Method for removing chlorine from bipolar membrane alkali liquor

Abstract

The invention relates to the technical field of lithium hydroxide preparation, and discloses a bipolar membrane alkali liquor dechlorination method. The method comprises the following steps: (1) carrying out bipolar membrane electrodialysis treatment on a lithium-rich concentrated solution to obtain a first lithium hydroxide solution of which the chloride ion content is greater than or equal to 2g / L; (2) the first lithium hydroxide solution is introduced into a cathode chamber of an electrolytic bath for electrolysis, a second lithium hydroxide solution with the chlorine ion content smaller than or equal to 1.5 g / L is obtained in the cathode chamber, and a diaphragm between the cathode chamber and an anode chamber of the electrolytic bath is an anion exchange membrane; and (3) the second lithium hydroxide solution is subjected to evaporative crystallization, battery-grade lithium hydroxide is obtained, and the number of times of evaporative crystallization is smaller than or equal to 2. According to the method, the electrolysis step is added after bipolar membrane electrodialysis treatment, chloride ions in bipolar membrane alkali liquor can be reduced to a great extent, then a lithium hydroxide product meeting the battery grade standard can be prepared after evaporation crystallization is conducted within two times, and the subsequent treatment cost is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of lithium hydroxide preparation, and in particular to a method for dechlorinating bipolar membrane alkali solution. Background Art

[0002] Traditionally, LiOH consumption areas are mainly in the dye, adsorbent, grease and other industries. After 2015, it gradually shifted to the lithium-ion battery industry, mainly used in the manufacture of lithium iron phosphate, lithium titanate and ternary materials. Driven by the lithium-ion battery industry, the demand for lithium hydroxide continues to rise. At present, major global LiOH producers mostly use the lithium carbonate causticization method, and a small number are developing processes for directly producing LiOH from salt lake brine. In recent years, with the rapid development of the downstream power battery industry chain, the demand for LiOH will continue to increase. Therefore, it is necessary to expand the types of lithium resources for producing LiOH. It is of great significance to develop new processes for directly producing LiOH from salt lake lithium resources.

[0003] At present, the main process of preparing lithium hydroxide from salt lake brine is: (1) preliminary extraction of lithium from salt lake brine; (2) concentration of lithium-rich brine, separation of magnesium and lithium, and deep impurity removal; (3) bipolar membrane electrodialysis cracking to obtain alkali and acid; (4) bipolar membrane brine is concentrated by RO and reused; (5) alkali solution evaporation crystallization and recrystallization.

[0004] For example, Qinghai Lithium's patent "Method for Directly Producing Battery-Grade Lithium Hydroxide Monohydrate from Lithium-Rich Salt Lake Brine" (CN106946275A) and Qinghai Salt Lake Industry Co., Ltd.'s patent "A New Process for Producing High-Purity Lithium Hydroxide from Salt Lake Brine" (CN108660476A) both use this process. However, since the bipolar membrane electrodialysis membrane itself cannot completely intercept chloride ions, some chloride ions migrate into the alkali chamber and are concentrated during the subsequent evaporation and crystallization, resulting in the Cl in the produced lithium hydroxide monohydrate being 2.5% to 1.3%. - Severely exceeded the standard. Traditional ion exchange resins cannot absorb chloride ions in high-concentration lithium hydroxide solutions, and more than two recrystallization processes are required to make the chloride ion content reach the battery-grade lithium hydroxide monohydrate standard. Summary of the invention

[0005] The purpose of the present invention is to overcome the problem of Cl in bipolar membrane alkali solution in the process of preparing lithium hydroxide from salt lake brine in the prior art. - The higher the concentration, the more Cl -In order to solve the problem that the chloride ion content seriously exceeds the standard, or more than two recrystallizations are required to make the chloride ion content reach the battery-grade lithium hydroxide monohydrate standard, a method for dechlorination of bipolar membrane alkali solution is provided. The method adds an electrolysis step after bipolar membrane electrodialysis treatment, which can reduce the chloride ions in the bipolar membrane alkali solution to below 1.5g / L, greatly reducing the chloride ions in the bipolar membrane alkali solution. After that, the lithium hydroxide product that meets the battery-grade standard can be prepared by evaporation and crystallization within two times, reducing the cost of subsequent processing.

