examples of monocarboxylic organic acids include formic acid and acetic acid. Examples of inorganic acids include hydrochloric acid and hydrobromic acid.

[0026] When compound (2) is added in addition to compound (1) in the wet treatment step, the molar ratio of compound (2):compound (1) is preferably 1:1 to 1:6, more preferably 1:1 to 1:2. By setting the ratio within this range, the recovery rate of desired valuable metals such as nickel and cobalt can be further increased.

[0027] To increase the recovery rate of desired valuable metals such as nickel and cobalt, the pH of the leachate after addition of compound (1) alone or after addition of compound (1) and compound (2) in the hydroprocessing step is preferably adjusted to 3.0 to 12.5, more preferably 9.5 to 11.0. The temperature of the leachate is preferably set to 25 to 80°C, and the leachate is preferably stirred at a stirring speed of 500 to 1,000 rpm for 8 to 24 hours.

[0028] (Solid-liquid separation step) Examples of a method for removing at least a portion of the undissolved metals from the leachate obtained in the wet treatment step include a method of separating the leachate in which at least cobalt and nickel have been dissolved from the target metals to be removed, such as aluminum or iron precipitates, by solid-liquid separation.

[0029] In the solvent extraction method of the present invention, cobalt is selectively extracted from a leachate obtained, for example, by the above-mentioned wet treatment method. The leachate used in the solvent extraction method of the present invention may be obtained by a treatment method known to those skilled in the art other than the above-mentioned wet treatment method. It may be an acidic aqueous solution, a neutral aqueous solution, or an alkaline solution containing at least cobalt and nickel, or more preferably an acidic aqueous solution, a neutral aqueous solution, or an alkaline solution containing at least cobalt, nickel, and copper. The solvent extraction method of the present invention is characterized by its ability to separate cobalt and nickel and selectively extract cobalt with a high extraction rate. However, it is also possible to separate not only cobalt and nickel but also cobalt and copper and selectively extract cobalt with a high extraction rate. Therefore, the solvent extraction method of the present invention is effective as a method for removing at least a portion of copper in the extraction process when the leachate contains copper.

[0030] The solvent extraction method of the present invention includes step A of adding at least a halide salt having an amine chelate skeleton to the leachate and step B of selectively extracting the cobalt from the leachate by using neodecanoic acid as an extractant. The solvent extraction method of the present invention may be, for example, solvent extraction method A, in which step A is a pretreatment step of adding the halide salt to the leachate to obtain a pretreated leachate and step B is an extraction step of selectively extracting the cobalt from the pretreated leachate by using neodecanoic acid as an extractant, in which the pretreatment step is performed before the extraction step. Alternatively, the solvent extraction method of the present invention may be solvent extraction method B, in which step B is an extraction step of using neodecanoic acid as an extractant to obtain an extract from the leachate, in which step A is a scrubbing step of adding the halide salt to the extract, in which the extraction step is performed before the scrubbing step. First, solvent extraction method A will be described below.

[0031] [Solvent Extraction Method A] Solvent extraction method A is a solvent extraction method for selectively extracting cobalt from a leachate containing at least cobalt and nickel, which is obtained by wet processing of lithium-ion battery waste. The solvent extraction method A includes a pretreatment step of adding a halide salt having an amine chelate skeleton to the leachate to obtain a pretreated leachate, and an extraction step of selectively extracting cobalt from the pretreated leachate by using neodecanoic acid as an extractant. In solvent extraction method A, the pretreatment step is carried out before the extraction step. The pretreatment step and the extraction step in solvent extraction method A are described below.

[0032] (Pretreatment Step) In the pretreatment step, a halide salt having at least one amino group is added to the leachate to obtain a pretreated leachate. The halide salt is a compound having at least one amino group, but is preferably a compound having two or more amino groups and an amine chelate skeleton. Furthermore, the halide salt is preferably a hydrochloride. Examples of halide salts that can be used in the present invention include ammonium chloride, piperazine dihydrochloride monohydrate, aminoguanidine hydrochloride, and ethylenediamine dihydrochloride. Among these, ethylenediamine dihydrochloride, which is a compound having an amine chelate skeleton and is a hydrochloride, is particularly preferred.

[0033] When the leachate is alkaline, it is preferable to adjust the pH of the pretreated leachate to 7.0 to 9.0 by adding an acid such as aqueous hydrochloric acid, since this adjustment is preferable because it ultimately enables cobalt to be extracted more selectively and with a higher extraction rate.

