Method for producing high-purity lithium hydroxide monohydrate

Abstract

A process for producing high purity lithium hydroxide monohydrate from a material containing lithium salts selected from Li2SO4, LiCl, Li2CO3 or mixtures thereof, comprising membrane electrolysis of a specified aqueous lithium salt solution using a cation exchange membrane and a nickel-plated stainless steel cathode. Catholyte is withdrawn from the circulation stream, evaporated to obtain lithium hydroxide monohydrate crystals, which are separated from the mother liquor, washed with water and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. A portion of the spent washing solution is fed to the catholyte evaporation process. A portion of the mother liquor formed after separation of the lithium hydroxide monohydrate crystals is returned to the catholyte evaporation process. The counterflowing anolyte is replenished with a concentrated lithium salt solution prepared from the original lithium salt. A portion of the spent catholyte withdrawn from the evaporation process is directed to the production of Li2CO3.

Description

[Technical Field]

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

[0002] It is known that lithium hydroxide solution can be produced from solid carbonate-containing lithium waste by contacting solid carbonate-containing lithium waste with water, allowing the resulting pulp to settle, decanting the clear liquid phase, filtering it, and recirculating the resulting lithium-containing solution through the central chamber of an electrodialysis unit to obtain a lithium hydroxide solution in the cathode chamber, a mixed acid solution in the anode chamber, and a desalination solution in the central chamber, and returning this to the process of leaching lithium from solid carbonate-containing lithium waste [1].

[0003] The disadvantage of this method is that it is suitable for low concentrations (maximum 25 kg / m³). 3 ) Preparation of LiOH solution, and a maximum of 2 A / dm 2 (0.2kA / m 2 ) Low production efficiency of the process due to operation at current density, low Li2CO3 concentration (maximum 10 kg / m³) 3 This results in the high electrical resistance of the recycled Li2CO3 solution and, consequently, the high specific energy consumption per unit of the produced product.

[0004] Another known method for producing lithium hydroxide solutions from lithium compound-containing materials, particularly from waste lithium-ion batteries [2], involves extracting lithium from the waste in the form of highly soluble lithium sulfate and membrane electrolyzing the lithium sulfate solution using a Nafion 350 cation exchange membrane separating the cathode and anode compartments. The electrolysis is performed at 20 A / dm 2The process is carried out with a DC current density of 5.3V and a voltage of 5.3V, continuously drawing out the LiOH solution (cathodeliquid) from the cathode compartment and the Li2SO4-depleted anodeliquid containing sulfuric acid formed at the anode from the anode compartment. The drawn anodeliquid stream is guided to a lithium leaching process to neutralize the sulfuric acid and simultaneously enhance the anodeliquid stream with lithium sulfate. The Li2SO4-enhanced anodeliquid is returned to the electrolysis process.

[0005] This anodic solution has the disadvantage of being limited to the production of LiOH solutions contaminated with impurities. It is not possible to produce high-purity products in the form of LiOH·H2O using this method.

[0006] It is known that high-purity lithium hydroxide can be produced by membrane electrolysis of aqueous solutions containing lithium chloride and lithium carbonate recovered from natural brine in the presence of a reducing agent [3]. The extracted cathode liquid is evaporated to crystallize 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 transfer medium for generating heating steam used in the cathode liquid evaporation process, and anodic chlorine is used to oxidize bromide ions to elemental bromine by directly contacting chlorine with bromide ion-rich natural brine.

[0007] Disadvantages of this method include the fact that the low-concentration LiCl solution initially recovered from lithium-containing natural brine by a LiCl selective adsorbent is used as the feed material for electrochemical conversion, and that a reducing agent is required to eliminate the risk of oxychloride species formation in the anode compartment 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 disadvantages of the above method. This method is based on the regeneration of an aqueous solution of highly soluble lithium sulfate supplied to replenish the anolyte solution circulating in the anolyte circuit of an electrolytic unit, which is undergoing depletion of Li2SO4 and enrichment of H2SO4. For this purpose, a portion of the lithium-depleted anolyte is continuously drawn from the anolyte circuit and brought into contact with an equal amount of lithium carbonate to convert the anodic sulfuric acid into lithium sulfate. This method also provides for the chemical purification of the regenerated Li2SO4 solution from Ca, Mg impurities and heavy metals by a carbonate-alkali method using a LiOH solution and CO2 released by the neutralization of carbonates in the anolyte.

[0009] This method has the disadvantage of using the cation exchange membrane MK-40, which has low mechanical and chemical stability in the membrane electrolysis process. Further disadvantages of this method include water contamination by liquid waste, contamination of the lithium carbonate solution by sodium carbonate and potassium carbonate, and insufficient chemical purification of the Li2SO4 solution supplied to the anodic solution circuit for replenishment, meaning that the need to periodically check for the recovery of acid from membranes contaminated with calcium and magnesium cations is required.

