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 alkali to a solution obtained in the dissolution step; a solid-liquid separation step for performing solid-liquid separation into insoluble matter and a solution A, following the alkali hydroxide addition step; an extraction step for sequentially extracting manganese, cobalt, and nickel in the solution A; a separation step for separating a lithium salt or the like from an alkali mixed salt aqueous solution obtained in the extraction step; and a lithium recovery step for recovering lithium from a lithium salt aqueous solution obtained in the separation step.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This 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 explored to recover valuable metals such as cobalt, nickel, manganese, and lithium from waste lithium-ion batteries and reuse them as materials for the aforementioned lithium-ion batteries.

[0003] Conventionally, when recovering the valuable metals from the waste lithium-ion batteries, cobalt, nickel, manganese, and lithium are separated and purified by a wet process from a powder containing the valuable metals obtained by heat treatment (roasting), pulverization, classification, etc. (see, for example, Patent Documents 1 and 2).

[0004] In this invention, "waste lithium-ion battery" refers to a used lithium-ion battery whose lifespan as a battery product has been exhausted, a lithium-ion battery discarded as a defective product during the manufacturing process, and residual positive electrode material, negative electrode material, etc., used in the manufacturing process. Furthermore, the powder containing the positive electrode and negative electrode obtained from the said waste lithium-ion battery is referred to as the active material powder. In addition, "impurity" 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 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] However, existing wet processes use compounds other than lithium compounds, which are the target material to be recovered, as alkali sources. As a result, the concentration of non-lithium cations increases, while the lithium ion concentration decreases. Consequently, conventional wet processes suffer a significant decrease in the recovery rate of lithium, the target material. Furthermore, conventional wet processes have the disadvantage that the mineral acid used to dissolve the active material powder and the compounds used as alkali sources are discharged as salts, and there is no technology to recycle these mineral acids and compounds used as alkali sources. In recent years, there has been a strong demand for a method to recover lithium from waste lithium-ion batteries that overcomes these drawbacks, recovers lithium with a high recovery rate, and preferably allows the salts generated in the recovery process to be reused as mineral acids and alkalis in the same process. However, no such method has been provided. The problem that the present invention aims to solve is to provide a method for recovering lithium from waste lithium-ion batteries that recovers lithium with a high recovery rate, and preferably allows the salts generated in the recovery process to be reused as mineral acids and alkalis in the same process. [Means for solving the problem]

[0007] In view of the above problems, the inventors conducted extensive research and found that by dissolving the active material powder in a mineral acid to obtain a solution, adding at least one of sodium hydroxide and potassium hydroxide, further separating the lithium salt aqueous solution from the sodium and potassium salt aqueous solution, and preferably reusing the mineral acid obtained by electrolyzing the separated sodium and potassium salt aqueous solution, as well as at least one of sodium hydroxide and potassium hydroxide, the present invention was completed based on these findings.

[0008] The present invention relates to a method for recovering lithium from a waste lithium-ion battery, comprising: a dissolution step of dissolving an active material powder obtained by pre-treating the waste lithium-ion battery with a mineral acid; an alkali hydroxide addition step of adding at least one of sodium hydroxide and potassium hydroxide to the solution obtained in the dissolution step; a solid-liquid separation step of separating the insoluble matter obtained in the alkali hydroxide addition step from solution A; a manganese extraction step of adding an organophosphorus compound extraction solvent to solution A to extract and separate manganese and obtain solution B; a cobalt extraction step of adding an organophosphorus compound extraction solvent to solution B to extract and separate cobalt and obtain solution C; a nickel extraction step of adding an organophosphorus compound extraction solvent to solution C to extract and separate nickel; a separation step of separating a lithium salt and at least one salt of sodium and potassium from an alkaline mixed salt aqueous solution obtained in the nickel extraction step; and a lithium recovery step of recovering lithium from a first lithium salt aqueous solution obtained in the separation step. The present invention preferably further includes a second electrolysis step in which an 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 alkali metal hydroxide solution. The alkali metal hydroxide aqueous 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 in which the first lithium salt aqueous solution obtained in the separation step is carbonated to obtain lithium carbonate. The lithium recovery step preferably further includes a first electrolysis step in which the first lithium salt aqueous solution obtained in the separation step is electrolyzed 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 lithium salt aqueous solution is preferably concentrated and added to the first lithium salt aqueous 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, preferably, hydrochloric acid produced by reacting chlorine and hydrogen obtained by electrolyzing the first lithium salt aqueous solution using an ion exchange membrane is used as the mineral acid. The electricity used in at least one selected from the group consisting of the first electrolysis step and the second electrolysis step is preferably electricity obtained from renewable energy, and more preferably electricity obtained from solar power generation or wind power generation. [Effects of the Invention]

