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.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; an extraction step for extracting, from a solution obtained in the alkali hydroxide addition step, valuable metals with an organic solvent by solvent extraction: a nickel removal step for mixing a first alkali mixed salt aqueous solution obtained in the extraction step with alkali to remove nickel, thereby obtaining a second alkali mixed salt aqueous solution; a separation step for separating a lithium salt and a salt of sodium or the like respectively from the second alkali mixed salt aqueous solution; and a lithium recovery 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 considered for recovering valuable metals such as cobalt, nickel, manganese, and lithium from discarded lithium ion batteries and reusing them as materials for the lithium ion batteries.

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

[0004] In the present invention, the waste lithium ion batteries refer to used lithium ion batteries that have run out of life as battery products, lithium ion batteries that have been discarded as defective products in the manufacturing process, and the remaining 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 called the active material powder. Furthermore, the impurities refer 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 the existing wet process, a compound other than the lithium compound to be recovered is used as an alkali source, so that the concentration of cations other than lithium is high and the concentration of lithium ions is low at the same time. As a result, the recovery rate of the target lithium is significantly reduced in the conventional wet process. Furthermore, in the conventional wet process, 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 a disadvantage that there is no technology to circulate and 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 can eliminate such inconveniences and recover lithium at a high recovery rate, preferably by reusing salts produced in the recovery process as mineral acids and alkalis 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 can recover lithium at a high recovery rate, preferably by reusing salts produced in the recovery process as mineral acids and alkalis in the process. [Means for solving the problem]

[0007] The present inventors have conducted extensive research in light of the above problems, and have found that it is possible to add at least one of sodium hydroxide and potassium hydroxide to a solution obtained by dissolving an active material powder in a mineral acid, and then separate the lithium salt aqueous solution from the at least one salt aqueous solution of sodium and potassium, and preferably electrolyze the separated at least one salt aqueous solution of sodium and potassium, thereby reusing the mineral acid and 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 an active material powder obtained by pretreating used lithium ion batteries with 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; an extraction step of extracting at least one of iron, aluminum, manganese, cobalt, and nickel contained in the active material powder with an organic solvent from the solution obtained in the alkali hydroxide adding step by solvent extraction; a nickel removal step of mixing a first aqueous solution of mixed alkali salt obtained in the extraction step with an alkali to remove nickel contained in the first aqueous solution of mixed alkali salt to obtain a second aqueous solution of mixed alkali salt; a separation step of separating a lithium salt and at least one salt of sodium and potassium from the second aqueous solution of mixed alkali salt; and a lithium recovery step of recovering lithium from the first aqueous solution of lithium salt obtained in the separation step. The extraction step includes a nickel extraction step of extracting nickel with an organic solvent. The present invention relates to a method for recovering lithium from used lithium ion batteries, the method comprising: The present invention preferably further comprises 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. The aqueous alkali metal hydroxide solution obtained in the second electrolysis step is preferably reused in at least one of the alkali metal hydroxide addition step, the extraction step, and the separation step. The lithium recovery step preferably includes a carbonation step of carbonating 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 an aqueous lithium hydroxide solution, an acid, and a second aqueous lithium salt solution that is more dilute than the first aqueous lithium salt solution. 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 chlorine obtained by electrolyzing the first lithium salt aqueous solution using an ion exchange membrane with hydrogen. 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. Effect 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 generated in the recovery process to be reused as mineral acids and alkalis in the process. [Brief description 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 used lithium ion batteries of the present invention. [Diagram 2] FIG. 2 is an explanatory diagram showing the configuration of another embodiment of the method for recovering lithium from used lithium ion batteries according to the present invention. [Diagram 3] FIG. 1 is an explanatory diagram showing the configuration of one embodiment of the lithium phosphate method. [Figure 4] FIG. 2 is an explanatory diagram showing the configuration of another embodiment of the lithium phosphate method. [Diagram 5] FIG. 2 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. [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 PREFERRED EMBODIMENTS

[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 dissolving step (STEP 1) of dissolving the active material powder 1 obtained by the pretreatment with 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 includes valuable metals such as lithium, iron, aluminum, cobalt, nickel, and manganese, a solution of the valuable metals included 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 metal hydroxide adding step (STEP 2) in which at least one selected from the group consisting of sodium hydroxide and potassium hydroxide is added to the solution of valuable metals obtained in the dissolution step. Figures 1 and 2 show a 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 at least one of the following: addition of at least one solid selected from the group consisting of sodium hydroxide and potassium hydroxide, addition of at least one selected from the group consisting of an aqueous sodium hydroxide solution and an aqueous potassium hydroxide solution, or a mixture thereof. The solution of valuable metals is neutralized in the alkali metal hydroxide adding step. Furthermore, iron hydroxide and aluminum hydroxide may be precipitated successively 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) of extracting at least one element selected from the group consisting of iron, aluminum, manganese, cobalt, and nickel contained in the active material powder 1 with an organic solvent by solvent extraction from the solution obtained in the alkali metal hydroxide addition step.

