How to recover lithium from used lithium-ion batteries

Abstract

To provide a method for recovering lithium from a waste lithium ion battery that enables lithium to be recovered with a high recovery rate and also enables salts generated during the recovery process to be reused in the process as mineral acid and alkali.SOLUTION: A method for recovering lithium from a waste lithium ion battery includes: a dissolution step for dissolving active material powder, obtained by pretreating a waste lithium ion battery, with mineral acid; an alkali hydroxide addition step for adding sodium hydroxide or the like to a solution obtained in the dissolution step; a step for separating, from a solution obtained in the alkali hydroxide addition step, at least one metal excluding lithium by organic solvent extraction, to obtain an alkali mixed salt aqueous solution; a separation step for separating a lithium salt and a salt of sodium or the like respectively from the alkali mixed salt aqueous solution; and a step for recovering lithium from a first lithium salt aqueous solution obtained in the separation step.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for recovering lithium from waste lithium-ion batteries. [Background technology]

[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 heat treatment (roasting), pulverization, classification, etc. to obtain powder containing the valuable metals, and cobalt, nickel, manganese, and lithium are separated and refined by a wet process (see, for example, Patent Documents 1 and 2).

[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. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6835820 [Patent Document 2] Patent No. 6869444 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in existing wet processes, compounds other than the lithium compound to be recovered are used as alkali sources, resulting in a high concentration of cations other than lithium and a low concentration of lithium ions. As a result, the recovery rate of the target lithium is significantly reduced in conventional wet processes. Furthermore, in conventional wet processes, the mineral acid used to dissolve the active material powder and the compound used as the alkali source are discharged as salts, and there is no technology to recycle the mineral acid and the compound used as the alkali source. In recent years, there has been a demand for a method for recovering lithium from used lithium ion batteries that overcomes these disadvantages, allows lithium to be recovered at a high recovery rate, and preferably allows the salts produced in the recovery process to be reused as the mineral acid and alkali in the process, but such a method has not been provided. The problem that the present invention aims to solve is to provide a method for recovering lithium from used lithium ion batteries that allows lithium to be recovered at a high recovery rate, and preferably allows the salts produced in the recovery process to be reused as the mineral acid and alkali in the process. [Means for solving the problem]

[0007] The present inventors have conducted extensive research in light of the above-mentioned problems and have found that it is possible to recycle the mineral acid obtained by adding at least one of sodium hydroxide and potassium hydroxide to a solution obtained by dissolving an active material powder in a mineral acid, separating the aqueous lithium salt solution from the aqueous sodium and potassium salt solution, and preferably reusing the mineral acid obtained by electrolyzing the separated aqueous sodium and potassium salt solution and the at least one of sodium hydroxide and potassium hydroxide. The present invention has been completed based on these findings.

[0008] The present invention is a method for recovering lithium from used lithium-ion batteries, comprising: a dissolving step of dissolving active material powder obtained by pretreating used lithium-ion batteries in a mineral acid; an alkali hydroxide adding step of adding at least one of sodium hydroxide and potassium hydroxide to the solution obtained in the dissolving step; a step of separating at least one metal, excluding lithium, from the metals contained in the active material powder from the solution obtained in the alkali hydroxide adding step by organic solvent extraction to obtain an aqueous solution of mixed alkali salts as a residue of the solvent extraction; a separation step of separating a lithium salt and at least one salt of sodium and potassium from the aqueous solution of mixed alkali salts; and a lithium recovery step of recovering lithium from the first aqueous lithium salt solution obtained in the separation step. The present invention preferably further comprises a second electrolysis step in which the aqueous solution of at least one salt of sodium and potassium obtained from the separation step is electrolyzed using an ion exchange membrane to obtain an aqueous solution of alkali metal hydroxide. The aqueous alkali metal hydroxide solution obtained in the second electrolysis step is preferably reused in at least one of the alkali hydroxide addition step, the extraction step, and the separation step. The lithium recovery step preferably includes a carbonation step of carbonate the first lithium salt aqueous solution obtained in the separation step to obtain lithium carbonate. The lithium recovery step preferably further includes a first electrolysis step of electrolyzing the first lithium salt aqueous solution obtained in the separation step using an ion exchange membrane to obtain a lithium hydroxide aqueous solution, an acid, and a second lithium salt aqueous solution that is more dilute than the first lithium salt aqueous solution. The second aqueous lithium salt solution is preferably concentrated and added to the first aqueous lithium salt solution. The mineral acid is preferably at least one selected from the group consisting of hydrochloric acid, sulfuric acid, and nitric acid, and more preferably hydrochloric acid. In the present invention, the mineral acid is preferably hydrochloric acid produced by reacting hydrogen with chlorine obtained by electrolyzing the first lithium salt aqueous solution using an ion exchange membrane. The electric power used in at least one selected from the group consisting of the first electrolysis step and the second electrolysis step is preferably electric power obtained from renewable energy, and more preferably electric power obtained from solar power generation or wind power generation. The organic solvent is preferably free of reducing and oxidizing agents. [Effects of the Invention]