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

[0010] [Figure 1] This diagram illustrates the configuration of one embodiment of the method for recovering lithium from waste lithium-ion batteries according to the present invention. [Figure 2] 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] An explanatory diagram showing the configuration of one embodiment of the lithium phosphate method. [Figure 4] An explanatory diagram showing the configuration of another embodiment of the lithium phosphate method. [Figure 5] This is an explanatory cross-sectional view showing the structure of an ion exchange membrane electrolytic cell used in the first electrolytic step of the lithium recovery method from waste lithium-ion batteries of the present invention. [Figure 6] This is an explanatory cross-sectional view showing the structure of an ion exchange membrane electrolytic cell used in the second electrolysis step of the lithium recovery method from waste lithium-ion batteries of the present invention. [Modes for carrying out the invention]

[0011] Next, the present invention will be described in more detail with reference to the accompanying drawings. As shown in FIGS. 1 and 2, a method for recovering lithium from a spent lithium-ion battery of the present invention (hereinafter referred to as "recovery method") uses the active material powder 1 as a starting material.

[0012] The recovery method of the present invention includes a dissolution step (STEP 1) of dissolving the active material powder 1 obtained by pretreatment with a mineral acid. The mineral acid preferably contains 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, still 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, a solution of the valuable metals contained in the active material powder 1 can be obtained by dissolving the active material powder 1 with the mineral acid.

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

[0014] The recovery method of the present invention includes a solvent extraction step (STEP 3) in which valuable metals contained in the active material powder 1 are extracted with an organic solvent from the solution obtained in the alkali hydroxide addition step by solvent extraction.

[0015] Solution A is separated from the insoluble matter generated from the neutralized solution of the valuable metal by solid-liquid separation. Manganese is extracted and separated by an organophosphorus compound extraction solvent to solution A, and solution B is obtained (manganese extraction step). Cobalt is extracted and separated by an organophosphorus compound extraction solvent to solution B, and solution C is obtained (cobalt extraction step). Nickel is extracted and separated by an organophosphorus compound extraction solvent to solution C, and a first lithium salt aqueous solution is obtained (nickel extraction step). The separation coefficients in these extraction steps are high, meaning that the separation of each metal is good in these extraction steps. Furthermore, these extraction steps can be easily controlled by pH.

[0016] The solvents used in the manganese extraction, cobalt extraction, and nickel extraction processes are organophosphorus compounds such as phosphate esters, phosphonic acid esters, phosphinic acids, and phosphine oxides. These organophosphorus compounds are commercially available, and examples include D2EHPA (di(2-ethylhexyl) phosphate) as an acidic phosphate ester, PC-88A manufactured by Daihachi Chemical Industry Co., Ltd. as a phosphonic acid ester, CYANEX272 manufactured by Solvay as a phosphinic acid, TBP (tributyl phosphate) as a neutral phosphate ester, and tory-n-octylphosphine (TOPO) as a phosphine oxide.

[0017] For example, D2EHPA is used as the extraction solvent in the manganese extraction process, while CYANEX272 is used in the cobalt and nickel extraction processes. The pH of CYANEX272 used in the cobalt and nickel extraction processes is different.

[0018] In the extraction step, the valuable metals, excluding lithium, are each extracted separately from the others in the order of manganese, cobalt, and nickel using a solvent, and removed as aqueous solutions of their respective metal sulfates, thereby obtaining the first aqueous lithium salt solution. The lithium salt contained in the first aqueous lithium salt solution becomes lithium chloride when hydrochloric acid is used in the acid dissolution in STEP 1.

[0019] The recovery method of the present invention includes a separation step (STEP 4) in which lithium obtained in the extraction step and an aqueous solution of an alkali metal mixed salt containing at least one selected from the group consisting of sodium and potassium are separated into lithium salt and at least one selected from the group consisting of sodium and potassium. The separation step is not limited to a specific method, but is preferably carried out by at least one of the lithium phosphate method, the evaporation concentration method, and the solvent extraction method.