[0015] Lithium, sodium, manganese, cobalt, and nickel are contained in the solution of valuable metals neutralized in the alkali metal hydroxide addition step. If iron and aluminum are not removed in the alkali metal hydroxide addition step, they are also contained in the solution of valuable metals.

[0016] The extraction step includes a first extraction step of extracting iron, aluminum, manganese, cobalt, or nickel from the valuable metal solution with a first organic solvent, the pH of the homogeneous mixture of the valuable metal solution and the first organic solvent being adjusted by adding at least one alkali selected from the group consisting of sodium hydroxide and potassium hydroxide, and a first metal-containing organic phase and a first extraction residue are obtained in the first extraction step.

[0017] The extraction step may include a second extraction step of extracting valuable metals not extracted in the first extraction step 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 being adjusted by adding at least one alkali selected from the group consisting of sodium hydroxide and potassium hydroxide, and a second metal-containing organic phase and a second extraction residue are obtained in the second extraction step.

[0018] The extraction step may include third to fifth extraction steps for sequentially extracting the valuable metals that have not been extracted in the first and second extraction steps from the second extraction residue.

[0019] The organic solvent used in the extraction step may be, for example, bis(2-ethylhexyl) hydrogen phosphate, 2-ethylhexyl(2-ethylhexyl)phosphonate, or bis(2,4,4-trimethylpentyl)phosphinic acid. The organic solvent may be diluted with a hydrocarbon, such as kerosene.

[0020] The iron-containing organic phase, the aluminum-containing organic phase, the manganese-containing organic phase, the cobalt-containing organic phase, and the 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, and a first aqueous lithium salt solution is obtained.

[0021] The first lithium salt aqueous solution is mixed with an alkali, the pH of the aqueous solution is adjusted to preferably 8 to 14, more preferably 10 to 12, and a trace amount of nickel contained in the first lithium salt aqueous solution is removed as nickel hydroxide, to obtain a second mixed alkali salt aqueous solution (STEP 3-1). The alkali mixed with the first lithium salt aqueous solution preferably contains at least one selected from the group consisting of lithium, sodium, potassium, rubidium, cesium, and francium, more preferably contains at least one selected from the group consisting of lithium, sodium, and potassium, further preferably contains at least one selected from the group consisting of lithium, sodium, and potassium, and particularly preferably is lithium. The alkali may be a solid or an aqueous solution. Nickel hydroxide is separated from the second mixed alkali salt aqueous solution in a solid-liquid separation process such as filtration. A flocculant may be used in the solid-liquid separation process of nickel hydroxide.

[0022] The recovery method of the present invention includes a separation step (STEP 4) of separating each of a lithium salt and at least one salt selected from the group consisting of sodium and potassium from a second aqueous solution of mixed alkali metal salt containing lithium obtained in the nickel removal step and at least one salt 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 a lithium phosphate method, an evaporation concentration method, and a solvent extraction method.

[0023] <Lithium phosphate method> The lithium phosphate method will be described with reference to Figures 3 and 4. The lithium phosphate method includes a phosphorylation 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 in which the solid material is produced. The alkali metal hydroxide is preferably sodium hydroxide. Figures 3 and 4 show a case in which only sodium hydroxide is used as the alkali metal.

[0024] 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.

[0025] In the lithium phosphate method, the solid matter separated in the first solid-liquid separation step may be washed. The method includes a pH adjustment step (STEP C) of adding a mineral acid to a suspension obtained by suspending the solid matter 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 illustrated in FIGS. 3 and 4.

[0026] 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. An example of the second solid-liquid separation step is 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 aluminum phosphate separated from the solid and liquid may be reused in the phosphorylation step.

[0027] 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 increased.

[0028] 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, and a carbonation step (STEP 6a) described later is carried out (FIG. 3). In the at least one salt aqueous solution selected from the group consisting of sodium and potassium produced in the carbonation step, 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 are dissolved, and preferably the pH of the at least one salt aqueous solution selected from the group consisting of sodium and potassium is about 12. When hydrochloric acid is added to the at least one salt aqueous solution selected from the group consisting of sodium and potassium to adjust the pH to 5 or less, at least one salt selected from the group consisting of sodium carbonate and potassium carbonate is decomposed to generate carbon dioxide and water, and the aqueous solution is obtained in which at least one salt selected from the group consisting of sodium chloride and potassium chloride is dissolved. The aqueous solution may be concentrated in a concentration step (STEP 9) described later. FIG. 3 shows a case in which the concentration step is carried out.

