Process for producing high purity lithium hydroxide monohydrate

Abstract

A process for producing high purity lithium hydroxide monohydrate from a material containing a lithium salt selected from Li2SO4, LiCl, Li2CO3 or mixtures thereof, comprising membrane electrolysis of an aqueous solution of said lithium salt using a cation exchange membrane and nickel-plated stainless steel. The catholyte is drawn from the circulation stream and evaporated to obtain lithium hydroxide monohydrate crystals which are separated from the mother liquor, washed with water and dried to obtain the final high purity lithium hydroxide monohydrate. Part of the used wash liquor is fed to the catholyte evaporation process. Part of the mother liquor formed after separation of the lithium hydroxide monohydrate crystals is returned to the catholyte evaporation process. The reverse flow of the anolyte is replenished with a concentrated lithium salt solution prepared from the original lithium salt. Part of the used catholyte drawn from the evaporation process is directed to Li2CO3 production.

Description

Technical Field

[0001] This invention belongs to the field of inorganic chemical technology, and specifically relates to a method for producing high-purity lithium hydroxide monohydrate from materials containing lithium salts. Background Technology

[0002] Lithium hydroxide solution is known to be produced by contacting lithium waste containing solid carbonate with water, precipitating the resulting slurry, decanting the clarified liquid phase, filtering, and then recycling the resulting lithium-containing solution through the central chamber of an electrodialysis unit, thereby obtaining a lithium hydroxide solution in the cathode chamber, a mixed acid solution in the anode chamber, and a desalted liquid in the central chamber, which is returned to the process of leaching lithium from lithium waste containing solid carbonate [1].

[0003] The disadvantage of this method is that the concentration of the produced LiOH solution is low (at most 25 kg / m³). 3 ), and because at most 2A / dm 2 (0.2kA / m 2 Operating at current densities of 10 kg / m³ results in low process efficiency; due to the low concentration of Li₂CO₃ (at most 10 kg / m³), the process is inefficient. 3 The recovered Li2CO3 solution has high resistance, resulting in high energy consumption per unit of the produced product.

[0004] Another known method for producing lithium hydroxide solution from lithium-containing materials (particularly from spent lithium-ion batteries) [2] involves extracting lithium in the form of highly soluble lithium sulfate from the waste and performing membrane electrolysis of the lithium sulfate solution using a Nafion 350 cation exchange membrane that separates the cathode and anode. Electrolysis is performed at a DC current density of 20 A / dm³. 2 The process is carried out at a voltage of 5.3V. A LiOH solution (catholyte stream) is continuously drawn from the cathode chamber, while a depleted anolyte stream containing sulfuric acid formed at the anode is continuously drawn from the anode chamber. The drawn anolyte stream is directed to the lithium leaching process to neutralize the sulfuric acid, while the electrolyte stream is simultaneously enhanced with lithium sulfate. The Li2SO4-enhanced anolyte is returned to the electrolysis process.

[0005] The drawback of this anolyte is that it can only produce LiOH solutions contaminated with impurities. This method cannot produce high-purity LiOH·H2O products.

[0006] It is known that high-purity lithium hydroxide can be produced by membrane electrolysis of an aqueous solution containing lithium chloride and lithium carbonate recovered from natural brine in the presence of a reducing agent [3]. The evaporated cathode electrolyte crystallizes LiOH·H2O. After separation from the mother liquor, LiOH·H2O is washed with demineralized water and dried to obtain high-purity LiOH·H2O. Here, cathode hydrogen is used to produce a heat carrier for generating heating steam in the cathode electrolyte evaporation process, and anode chlorine is used to oxidize bromide ions to elemental bromine by contacting natural brine rich in bromide ions.

[0007] The disadvantages of this method include: using a low-concentration LiCl solution, which is first recovered from lithium-containing natural brine with the aid of a LiCl selective adsorbent, as the feed for the electrochemical conversion, and the need to use a reducing agent to eliminate the risk of chlorine oxide formation in the anode chamber during the electrolysis of the low-concentration LiCl solution.

[0008] A method for producing high-purity lithium monohydrate from lithium carbonate-containing materials [4] overcomes most of the drawbacks of the above methods. The method is based on the reproduction of a highly soluble aqueous solution of lithium sulfate to replenish the anolyte that has undergone Li2SO4 depletion and H2SO4 enrichment during the circulation of the anolyte loop in the electrolysis unit. For this purpose, a portion of the lithium-depleted anolyte is continuously drawn from the anolyte loop and contacted with an equal amount of lithium carbonate to convert the anolyte sulfuric acid into lithium sulfate. The method also provides for the chemical purification of the reproduced Li2SO4 solution by using a carbonate-alkali method with LiOH solution and CO2 released during the neutralization of carbonates in the anolyte to remove Ca, Mg impurities and heavy metals.

[0009] The disadvantage of this method is the use of the MK-40 cation exchange membrane, which has relatively low mechanical and chemical stability, in the membrane electrolysis process. Furthermore, the method suffers from drawbacks including: water contamination by liquid waste, contamination of the lithium carbonate solution by sodium and potassium carbonate, and unsatisfactory chemical purification of the Li₂SO₄ solution supplied to replenish the anolyte circuit. This means that membranes contaminated with calcium and magnesium cations should be periodically inspected to determine if acid recovery is necessary.

[0010] A method and apparatus for producing lithium hydroxide monohydrate from brine [5] overcomes the disadvantages of the above method. The LiOH solution used for evaporation, crystallization, washing and drying of LiOH·H2O is obtained by chemical purification of concentrated LiCl solution by carbonate-alkali method and then ion exchange purification on a Li-type Lewatit-208-TP ion exchanger. The method also involves using the spent cathode electrolyte stream in the form of LiOH solution containing NaOH and KOH extracted from the evaporation process as a reagent to obtain a LiCl-rich solution, thereby removing sodium and potassium from the process in the form of NaCl and KCl crystals. In terms of its technical nature and the parameters of implementation, this method for producing lithium hydroxide monohydrate from lithium salt-containing materials is closest to the claimed method and is therefore selected as the closest prior art.

[0011] The disadvantages of this method are as follows:

[0012] 1) The range of raw materials that can be used to produce LiOH·H2O is limited to lithium chloride aqueous solution produced from lithium-containing natural brine;

[0013] 2) Sodium and potassium impurities accumulated in the cathode electrolyte can only be removed in the form of NaCl and KCl. The production process of LiOH·H2O is limited to concentrating and removing impurities from low-concentration LiCl raw materials (which are in the form of primary lithium concentrate produced from lithium-containing natural brine using LiCl selective adsorbent) to prepare lithium-rich concentrate (suitable for the production of lithium concentrates of LiCl·H2O and LiCl).

[0014] 3) The range of byproducts generated by anodic chlorine gas is limited;

[0015] 4) There is a lack of solutions for utilizing cathode hydrogen.

[0016] The above-mentioned disadvantages can be overcome by implementing the following technical solutions that form the basis of the claimed method:

[0017] -LiOH solution is obtained by membrane electrolysis of an aqueous solution of Li2SO4, an aqueous solution of LiCl, or a mixed solution of Li2SO4 and LiCl produced from a material containing lithium salts in the form of Li2SO4, LiCl, or Li2CO3, or various mixtures of these salts;

[0018] - The sodium and potassium-rich liquid stream extracted from the cathode electrolyte evaporation process (used cation exchanger) will be recovered as solid lithium carbonate and solid sodium bicarbonate and potassium bicarbonate.

[0019] - Using nickel-plated stainless steel as the cathode eliminates the risk of hydrogen adsorption (hydrogenation) and corrosion of the cathode.

[0020] - In the process of pretreating the lithium salt aqueous solution before membrane electrolysis, the remaining used washing solution after washing LiOH·H2O crystals is used as an alkaline reagent.

[0021] - A new solution is used to utilize the cathode and anode byproducts of membrane electrolysis of lithium salt aqueous solutions.

[0022] By implementing the provided technical solutions, the range of raw materials applicable to the production of lithium hydroxide monohydrate can be expanded, the reliability of the membrane electrolysis process can be improved, the range of by-products can be expanded, the formation of liquid and gaseous waste can be eliminated, and thus the environmental performance of the production process can be improved. Summary of the Invention

[0023] The technical effect is achieved by using lithium sulfate, lithium chloride, lithium carbonate, or various mixtures of these salts as the lithium salt material; using a cathode made of nickel-plated stainless steel in the membrane electrolysis process of the lithium salt aqueous solution; and using membranes of the Nafion-348, CTIEM-3, MF-4SK-100 type or equivalent membranes as cation exchange membranes.

[0024] The technical effect is achieved by first using a portion of the used washing liquid supplied to the cathode electrolyte evaporation process as an alkaline reagent in the step of chemically purifying the salt solution to remove impurities, in the process of pretreating the lithium salt solution to a predetermined concentration before electrolysis, and then using it as a regeneration solution in the ion exchange purification step to convert the ion exchanger from the H-type to the Li-type.