[0010] A method for producing lithium monohydrate from brine and apparatus for carrying out the same [5] overcomes the disadvantages of the above method. The LiOH solution supplied for evaporation, crystallization, washing and drying of LiOH·H2O is obtained from a concentrated LiCl solution subjected to chemical purification by the carbonate-alkali method and subsequent ion exchange purification with a Lewatit-208-TP ion exchanger in Li form. The method also includes using a spent cathode liquid stream drawn from the evaporation process in the form of a LiOH solution containing NaOH and KOH as a reagent to obtain a solution of enriched (pregnant) LiCl, thereby removing sodium and potassium from the process in the form of NaCl and KCl crystals. This method for producing lithium hydroxide monohydrate from lithium salt-containing material is selected as the closest prior art because, by its technical essence and the parameters achieved, it is the closest to the claimed method.

[0011] The disadvantages of this method are as follows: 1) The range of raw materials that can be used in the production of LiOH·H2O is limited to aqueous solutions of lithium chloride produced from lithium-containing natural brine. 2) Sodium and potassium impurities accumulated in the cathode solution can only be removed in the form of NaCl and KCl, and the production process of LiOH·H2O is limited to the preparation of a pregnant lithium concentrate (a lithium concentrate suitable for the production of LiCl·H2O and LiCl) by concentrating and removing impurities from a low-concentration LiCl raw material in the form of a primary lithium concentrate produced from lithium-containing natural brine using a LiCl-selective adsorbent. 3) The range of by-products generated is limited by the use of anodic chlorine. 4) Lack of solutions for utilizing cathode hydrogen.

[0012] The above-mentioned drawbacks can be overcome by implementing the following technical solutions that constitute the basis of the claimed method. A 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, which is produced from a material containing lithium salts in the form of Li2SO4, LiCl, Li2CO3, or various mixtures of these salts. The sodium and potassium enriched streams extracted from the cathode liquid evaporation process (used cation exchanger) are reused as solid-phase lithium carbonate, solid-phase sodium bicarbonate, and solid-phase potassium bicarbonate. By using nickel-plated stainless steel as the cathode, both the risk of hydrogen absorption (hydrogenation) and corrosion at the cathode are eliminated. The used cleaning solution remaining after washing LiOH·H2O crystals is used as an alkaline reagent in the process of pre-treating aqueous lithium salts before membrane electrolysis. To employ a novel solution for utilizing the cathode and anode byproducts of film electrolysis of lithium salt aqueous solutions.

[0013] The implementation of the provided technical solutions will expand the range of raw materials suitable for the production of lithium hydroxide monohydrate, enhance the reliability of the membrane electrolysis process, broaden the range of by-products generated, eliminate the formation of liquid and gaseous waste, and consequently improve the environmental performance of the manufacturing process. [Overview of the project]

[0014] Technical benefits are achieved by using lithium sulfate, lithium chloride, lithium carbonate, or various mixtures of these salts as lithium salt-containing materials; using nickel-plated stainless steel cathodes in the membrane electrolysis process of lithium salt aqueous solutions; and using Nafion-348, CTIEM-3, MF-4SK-100 type membranes or equivalent membranes as cation exchange membranes.

[0015] In a process of pretreating a lithium salt solution, which has been adjusted to a predetermined concentration before electrolysis, for use as an alkaline reagent in a process for treating a spent cleaning solution supplied to a cathode liquid evaporation process, a technical effect is achieved by partially using this salt solution in a step of chemically purifying it from impurities and then partially using it as a regeneration solution for converting an ion exchanger from an H form to a Li form in an ion exchange purification step.

[0016] A spent cathode liquid stream, which is a lithium hydroxide solution containing sodium hydroxide and potassium hydroxide as additives, is reused by mixing it with an aqueous solution stream containing sodium bicarbonate, potassium bicarbonate, and lithium bicarbonate, concentrated by removing a predetermined amount of water from a pulp obtained as a result of the reuse, which is a mixture of a solid phase of lithium carbonate and a solution containing Na2CO3, K2CO3, and Li2CO3, separating the solid phase of lithium carbonate from the liquid phase, carbonizing the liquid phase by contacting it with carbon dioxide to convert the carbonate solution into a bicarbonate suspension, which is a mixture of a solid phase of sodium bicarbonate and a solid phase of potassium bicarbonate in a solution of sodium bicarbonate, potassium bicarbonate, and lithium bicarbonate, filtering the resulting suspension to separate the solid phases of sodium bicarbonate and potassium bicarbonate from the solution containing sodium bicarbonate, potassium bicarbonate, and lithium bicarbonate, and guiding this to mixing with the spent cathode liquid stream withdrawn from an evaporation process containing lithium hydroxide, sodium hydroxide, and potassium hydroxide, thereby achieving a technical effect.