[0029] 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) described below (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).

[0030] In the lithium phosphate method, the filtrate in which the alkali metal chloride is dissolved and which is separated in the first solid-liquid separation step may be concentrated in a concentration step (STEP 9) described below.

[0031] <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 selected from the group consisting of sodium salt and potassium salt, 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 the mixed salt of alkali metals. The separated at least one selected from the group consisting of sodium salt and potassium salt, such as at least one 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 later. The first aqueous solution of lithium salt from which at least one salt selected from the group consisting of sodium salt and potassium salt has been separated is preferably subjected to a pH adjustment step (STEP 5) described later, 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.

[0032] 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.

[0033] <Solvent extraction method> The pH of the homogeneous mixture of the lithium, at least one mixed salt aqueous solution selected from the group consisting of sodium and potassium, and the lithium extraction organic solvent is adjusted to preferably within the range of 5 to 9 by adding at least one alkali selected from the group consisting of sodium hydroxide and potassium hydroxide, and a lithium-containing organic phase and at least one salt aqueous solution selected from the group consisting of sodium and potassium are obtained as the extraction residue. An example of the lithium extraction organic solvent is bis(2-ethylhexyl) hydrogen phosphate. The lithium-containing organic phase is scrubbed with a mineral acid to recover a first lithium salt aqueous solution. The first lithium salt aqueous solution is preferably subjected to a pH adjustment step (STEP 5) described below, similar to the first lithium salt aqueous solution obtained by the lithium phosphate method, and is further subjected to a 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 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 concentrating step (STEP 9) described below. In addition, the first aqueous lithium salt solution is preferably subjected to a pH adjustment step (STEP 5) and a first concentrating step (STEP E) described below, similarly to the aqueous lithium salt solution obtained by the lithium phosphate method, and may be subjected to a first electrolysis step (STEP 6b) described below.

[0034] A second electrolysis step (STEP 7) described later is carried out in which the 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, from which lithium has been separated by extraction, is electrolyzed 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 later, preferably using a reverse osmosis membrane (RO membrane) or the like.

[0035] 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 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 adjusted to preferably 8 to 14, more preferably 10 to 11.

[0036] [Recovery of lithium] <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) 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 selected from the group consisting of sodium carbonate and potassium carbonate (excluding lithium carbonate) obtained in a carbon dioxide absorption step (STEP 8) of absorbing carbon dioxide into an aqueous solution 4 in which at least one selected from the group consisting of sodium hydroxide and potassium hydroxide is dissolved, obtained in a second electrolysis step described later, may be added to the first lithium salt aqueous solution.

[0037] The alkali metal of the alkali metal carbonate 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.

[0038] <First electrolysis step> The recovery method of the present invention includes, as another lithium recovery step, a first electrolysis step (STEP 6b) of electrolyzing 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) using an ion exchange membrane to obtain an aqueous lithium hydroxide solution.

[0039] The first electrolysis step can be carried out using, for example, an electrolytic cell 11 shown in FIG. The electrolytic cell 11 is equipped 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 equipped with the anode plate 12 and a cathode chamber 18 equipped with the cathode plate 13.

[0040] In the electrolytic cell 11, when the lithium salt aqueous solution in which lithium chloride is dissolved is supplied to the anode chamber 17 to perform electrolysis, 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.

[0041] In the cathode chamber 18, water (HO) 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.

[0042] The power required for the electrolysis is, for example, renewable energy, preferably at least one of solar power generation and wind power generation.

[0043] Hydrogen gas (H2) and chlorine gas (Cl2) generated in the first electrolysis step can be reacted to obtain hydrochloric acid. Although not shown in FIG. 5, when the lithium chloride aqueous solution contains sulfate ions, sulfuric acid can be obtained in the anode chamber 17. When 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 the mineral acid 5 can be used for at least one of dissolving the active material powder 1 in STEP 1 and adjusting the pH in STEP C.

[0044] (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.

[0045] (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 generate 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 performing 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 Figs. 2 and 4 show a case in which the lithium salt dissolved in the second lithium salt aqueous solution is lithium chloride.