[0025] The technical effect is achieved by: recovering the used cathode electrolyte stream by mixing it with an aqueous solution containing sodium bicarbonate, potassium bicarbonate, and lithium bicarbonate; concentrating the resulting slurry (representing a mixture of lithium carbonate solid phase and solution containing Na2CO3, K2CO3, and Li2CO3) by removing a predetermined amount of water; separating the lithium carbonate solid phase from the liquid phase by carbonizing the liquid phase by contacting it with carbon dioxide, thus converting the carbonate solution into a bicarbonate suspension (representing a mixture of sodium bicarbonate and potassium bicarbonate solid phases in a solution of sodium bicarbonate, potassium bicarbonate, and lithium bicarbonate); filtering the resulting suspension to separate the sodium bicarbonate and potassium bicarbonate solid phases from the solution containing sodium bicarbonate, potassium bicarbonate, and lithium bicarbonate; and guiding the solution to mix with the used cathode electrolyte stream containing lithium hydroxide, sodium hydroxide, and potassium hydroxide extracted from the evaporation process.

[0026] The technical effect is achieved through the following method: When lithium sulfate is used as a lithium salt material, titanium coated with noble metals such as platinum, ruthenium, iridium, or tantalum is used as the anode in the membrane electrolysis process. A predetermined volume of anolyte is continuously drawn from the circulating anolyte stream that has undergone Li2SO4 depletion and H2SO4 enrichment at a predetermined rate. The drawn anolyte stream is contacted with CaO, Ca(OH)2, or CaCO3 until H2SO4 is completely neutralized. The resulting CaSO4·2H2O solid phase is separated from the Li2SO4 solution. The Li2SO4 solution is then contacted with a predetermined mass of initial Li2SO4 salt to dissolve it, obtaining a Li2SO4 solution of a predetermined concentration. A predetermined volume of [unspecified substance] is added to the obtained solution. The washing solution is then carbonized with carbon dioxide from the neutralization process of the extracted anolyte stream until the calcium and magnesium in the solution are converted into insoluble compounds CaCO3 and Mg(OH)2·3MgCO3·3H2O. The resulting suspension is filtered, and the precipitate is separated from the Li2SO4 solution. The chemically purified Li2SO4 solution is then purified by ion exchange using a layer of Li-type Lewatit-208-TP ion exchanger or an equivalent Li-type ion exchanger. The ion-exchange purified Li2SO4 solution is used as a replenishment solution for the circulating anolyte stream in the membrane electrolysis process. The regeneration of the used ion exchanger consists of two steps: the first step is treatment with 2.0N sulfuric acid solution, and the second step is treatment with 2N... The process consists of a LiOH solution (prepared from a used washing solution) and a used anolyte stream mixed with used recycled biomass before chemical purification. Cathode hydrogen, an electrolysis byproduct, is discharged from the cathode gas separator of the electrolysis unit along with the natural gas stream. The resulting gaseous mixture is directed to a steam generator as fuel for generating heating steam, which serves as a heat carrier in the evaporation process of the solution (particularly the cathode electrolyte).

[0027] The technical effect is achieved as follows: When lithium sulfate is used as a lithium salt material, a predetermined volume of anolyte stream, continuously drawn at a predetermined volume rate from a circulating anolyte stream undergoing Li2SO4 depletion and H2SO4 enrichment, is contacted with an air-ammonia mixture to neutralize H2SO4, thereby obtaining a mixed solution of Li2SO4 and (NH4)2SO4. This solution is then evaporated to precipitate (NH4)2SO4. The evaporated solution containing the remaining (NH4)2SO4 is mixed with a predetermined volume of used washing solution. Simultaneously, it is contacted with the gas stream from the process of contacting the used alkaline anolyte stream with an ammonia-air mixture to remove residual ammonia from the Li2SO4 solution; the gas stream containing gaseous ammonia is enriched by an ammonia source and guided to the neutralization process of the used anolyte stream; the ammonia-free Li2SO4 solution, after being pre-enhanced with Li2SO4 by dissolving a predetermined mass of initial lithium sulfate in it and purified by chemical and ion exchange to remove impurities, is used as a replenishing solution for the circulating anolyte stream in the membrane electrolysis process.

[0028] The technical effect is achieved as follows: When lithium chloride or lithium chloride monohydrate is used as a lithium salt material, a titanium anode coated with ruthenium oxide is used in the membrane electrolysis process, and a predetermined volume of anolyte is continuously drawn from the circulating anolyte stream that has experienced LiCl depletion at a predetermined volume rate; the drawn anolyte stream is contacted with an initial salt containing lithium chloride to bring the LiCl concentration in the drawn anolyte stream to a predetermined value; in addition to removing metal cation impurities through chemical purification, the drawn LiCl-rich anolyte stream is further purified by adding a predetermined amount of barium chloride to convert sulfate ions into insoluble BaSO4 precipitate to remove sulfate ions; the liquid phase is separated from the precipitate, purified by ion exchange, and used as a replenishing solution for the circulating anolyte stream in the membrane electrolysis process; cathode hydrogen and anode chlorine gas drawn from the gas separator are mixed and flame-combusted; the resulting hydrogen chloride is absorbed by softened water to produce 36% concentrated hydrochloric acid.

[0029] The technical effect is achieved as follows: When lithium chloride or lithium chloride monohydrate is used as a lithium salt material, the anolyte chlorine gas extracted from the gas separator is absorbed by ammonia water to produce NH4Cl solution at a molar ratio of NH3:Cl2 = 8:3 and 6N HCl solution at a molar ratio of NH3:Cl2 = 2:3; the obtained NH4Cl solution is evaporated, NH4Cl is crystallized, and dried to form crystals. In this case, the extracted hydrogen gas is used as a heat carrier to generate heating steam.

[0030] The technical effect is achieved through the following methods: When lithium chloride or lithium chloride monohydrate is used as a lithium salt-containing material, the anolyte chlorine gas extracted from the gas separator is completely absorbed by NaOH solution to produce a sodium hypochlorite disinfectant solution, or chlorine gas extracted at a flow rate of 0.5% is absorbed by NaOH solution to produce a saturated sodium hypochlorite solution; additionally, anolyte chlorine gas extracted at a flow rate of 0.5% is absorbed by Ca(OH)₂ suspension to produce a saturated calcium hypochlorite solution; the produced solutions are mixed to precipitate neutral calcium hypochlorite, the calcium hypochlorite is separated from the mother liquor and dried, and then calcium is precipitated from the obtained mother liquor. First, a predetermined amount of NaOH is added to precipitate Ca(OH)2, and then a predetermined amount of Na2CO3 is added to precipitate CaCO3. The precipitate containing Ca(OH)2 and CaCO3 is separated from the solution containing active chlorine in the form of hypochlorite ions. The solution is divided into two equal parts: one part is mixed with a predetermined amount of NaOH and directed to chlorination to obtain a sodium hypochlorite solution, and the other part is mixed with a predetermined amount of Ca(OH)2 and also directed to the chlorination process to obtain a calcium hypochlorite solution. Cathode hydrogen is used as the heat carrier for producing heating steam.

[0031] The technical effect is achieved by the following method: when lithium carbonate is used as a lithium salt material, the lithium carbonate is used to regenerate highly soluble lithium chloride or lithium sulfate salts that circulate in aqueous solution in the anolyte circuit of the electrolysis unit and undergo depletion of LiCl or Li2SO4 in the membrane electrolysis process. If an aqueous lithium chloride solution is used as the anolyte, a titanium anode coated with ruthenium oxide is used in the membrane electrolysis process. According to the first scheme, extracted cathode hydrogen and anode chlorine are mixed and burned to produce high-temperature hydrogen chloride vapor. The hydrogen chloride vapor is cooled and absorbed by softened water in a progressive countercurrent mode, thereby obtaining a concentrated (36%) hydrochloric acid stream from the first absorption step along the path of HCl vapor. The obtained concentrated hydrochloric acid stream is mixed with an anolyte stream purified to remove sulfate ions using BaCl2 as a reagent (which is extracted from the circulating anolyte stream in the membrane electrolysis process for purification to remove sulfate ions); the mixed stream of concentrated hydrochloric acid and purified anolyte is contacted with a predetermined amount of initial lithium carbonate and softened water to obtain a LiCl solution stream of a predetermined concentration. After purification to remove calcium and magnesium impurities, the LiCl solution stream is used as a supplementary solution for the circulating anolyte stream in the membrane electrolysis process; according to the second scheme, in the presence of ammonia, the extracted anolyte chlorine is absorbed by softened water at a molar ratio of NH3:Cl2 = 2:3 to obtain a 6N hydrochloric acid solution, which is then mixed with the purified anolyte stream. The anolyte stream purified to remove sulfate ions using BaCl2 as a reagent (which is drawn from the circulating anolyte stream in the membrane electrolysis process for purification to remove sulfate ions) is mixed; the mixed stream of hydrochloric acid solution and the purified anolyte stream is contacted with a predetermined amount of initial lithium carbonate to obtain a LiCl salt solution stream. After purifying to remove calcium and magnesium impurities, the LiCl salt solution stream is used as a supplementary solution for the circulating anolyte stream in the membrane electrolysis process, and cathode hydrogen is used as fuel for generating heating steam; according to the third scheme, in the presence of a predetermined amount of elemental chlorine reducing agent (whose material composition prevents contamination of the absorbent by foreign cations and anions, such as ammonia, hydrazine, hydroxyl), The anode chlorine gas is absorbed by an aqueous slurry of lithium carbonate with a predetermined content of Li2CO3 to obtain a lithium chloride solution with a predetermined LiCl concentration as the absorption product, which is used as a supplementary solution for the circulating anode electrolyte stream in the membrane electrolysis process. The aqueous slurry for absorbing anode chlorine gas is prepared by softened water, lithium carbonate obtained from used cathode electrolyte, lithium carbonate in the form of initial Li2CO3 salt, reducing agent, and anode electrolyte stream purified to remove sulfate ions using BaCl2 as a reagent (which is extracted from the circulating anode electrolyte stream at a predetermined volumetric flow rate in the membrane electrolysis process). Cathode hydrogen gas is used as fuel to generate heating steam.

