Method for recovering valuable metals

Abstract

The present invention provides a method for recovering cobalt, nickel, manganese and lithium from a waste lithium ion battery by a wet process with a very high recovery rate. The method for recovering valuable metals includes a first solvent extraction step in which an organic solvent is added to a solution that contains lithium and at least one valuable metal selected from the group consisting of magnesium, strontium, aluminum, and transition metals other than manganese, cobalt, and nickel, thereby extracting the valuable metal. The organic solvent includes at least one substance that is selected from the group consisting of a compound represented by formula (1), a phosphonic acid ester, a phosphoric acid ester, phosphinic acid, methyl isobutyl ketone, and trioctylamine. In formula (1), R1 and R2 each independently represent a hydrocarbon group having 6 to 20 carbon atoms.

Description

Valuable metal recovery methods

[0001] The present invention relates to a method for recovering valuable metals.

[0002] In recent years, with the widespread use of lithium ion batteries, methods have been investigated for recovering valuable metals such as cobalt, nickel, manganese, and lithium from discarded lithium ion batteries and reusing them as materials for the lithium ion batteries.

[0003] Conventionally, when recovering the valuable metals from the waste lithium-ion batteries, the waste lithium-ion batteries are subjected to a heat treatment (roasting), or are crushed and classified without being subjected to a heat treatment to obtain a powder containing the valuable metals, and cobalt, nickel, manganese, and lithium are separated and refined by a wet process (see, for example, Patent Document 1).

[0004] In the present invention, "waste lithium ion batteries" refers to used lithium ion batteries that have reached the end of their life as battery products, lithium ion batteries that have been discarded as defective products during the manufacturing process, and residual positive and negative electrode materials used in the manufacturing process. The powder containing the positive and negative electrodes obtained from the waste lithium ion batteries is referred to as "active material powder." Furthermore, "impurities" refers to metals contained in the active material powder that do not require recovery.

[0005] Patent No. 7060899

[0006] In the manufacture of lithium-ion batteries, attempts have been made to improve battery performance by adding appropriate amounts of transition metals (excluding manganese, cobalt, and nickel), magnesium, strontium, and other elements to the cathode material, with precise proportions selected to suit the purpose. The presence of elements such as transition metals, magnesium, and strontium in lithium-ion batteries can adversely affect the separation and purification of manganese, cobalt, and nickel. In particular, in wet processes using solvent extraction, these elements accumulate in the organic solvent, inhibiting the extraction of valuable metals such as manganese, cobalt, and nickel, which are the intended targets for recovery. This results in a disadvantageous decrease in the recovery rate of valuable metals. Despite these disadvantages, there has been a demand in recent years for further improvement in the recovery rate of cobalt, nickel, manganese, and lithium from used lithium-ion batteries in general, including those containing these elements, in wet process separation and purification.

[0007] Therefore, the problem to be solved by the present invention is to provide a method for recovering cobalt, nickel, manganese, and lithium from waste lithium-ion batteries by a wet process with a very high recovery rate.

[0008] The present inventors have conducted extensive research in light of the above-mentioned problems and have found that adding a specific organic solvent to a solution containing lithium and at least one valuable metal selected from the group consisting of transition metals other than manganese, cobalt, and nickel, magnesium, strontium, and aluminum can separate the valuable metal from lithium. The present invention was completed based on these findings.

[0009] The present invention provides a method for recovering valuable metals, which comprises a first solvent extraction step of adding an organic solvent to a solution containing lithium and at least one valuable metal selected from the group consisting of transition metals excluding manganese, cobalt, and nickel, alkaline earth metals, and aluminum, to extract the valuable metal, wherein the organic solvent contains at least one selected from the group consisting of a compound represented by the following formula (1), a phosphonic acid ester, a phosphate ester, phosphinic acid, methyl isobutyl ketone, and trioctylamine, and in formula (1), R １, R ２ and each independently represent a hydrocarbon group having 6 to 20 carbon atoms.