[0046] <Second electrolysis process> The recovery method of the present invention includes a second electrolysis step (STEP 7) of electrolyzing the aqueous solution of at least one salt selected from the group consisting of sodium and potassium, in which at least one salt selected from the group consisting of sodium chloride and potassium chloride is dissolved, using an ion exchange membrane to obtain an aqueous solution of an alkali metal hydroxide. The second electrolysis step can be performed using, for example, an electrolytic cell 21 shown in FIG. 6.

[0047] 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 including the anode plate 22 and a cathode chamber 28 including the cathode plate 23.

[0048] 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 to perform electrolysis, 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 migrate to the cathode chamber 28 through the ion exchange membrane 26.

[0049] In the cathode chamber 28, water (HO) 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 aqueous alkali metal solution 4 is generated in which at least one ion selected from the group consisting of hydroxide ions, sodium ions, and potassium ions, and at least one ion selected from the group consisting of sodium hydroxide and potassium hydroxide, is dissolved.

[0050] The power required for the electrolysis is, for example, renewable energy, preferably at least one of solar power generation and wind power generation.

[0051] When the at least one aqueous salt solution selected from the group consisting of sodium and potassium contains chloride ions, hydrogen gas (H2) generated in the second electrolysis step can be reacted with chlorine gas (Cl2) to obtain hydrochloric acid. When the 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. When the 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 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.

[0052] The recovery method of the present invention may include a carbon dioxide absorption step (STEP 8) of absorbing carbon dioxide into the aqueous alkali metal hydroxide solution 4 in which at least one selected from the group consisting of sodium hydroxide and potassium hydroxide is dissolved, obtained in the second electrolysis step. 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).

[0053] The aqueous alkali metal hydroxide solution 4 generated in the second electrolysis step may be reused in at least one step selected from the group consisting of the alkali metal hydroxide addition step, the extraction step, the separation step using the lithium phosphate method, and the separation step using the solvent extraction method.

[0054] In the second electrolysis step, the 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, which 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 at least one 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. The concentration step can be performed, for example, using a reverse osmosis membrane (RO membrane). EXAMPLES

[0055] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these.

[0056] 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 spectrometry (ICP-OES) using an Optima 8300 manufactured by PerkinElmer.

[0057] Example 1 Used lithium ion batteries that had run out of life as battery products were discharged to discharge all remaining charges. The waste lithium ion batteries were then heated (roasted) and pulverized with a hammer mill, and the casings, current collectors, etc. constituting 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 solution was added to the obtained solution to neutralize the solution. 5.8 L of the neutralized solution was mixed with 5.8 L of bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex272, diluent kerosene) as an extractant, and cobalt was extracted with a solvent. 5 mol / L aqueous sodium hydroxide solution was added to the mixture to adjust the pH to 4, and a cobalt-containing organic phase and a first extraction residue were obtained. 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 that used in the cobalt extraction step, and an aqueous solution of lithium and sodium mixed salt was obtained as the residue. The aqueous solution contained 3.5 g / L of lithium and 38.2 g / L of sodium.

[0058] 187g of aluminum phosphate was added to 8.3L of the aqueous solution, and then sodium hydroxide was added to adjust the pH of the aqueous solution to 10.5, and 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 614g of a white cake A with a water content of 55%. The white cake A was suspended in 300mL of pure water, 35% by mass of hydrochloric acid was added to adjust the pH of the suspension to 2.5, and 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 467g of a white cake B with a water content of 60%, and a total of 1060mL of filtrate and washing water. Sodium hydroxide was added to the 1060mL of filtrate and washing water to adjust the pH to 7, and the filtrate was filtered, to which 680g of a 35% by mass aqueous sodium carbonate solution was added, 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 sodium content in the lithium carbonate was less than 200ppm, the aluminum content was less than 10ppm, the phosphorus content was less than 10ppm, and the water content was less than 0.1% by mass.

[0059] The filtrate and washing water (10.5 L, sodium chloride concentration: 98 g / L) obtained by filtering and washing the white slurry A 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 The electrolysis was carried out under the condition of current flow time of 4 hours, and 1.6 kg of 21.2 mass% sodium hydroxide was obtained. Furthermore, the reaction product of the generated chlorine gas and hydrogen gas was absorbed in water, and 1.04 kg of 30 mass% hydrochloric acid was also obtained. The sodium hydroxide produced in the electrolysis process was reusable 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 was reusable in the dissolution process (STEP 1). The current efficiency in the electrolysis process was 81.5%.

