Method for collecting lithium from lithium salt solution

Abstract

To provide a method for collecting lithium from a lithium salt aqueous solution, in which the concentration of the lithium salt aqueous solution to be subjected to a membrane electrolysis step can be made high and its composition can be kept constant, without using a large-size apparatus or consuming a large amount of energy.SOLUTION: A method for collecting lithium from a lithium salt aqueous solution includes: a concentration step for concentrating a first lithium salt aqueous solution; a post-membrane-electrolysis solution purification step for purifying a third lithium salt aqueous solution by adding a mineral acid; and a membrane electrolysis step for obtaining a lithium hydroxide aqueous solution, the mineral acid, and the third lithium salt aqueous solution, by performing membrane electrolysis on a second lithium salt aqueous solution obtained by mixing a fourth lithium salt aqueous solution acquired in the post-membrane-electrolysis solution purification step with the lithium salt aqueous solution obtained in the concentration step.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for recovering lithium from an aqueous lithium salt solution. [Background technology]

[0002] 2. Description of the Related Art 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] Cited Document 1 discloses a system for recovering lithium from waste lithium-ion batteries, the system including the steps of: dissolving active material powder obtained by pretreating waste lithium-ion batteries in a mineral acid to obtain an acid solution of the active material containing at least lithium; separating at least one metal other than lithium from the acid solution to which lithium hydroxide has been added by solvent extraction to obtain a first aqueous lithium salt solution as a residual solution of the solvent extraction; and performing membrane electrolysis of the first aqueous lithium salt solution 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. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 7060899 Summary of the Invention [Problem to be solved by the invention]

[0005] It is necessary to increase the concentration of the lithium salt aqueous solution to be subjected to the membrane electrolysis process and to keep its composition constant, but the lithium concentration of the lithium salt aqueous solution is not constant due to changes in the composition of the active material powder. As a means of realizing this, a method is considered in which water from the lithium salt aqueous solution is evaporated to obtain lithium salt crystals, and the crystals are added to the freshwater salt after membrane electrolysis to increase the lithium salt concentration of the lithium salt aqueous solution to be subjected to the membrane electrolysis process and keep its composition constant. However, evaporation of water requires large equipment and a large amount of energy.

[0006] An object of the present invention is to provide a method for recovering lithium from an aqueous lithium salt solution, which does not require a large-scale device or consumes a large amount of energy, can increase the concentration of the aqueous lithium salt solution to be subjected to a membrane electrolysis step, and can control the composition of the aqueous lithium salt solution to be constant. [Means for solving the problem]

[0007] The present inventors have conducted extensive research in light of the above problems, and have found that the above technical problems of the present invention can be solved by adding a mineral acid to a third lithium salt aqueous solution (a post-membrane electrolysis solution) obtained by membrane electrolysis of a lithium salt aqueous solution, purifying the solution to obtain a fourth lithium salt aqueous solution, and mixing the concentrated lithium salt aqueous solution with the fourth lithium salt aqueous solution to obtain a second lithium salt aqueous solution, thereby performing membrane electrolysis. The present invention has been completed based on these findings.

[0008] The present invention relates to a method for recovering lithium from an aqueous lithium salt solution, the method including: a concentrating step of concentrating a first aqueous lithium salt solution; a post-membrane electrolysis solution refining step of refining a third aqueous lithium salt solution by adding a mineral acid; and a membrane electrolysis step of performing membrane electrolysis on a second aqueous lithium salt solution obtained by mixing a fourth aqueous lithium salt solution obtained in the post-membrane electrolysis solution refining step with the aqueous lithium salt solution obtained in the concentrating step to obtain an aqueous lithium hydroxide solution, a mineral acid, and the third aqueous lithium salt solution. The sum of the mass of water in the first lithium salt aqueous solution and the mass of water contained in the mineral acid added in the membrane electrolysis post-solution purification step is preferably equal to or greater than the sum of the mass of water separated in the concentration step and the mass of water accompanying the lithium ions moving in the membrane electrolysis. The solute of each of the first to fourth aqueous lithium salt solutions preferably contains lithium chloride. The mineral acid added to the third aqueous lithium salt solution preferably comprises hydrochloric acid. Effect of the Invention