[0020] <Lithium phosphate method> The lithium phosphate method will be explained using Figures 3 and 4. The lithium phosphate method includes a phosphorylation step (STEP A) in which aluminum phosphate and an aqueous solution of at least one alkali metal hydroxide (MOH) selected from the group consisting of sodium hydroxide and potassium hydroxide are added to the aqueous solution of the alkali metal mixed salt to produce a solid containing lithium phosphate and aluminum hydroxide. Alkali metal chloride (MCl) is dissolved in the aqueous solution in which the solid 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.

[0021] The lithium phosphate method includes a first solid-liquid separation (STEP B) for separating the solid material produced in the phosphorylation step into a solid-liquid state. For example, filtration may be used as this first solid-liquid separation step.

[0022] The lithium phosphate method may include washing the solid separated in the first solid-liquid separation step. It also includes a pH adjustment step (STEP C) in which a mineral acid is added to a suspension obtained by suspending the solid in water to adjust the pH of the suspension to 2-3. 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. Preferably, the mineral acid is 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, which is illustrated in Figures 3 and 4.

[0023] The lithium phosphate method includes a second solid-liquid separation step (STEP D) for solid-liquid separation of the aluminum phosphate obtained in the pH adjustment step and the first lithium salt aqueous solution. For example, filtration can be used as the second solid-liquid separation step. The aluminum phosphate obtained in the second solid-liquid separation step can be separated from the solid-liquid in a short time, and the solid-liquid separated aluminum phosphate may be reused in the phosphorylation step.

[0024] 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 later. Since the pH of the suspension is adjusted to 2-3 in the pH adjustment step (STEP C), the pH of the first lithium salt aqueous solution is 2-3, but in the pH adjustment step (STEP 5), the pH is preferably adjusted to 6-8. In this case, unreacted aluminum and phosphorus precipitate, and the purity of the first lithium salt aqueous solution becomes higher.

[0025] Preferably, the first lithium salt aqueous solution, whose pH has been adjusted in the pH adjustment step (STEP 5), is carbonated to obtain lithium carbonate in a carbonation step (STEP 6a) described later (Figure 3). In the carbonation step, at least one salt aqueous solution selected from the group consisting of sodium and potassium is produced, in which at least one selected from the group consisting of sodium chloride and potassium chloride, a trace amount of lithium chloride, and at least one selected from the group consisting of sodium carbonate and potassium carbonate are dissolved, and preferably the pH of the salt aqueous solution selected from the group consisting of sodium and potassium is about 12. When hydrochloric acid is added to the salt aqueous solution selected from the group consisting of sodium and potassium to adjust its pH to 5 or less, at least one selected from the group consisting of sodium carbonate and potassium carbonate decomposes to produce carbon dioxide and water, and an aqueous solution in which at least one selected from the group consisting of sodium chloride and potassium chloride is dissolved. This aqueous solution may be concentrated in a concentration step (STEP 9) described later. Figure 3 shows the case in which this concentration step is performed.

[0026] Preferably, the first lithium salt aqueous solution, whose pH 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), which will be described later (Figure 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. This first concentration step can be carried out, for example, using a reverse osmosis membrane (RO membrane).

[0027] In the lithium phosphate method, the filtrate containing the dissolved alkali metal chloride, separated in the first solid-liquid separation step, may be concentrated in a concentration step (STEP 9) described later.

[0028] <Evaporation concentration method> An aqueous solution of lithium and at least one alkali metal mixed salt selected from the group consisting of sodium and potassium is evaporated and concentrated, and at least one selected from the group consisting of sodium salts and potassium salts, such as at least one selected from the group consisting of sodium chloride and potassium chloride, is sequentially crystallized and separated from the aqueous solution of alkali metal mixed salt. At least one selected from the group consisting of sodium salts and potassium salts, such as at least one selected from the group consisting of sodium chloride and potassium chloride, is dissolved in water, and an 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 later. The first lithium salt aqueous solution from which at least one 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 later, and further subjected to a carbonation step (STEP 6a), similar to the first lithium salt aqueous solution obtained by the lithium phosphate method. If 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 selected from the group consisting of sodium chloride and potassium chloride is dissolved, as described above, the aqueous solution may be concentrated in the concentration step described later (STEP 9).