[0017] When lithium sulfate is used as the lithium salt-containing material, titanium coated with a noble metal (platinum, ruthenium, iridium, tantalum) is used as the anode in the film electrolysis process. A predetermined volume of anode liquid is continuously drawn at a predetermined rate from the circulating anode liquid flow that has undergone Li2SO4 depletion and H2SO4 enrichment. The drawn anode liquid flow is brought into contact with CaO, Ca(OH)2, or CaCO3 until the H2SO4 is completely neutralized. The resulting CaSO4·2H2O solid phase is separated from the Li2SO4 solution, and a predetermined mass amount of the Li2SO4 solution is removed. The initial Li2SO4 salt (quantity) is brought into contact with the solution and dissolved to obtain a Li2SO4 solution of a predetermined concentration. A predetermined volume of washing solution is added to the obtained solution, and then carbon is added to the solution with carbon dioxide derived from a process of neutralizing the extracted anodic liquid flow until the calcium and magnesium contained in the solution are converted into the insoluble compounds CaCO3 and Mg(OH)2·3MgCO3·3H2O. The obtained suspension is filtered to separate the precipitate from the Li2SO4 solution, and the chemically purified Li2SO4 solution is subjected to ion exchange purification by passing it through a layer of Li-form Lewatit-208-TP ion exchanger or an equivalent Li-form ion exchanger. The technical benefits are achieved by using a purified Li2SO4 solution as a replenishment solution for the circulating anode liquid flow in the membrane electrolysis process, regenerating the spent ion exchanger in two steps: a first step of treatment with a 2.0N sulfuric acid solution and a second step of treatment with a 2N LiOH solution prepared from the spent washing solution, mixing the spent regenerated solution with the spent anode liquid flow before chemical purification, and discharging the cathode hydrogen, a byproduct of electrolysis, from the cathode gas separator of the electrolysis unit along with the natural gas flow to obtain a gaseous mixture, which is then introduced into a steam generator as fuel to produce heated steam used as a heat transfer medium in the evaporation process, particularly with the cathode liquid.

[0018] When using lithium sulfate as the lithium salt-containing material, a predetermined volume of anolyte that is constantly withdrawn at a predetermined volumetric flow rate from a circulating anolyte stream that has undergone depletion of Li2SO4 and enrichment of H2SO4 is contacted with an air-ammonia mixture to neutralize H2SO4, obtaining a mixed solution of Li2SO4 and (NH4)2SO4, evaporating this to salify (NH4)2SO4, mixing the remaining evaporation solution containing (NH4)2SO4 with a predetermined volume of used washing solution, while contacting the used alkaline anolyte stream with an air stream derived from the process of contacting the ammonia-air mixture to remove the remaining ammonia from the Li2SO4 solution, enriching the air stream containing gaseous ammonia with ammonia from an ammonia source, inducing the process of neutralizing the used anolyte stream, and subjecting the solution obtained after the predetermined strengthening of Li2SO4 by dissolution of a predetermined mass amount of initial lithium sulfate salt with respect to the Li2SO4 solution free of ammonia, chemical purification from impurities, and ion exchange purification to be used as a replenishing solution for the circulating anolyte stream in the membrane electrolysis process, thereby achieving a technical effect.

[0019] When using lithium chloride or lithium chloride monohydrate as the lithium salt-containing material, a titanium anode coated with ruthenium oxide is used in the membrane electrolysis process, a predetermined volume of anolyte is constantly withdrawn at a predetermined volumetric flow rate from a circulating anolyte stream in which depletion of LiCl is occurring, the withdrawn anolyte stream is contacted with an initial salt containing lithium chloride to set the LiCl concentration in the withdrawn anolyte stream to a predetermined value, and for the anolyte stream enriched with LiCl by withdrawal, in addition to chemical purification from metal cation impurities, purification from sulfate ions is carried out by conversion of sulfate ions to insoluble BaSO4 precipitates by addition of a predetermined amount of barium chloride, separating the liquid phase from the precipitate, and after ion exchange purification, using it as a replenishing solution for the circulating anolyte stream in the membrane electrolysis process. By mixing the cathode hydrogen and anode chlorine drawn from the gas separation device and subjecting them to flame combustion, and absorbing the resulting hydrogen chloride in deionized water to produce 36% concentrated hydrochloric acid, a technical effect is achieved.

[0020] When lithium chloride or lithium chloride monohydrate is used as the lithium salt-containing material, the anodic chlorine extracted from the gas separation device is absorbed into ammonia water to produce an NH4Cl solution under a molar ratio of NH3:Cl2 of 8:3, and a 6N HCl solution under a molar ratio of NH3:Cl2 of 2:3. The resulting NH4Cl solution is evaporated to crystallize the NH4Cl, the crystals are dried, and the hydrogen extracted in this process is used as a heat transfer medium for generating heated steam, thereby achieving the technical benefits.