[0006] In order to achieve the above object, the present invention provides a method for dechlorinating alkaline solution with a bipolar membrane, the method comprising the following steps:

[0007] (1) subjecting the lithium-rich concentrated solution to bipolar membrane electrodialysis to obtain a first lithium hydroxide solution with a chloride ion content of ≥2 g / L;

[0008] (2) passing the first lithium hydroxide solution into the cathode chamber of an electrolytic cell for electrolysis, and obtaining a second lithium hydroxide solution having a chloride ion content of ≤1.5 g / L in the cathode chamber, wherein the diaphragm between the cathode chamber and the anode chamber of the electrolytic cell is an anion exchange membrane;

[0009] (3) subjecting the second lithium hydroxide solution to evaporation and crystallization to obtain battery-grade lithium hydroxide, wherein the number of evaporation and crystallization is ≤2.

[0010] Preferably, in step (1), the lithium-rich concentrated solution contains the following components: + ≥12g / L, Mg 2+ ≤100mg / L, Na + ≤2.0g / L, K + ≤0.3g / L, B 3+ ≤150mg / L, Ca 2+ ≤50mg / L, Cl - 60~70g / L.

[0011] Preferably, in step (1), the first lithium hydroxide solution contains the following components: Li + ≥13g / L, Mg 2+ ≤10mg / L, Na + ≤2.0g / L, K + ≤0.3g / L, B 3+ ≤20mg / L, Ca 2+ ≤10mg / L, OH — ≥30g / L, Cl - 2~6g / L.

[0012] Preferably, in step (2), the electrolysis conditions include: current density 3-4 kA / ㎡, cell voltage 2-12 V, and electrolysis time 20-60 min.

[0013] Preferably, in step (2), the second lithium hydroxide solution contains the following components: Li + ≥14g / L, Mg 2+ ≤10mg / L, Na + ≤2.0g / L, K + ≤0.3g / L, B 3+ ≤20mg / L, Ca 2+ ≤10mg / L, OH — ≥30g / L, Cl - ≤1.5g / L.

[0014] Preferably, in step (2), the solution introduced into the anode chamber of the electrolytic cell is an alkali metal chloride solution.

[0015] Preferably, the concentration of the alkali metal chloride solution is ≥0.5 mol / L.

[0016] Preferably, the alkali metal chloride solution is a sodium chloride solution and / or a lithium chloride solution.

[0017] Preferably, in step (2), after electrolysis, an alkali metal hydroxide solution is obtained in the anode chamber, wherein the chloride ion content is ≥0.5 mol / L and the concentration of the alkali metal hydroxide is 20-30 g / L.

[0018] Preferably, the alkali metal hydroxide solution is a sodium hydroxide solution and / or a lithium hydroxide solution.

[0019] Preferably, in step (3), the evaporative crystallization process comprises a first evaporative crystallization and an optional second evaporative crystallization performed sequentially.

[0020] Preferably, the conditions of the first evaporation crystallization include: a temperature of 85-100° C. and a pressure of 350-450 mbar; and / or,

[0021] The conditions of the second evaporation crystallization include: temperature of 85-100° C. and pressure of 350-450 mbar.

[0022] Preferably, in step (3), the battery-grade lithium hydroxide contains the following components: a main content of 56.5-57.5%, Ca 2+ ≤100ppm, Mg 2+ ≤10ppm, Na + ≤100ppm, K + ≤50ppm, B 3+≤100ppm, Si≤50ppm, Fe≤7ppm, SO4 2- ≤100ppm, Cl - ≤20ppm, CO3 2- ≤0.5%, acid insoluble matter ≤0.005%, magnetic material ≤200ppb.

[0023] Compared with the prior art, the present invention has at least the following beneficial effects:

[0024] Due to the equipment itself and a certain period of operation, the interception rate of bipolar membrane and cation exchange membrane for chloride ions in the chloride system cannot reach 100%, resulting in a large amount of Cl - Enter the alkali chamber. During the concentration process, the Cl in the LiOH solution is refined. - The concentration will exceed 2g / L, and the chloride ion concentration will increase linearly during the subsequent crystallization process, making it difficult for the product to meet the battery-grade standard, or more than 2 recrystallizations are required to make the chloride ion content reach the battery-grade lithium hydroxide monohydrate standard. The inventors of the present invention have found through research that adding an electrolytic cell to electrolyze the alkali solution containing a large amount of chloride ions after bipolar membrane electrodialysis treatment, and using an anion exchange membrane as a diaphragm, can reduce the chloride ions in the bipolar membrane alkali solution to less than 1.5g / L, greatly reducing the chloride ions in the bipolar membrane alkali solution, and subsequently obtaining a lithium hydroxide product that meets the battery-grade standard after less than two evaporation crystallizations, reducing the cost of subsequent processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the electrolysis process of the present invention. DETAILED DESCRIPTION

[0026] The specific embodiments of the present invention are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0027] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0028] The method for dechlorination of bipolar membrane alkali solution provided by the present invention comprises the following steps:

[0029] (1) subjecting the lithium-rich concentrated solution to bipolar membrane electrodialysis to obtain a first lithium hydroxide solution with a chloride ion content of ≥2 g / L;

[0030] (2) passing the first lithium hydroxide solution into the cathode chamber of an electrolytic cell for electrolysis, and obtaining a second lithium hydroxide solution having a chloride ion content of ≤1.5 g / L in the cathode chamber, wherein the diaphragm between the cathode chamber and the anode chamber of the electrolytic cell is an anion exchange membrane;

[0031] (3) subjecting the second lithium hydroxide solution to evaporation and crystallization to obtain battery-grade lithium hydroxide, wherein the number of evaporation and crystallization is ≤2.

[0032] In the method of the present invention, the lithium-rich concentrated solution can be obtained from salt lake brine according to conventional lithium extraction steps. In some embodiments, in step (1), the lithium-rich concentrated solution contains the following components: Li + ≥12g / L, Mg 2+ ≤100mg / L, Na + ≤2.0g / L, K + ≤0.3g / L, B 3+ ≤150mg / L, Ca 2+ ≤50mg / L, Cl - 60~70g / L.

[0033] In the present invention, after the lithium-rich concentrated solution is treated by bipolar membrane electrodialysis, the first lithium hydroxide solution obtained still contains a large amount of chloride ions, and the chloride ion content exceeds 2g / L. The process and equipment of the bipolar membrane electrodialysis treatment are conventional choices well known to those skilled in the art. In some embodiments, in step (1), the first lithium hydroxide solution contains the following components: Li + ≥13g / L, Mg 2+ ≤10mg / L, Na + ≤2.0g / L, K + ≤0.3g / L, B 3+ ≤20mg / L, Ca 2+ ≤10mg / L, OH — ≥30g / L, Cl - 2~6g / L.

[0034] If a large amount of chloride ions contained in the first lithium hydroxide solution are not removed, the chloride ion concentration will increase linearly during the subsequent crystallization process, resulting in the lithium hydroxide product being difficult to meet the battery-grade standard, or requiring more than two recrystallizations to make the chloride ion content reach the battery-grade lithium hydroxide monohydrate standard. The inventors have found through research that adding an electrolytic cell to electrolyze the alkaline solution containing a large amount of chloride ions after the bipolar membrane electrodialysis treatment, and using an anion exchange membrane as a diaphragm can greatly reduce the chloride ions in the bipolar membrane alkaline solution. After subsequent evaporation and crystallization within two times, a lithium hydroxide product that meets the battery-grade standard can be obtained, thereby reducing the cost of subsequent processing.

[0035] In the present invention, the electrolytic cell used for the electrolysis in step (2) may be a common structure in the art. In a more specific embodiment, the electrolytic cell comprises an anode chamber, a cathode chamber, a diaphragm, an electrode plate, a tail gas recovery system, and a crude alkali metal hydroxide solution recycling portion. In the method described in the present invention, the conditions for the electrolysis in step (2) include: a current density of 3 to 4 kA / ㎡, a cell voltage of 2 to 12 V, and an electrolysis time of 20 to 60 min.

[0036] In a preferred embodiment, in order to further reduce the content of chloride ions in the first lithium hydroxide solution, in step (2), the anion exchange membrane uses polystyrene and / or polytetrafluoroethylene as the matrix material of the anion exchange membrane, and quaternary ammonium salts and / or imidazole salts as the cationic functional groups of the anion exchange membrane.

[0037] In the present invention, after the first lithium hydroxide solution is electrolyzed in the cathode chamber of the electrolytic cell, a second lithium hydroxide solution with a lower chloride ion content is obtained in the cathode chamber. In some embodiments, in step (2), the second lithium hydroxide solution contains the following components: Li + ≥14g / L, Mg 2+ ≤10mg / L, Na + ≤2.0g / L, K + ≤0.3g / L, B 3+ ≤20mg / L, Ca 2+ ≤10mg / L, OH — ≥30g / L, Cl - ≤1.5g / L.

[0038] In the method of the present invention, the solution introduced into the anode chamber can be an alkali metal chloride solution commonly used in the art. In some embodiments, the alkali metal chloride solution is a sodium chloride solution and / or a lithium chloride solution. In some preferred embodiments, in order to further improve the removal effect of chloride ions, the concentration of the alkali metal chloride solution is ≥0.5 mol / L.