[0009] The method for recovering lithium from an aqueous lithium salt solution of the present invention provides a method for recovering lithium from an aqueous lithium salt solution, which does not require a large-scale device, does not consume a large amount of energy, increases the concentration of the aqueous lithium salt solution to be subjected to a membrane electrolysis step, and enables the composition of the aqueous lithium salt solution to be controlled to be constant. [Brief description of the drawings]

[0010] [Figure 1] FIG. 2 is an explanatory diagram showing a method for recovering lithium from an aqueous lithium salt solution according to the present invention. [Diagram 2] FIG. 1 is an explanatory cross-sectional view showing one embodiment of the structure of an ion exchange membrane electrolytic cell used in the method of recovering lithium from an aqueous lithium salt solution of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The present invention will now be described in further detail. In addition, unless otherwise specified, "~" in a numerical range means from above to below, and both ends of the range are included. In addition, when a numerical range is indicated, the upper limit and the lower limit can be appropriately combined, and the numerical range obtained by combining them is also disclosed. In addition, in the description of the drawings, the same elements are denoted by the same reference numerals, and duplicated description will be omitted. Also, the dimensional ratios of the drawings are exaggerated for the convenience of explanation, and may differ from the actual ratios.

[0012] The invention will now be described in more detail with reference to the drawings. The method of the present invention for recovering lithium from an aqueous lithium salt solution (hereinafter sometimes referred to as the "recovery method of the present invention") starts with active material powder 1 as shown in FIG.

[0013] When the waste lithium ion battery is a used lithium ion battery whose life as a battery product has expired, or a lithium ion battery that has been discarded as a defective product in the manufacturing process, the active material powder 1 is first subjected to a discharge treatment. Various highly safe methods such as resistance discharge can be adopted for the discharge treatment. After discharging all remaining charges by discharging, and then forming an opening in the housing of the waste lithium ion battery, for example, heat treatment (roasting) at a temperature in the range of 100 to 800 ° C. or without heat treatment, the battery is crushed with a crusher such as a hammer mill or a jaw crusher, and the housing, current collector, etc. constituting the waste lithium ion battery are removed by sieving (classification), thereby obtaining the active material powder 1. Alternatively, the waste lithium ion battery after the discharge treatment may be crushed with the crusher, the housing, current collector, etc. are removed by sieving, and then the active material powder 1 may be obtained by heat treatment at a temperature in the range.

[0014] When the waste lithium ion batteries are residual positive electrode materials or the like used in commercialization in a manufacturing process, the waste lithium ion batteries may be pulverized in the pulverizer after being heat-treated at a temperature in the above range or without being heat-treated without being subjected to the discharge treatment and the formation of openings, and the current collectors and the like may be removed by sieving to obtain the active material powder 1. Furthermore, the waste lithium ion batteries may be pulverized in the pulverizer, the current collectors and the like may be removed by sieving, and the active material powder 1 may be obtained by being heat-treated at a temperature in the above range or without being heat-treated.

[0015] In the recovery method of the present invention, next, in STEP 1, the active material powder 1 is dissolved in a mineral acid to obtain an acid solution of the active material powder 1 containing at least lithium. The mineral acid contains at least one selected from the group consisting of hydrochloric acid, sulfuric acid, and nitric acid, preferably hydrochloric acid, and more preferably hydrochloric acid. In addition to lithium, the active material powder 1 contains valuable metals such as iron, aluminum, manganese, cobalt, and nickel.

[0016] Next, in STEP 2, lithium hydroxide (LiOH) is added to the acid solution to neutralize the mineral acid. The neutralized acid solution is then subjected to solvent extraction in STEP 3. In the solvent extraction, manganese, cobalt, and nickel, excluding lithium, among the valuable metals are each extracted with a solvent, or iron and aluminum are separated and removed as their respective metal salt aqueous solutions 2, thereby obtaining a first lithium salt aqueous solution. When hydrochloric acid is used in the acid dissolution in STEP 1, the lithium salt contained in the first lithium salt aqueous solution becomes lithium chloride.

