Method for treating diluted brine after lithium film electrolysis

Abstract

To provide a method of treating weak saline water after lithium membrane electrolysis, capable of preventing deterioration of the quality of sodium hydroxide and deterioration of a facility.SOLUTION: The method of treating weak saline water after lithium membrane electrolysis, includes: a first membrane electrolysis step of subjecting a first aqueous lithium chloride solution to membrane electrolysis, to obtain an aqueous lithium hydroxide solution, hydrochloric acid, and a second aqueous lithium chloride solution weaker than the first aqueous lithium chloride solution; and a second membrane electrolysis step of subjecting an aqueous lithium chloride solution containing the chlorate generated in the first membrane electrolysis step to membrane electrolysis.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for treating diluted brine after lithium membrane electrolysis.

Background Art

[0002] In recent years, with the popularization of lithium-ion batteries, methods for recovering valuable metals such as cobalt, nickel, manganese, and lithium from waste lithium-ion batteries and reusing them as materials for lithium-ion batteries have been studied.

[0003] Citation Document 1 discloses a lithium recovery system from waste lithium-ion batteries, which includes a step of dissolving the active material powder obtained by pretreating waste lithium-ion batteries in a mineral acid to obtain an acid-dissolved solution of the active material containing at least lithium, a step of separating at least one metal other than lithium from the acid-dissolved solution added with lithium hydroxide by solvent extraction to obtain a first lithium salt aqueous solution as the residual liquid of the solvent extraction, and a step of subjecting the first lithium salt aqueous solution to membrane electrolysis using an ion exchange membrane to obtain an aqueous lithium hydroxide solution, an acid, and a second lithium salt aqueous solution that is more dilute than the first lithium salt aqueous solution.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the membrane electrolysis of an aqueous lithium chloride solution, there has been a growing demand for preventing the deterioration of the quality of lithium hydroxide generated by membrane electrolysis and the deterioration of equipment.

[0006] Therefore, the problem to be solved by the present invention is to provide a method for treating diluted brine after lithium membrane electrolysis that prevents the deterioration of the quality of lithium hydroxide and the deterioration of equipment.

Means for Solving the Problems

[0007] In view of the above problems, the present inventors have conducted extensive studies and found that chlorate is one of the causes of the deterioration of the quality of lithium hydroxide and the deterioration of equipment in the membrane electrolysis of an aqueous lithium chloride solution, that chlorate is generated and accumulated by hydroxide ions that back-diffuse from the cathode chamber, and that the accumulation of chlorate can be prevented by subjecting a lithium salt aqueous solution containing chlorate generated in the membrane electrolysis step of an aqueous lithium chloride solution to membrane electrolysis. The present invention has been completed based on these findings.

[0008] The present invention relates to a method for treating the dilute brine after lithium membrane electrolysis, which includes a first membrane electrolysis step of subjecting a first aqueous lithium chloride solution to membrane electrolysis to obtain an aqueous lithium hydroxide solution, hydrochloric acid, and a second aqueous lithium chloride solution that is more dilute than the first aqueous lithium chloride solution, and a second membrane electrolysis step of subjecting a lithium chloride aqueous solution containing 、 containing chlorate chlorate to membrane electrolysis. the salt chlorate to membrane electrolysis. second chlorate to membrane electrolysis.

