Method for obtaining high-purity lithium salts from low-grade lithium carbonate

Abstract

To provide a method for obtaining a high-purity lithium salt from a low-grade lithium carbonate, which does not consume a lot of energy and does not generate a large amount of waste.SOLUTION: A method for obtaining a high-purity lithium salt from low-grade lithium carbonate includes an acid dissolution step in which low-grade lithium carbonate is dissolved in a mineral acid, an impurity removal step in which impurities are removed from the crude lithium salt aqueous solution obtained in the acid dissolution step, and a membrane electrolysis step in which the first lithium salt aqueous solution obtained in the impurity removal step is membrane-electrolyzed to produce a second lithium salt aqueous solution and a high-purity lithium hydroxide aqueous solution, wherein the mineral acid produced in this membrane electrolysis step is used in this acid dissolution step, and a lithium salt concentration in the second lithium salt aqueous solution is smaller than the lithium salt concentration in the first lithium salt aqueous solution.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for obtaining high-purity lithium salts from low-grade lithium carbonate.

Background Art

[0002] High-purity lithium salts are produced from low-grade lithium carbonate recovered from salt lake brine, ores, waste lithium-ion batteries, etc. Patent Document 1 discloses a method for producing lithium hydroxide using an electrodialysis device, supplying a lithium carbonate solution to a salt chamber, and repeatedly taking out an aqueous lithium carbonate solution from an acid chamber, and further discloses a production method provided with a purification step for increasing purity.

[0003] Patent Document 2 discloses a lithium hydroxide production method in which lithium carbonate is reacted with calcium hydroxide in a liquid to obtain a lithium hydroxide solution, a calcium removal step of adsorbing and removing calcium ions present in the lithium hydroxide solution due to the addition of calcium hydroxide in the hydroxylation step with a cation exchange resin and / or a chelating resin, and a crystallization step, and discloses a production method of high-purity lithium hydroxide with a low calcium content.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the method for producing lithium hydroxide disclosed in Patent Document 1, the solubility of lithium hydrogen carbonate produced by mixing a lithium carbonate solution and carbonic acid water in water is several g / L, and the amount of electrolyte becomes enormous. Further, since the concentration of the aqueous lithium hydroxide solution obtained by electrodialysis is not high, in order to recover lithium hydroxide crystals from the aqueous solution, it is necessary to evaporate a large amount of water at the cost of a great deal of energy. Also, in the method for producing lithium hydroxide disclosed in Cited Document 2, a large amount of calcium carbonate is generated as waste.

[0006] Therefore, the problem to be solved by the present invention is to provide a method for obtaining a high-purity lithium salt from low-grade lithium carbonate without consuming a great deal of energy and without generating a large amount of waste.

Means for Solving the Problem

[0007] In view of the above problems, the present inventors repeated studies and found that when a lithium salt aqueous solution obtained by dissolving low-grade lithium carbonate in a mineral acid and removing impurities is subjected to membrane electrolysis, a high-purity lithium salt can be obtained without consuming a great deal of energy and without generating a large amount of waste. The present invention has been completed based on these findings.

[0008] The present invention relates to A step of obtaining low-grade lithium carbonate from at least one selected from the group consisting of minerals, brine obtained from natural salt lakes, and seawater, the a method for recovering a high-purity lithium salt from low-grade lithium carbonate, comprising an acid dissolution step of dissolving low-grade lithium carbonate in a mineral acid, an impurity removal step of removing impurities from the crude lithium salt aqueous solution obtained in the acid dissolution step, and a membrane electrolysis step of subjecting the first lithium salt aqueous solution obtained in the impurity removal step to membrane electrolysis to produce a second lithium salt aqueous solution and a high-purity lithium hydroxide aqueous solution, wherein the impurities are removed by an ion exchange resin in the impurity removal step, the mineral acid generated in the membrane electrolysis step is used in the acid dissolution step, and the lithium salt concentration in the second lithium salt aqueous solution is smaller than the lithium salt concentration in the first lithium salt aqueous solution. The present invention preferably further includes a carbonation step of reacting carbon dioxide generated in the acid dissolution step with high-purity lithium hydroxide generated in the membrane electrolysis step to obtain high-purity lithium carbonate. Thereby, a part of the carbon dioxide generated in the acid dissolution step can be effectively utilized without being discarded. The present invention preferably further includes a concentration and mixing step of concentrating the second lithium salt aqueous solution and mixing the concentrated lithium salt aqueous solution with the first lithium salt aqueous solution. The electric power used for membrane electrolysis preferably includes electric power obtained by renewable energy. The electric power obtained by the renewable energy preferably includes at least one selected from the group consisting of electric power obtained by solar power generation and electric power obtained by wind power generation.