[0032] When using an aqueous lithium sulfate solution as the anolyte, a titanium anode coated with noble metals such as platinum, ruthenium, iridium, or tantalum is used in the membrane electrolysis process. A predetermined volume of depleted lithium sulfate and sulfuric acid-enriched anolyte stream is drawn from the anolyte circulation loop at a predetermined rate and brought into contact with a predetermined amount of initial lithium carbonate to obtain a lithium sulfate solution of a predetermined concentration. This solution is then purified to remove impurities and used as a replenishment solution for the anolyte circulation loop.

[0033] The technical effect is achieved as follows: When a mixture of lithium sulfate and lithium carbonate is used as a lithium salt material, titanium coated with noble metals such as platinum, ruthenium, iridium, and tantalum is used as the anode in the membrane electrolysis process. A predetermined volume of depleted lithium sulfate and sulfuric acid-enriched anolyte is drawn from the anolyte circulation loop at a predetermined rate and brought into contact with a predetermined amount of an initial mixture of Li2SO4 and Li2CO3 to obtain a lithium sulfate solution of a predetermined concentration with residual H2SO4. The resulting Li2SO4 solution is then purified to remove residual sulfuric acid and used as a supplement to the circulating anolyte flow in the membrane electrolysis process.

[0034] The technical effect is achieved by the following method: when a mixture of lithium chloride and lithium carbonate is used as a lithium salt material, titanium coated with ruthenium oxide is used as the anode in the membrane electrolysis process. The initial mixture of lithium chloride and lithium carbonate is contacted with a predetermined volume of hydrochloric acid of a predetermined concentration and a predetermined volume flow rate of anolyte (LiCl is depleted during the membrane electrolysis process) drawn from the circulating anolyte stream to produce a lithium chloride solution. The resulting lithium chloride solution after purification to remove impurities is used as a replenishment solution for the circulating anolyte stream in the membrane electrolysis process.

[0035] The technical effect is achieved as follows: When a mixture of lithium sulfate and lithium chloride is used as a lithium salt material, titanium coated with noble metals (platinum, ruthenium, iridium, tantalum) is used as the anode in the membrane electrolysis process. A predetermined volume of anolyte is continuously drawn from the circulating anolyte flow that has undergone lithium sulfate and lithium chloride consumption and H2SO4 enrichment at a predetermined rate. The drawn predetermined volume of anolyte is contacted with a predetermined amount of ammonia contained in an ammonia-air mixture. Then, a mixed sulfate solution of Li2SO4 and (NH4)2SO4 is concentrated, and (NH4)2SO4 salt is precipitated until a Li2SO4 solution is obtained. Alternatively, the drawn predetermined volume of anolyte is contacted with a predetermined amount of C... The solution is contacted with OH)2 or CaCO3 until H2SO4 is completely neutralized and a Li2SO4 solution is obtained. The Li2SO4 solution is then separated from the precipitate by CaSO4·2H2O. The Li2SO4 solution obtained by either method is contacted with a predetermined amount of an initial mixture of Li2SO4 and LiCl salt to dissolve it and obtain a mixed solution of Li2SO4 and LiCl with a predetermined concentration of lithium. This solution is purified to remove impurities and then used as a supplementary solution for the circulating anolyte stream in the membrane electrolysis process. The anolyte chlorine gas extracted from the gas separator is recovered as 36% hydrochloric acid, or as NH4Cl salt, or as sodium hypochlorite solution, or as neutral calcium hypochlorite.

[0036] The technical effect is achieved by the following method: when a mixture of lithium sulfate, lithium chloride and lithium carbonate salts is used as the lithium salt material, titanium coated with noble metals is used as the anode in the membrane electrolysis process. A predetermined volume of anolyte is continuously drawn from the circulating anolyte flow that has undergone depletion of Li2SO4 and LiCl and enrichment of H2SO4 at a predetermined volume rate. This anolyte is first contacted with an initial mixture of a predetermined amount of Li2SO4, LiCl and Li2CO3 salts to produce a mixed solution of Li2SO4, LiCl and H2SO4 with a predetermined concentration of lithium. The resulting mixed solution is then converted into a mixed solution of Li2SO4 and LiCl, which is used as a replenishment solution for the circulating anolyte flow in the membrane electrolysis process. Attached Figure Description

[0037] Figure 1 A flowchart is shown for the production of LiOH·H2O from a material containing lithium salts in the form of Li2SO4 salt.

[0038] Figure 2 A flowchart is shown for the production of LiOH·H2O from a material containing lithium salts in the form of LiCl salts.

[0039] Figure 3 A flowchart is shown for the production of LiOH·H2O from a material containing lithium salts in the form of Li2CO3 salt.

[0040] Figure 4 A flowchart is shown for the production of LiOH·H2O from a lithium salt material in the form of a mixture of salts containing Li2SO4 and Li2CO3.

[0041] Figure 5 A flowchart is shown for the production of LiOH·H2O from a lithium salt material in the form of a mixture of LiCl and Li2CO3 salts.

[0042] Figure 6 A flowchart is shown for the production of LiOH·H2O from a lithium salt material in the form of a mixture of Li2SO4 and LiCl salts.

[0043] Figure 7 A flowchart is shown for the production of LiOH·H2O from a lithium salt material in the form of a mixture of salts containing Li2SO4, LiCl and Li2CO3.

[0044] The implementation of the provided invention is based on, for example Figures 1 to 7 The flowchart shown illustrates the production of lithium hydroxide monohydrate from materials containing lithium salts or mixtures thereof, and is supported by the provided embodiments.

[0045] The process flow diagram for producing LiOH·H2O from lithium salts containing Li2SO4 salts is as follows: Figure 1 As shown. This technology is based on a membrane electrolysis process capable of converting Li₂SO₄ solution into LiOH solution. Here, the electrochemical conversion process takes place under direct current, and a cation exchange membrane, stable in both alkaline and acidic solutions, separates the cathode and anode chambers of the electrolysis unit. The LiOH solution (cathode electrolyte) and the Li₂SO₄ solution (anolyte) continuously circulate in the cathode and anode chambers, respectively. During the circulation of the solutions, an electrode process occurs when they come into contact with the electrodes. Here, an electrochemical oxidation reaction of water occurs at the anode, producing oxygen and H₂ according to the following reaction. + ion:

[0046] H2O-2e - →2H + +1 / 2O2↑ (1)

[0047] Accordingly, electrochemical oxidation of water occurs at the cathode, producing oxygen and OH- according to the following reaction. - ion:

[0048] 2H2O+2e - →2ОН+Н2↑ (2)

[0049] In general, the electrochemical conversion of Li₂SO₄ to LiOH can be described by the following reaction:

[0050]

[0051] Cation exchange membranes allow cations to move unimpeded from the anode chamber to the cathode chamber. At this point, due to the specific characteristics of the cation exchange membrane, SO42-... 2 Ions do not transfer from the anode chamber to the cathode chamber, OH - Ions do not transfer from the cathode chamber to the anode chamber. Since the anolyte continuously consumes Li₂SO₄ and accumulates H₂SO₄, while the cathode electrolyte continuously accumulates LiOH, fresh Li₂SO₄ solution is continuously replenished to the circulating anolyte. The lithium concentration in the circulating anolyte is maintained at 20 kg / m³. 3 Up to 25kg / m 3 The optimal range for current density is 2 kA / m. 2 Up to 4kA / m 2 The optimal concentration of lithium hydroxide in the circulating cathode electrolyte is 50 kg / m³. 3 Up to 80kg / m 3Nafion-434, Nafion-438, Nafion-324, CTIEM-3, MF-4SK-100 type membranes, and other alkali- and acid-resistant equivalent membranes can all be used as cation exchange membranes. For the cathode, it is recommended to use a perforated plate made of nickel-plated stainless steel, which eliminates the risk of the cathode structural material being hydrogenated by cathode hydrogen gas, and also eliminates the risk of cathode corrosion during emergency shutdowns and current load interruptions. The most durable anode in the electrolysis of sulfate solutions is a platinum-plated titanium anode; in addition, titanium with an iridium-ruthenium oxide coating can also be used as an anode. A predetermined amount of cathode electrolyte stream is continuously drawn from the circulating cathode electrolyte (containing the Li2SO4 solution produced by membrane electrolysis) and then sent to the process of evaporating and crystallizing LiOH·H2O. LiOH·H2O crystals are usually separated from the mother liquor by centrifugation, the separated crystals are washed with softened water to remove the remaining portion of the mother liquor, and then dried to obtain LiOH·H2O product that meets the requirements of LGO-1GOST 8595-83 grade. The mother liquor formed after evaporation and crystal separation is returned to the evaporation process. Since sodium and potassium, as impurities, are contained in the lithium sulfate salt during electrolysis and enter the cathode electrolyte along with lithium, they gradually accumulate in the evaporated cathode electrolyte to concentration levels that prevent the production of products meeting LGO-1 grade requirements. Therefore, a predetermined volume is continuously drawn from the alkaline solution returned to the cathode electrolyte during the evaporation process from the separation of LiOH·H2O crystals and guided for recovery, thereby ensuring the return of lithium to the production process. The recovery of used cathode electrolyte involves separating lithium from alkali metal impurities based on the significant differences in solubility of compounds Li2CO3, LiHCO3, Na2CO3, NaHCO3, K2CO3, and KHCO3. Here, lithium carbonate is the least soluble compound in the given list, while K2CO3 is the most soluble. Conversely, sodium bicarbonate and potassium bicarbonate have much lower solubility than their carbonates, while lithium bicarbonate has a much higher solubility than lithium carbonate. In the initial step of the recovery process, a mixed bicarbonate solution saturated with KHCO3, NaHCO3, and LiHCO3 is prepared, and this solution stream is mixed with the recovered used cathode electrolyte stream. The mixing of these streams results in the precipitation of poorly soluble lithium carbonate and the conversion of potassium bicarbonate and sodium bicarbonate into carbonates with significantly higher solubility than their respective bicarbonates:

[0052] 2LiOH (溶液) (Na,K) + 2KHCO3 3(溶液) →Li2CO 3(s) ↓+K2CO 3(溶液) (4)

[0053] 2LiOH (溶液) (Na,K) + 2NaHCO3 3(溶液)→Li2CO 3(s) ↓+Na2CO 3(溶液) (5)

[0054] 2LiOH (溶液) (Na,K) + 2LiHCO3 3(溶液) →Li2CO 3(s) ↓+Li2CO 3(溶液) (6)

[0055] The mixing process is combined with a process to remove excess water from the used cathode electrolyte stream. Water is removed by directly contacting the resulting suspension with a predetermined stream heated to above 100°C. Water evaporates from the suspension due to contact with heated air, while the air is cooled to the temperature of a wet thermometer. The removal of water from the suspension results in an increased degree of Li₂CO₃ conversion to the solid phase. Simultaneously, the liquid phase is rich in sodium and potassium from the used cathode electrolyte. The resulting solid phase of Li₂CO₃ is separated from the carbonate solution by centrifugation, and a neutralization process with the used anolyte is performed. The resulting carbonate solution is converted to a bicarbonate solution by carbon dioxide treatment according to the following reaction:

[0056] K2CO 3(溶液) +CO 2(g) +Н2О (l) →2KHCO 3(溶液,s) (7)

[0057] Na2CO 3(溶液) +CO 2(g) +Н2О (l) →2NaHCO 3(溶液,s) (8)

[0058] Li2CO (溶液) +CO 2(g) +Н2О (l) →2LiHCO 3(溶液) (9)

[0059] Because the NaHCO3 and KHCO3 solutions are rich in sodium and potassium from the used cathode electrolyte, a supersaturated state occurs, and some sodium bicarbonate and potassium bicarbonate remain in the solid phase. However, due to the high solubility of lithium bicarbonate formed from dissolved Li2CO3, lithium bicarbonate will never remain in the solid phase. The resulting solid phases of sodium bicarbonate and potassium bicarbonate are separated from the bicarbonate solution by filtration. The bicarbonate solution is then mixed with the next batch of used cathode electrolyte.

[0060] Because the circulating anolyte undergoes Li₂SO₄ consumption and H₂SO₄ enrichment during membrane electrolysis, a predetermined anolyte stream is continuously drawn from the circulating anolyte stream and first contacted with lithium carbonate obtained during the recovery of used cathode electrolyte to neutralize part of the sulfuric acid according to the following reaction:

[0061] H2SO 4(溶液) +Li2CO 3(s) →Li2SO 4(溶液) +CO 2(g) +Н2О (l) (10)

[0062] In the process of acid neutralization with lithium carbonate, the used anolyte is partially enhanced by Li₂SO₄. Subsequently, there are two possible schemes for preparing the neutralized anolyte for electrolysis. According to the first scheme (Scheme A), the used anolyte neutralized with lithium carbonate is contacted with calcium oxide, or calcium hydroxide, or calcium carbonate, or mixtures thereof, according to the following reaction, to convert sulfuric acid into a solid phase CaSO₄·2H₂O:

[0063] H2SO 4(溶液) +CaO (s) +Н2О (l) →CaSO4·2H2O (s) (11)

[0064] H2SO 4(溶液) +Ca(OH) 2(g) →CaSO4·2H2O (s) (12)

[0065] H2SO 4(溶液) +CaCO 3(s) +Н2О (l) →CaSO4·2H2O (s) +CO 2(g) (13)

[0066] After separating and removing the precipitate, the used anolyte (i.e., the Li₂SO₄ solution with sulfuric acid completely removed) is contacted with a predetermined mass of initial Li₂SO₄ salt. After the latter dissolves, the solution will have a predetermined content of Li₂SO₄. Next, if necessary, the resulting Li₂SO₄ solution is chemically purified to remove calcium and magnesium. The chemical purification step is necessary if the calcium and magnesium content in the initial Li₂SO₄ salt is high. A predetermined portion of the used washing solution (containing a total level of 0.1 kg / m³) is then used. 3 120 kg / m³ of NaOH and KOH 3 LiOH solution and carbon dioxide were used as reagents. The purification process is described by the following chemical equation:

[0067] Ca (溶液) +2LiOH (溶液) +CO 2(g) →CaCO 3(s) ↓+2Li (溶液) + +Н2О (l) (14)

[0068] 4Mg (溶液) 2+ +8LiOH (溶液) +3CO 2(g) →Mg(OH)2·3MgCO3·3Н2О (s) ↓+8Li (溶液) + (15)

[0069] Chemical purification typically reduces the total remaining calcium and magnesium content in the analyzed solution to 10 g / m³. 3 Up to 15g / m 3 The Li₂SO₄ solution is purified by ion exchange after the precipitate is separated; for this purpose, a Li-type Lewatit 208TP ion exchanger or a Li-type anolyte is used. The ion exchange purification process is described by the following reaction equation:

[0070] Absorption steps

[0071]

[0072] Regeneration steps:

[0073]

[0074] Steps to convert H-type to Li-type

[0075]

[0076] Ion exchange purification can reduce the total concentration of residual calcium and magnesium in Li₂SO₄ solution to no more than 0.1 g / m³. 3 The solution is used at the specified level and is used as a supplementary solution for the circulating anolyte flow in the membrane electrolysis process.

[0077] According to another scheme (Scheme B), the extracted anolyte stream is first partially neutralized with lithium carbonate obtained in the stage of recovering used cathode electrolyte. Then, the partially neutralized used anolyte stream is neutralized with ammonia gas when it is directly contacted with an air-ammonia mixture. The remaining sulfuric acid is converted into ammonium sulfate according to the following reaction:

[0078] 2NH 3(g) +H2SO 4(溶液)→(NH4)2SO 4(溶液) (19)

[0079] The used anolyte stream is completely neutralized to obtain a mixed solution of Li₂SO₄ and (NH₄)₂SO₄. The (NH₄)₂SO₄ is then evaporated by salting out the mixed solution. The ammonium sulfate, washed and dried from the brine mother liquor, represents a commercially available fertilizer. The Li₂SO₄ solution with residual (NH₄)₂SO₄ obtained from the used anolyte is then alkalized using a portion of the washing solution formed during the washing process of LiOH·H₂O crystals.

[0080] After alkalization, the solution is deaminated by air circulation. The deamination process is described by the following chemical equation:

[0081] (NH4)2SO 4(溶液) +2LiOH (溶液) →2NH 3(g) +Li2SO 4(溶液) +2H2O (20)

[0082] An air stream containing gaseous ammonia is enriched with a predetermined amount of ammonia and directed to neutralize the next used and partially neutralized anolyte.

[0083] The Li2SO4 solution after the deammoniation step is further enhanced by dissolving a predetermined mass of initial Li2SO4 salt, and after chemical purification and ion exchange purification, it is used as a replenishment solution for the circulating anolyte stream.

[0084] The byproduct of membrane electrolysis, cathode hydrogen, is discharged from the cathode gas separator along with the natural gas stream. The resulting gaseous mixture is used as fuel for producing heating steam. The heating steam is then used in the evaporation process. The condensate of the juice vapor formed in the evaporation process is used as softened water in the process of washing crystals obtained through solution evaporation.

[0085] The process flow diagram for producing LiOH·H2O from lithium salts containing LiCl or LiOH·H2O salts is as follows: Figure 2 As shown. In this case, the technology is based on a membrane electrolysis process, which can electrochemically convert LiCl solution into LiOH solution. Here, the cathode process under the conditions of LiCl solution membrane electrolysis is similar to the cathode process under the conditions of Li2SO4 solution membrane electrolysis. However, the anodic process under the conditions of LiCl solution membrane electrolysis is significantly different because it is accompanied by the electrochemical oxidation of chloride ions to produce chlorine gas according to the following reaction:

[0086] Cl - -e -→1 / 2Cl2 (21)

[0087] In this case, no acid is formed during electrolysis; only the LiCl in the anolyte is depleted.