[0010]

[0011] The method for recovering valuable metals preferably further includes a dissolving step of dissolving active material powder obtained by pretreating waste lithium-ion batteries in a mineral acid to obtain a solution; a neutralization step of neutralizing the solution with an alkali; a second solvent extraction step of separating at least one element selected from the group consisting of manganese, cobalt, and nickel from the residual solution of the first solvent extraction step by organic solvent extraction to obtain a first aqueous lithium salt solution as the residual solution of the solvent extraction; and a membrane electrolysis step of subjecting the first aqueous lithium salt solution to membrane electrolysis using an ion exchange membrane to obtain an aqueous lithium hydroxide solution, an acid, and a second aqueous lithium salt solution that is more dilute than the first aqueous lithium salt solution, wherein the aqueous lithium hydroxide solution obtained in the membrane electrolysis step is reused in at least one step selected from the group consisting of the neutralization step, the first solvent extraction step, and the second solvent extraction step, and the acid obtained in the membrane electrolysis step is reused as the mineral acid used in the dissolving step.

[0012] The mineral acid preferably includes at least one selected from the group consisting of hydrochloric acid, sulfuric acid, and nitric acid, and more preferably includes hydrochloric acid. The alkali used in the neutralization step preferably includes lithium hydroxide. The concentration of at least one selected from the group consisting of the compound represented by formula (1), phosphonic acid esters, phosphoric acid esters, phosphinic acid, methyl isobutyl ketone, and trioctylamine in the organic solvent is preferably in the range of 0.001 M to 1.5 M. The electricity used in the membrane electrolysis step preferably includes electricity obtained from renewable energy, and more preferably includes electricity obtained from at least one selected from the group consisting of solar power generation, wind power generation, geothermal power generation, hydroelectric power generation, and biomass power generation.

[0013] The method for recovering valuable metals of the present invention provides a method for recovering cobalt, nickel, manganese, and lithium from waste lithium-ion batteries at a very high recovery rate by a wet process.

[0014] The present invention relates to a method for recovering valuable metals, a method for recovering valuable metals from metals, and a method for recovering valuable metals from metals.

[0015] The present invention will be described in more detail. Unless otherwise specified, the "to" in a numerical range indicates a range from above to below, and both end values ​​are included. When a numerical range is indicated, the upper and lower limits can be combined as appropriate, and the resulting numerical range is also considered to be disclosed. Furthermore, in the description of the drawings, identical elements are given the same reference numerals, and redundant explanations will be omitted. Also, the dimensional proportions in the drawings have been exaggerated for the sake of explanation and may differ from the actual proportions.

[0016] The method for recovering valuable metals of the present invention includes a first solvent extraction step in which an organic solvent is added to a solution containing at least one valuable metal selected from the group consisting of (1) transition metals excluding manganese, cobalt, and nickel, (2) alkaline earth metals, and (3) aluminum, and lithium, to extract the valuable metal, i.e., at least one valuable metal selected from the group consisting of the valuable metals (1) to (3). The alkaline earth metal (2) recovered by the method for recovering valuable metals of the present invention preferably includes at least one selected from the group consisting of beryllium, magnesium, calcium, strontium, and barium, more preferably includes at least one selected from the group consisting of magnesium, calcium, and strontium, and even more preferably is magnesium, calcium, or strontium.

[0017] The organic solvent contains at least one selected from the group consisting of a compound represented by the following formula (1), a phosphonic acid ester, a phosphoric acid ester, a phosphinic acid, methyl isobutyl ketone, and trioctylamine. The organic solvent is preferably at least one selected from the group consisting of these compounds:

[0018]

[0019] In the formula (1), R １ , R ２each independently represents a hydrocarbon group having 6 to 20 carbon atoms. The hydrocarbon group is not particularly limited, but is preferably an alkyl group, a cycloalkyl group, an alkenyl group, an alkynyl group, an aryl group, a heteroaryl group (aromatic heterocyclic group), or an aliphatic heterocyclic group.