[0009] Preferably, the method for treating the dilute brine after lithium membrane electrolysis further includes an acid dissolution step of dissolving a lithium-containing solid in hydrochloric acid to obtain an acid dissolution solution, a neutralization step of adding lithium hydroxide to the acid dissolution solution, and a solvent extraction step of separating at least one metal excluding lithium from the acid dissolution solution obtained in the neutralization step by solvent extraction to obtain the first aqueous lithium chloride solution as the residual liquid of the solvent extraction. A part of the aqueous lithium hydroxide solution is used as the lithium hydroxide used in at least one selected from the group consisting of the neutralization step and the solvent extraction step, and the hydrochloric acid generated in the first membrane electrolysis step is used in the acid dissolution step. Preferably, the method for treating the dilute brine after lithium membrane electrolysis further includes a mixing and concentration step of mixing a part of the second aqueous lithium chloride solution and the first aqueous lithium chloride solution and concentrating them to obtain a third aqueous lithium chloride solution. The third lithium chloride aqueous solution is preferably subjected to membrane electrolysis using an ion exchange membrane, and hydrochloric acid produced by reacting the obtained chlorine and hydrogen is used in the acid dissolution step. The electric power used for at least one selected from the group consisting of the first membrane electrolysis step and the second membrane electrolysis step preferably includes electric power obtained by renewable energy. The electric power obtained by the renewable energy preferably includes electric power obtained by at least one selected from the group consisting of solar power generation, wind power generation, hydraulic power generation, and biomass power generation. Preferably, a part of the chlorate is decomposed in the second membrane electrolysis step, and the lithium chloride aqueous solution containing the chlorate subjected to the second membrane electrolysis step is returned to the first membrane electrolysis step.

Advantages of the Invention

[0010] The method for treating the fresh brine after lithium membrane electrolysis of the present invention provides a method for treating the fresh brine after lithium membrane electrolysis, which prevents deterioration of the quality of lithium hydroxide and deterioration of equipment.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0012] The present invention will be described in more detail. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant descriptions are omitted. Also, the dimensional ratios in the drawings are exaggerated for the convenience of explanation and may be different from the actual ratios.

[0013] The embodiments of the present invention will be described in more detail with reference to the accompanying drawings. As shown in FIG. 1, the method for treating light brine after lithium film electrolysis in the embodiment (FIG. 1) may use the lithium-containing substance 1 as a starting material. The lithium-containing substance 1 may be an active material powder.

[0014] The active material powder will be described. When the waste lithium-ion battery is a used lithium-ion battery whose battery life as a battery product has expired, or a lithium-ion battery discarded as a defective product or the like in the manufacturing process, first, a discharge treatment is performed. For the discharge treatment, various highly safe methods such as resistance discharge can be adopted. By discharging, all the remaining charges are discharged, and then, after forming an opening in the casing of the waste lithium-ion battery, for example, after heat treatment (roasting) at a temperature in the range of 100 to 800 ° C, or without heat treatment, it is pulverized with a pulverizer such as a hammer mill or a jaw crusher, and the active material powder can be obtained by removing (classifying) the casing, current collector, etc. constituting the waste lithium-ion battery by sieving. Alternatively, after pulverizing the waste lithium-ion battery after the discharge treatment with the pulverizer and removing the casing, current collector, etc. by sieving, the active material powder may be obtained by heat treatment at the temperature in the above range.

[0015] When the waste lithium-ion battery is the remaining positive electrode material or the like used for productization in the manufacturing process, without performing the discharge treatment and the formation of the opening, after heat treatment at the temperature in the above range, or without heat treatment, it is pulverized with the pulverizer, and the current collector, etc. are removed by sieving to obtain the active material powder. Further, the waste lithium-ion battery may be pulverized with the pulverizer, the current collector, etc. are removed by sieving, and then heat treatment is performed at the temperature in the above range, or the active material powder may be obtained without heat treatment.

[0016] Furthermore, the lithium-containing substance 1 may be spodumene, which is a kind of silicate mineral containing lithium and aluminum.

[0017] <Acid Dissolution Step> In an embodiment, next, in STEP1, the lithium-containing substance 1 is dissolved in hydrochloric acid to obtain at least an acid dissolution solution of the lithium-containing substance 1. The lithium-containing substance 1 may contain valuable metals such as iron, aluminum, manganese, cobalt, and nickel in addition to the lithium.

[0018] <Neutralization Step> In an embodiment, the acid dissolution solution is then neutralized by adding lithium hydroxide (LiOH) in STEP2.

