Method of treating weak saline water after lithium membrane 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 fresh salt water after lithium membrane electrolysis. [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 Publication Summary of the Invention [Problem to be solved by the invention]

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

[0006] Therefore, an object of the present invention is to provide a method for treating fresh salt water after lithium membrane electrolysis, which can prevent deterioration of the quality of lithium hydroxide and deterioration of the equipment. [Means for solving the problem]

[0007] The present inventors have conducted extensive research in light of the above problems and have found that chlorate is one of the causes of deterioration of the quality of lithium hydroxide and deterioration of equipment in the membrane electrolysis of a lithium chloride aqueous solution, that chlorate is generated and accumulated by hydroxide ions that migrate backward from the cathode chamber, and that the accumulation of chlorate can be prevented by performing membrane electrolysis on a lithium salt aqueous solution that contains chlorate generated in the membrane electrolysis process of a lithium chloride aqueous solution.The present invention has been completed based on these findings.

[0008] The present invention relates to a method for treating fresh salt water after lithium membrane electrolysis, comprising: a first membrane electrolysis step of performing membrane electrolysis on a first lithium chloride aqueous solution to obtain a lithium hydroxide aqueous solution, hydrochloric acid, and a second lithium chloride aqueous solution that is more dilute than the first lithium chloride aqueous solution; and a second membrane electrolysis step of performing membrane electrolysis on a lithium chloride aqueous solution containing chlorate generated in the first membrane electrolysis step.

[0009] The method for treating fresh brine after lithium membrane electrolysis preferably further includes an acid dissolution step of dissolving a lithium-containing solid with hydrochloric acid to obtain an acid solution, a neutralization step of adding lithium hydroxide to the acid solution, and a solvent extraction step of separating at least one metal other than lithium from the acid solution obtained in the neutralization step by solvent extraction to obtain the first lithium chloride aqueous solution as a residual solution of the solvent extraction, wherein a part of the lithium hydroxide aqueous solution is used as lithium hydroxide used in at least one selected from the group consisting of the neutralization step and the solvent extraction step, and hydrochloric acid generated in the first membrane electrolysis step is used in the acid dissolution step. The method for treating fresh salt water after lithium membrane electrolysis preferably further includes a mixing and concentrating step of mixing a part of the second lithium chloride aqueous solution with the first lithium chloride aqueous solution and concentrating the mixture to obtain a third lithium chloride aqueous solution. The third lithium chloride aqueous solution is preferably subjected to membrane electrolysis using an ion exchange membrane, and the resulting chlorine is reacted with hydrogen to produce hydrochloric acid, which is used in the acid dissolution step. 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 preferably includes electric power obtained from renewable energy. The electricity obtained by the renewable energy preferably includes electricity obtained by at least one selected from the group consisting of solar power generation, wind power generation, hydroelectric power generation, and biomass power generation. Preferably, a portion 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. Effect of the Invention

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

[0011] [Figure 1] FIG. 2 is an explanatory diagram showing a method for treating fresh salt water after lithium membrane electrolysis 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 first membrane electrolysis step of the method for treating fresh salt water after lithium membrane electrolysis of the present invention. [Diagram 3] FIG. 2 is an explanatory cross-sectional view showing one embodiment of the structure of an ion exchange membrane electrolytic cell used in the second membrane electrolysis step of the method for treating fresh salt water after lithium membrane electrolysis of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The present invention will now be described in further detail. 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.

[0013] The embodiments of the present invention will now be described in more detail with reference to the accompanying drawings. As shown in Fig. 1, the method for treating fresh salt water after lithium membrane electrolysis according to the embodiment (Fig. 1) may start with a lithium-containing material 1. The lithium-containing material 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 life as a battery product has expired, or a lithium ion battery that has been discarded as a defective product in the manufacturing process, a discharge treatment is first performed. 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. 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 may be obtained by heat treatment at a temperature in the range.

[0015] When the waste lithium ion batteries are residual positive electrode materials or the like used in commercialization in a manufacturing process, the active material powder may be obtained by pulverizing the waste lithium ion batteries in the pulverizer after heat treatment at a temperature in the above range or without heat treatment without performing the discharge treatment and the formation of openings, and removing the current collectors and the like by sieving.Furthermore, the waste lithium ion batteries may be pulverized in the pulverizer, removing the current collectors and the like by sieving, and then heat treatment at a temperature in the above range or without heat treatment to obtain the active material powder.

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

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

[0018] <Neutralization process> In an embodiment, the acid dissolution is then neutralized in STEP 2 by adding lithium hydroxide (LiOH).

[0019] <Extraction process> 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 the respective metal sulfate aqueous solutions 2, to obtain a first lithium chloride aqueous solution.

[0020] 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, for example, kerosene.

[0021] 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.

[0022] In another embodiment of the present invention, the lithium-containing material 1 may be a brine derived from at least one selected from the group consisting of a salt lake, seawater, and brackish water, more preferably a 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 a method shown in Japanese Patent No. 6122944. That is, the brine is mixed with at least one of an alkali metal hydroxide and an aqueous solution thereof, and magnesium can be produced as magnesium hydroxide. At this time, the pH of the saltwater mixed with the alkali metal hydroxide is maintained at 8.5 to 10.5, and boron (for example, boron ions) can be adsorbed onto the magnesium hydroxide to co-precipitate magnesium and boron. In order to separate the magnesium hydroxide precipitated by adsorption of boron from the saltwater, magnesium and boron are simultaneously recovered by solid-liquid separation such as filtration, and a filtrate is obtained. The filtrate can be mixed with an alkali metal hydroxide or alkali metal carbonate (e.g., NaOH or carbonate, alone or in admixture) to maintain the pH of the filtrate at or above 12 to precipitate calcium. Depending on the type of alkali metal hydroxide or alkali metal carbonate mixed with the filtrate, calcium hydroxide or calcium carbonate precipitates and calcium is removed from the brine to obtain a first aqueous lithium chloride solution. 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 is lithium.