[0020] The alkyl group preferably has 6 to 15 carbon atoms, and more preferably has 10 to 15 carbon atoms. １ and R ２ More preferably, is a dodecyl group.

[0021] The alkenyl group preferably has 6 to 15 carbon atoms, and more preferably has 10 to 15 carbon atoms.

[0022] The alkynyl group preferably has 6 to 15 carbon atoms, and more preferably has 10 to 15 carbon atoms.

[0023] The aryl group is preferably an aryl group having 6 to 18 carbon atoms, more preferably an aryl group having 6 to 10 carbon atoms. An example of the aryl group is a phenyl group.

[0024] When the aromatic heterocycle is a fused ring, it includes not only groups consisting of a monocyclic aromatic heterocycle, but also groups consisting of a fused heterocycle in which another ring, for example, an aromatic hydrocarbon ring, an aliphatic hydrocarbon ring, or a heterocycle, is fused to the monocyclic aromatic heterocycle. The number of ring-constituting heteroatoms constituting the aromatic heterocycle may be one or more, and the heteroatom is preferably a nitrogen atom, an oxygen atom, or a sulfur atom. The number of ring members in the aromatic heterocycle is preferably a 3- to 8-membered ring, more preferably a 5- or 6-membered ring. Examples of 5-membered aromatic heterocycles and fused heterocycles containing a 5-membered aromatic heterocycle include a pyrrole ring, an imidazole ring, a pyrazole ring, an oxazole ring, a thiazole ring, a triazole ring, a furan ring, a thiophene ring, a benzimidazole ring, a benzoxazole ring, a benzothiazole ring, an indoline ring, and an indazole ring. Furthermore, examples of the six-membered aromatic heterocycle and the fused heterocycle containing a six-membered aromatic heterocycle include a pyridine ring, a pyrimidine ring, a pyrazine ring, a triazine ring, a quinoline ring, and a quinazoline ring.

[0025] The aliphatic heterocyclic group includes a monocyclic group consisting of only an aliphatic heterocycle and a group consisting of an aliphatic fused heterocycle in which another ring (e.g., an aliphatic ring) is fused to an aliphatic heterocycle. The number of ring-constituting heteroatoms constituting the aliphatic heterocycle may be one or more, and preferred heteroatoms are nitrogen, oxygen, and sulfur atoms. Furthermore, the number of ring members in the aliphatic heterocycle is preferably a 3- to 8-membered ring, and more preferably a 5- or 6-membered ring. Specific preferred examples of the aliphatic heterocycle include a pyrrolidine ring, an oxolane ring, a thiolane ring, a piperidine ring, a tetrahydrofuran ring, an oxane ring (tetrahydropyran ring), a thiane ring, a piperazine ring, a morpholine ring, a quinuclidine ring, a pyrrolidine ring, an azetidine ring, an oxetane ring, an aziridine ring, a dioxane ring, a pentamethylene sulfide ring, and γ-butyrolactone.