[0019] <Extraction Step> The acid dissolution solution after the neutralization is then subjected to solvent extraction in STEP3. In the solvent extraction, among the valuable metals, manganese, cobalt, and nickel excluding lithium are separately solvent-extracted, or iron and aluminum are separated and removed as respective metal sulfate aqueous solutions 2, and a first lithium chloride aqueous solution can be obtained.

[0020] Examples of the organic solvent used in the extraction step include bis(2-ethylhexyl) hydrogen phosphate, 2-ethylhexyl(2-ethylhexyl) phosphonate, and bis(2,4,4-trimethylpentyl) phosphinic acid. The organic solvent may be diluted with a hydrocarbon such as kerosene.

[0021] Back-extraction with sulfuric acid is carried out for each of the iron-containing organic phase, aluminum-containing organic phase, manganese-containing organic phase, cobalt-containing organic phase, and nickel-containing organic phase, and metal sulfate (iron sulfate, aluminum sulfate, manganese sulfate, cobalt sulfate, and nickel sulfate) aqueous solutions 2 are recovered.

[0022] In another embodiment of the present invention, the lithium-containing substance 1 may be brine derived from at least one selected from the group consisting of salt lakes, seawater, and brackish water, more preferably brine derived from a salt lake. At least one of calcium, magnesium, and boron may be removed from the brine. The removal is carried out, for example, by the method disclosed in Japanese Patent No. 6122944. That is, at least one of an alkali metal hydroxide and its aqueous solution is mixed with the brine, and magnesium can be produced as magnesium hydroxide. At this time, the pH of the brine mixed with the alkali metal hydroxide is maintained at 8.5 to 10.5, and boron (for example, boron ions) can be adsorbed on magnesium hydroxide to coprecipitate magnesium and boron. In order to separate magnesium hydroxide on which boron is adsorbed and precipitated from the brine, magnesium and boron are simultaneously recovered by solid-liquid separation such as filtration, and a filtrate is obtained. An alkali metal hydroxide or an alkali metal carbonate (for example, NaOH or a carbonate alone or in combination) is mixed with the filtrate, and the pH of the filtrate is maintained at 12 or more to precipitate calcium. Calcium hydroxide or calcium carbonate precipitates depending on the type of the alkali metal hydroxide or the alkali metal carbonate mixed with the filtrate, and calcium is removed from the brine, and a first lithium chloride aqueous solution can be obtained. The alkali metal of the alkali metal hydroxide includes at least one of lithium, sodium, potassium, rubidium, cesium, and francium. The alkali metal preferably includes at least one of lithium, sodium, and potassium, and more preferably lithium.

[0023] <First membrane electrolysis step> Next, the two embodiments include a first membrane electrolysis step of membrane-electrolyzing the first lithium chloride aqueous solution using an ion exchange membrane in STEP4. The first membrane electrolysis step of STEP4 can be carried out, for example, using the membrane electrolysis cell 11 shown in FIG. 2.

[0024] The membrane electrolysis cell 11 is provided with an anode plate 12 on one inner surface, a cathode plate 13 on the inner surface facing 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. Further, the membrane electrolysis cell 11 is partitioned by an ion exchange membrane 16 into an anode chamber 17 provided with the anode plate 12 and a cathode chamber 18 provided with the cathode plate 13.

[0025] In the membrane electrolysis cell 11, when the first lithium chloride aqueous solution is supplied to the anode chamber 17 for 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.

[0026] In the cathode chamber 18, water (H2O) ionizes into hydroxide ions (OH - ) and hydrogen ions (H + ), hydrogen ions generate hydrogen gas (H2) on the cathode plate 13, while hydroxide ions combine with lithium to generate an aqueous lithium hydroxide solution 3.