[0034] In the pretreatment step, the concentration of the halide salt added to the leaching solution is preferably 1.0 to 20.0 mass %, more preferably 10.0 to 15.0 mass %. Adjusting the conditions to these levels is preferred because it ultimately enables cobalt to be extracted more selectively and with a higher extraction rate.

[0035] (Extraction Step) In the extraction step, neodecanoic acid is used as an extractant to selectively extract cobalt from the pretreated leachate. The neodecanoic acid used as the extractant is preferably diluted with a diluent such as cyclohexane or benzene. When diluting neodecanoic acid, the ratio of neodecanoic acid to diluent is preferably 10 to 30% by volume of neodecanoic acid and 70 to 90% by volume of diluent.

[0036] In the extraction step, the concentration of halide ions derived from the halide ion salt is preferably set to 1.5 M or more, and more preferably set to 1.5 M or more. By setting the concentration in this manner, cobalt can be finally extracted more selectively and with a high extraction rate, which is preferable.

[0037] After the extraction step, cobalt migrates to the organic phase, while nickel and copper remain in the aqueous phase. A back-extraction step can be performed as needed to transfer cobalt from the organic phase to the aqueous phase. In the back-extraction step, an aqueous sulfuric acid solution can be used as the back-extractant. When using an aqueous sulfuric acid solution as the back-extractant, the concentration can be, for example, 5.0 to 20.0 mass%. The solvent extraction method of the present invention is capable of selectively separating cobalt from cobalt and nickel, and can also selectively separate cobalt from cobalt, nickel, and copper. Therefore, the present invention is particularly useful as a solvent extraction method for recovering cobalt from lithium-ion battery waste.

[0038] [Solvent Extraction Method B] Next, a solvent extraction method for selectively extracting cobalt from a leachate containing at least cobalt and nickel, which is obtained by wet treating lithium-ion battery waste, will be described below. The solvent extraction method includes a step A of adding a halide salt having an amine chelate skeleton to the leachate, and a step B of selectively extracting the cobalt from the leachate by using neodecanoic acid as an extractant, wherein the step B is an extraction step of obtaining an extract from the leachate by using neodecanoic acid as an extractant, and the step A is a scrubbing step of adding the halide salt to the extract, and the extraction step is performed before the scrubbing step.

[0039] (Extraction Step) In the extraction step, neodecanoic acid is used as an extractant to selectively extract cobalt from the leachate. The neodecanoic acid used as the extractant is preferably diluted with a diluent such as cyclohexane or benzene. When diluting neodecanoic acid, the ratio of neodecanoic acid to diluent is preferably 10 to 30% by volume neodecanoic acid and 70 to 90% by volume diluent. When the leachate is alkaline, it is preferable to adjust the pH of the leachate to 7.0 to 9.0 by adding an acid such as aqueous hydrochloric acid. Adjusting the conditions in this way is preferable because it ultimately enables cobalt to be extracted more selectively and at a high extraction rate.

[0040] (Scrubbing step) In the scrubbing step, a halide salt having at least one amino group is added to the extract. The halide salt is a compound having at least one amino group, and more preferably a compound having two or more amino groups and an amine chelate skeleton. The halide salt is preferably a hydrochloride salt. Examples of halide salts that can be used in the present invention include ammonium chloride, piperazine dihydrochloride monohydrate, aminoguanidine hydrochloride, and ethylenediamine dihydrochloride. Among these, ethylenediamine dihydrochloride, which is a compound having an amine chelate skeleton and is a hydrochloride salt, is particularly preferred.

[0041] The pH of the solution used in the scrubbing step is preferably adjusted to 3.5 to 4.0, as adjusting the conditions in this manner is preferable because it ultimately allows for more selective extraction of cobalt.

[0042] In the scrubbing step, the concentration of the halide salt when added to the leachate is preferably 3.0 mass % or more, because adjusting the conditions to these values ​​ultimately enables cobalt to be extracted more selectively and with a higher extraction rate, which is preferable.

[0043] In the scrubbing step, the concentration of halide ions derived from the halide ion salt is preferably set to 1.5 M or more. Setting it in this manner is preferable because cobalt can ultimately be extracted more selectively and with a high extraction rate.