[0039] In the method of the present invention, after electrolysis in step (2), the anode chamber obtains an alkali metal hydroxide solution with a high chloride ion content. In some embodiments, after electrolysis in step (2), an alkali metal hydroxide solution is obtained in the anode chamber, wherein the chloride ion content is ≥0.5 mol / L and the concentration of the alkali metal hydroxide is 20-30 g / L. In other embodiments, the alkali metal hydroxide solution is a sodium hydroxide solution and / or a lithium hydroxide solution.

[0040] In a more specific embodiment, the electrolysis process is as follows Figure 1 As shown, it includes: passing the first lithium hydroxide solution into the cathode chamber of the electrolytic cell, passing the alkali metal chloride solution into the anode chamber, the diaphragm between the cathode chamber and the anode chamber adopts an anion exchange membrane for electrolysis, a large amount of chloride ions in the cathode chamber enter the anode chamber through the anion exchange membrane under the action of the electric field, and undergo oxidation reaction at the anode to become chlorine gas, which can enter the chlorine gas scrubber for treatment, and part of the hydroxide and lithium ions in the cathode chamber will enter the anode chamber along with the chloride ions, so as to obtain a second lithium hydroxide solution with a low chloride ion content in the cathode chamber, and the hydrogen obtained in the cathode chamber can be collected, while the alkali metal hydroxide solution with a high chloride ion content in the anode chamber can be obtained, which can be used for resin regeneration and alkali adjustment of other solutions.

[0041] In the method of the present invention, since the chloride ion content in the second lithium hydroxide solution obtained in step (2) is relatively low, only one or two evaporation crystallizations are required in step (3) to obtain a battery-grade lithium hydroxide product, that is, in step (3), the evaporation crystallization process includes a first evaporation crystallization and an optional second evaporation crystallization performed sequentially.

[0042] In the present invention, the first evaporation crystallization and the second evaporation crystallization can be performed according to conventional operations. In some preferred embodiments, the conditions of the first evaporation crystallization include: a temperature of 85-100° C. and a pressure of 350-450 mbar. In other preferred embodiments, the conditions of the second evaporation crystallization include: a temperature of 85-100° C. and a pressure of 350-450 mbar.

[0043] In one embodiment, the first evaporation crystallization process includes: preheating the second lithium hydroxide solution to 70-90° C. and then performing a first evaporation crystallization in a crystallization separator to obtain a first concentrated solution with a solid content of 15-40%, then centrifuging the first concentrated solution to obtain a first solid product, and washing the first solid product to obtain a first crude salt.

[0044] In another embodiment, the second evaporation crystallization process includes: adding the first crude salt to distilled water for salt dissolving operation to obtain a heavy solution, and then preheating the heavy solution to 70-90°C and performing a second evaporation crystallization in a crystallization separator to obtain a second concentrated solution with a solid content of 15-40%, and then centrifuging the second concentrated solution to obtain a second solid product, and washing the second solid product to obtain a second crude salt, and sending the second crude salt to a rotary kiln drying system. The dried salt is separated by a vibrating screen, and the screened material is a lithium hydroxide product.

[0045] By adopting the method of the present invention, the lithium hydroxide product obtained by evaporation and crystallization within 2 times is battery-grade lithium hydroxide. In some embodiments, in step (3), the battery-grade lithium hydroxide contains the following components: a main content of 56.5-57.5wt%, Ca 2+ ≤100ppm, Mg 2+ ≤10ppm, Na + ≤100ppm, K + ≤50ppm, B 3+ ≤100ppm, Si≤50ppm, Fe≤7ppm, SO4 2- ≤100ppm, Cl - ≤20ppm, CO3 2- ≤0.5%, acid insoluble matter ≤0.005%, magnetic material ≤200ppb. Herein, the main content refers to lithium hydroxide.

[0046] The bipolar membrane alkaline solution dechlorination method of the present invention is further illustrated by examples. The examples are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operation processes are given, but the protection scope of the present invention is not limited to the following examples.

[0047] The experimental methods in the following examples, unless otherwise specified, are all conventional methods in the art. The experimental materials used in the following examples, unless otherwise specified, are all commercially available.

[0048] In this embodiment, the quality of the battery-grade lithium hydroxide monohydrate product must meet the composition and content requirements shown in Table 1. Among them, the main content (LiOH) and carbonate are determined by titration, chloride ions are determined by spectrophotometry, acid insolubles are determined by constant weight method, and the remaining elements are determined by standard working curves on an inductively coupled plasma atomic emission spectrometer.