[0023] <First membrane electrolysis process> The two embodiments described above then include a first membrane electrolysis step of performing membrane electrolysis on the first lithium chloride aqueous solution using an ion exchange membrane in STEP 4. The first membrane electrolysis step in STEP 4 can be performed using, for example, a membrane electrolysis cell 11 shown in FIG.

[0024] 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.

[0025] In the membrane electrolysis cell 11, when the first lithium chloride aqueous solution is supplied 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.

[0026] 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.

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

[0028] In the embodiment, hydrochloric acid 4 can be obtained by reacting hydrogen gas (H2) generated in the first membrane electrolysis process with chlorine gas (Cl2), and the hydrochloric acid 4 can be used to dissolve the solid 1 in STEP 1.

[0029] <Recovery of lithium> The lithium in the lithium hydroxide aqueous solution 3 obtained in the first membrane electrolysis step can be recovered as lithium hydroxide monohydrate (LiOH·H2O) by crystallization in STEP 5, and can also be recovered as lithium carbonate (Li2CO3) by carbonation in STEP 6. The carbonation can be performed by reacting the lithium hydroxide aqueous solution 3 with carbon dioxide gas (CO2). The lithium chloride aqueous solution obtained by performing solid-liquid separation of the slurry obtained in the carbonation step by filtration or the like may be concentrated in STEP 7 described later.

[0030] 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, continued use of the solvent will cause the liquid to become acidic and the extraction rate to decrease, but the addition of the lithium hydroxide aqueous solution 3 can suppress the decrease in the extraction rate.

[0031] In addition, when the lithium hydroxide aqueous solution 3 is used for solvent extraction in STEP 3, the lithium hydroxide aqueous solution 3 may be used for at least one of the solvent extractions of manganese, cobalt, and nickel which are carried out separately.

[0032] In the first membrane electrolysis step, the first lithium chloride aqueous solution is subjected to membrane electrolysis, resulting in the production of a second lithium chloride aqueous solution that is more dilute than the first lithium chloride aqueous solution. In the embodiment, therefore, a part of the second lithium chloride aqueous solution and the first lithium chloride aqueous solution may be mixed and concentrated in STEP 7 to obtain a third lithium chloride aqueous solution. The concentration in STEP 7 may be performed using at least one selected from the group consisting of a reverse osmosis membrane (RO membrane) and evaporation concentration.

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

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

[0035] The membrane electrolytic cell 21 is provided with an anode plate 22 on one of its inner surfaces and a cathode plate 23 on its inner surface opposite the anode plate 22, the anode plate 22 being connected to an anode 24 of a power source, and the cathode plate 23 being connected to a cathode 25 of the power source. The membrane 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.

[0036] In the membrane electrolysis cell 21, when dilute sulfuric acid is supplied to the anode chamber 27 to perform membrane electrolysis, water (HO) is converted into hydroxide ions (OH - ) and hydrogen ions (H + ) on the anode plate 22 to produce oxygen gas (O2), while hydrogen ions (H + ) moves through the ion exchange membrane 26 to the cathode chamber 28, where the reaction shown in the following formula (1) occurs. 3H2O → 1.5O2 + 6H + +6e - (1)

[0037] In the cathode chamber 28, a lithium chloride aqueous solution containing the chlorate is supplied, and the chlorate reacts with water to produce lithium chloride and hydroxide ions (OH - ) is produced, as shown in the following reaction (2): LiClO3+3H2O+6e - →LiCl+6OH - (2) Hydrogen ions (H + ) is the hydroxide ion (OH - ) and is neutralized.

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

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

[0040] 1. Lithium-containing substance, 2. Metal sulfate aqueous solution, 3 Lithium hydroxide solution, 3A Lithium hydroxide monohydrate, 4 Hydrochloric acid 4A Alkali metal hydroxide solution, 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 fresh salt water after lithium membrane electrolysis, comprising the steps of: A first membrane electrolysis step of performing membrane electrolysis on a first lithium chloride aqueous solution to obtain a lithium hydroxide aqueous solution, hydrochloric acid, and a second lithium chloride aqueous solution that is more dilute than the first lithium chloride aqueous solution; and a second membrane electrolysis step of performing membrane electrolysis on an aqueous lithium chloride solution containing chlorate generated in the first membrane electrolysis step,

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

3. 3. The method for treating fresh salt water after lithium membrane electrolysis according to claim 1, further comprising a mixing and concentrating step of mixing a part of the second lithium chloride aqueous solution and the first lithium chloride aqueous solution and concentrating the mixture to obtain a third lithium chloride aqueous solution.

4. 3. The method for treating fresh salt water after lithium membrane electrolysis according to claim 1, wherein hydrochloric acid produced by reacting chlorine obtained by membrane electrolysis of the first lithium chloride aqueous solution using an ion exchange membrane with hydrogen is used in the acid dissolution step.

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

6. 6. The method for treating fresh saltwater after lithium membrane electrolysis according to claim 5, wherein the electricity obtained by the renewable energy includes electricity obtained by at least one selected from the group consisting of solar power generation, wind power generation, hydroelectric power generation, and biomass power generation.

7. 3. The method for treating fresh salt water after lithium membrane electrolysis according to claim 1 or 2, further comprising the steps of: decomposing a part of the chlorate in the second membrane electrolysis step; and returning the lithium chloride aqueous solution containing the chlorate subjected to the second membrane electrolysis step to the first membrane electrolysis step.

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