[0088] The electrochemical conversion of LiCl salt solution to LiOH can typically be described by the following reaction:

[0089]

[0090] The same cathode and cation exchange membrane are used under the same conditions as those for Li₂SO₄ salt solution electrolysis. The main parameters for the soluble salt membrane electrolysis process are almost identical. However, ruthenium oxide-coated titanium anodes (ruthenium titanium oxide anodes (ORTA)) can be successfully used for the electrolysis of lithium chloride solutions (provided the chloride anolyte is acidified to pH 2) instead of the expensive anodes typically used for lithium sulfate electrolysis, which are made of platinum-plated titanium or titanium coated with other precious metals. Acidifying the chloride-containing anolyte also eliminates the risk of chlorate formation in the circulating anolyte. For the electrochemical conversion of lithium sulfate and chloride solutions, the extraction of the cathode electrolyte and its processing into the final LiOH·H₂O are the same. The extraction and pretreatment of used (LiCl depleted) anolyte are similar to those for sulfate anolyte, except that the pretreatment of used chloride anolyte does not require a neutralization step, and the used anolyte is enhanced to a predetermined lithium concentration by dissolving a predetermined amount of initial LiCl salt. Since sulfate ions introduced from impurities in the initial lithium chloride used in the process may accumulate in the circulating anolyte stream, chemical purification of the LiCl-enhanced used anolyte is provided, in addition to removing calcium and magnesium, by using BaCl2 as a precipitant to convert sulfate ions into insoluble BaSO4 salt. During the ion exchange purification step of the LiCl-enhanced lithium chloride solution, an acid regeneration step is performed using 2N hydrochloric acid solution.

[0091] Hydrogen (cathode gas) and chlorine (anode gas), byproducts of membrane electrolysis, can be utilized in various ways. According to scheme A, hydrogen and chlorine extracted from the gas separator are mixed and subjected to high-temperature combustion to produce hydrogen chloride gas according to the following reaction:

[0092]

[0093] The resulting high-temperature hydrogen chloride stream is forced-cooled and subjected to gradual countercurrent absorption using softened water as the initial absorbent (which can be represented by the condensate, a byproduct of the evaporation process). Scheme B involves using cathode hydrogen as fuel to produce heating steam for the solution evaporation process. According to this scheme, an NH4Cl solution can be obtained by water absorption of a gaseous mixture of NH3 and Cl2 in a molar ratio of NH3:Cl2 = 8:3, followed by evaporation of the NH4Cl solution to obtain an NH4Cl salt, thereby utilizing chlorine gas as an NH4Cl salt:

[0094] 8NH 3(g) +3Cl 2(g) →6NH4Cl (溶液) +N 2(g) , (twenty four)

[0095] Alternatively, a 6N HCl solution can be obtained by water absorption of a gaseous mixture of NH3 and Cl2 in a molar ratio of NH3:Cl2 = 2:3, thereby utilizing chlorine gas as a 6N HCl solution:

[0096] 2NH 3(g) +3Cl 2(g) →6HCl (溶液) +N 2(g) (25)

[0097] Alternatively, chlorine gas can be absorbed by an aqueous solution of NaOH according to the following reaction, thus utilizing the chlorine gas as a sodium hypochlorite solution (disinfectant and preservative solution):

[0098] Cl 2(g) +2NaOH (溶液) →NaOCl (溶液) +NaCl (溶液) +H2O (l) (26)

[0099] Alternatively, it can be used as neutral calcium hypochlorite by drying the Ca(OCl)2 salt, which is separated after an exchange reaction between a NaOCl-saturated sodium hypochlorite solution and a Ca(OCl)2-saturated solution: A NaOCl-saturated sodium hypochlorite solution is obtained by absorbing half of the anolyte chlorine gas with concentrated NaOH solution according to the following reaction:

[0100]

[0101] A Ca(OCl)2 saturated solution is obtained by absorbing half of the anolyte chlorine gas through a calcium hydroxide slurry according to the following reaction:

[0102] 2Cl 2(g) +2Ca(OH) 2(s,溶液)→Ca(OCl) 2(溶液) +CaCl 2(溶液) +2H2O (l) (28)

[0103] The Ca-containing product obtained after the exchange reaction 2+ Na + A predetermined amount of NaOH is introduced into the mother liquor containing active chlorine ions (Cl-, OCl-), and the following reaction precipitates the main amount of calcium:

[0104] Ca 2+ (溶液) +2NaOH (溶液) →Ca(OH) 2(溶液) ↓+2Na + (溶液) (29)

[0105] The remaining amount of calcium is removed from the solution by adding a predetermined amount of Na₂CO₃ according to the following reaction:

[0106] Ca 2+ (溶液) +Na2CO 3(溶液) →CaCO 3(g) ↓+2Na + (溶液) (30)

[0107] The resulting Ca(OH)2 precipitate mixed with CaCO3 is subjected to a chlorination process to form a Ca(OH)2 slurry. The solution containing an equal proportion of active chlorine formed after calcium precipitation is returned to the chlorination process of NaOH solution and Ca(OH)2 slurry.

[0108] The process flow diagram for producing LiOH·H2O from materials containing lithium salts in the form of Li2CO3 salts is as follows: Figure 3As shown. According to this scheme, the method for preparing LiOH·H2O using Li2CO3 salt includes: using the salt as a reagent to regenerate the lithium-depleted anolyte in the membrane electrolysis process, which can be recycled either as a Li2SO4 solution (Scheme A) or as a LiCl solution (Schemes B, C). Here, according to Scheme A, the used anolyte is lithium-fortified, while simultaneously neutralizing sulfuric acid by mixing the used anolyte with a predetermined amount of initial lithium carbonate salt (including lithium carbonate obtained by recovering and evaporating the used cathode electrolyte); according to this scheme, cathode hydrogen is used as a flue gas component for producing heating steam. If the production process follows Scheme B, cathode hydrogen and anode chlorine are used to obtain concentrated hydrochloric acid (reaction 23) by burning their mixture and absorbing hydrogen chloride with water. The resulting acid is mixed with a purified anolyte stream to remove sulfate ions, which is drawn from a sulfate-rich circulating anolyte stream at a predetermined volumetric flow rate during the electrolysis process. A mixed solution of concentrated hydrochloric acid and purified anolyte (with sulfate ions removed) is contacted with a predetermined amount of initial Li₂CO₃ and softened water to produce a LiCl solution of a predetermined concentration. After purification to remove calcium and magnesium, this solution is used to replenish the LiCl solution in the circulating anolyte stream during the membrane electrolysis process. According to Scheme B, 6N hydrochloric acid solution (reaction 25) is produced by absorbing anode chlorine gas mixed with ammonia (molar ratio NH₃:Cl₂ = 2:3) into softened water. The resulting acid is mixed with a purified anolyte stream (with sulfate ions removed), which is drawn from a sulfate-rich circulating anolyte stream at a predetermined volumetric flow rate during the electrolysis process. The mixed solution of hydrochloric acid and purified anolyte (with sulfate ions removed) is contacted with a predetermined amount of initial Li₂CO₃ salt solution to produce a LiCl solution of a predetermined concentration. After purification to remove calcium and magnesium, this solution is used to replenish the circulating anolyte stream during the membrane electrolysis process. According to this scheme, cathode hydrogen is used as fuel to generate heating steam. According to scheme B, in the presence of a predetermined amount of reducing agent (whose material composition prevents contamination by the absorbent, such as ammonia, hydrazine, hydroxylamine, urea, or formic acid), a LiCl solution is produced according to the following reaction:

[0109] 3Cl 2(g) +3Li2CO 3(s) +2NH 3(g) →6LiCl (溶液) +N 2(g) +3CO 2(g) +3H2O (l) (31)

[0110] The aqueous slurry used to absorb chlorine gas from the anode is prepared by: softened water, lithium carbonate in the form of an initial Li₂CO₃ salt obtained from the used cathode electrolyte, a suitable reducing agent, and a purified anolyte stream to remove sulfate ions (which is extracted from the circulating anolyte stream at a predetermined volumetric rate during electrolysis). According to this scheme, hydrogen gas from the cathode is used as fuel to generate heating steam.

[0111] The process flow diagram for producing LiOH·H2O from lithium salts in the form of a mixture of Li2SO4 and Li2CO3 is as follows: Figure 4 As shown. This flowchart is related to... Figure 1 The flowcharts shown are essentially the same. The differences include that, prior to the complete neutralization of sulfuric acid, the used anolyte is enhanced (lithium enriched) to a predetermined lithium concentration by dissolving a predetermined amount of the initial mixed salt of Li₂SO₄ and Li₂CO₃. Otherwise, the flowcharts are identical.

[0112] The process flow diagram for producing LiOH·H2O from lithium salts in the form of a mixture of LiCl and Li2CO3 is as follows: Figure 5 As shown. This flowchart is related to... Figure 2 The flowcharts shown are essentially the same. The differences include the fact that the enhancement (lithium enrichment) of the used anolyte is carried out by mixing it with a concentrated LiCl solution, which is obtained by decarbonizing the initial LiCl and Li₂CO₃ mixed salt and the carbonates obtained from the recovery of the used evaporated cathode electrolyte with hydrochloric acid. Otherwise, the flowcharts are identical.