[0021] When using lithium chloride or lithium chloride monohydrate as a lithium salt-containing material, either completely absorb the anodic chlorine extracted from the gas separation device into a NaOH solution to produce a sodium hypochlorite disinfectant solution, or absorb 0.5 of the volumetric flow rate of the extracted chlorine into a NaOH solution to produce a solution saturated with sodium hypochlorite, absorb the remaining 0.5 of the volumetric flow rate of the extracted anodic chlorine into a Ca(OH)2 suspension to produce a solution saturated with calcium hypochlorite, mix the produced solutions to salt out neutral calcium hypochlorite, separate it from the mother liquor and dry it, and first add a predetermined amount of NaOH to the obtained mother liquor. By precipitating calcium in the form of Ca(OH)2, then adding a predetermined amount of Na2CO3 to precipitate calcium in the form of CaCO3, separating the precipitate containing Ca(OH)2 and CaCO3 from the solution containing activated chlorine in the form of hypochlorite ions, then dividing the solution into two equal parts, mixing one with a predetermined amount of NaOH to induce chlorination and obtain a sodium hypochlorite solution, mixing the other with a predetermined amount of Ca(OH)2 and similarly inducing a chlorination process to obtain a calcium hypochlorite solution, and further utilizing cathode hydrogen as a heat transfer medium for generating heated steam, the technical effect is achieved.

[0022] When lithium carbonate is used as a lithium salt-containing material, the lithium carbonate salt is circulated in the form of an aqueous solution within the anode circuit of the electrolytic unit. The technical benefits are achieved by using the lithium carbonate salt to regenerate highly soluble salts of lithium chloride or lithium sulfate, which are depleted during membrane electrolysis due to the depletion of LiCl or Li2SO4. Here, when using an aqueous solution of lithium chloride as the anodelite, a titanium anode coated with ruthenium oxide is used in the membrane electrolysis process. According to the first option, the extracted cathode hydrogen and anode chlorine are mixed and then burned to generate high-temperature hydrogen chloride vapor. The hydrogen chloride vapor is cooled and absorbed into demineralized water in a stepwise countercurrent manner to obtain a concentrated (36%) hydrochloric acid stream along the HCl vapor path from the first absorption step. The obtained concentrated hydrochloric acid stream is mixed with an anodelite stream extracted from the circulating anodelite stream in the membrane electrolysis process for purification from sulfate ions, using BaCl2 as a reagent to remove sulfate ions. The mixed stream of concentrated hydrochloric acid and the purified anodelite is brought into contact with a predetermined amount of initial lithium carbonate and demineralized water to obtain a LiCl solution stream of a predetermined concentration. This is then purified from calcium and magnesium impurities and used as a replenishment solution for the circulating anodelite stream in the membrane electrolysis process. According to the second option, anodic chlorine extracted in the presence of ammonia with an NH3:Cl2 molar ratio of 2:3 is absorbed into desalinated water to obtain a 6N hydrochloric acid solution. This solution is then extracted from the circulating anode liquid flow in the membrane electrolysis process for purification from sulfate ions, and mixed with the anode liquid flow purified from sulfate ions using BaCl2 as a reagent. The mixed flow of the hydrochloric acid solution and the anode liquid purified from sulfate ions is then brought into contact with a predetermined amount of initial lithium carbonate to obtain a LiCl salt solution flow. After purifying calcium and magnesium impurities from this solution, it is used as a replenishment solution for the circulating anode liquid flow in the membrane electrolysis process, and cathode hydrogen is used as fuel for generating heating steam.According to the third option, anodic chlorine is absorbed into aqueous pulp of lithium carbonate having a predetermined Li2CO3 content in the presence of a predetermined amount of elemental chlorine reducing agent, such as ammonia, hydrazine, hydroxylamine, carbamide, formic acid, or an equivalent reducing agent, in a material composition that prevents the absorbent from being contaminated with foreign cations and anions, to obtain a lithium chloride solution having a predetermined LiCl concentration as an absorption product, which is used as a replenishment solution for the circulating anode liquid flow in the membrane electrolysis process. Here, the aqueous pulp for absorbing anodic chlorine is prepared from demineralized water, lithium carbonate obtained from spent cathode liquid, lithium carbonate in the form of an initial Li2CO3 salt, a reducing agent, and an anode liquid flow purified from sulfate ions using BaCl2 as a reagent, drawn from a predetermined volumetric flow rate circulating anode liquid flow in the membrane electrolysis process, and cathode hydrogen is used as fuel for generating heated steam.

[0023] When using an aqueous solution of lithium sulfate as the anode liquid, the technical benefits are achieved by using a titanium anode coated with a precious metal (platinum, ruthenium, iridium, tantalum) in the membrane electrolysis process, drawing it out at a predetermined rate from the anode liquid circulation circuit, and contacting a predetermined volume of anode liquid flow, which has depleted the lithium sulfate and enriched with sulfuric acid, with a predetermined amount of initial lithium carbonate to obtain a lithium sulfate solution of a predetermined concentration. This solution is then purified from impurities and used as a replenishment solution for the anode liquid circulation circuit.