[0009] The method for recovering lithium from waste lithium-ion batteries of the present invention provides a method that can recover lithium with a high recovery rate and preferably allows the salts produced in the recovery process to be reused as mineral acids and alkalis in the process. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is an explanatory diagram showing the configuration of one embodiment of the method for recovering lithium from waste lithium-ion batteries of the present invention. [Figure 2] FIG. 3 is an explanatory diagram showing the configuration of another embodiment of the method for recovering lithium from waste lithium-ion batteries according to the present invention. [Figure 3] FIG. 1 is an explanatory diagram showing the configuration of one embodiment of the lithium phosphate method. [Figure 4] FIG. 10 is an explanatory diagram showing the configuration of another embodiment of the lithium phosphate method. [Figure 5] 1 is an explanatory cross-sectional view showing the structure of an ion exchange membrane electrolytic cell used in the first electrolysis step of the method for recovering lithium from waste lithium ion batteries of the present invention. FIG. [Figure 6] FIG. 2 is an explanatory cross-sectional view showing the structure of an ion-exchange membrane electrolytic cell used in the second electrolysis step of the method for recovering lithium from waste lithium-ion batteries of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] The invention will now be described in more detail with reference to the accompanying drawings. As shown in FIGS. 1 and 2, the method of recovering lithium from used lithium ion batteries of the present invention (hereinafter referred to as the "recovery method") starts with active material powder 1 as a starting material.

[0012] The recovery method of the present invention includes a dissolution step (STEP 1) in which the active material powder 1 obtained by pretreatment is dissolved in a mineral acid. The mineral acid preferably includes at least one selected from the group consisting of hydrochloric acid, sulfuric acid, and nitric acid, more preferably at least one selected from the group consisting of hydrochloric acid, sulfuric acid, and nitric acid, even more preferably hydrochloric acid, sulfuric acid, or nitric acid, and particularly preferably hydrochloric acid. Since the active material powder 1 contains valuable metals such as lithium, iron, aluminum, cobalt, nickel, and manganese, dissolution of the active material powder 1 with the mineral acid can provide a solution of the valuable metals contained in the active material powder 1.

[0013] The recovery method of the present invention includes an alkali hydroxide addition step (STEP 2) in which at least one selected from the group consisting of sodium hydroxide and potassium hydroxide is added to the valuable metal solution obtained in the dissolution step. Figures 1 and 2 show the case in which only sodium hydroxide is added as the alkali metal hydroxide. The addition of at least one selected from the group consisting of sodium hydroxide and potassium hydroxide may be in the form of at least one solid selected from the group consisting of sodium hydroxide and potassium hydroxide, at least one solution selected from the group consisting of an aqueous sodium hydroxide solution and an aqueous potassium hydroxide solution, or a mixture thereof. The valuable metal solution is neutralized in the alkali hydroxide addition step. Furthermore, iron hydroxide and aluminum hydroxide may be sequentially precipitated by adding at least one selected from the group consisting of sodium hydroxide and potassium hydroxide to the solution of valuable metals, and iron and aluminum may be separated from the solution of valuable metals.

[0014] The recovery method of the present invention includes an extraction step (STEP 3) in which, among the valuable metals contained in the active material powder 1, iron and aluminum are separated as needed by solvent extraction from the solution obtained in the alkali hydroxide addition step, and manganese, cobalt, and nickel, excluding lithium, are each extracted with an organic solvent, and the respective metal sulfate aqueous solutions 2 are removed.

[0015] The extraction process includes a first extraction step in which iron, aluminum, manganese, cobalt, or nickel is extracted from the valuable metal solution using a first organic solvent. The pH of a homogeneous mixture of the valuable metal solution and the first organic solvent is adjusted by adding at least one alkali, such as sodium hydroxide and potassium hydroxide, to obtain a first metal-containing organic phase and a first extraction residue in the first extraction process.

[0016] The extraction step may include a second extraction step in which valuable metals not extracted in the first extraction step are extracted from the first extraction residue with a second organic solvent. The pH of a homogeneous mixture of the first extraction residue and the second organic solvent is adjusted by adding at least one alkali, such as sodium hydroxide and potassium hydroxide, to obtain a second metal-containing organic phase and a second extraction residue in the second extraction step.

[0017] The extraction step may include third to fifth extraction steps in which the valuable metals that have not been extracted in the first and second extraction steps are sequentially extracted from the second extraction residue.

[0018] The organic solvent used in the extraction step may be at least one selected from the group consisting of organic phosphorus compounds such as phosphate esters, phosphonate esters, phosphinic acids, and phosphine oxides, hydroximes, and organic amine compounds. The organic solvent preferably does not contain a reducing agent or an oxidizing agent. If the organic solvent does not contain an oxidizing agent, metals, particularly manganese, contained in the acid solution after neutralization will not precipitate, causing pipe clogging, and the organic solvent will not be deteriorated by the oxidizing agent.