[0049] Table 1

[0050]

[0051] Example 1

[0052] (1) subjecting the lithium-rich concentrated solution to bipolar membrane electrodialysis to obtain a first lithium hydroxide solution, wherein the lithium-rich concentrated solution contains the following components: Li + 14.5g / L, Mg 2+ 4.6mg / L, Na + 1.92g / L, K + 0.28g / L, B 3+ 110.6mg / L, Ca 2+ 1.5mg / L, Cl - 64.1g / L, the first lithium hydroxide solution contains the following components: Li + 13.3g / L, Mg 2+ 2mg / L, Na + 1.6g / L, K + 0.22g / L, B 3+ 14mg / L, Ca 2+ 0.4mg / L, OH — 32g / L, Cl - 3g / L;

[0053] (2) The first lithium hydroxide solution is introduced into the cathode chamber of the electrolytic cell, and a sodium chloride solution with a concentration of 0.5 mol / L is introduced into the anode chamber. The diaphragm between the cathode chamber and the anode chamber is electrolyzed using an anion exchange membrane, wherein the electrolysis conditions include: a current density of 3 kA / ㎡, a cell voltage of 3.5 V, and an electrolysis time of 30 min. During the electrolysis process, chloride ions in the cathode chamber pass through the anion exchange membrane under the action of the electric field and enter the anode chamber, and undergo an oxidation reaction at the anode to become chlorine gas, thereby obtaining a second lithium hydroxide solution with a low chloride ion content in the cathode chamber, wherein the second lithium hydroxide solution contains the following components: Li + 14g / L, Mg 2+ 3mg / L, Na + 2.0g / L, K + 0.3g / L, B 3+ 20mg / L, Ca 2+ 0.5mg / L, OH - 30g / L, Cl - 0.9g / L, while the hydrogen obtained in the cathode chamber can be collected, and the anode chamber obtains a sodium hydroxide solution with a high chloride ion content, the chloride ion content in the sodium hydroxide solution is 0.56moL / L, and the concentration of sodium hydroxide is 21.4g / L;

[0054] (3) The second lithium hydroxide solution is preheated to 85° C. and then subjected to a first evaporation crystallization in a crystallizer to obtain a first concentrated solution with a solid content of 25%, wherein the conditions for the first evaporation crystallization include: a temperature of 85° C. and a pressure of 420 mbar; the first concentrated solution is centrifuged to obtain a first solid product, and the first solid product is washed to obtain a first crude salt; the first crude salt is then added to distilled water for salt dissolution to obtain a heavy solution, and the heavy solution is preheated to 85° C. and then subjected to a second evaporation crystallization in a crystallizer to obtain a second concentrated solution with a solid content of 30%, wherein the conditions for the second evaporation crystallization include: a temperature of 85° C. and a pressure of 420 mbar; the second concentrated solution is centrifuged to obtain a second solid product, and the second solid product is washed to obtain a second crude salt, and the second crude salt is sent to a rotary kiln drying system, and the dried salt is separated by a vibrating screen, and the screened material is a lithium hydroxide product.

[0055] After testing, the composition and content of the lithium hydroxide product obtained in this embodiment are shown in Table 1.

[0056] Table 1

[0057]

[0058] Example 2

[0059] (1) subjecting the lithium-rich concentrated solution to bipolar membrane electrodialysis to obtain a first lithium hydroxide solution, wherein the lithium-rich concentrated solution contains the following components: Li + 14.5g / L, Mg 2+ 4.6mg / L, Na + 1.92g / L, K + 0.28g / L, B 3+ 110.6mg / L, Ca 2+ 1.5mg / L, Cl - 64.1g / L, the first lithium hydroxide solution contains the following components: Li + 13.3g / L, Mg 2+ 4mg / L, Na + 1.6g / L, K + 0.22g / L, B 3+ 14mg / L, Ca 2+ 1mg / L, OH — 32g / L, Cl - 3g / L;

[0060] (2) The first lithium hydroxide solution is introduced into the cathode chamber of the electrolytic cell, and a sodium chloride solution with a concentration of 0.5 mol / L is introduced into the anode chamber. The diaphragm between the cathode chamber and the anode chamber is electrolyzed using an anion exchange membrane, wherein the electrolysis conditions include: a current density of 3.5 kA / ㎡, a cell voltage of 4 V, and an electrolysis time of 30 min. During the electrolysis process, chloride ions in the cathode chamber pass through the anion exchange membrane under the action of the electric field and enter the anode chamber, and undergo an oxidation reaction at the anode to become chlorine gas, thereby obtaining a second lithium hydroxide solution with a low chloride ion content in the cathode chamber, wherein the second lithium hydroxide solution contains the following components: Li + 14.5g / L, Mg 2+ 4mg / L, Na + 2.2g / L, K + 0.32g / L, B 3+ 22mg / L, Ca 2+ 1mg / L, OH - 32g / L, Cl - 0.76g / L, while the hydrogen obtained in the cathode chamber can be collected, and the anode chamber obtains a sodium hydroxide solution with a high chloride ion content, the chloride ion content in the sodium hydroxide solution is 0.61moL / L, and the concentration of sodium hydroxide is 22.5g / L;