[0029] Furthermore, the first lithium salt aqueous solution is preferably subjected to a pH adjustment step (STEP 5) and a first concentration step (STEP E), and then to a first electrolysis step (STEP 6b), which will be described later, similar to the first lithium salt aqueous solution obtained by the lithium phosphate method.

[0030] <Solvent extraction method> The pH of a homogeneous mixture of lithium, at least one aqueous solution of a mixed salt selected from the group consisting of sodium and potassium, and an organic solvent for lithium extraction is preferably adjusted to a range of 5 to 9 by adding an alkali such as at least one selected from the group consisting of sodium hydroxide and potassium hydroxide, thereby obtaining a lithium-containing organic phase and at least one aqueous solution of a salt selected from the group consisting of sodium and potassium as the extraction residue. Examples of organic solvents for lithium extraction include bis(2-ethylhexyl) hydrogen phosphate. The lithium-containing organic phase is scrubbed with a mineral acid to recover the first aqueous lithium salt solution. This first aqueous lithium salt solution is preferably subjected to a pH adjustment step (STEP 5) described later, similar to the first aqueous lithium salt solution obtained by the lithium phosphate method, and further subjected to a carbonation step (STEP 6a). If 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 selected from the group consisting of sodium chloride and potassium chloride is dissolved, as described above, the aqueous solution may be concentrated in the concentration step (STEP 9) described later. Furthermore, the first aqueous lithium salt solution may be subjected to the pH adjustment step (STEP 5) and the first concentration step (STEP E) described later, similar to the aqueous lithium salt solution obtained by the lithium phosphate method, and may also be subjected to the first electrolysis step (STEP 6b) described later.

[0031] A second electrolysis step (STEP 7), described later, is performed, in which at least one of the sodium and potassium salts, such as at least one selected from the group consisting of sodium chloride and potassium chloride, in which at least one sodium salt and potassium salt is dissolved, is electrolyzed using an ion exchange membrane. The aqueous solution of at least one sodium and potassium salt is concentrated in a concentration step (STEP 9), described later, preferably using a reverse osmosis membrane (RO membrane) or the like.

[0032] The recovery method of the present invention may include a pH adjustment step (STEP 5) in which at least one of sodium hydroxide and potassium hydroxide is added to the first lithium salt aqueous solution obtained in the separation step to adjust the pH of the first lithium salt aqueous solution. The pH of the first lithium salt aqueous solution is preferably adjusted to 8 to 14, more preferably to 10 to 11.

[0033] [Lithium recovery] <Carbonation of the first lithium salt aqueous solution> The recovery method of the present invention includes, as a lithium recovery step, a carbonation step (STEP 6a) in which the first lithium salt aqueous solution obtained in the separation step is carbonated to obtain lithium carbonate. In this carbonation step, an alkali metal carbonate (excluding lithium carbonate), such as at least one selected from the group consisting of sodium carbonate and potassium carbonate, obtained in a carbon dioxide absorption step (STEP 8) in which carbon dioxide is absorbed into an aqueous solution 4 in which at least one selected from the group consisting of sodium hydroxide and potassium hydroxide obtained in the second electrolysis step described later is dissolved, may be added to the first lithium salt aqueous solution.

[0034] The alkali metal of the alkali metal carbonate salt is at least one selected from the group consisting of sodium, potassium, rubidium, cesium, and francium. The alkali metal is preferably at least one selected from the group consisting of sodium and potassium, and more preferably sodium.

[0035] <First electrolysis process> The recovery method of the present invention includes, as another lithium recovery step, a first electrolysis step (STEP 6b) in which the first lithium salt aqueous solution obtained in the separation step and optionally 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 a lithium hydroxide aqueous solution.

[0036] The first electrolysis step can be carried out, for example, using the electrolytic cell 11 shown in Figure 5. The electrolytic cell 11 has an anode plate 12 on one inner surface and a cathode plate 13 on the inner surface opposite to the anode plate 12. The anode plate 12 is connected to the anode 14 of the power supply, and the cathode plate 13 is connected to the cathode 15 of the power supply. The electrolytic cell 11 is also divided 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.

[0037] 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 via the ion exchange membrane 16.