[0019] Organophosphorus compounds are commercially available, including acidic phosphate esters such as di(2-ethylhexyl)phosphate (DEHPA), phosphonate esters such as PC-88A (manufactured by Daihachi Chemical Industry Co., Ltd.), phosphinic acid esters such as CYANEX 272 (manufactured by Solvay), neutral phosphate esters such as tributyl phosphate (TBP), and phosphine oxides such as tri-n-octylphosphine (TOPO). Hydroximes 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 organic amine compounds 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.

[0020] The iron-containing organic phase, aluminum-containing organic phase, manganese-containing organic phase, cobalt-containing organic phase, and nickel-containing organic phase are each subjected to back extraction with sulfuric acid, and an aqueous solution 2 of metal sulfates (iron sulfate, aluminum sulfate, manganese sulfate, cobalt sulfate, and nickel sulfate) is recovered.

[0021] The recovery method of the present invention includes a separation step (STEP 4) of separating a lithium salt and at least one salt selected from the group consisting of sodium and potassium from the aqueous solution of mixed alkali metal salts containing lithium and at least one salt selected from the group consisting of sodium and potassium obtained in the extraction step. The separation step is not limited to a particular method, but is preferably carried out by at least one of a lithium phosphate method, an evaporation concentration method, and a solvent extraction method.

[0022] <Lithium phosphate method> The lithium phosphate method will be described with reference to Figures 3 and 4. The lithium phosphate method includes a phosphating step (STEP A) in which an aqueous solution of aluminum phosphate and at least one alkali metal hydroxide (MOH) selected from the group consisting of sodium hydroxide and potassium hydroxide is added to the aqueous solution of the alkali metal mixed salt to produce a solid material containing lithium phosphate and aluminum hydroxide. An alkali metal chloride (MCl) is dissolved in the aqueous solution from which the solid material is produced. The alkali metal hydroxide is preferably sodium hydroxide. Figures 3 and 4 show the case in which only sodium hydroxide is used as the alkali metal.

[0023] The lithium phosphate method includes a first solid-liquid separation (STEP B) in which the solid produced in the phosphorylation step is separated into solid and liquid. An example of the first solid-liquid separation step is filtration.

[0024] In the lithium phosphate method, the solid material separated in the first solid-liquid separation step may be washed. The method also includes a pH adjustment step (STEP C) in which a mineral acid is added to a suspension obtained by suspending the solid material in water to adjust the pH of the suspension to 2 to 3. The mineral acid is not limited to a specific mineral acid. The mineral acid includes at least one selected from the group consisting of hydrochloric acid, sulfuric acid, and nitric acid. The mineral acid is preferably at least one selected from the group consisting of hydrochloric acid, sulfuric acid, and nitric acid, more preferably hydrochloric acid, sulfuric acid, or nitric acid, and even more preferably hydrochloric acid. When the mineral acid is hydrochloric acid, the lithium salt is lithium chloride, and this case is depicted in FIGS. 3 and 4.

[0025] The lithium phosphate method includes a second solid-liquid separation step (STEP D) in which the aluminum phosphate obtained in the pH adjustment step and the first lithium salt aqueous solution are subjected to solid-liquid separation. The second solid-liquid separation step can be exemplified by filtration. The aluminum phosphate obtained in the second solid-liquid separation step can be separated into solid and liquid in a short time, and the separated aluminum phosphate may be reused in the phosphorylation step.

[0026] The pH of the first lithium salt aqueous solution obtained in the second solid-liquid separation step is preferably adjusted in a pH adjustment step (STEP 5) described below. Since the pH of the suspension is adjusted to 2 to 3 in the pH adjustment step (STEP C), the pH of the first lithium salt aqueous solution is 2 to 3, but the pH is preferably adjusted to 6 to 8 in the pH adjustment step (STEP 5). In this case, unreacted aluminum and phosphorus are precipitated, and the purity of the first lithium salt aqueous solution is further increased.

[0027] Preferably, the first lithium salt aqueous solution, the pH of which has been adjusted in the pH adjustment step (STEP 5), is carbonated to obtain lithium carbonate, in a carbonation step (STEP 6a) described below (FIG. 3). The aqueous solution of at least one salt selected from the group consisting of sodium and potassium, produced in the carbonation step, contains at least one salt selected from the group consisting of sodium chloride and potassium chloride, a trace amount of lithium chloride, and at least one salt selected from the group consisting of sodium carbonate and potassium carbonate. Preferably, the pH of the aqueous solution of at least one salt selected from the group consisting of sodium and potassium is approximately 12. Adding hydrochloric acid to the aqueous solution of at least one salt selected from the group consisting of sodium and potassium to adjust the pH to 5 or less decomposes the at least one salt selected from the group consisting of sodium carbonate and potassium carbonate to produce carbon dioxide and water, resulting in an aqueous solution containing at least one salt selected from the group consisting of sodium chloride and potassium chloride. This aqueous solution may be concentrated in a concentration step (STEP 9) described below. FIG. 3 illustrates a case in which the concentration step is performed.