[0061] (3) The second lithium hydroxide solution is preheated to 85° C. and then subjected to a first evaporation crystallization in a crystallizer to obtain a first concentrated solution with a solid content of 25%, wherein the conditions for the first evaporation crystallization include: a temperature of 85° C. and a pressure of 420 mbar; the first concentrated solution is centrifuged to obtain a first solid product, and the first solid product is washed to obtain a first crude salt; the first crude salt is then added to distilled water for salt dissolution to obtain a heavy solution, and the heavy solution is preheated to 85° C. and then subjected to a second evaporation crystallization in a crystallizer to obtain a second concentrated solution with a solid content of 30%, wherein the conditions for the second evaporation crystallization include: a temperature of 85° C. and a pressure of 420 mbar; the second concentrated solution is centrifuged to obtain a second solid product, and the second solid product is washed to obtain a second crude salt, and the second crude salt is sent to a rotary kiln drying system, and the dried salt is separated by a vibrating screen, and the screened material is a lithium hydroxide product.

[0062] After testing, the composition and content of the lithium hydroxide product obtained in this embodiment are shown in Table 2.

[0063] Table 2

[0064]

[0065] Example 3

[0066] (1) subjecting the lithium-rich concentrated solution to bipolar membrane electrodialysis to obtain a first lithium hydroxide solution, wherein the lithium-rich concentrated solution contains the following components: Li + 14.5g / L, Mg 2+ 4.6mg / L, Na + 1.92g / L, K + 0.28g / L, B 3+ 110.6mg / L, Ca 2+ 1.5mg / L, Cl - 64.1g / L, the first lithium hydroxide solution contains the following components: Li + 13.3g / L, Mg 2+ 4mg / L, Na + 1.6g / L, K + 0.22g / L, B 3+ 14mg / L, Ca 2+ 1mg / L, OH — 32g / L, Cl - 3g / L;

[0067] (2) The first lithium hydroxide solution is introduced into the cathode chamber of the electrolytic cell, and a sodium chloride solution with a concentration of 0.5 mol / L is introduced into the anode chamber. The diaphragm between the cathode chamber and the anode chamber is electrolyzed using an anion exchange membrane, wherein the electrolysis conditions include: a current density of 3.5 kA / ㎡, a cell voltage of 10 V, and an electrolysis time of 30 min. During the electrolysis process, chloride ions in the cathode chamber pass through the anion exchange membrane under the action of the electric field and enter the anode chamber, and undergo an oxidation reaction at the anode to become chlorine gas, thereby obtaining a second lithium hydroxide solution with a lower chloride ion content in the cathode chamber, wherein the second lithium hydroxide solution contains the following components: Li + 15.2g / L, Mg 2+ 3mg / L, Na + 2.7g / L, K + 0.38g / L, B 3+ 26mg / L, Ca 2+ 2mg / L, OH - 35g / L, Cl - 0.6g / L, while the hydrogen obtained in the cathode chamber can be collected, and the anode chamber obtains a sodium hydroxide solution with a high chloride ion content, the chloride ion content in the sodium hydroxide solution is 0.65moL / L, and the concentration of sodium hydroxide is 25.7g / L;

[0068] (3) The second lithium hydroxide solution is preheated to 85° C. and then subjected to a first evaporation crystallization in a crystallizer to obtain a first concentrated solution with a solid content of 25%, wherein the conditions for the first evaporation crystallization include: a temperature of 85° C. and a pressure of 420 mbar; the first concentrated solution is centrifuged to obtain a first solid product, and the first solid product is washed to obtain a first crude salt; the first crude salt is then added to distilled water for salt dissolution to obtain a heavy solution, and the heavy solution is preheated to 85° C. and then subjected to a second evaporation crystallization in a crystallizer to obtain a second concentrated solution with a solid content of 30%, wherein the conditions for the second evaporation crystallization include: a temperature of 85° C. and a pressure of 420 mbar; the second concentrated solution is centrifuged to obtain a second solid product, and the second solid product is washed to obtain a second crude salt, and the second crude salt is sent to a rotary kiln drying system, and the dried salt is separated by a vibrating screen, and the screened material is a lithium hydroxide product.

[0069] After testing, the composition and content of the lithium hydroxide product obtained in this embodiment are shown in Table 3.