[0044] After the scrubbing step, cobalt remains in the organic phase, while nickel and copper migrate to the aqueous phase. A back-extraction step is optionally performed to transfer cobalt from the organic phase to the aqueous phase. In the back-extraction step, an aqueous sulfuric acid solution can be used as the back-extractant. When using an aqueous sulfuric acid solution as the back-extractant, the concentration can be, for example, 5.0 to 20.0 mass%. The solvent extraction method according to the present invention is capable of selectively separating cobalt from cobalt and nickel, and can also selectively separate cobalt from cobalt, nickel, and copper. Therefore, the present invention is particularly useful as a solvent extraction method for recovering cobalt from lithium-ion battery waste.

[0045] An example of an embodiment of the present invention will be described below, but the present invention is not limited to this description in any way.

[0046] (Embodiment 1) In embodiment 1, the method was carried out based on solvent extraction method A. That is, step A is a pretreatment step in which a halide salt is added to the leachate to obtain a pretreated leachate, and step B is an extraction step in which cobalt is selectively extracted from the pretreated leachate by using neodecanoic acid as an extractant, and the pretreatment step was carried out before the extraction step. Specific embodiments are as follows:

[0047] (Example of production of leachate) Lithium ion battery waste was roasted and crushed to obtain lithium ion battery powder, which was then subjected to wet treatment to obtain a leachate containing at least cobalt, nickel, and copper. Table 1 shows the metal concentrations in the leachate.

[0048]

[0049] Example 1 (Pretreatment Step) To the leachate obtained above, ammonium chloride as a halide salt was added so as to give a concentration of 10 mass %, and the pH was adjusted to 7.0 to 9.0 with 35% hydrochloric acid water, and the chloride ion concentration was adjusted to 1.5 M or more, thereby obtaining a pretreated leachate.

[0050] (Extraction step) 50 ml of the pretreated leachate obtained above (hereinafter also referred to as the "aqueous phase") and 50 ml of an extractant (neodecanoic acid / cyclohexane = 30 / 70 (volume ratio) (hereinafter also referred to as the "organic phase") were sequentially added to a separatory funnel and stirred at a volume ratio of 1:1. After stirring, the aqueous phase was removed, and the same amount of new organic phase was added and stirred again. The obtained organic phase was mixed with the originally obtained organic phase to obtain an organic phase with a total volume of 100 ml.

[0051] (Back-extraction step) 100 ml of the organic phase obtained above and 100 ml of 6.25% aqueous sulfuric acid (hereinafter also referred to as "aqueous phase 2") were added sequentially to a volume ratio of 1:1 and stirred. After stirring, the aqueous phase 2 was removed, and the metal concentration in the aqueous phase 2 was measured using an ICP optical emission spectrometer (ICP-OES).

[0052] The more selectively cobalt is extracted in the aqueous phase 2, and the lower the extraction rates of nickel and copper, the higher the cobalt is selectively extracted. Table 2 shows the results of the extraction rates of cobalt, nickel, and copper. The evaluation criteria for the extraction rates are as follows:

[0053] ・About Co ◎: Extraction rate 90% or more 〇: Extraction rate 80% to 90% △: Extraction rate 70% to 80% ×: Extraction rate 70% or less ・About Ni ◎: Extraction rate 10% or less 〇: Extraction rate 10% to 20% △: Extraction rate 20 to 30 ×: Extraction rate 30% or more ・About Cu ◎: Extraction rate 10% or less 〇: Extraction rate 10% to 20% △: Extraction rate 20 to 30% ×: Extraction rate 30% or more

[0054] Examples 2 to 4 and Comparative Examples 1 and 2 Solvent extraction was carried out in the same manner as in Example 1, except that the halide salt and extractant were changed to those shown in Table 2.

[0055]

[0056] The results in Table 2 show that cobalt and copper were separated extremely efficiently in Examples 1 to 4. It is also clear that cobalt and nickel were separated efficiently. In particular, it is clear that cobalt and copper were separated particularly efficiently in Examples 2 to 4, which used piperazine dihydrochloride monohydrate, aminoguanidine, and ethylenediamine dihydrochloride, which are compounds having an amine chelate skeleton, as halide salts.

[0057] (Embodiment 2) In embodiment 2, the method was carried out based on solvent extraction method B. That is, step B is an extraction step in which an extract is obtained from the leachate by using neodecanoic acid as an extractant, and step A is a scrubbing step in which a halide salt is added to the extract, and the extraction step was carried out before the scrubbing step. Specific embodiments are as follows.