[0038] In cathode chamber 18, water (H2O) is converted into hydroxide ions (OH - ) and hydrogen ions (H + ) ionizes, and hydrogen ions generate hydrogen gas (H2) on the cathode plate 13, while hydroxide ions and lithium ions generate an aqueous lithium hydroxide solution.

[0039] For example, renewable energy, preferably at least one of solar power generation and wind power generation, is used as the electricity required for the electrolysis.

[0040] Hydrochloric acid can be obtained by reacting the hydrogen gas (H2) and chlorine gas (Cl2) generated in the first electrolysis step. Although not shown in Figure 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. In other words, mineral acid 5 can be obtained in the first electrolysis step, and this mineral acid 5 may be used in at least one of the following: dissolving the active material powder 1 in STEP 1 and adjusting the pH in STEP C.

[0041] (Separation of lithium hydroxide monohydrate) The recovery method of the present invention may include a crystallization step (STEP F) in which the lithium hydroxide aqueous solution obtained in the first electrolysis step is evaporated and concentrated to crystallize lithium hydroxide monohydrate 3.

[0042] (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 slurry obtained in the carbonation step is separated into solid and liquid by filtration or the like to obtain an aqueous solution containing a second lithium salt, such as lithium chloride, which is more dilute than the first lithium salt aqueous solution, and this aqueous solution may be concentrated in the first concentration step (STEP E). Figures 2 and 4 show the case in which the lithium salt dissolved in the second lithium salt aqueous solution is lithium chloride.

[0043] <Second electrolysis process> The recovery method of the present invention includes a second electrolysis step (STEP 7) in which an aqueous solution of at least one salt selected from the group consisting of sodium and potassium, which is obtained from the separation step and contains at least one selected from the group consisting of sodium chloride and potassium chloride, is electrolyzed using an ion exchange membrane to obtain an aqueous alkali metal hydroxide solution 4. This second electrolysis step can be carried out using, for example, the electrolytic cell 21 shown in Figure 6.

[0044] The electrolytic cell 21 is equipped with an anode plate 22 on one inner surface and a cathode plate 23 on the inner surface opposite to the anode plate 22. The anode plate 22 is connected to the anode 24 of the power supply, and the cathode plate 23 is connected to the cathode 25 of the power supply. The electrolytic cell 21 is also divided 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.

[0045] In the electrolytic cell 21, when electrolysis is performed by supplying at least one aqueous salt solution selected from the group consisting of sodium and potassium to the anode chamber 27, 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 moves to the cathode chamber 28 via the ion exchange membrane 26.

[0046] In cathode chamber 28, water (H2O) is converted into hydroxide ions (OH -) and hydrogen ions (H + ) dissociates into hydrogen ions, and hydrogen ions generate hydrogen gas (H2) on the cathode plate 23, while hydroxide ions and at least one selected from the group consisting of sodium ions and potassium ions, selected from the group consisting of sodium hydroxide and potassium hydroxide, are dissolved in alkali metal hydroxide aqueous solution 4.

[0047] For example, renewable energy, preferably at least one of solar power generation and wind power generation, is used as the electricity required for the electrolysis.

[0048] If at least one aqueous salt solution selected from the group consisting of sodium and potassium contains chloride ions, hydrochloric acid can be obtained by reacting the hydrogen gas (H2) and chlorine gas (Cl2) produced in the second electrolysis step. If at least one aqueous salt solution selected from the group consisting of sodium and potassium contains sulfate ions, sulfuric acid can be obtained in the anode chamber 27. If at least one aqueous salt solution selected from the group consisting of sodium and potassium contains nitrate ions, nitric acid can be obtained in the anode chamber 27. That is, mineral acid 5 can be obtained in the second electrolysis step, and this mineral acid 5 is used in at least one of the steps selected from the group consisting of dissolving the active material powder 1 in STEP 1 and adjusting the pH in STEP C.

[0049] The recovery method of the present invention may include a carbon dioxide absorption step (STEP 8) in which carbon dioxide is absorbed into an aqueous alkali metal hydroxide solution 4 obtained by the second electrolysis step, which contains at least one selected from the group consisting of sodium hydroxide and potassium hydroxide. 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).

[0050] 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 by lithium phosphate, and the separation step by solvent extraction.