[0026] The hydrocarbon group also includes the following groups. alkoxy groups, aryloxy groups, heterocyclic oxy groups (groups in which an —O— group is bonded to the above heterocyclic group), alkoxycarbonyl groups, aryloxycarbonyl groups, amino groups (having 6 to 20 carbon atoms), sulfamoyl groups, acyl groups (including alkylcarbonyl groups, alkenylcarbonyl groups, alkynylcarbonyl groups, arylcarbonyl groups, and heterocyclic carbonyl groups, and having 6 to 20 carbon atoms, for example, octanoyl, hexadecanoyl, benzoyl, naphthoyl, and nicotinoyl), acyloxy groups (including alkylcarbonyloxy groups, alkenylcarbonyloxy groups, alkynylcarbonyloxy groups, arylcarbonyloxy groups, and heterocyclic carbonyloxy groups, and having 6 to 20 carbon atoms, for example, octanoyloxy, hexadecanoyloxy, benzoyloxy, naphthoyloxy, and nicotinoyloxy), aryloyloxy groups, carbamoyl groups, acylamino groups (acylamino groups having 6 to 20 carbon atoms, for example, benzoylamino), alkylthio groups (alkylthio groups having 6 to 20 carbon atoms or less, for example, benzylthio), arylthio groups (arylthio groups having 6 to 20 carbon atoms, for example, phenylthio, 1-naphthylthio, 3-methylphenylthio, 4-methoxyphenylthio), heterocyclic thio groups (groups in which an -S- group is bonded to the above heterocyclic group), alkylsulfonyl groups (alkylsulfonyl groups having 6 to 20 carbon atoms), arylsulfonyl groups (arylsulfonyl groups having 6 to 20 carbon atoms, for example, benzenesulfonyl), alkylsilyl groups (alkylsilyl groups having 6 to 20 carbon atoms, for example, triethylsilyl), arylsilyl groups (arylsilyl groups having 6 to 20 carbon atoms, for example, triphenylsilyl), phosphoryl groups (phosphate groups having 6 to 20 carbon atoms, for example, -OP(=O)(R Ｐ ) ２ ), a phosphonyl group (a phosphonyl group having 6 to 20 carbon atoms, for example, —P(═O)(R Ｐ ) ２ ), a phosphinyl group (a phosphinyl group having 6 to 20 carbon atoms, for example, —P(R Ｐ ) ２ ). Ｐis a hydrogen atom or a substituent (preferably a group selected from the above-mentioned substituents). Each of these groups listed as the substituents may be further substituted with the above-mentioned substituents.

[0027] A specific example of the compound represented by the formula (1) is N,N-didodecyl-2-hydroxyacetamide.

[0028] An example of a commercially available phosphonate ester is PC-88A manufactured by Daihachi Chemical Industry Co., Ltd. An example of a commercially available phosphate ester is tributyl phosphate (TBP) or di(2-ethylhexyl)phosphate (D2EHPA). An example of a commercially available phosphinic acid is CYANEX272 manufactured by Solvay.

[0029] The concentration of at least one selected from the group consisting of the compound represented by formula (1), phosphonic acid ester, phosphate ester, phosphinic acid, methyl isobutyl ketone, and trioctylamine in the organic solvent is preferably in the range of 0.001 M to 1.5 M, more preferably in the range of 0.005 M to 1 M. When the concentration is in the above range, the valuable metal extracted with the organic solvent in the first solvent extraction step is stripped from the organic solvent more stably, and the organic solvent can be reused repeatedly.

[0030] The valuable metal recovery method of the present invention will be described in more detail with reference to the accompanying drawings. As shown in Figure 1, the valuable metal recovery method of the present invention may start with an active material powder 1 as a starting material.

[0031] Next, in STEP 1, the active material powder 1 is dissolved in a mineral acid to obtain an acid solution of the active material powder 1 containing at least lithium. The mineral acid preferably contains at least one acid selected from the group consisting of hydrochloric acid, sulfuric acid, and nitric acid, more preferably hydrochloric acid, and even more preferably hydrochloric acid. In addition to lithium, the active material powder 1 contains valuable metals such as iron, transition metals, magnesium, strontium, and aluminum.

[0032] In the valuable metal recovery method of the present invention, next, in STEP 2, an alkali is added to the acid solution to neutralize the mineral acid. The alkali may be added in at least one form selected from the group consisting of an aqueous solution and a solid. The alkali preferably includes at least one selected from the group consisting of an alkali metal hydroxide and ammonia. The alkali metal constituting the alkali metal hydroxide preferably includes at least one selected from the group consisting of lithium, sodium, potassium, rubidium, cesium, and francium, more preferably includes lithium, sodium, and potassium, even more preferably lithium, sodium, or potassium, and particularly preferably lithium.