[0113] The process flow diagram for producing LiOH·H2O from lithium salts in the form of a mixture of Li2SO4 and LiCl is as follows: Figure 6 As shown. A significant feature of this technology is that two highly soluble lithium salts (lithium chloride and lithium sulfate) participate simultaneously in the anodic process, with reactions (1) and (21) occurring simultaneously at the anode, forming H2SO4, Cl2, and O2 in the anode chamber. Therefore, the reliability of the membrane electrolysis process of the mixed salts can be ensured by using an anode made of platinum-plated titanium. Here, the cathode process remains unchanged, similar to the membrane electrolysis process of highly soluble Li2SO4 and LiCl salt solutions.

[0114] The preparation of LiOH·H2O based on the electrochemical conversion of a mixed solution of Li2SO4 and LiCl does not require special procedures to purify and remove sulfate ions from the anolyte. In addition, Figure 6 The technology described is Figure 1 and Figure 2 The flowchart shows the combination of process steps.

[0115] The process flow diagram for producing LiOH·H2O from lithium salts in the form of a mixture of Li2SO4, LiCl, and Li2CO3 is as follows: Figure 7 As shown. This flowchart is the same as the flowchart for processing a mixed salt of Li₂SO₄ and LiCl. Figure 6 The only difference is that a process for strengthening the used anolyte is performed before the sulfuric acid neutralization step. Otherwise, the flow chart is the same.

[0116] Example 1

[0117] A laboratory-scale apparatus comprising a membrane electrolysis unit, a unit for processing a cathode electrolyte into LiOH·H2O, a unit for pretreatment and purification of a supplementary lithium salt solution used as feed to the circulating anolyte, a unit for treating used evaporated cathode electrolyte, and an anolyte gas utilization unit, for conducting comparative experiments on technologies for producing LiOH·H2O from various lithium salts (lithium sulfate, lithium chloride, and mixtures of lithium sulfate and lithium chloride). Based on Figure 1 , 2 The flowchart shown reproduces the technical process on the laboratory apparatus. Here, for the aforementioned purposes, a scheme using slaked lime is adopted to neutralize the sulfate-containing anolyte, lithium carbonate pre-dissolved in hydrochloric acid is used to strengthen the chloride-containing anolyte, and anolyte chlorine gas is utilized as neutral calcium hypochlorite. The following lithium salts are used in the tests: industrial-grade lithium sulfate monohydrate (composition shown in Table 1) and lithium chloride according to TU2152-017-07622236-2015 (composition shown in Table 2).

[0118] Table 1. Composition of industrial grade Li2SO4·H2O

[0119] Parameter name Content, weight % <![CDATA[Mass fraction of Li2SO4·H2O]]> 98.10 <![CDATA[Li3PO4]]> 1.90 Na 0.020 K 0.003 Ca 0.0064 Mg 0.0002 Fe 0.0005 water 10.5 Cl+Fe Not detected

[0120] Table 2. Composition of Industrial Grade LiCl·H2O

[0121] Parameter name Content, weight % Na+K 0.1 Ca+Mg 0.03 Fe 0.005 Al 0.01 Pb 0.003 <![CDATA[PO4]]> 0.007 <![CDATA[SO4]]> 0.1 OH 0.03

[0122] Calcium hydroxide used to neutralize sulfuric acid and to utilize anodic chlorine as neutral calcium hypochlorite is obtained by precipitation from a CaCl2 solution produced by dissolving hydrated industrial-grade CaCl2·6H2O salt (using NaOH as a precipitant).

[0123] Table 3 shows the main comparative parameters and characteristics of the techniques for producing LiOH·H2O from various lithium salts according to the claimed method. Table 4 shows the composition of the obtained LiOH·H2O samples.

[0124] Table 3. Comparative characteristics of technologies for producing LiOH·H2O from various lithium salts according to the claimed method.

[0125]

[0126] Table 4. Composition of LiOH·H2O samples obtained from various lithium salts by the claimed method

[0127]

[0128] The results show that the claimed method can produce high-quality LiOH·H2O products from the tested lithium salts that meet the LGO-1GOST 8595-83 grade requirements. Here, the electrochemical parameters of the membrane electrolytic conversion process from a highly soluble lithium salt solution to a LiOH solution exhibit very similar characteristics.

[0129] Tests also showed that when anolyl chlorine was used according to the scheme proposed in the claimed method (involving the recovery of anolyl chlorine into neutral calcium hypochlorite), the active chlorine content in the product sample was 62% to 63% by weight, and the content of water-insoluble impurities did not exceed 4.3%. The utilization rate of anolyl chlorine was 99.7%.

[0130] Tests also showed that sulfuric acid in the used sulfuric acid anolyte should be neutralized by adding a stoichiometric amount of Ca(OH)2, provided that the operation is carried out in two steps, so as to completely neutralize the H2SO4 in the anolyte without introducing excess Ca(OH)2.

[0131] Here, in the first step, the initial used anolyte is contacted with the precipitate (a mixture of CaSO4·2H2O and Ca(OH)2) used in the second step, ensuring that all free Ca(OH)2 is converted to CaSO4·2H2O, and the resulting CaSO4·2H2O precipitate is extracted by filtration. The filtrate containing unreacted H2SO4 residue is then contacted with Ca(OH)2, which is stoichiometric in proportion to the H2SO4 contained in the initial used anolyte supplied in the first step of the neutralization step. During the phase contact in the second step, a mixed precipitate of CaSO4·2H2O and Ca(OH)2 is formed, ensuring complete neutralization of the sulfuric acid. The contact between the anolyte and Ca(OH)2 is carried out under vigorous mixing conditions.

[0132] Example 2

[0133] The experimental setup included three membrane electrolysis units to test the suitability of three cation exchange membranes (Nafion-438, CTIEM-3, and MF-4SK-100) for the electrochemical conversion of Li₂SO₄ and LiCl solutions to LiOH solutions. The total testing time was 219 working hours. The following anodes were tested: for LiCl solution electrolysis, the anode was ruthenium oxide-coated titanium (ORTA); for Li₂SO₄ solution electrolysis, the anode was platinum-plated titanium. The results are shown in Table 5.

[0134] Table 5. Test results of electrochemical conversion of Li₂SO₄ solution and LiCl solution to LiOH solution using various cation exchange membranes.

[0135]

[0136] The results show that all tested membranes are suitable for membrane electrolysis of lithium sulfate and lithium chloride solutions to obtain a cathode electrolyte in the form of LiOH solution. Here, the membrane electrolysis parameters (e.g., cell voltage and LiOH flow output of the tested membranes) are almost identical. The tests also indicate that the energy consumption for electrolyzing LiCl solution to obtain LiOH solution is lower because the cell voltage of the membrane electrolysis unit is consistently higher during the electrolysis of sulfate solutions than during the electrolysis of chloride-containing solutions. This finding is attributed to the higher conductivity of Li₂SO₄ solution compared to LiCl solution.

[0137] The data obtained show that other cation exchange membranes, comparable to the tested cation exchange membranes and chemically stable in these media, can also be used for the conversion of Li2SO4 and LiCl solutions.

[0138] Example 3

[0139] according to Figure 3The laboratory apparatus shown in the flowchart is used to test a technology for producing LiOH·H2O from lithium carbonate, where lithium carbonate is used to regenerate LiCl and Li2SO4 supplied to the anolyte circulation loop, thereby replenishing the used electrolyte from the membrane electrolysis process that has been depleted of LiCl and Li2SO4. Here, the Li2SO4 solution is regenerated and replenished by directly contacting a predetermined amount of Li2CO3 with the used anolyte in a step of neutralizing the used sulfate-containing anolyte. The regeneration of the replenished LiCl solution is carried out according to two schemes. According to the first scheme, anolyte chlorine gas, as part of a mixture, is absorbed with ammonia gas (molar ratio NH3:Cl2 = 2:3) by softened water to obtain a hydrochloric acid solution of a predetermined concentration. This hydrochloric acid solution is contacted with a predetermined amount of Li2CO3, and the resulting solution is mixed with the used anolyte previously neutralized to pH = 7 with lithium carbonate to obtain a LiCl-enhanced lithium chloride solution, which is used to replenish the circulating anolyte in the membrane electrolysis process. According to the second scheme, in the presence of a predetermined amount of urea reducing agent, chlorine gas is absorbed by a lithium carbonate slurry containing a predetermined amount of Li₂CO₃ to obtain a LiCl solution of a predetermined concentration. This solution is then mixed with used anolyte pre-neutralized to pH=7 to obtain a LiCl-enhanced lithium chloride solution, which is used to replenish the circulating anolyte. Industrial-grade lithium carbonate produced by SQM (Chile) is used as the initial lithium carbonate, the composition of which is shown in Table 6.

[0140] Table 6. Composition of the industrial-grade lithium carbonate used

[0141]

[0142] The enhanced and purified lithium salt solution generated from the used anolyte stream was adjusted to the predetermined concentrations of Li₂SO₄ and LiCl in the replenishment solution by evaporation. The main test parameters are shown in Table 7. The composition of the obtained LiOH·H₂O sample is shown in Table 8. The results clearly demonstrate that the proposed method can produce high-purity LiOH·H₂O meeting LGO-1 grade requirements from industrial-grade lithium carbonate.