[0070] Table 3

[0071]

[0072] Example 4

[0073] (1) subjecting the lithium-rich concentrated solution to bipolar membrane electrodialysis to obtain a first lithium hydroxide solution, wherein the lithium-rich concentrated solution contains the following components: Li + 14.5g / L, Mg 2+ 4.6mg / L, Na + 1.92g / L, K + 0.28g / L, B 3+ 110.6mg / L, Ca 2+ 1.5mg / L, Cl - 64.1g / L, the first lithium hydroxide solution contains the following components: Li + 13.3g / L, Mg 2+ 4mg / L, Na + 1.6g / L, K + 0.22g / L, B 3+ 14mg / L, Ca 2+ 1mg / L, OH — 32g / L, Cl - 3g / L;

[0074] (2) The first lithium hydroxide solution is introduced into the cathode chamber of the electrolytic cell, and a sodium chloride solution with a concentration of 0.5 mol / L is introduced into the anode chamber. The diaphragm between the cathode chamber and the anode chamber is electrolyzed using an anion exchange membrane, wherein the electrolysis conditions include: a current density of 3.5 kA / ㎡, a cell voltage of 4 V, and an electrolysis time of 60 min. During the electrolysis process, chloride ions in the cathode chamber pass through the anion exchange membrane under the action of the electric field and enter the anode chamber, and undergo an oxidation reaction at the anode to become chlorine gas, thereby obtaining a second lithium hydroxide solution with a low chloride ion content in the cathode chamber, wherein the second lithium hydroxide solution contains the following components: Li + 14.8g / L, Mg 2+ 5mg / L, Na + 2.5g / L, K + 0.36g / L, B 3+ 25.6mg / L, Ca 2+ 1mg / L, OH - 34.6g / L, Cl - 0.68g / L, while the hydrogen obtained in the cathode chamber can be collected, and the anode chamber obtains a sodium hydroxide solution with a high chloride ion content, the chloride ion content in the sodium hydroxide solution is 0.72moL / L, and the concentration of sodium hydroxide is 33.4g / L;

[0075] (3) The second lithium hydroxide solution is preheated to 85° C. and then subjected to a first evaporation crystallization in a crystallizer to obtain a first concentrated solution with a solid content of 25%, wherein the conditions for the first evaporation crystallization include: a temperature of 85° C. and a pressure of 420 mbar; the first concentrated solution is centrifuged to obtain a first solid product, and the first solid product is washed to obtain a first crude salt; the first crude salt is then added to distilled water for salt dissolution to obtain a heavy solution, and the heavy solution is preheated to 85° C. and then subjected to a second evaporation crystallization in a crystallizer to obtain a second concentrated solution with a solid content of 30%, wherein the conditions for the second evaporation crystallization include: a temperature of 85° C. and a pressure of 420 mbar; the second concentrated solution is centrifuged to obtain a second solid product, and the second solid product is washed to obtain a second crude salt, and the second crude salt is sent to a rotary kiln drying system, and the dried salt is separated by a vibrating screen, and the screened material is a lithium hydroxide product.

[0076] After testing, the composition and content of the lithium hydroxide product obtained in this embodiment are shown in Table 4.

[0077] Table 4

[0078]

[0079] Comparative Example 1

[0080] (1) subjecting the lithium-rich concentrated solution to bipolar membrane electrodialysis to obtain a first lithium hydroxide solution, wherein the lithium-rich concentrated solution contains the following components: Li + 14.5g / L, Mg 2+ 4.6mg / L, Na + 1.92g / L, K + 0.28g / L, B 3+ 110.6mg / L, Ca 2+ 1.5mg / L, Cl - 64.1g / L, the first lithium hydroxide solution contains the following components: Li + 13.3g / L, Mg 2+ 4mg / L, Na + 1.6g / L, K + 0.22g / L, B 3+ 14mg / L, Ca 2+ 1mg / L, OH — 32g / L, Cl - 3g / L;

[0081] (2) The second lithium hydroxide solution is preheated to 85° C. and then subjected to a first evaporation crystallization in a crystal separator to obtain a first concentrated solution with a solid content of 25%, wherein the conditions for the first evaporation crystallization include: a temperature of 85° C. and a pressure of 420 mbar; the first concentrated solution is centrifuged to obtain a first solid product, and the first solid product is washed to obtain a first crude salt; the first crude salt is then added to distilled water for salt dissolution to obtain a heavy solution, and the heavy solution is preheated to 85° C. and then subjected to a second evaporation crystallization in a crystal separator to obtain a second concentrated solution with a solid content of 30%, wherein the conditions for the second evaporation crystallization include: a temperature of 85° C. and a pressure of 420 mbar; the second concentrated solution is centrifuged to obtain a second solid product, and the second solid product is washed to obtain a second crude salt, and the second crude salt is sent to a rotary kiln drying system, and the dried salt is separated by a vibrating screen, and the screened material is a lithium hydroxide product.