[0028] Preferably, the first lithium salt aqueous solution, the pH of which has been adjusted in the pH adjustment step (STEP 5), may be electrolyzed using an ion exchange membrane to obtain a lithium hydroxide aqueous solution, in a first electrolysis step (STEP 6b) (FIG. 4). The first lithium salt aqueous solution may be concentrated in a first concentration step (STEP E) before being subjected to the first electrolysis step. The first concentration step may be performed using, for example, a reverse osmosis membrane (RO membrane).

[0029] In the lithium phosphate method, the filtrate separated in the first solid-liquid separation step and containing the dissolved alkali metal chloride may be concentrated in a concentration step (STEP 9) described below.

[0030] <Evaporation concentration method> The aqueous solution of the mixed salt of lithium and at least one alkali metal selected from the group consisting of sodium and potassium is evaporated and concentrated, and at least one salt selected from the group consisting of sodium salts and potassium salts, such as at least one salt selected from the group consisting of sodium chloride and potassium chloride, is sequentially crystallized and separated from the aqueous solution of the mixed alkali metal salt. The separated at least one salt selected from the group consisting of sodium salts and potassium salts, such as at least one salt selected from the group consisting of sodium chloride and potassium chloride, is dissolved in water, and the aqueous solution of at least one salt selected from the group consisting of sodium and potassium is electrolyzed using an ion exchange membrane in a second electrolysis step (STEP 7) described below. The first aqueous solution of lithium salt from which at least one salt selected from the group consisting of sodium salts and potassium salts has been separated is preferably subjected to a pH adjustment step (STEP 5) described below, and further to a carbonation step (STEP 6a), similar to the first aqueous solution of lithium salt obtained by the lithium phosphate method. When the aqueous solution of at least one salt selected from the group consisting of sodium and potassium produced in the carbonation step is an aqueous solution in which at least one salt selected from the group consisting of sodium chloride and potassium chloride is dissolved as described above, the aqueous solution may be concentrated in a concentration step (STEP 9) described below.

[0031] Similarly to the first lithium salt aqueous solution obtained by the lithium phosphate method, the first lithium salt aqueous solution is preferably subjected to a pH adjustment step (STEP 5) and a first concentration step (STEP E) described below, and is also subjected to a first electrolysis step (STEP 6b) described below.

[0032] <Solvent extraction method> The pH of the homogeneous mixture of the aqueous solution of the mixed salt of lithium and at least one selected from the group consisting of sodium and potassium, and the organic solvent for lithium extraction is adjusted to preferably within the range of 5 to 9 by adding at least one alkali, such as sodium hydroxide and potassium hydroxide, to obtain a lithium-containing organic phase and, as the extraction residue, an aqueous solution of at least one salt selected from the group consisting of sodium and potassium. An example of the organic solvent for lithium extraction is bis(2-ethylhexyl) hydrogen phosphate. The lithium-containing organic phase is scrubbed with a mineral acid to recover a first aqueous lithium salt solution. Like the first aqueous lithium salt solution obtained by the lithium phosphate method, the first aqueous lithium salt solution is preferably subjected to the pH adjustment step (STEP 5) described below, and then further subjected to the carbonation step (STEP 6a). When the aqueous solution of at least one salt selected from the group consisting of sodium and potassium produced in the carbonation step is an aqueous solution containing at least one salt selected from the group consisting of sodium chloride and potassium chloride dissolved therein as described above, the aqueous solution may be concentrated in a concentration step (STEP 9) described below. Furthermore, the first aqueous lithium salt solution is preferably subjected to a pH adjustment step (STEP 5) and a first concentration step (STEP E) described below, as with the aqueous lithium salt solution obtained by the lithium phosphate method, and may also be subjected to a first electrolysis step (STEP 6b) described below.

[0033] A second electrolysis step (STEP 7) described below is carried out in which an aqueous solution of at least one salt selected from the group consisting of sodium and potassium, in which at least one salt of sodium and potassium, such as at least one salt selected from the group consisting of sodium chloride and potassium chloride, is dissolved, using an ion exchange membrane. The aqueous solution of at least one salt of sodium and potassium is concentrated in a concentration step (STEP 9) described below, preferably using a reverse osmosis membrane (RO membrane) or the like.

[0034] The recovery method of the present invention may include a pH adjustment step (STEP 5) of adding at least one of sodium hydroxide and potassium hydroxide to the first aqueous lithium salt solution obtained in the separation step to adjust the pH of the first aqueous lithium salt solution. The pH of the first aqueous lithium salt solution is adjusted to preferably 8 to 14, more preferably 10 to 11.

[0035] [Lithium recovery] <Carbonation of the first lithium salt aqueous solution> The recovery method of the present invention includes, as the lithium recovery step, a carbonation step (STEP 6a) of obtaining lithium carbonate by carbonate-treating the first lithium salt aqueous solution obtained in the separation step. In the carbonation step, at least one alkali metal carbonate salt (excluding lithium carbonate) selected from the group consisting of sodium carbonate and potassium carbonate, which is obtained in a carbon dioxide absorption step (STEP 8) of absorbing carbon dioxide into an aqueous solution 4 containing dissolved therein at least one selected from the group consisting of sodium hydroxide and potassium hydroxide, obtained in the second electrolysis step described below, may be added to the first lithium salt aqueous solution.

