Method for treating brackish water after lithium membrane electrolysis

Abstract

Provided is a method for treating brackish water after lithium membrane electrolysis to prevent quality deterioration of lithium hydroxide and degradation of equipment. This method for treating brackish water after lithium membrane electrolysis comprises: a first membrane electrolysis step for performing membrane electrolysis on a first lithium chloride solution to obtain a lithium hydroxide solution, hydrochloric acid, and a second lithium chloride solution that is more dilute than the first lithium chloride solution; and a second membrane electrolysis step for performing membrane electrolysis on the lithium chloride solution containing a chlorate generated in the first membrane electrolysis step.

Description

Treatment method for fresh saltwater after lithium membrane electrolysis

[0001] The present invention relates to a method for treating fresh salt water after lithium membrane electrolysis.

[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] Cited Document 1 discloses a system for recovering lithium from waste lithium-ion batteries, which includes 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 from 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.

[0004] Patent No. 7060899 Publication

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

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

[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 in the quality of lithium hydroxide and deterioration of equipment during membrane electrolysis of a lithium chloride aqueous solution, that chlorate is generated by hydroxide ions that reversely migrate from the cathode chamber and accumulates, and that the accumulation of chlorate can be prevented by membrane electrolysis of a lithium salt aqueous solution containing 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 brine after lithium membrane electrolysis, comprising: a first membrane electrolysis step of subjecting a first lithium chloride aqueous solution to membrane electrolysis 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 subjecting a lithium chloride aqueous solution containing chlorate generated in the first membrane electrolysis step to membrane electrolysis.

[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 excluding lithium from the acid solution obtained in the neutralization step by solvent extraction to obtain the first lithium chloride aqueous solution as a residue of the solvent extraction, wherein a portion of the lithium hydroxide aqueous solution is used as the lithium hydroxide to be used in at least one step 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 brine after lithium membrane electrolysis preferably further includes a mixing and concentration step of mixing a portion 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 obtained by membrane electrolysis using an ion exchange membrane, and hydrochloric acid generated by reacting the resulting chlorine with hydrogen is used in the acid dissolution step. The electricity used in at least one selected from the group consisting of the first membrane electrolysis step and the second membrane electrolysis step preferably includes electricity obtained from renewable energy. The electricity obtained from renewable energy 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. Preferably, a portion of the chlorate is decomposed in the second membrane electrolysis step, and the chlorate-containing lithium chloride aqueous solution subjected to the second membrane electrolysis step is returned to the first membrane electrolysis step.

[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 that prevents deterioration of the quality of lithium hydroxide and deterioration of the equipment.

[0011] 1 is an explanatory diagram showing a method for treating fresh saltwater after lithium membrane electrolysis according to the present invention; 2 is an explanatory cross-sectional view showing one embodiment of the structure of an ion exchange membrane electrolytic cell used in a first membrane electrolysis step of the method for treating fresh saltwater after lithium membrane electrolysis according to the present invention; 3 is an explanatory cross-sectional view showing one embodiment of the structure of an ion exchange membrane electrolytic cell used in a second membrane electrolysis step of the method for treating fresh saltwater after lithium membrane electrolysis according to the present invention;

[0012] The present invention will be described in more detail below. In the description of the drawings, the same elements are designated by the same reference numerals, and duplicate explanations will be omitted. Furthermore, the dimensional proportions of the drawings are exaggerated for the convenience of explanation, and may differ from the actual proportions.

[0013] The present invention will be described in more detail with reference to the accompanying drawings. As shown in Fig. 1, the method for treating fresh saltwater 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 now be described. When the used lithium-ion batteries are used lithium-ion batteries whose battery life as a battery product has expired or lithium-ion batteries discarded as defective products during the manufacturing process, they are first subjected to a discharge treatment. Various highly safe methods, such as resistance discharge, can be used for the discharge treatment. After discharging all remaining charge, openings are formed in the casings of the used lithium-ion batteries. The batteries are then heat-treated (roasted) at a temperature ranging from 100 to 800°C, or the batteries are pulverized in a pulverizer such as a hammer mill or jaw crusher without being heat-treated. The casings, current collectors, and other components of the used lithium-ion batteries are removed by sieving (classification), thereby obtaining the active material powder. Alternatively, the used lithium-ion batteries after the discharge treatment may be pulverized in the pulverizer, the casings, current collectors, and other components are removed by sieving, and the active material powder may be obtained by heat-treating the batteries at a temperature within the range.

[0015] When the used 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 used 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 forming openings, and removing current collectors and the like by sieving.Furthermore, the used lithium ion batteries may be pulverized in the pulverizer, removing 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 Step> In the embodiment, next, in STEP 1, the lithium-containing material 1 is dissolved in hydrochloric acid to obtain an acid solution of at least 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 Step> In this embodiment, the acid solution is then neutralized in STEP 2 by adding lithium hydroxide (LiOH).

[0019] <Extraction Step> 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 aqueous metal sulfate solutions 2, thereby obtaining a first aqueous lithium chloride solution.