[0143] Table 7. Main parameters for the production of LiOH·H2O from Li2CO3 via membrane electrolysis of highly soluble lithium salts.

[0144]

[0145] Table 8. Composition of LiOH·H2O samples produced from Li2CO3 by membrane electrolysis of highly soluble lithium salts

[0146]

[0147] Here, the recovery rate of the conversion alkali (LiOH solution) to solid product (LiOH·H2O) largely depends on the sodium and potassium content in the initial lithium carbonate.

[0148] Example 4

[0149] Using a laboratory workbench represented by an assembly utilizing sulfate ions present in H₂SO₄ salts, a utilization scheme was tested by converting sulfuric acid contained in a used sulfate electrolyte into (NH₄)₂SO₄. This was achieved by contacting the used anolyte with ammonia gas and precipitating (NH₄)₂SO₄ salt from a mixed electrolyte of used Li₂SO₄ and (NH₄)₂SO₄ during evaporation, while simultaneously increasing the Li₂SO₄ content in the anolyte. The technical process for utilizing sulfuric acid contained in the used anolyte in the form of (NH₄)₂SO₄ salt is as follows: Figure 1 As shown in the figure. The results are shown in Table 9.

[0150] Table 9. Main parameters of the process for recovering anolyl sulfuric acid from used sulfate anolyl electrolyte into (NH4)2SO4 salt.

[0151]

[0152] The (NH4)2SO4 salt sample obtained after three-step countercurrent washing with softened water and drying at 110°C contained 99.7% by weight (NH4)2SO4 as the main substance, and the lithium impurity content was less than 0.002% by weight. The utilization rate of ammonia was 99.84%.

[0153] Example 5

[0154] According to the method of protection required ( Figures 1 to 7 ), recovering 10 dm³ on a device under stable operating conditions. 3 It has the following composition (g / dm 3 The used cathode electrolyte stream was: LiOH—120; NaOH—8.7; KOH—0.3. After recovery, 1850g of dry Li₂CO₃ was obtained, with a main substance content of 99.9% and a total sodium and potassium impurity content of less than 0.01%. The total weight of the dry precipitate of NaHCO₃ and KHCO₃ salts was 188.1g, with a residual lithium content of less than 0.002%.

[0155] References

[0156] 1. Russian Patent No. 2071819, published on January 20, 1997.

[0157] 2. WO application number New Zealand 9859385, published in 1998.

[0158] 3. Russian Patent No. 2157338, published on October 10, 2000.

[0159] 4. Russian Patent No. 21967335, published on January 20, 2003.

[0160] 5. Russian Patent No. 2656452, published on June 5, 2018.

Claims

1. A method for producing high-purity lithium hydroxide monohydrate from a material containing a lithium salt, wherein the lithium salt is selected from lithium sulfate, lithium chloride, lithium chloride monohydrate, lithium carbonate, or mixtures thereof, the method comprising: A cation exchange membrane is used as the membrane separating the cathode and anode circuits of the electrolysis unit. Membrane electrolysis of the lithium salt aqueous solution is performed in a circulating mode of cathode electrolyte in the form of lithium hydroxide solution and anode electrolyte in the form of lithium salt solution. The cathode used for membrane electrolysis is made of nickel-plated stainless steel, and the cation exchange membrane is selected from alkali- and acid-resistant membranes. The current density of the anode electrolyte is 2 kA / m³. 2 to 4 kA / m 2 Furthermore, the lithium concentration in the anolyte is maintained at 20 kg / m³. 3 Up to 25 kg / m 3 Within the range; A certain volume of cathode electrolyte is extracted from the circulating cathode electrolyte stream and the extracted volume of cathode electrolyte is evaporated to obtain lithium hydroxide monohydrate crystals. The crystals formed from the mother liquor were washed with water and dried to obtain the final high-purity lithium hydroxide monohydrate. The method is further characterized by the following steps: Remove cathode and anode gases formed during electrolysis; A portion of the generated used washing solution stream is supplied to the evaporation process of the cathode electrolyte, and a portion of the used washing solution supplied to the evaporation process of the cathode electrolyte is used to recover the extracted used anolyte stream. A portion of the mother liquor formed after separating lithium hydroxide monohydrate crystals is returned to the evaporation process of the cathode electrolyte; A portion of the used cathode electrolyte stream is recycled to obtain lithium carbonate, wherein the used cathode electrolyte stream is extracted from the evaporation process and represents a concentrated lithium hydroxide solution mixed with sodium hydroxide and potassium hydroxide. The used cathode electrolyte stream is recovered by mixing it with an aqueous solution containing sodium bicarbonate, potassium bicarbonate, and lithium bicarbonate; the resulting slurry, representing a mixture of a lithium carbonate solid phase and a carbonate solution containing Na₂CO₃, K₂CO₃, and Li₂CO₃, is concentrated by removing water; the lithium carbonate solid phase is separated from the liquid phase by carbonizing the liquid phase through direct contact with carbon dioxide, converting the carbonate solution into a bicarbonate suspension, representing a mixture of sodium bicarbonate and potassium bicarbonate solid phases in a sodium bicarbonate, potassium bicarbonate, and lithium bicarbonate solution; the resulting suspension is filtered to separate the sodium bicarbonate and potassium bicarbonate solid phases from the solution containing sodium bicarbonate, potassium bicarbonate, and lithium bicarbonate, which is then directed to be mixed with a used cathode electrolyte stream containing lithium hydroxide, sodium hydroxide, and potassium hydroxide drawn from the evaporation process; and The circulating anolyte stream is replenished with a concentrated lithium salt solution prepared from the original source of the lithium salt and a lithium salt solution obtained by recovering the extracted used anolyte stream.

2. The method as described in claim 1, characterized in that, Using a portion of the used washing solution supplied to the cathode electrolyte evaporation process for recycling the extracted used anolyte stream includes: using the used washing solution as an alkaline reagent in a step of chemically purifying the lithium salt solution to remove impurities and / or using the used washing solution as a regeneration solution to convert the ion exchanger from the H-form to the Li-form in an ion exchange purification step.

3. The method as described in claim 2, characterized in that, The cation exchange membrane used for membrane electrolysis is a Nafion-438, CTIEM-3, MF-4SK-100 type membrane or its equivalent; Lewatit 208-TP ion exchanger is used in the ion exchange purification step.

4. The method as described in claim 3, characterized in that, When lithium sulfate is used as a lithium salt material, in the membrane electrolysis process, titanium coated with a noble metal selected from platinum, iridium, ruthenium, or tantalum is used as the anode. An anolyte stream is continuously drawn from a circulating anolyte stream undergoing Li₂SO₄ depletion and H₂SO₄ enrichment. The drawn anolyte stream is contacted with CaO, Ca(OH)₂, or CaCO₃ until H₂SO₄ is completely neutralized. The resulting CaSO₄·2H₂O solid phase is separated from the Li₂SO₄ solution, and the Li₂SO₄ solution is contacted with the initial lithium sulfate salt to dissolve it and obtain a lithium sulfate solution. A used washing solution is added to the obtained solution, and then the solution is treated with a medium from the drawn anolyte stream. The carbon dioxide in the process carbonizes the solution until the calcium and magnesium contained in the solution are converted into insoluble compounds CaCO3 and Mg(OH)2·3MgCO3·3H2O; the resulting suspension is filtered, the precipitate is separated from the Li2SO4 solution, and the chemically purified Li2SO4 solution is guided to pass through a layer of Li-type Lewatit-208-TP ion exchanger or an equivalent Li-type ion exchanger for ion exchange purification; the ion-exchange purified Li2SO4 solution is used as a replenishing solution for the circulating anolyte stream in the membrane electrolysis process; the used ion exchanger is regenerated in two steps: the first step consists of treatment with 2.0N sulfuric acid solution, and the second step consists of treatment with 2.0N LiOH solution; the used anolyte stream is mixed with the used regenerated biomass before chemical purification; the cathode hydrogen, as an electrolysis byproduct, is discharged from the cathode gas separator of the electrolysis unit along with the natural gas stream, and the resulting gaseous mixture is guided to a steam generator as fuel for generating heating steam, which is used as a heat carrier in the evaporation process of the solution, especially the cathode electrolyte.

5. The method as described in claim 4, characterized in that, A certain volume of anolyte stream, continuously drawn from the circulating anolyte stream undergoing Li2SO4 depletion and H2SO4 enrichment, is contacted with an air-ammonia mixture to neutralize H2SO4, resulting in a mixed solution of Li2SO4 and (NH4)2SO4. This solution is then evaporated to precipitate (NH4)2SO4 and increase the Li2SO4 concentration in the evaporated solution. The evaporated solution containing residual (NH4)2SO4 is mixed with a certain volume of used alkaline washing solution. This mixed solution is then contacted with an air stream from the used anolyte stream in the ammonia-air mixture contact process to remove residual ammonia from the Li2SO4 solution. The air stream containing gaseous ammonia is enriched with ammonia by an ammonia source and guided to the neutralization process of the used anolyte stream. The ammonia-free Li2SO4 solution, which has been enhanced with Li2SO4 and purified to remove impurities by dissolving initial Li2SO4 salts in it, is used as a replenishment solution for the circulating anolyte stream in the membrane electrolysis process.