Advantages of the Invention

[0009] The present invention provides a method for obtaining a high-purity lithium salt from low-grade lithium carbonate without consuming a large amount of energy and without generating a large amount of waste.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0011] The present invention will be described in more detail. Note that "~" in a numerical range represents "above to below" and includes both end values unless otherwise stated. Also, when a numerical range is indicated, the upper limit value and the lower limit value can be appropriately combined, and the numerical range thus obtained is also disclosed. In the following 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 sake of explanation and may be different from the actual ratios.

[0012] The present invention will be described in more detail with reference to the drawings. <Low-grade lithium carbonate> Examples of the source of the low-grade lithium carbonate include low-grade lithium carbonate recycled from waste lithium-ion batteries, minerals, brine obtained from natural salt lakes, seawater, and the like. The method for obtaining a high-purity lithium salt from the low-grade lithium carbonate of the present invention (hereinafter referred to as "the method of the present invention") uses the low-grade lithium carbonate 1 as a starting material, as shown in FIG. 1.

[0013] <Acid dissolution step> The method of the present invention includes an acid dissolution step (STEP1) of dissolving the low-grade lithium carbonate 1 in a mineral acid. The mineral acid includes at least one selected from the group consisting of hydrochloric acid, sulfuric acid, and nitric acid, preferably includes hydrochloric acid, and more preferably is hydrochloric acid. In the acid dissolution step, a crude lithium salt aqueous solution 2 and carbon dioxide 3 are generated. When the mineral acid is hydrochloric acid, the crude lithium salt aqueous solution 2 is a crude lithium chloride aqueous solution. The carbon dioxide 3 generated in the acid dissolution step can preferably react with the high-purity lithium hydroxide 4 generated in the membrane electrolysis step described later to generate high-purity lithium carbonate 7. Therefore, in the method of the present invention, a part of a large amount of carbon dioxide can be effectively utilized without being discarded.

[0014] <Impurity removal step> The method of the present invention includes an impurity removal step of removing impurities from the crude lithium salt aqueous solution. The crude lithium chloride aqueous solution contains impurities such as alkali metals and alkaline earth metals. In the impurity removal step, the impurities are removed by an ion exchange resin such as a strongly acidic cation exchange resin or a chelating resin, and a first lithium salt aqueous solution is obtained. Examples of the strongly acidic cation exchange resin include SK110 (manufactured by Mitsubishi Chemical Corporation), and examples of the chelating resin include CR-11 (manufactured by Mitsubishi Chemical Corporation).

[0015] <Membrane electrolysis step> The method of the present invention includes a membrane electrolysis step (STEP3) of subjecting the first lithium salt aqueous solution to membrane electrolysis using an ion exchange membrane to produce a second lithium salt aqueous solution and high-purity lithium hydroxide. The membrane electrolysis can be performed, for example, using the membrane electrolysis cell 11 shown in FIG. 2.

[0016] 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.

[0017] 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 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.

[0018] 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 produce a high-purity lithium hydroxide aqueous solution 4.

[0019] When the lithium salt aqueous solution subjected to the membrane electrolysis step contains sulfate ions, sulfuric acid can be obtained in the anode chamber 17. When the lithium salt aqueous solution subjected to the membrane electrolysis step contains nitrate ions, nitric acid can be obtained in the anode chamber 17. That is, mineral acid 5 can be obtained in the membrane electrolysis step, and the mineral acid 5 may be used in the acid dissolution step of STEP1.