[0027] The electric power used in the first membrane electrolysis step preferably includes electric power obtained from renewable energy, more preferably includes electric power obtained by at least one selected from the group consisting of solar power generation, wind power generation, hydraulic power generation, and biomass power generation.

[0028] In the above embodiment, hydrochloric acid 4 can be obtained by reacting the hydrogen gas (H2) and chlorine gas (Cl2) generated in the first membrane electrolysis step, and the hydrochloric acid 4 can be used for dissolving the solid 1 in STEP1.

[0029] <Recovery of Lithium> The lithium in the lithium hydroxide aqueous solution 3 obtained by the first membrane electrolysis step can be recovered as lithium hydroxide monohydrate (LiOH·H2O) by crystallization in STEP5, and can also be recovered as lithium carbonate (Li2CO3) by carbonation in STEP6. The carbonation can be carried out by reacting the lithium hydroxide aqueous solution 3 with carbon dioxide gas (CO2). The lithium chloride aqueous solution obtained by solid-liquid separation of the slurry obtained in the carbonation step by filtration or the like may be concentrated in STEP7 described later.

[0030] When the lithium hydroxide aqueous solution 3 is used for solvent extraction in STEP3, the lithium hydroxide aqueous solution 3 is added to the extraction solvent. Since the extraction solvent used for solvent extraction in STEP3 is a cation exchange extractant, if it is continuously used, the liquid property will be biased to the acidic side and the extraction rate will decrease. However, by adding the lithium hydroxide aqueous solution 3, a decrease in the extraction rate can be suppressed.

[0031] Also, when the lithium hydroxide aqueous solution 3 is used for solvent extraction in STEP3, the lithium hydroxide aqueous solution 3 may be used for at least one of the solvent extractions of manganese, cobalt, and nickel performed separately.

[0032] In the first membrane electrolysis step, as a result of membrane electrolysis of the first lithium chloride aqueous solution, a second lithium chloride aqueous solution that is more dilute than the first lithium chloride aqueous solution is generated. Therefore, in the embodiment, a part of the second lithium chloride aqueous solution and the first lithium chloride aqueous solution may be mixed and concentrated in STEP7 to obtain a third lithium chloride aqueous solution. The concentration in STEP7 can be carried out using at least one selected from the group consisting of, for example, a reverse osmosis membrane (RO membrane) and evaporation concentration.

[0033] <Second Membrane Electrolysis Step> In the first electrolysis step, chlorate is generated and accumulated by the hydroxide ions that migrate backward from the cathode chamber 18. The accumulated chlorate causes deterioration of the quality of the alkali metal hydroxide and deterioration of the equipment in the membrane electrolysis of the aqueous alkali metal hydroxide solution. Therefore, the embodiment includes a second membrane electrolysis step of subjecting the lithium chloride aqueous solution containing chlorate generated in the first membrane electrolysis step to membrane electrolysis.

[0034] A part of the lithium chloride aqueous solution containing chlorate in the anode chamber 17 is subjected to the second membrane electrolysis step. The second membrane electrolysis step can be carried out, for example, using the membrane electrolysis cell 21 shown in FIG. 3.

[0035] The membrane electrolysis cell 21 is provided with an anode plate 22 on one inner surface, a cathode plate 23 on the inner surface facing 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. Further, the membrane electrolysis cell 21 is partitioned by an ion exchange membrane 26 into an anode chamber 27 provided with the anode plate 22 and a cathode chamber 28 provided with the cathode plate 23.

[0036] In the membrane electrolysis cell 21, when dilute sulfuric acid is supplied to the anode chamber 27 for membrane electrolysis, water (H2O) ionizes into hydroxide ions (OH - ) and hydrogen ions (H + ), and oxygen gas (O2) is generated on the anode plate 22. On the other hand, hydrogen ions (H + ) move to the cathode chamber 28 through the ion exchange membrane 26, and the reaction represented by the following formula (1) occurs. 3H2O→1.5O2+6H + +6e - (1)

[0037] In the cathode chamber 28, the lithium chloride aqueous solution containing the chlorate is supplied, and the chlorate reacts with water to generate lithium chloride and hydroxide ions (OH - ), and the reaction represented by the following formula (2) occurs. LiClO3+3H2O+6e - →LiCl+6OH - (2) Hydrogen ions (H + ) that have moved from the anode chamber 27 are neutralized with the generated hydroxide ions (OH - ).