[0024] When using a mixture of lithium sulfate and lithium carbonate, which are lithium salts, as a lithium salt-containing material, the technical benefits are achieved by using titanium coated with a precious metal (platinum, ruthenium, iridium, tantalum) as the anode in the membrane electrolysis process, drawing it out from the anodic acid circulation circuit at a predetermined rate to deplete the lithium sulfate, and contacting a predetermined volume of anodic acid-enriched anodic acid flow with a predetermined amount of an initial mixture of Li2SO4 salt and Li2CO3 salt to obtain a lithium sulfate solution of a predetermined concentration containing residual H2SO4, removing residual sulfuric acid from the obtained Li2SO4 solution, purifying it from impurities, and then using it as a replenishment solution for the circulating anodic acid flow in the membrane electrolysis process.

[0025] When using a mixture of lithium chloride and lithium carbonate as a lithium salt-containing material, the technical benefits are achieved by using titanium coated with ruthenium oxide as the anode in the membrane electrolysis process, drawing the initial mixture of lithium chloride and lithium carbonate in a predetermined volume with hydrochloric acid of a predetermined concentration and from the circulating anode flow, contacting it with a predetermined volume flow rate of anode where LiCl has been depleted during membrane electrolysis to produce a lithium chloride solution, and then using the resulting lithium chloride solution, after purification from impurities, as a replenishment solution for the circulating anode flow in the membrane electrolysis process.

[0026] When using a mixture of lithium sulfate and lithium chloride, which are lithium salts, as a lithium salt-containing material, titanium coated with a noble metal (platinum, ruthenium, iridium, tantalum) is used as the anode in the film electrolysis process. A predetermined volume of anode liquid is drawn at a predetermined rate from the circulating anode liquid flow that has been depleted of lithium sulfate and lithium chloride and enriched with H2SO4, and this is brought into contact with a predetermined amount of ammonia contained in an ammonia-air mixture. Subsequently, the mixed sulfite solution of Li2SO4 and (NH4)2SO4 is concentrated, and the (NH4)2SO4 salt is salted out until a Li2SO4 solution is obtained, or the solution is brought into contact with a predetermined amount of either Ca(OH)2 or CaCO3 until H2SO4 is completely neutralized and a Li2SO4 solution is obtained, and separated from the CaSO4·2H2O precipitate. The Li2SO4 solution obtained by either method is dissolved by contacting it with a predetermined amount of an initial mixture of Li2SO4 salt and LiCl salt to obtain a mixed solution of Li2SO4 and LiCl containing a predetermined concentration of lithium. After purification from impurities, this solution is used as a replenishment solution for the circulating anode liquid flow in the membrane electrolysis process. Furthermore, the anodic chlorine extracted from the gas separation device is reused in 36% hydrochloric acid, NH4Cl salt, sodium hypochlorite solution, or neutral calcium hypochlorite, thereby achieving technical benefits.

[0027] When using a mixture of lithium sulfate, lithium chloride, and lithium carbonate as the lithium salt-containing material, the technical benefits are achieved by using titanium coated with a precious metal as the anode in the membrane electrolysis process, continuously drawing a predetermined volume of anode liquid at a predetermined volumetric flow rate from the circulating anode liquid flow that has undergone depletion of Li2SO4 and LiCl and enrichment of H2SO4, and first contacting this with an initial mixture of predetermined amounts of Li2SO4 salt, LiCl salt, and Li2CO3 salt to produce a mixed solution of Li2SO4, LiCl, and H2SO4 containing lithium at a predetermined concentration, converting the resulting mixed solution into a mixed solution of Li2SO4 and LiCl, and using this as a replenishment solution for the circulating anode liquid flow in the membrane electrolysis process. [Brief explanation of the drawing]

[0028] [Figure 1] This flowchart illustrates the production of LiOH·H2O from materials containing lithium salts in the form of Li2SO4 salts. [Figure 2] This flowchart illustrates the production of LiOH·H2O from a material containing a lithium salt in the form of a LiCl salt. [Figure 3] This flowchart illustrates the production of LiOH·H2O from a material containing lithium salts in the form of Li2CO3 salts. [Figure 4] This flowchart illustrates the production of LiOH·H2O from a material containing lithium salts in the form of a mixture of Li2SO4 salt and Li2CO3 salt. [Figure 5] This flowchart illustrates the production of LiOH·H2O from a material containing lithium salts in the form of a mixture of LiCl salt and Li2CO3 salt. [Figure 6] This flowchart illustrates the production of LiOH·H2O from a material containing lithium salts in the form of a mixture of Li2SO4 salt and LiCl salt. [Figure 7] This flowchart illustrates the production of LiOH·H2O from materials containing lithium salts in the form of a mixture of Li2SO4 salt, LiCl salt, and Li2CO3 salt. [Modes for carrying out the invention]

[0029] The invention provided is carried out according to a flowchart for producing lithium hydroxide monohydrate from a material containing a lithium salt or a mixture thereof, as shown in Figures 1 to 7, and is supported by the provided examples.