[0017] The recovery method of the present invention includes a concentration step (STEP 4) of concentrating the first lithium salt aqueous solution. The concentration method includes at least one selected from the group consisting of an electrodialysis method, a reverse osmosis membrane method, and an evaporation concentration method. The concentrated lithium salt aqueous solution obtained in the concentration step is mixed with a fourth lithium salt aqueous solution described below to obtain a second lithium salt aqueous solution.

[0018] The condensed water obtained in the concentration step may be reused in a series of steps included in the recovery method of the present invention as at least one dilution water selected from the group consisting of the dilution water of the acid used in STEP 1, the mineral acid obtained in the membrane electrolysis step described below, and an aqueous lithium hydroxide solution.

[0019] The recovery method of the present invention includes a membrane electrolysis step (STEP 5) of performing membrane electrolysis on the second lithium salt aqueous solution to obtain a lithium hydroxide aqueous solution, a mineral acid, and a third lithium salt aqueous solution. The membrane electrolysis in STEP 5 can be performed, for example, using a membrane electrolytic cell 11 shown in Fig. 2. The lithium concentration in the third lithium salt aqueous solution is lower than the lithium concentration in the second lithium salt aqueous solution.

[0020] The membrane electrolytic cell 11 is provided with an anode plate 12 on one of its inner surfaces and a cathode plate 13 on its 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 membrane electrolytic cell 11 is also partitioned by an ion exchange membrane 16 into an anode chamber 17 including the anode plate 12 and a cathode chamber 18 including the cathode plate 13.

[0021] In the membrane electrolysis cell 11, when, for example, lithium chloride is supplied as the first lithium salt aqueous solution to the anode chamber 17 to perform membrane electrolysis, chloride ions generate chlorine gas (Cl2) on the anode plate 12, while lithium ions move to the cathode chamber 18 through the ion exchange membrane 16. As the lithium ions move, water accompanying the lithium ions (the amount of water that moves is proportional to the amount of lithium ions that move) also moves to the cathode chamber 18 through the ion exchange membrane 16.

[0022] 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 combine with lithium to generate a lithium hydroxide aqueous solution 3.

[0023] When the lithium salt aqueous solution subjected to the membrane electrolysis process contains sulfate ions, sulfuric acid can be obtained in the anode chamber 17. When the lithium salt aqueous solution subjected to the membrane electrolysis process contains nitrate ions, nitric acid can be obtained in the anode chamber 17. That is, mineral acid 4 can be obtained in the membrane electrolysis process, and the mineral acid 4 can be used to dissolve the active material powder 1 in STEP 1.

[0024] The lithium hydroxide aqueous solution 3 obtained in the membrane electrolysis step can be recovered as lithium hydroxide monohydrate (LiOH·H2O) by crystallization in STEP 7, or can be recovered as lithium carbonate (Li2CO3) by carbonation in STEP 8. The carbonation can be performed by reacting the lithium hydroxide aqueous solution 3 with carbon dioxide gas (CO2).

[0025] In the recovery method of the present invention, a part of the lithium hydroxide aqueous solution 3 obtained in the membrane electrolysis step may be used as at least one selected from the group consisting of the lithium hydroxide added to the acid dissolution solution in STEP 2 and the alkali used for solvent extraction in STEP 3.

[0026] When the lithium hydroxide aqueous solution 3 is used for solvent extraction in STEP 3, the lithium hydroxide aqueous solution 3 is added to the extraction solvent. Since the extraction solvent used for solvent extraction in STEP 3 is a cation exchange extractant, if it is used continuously, the liquid tends to become acidic and the extraction rate decreases. However, by adding the lithium hydroxide aqueous solution 3, the decrease in the extraction rate can be suppressed.