[0020] The high-purity lithium hydroxide aqueous solution 4 obtained in the membrane electrolysis step can also be recovered as high-purity lithium hydroxide monohydrate (LiOH·H2O) 6 by crystallization in STEP4, or can also be recovered as high-purity lithium carbonate (Li2CO3) 7 by carbonation in STEP5. The carbonation is preferably carried out by reacting the high-purity lithium hydroxide aqueous solution 4 with the carbon dioxide 3 generated in the acid dissolution step (STEP1).

[0021] In the membrane electrolysis step, as a result of membrane electrolysis of the first lithium salt aqueous solution, a second lithium salt aqueous solution having a lithium salt concentration lower than the lithium salt concentration in the first lithium salt aqueous solution and a high-purity lithium hydroxide aqueous solution 4 are generated. The purity of the monohydrate of high-purity lithium hydroxide obtained by crystallizing the high-purity lithium hydroxide aqueous solution 4 is, for example, 99.5% by mass or more. The method of the present invention preferably further includes a concentration mixing step of concentrating the second lithium salt aqueous solution (STEP6) and mixing the concentrated lithium salt aqueous solution with the first lithium salt aqueous solution. Examples of the concentration method include the reverse osmosis membrane method.

[0022] The electric power used in the membrane electrolysis step may include at least one renewable energy selected from the group consisting of, for example, electric power obtained by solar power generation and electric power obtained by wind power generation.

Explanation of symbols

[0023] 1…Low-grade lithium carbonate, 2…Crude lithium salt aqueous solution, 3…Carbon dioxide, 4... High-purity lithium hydroxide aqueous solution, 5... Mineral acid, 6... High-purity lithium hydroxide monohydrate, 7... High-purity lithium carbonate, 11... Membrane electrolytic cell, 16... Ion exchange membrane, 17... Anode chamber, 18... Cathode chamber.

Claims

1. A method for obtaining high-purity lithium salts from low-grade lithium carbonate, comprising: a step of obtaining low-grade lithium carbonate from at least one selected from the group consisting of minerals, brine obtained from natural salt lakes, and seawater; an acid dissolution step of dissolving the low-grade lithium carbonate in a mineral acid; an impurity removal step of removing impurities from the crude lithium salt aqueous solution obtained in the acid dissolution step; and a membrane electrolysis step of subjecting the first lithium salt aqueous solution obtained in the impurity removal step to membrane electrolysis to produce a second lithium salt aqueous solution and a high-purity lithium hydroxide aqueous solution, wherein the impurities are removed by an ion exchange resin in the impurity removal step, the mineral acid generated in the membrane electrolysis step is used in the acid dissolution step, and the lithium salt concentration in the second lithium salt aqueous solution is smaller than the lithium salt concentration in the first lithium salt aqueous solution. A method for obtaining high-purity lithium salts from low-grade lithium carbonate.

2. The method for obtaining high-purity lithium salts from low-grade lithium carbonate according to Claim 1, further comprising a carbonation step of reacting carbon dioxide generated in the acid dissolution step with the high-purity lithium hydroxide generated in the membrane electrolysis step to obtain high-purity lithium carbonate. A method for obtaining high-purity lithium salts from low-grade lithium carbonate.

3. The method for obtaining high-purity lithium salts from low-grade lithium carbonate according to Claim 1, further comprising a concentration mixing step of concentrating the second lithium salt aqueous solution and mixing the concentrated lithium salt aqueous solution with the first lithium salt aqueous solution. A method for obtaining high-purity lithium salts from low-grade lithium carbonate.

4. A method for obtaining high-purity lithium salts from low-grade lithium carbonate according to any one of Claims 1 to 3, characterized in that the electric power used for membrane electrolysis includes electric power obtained from renewable energy. A method for recovering lithium from lithium carbonate.

5. The method for obtaining high-purity lithium salts from low-grade lithium carbonate according to Claim 4, characterized in that the electric power obtained from renewable energy includes at least one selected from the group consisting of electric power obtained from solar power generation and electric power obtained from wind power generation. A method for obtaining high-purity lithium salts from low-grade lithium carbonate.

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