[0030] Figure 1 shows a flowchart of the process for producing LiOH·H2O from a material containing lithium salts in the form of Li2SO4 salts. This technology is based on a membrane electrolysis process that enables the electrochemical conversion of a Li2SO4 solution to a LiOH solution. Here, the electrochemical conversion process occurs by applying a DC current, and a cation exchange membrane stable in alkaline and acidic solutions is used to separate the cathode compartment and anode compartment of an electrolytic unit in which the LiOH solution (cathode liquid) and Li2SO4 solution (anode liquid) are constantly circulating, respectively. The solution undergoes an electrode process by contact with the electrodes during circulation. This causes electrochemical oxidation of water at the anode, and oxygen gas and H2O are produced according to the following reaction. + Ions are generated. [ka]

[0031] Therefore, electrochemical decomposition of water occurs at the cathode, producing hydrogen gas and OH according to the following reaction. - Ions are generated. [ka]

[0032] In its general form, the electrochemical conversion process from Li2SO4 to LiOH can be represented by the following reaction. [ka]

[0033] The cation exchange membrane enables the unhindered movement of cations from the anode compartment to the cathode compartment. In so doing, the movement of SO4 2- ions from the anode compartment to the cathode compartment and the movement of OH - ions from the cathode compartment are impeded by the unique characteristics of the cation exchange membrane. Since Li2SO4 is always depleted and H2SO4 is enriched in the anolyte, and LiOH is always enriched in the catholyte, fresh Li2SO4 solution is always replenished in the circulating anolyte. The optimal range of the current density is 2 kA / m 2 ~4 kA / m 2 , and the concentration of lithium in the circulating anolyte is maintained in the range of 20 kg / m 3 ~25 kg / m 3 . The optimal concentration of lithium hydroxide in the circulating catholyte is 50 kg / m 3 ~80 kg / m 3This is within the range. Nafion-434, Nafion-438, Nafion-324, CTIEM-3, MF-4SK-100 type membranes, as well as other equivalent membranes that exhibit resistance to alkalis and acids, can be used as cation exchange membranes. For the cathode, it is preferable to use a porous plate made of nickel-plated stainless steel, which eliminates both the risk of hydrogenation of the cathode's structural material by cathode hydrogen and the risk of cathode corrosion during emergency shutdowns and interruptions of the current load. 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 be used as the anode. A predetermined volume of cathode liquid flow is constantly drawn from the circulating cathode liquid containing the Li2SO4 solution produced by membrane electrolysis and sent to the processes of evaporation and crystallization of LiOH·H2O. LiOH·H2O crystals are typically separated from the mother liquor during evaporation by centrifugation. The separated crystals are washed with demineralized water from the remaining mother liquor and dried to obtain a LiOH·H2O product that meets the requirements of LGO-1 GOST 8595-83 grade. The mother liquor formed after evaporation and crystal separation is returned to the evaporation process. Sodium and potassium are present as impurities in the lithium sulfate salt that is electrolyzed with lithium and migrate to the cathode solution. As a result, they gradually accumulate in the evaporated cathode solution, reaching concentrations that prevent the production of a product that meets the requirements of LGO-1 grade. For this reason, a predetermined volume is always drawn from the alkaline solution formed after the separation of LiOH·H2O crystals and returned to the cathode solution evaporation process, and this is used to ensure that lithium is returned to the production process for reuse. The reuse of spent cathode solution involves separating lithium from alkali metal impurities based on the large differences in solubility of the compounds Li2CO3, LiHCO3, Na2CO3, NaHCO3, K2CO3, and KHCO3. In the given list, lithium carbonate is the least soluble compound, and K2CO3 is the most soluble. Sodium bicarbonate and potassium bicarbonate are far less soluble than their carbonates, while lithium bicarbonate is far more soluble than lithium carbonate.In the first step of the reuse process, a mixed bicarbonate solution saturated with KHCO3, NaHCO3, and LiHCO3 is prepared, and this solution stream is mixed with the reused spent cathode liquid stream. The mixing of these liquid streams causes the following reactions, resulting in the precipitation of sparingly soluble lithium carbonate and the conversion of potassium bicarbonate and sodium bicarbonate into carbonates that are significantly more soluble than their corresponding bicarbonates. [ka]

[0034] The mixing process is combined with a process to remove excess water accompanying the spent cathode liquid stream. Water removal is performed by bringing the resulting suspension into direct contact with a predetermined stream heated to a temperature above 100°C. As a result of the contact between the heated air and the suspension, water evaporates from the suspension, while the air is cooled to the temperature of a wet thermometer. In addition, the removal of water from the suspension increases the degree of conversion of Li2CO3 to the solid phase. At the same time, the liquid phase is enriched with sodium and potassium derived from the spent cathode liquid. The resulting solid phase of Li2CO3 is separated from the carbonate solution by centrifugation and led to a process to neutralize the spent anode liquid, and the resulting carbonate solution is converted to a bicarbonate solution by treatment with carbon dioxide according to the following reaction. [ka]

[0035] Due to supersaturation of the NaHCO3 and KHCO3 solutions by enrichment with sodium and potassium derived from the spent cathode solution, some sodium bicarbonate and potassium bicarbonate remain in the solid phase. However, lithium bicarbonate, formed from dissolved Li2CO3, does not remain in the solid phase due to its higher solubility. The resulting solid phase of sodium bicarbonate and potassium bicarbonate is separated from the bicarbonate solution by filtration. The bicarbonate solution is then mixed with the next batch of spent cathode solution.