[0027] When the lithium hydroxide aqueous solution 3 is used for solvent extraction in STEP 3, the lithium hydroxide aqueous solution 3 can be used for at least one of the solvent extractions of manganese, cobalt, and nickel, which are performed separately.

[0028] In the membrane electrolysis step, the second lithium salt aqueous solution is subjected to the membrane electrolysis step, and as a result, a third lithium salt aqueous solution that is more dilute than the second lithium salt aqueous solution is produced.

[0029] The recovery method of the present invention includes a post-membrane electrolysis solution refining step (STEP 6) of obtaining a fourth lithium salt aqueous solution by adding a mineral acid to the third lithium salt aqueous solution. In the third lithium salt aqueous solution, chlorate is generated from chlorine generated as an impurity by the membrane electrolysis and hydroxide ions moving through the ion exchange membrane 16. In the post-membrane electrolysis solution refining step, chlorine and chlorate in the third lithium salt aqueous solution are decomposed and removed. Another preferred method for treating the chlorate salt contained in the third lithium salt aqueous solution is disclosed in Japanese Patent No. 3304221. The electrolysis method, which involves introducing an electrolyte that generates protons in a cathode chamber of an electrolytic cell separated by a cation exchange membrane, can reduce the amount of hydrochloric acid to be added.

[0030] The mineral acid added to the third aqueous lithium salt solution preferably comprises hydrochloric acid, more preferably is hydrochloric acid.

[0031] By mixing the concentrated lithium salt aqueous solution obtained in the concentration step with the fourth lithium salt aqueous solution, the lithium concentration in the second lithium salt aqueous solution obtained by the mixing can be increased and the composition of the aqueous solution can be made constant. As a result, the recovery method of the present invention does not require a large-scale evaporator and can reduce energy consumption.

[0032] In the recovery method of the present invention, the mass A of water in the first lithium salt aqueous solution, the mass B of water contained in the mineral acid added in the membrane electrolysis post-solution purification step, the mass C of water separated in the concentration step, and the mass D of water accompanying the lithium ions moving in the membrane electrolysis are preferably adjusted so as to satisfy the following formula (1), whereby the lithium salt concentration of the lithium salt aqueous solution to be subjected to the membrane electrolysis step can be increased and its composition can be controlled to be constant. A+B≧C+D (1) [Explanation of symbols]

[0033] 1...active material powder, 2...metal salt aqueous solution, 3...lithium hydroxide aqueous solution, 4...mineral acid, 11...membrane electrolytic cell, 16...ion exchange membrane, 17...anode chamber, 18...cathode chamber.

Claims

1. 1. A method for recovering lithium from an aqueous lithium salt solution, comprising the steps of: A step of concentrating the first aqueous lithium salt solution; A method for recovering lithium from an aqueous lithium salt solution, comprising: a post-membrane electrolysis solution refining step of refining a third aqueous lithium salt solution by adding a mineral acid; and a membrane electrolysis step of performing membrane electrolysis on a second aqueous lithium salt solution obtained by mixing a fourth aqueous lithium salt solution obtained in the post-membrane electrolysis solution refining step with the aqueous lithium salt solution obtained in the concentration step to obtain an aqueous lithium hydroxide solution, a mineral acid, and the third aqueous lithium salt solution.

2. 2. The method for recovering lithium from a lithium salt aqueous solution according to claim 1, wherein the sum of the mass of water in the first lithium salt aqueous solution and the mass of water contained in the mineral acid added in the membrane electrolysis post-solution purification step is equal to or greater than the sum of the mass of water separated in the concentration step and the mass of water accompanying the lithium ions moving in the membrane electrolysis.

3. 2. The method for recovering lithium from an aqueous lithium salt solution according to claim 1, wherein the solute of each of the first to fourth aqueous lithium salt solutions contains lithium chloride.

4. The method for recovering lithium from a lithium salt aqueous solution according to any one of claims 1 to 3, wherein the mineral acid added to the third lithium salt aqueous solution contains hydrochloric acid.

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