[0038] The electric power used in the second membrane electrolysis step preferably includes electric power obtained from renewable energy, more preferably includes electric power obtained by at least one selected from the group consisting of solar power generation, wind power generation, hydraulic power generation, and biomass power generation.

[0039] The lithium chloride aqueous solution containing chlorate, in which the chlorate is decomposed and its concentration is reduced in the second membrane electrolysis step, is returned to the anode chamber 17 of the electrolytic cell 11 used in the first membrane electrolysis step.

Explanation of Symbols

[0040] 1... Substance containing lithium, 2... Aqueous solution of metal sulfate 3... Aqueous solution of lithium hydroxide, 3A... Lithium hydroxide monohydrate, 4... Hydrochloric acid 4A... Aqueous solution of alkali metal hydroxide, 5... Hydrochloric acid, 6... Lithium 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 treating diluted brine after lithium membrane electrolysis, comprising: a first membrane electrolysis step of subjecting a first lithium chloride aqueous solution to membrane electrolysis to obtain an aqueous lithium hydroxide solution, hydrochloric acid, and a second lithium chloride aqueous solution containing chlorate and being more dilute than the first lithium chloride aqueous solution; and a second membrane electrolysis step of subjecting the second lithium chloride aqueous solution containing chlorate to membrane electrolysis.

2. The method for treating diluted brine after lithium membrane electrolysis according to claim 1, further comprising: an acid dissolution step of dissolving a lithium-containing solid in hydrochloric acid to obtain an acid dissolution solution; a neutralization step of adding lithium hydroxide to the acid dissolution solution; and a solvent extraction step of separating at least one metal excluding lithium from the acid dissolution solution obtained in the neutralization step by solvent extraction, and obtaining the first lithium chloride aqueous solution as a residual solution of the solvent extraction. A part of the aqueous lithium hydroxide solution is used as the lithium hydroxide used in at least one selected from the group consisting of the neutralization step and the solvent extraction step, and the hydrochloric acid generated in the first membrane electrolysis step is used in the acid dissolution step.

3. The method for treating diluted brine after lithium membrane electrolysis according to claim 1 or 2, further comprising a mixing and concentration step of mixing a part of the second lithium chloride aqueous solution and the first lithium chloride aqueous solution and concentrating them to obtain a third lithium chloride aqueous solution.

4. The method for treating diluted brine after lithium membrane electrolysis according to claim 2, wherein hydrochloric acid generated by reacting chlorine and hydrogen obtained by subjecting the first lithium chloride aqueous solution to membrane electrolysis using an ion exchange membrane is used in the acid dissolution step.

5. The method for treating diluted brine after lithium membrane electrolysis according to claim 1 or 2, wherein the electric power used in at least one selected from the group consisting of the first membrane electrolysis step and the second membrane electrolysis step includes electric power obtained from renewable energy.

6. The method for treating diluted brine after lithium membrane electrolysis according to claim 5, wherein the electric power obtained from renewable energy includes electric power obtained from at least one selected from the group consisting of solar power generation, wind power generation, hydraulic power generation, and biomass power generation.

7. In the method for treating diluted brine after lithium membrane electrolysis according to Claim 1 or 2, a part of the chlorate is decomposed in the second membrane electrolysis step, and the lithium chloride aqueous solution containing the chlorate subjected to the second membrane electrolysis step is returned to the first membrane electrolysis step. A method for treating diluted brine after lithium membrane electrolysis.

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