[0060] Example 2 Used lithium ion batteries that had run out of life as battery products were discharged to discharge all remaining charges. The waste lithium ion batteries were then heated (roasted) and pulverized with a hammer mill, and the casings, current collectors, etc. constituting 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 solution was added to the obtained solution to neutralize the solution. 5.8 L of the neutralized solution was mixed with 5.8 L of bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex272, diluent kerosene) as an extractant, and cobalt was extracted with a solvent. 5 mol / L aqueous sodium hydroxide solution was added to the mixture to adjust the pH to 4, and a cobalt-containing organic phase and a first extraction residue were obtained. 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 that used in the cobalt extraction step, and an aqueous solution of lithium and sodium mixed salt was obtained as the residue. The aqueous solution contained 3.5 g / L of lithium and 38.2 g / L of sodium.

[0061] 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, and 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 mass % of hydrochloric acid was added to adjust the pH of the suspension to 2.5, and 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. The 1,060 mL of filtrate and washing water were added with lithium hydroxide to adjust the pH to 7, and the filtrate (filtrate 1) was filtered to obtain 1,060 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 performed under the above conditions (first electrolysis step), and 1100 g of a 6.2 mass% lithium hydroxide aqueous solution was obtained. Furthermore, the reaction product of the generated chlorine gas and hydrogen gas was absorbed in water, and 350 g of 30 mass% hydrochloric acid was also obtained. The recovery rate of lithium in the first electrolysis step was 70.3%.

[0062] 380 g of the 6.2% by mass lithium hydroxide aqueous solution was taken, and 80% by mass of the aqueous solution was crystallized to obtain 19.3 g (mass after drying) of lithium hydroxide monohydrate crystals. 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.

[0063] The filtrate and washing water (10.5 L, sodium chloride concentration: 98 g / L) obtained by filtering and washing the white slurry A 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 2The electrolysis was carried out under the condition of current flow time of 4 hours, and 1.6 kg of 21.2 mass% sodium hydroxide was obtained. Furthermore, the reaction product of the generated chlorine gas and hydrogen gas was absorbed in water, and 1.04 kg of 30 mass% hydrochloric acid was also obtained. The sodium hydroxide produced in the electrolysis process was reusable 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 was reusable in the dissolution process (STEP 1). The current efficiency in the electrolysis process was 81.5%.

[0064] 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 recovering lithium from waste lithium-ion batteries and the recovery rate of lithium were very high.

[0065] 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 of the aqueous sodium / potassium salt solution. Since the mineral acid and alkali generated in the second electrolysis step can be recycled and reused in the recovery method of the present invention, a closed-loop recycle process can be realized. Furthermore, since the recovery method of the present invention preferably recycles the mineral acid and alkali, the amount of carbon dioxide emitted in the distribution process of the mineral acid and alkali can be reduced compared to the conventional case in which the mineral acid and alkali are purchased from outside. [Explanation of symbols]

[0066] 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 the steps of: A dissolving step of dissolving the active material powder obtained by pretreating the waste lithium ion batteries with 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; an extraction step of extracting at least one of iron, aluminum, manganese, cobalt, and nickel contained in the active material powder with an organic solvent by solvent extraction from the solution obtained in the alkali hydroxide addition step; a nickel removal step of mixing the first aqueous solution of mixed alkali salt obtained in the extraction step with an alkali to remove nickel contained in the first aqueous solution of mixed alkali salt to obtain a second aqueous solution of mixed alkali salt; a separation step of separating the lithium salt and at least one salt of sodium and potassium from the second aqueous alkali mixed salt solution; a lithium recovery step of recovering lithium from the first lithium salt aqueous solution obtained in the separation step, A method for recovering lithium from used lithium ion batteries, characterized in that the extraction step includes a nickel extraction step of extracting nickel with an organic solvent.

2. 2. The method for recovering lithium from used 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 used 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 used lithium ion batteries according to claim 1, wherein the lithium recovery step includes a carbonation step of carbonate 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 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.

6. 6. The method for recovering valuable metals from waste lithium ion batteries according to claim 5, further comprising the steps of: concentrating the second lithium salt aqueous solution and adding the concentrated solution to the first lithium salt aqueous solution.

7. 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 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. The method for recovering valuable metals from waste lithium ion batteries according to any one of claims 1 to 6, characterized in that hydrochloric acid produced by electrolyzing the first lithium salt aqueous solution using an ion exchange membrane and reacting chlorine and hydrogen therewith is used as the mineral acid.

10. 3. The method for recovering valuable metals from waste lithium-ion batteries according to claim 2, wherein the electricity used in the second electrolysis step is electricity obtained from renewable energy.

11. A method for recovering valuable metals from waste lithium ion batteries as described in claim 5, characterized in that the electricity used in the first electrolysis process is electricity obtained from renewable energy.

12. 12. The method for recovering valuable metals from waste lithium-ion batteries according to claim 10 or 11, 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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