[0020] Examples of organic solvents 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] The iron-containing organic phase, aluminum-containing organic phase, manganese-containing organic phase, cobalt-containing organic phase, and 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 brine derived from at least one selected from the group consisting of a salt lake, 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 may be performed, for example, by the method disclosed in Japanese Patent No. 6122944. Specifically, magnesium can be produced as magnesium hydroxide by mixing the brine with at least one of an alkali metal hydroxide and its aqueous solution. The pH of the brine containing the alkali metal hydroxide is maintained at 8.5 to 10.5, and boron (e.g., boron ions) can be adsorbed onto the magnesium hydroxide, resulting in the co-precipitation of magnesium and boron. To separate the magnesium hydroxide precipitated by the adsorption of boron from the brine, magnesium and boron are simultaneously recovered by solid-liquid separation, such as filtration, to obtain a filtrate. The filtrate can be mixed with an alkali metal hydroxide or alkali metal carbonate (e.g., NaOH or a carbonate, alone or in combination) to maintain the pH of the filtrate at 12 or higher 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, removing calcium from the brine and yielding a first lithium chloride aqueous 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 lithium.

[0023] <First Membrane Electrolysis Step> The two embodiments described above next 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 has 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 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 and membrane electrolysis is performed, chloride ions are converted into chlorine gas (Cl ) on the anode plate 12. ２ ), while the lithium ions migrate through the ion exchange membrane 16 to the cathode chamber 18.

[0026] In the cathode chamber 18, water (H ２ O) is hydroxide ion (OH － ) and hydrogen ions (H ＋ ) and hydrogen ions are ionized into hydrogen gas (H ２ ), while hydroxide ions combine with lithium to produce 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, the hydrogen gas (H ２ ) and chlorine gas (Cl ２ ) to obtain hydrochloric acid 4, which can be used to dissolve the solid 1 in STEP 1.

[0029] <Recovery of lithium> In STEP 5, lithium in the lithium hydroxide aqueous solution 3 obtained in the first membrane electrolysis step is crystallized to form lithium hydroxide monohydrate (LiOH·H ２ O), and by carbonating it in STEP 6, lithium carbonate (Li ２ CO ３ The carbonation is carried out by converting the lithium hydroxide aqueous solution 3 into carbon dioxide gas (CO ２ The aqueous lithium chloride solution obtained by subjecting the slurry obtained in the carbonation step to solid-liquid separation by filtration or the like may be concentrated in STEP 7 described below.

[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. However, the addition of the lithium hydroxide aqueous solution 3 can suppress the decrease in the extraction rate.

[0031] Furthermore, 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] Furthermore, 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. Therefore, in the above embodiment, 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 can be performed using, for example, at least one selected from the group consisting of a reverse osmosis membrane (RO membrane) and evaporative concentration.

[0033] <Second Membrane Electrolysis Step> In the first electrolysis step, chlorate is generated by hydroxide ions that reverse migrate from the cathode chamber 18 and accumulates. 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 in which a lithium chloride aqueous solution containing chlorate generated in the first membrane electrolysis step is subjected to membrane electrolysis.

[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 using, for example, a membrane electrolysis cell 21 shown in FIG.

[0035] The membrane electrolytic cell 21 has 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 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, dilute sulfuric acid is supplied to the anode chamber 27 to perform membrane electrolysis, and water (H ２ O) is hydroxide ion (OH － ) and hydrogen ions (H ＋ ) and oxygen gas (O ２ ), 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: ２ O → 1.5O ２ +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 － The reaction shown in the following formula (2) occurs, producing LiClO ３ +3H ２ O+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 thereof has been reduced, is returned to the anode chamber 17 of the electrolytic cell 11 used in the first membrane electrolysis step.

[0040] 1...lithium-containing substance, 2...metal sulfate aqueous solution, 3...lithium hydroxide aqueous solution, 3A...lithium hydroxide monohydrate, 4...hydrochloric acid, 4A...alkali metal hydroxide aqueous 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 brine 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 the lithium chloride aqueous solution containing chlorate generated in the first membrane electrolysis step.

2. A method for treating fresh brine after lithium membrane electrolysis according to claim 1, further comprising: an acid dissolving step of dissolving a solid containing lithium with hydrochloric acid to obtain an acid solution; a neutralizing 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 neutralizing step by solvent extraction to obtain the first lithium chloride aqueous solution as a residual liquid of the solvent extraction, wherein a part of the lithium hydroxide aqueous solution is used as lithium hydroxide used in at least one step selected from the group consisting of the neutralizing step and the solvent extraction step, and hydrochloric acid generated in the first membrane electrolysis step is used in the acid dissolving step.

3. A method for treating freshly brackish water after lithium membrane electrolysis according to claim 1 or 2, further comprising 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.

4. A method for treating fresh salt water after lithium membrane electrolysis according to claim 1 or 2, wherein the 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. A method for treating fresh saltwater after lithium membrane electrolysis as described in claim 1 or 2, wherein the electricity used in at least one process selected from the group consisting of the first membrane electrolysis process and the second membrane electrolysis process includes electricity obtained from renewable energy.

6. A method for treating freshwater saltwater after lithium membrane electrolysis as described in 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. A method for treating fresh salt water after lithium membrane electrolysis as described in claim 1 or 2, comprising the steps of decomposing a portion of the chlorate salt in the second membrane electrolysis step, and returning the lithium chloride aqueous solution containing the chlorate salt that has been subjected to the second membrane electrolysis step to the first membrane electrolysis step.

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