6. The method as described in claim 3, characterized in that, When lithium chloride or lithium chloride monohydrate is used as a lithium salt material, a titanium anode coated with ruthenium oxide is used in the membrane electrolysis process, and a certain volume of anolyte is continuously drawn from the circulating anolyte stream that is experiencing LiCl depletion. The extracted anolyte stream is contacted with the initial lithium chloride salt to bring the LiCl concentration in the extracted anolyte stream to a predetermined value. In addition to removing metal cation impurities through chemical purification, the extracted LiCl-rich anolyte stream is also purified by adding barium chloride to convert sulfate ions into insoluble BaSO4 precipitate. The liquid phase is separated from the precipitate and purified by ion exchange, then used as a supplementary solution for the circulating anolyte flow in the membrane electrolysis process; the cathode hydrogen and anode chlorine extracted from the gas separator are mixed and flame-burned; the resulting hydrogen chloride is absorbed by softened water to produce 36% concentrated hydrochloric acid.

7. The method as described in claim 6, characterized in that, The chlorine gas extracted from the anode of the gas separator is absorbed by ammonia water to produce NH4Cl solution at a molar ratio of NH3:Cl2 = 8:3 and 6NHCl solution at a molar ratio of NH3:Cl2 = 2:

3. The resulting NH4Cl solution is evaporated, crystallized, and dried. The hydrogen gas extracted from the cathode of the gas separator is used as a heat carrier to generate heating steam.

8. The method as described in claim 6, characterized in that, Anode chlorine gas extracted from the gas separator is completely absorbed by NaOH solution to produce a sodium hypochlorite disinfectant solution, or chlorine gas extracted at a flow rate of 0.5% is absorbed by NaOH solution to produce a saturated sodium hypochlorite solution, while chlorine gas extracted at another flow rate of 0.5% is absorbed by Ca(OH)2 suspension to produce a saturated calcium hypochlorite solution. The produced solutions are mixed to precipitate neutral calcium hypochlorite, and the calcium hypochlorite is separated from the mother liquor and dried. Calcium is precipitated from the resulting mother liquor by first adding a predetermined amount of NaOH, followed by adding Na2CO3. The Ca(OH)2 precipitate mixed with CaCO3 is separated from the solution and directed to prepare a Ca(OH)2 suspension containing active chlorine in the form of hypochlorite ions. The solution is divided into two equal parts: one part is mixed with NaOH and directed to the chlorination process to obtain a sodium hypochlorite solution, and the other part is mixed with Ca(OH)2 and directed to the chlorination process to obtain a calcium hypochlorite solution.

9. The method as described in claim 3, characterized in that, When lithium carbonate is used as a lithium salt material, the lithium carbonate is used to regenerate the anolyte by converting Li2CO3 into highly soluble lithium salts lithium chloride or lithium sulfate, which circulate as anolyte in the anolyte circuit of the electrolysis unit and undergo depletion of LiCl or Li2SO4 during membrane electrolysis.

10. The method as described in claim 3, characterized in that, When an aqueous lithium chloride solution is used as the anolyte, a titanium anode coated with ruthenium oxide is used in the membrane electrolysis process. Cathode hydrogen and anode chlorine are mixed and burned to produce high-temperature hydrogen chloride vapor. The hydrogen chloride vapor is cooled and absorbed by softened water in a stepwise countercurrent manner to obtain a 36% concentrated hydrochloric acid stream extracted from a first absorption step along the path of HCl vapor. The resulting concentrated hydrochloric acid stream is mixed with a stream extracted from the circulating anolyte stream in the membrane electrolysis process for purification to remove sulfate ions, and further purified using BaCl2 as a reagent to remove sulfate ions. The mixed stream of concentrated hydrochloric acid and the purified anolyte stream is contacted with initial lithium carbonate and softened water to obtain a LiCl solution stream. After purification to remove calcium and magnesium impurities, the LiCl solution stream is used as a replenishing solution for the circulating anolyte stream in the membrane electrolysis process.

11. The method as described in claim 10, characterized in that, In the presence of ammonia, chlorine gas is absorbed by softened water at a molar ratio of NH3:Cl2 = 2:3 to obtain a 6N hydrochloric acid solution, which is then mixed with a chemically purified anolyte stream. The chemically purified anolyte stream is a stream extracted from the circulating anolyte stream during the membrane electrolysis process and purified to remove sulfate ions. A mixed stream of hydrochloric acid solution and purified anolyte to remove sulfate ions is contacted with initial lithium carbonate to obtain a LiCl solution stream. After purification to remove calcium and magnesium impurities, the LiCl solution stream is used as a supplementary solution for the circulating anolyte stream in the membrane electrolysis process, and cathode hydrogen is used as fuel to generate heating steam.

12. The method as described in claim 10, characterized in that, Anode chlorine gas is absorbed by an aqueous slurry of lithium carbonate in the presence of a elemental chlorine reducing agent to obtain a lithium chloride solution as the absorption product. The material composition of the elemental chlorine reducing agent prevents contamination of the absorbent by foreign cations and anions during chlorine absorption. The lithium chloride solution, after purification to remove calcium and magnesium impurities, is used as a replenishment solution for the circulating anolyte stream in the membrane electrolysis process. The aqueous slurry for absorbing anode chlorine gas is prepared by softened water, lithium carbonate obtained from used cathode electrolyte, lithium carbonate in the initial salt form, reducing agent, and an anolyte stream purified to remove sulfate ions after being extracted from the circulating anolyte stream in the membrane electrolysis process. Cathode hydrogen gas is used as fuel to generate heating steam.

13. The method as described in claim 3, characterized in that, When an aqueous lithium sulfate solution is used as the anolyte, titanium coated with a noble metal selected from platinum, iridium, tantalum or ruthenium is used as the anode in the electrolysis process. The depleted lithium sulfate and sulfuric acid-enriched anolyte stream drawn from the anolyte circulation loop is contacted with the initial lithium carbonate to obtain a lithium sulfate solution, which is used as a replenishment solution for the anolyte circulation loop after purification to remove impurities.

14. The method as described in claim 3, characterized in that, When a mixture of lithium sulfate and lithium carbonate is used as a lithium salt material, a predetermined volume of anolyte is continuously drawn from a circulating anolyte stream undergoing Li2SO4 depletion and H2SO4 enrichment; the drawn anolyte stream is contacted with an initial mixture of Li2SO4 and Li2CO3 salts to obtain a lithium sulfate solution containing residual H2SO4; the resulting solution is recovered as a Li2SO4 solution suitable for replenishing the circulating anolyte stream in the membrane electrolysis process.

15. The method as described in claim 3, characterized in that, When a mixture of lithium chloride and lithium carbonate is used as a lithium salt-containing material, the initial mixture of lithium chloride and lithium carbonate is contacted with a hydrochloric acid solution and an anolyte stream drawn from a circulating anolyte stream that has undergone LiCl depletion during membrane electrolysis to produce a lithium chloride solution of a predetermined concentration. The resulting lithium chloride solution, after purification to remove impurities, was used as a replenishment solution for the circulating anolyte stream in the membrane electrolysis process.

16. The method as described in claim 3, characterized in that, When a mixture of lithium sulfate and lithium chloride is used as the lithium salt material, titanium coated with a noble metal selected from platinum, iridium, tantalum, or ruthenium is used as the anode in the membrane electrolysis process. The anode electrolyte stream is extracted from the circulating anode electrolyte stream that has undergone lithium sulfate and lithium chloride depletion and H2SO4 enrichment. This anode electrolyte stream is contacted with a predetermined amount of CaO, or Ca(OH)2, or CaCO3 until H2SO4 is completely neutralized. The resulting mixed solution of Li2SO4 and LiCl is separated from the CaSO4·2H2O precipitate and contacted with the initial mixture of Li2SO4 and LiCl salts to dissolve them, resulting in a mixed solution of Li2SO4 and LiCl with a predetermined lithium concentration. This mixed solution of Li2SO4 and LiCl is used as a replenishment solution for the circulating anode electrolyte stream in the membrane electrolysis process after purification to remove impurities. Hydrogen gas is used as the heating steam at the cathode.

17. The method as described in claim 16, characterized in that, The amount of anolyte continuously extracted from the circulating anolyte stream after the depletion of Li2SO4 and LiCl is recovered and used as a Li2SO4 and LiCl replenishment solution for the circulating anolyte stream; the anolyte chlorine extracted from the gas separator is recovered as 36% hydrochloric acid, or NH4Cl, or sodium hypochlorite solution, or neutral calcium hypochlorite.

18. The method as described in claim 3, characterized in that, When a mixture of lithium sulfate, lithium chloride, and lithium carbonate is used as a lithium-containing salt material, a certain volume of anolyte is continuously drawn from the circulating anolyte stream that has undergone depletion of Li2SO4 and LiCl and enrichment of H2SO4. This anolyte is first contacted with an initial mixture of Li2SO4, LiCl, and Li2CO3 salts to produce a mixed solution with a predetermined lithium concentration. The resulting mixed solution is then recovered as a Li2SO4 and LiCl mixed solution to be used as a replenishment solution for the anolyte circulation stream in the membrane electrolysis process.

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