[0036] The alkali metal of the alkali metal carbonate is at least one selected from the group consisting of sodium, potassium, rubidium, cesium, and francium, preferably at least one selected from the group consisting of sodium and potassium, and more preferably sodium.

[0037] <First electrolysis step> The recovery method of the present invention includes, as another lithium recovery step, a first electrolysis step (STEP 6b) in which the first aqueous lithium salt solution obtained in the separation step and, if necessary, subjected to at least one of the pH adjustment step (STEP 5) and the first concentration step (STEP E) is electrolyzed using an ion exchange membrane to obtain an aqueous lithium hydroxide solution.

[0038] The first electrolysis step can be carried out using, for example, an electrolytic cell 11 shown in FIG. 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.

[0039] In the electrolytic cell 11, when the lithium salt aqueous solution in which lithium chloride is dissolved is supplied to the anode chamber 17 and electrolysis is performed, chloride ions generate chlorine gas (Cl2) on the anode plate 12. Meanwhile, lithium ions move to the cathode chamber 18 through the ion exchange membrane 16.

[0040] In the cathode chamber 18, water (H2O) is converted into hydroxide ions (OH - ) and hydrogen ions (H + ) and the hydrogen ions generate hydrogen gas (H2) on the cathode plate 13, while the hydroxide ions and lithium ions generate a lithium hydroxide aqueous solution.

[0041] The power required for the electrolysis is, for example, renewable energy, preferably at least one of solar power generation and wind power generation.

[0042] Hydrochloric acid can be obtained by reacting hydrogen gas (H2) and chlorine gas (Cl2) generated in the first electrolysis step. Although not shown in FIG. 5, if the lithium chloride aqueous solution contains sulfate ions, sulfuric acid can be obtained in the anode chamber 17. If the lithium chloride aqueous solution contains nitrate ions, nitric acid can be obtained in the anode chamber 17. That is, mineral acid 5 can be obtained in the first electrolysis step, and this mineral acid 5 can be used for at least one of dissolving active material powder 1 in STEP 1 and adjusting the pH in STEP C.

[0043] (Isolation of lithium hydroxide monohydrate) The recovery method of the present invention may include a crystallization step (STEP F) of crystallizing lithium hydroxide monohydrate 3 by evaporating and concentrating the lithium hydroxide aqueous solution obtained in the first electrolysis step.

[0044] (Separation of lithium carbonate) The recovery method of the present invention may include a carbonation step (STEP G) in which carbon dioxide is blown into the lithium hydroxide aqueous solution obtained in the first electrolysis step to produce lithium carbonate 6. The aqueous solution in which a second lithium salt, such as lithium chloride, which is more dilute than the first lithium salt aqueous solution, is dissolved, and which is obtained by solid-liquid separation of the slurry obtained in the carbonation step by filtration or the like, may be concentrated in the first concentration step (STEP E). Note that Figures 2 and 4 show the case in which the lithium salt dissolved in the second lithium salt aqueous solution is lithium chloride.

[0045] <Second electrolysis step> The recovery method of the present invention includes a second electrolysis step (STEP 7) in which the aqueous solution of at least one salt selected from the group consisting of sodium and potassium, in which at least one selected from the group consisting of sodium chloride and potassium chloride is dissolved, obtained from the separation step, is electrolyzed using an ion exchange membrane to obtain an aqueous alkali metal hydroxide solution 4. The second electrolysis step can be performed using, for example, an electrolytic cell 21 shown in FIG.

[0046] The electrolytic cell 21 is provided with an anode plate 22 on one of its inner surfaces and a cathode plate 23 on the inner surface opposite the anode plate 22, the anode plate 22 being connected to an anode 24 of a power supply, and the cathode plate 23 being connected to a cathode 25 of the power supply. The electrolytic cell 21 is also partitioned by an ion exchange membrane 26 into an anode chamber 27 equipped with the anode plate 22 and a cathode chamber 28 equipped with the cathode plate 23.

[0047] In the electrolytic cell 21, when an aqueous solution of at least one salt selected from the group consisting of sodium and potassium is supplied to the anode chamber 27 and electrolysis is performed, chloride ions generate chlorine gas (Cl2) on the anode plate 22. Meanwhile, at least one alkali metal ion selected from the group consisting of sodium ions and potassium ions migrates to the cathode chamber 28 through the ion exchange membrane 26.

[0048] In the cathode chamber 28, water (H2O) is converted into hydroxide ions (OH -) and hydrogen ions (H + ) and the hydrogen ions generate hydrogen gas (H2) on the cathode plate 23, while an alkali metal hydroxide aqueous solution 4 is generated in which hydroxide ions and at least one selected from the group consisting of sodium ions and potassium ions, and at least one selected from the group consisting of sodium hydroxide and potassium hydroxide, are dissolved.

[0049] The power required for the electrolysis is, for example, renewable energy, preferably at least one of solar power generation and wind power generation.