[0033] The neutralized acid solution is then subjected to the first solvent extraction step in STEP 3A. The residual solution from the first solvent extraction step contains valuable metals such as lithium, manganese, cobalt, and nickel. Furthermore, the extract 2A from the first solvent extraction step contains at least one valuable metal selected from the group consisting of the valuable metals (1) to (3). A typical example of the valuable metal (1) contained in the extract from the first solvent extraction step is zirconium. The valuable metals (1) to (3) can hinder the recovery of lithium, manganese, cobalt, and nickel contained in the acid solution.

[0034] The extraction residue from the first solvent extraction step is then subjected to a second organic solvent extraction in STEP 3B. In the second organic solvent extraction, manganese, cobalt, and nickel, excluding lithium, are each extracted with an organic solvent, or iron is separated and removed as a metal sulfate aqueous solution 2B. When the alkali is lithium hydroxide, a first lithium salt aqueous solution can be obtained. Furthermore, when the alkali is at least one selected from the group consisting of sodium hydroxide and potassium hydroxide, the first lithium salt aqueous solution and at least one salt of sodium and potassium are separated from the alkali mixed salt aqueous solution obtained in the first solvent extraction step by the method disclosed in Japanese Patent No. 7084669. When hydrochloric acid is used in the acid dissolution in STEP 1, the lithium salt contained in the first lithium salt aqueous solution becomes lithium chloride. The organic solvent is at least one selected from the group consisting of the phosphate esters, the phosphonate esters, the phosphinic acids, organic phosphorus compounds such as phosphine oxides, hydroximes, and organic amine compounds.

[0035] Examples of the phosphine oxide include tri-n-octylphosphine (TOPO). Examples of the hydroxime include 7-hydroxy-5,8-diethyl-6-dodecanone oxime (LIX-63), 5-dodecyl-2-hydroxybenzaldehyde oxime (LIX 860), 2-hydroxy-5-nonylbenzophenone oxime (LIX 65N), 2-hydroxy-5-nonylacetophenone oxime (SME 529), and 2-hydroxy-5-nonylphenylbenzyl ketone oxime (Acorga P-17). Examples of the organic amine compound include Primene (registered trademark) JM-T manufactured by Dow Chemical Company, which is a primary amine; Amberlite (registered trademark) LA-2 manufactured by Sigma-Aldrich, which is a secondary amine; Alamine 336 (trioctylamine) manufactured by Sigma-Aldrich, which is a tertiary amine; and Aliquat (registered trademark) 336 manufactured by Sigma-Aldrich, which is a quaternary ammonium salt.

[0036] In the valuable metal recovery method of the present invention, the first lithium salt aqueous solution is then subjected to membrane electrolysis using an ion exchange membrane in STEP 4. The membrane electrolysis in STEP 4 can be performed using, for example, an electrolytic cell 11 shown in FIG.

[0037] The electrolytic cell 11 is provided with an anode plate 12 on one of its inner surfaces and a cathode plate 13 on the inner surface opposite the anode plate 12, the anode plate 12 being connected to an anode 14 of a power supply, and the cathode plate 13 being connected to a cathode 15 of the power supply. The electrolytic cell 11 is also partitioned by an ion exchange membrane 16 into an anode chamber 17 containing the anode plate 12 and a cathode chamber 18 containing the cathode plate 13.

[0038] In the electrolytic cell 11, when electrolysis is performed by supplying, for example, lithium chloride as the second lithium salt aqueous solution to the anode chamber 17, chloride ions are converted into chlorine gas (Cl) on the anode plate 12. ２ ), while the lithium ions migrate through the ion exchange membrane 16 to the cathode chamber 18.

[0039] In the cathode chamber 18, water (H ２ O) is hydroxide ion (OH － ) and hydrogen ions (H ＋ ) and hydrogen ions are ionized into hydrogen gas (H ２ ), while hydroxide ions combine with lithium to produce a lithium hydroxide aqueous solution 3.