[0058] (Example of production of leachate) Lithium ion battery powder obtained by roasting and crushing lithium ion battery waste was subjected to wet treatment to obtain a leachate having the metal concentrations shown in Table 1.

[0059] Example 5 (Extraction Step) 50 ml of the leachate obtained above, whose pH had been adjusted to 7.0 to 9.0 with 35% aqueous hydrochloric acid (hereinafter also referred to as the "aqueous phase"), and 50 ml of an extractant consisting of neodecanoic acid and cyclohexane at a volume ratio of 30 / 70 (hereinafter also referred to as the "organic phase"), were added sequentially to a separatory funnel and stirred at a volume ratio of 1:1. After stirring, the aqueous phase was removed, and the same amount of organic phase was added, followed by stirring again. The resulting organic phase was mixed with the organic phase obtained initially to obtain a total volume of 100 ml of organic phase.

[0060] (Scrubbing Step) 100 ml of a 3% by mass aqueous solution of piperazine dihydrochloride monohydrate and 100 ml of the organic phase obtained above were added successively so that the volume ratio was 1:1, and the mixture was stirred, and 100 ml of the organic phase was recovered.

[0061] (Back-extraction step) 100 ml of the organic phase obtained above and 100 ml of 6.25% aqueous sulfuric acid (hereinafter also referred to as "aqueous phase 2") were added sequentially to a volume ratio of 1:1 and stirred. After stirring, the aqueous phase 2 was removed, and the metal concentration in the aqueous phase 2 was measured using an ICP optical emission spectrometer (ICP-OES).

[0062] The more selectively cobalt is extracted in the aqueous phase 2, and the lower the extraction rates of nickel and copper, the higher the cobalt is extracted selectively. Table 3 shows the results of the extraction rates of cobalt, nickel, and copper. The evaluation criteria for the extraction rates are as follows:

[0063] ・About Co ◎: Extraction rate 90% or more 〇: Extraction rate 80% to 90% △: Extraction rate 70% to 80% ×: Extraction rate 70% or less ・About Ni ◎: Extraction rate 10% or less 〇: Extraction rate 10% to 20% △: Extraction rate 20 to 30 ×: Extraction rate 30% or more ・About Cu ◎: Extraction rate 10% or less 〇: Extraction rate 10% to 20% △: Extraction rate 20 to 30% ×: Extraction rate 30% or more

[0064] Examples 6 to 8 and Comparative Examples 3 and 4 Solvent extraction was carried out in the same manner as in Example 5, except that the halide salts were changed to those shown in Table 3.

[0065]

[0066] The results in Table 3 show that cobalt and copper were separated extremely efficiently in Examples 5 to 8. In particular, in Examples 5 to 8, which used piperazine dihydrochloride monohydrate and ethylenediamine dihydrochloride as the halide salts, cobalt and nickel were separated particularly efficiently.

Claims

1. A solvent extraction method for selectively extracting cobalt from a leachate containing at least cobalt and nickel, the leachate being obtained by wet processing of lithium ion battery waste, the method comprising: a step A of adding a halide salt having an amine chelate skeleton to the leachate; and a step B of selectively extracting the cobalt from the leachate by using neodecanoic acid as an extractant.

2. A solvent extraction method as claimed in claim 1, wherein step A is a pretreatment step of adding the halide salt to the leachate to obtain a pretreated leachate, and step B is an extraction step of selectively extracting the cobalt from the pretreated leachate by using the neodecanoic acid as an extractant, and wherein the pretreatment step is carried out prior to the extraction step.

3. The solvent extraction method according to claim 1, wherein step B is an extraction step in which an extract is obtained from the leaching solution by using the neodecanoic acid as an extractant, and step A is a scrubbing step in which the halide salt is added to the extract, and the extraction step is carried out prior to the scrubbing step.

4. The solvent extraction method according to any one of claims 1 to 3, wherein the halide salt is a hydrochloride salt.

5. A solvent extraction method according to any one of claims 1 to 4, wherein the leachate contains copper, and in the extraction step, at least a portion of the copper is removed.

6. A solvent extraction method according to any one of claims 1 to 5, wherein in the pretreatment step, the pH of the leaching solution is adjusted to 7.0 to 9.

0.

7. A solvent extraction method according to any one of claims 1 to 7, wherein the concentration of halide ions derived from the halide salt is 1.5M or more.

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