[0050] When the aqueous solution of at least one salt selected from the group consisting of sodium and potassium contains chloride ions, the hydrogen gas (H2) generated in the second electrolysis step can be reacted with chlorine gas (Cl2) to produce hydrochloric acid. When the aqueous solution of at least one salt selected from the group consisting of sodium and potassium contains sulfate ions, sulfuric acid can be produced in the anode chamber 27. When the aqueous solution of at least one salt selected from the group consisting of sodium and potassium contains nitrate ions, nitric acid can be produced in the anode chamber 27. That is, mineral acid 5 can be produced in the second electrolysis step, and mineral acid 5 is used in at least one step selected from the group consisting of dissolving active material powder 1 in STEP 1 and adjusting the pH in STEP C.

[0051] The recovery method of the present invention may include a carbon dioxide absorption step (STEP 8) of absorbing carbon dioxide into the alkali metal hydroxide aqueous solution 4 obtained in the second electrolysis step, in which at least one alkali metal carbonate selected from the group consisting of sodium hydroxide and potassium hydroxide is dissolved. At least one alkali metal carbonate 6 selected from the group consisting of sodium carbonate and potassium carbonate produced in the carbon dioxide absorption step may be used in the carbonation step (STEP 6a).

[0052] The alkali metal hydroxide aqueous solution 4 produced in the second electrolysis step may be reused in at least one step selected from the group consisting of the alkali hydroxide addition step, the extraction step, the separation step using the lithium phosphate method, and the separation step using the solvent extraction method.

[0053] In the second electrolysis step, the aqueous solution of at least one salt selected from the group consisting of sodium and potassium is electrolyzed, resulting in the production of an aqueous solution of at least one salt selected from the group consisting of sodium and potassium, which is more dilute than the aqueous solution of at least one salt selected from the group consisting of sodium and potassium. Therefore, the recovery method of the present invention may include a concentration step (STEP 9) in which the dilute aqueous solution of at least one salt selected from the group consisting of sodium and potassium is concentrated and added to the aqueous solution of at least one salt selected from the group consisting of sodium and potassium obtained in the separation step. The concentration step can be performed using, for example, a reverse osmosis membrane (RO membrane). [Example]

[0054] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0055] In the examples, various physical properties were measured or calculated as follows. <Metal content in lithium and sodium mixed salt aqueous solution, impurity content in lithium carbonate> The metal contents in the lithium and sodium mixed salt aqueous solution and the impurity contents in the lithium carbonate were measured by inductively coupled plasma optical emission spectroscopy (ICP-OES) using an Optima 8300 manufactured by PerkinElmer.

[0056] Example 1 Used lithium-ion batteries that had reached the end of their useful life as battery products were discharged to completely remove any remaining charge. The waste lithium-ion batteries were then heated (roasted) and pulverized in a hammer mill. The casings, current collectors, and other components of the waste lithium-ion batteries were sieved to obtain active material powder. 500 g of the active material powder was dissolved in 3 L of 6 mol / L hydrochloric acid, and 2.8 L of 2 mol / L aqueous sodium hydroxide was added to the resulting solution to neutralize it. 5.8 L of the neutralized solution was mixed with 5.8 L of bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex 272, diluent: kerosene) as an extractant, and cobalt was extracted with a solvent. 5 mol / L aqueous sodium hydroxide was added to the mixture to adjust the pH to 4, yielding a cobalt-containing organic phase and a first extraction residue. The cobalt-containing organic phase was scrubbed with dilute sulfuric acid and then back-extracted with 1.5 mol / L sulfuric acid to obtain a cobalt sulfate solution. Nickel was extracted from the first residue using the same organic solvent as used in the cobalt extraction step, yielding an aqueous solution of lithium and sodium mixed salts as the residue. The aqueous solution contained 3.5 g / L of lithium and 38.2 g / L of sodium.

[0057] 187 g of aluminum phosphate was added to 8.3 L of the aqueous solution, and then sodium hydroxide was added to adjust the pH of the aqueous solution to 10.5. The reaction was carried out for 2 hours to obtain white slurry A. Next, white slurry A was filtered and washed to obtain 614 g of white cake A with a moisture content of 55%. White cake A was suspended in 300 mL of pure water, and 35% by mass of hydrochloric acid was added to adjust the pH of the suspension to 2.5. The suspension was heated to 60°C and reacted for 6 hours to obtain white slurry B. White slurry B was filtered and washed to obtain 467 g of white cake B with a moisture content of 60%, as well as a total of 1060 mL of filtrate and wash water. Sodium hydroxide was added to the 1060 mL of filtrate and wash water to adjust the pH to 7, and the filtrate was filtered. 680 g of a 35% by mass aqueous sodium carbonate solution was added to the filtrate, which was then heated to 60°C and reacted for 1 hour. The obtained solid was filtered and washed to obtain hydrous lithium carbonate. The hydrous lithium carbonate was dried at 500°C for 4 hours to obtain 129g of lithium carbonate. The lithium recovery rate was 83.5%. The lithium carbonate had a sodium content of less than 200ppm, an aluminum content of less than 10ppm, a phosphorus content of less than 10ppm, and a water content of less than 0.1% by mass.