[0036] During membrane electrolysis, the circulating anode liquid undergoes depletion of Li2SO4 and enrichment of H2SO4. Therefore, a predetermined anode liquid flow is constantly drawn from the circulating anode liquid flow and initially brought into contact with lithium carbonate obtained by reusing spent cathode liquid, and a portion of the sulfuric acid is neutralized according to the following reaction. [ka]

[0037] During acid neutralization with lithium carbonate, the spent anode is partially fortified with Li2SO4. Subsequently, there are two possible options for preparing the neutralized anode for electrolysis. According to the first option (Option A), the solution of the spent anode after neutralization with lithium carbonate is brought into contact with calcium oxide, calcium hydroxide, calcium carbonate, or a mixture thereof, and sulfuric acid is converted to the solid phase of CaSO4·2H2O according to the following reaction. [ka]

[0038] After separation from the precipitate, the spent anode solution, which is a Li2SO4 solution from which sulfuric acid has been completely removed, is dissolved until the solution has a predetermined Li2SO4 content, and then brought into contact with a predetermined mass amount of the initial Li2SO4 salt. Next, the resulting Li2SO4 solution is chemically purified from calcium and magnesium as needed. If the levels of calcium and magnesium in the initial Li2SO4 salt are high, the chemical purification process is necessary. A predetermined portion of the spent washing solution (containing 0.1 kg / m³ of NaOH and KOH) is added. 3 The total amount contained is 120 kg / m³ 3 The LiOH solution and carbon dioxide are used as reagents. The purification process is represented by the following chemical equation. [ka]

[0039] Generally, chemical purification removes the remaining total calcium and magnesium content in the analytical solution from 10 g / m². 3~15g / m 3 It is possible to achieve this level. After separation of the precipitate, the Li2SO4 solution is subjected to ion exchange purification. For this purpose, Lewatit 208 TP ion exchanger in Li form or its anolyte in Li form is used. The ion exchange purification process is represented by the following reaction equation. [ka]

[0040] By ion exchange purification, the residual total concentration of calcium and magnesium in the Li2SO4 solution was reduced to 0.1 g / m³. 3 It is possible to keep the level below a certain point, and this solution is used as a replenishment solution for the circulating anodic acid flow in the membrane electrolysis process.

[0041] According to another option (Option B), the extracted anode liquid stream is first partially neutralized with lithium carbonate obtained in the spent cathode liquid reuse stage, and then the partially neutralized spent anode liquid is partially neutralized with ammonia by bringing it into direct contact with an air-ammonia mixture, thereby converting the remaining sulfuric acid to ammonium sulfate according to the following reaction. [ka]

[0042] A mixed solution of Li2SO4 and (NH4)2SO4 obtained by complete neutralization of the spent anode liquid is evaporated by salting out the (NH4)2SO4 from the mixed solution. After washing from the mother liquor brine and drying, the ammonium sulfate becomes a commercially available fertilizer. The Li2SO4 solution obtained from the spent anode liquid containing (NH4)2SO4 residue is then alkalized using a portion of the spent washing solution formed during the washing process of the LiOH·H2O crystals.

[0043] After alkalization, the solution is deammonized by aeration with an airflow. The deammonization process is represented by the following chemical equation. [ka]

[0044] An airflow containing gaseous ammonia is enriched with a predetermined amount of ammonia to guide the neutralization of the next portion of the used, partially neutralized anode liquid.

[0045] The Li2SO4 solution subjected to the ammonia removal process is sent for additional enhancement by dissolving a predetermined mass amount of initial Li2SO4 salt, and after chemical purification and ion exchange purification, it is used as a replenishment solution for the circulating anode liquid flow.

[0046] Cathode hydrogen, a byproduct of membrane electrolysis, is discharged from the cathode gas separator along with the natural gas flow. The resulting gaseous mixture is used as fuel for generating heating steam. The heating steam is used in the evaporation process. The juice vapor condensate formed during the evaporation process is used as demineralized water in the process of washing the crystals obtained by the evaporation of the solution.

[0047] Figure 2 shows a process flowchart for the production of LiOH·H2O from materials containing lithium salts in the form of LiCl salt or LiOH·H2O salt. In this case, the technique is based on a membrane electrolysis process that enables the electrochemical conversion of a LiCl solution to a LiOH solution. Here, the cathode process that occurs under the conditions of membrane electrolysis of a LiCl solution is similar to the cathode process that occurs under the conditions of membrane electrolysis of a Li2SO4 solution. On the other hand, the anode process under the conditions of membrane electrolysis of a LiCl solution is significantly different because it involves the electrochemical oxidation of chloride ions to produce chlorine gas according to the following reaction: [ka]

[0048] In this case, no acid is formed, and only the depletion of LiCl in the anodic acid occurs during electrolysis.