[0051] In the second electrolysis step described above, at least one aqueous salt solution selected from the group consisting of sodium and potassium is electrolyzed, resulting in the production of at least one aqueous salt solution selected from the group consisting of sodium and potassium that is more dilute than the at least one aqueous salt solution 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 salt solution selected from the group consisting of sodium and potassium is concentrated and added to the at least one aqueous salt solution selected from the group consisting of sodium and potassium obtained in the separation step. This concentration step can be carried out, for example, using a reverse osmosis membrane (RO membrane). [Examples]

[0052] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0053] In the examples, various physical properties were measured or calculated as follows. <Metal content in lithium and sodium mixed salt aqueous solution, and impurity content in lithium carbonate> Using a PerkinElmer Optima8300, the metal content in a mixed lithium and sodium salt aqueous solution and the impurity content in lithium carbonate were measured by inductively coupled plasma atomic emission spectroscopy (ICP-OES).

[0054] Example 1 Used lithium-ion batteries, whose lifespan as battery products had reached its limit, were discharged to completely remove any remaining charge. Next, the waste lithium-ion batteries were heat-treated (roasted), then crushed in a hammer mill. The casing, current collector, and other components constituting the waste lithium-ion batteries were sieved to obtain active material powder. 500 g of this active material powder was dissolved in 3 L of 6 mol / L hydrochloric acid. 2.8 L of 2 mol / L sodium hydroxide aqueous solution 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, kerosene as diluent) as an extractant, and cobalt was extracted using solvent extraction. 5 mol / L sodium hydroxide aqueous solution was added to the mixture to adjust the pH to 4, obtaining a cobalt-containing organic phase and the 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. Using the same organic solvent as used in the cobalt extraction step, nickel was extracted from the first extraction residue, and an aqueous solution of a lithium and sodium mixed salt was obtained as the extraction residue. This aqueous solution contained 3.5 g / L of lithium and 38.2 g / L of sodium.

[0055] 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 water content of 55%. White cake A was suspended in 300 mL of pure water, and 35% by mass 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 water content of 60%, and a total of 1060 mL of filtrate and washing water. Sodium hydroxide was added to the 1060 mL of filtrate and washing water to adjust the pH to 7, and the filtered filtrate was mixed with 680 g of 35% by mass sodium carbonate aqueous solution. The mixture was heated to 60°C and reacted for 1 hour. The obtained solid was filtered and washed to obtain hydrated lithium carbonate. The hydrated lithium carbonate was dried at 500°C for 4 hours to obtain 129 g of lithium carbonate. The lithium recovery rate was 83.5%. The sodium content in the lithium carbonate was less than 200 ppm, the aluminum content was less than 10 ppm, the phosphorus content was less than 10 ppm, and the water content was less than 0.1 mass%.

[0056] The filtrate and washing water (10.5 L, sodium chloride concentration 98 g / L) obtained by filtration and washing of the white slurry A were concentrated using the RO membrane, and the resulting sodium chloride aqueous solution (sodium chloride concentration 300 g / L) was subjected to a current density of 40 A / dm² using an ion exchange membrane (Nafion N324, manufactured by Chemours). 2 , electrode area 1.75dm 2 Under conditions of electrolysis with an energizing time of 4 hours, 1.6 kg of 21.2% by mass sodium hydroxide was obtained. Furthermore, the reaction product of the generated chlorine gas and hydrogen gas was absorbed into water to obtain 1.04 kg of 30% by mass hydrochloric acid. The sodium hydroxide produced in the electrolysis process could be reused in the sodium hydroxide addition process (STEP 2), the extraction process (STEP 3), and the separation process (STEP 4). Furthermore, the hydrochloric acid synthesized in the electrolysis process could be reused in the dissolution process (STEP 1). The current efficiency in the electrolysis process was 81.5%.

[0057] Example 2 Used lithium-ion batteries, whose lifespan as battery products had reached its limit, were discharged to completely remove any remaining charge. Next, the waste lithium-ion batteries were heat-treated (roasted), then crushed in a hammer mill. The casing, current collector, and other components constituting the waste lithium-ion batteries were sieved to obtain active material powder. 500 g of this active material powder was dissolved in 3 L of 6 mol / L hydrochloric acid. 2.8 L of 2 mol / L sodium hydroxide aqueous solution 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, kerosene as diluent) as an extractant, and cobalt was extracted using solvent extraction. 5 mol / L sodium hydroxide aqueous solution was added to the mixture to adjust the pH to 4, obtaining a cobalt-containing organic phase and the 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. Using the same organic solvent as used in the cobalt extraction step, nickel was extracted from the first extraction residue, and an aqueous solution of a lithium and sodium mixed salt was obtained as the extraction residue. This aqueous solution contained 3.5 g / L of lithium and 38.2 g / L of sodium.