[0058] The filtrate obtained by filtering and washing the white slurry A and 10.5 L of washing water (sodium chloride concentration: 98 g / L) were concentrated using the RO membrane, and the resulting aqueous sodium chloride solution (sodium chloride concentration: 300 g / L) was passed through an ion exchange membrane (Nafion N324 manufactured by Chemours) at a current density of 40 A / dm 2 , electrode area 1.75dm 2 Electrolysis was carried out under the conditions of a current application time of 4 hours, yielding 1.6 kg of 21.2 mass% sodium hydroxide. Furthermore, the reaction product of the generated chlorine gas and hydrogen gas was absorbed in water, yielding 1.04 kg of 30 mass% hydrochloric acid. The sodium hydroxide produced in this electrolysis process could be reused in the sodium hydroxide addition process (STEP 2), extraction process (STEP 3), and separation process (STEP 4). Furthermore, the hydrochloric acid synthesized in this electrolysis process could be reused in the dissolution process (STEP 1). The current efficiency in this electrolysis process was 81.5%.

[0059] Example 2 Used lithium-ion batteries that had reached the end of their useful life as battery products were discharged to completely remove any remaining charge. The waste lithium-ion batteries were then heated (roasted) and pulverized in a hammer mill. The casings, current collectors, and other components of the waste lithium-ion batteries were sieved to obtain active material powder. 500 g of the active material powder was dissolved in 3 L of 6 mol / L hydrochloric acid, and 2.8 L of 2 mol / L aqueous sodium hydroxide was added to the resulting solution to neutralize it. 5.8 L of the neutralized solution was mixed with 5.8 L of bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex 272, diluent: kerosene) as an extractant, and cobalt was extracted with a solvent. 5 mol / L aqueous sodium hydroxide was added to the mixture to adjust the pH to 4, yielding a cobalt-containing organic phase and a first extraction residue. The cobalt-containing organic phase was scrubbed with dilute sulfuric acid and then back-extracted with 1.5 mol / L sulfuric acid to obtain a cobalt sulfate solution. Nickel was extracted from the first residue using the same organic solvent as used in the cobalt extraction step, yielding an aqueous solution of lithium and sodium mixed salts as the residue. The aqueous solution contained 3.5 g / L of lithium and 38.2 g / L of sodium.

[0060] 187 g of aluminum phosphate was added to 8.3 L of the aqueous solution, and then sodium hydroxide was added to adjust the pH of the aqueous solution to 10.5. The reaction was carried out for 2 hours to obtain white slurry A. Next, the white slurry A was filtered and washed to obtain 614 g of white cake A with a moisture content of 55%. The white cake A was suspended in 300 mL of pure water, and 35% by mass of hydrochloric acid was added to adjust the pH of the suspension to 2.5. The suspension was heated to 60°C and reacted for 6 hours to obtain white slurry B. The white slurry B was filtered and washed to obtain 467 g of white cake B with a moisture content of 60%, and a total of 1,060 mL of filtrate and wash water. Lithium hydroxide was added to the 1060 mL of filtrate and wash water to adjust the pH to 7, and the filtrate (filtrate 1) was filtered to obtain 1060 mL (lithium chloride concentration: 92 g / L). The filtrate was concentrated using the RO membrane, and the resulting lithium chloride aqueous solution (lithium chloride concentration: 200 g / L) was passed through an ion exchange membrane (Nafion N324, manufactured by Chemours) at a current density of 40 A / dm 2 , electrode area 0.7dm 2 Electrolysis was carried out under the conditions (first electrolysis step) to obtain 1100 g of a 6.2 mass% lithium hydroxide aqueous solution. Furthermore, the reaction product of the generated chlorine gas and hydrogen gas was absorbed in water to obtain 350 g of 30 mass% hydrochloric acid. The lithium recovery rate in the first electrolysis step was 70.3%.

[0061] 380 g of the 6.2% by mass lithium hydroxide aqueous solution was taken, and 80% by mass of the solution was crystallized to obtain 19.3 g (mass after drying) of lithium hydroxide monohydrate crystals, which had a sodium content of less than 50 ppm, an aluminum content of less than 10 ppm, and a phosphorus content of less than 10 ppm.

[0062] The filtrate obtained by filtering and washing the white slurry A and 10.5 L of washing water (sodium chloride concentration: 98 g / L) were concentrated using the RO membrane, and the resulting aqueous sodium chloride solution (sodium chloride concentration: 300 g / L) was passed through an ion exchange membrane (Nafion N324 manufactured by Chemours) at a current density of 40 A / dm 2 , electrode area 1.75dm 2Electrolysis was carried out under the conditions of a current application time of 4 hours, yielding 1.6 kg of 21.2 mass% sodium hydroxide. Furthermore, the reaction product of the generated chlorine gas and hydrogen gas was absorbed in water, yielding 1.04 kg of 30 mass% hydrochloric acid. The sodium hydroxide produced in this electrolysis process could be reused in the sodium hydroxide addition process (STEP 2), extraction process (STEP 3), and separation process (STEP 4). Furthermore, the hydrochloric acid synthesized in this electrolysis process could be reused in the dissolution process (STEP 1). The current efficiency in this electrolysis process was 81.5%.