[0040] The electricity used in the membrane electrolysis step preferably includes electricity obtained from renewable energy, and more preferably includes electricity obtained from at least one selected from the group consisting of solar power generation, wind power generation, geothermal power generation, hydroelectric power generation, and biomass power generation.

[0041] The hydrogen gas (H ２ ) and chlorine gas (Cl ２ ) to obtain hydrochloric acid as mineral acid 4, which can be used to dissolve active material powder 1 in STEP 1.

[0042] The lithium hydroxide aqueous solution 3 obtained by the membrane electrolysis is crystallized in STEP 5 to form lithium hydroxide monohydrate (LiOH.H ２O), and by carbonating in STEP 6, lithium carbonate (Li ２ CO ３ The carbonation can be carried out by converting the lithium hydroxide aqueous solution 3 into carbon dioxide gas (CO ２ ) can be reacted with

[0043] When the lithium hydroxide aqueous solution 3 is used for solvent extraction in at least one selected from the group consisting of STEPs 3A and 3B, the lithium hydroxide aqueous solution 3 is added to the extraction solvent. The extraction solvent used for solvent extraction in at least one selected from the group consisting of STEPs 3A and 3B is a cation exchange extractant, and so continued use of the solvent will cause the liquid to become acidic and the extraction rate to decrease. However, the addition of the lithium hydroxide aqueous solution 3 can suppress this decrease in the extraction rate.

[0044] In addition, when the lithium hydroxide aqueous solution 3 is used for solvent extraction in STEP 3B, the lithium hydroxide aqueous solution 3 can be used for at least one of the solvent extractions of manganese, cobalt, and nickel, which are carried out separately.

[0045] Furthermore, in the membrane electrolysis, the first lithium salt aqueous solution is subjected to membrane electrolysis, resulting in the production of a second lithium salt aqueous solution that is more dilute than the first lithium salt aqueous solution. Therefore, in the valuable metal recovery method of the present invention, the second lithium salt aqueous solution may be concentrated in STEP 7 and added to the first lithium salt aqueous solution. The concentration in STEP 7 can be performed using, for example, a reverse osmosis membrane (RO membrane).

[0046] The valuable metal recovery method of the present invention can separate lithium, manganese, cobalt, and nickel from valuable metals that inhibit the recovery of these valuable metals, thereby improving the recovery rate of lithium, manganese, cobalt, and nickel from discarded lithium-ion batteries. The valuable metal recovery method of the present invention can obtain a highly concentrated lithium salt aqueous solution because no alkaline source other than lithium is supplied. Furthermore, the valuable metal recovery method of the present invention can obtain lithium hydroxide by membrane electrolysis of the highly concentrated lithium salt aqueous solution, thereby improving the recovery rate of lithium. Furthermore, the valuable metal recovery method of the present invention can return the lithium hydroxide obtained by membrane electrolysis directly to the process because no unnecessary alkaline source other than lithium is present, enabling resource recycling.

[0047] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0048] In the examples and comparative examples, the content of valuable metals in each solution was measured by inductively coupled plasma optical emission spectrometry (ICP-OES) using an Optima 8300 manufactured by PerkinElmer.

[0049] Example 1: 10 kg of cathode powder obtained from waste lithium-ion batteries was dissolved in hydrochloric acid adjusted to a hydrochloric acid concentration of 9 to 10 mol / L to obtain 50 L of a solution containing 13 g / L of cobalt, 13 g / L of manganese, 39 g / L of nickel, 100 mg / L of zirconium, 7 mg / L of calcium, 3 mg / L of magnesium, and 0.1 mg / L of tungsten. A 1 M solution of di(2-ethylhexyl)phosphate (D2EHPA) in kerosene was added as an extractant to the solution, and the equilibrium pH was adjusted to 3 with a 6 mol / L aqueous lithium hydroxide solution to separate the lithium and valuable metals in the solution. The extraction yields of each valuable metal are shown in Table 1.