[0082] After testing, the composition and content of the lithium hydroxide product obtained in this comparative example are shown in Table 5.

[0083] Table 5

[0084]

[0085] It can be seen from the embodiments and comparative examples that the lithium hydroxide product obtained by the method described in the present invention has a low chloride ion content and is a lithium hydroxide product that meets battery-grade standards; while the lithium hydroxide product prepared according to the comparative example has a high chloride ion content and is a lithium hydroxide product that does not meet battery-grade standards.

[0086] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for dechlorination of alkali solution using a bipolar membrane, characterized in that: The method comprises the following steps: (1) subjecting the lithium-rich concentrated solution to bipolar membrane electrodialysis to obtain a first lithium hydroxide solution with a chloride ion content of ≥2 g / L; (2) passing the first lithium hydroxide solution into the cathode chamber of an electrolytic cell for electrolysis, and obtaining a second lithium hydroxide solution having a chloride ion content of ≤1.5 g / L in the cathode chamber, wherein the diaphragm between the cathode chamber and the anode chamber of the electrolytic cell is an anion exchange membrane; (3) Evaporating and crystallizing the second lithium hydroxide solution to obtain battery-grade lithium hydroxide, wherein the number of evaporation and crystallization is ≤2.

2. The method according to claim 1, characterized in that In step (1), the lithium-rich concentrated solution contains the following components: Li + ≥12g / L, Mg 2+ ≤100mg / L, Na + ≤2.0g / L, K + ≤0.3g / L, B 3+ ≤150mg / L, Ca 2+ ≤50mg / L, Cl - 60~70g / L.

3. The method according to claim 1 or 2, characterized in that: In step (1), the first lithium hydroxide solution contains the following components: Li + ≥13g / L, Mg 2+ ≤10mg / L, Na + ≤2.0g / L, K + ≤0.3g / L, B 3+ ≤20mg / L, Ca 2+ ≤10mg / L, OH — ≥30g / L, Cl - 2~6g / L.

4. The method according to any one of claims 1 to 3, characterized in that: In step (2), the electrolysis conditions include: current density 3-4 kA / ㎡, cell voltage 2-12 V, and electrolysis time 20-60 min.

5. The method according to any one of claims 1 to 4, characterized in that: In step (2), the second lithium hydroxide solution contains the following components: Li + ≥14g / L, Mg 2+ ≤10mg / L, Na + ≤2.0g / L, K + ≤0.3g / L, B 3+ ≤20mg / L, Ca 2+ ≤10mg / L, OH — ≥30g / L, Cl - ≤1.5g / L.

6. The method according to any one of claims 1 to 4, characterized in that: In step (2), the solution introduced into the anode chamber of the electrolytic cell is an alkali metal chloride solution; Preferably, the concentration of the alkali metal chloride solution is ≥0.5 moL / L; Preferably, the alkali metal chloride solution is a sodium chloride solution and / or a lithium chloride solution.

7. The method according to claim 6, characterized in that In step (2), after electrolysis, an alkali metal hydroxide solution is obtained in the anode chamber, wherein the chloride ion content is ≥0.5 mol / L and the concentration of the alkali metal hydroxide is 20-30 g / L; Preferably, the alkali metal hydroxide solution is a sodium hydroxide solution and / or a lithium hydroxide solution.

8. The method according to any one of claims 1 to 7, characterized in that: In step (3), the evaporative crystallization process includes a first evaporative crystallization and an optional second evaporative crystallization performed sequentially.

9. The method according to claim 8, characterized in that The conditions of the first evaporation crystallization include: temperature of 85-100° C. and pressure of 350-450 mbar; And / or, the conditions of the second evaporation crystallization include: temperature of 85-100° C. and pressure of 350-450 mbar.

10. The method according to any one of claims 1 to 9, characterized in that: In step (3), the battery-grade lithium hydroxide contains the following components: a main content of 56.5-57.5%, Ca 2+ ≤100ppm, Mg 2+ ≤10ppm, Na + ≤100ppm, K + ≤50ppm, B 3+ ≤100ppm, Si≤50ppm, Fe≤7ppm, SO4 2- ≤100ppm, Cl - ≤20ppm, CO3 2- ≤0.5%, acid insoluble matter ≤0.005%, magnetic material ≤200ppb.

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