[0063] In this example, it was found that the mineral acid and alkali used could be regenerated and reused. Furthermore, it was found that the purity of the lithium carbonate obtained in the final stage of lithium recovery from waste lithium-ion batteries and the recovery rate of lithium were very high.

[0064] In the recovery method of the present invention, sodium hydroxide / potassium hydroxide can be directly obtained in the second electrolysis step using an ion exchange membrane for the aqueous sodium / potassium salt solution. The mineral acid and alkali produced in the second electrolysis step can be recycled for use in the recovery method of the present invention, thereby realizing a closed-loop recycling process. Furthermore, since the recovery method of the present invention preferably recycles the mineral acid and alkali, it is possible to reduce the amount of carbon dioxide emitted in the distribution process of the mineral acid and alkali compared to conventional methods in which the mineral acid and alkali are purchased from outside. [Explanation of symbols]

[0065] 1...active material powder, 2...metal sulfate aqueous solution, 3...lithium carbonate, 4...sodium hydroxide aqueous solution, 5...mineral acid, 6...sodium carbonate, 11, 21...electrolytic cell, 12, 22...anode plate, 13, 23...cathode plate, 14, 24...Anode, 15, 25...Cathode, 16, 26...Ion exchange membrane, 17, 27...Anode chamber, 18, 28...Cathode chamber.

Claims

1. A method for recovering lithium from waste lithium-ion batteries, comprising: a dissolving step of dissolving the active material powder obtained by pretreating the waste lithium ion batteries in a mineral acid; an alkali hydroxide adding step of adding at least one of sodium hydroxide and potassium hydroxide to the solution obtained in the dissolving step; a step of separating at least one metal, excluding lithium, among the metals contained in the active material powder from the solution obtained in the alkali hydroxide addition step by organic solvent extraction, and obtaining an aqueous alkali mixed salt solution as a residue of the solvent extraction; a separation step of separating a lithium salt and at least one salt of sodium and potassium from the aqueous alkali mixed salt solution; A method for recovering lithium from waste lithium-ion batteries, comprising: a lithium recovery step of recovering lithium from the first lithium salt aqueous solution obtained in the separation step.

2. 2. The method for recovering lithium from waste lithium-ion batteries according to claim 1, further comprising a second electrolysis step of electrolyzing the aqueous salt solution of at least one of sodium and potassium obtained from the separation step using an ion exchange membrane to obtain an aqueous alkali metal hydroxide solution.

3. 3. The method for recovering lithium from waste lithium-ion batteries according to claim 2, wherein the aqueous alkali metal hydroxide solution obtained in the second electrolysis step is reused in at least one of the alkali hydroxide adding step, the extraction step, and the separation step.

4. 2. The method for recovering lithium from waste lithium-ion batteries according to claim 1, wherein the lithium recovery step includes a carbonation step of carbonate the first lithium salt aqueous solution obtained in the separation step to obtain lithium carbonate.

5. 2. The method for recovering lithium from used lithium-ion batteries according to claim 1, wherein the lithium recovery step further comprises a first electrolysis step of electrolyzing the first lithium salt aqueous solution obtained in the separation step using an ion exchange membrane to obtain a lithium hydroxide aqueous solution, an acid, and a second lithium salt aqueous solution that is more dilute than the first lithium salt aqueous solution.

6. 6. The method for recovering valuable metals from waste lithium ion batteries according to claim 5, wherein the second lithium salt aqueous solution is concentrated and added to the first lithium salt aqueous solution.

7. 7. The method for recovering valuable metals from waste lithium-ion batteries according to claim 1, wherein the mineral acid is at least one selected from the group consisting of hydrochloric acid, sulfuric acid, and nitric acid.

8. The method for recovering valuable metals from waste lithium ion batteries according to any one of claims 1 to 6, wherein the mineral acid is hydrochloric acid.

9. 7. The method for recovering valuable metals from waste lithium-ion batteries according to claim 1, wherein the mineral acid is hydrochloric acid produced by electrolyzing the first lithium salt aqueous solution using an ion exchange membrane, reacting chlorine with hydrogen, and using the hydrochloric acid as the mineral acid.

10. 6. The method for recovering valuable metals from waste lithium-ion batteries according to claim 2 or 5, wherein the electric power used in at least one selected from the group consisting of the first electrolysis step and the second electrolysis step is electric power obtained from renewable energy.

11. 11. The method for recovering valuable metals from waste lithium-ion batteries according to claim 10, wherein the electricity obtained by renewable energy is electricity obtained by solar power generation or electricity obtained by wind power generation.

12. The method for recovering valuable metals from waste lithium-ion batteries according to any one of claims 1 to 6, wherein the organic solvent does not contain a reducing agent or an oxidizing agent.

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