[0058] 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 a white slurry A. Next, the white slurry A was filtered and washed to obtain 614 g of a white cake A with a water content of 55%. The white cake A was suspended in 300 mL of pure water, and 35% by mass 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 a white slurry B. The white slurry B was filtered and washed to obtain 467 g of a white cake B with a water content of 60% and a total of 1060 mL of filtrate and washing water. Lithium hydroxide was added to the 1060 mL of the filtrate and washing water to adjust the pH to 7, and the filtered filtrate (filtrate 1) of 1060 mL (lithium chloride concentration 92 g / L) was concentrated using the RO membrane. The obtained aqueous lithium chloride solution (lithium chloride concentration was 200 g / L) was electrolyzed under the conditions of a current density of 40 A / dm 2 and an electrode area of 0.7 dm 2 (the first electrolysis step) to obtain 1100 g of a 6.2% by mass aqueous lithium hydroxide solution. Further, the reactants of the generated chlorine gas and hydrogen gas were absorbed in water to obtain 350 g of 30% by mass hydrochloric acid. The recovery rate of lithium in the first electrolysis step was 70.3%.

[0059] 380 g of the 6.2% by mass aqueous lithium hydroxide solution was separated, and 80% by mass of the aqueous solution was crystallized to obtain 19.3 g (mass after drying) of crystals of lithium hydroxide monohydrate. The sodium content in the lithium hydroxide monohydrate was less than 50 ppm, the aluminum content was less than 10 ppm, and the phosphorus content was less than 10 ppm.

[0060] 10.5 L of the filtrate and washing water (sodium chloride concentration was 98 g / L) obtained by filtering and washing the white slurry A was concentrated using the RO membrane. The obtained aqueous sodium chloride solution (sodium chloride concentration was 300 g / L) was electrolyzed under the conditions of a current density of 40 A / dm 2 and an electrode area of 1.75 dm 2Under conditions of electrolysis with an energizing time of 4 hours, 1.6 kg of 21.2% by mass sodium hydroxide was obtained. Furthermore, the reaction product of the generated chlorine gas and hydrogen gas was absorbed into water to obtain 1.04 kg of 30% by mass hydrochloric acid. The sodium hydroxide produced in the electrolysis process could be reused in the sodium hydroxide addition process (STEP 2), the extraction process (STEP 3), and the separation process (STEP 4). Furthermore, the hydrochloric acid synthesized in the electrolysis process could be reused in the dissolution process (STEP 1). The current efficiency in the electrolysis process was 81.5%.

[0061] In this example, it was found that the mineral acid and alkali used can 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, as well as the lithium recovery rate, are very high.

[0062] In the recovery method of the present invention, sodium hydroxide / potassium can be directly obtained in a second electrolysis step using an ion exchange membrane for the sodium / potassium salt aqueous solution. Since the mineral acid and alkali produced in the second electrolysis step can be recycled into the recovery method of the present invention, a closed-loop recycling process can be realized. Furthermore, since the recovery method of the present invention preferably recycles the mineral acid and alkali, it can reduce the amount of carbon dioxide emitted in the logistics process of the mineral acid and alkali compared to when the mineral acid and alkali are purchased from external sources as in the conventional method. [Explanation of Symbols]

[0063] 1…Active material powder, 2…Metal sulfate aqueous solution, 3…Lithium carbonate, 4…Sodium hydroxide 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 solid-liquid separation step of separating the insoluble matter obtained in the alkali hydroxide addition step from Solution A; a manganese extraction step of adding an organic phosphorus compound extraction solvent to the solution A to extract and separate manganese and obtain a solution B; a cobalt extraction step in which an organic phosphorus compound extraction solvent is added to the solution B to extract and separate cobalt and obtain a solution C; a nickel extraction step of adding an organic phosphorus compound extraction solvent to the solution C to extract and separate nickel; a separation step of separating a lithium salt and at least one salt of sodium and potassium from the aqueous alkali mixed salt solution obtained in the nickel extraction step; 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 carbonated the 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 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.

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