[0050] Examples 2 to 6 Instead of a 1 M di(2-ethylhexyl)phosphate (D2EHPA) kerosene solution, a 0.1 M di(2-ethylhexyl)phosphate (D2EHPA) kerosene solution (Example 2), a 1 M kerosene solution of 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (PC-88A manufactured by Daihachi Chemical Industry Co., Ltd.) (Example 3), a 0.1 M kerosene solution of 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (Example 4), a decane solution of 1 M phosphinic acid (CYANEX 272 manufactured by Solvay) (Example 5), and a decane solution of 0.1 M phosphinic acid (Example 6) were used as the extractant, and lithium and the valuable metals in the solution were separated in the same manner as in Example 1. The extraction yields of each valuable metal are shown in Table 1.

[0051]

[0052] It was confirmed that calcium and zirconium could be extracted from the solution containing the various valuable metals using di(2-ethylhexyl)phosphate (D2EHPA), zirconium could be extracted using 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester, and magnesium could be extracted using phosphinic acid.

[0053] 1...active material powder, 2A...extract, 2B...metal sulfate aqueous solution, 3...lithium hydroxide aqueous solution, 4...mineral acid, 11...electrolytic cell, 16...ion exchange membrane.

Claims

1. A method for recovering valuable metals, comprising a first solvent extraction step of adding an organic solvent to a solution containing at least one valuable metal selected from the group consisting of transition metals excluding manganese, cobalt, and nickel, alkaline earth metals, and aluminum, and lithium, to extract the valuable metal, wherein the organic solvent contains at least one selected from the group consisting of a compound represented by the following formula (1), a phosphonic acid ester, a phosphoric acid ester, phosphinic acid, methyl isobutyl ketone, and trioctylamine, In the formula (1), R １ , R ２ each independently represents a hydrocarbon group having 6 to 20 carbon atoms.

2. A method for recovering valuable metals as described in claim 1, further comprising: a dissolving step of dissolving active material powder obtained by pretreating waste lithium ion batteries in a mineral acid to obtain a dissolved solution; a neutralizing step of neutralizing the dissolved solution with an alkali; a second solvent extraction step of separating at least one selected from the group consisting of manganese, cobalt, and nickel from the residual solution of the first solvent extraction step by organic solvent extraction to obtain a first aqueous lithium salt solution as the residual solution of the solvent extraction; and a membrane electrolysis step of subjecting the first aqueous lithium salt solution to membrane electrolysis using an ion exchange membrane to obtain an aqueous lithium hydroxide solution, an acid, and a second aqueous lithium salt solution that is more dilute than the first aqueous lithium salt solution, wherein the aqueous lithium hydroxide solution obtained in the membrane electrolysis step is reused in at least one step selected from the group consisting of the neutralizing step, the first solvent extraction step, and the second solvent extraction step, and the acid obtained in the membrane electrolysis step is reused as the mineral acid used in the dissolving step.

3. A method for recovering valuable metals as described in claim 2, wherein the mineral acid includes at least one selected from the group consisting of hydrochloric acid, sulfuric acid, and nitric acid.

4. A method for recovering valuable metals as described in claim 3, wherein the mineral acid comprises hydrochloric acid.

5. A method for recovering valuable metals as described in claim 2, wherein the alkali used in the neutralization step comprises lithium hydroxide.

6. The method for recovering valuable metals according to claim 1, wherein the concentration of at least one selected from the group consisting of the compound represented by formula (1), phosphonic acid esters, phosphoric acid esters, phosphinic acid, methyl isobutyl ketone, and trioctylamine in the organic solvent is in the range of 0.001M to 1.5M.

7. A method for recovering valuable metals according to any one of claims 1 to 6, wherein the electricity used in the membrane electrolysis process includes electricity obtained from renewable energy.

8. A method for recovering valuable metals as described in claim 7, wherein the electricity obtained by renewable energy includes electricity obtained by at least one selected from the group consisting of solar power generation, wind power generation, geothermal power generation, hydroelectric power generation, and biomass power generation.