[0049] In its general form, the electrochemical conversion process from a LiCl salt solution to a LiOH solution can be represented by the following overall reaction: [ka]

[0050] The same cathode and cation exchange membrane used for the electrolysis of LiCl salt solution are employed for the membrane electrolysis of LiCl salt solution. The main parameters of the membrane electrolysis process for soluble salts are substantially the same. However, instead of the expensive platinum-plated titanium or titanium coated with other precious metals anodes typically used for the electrolysis of lithium sulfate solution, a ruthenium oxide-coated titanium anode (ruthenium oxide-titanium anode (ORTA)) can be successfully used for the electrolysis of lithium chloride solution. However, the chloride anode solution must be acidified to pH 2. Acidifying the chloride-containing anode solution also eliminates the risk of chlorate formation in the circulating anode solution. The scheme for drawing and treating the cathode solution to the final LiOH·H2O for the electrochemical conversion of lithium sulfate and chloride solutions is the same. The extraction and pretreatment of spent (LiCl depleted) anodelite for electrolysis is the same scheme and pretreatment as for sulfate anodelite, except that the pretreatment of spent chloride anodelite does not require a neutralization process, and the fortification of spent anodelite to a predetermined lithium concentration is performed by dissolving a predetermined amount of initial LiCl salt. Since sulfate ions introduced as impurities in the initial lithium chloride used in this process may accumulate in the circulating anodelite flow, the chemical purification of LiCl-fortified spent anodelite includes purification from calcium and magnesium, as well as purification from sulfate ions by converting them to insoluble BaSO4 salts using BaCl2 as a precipitant. An acid regeneration step with 2N hydrochloric acid solution is performed during the ion exchange purification process of the LiCl-fortified lithium chloride solution.

[0051] The hydrogen (cathode gas) and chlorine (anodic gas) byproducts of membrane electrolysis can be utilized in various ways. According to option A, the hydrogen and chlorine extracted from the gas separation device are mixed and subjected to high-temperature combustion to produce hydrogen chloride gas according to the following reaction. [ka]

[0052] The resulting high-temperature hydrogen chloride stream is subjected to forced cooling to induce stepwise countercurrent absorption using demineralized water as the initial absorbent. This can be represented as juice vapor condensate, a byproduct of the evaporation process. Option B includes using cathode hydrogen as fuel to generate the heating vapor used in the solution evaporation process. According to this option, an NH4Cl solution can be obtained by water absorption according to the following reaction of a gaseous mixture of NH3 and Cl2 with a molar ratio of NH3:Cl2 of 8:3, and chlorine can be utilized as an NH4Cl salt by evaporating it. [ka] Alternatively, chlorine can be used as a 6N HCl solution by water absorption according to the following reaction of a gaseous mixture of NH3 and Cl2 with a molar ratio of NH3:Cl2 of 2:3. [ka] Alternatively, chlorine can be absorbed into an aqueous solution of NaOH according to the reaction described below, thereby utilizing it as a sodium hypochlorite solution (disinfectant and sterilizing solution). [ka] Alternatively, NaOCl can be obtained by absorbing half of the anodic chlorine into a concentrated NaOH solution according to the reaction described below. [ka] The obtained sodium hypochlorite solution saturated with NaOCl was used, and according to the reaction described below, half of the anodic chlorine was absorbed by calcium hydroxide pulp to obtain Ca(OCl)2. [ka] By drying the Ca(OCl)2 salt isolated by an exchange reaction with the resulting Ca(OCl)2-saturated solution, chlorine can be utilized as neutral calcium hypochlorite.

[0053] Obtained by performing an exchange reaction, Ca 2+ Ion, Na + Ions, Cl - Ion, OCl - By introducing a predetermined amount of NaOH into a solution from a mother liquor containing ions and activated chlorine, the main amount of calcium is precipitated according to the following reaction. [ka]

[0054] The residual calcium is removed from the solution by adding a predetermined amount of Na2CO3 according to the following reaction. [ka]

[0055] The resulting Ca(OH)2 precipitate containing a mixture of CaCO3 is introduced into the Ca(OH)2 pulp chlorination process. The solution formed after calcium precipitation, containing the same proportion of active chlorine, is returned to the NaOH solution and the Ca(OH)2 pulp chlorination process.

[0056] Figure 3 shows a process flowchart for producing LiOH·H2O from a material containing a lithium salt in the form of a Li2CO3 salt. As can be seen from the scheme, the use of Li2CO3 salt in the preparation of LiOH·H2O involves using this salt as a reagent for regenerating lithium-depleted anode in a membrane electrolysis process that circulates in either the form of a Li2SO4 solution (option A) or a LiCl solution (options B and C). According to option A, the spent anode is fortified with lithium at the same time as complete neutralization with sulfuric acid, and the neutralization is carried out by mixing it with a predetermined amount of initial lithium carbonate salt, which contains lithium carbonate obtained by reusing spent cathode liquid that has been subjected to evaporation. According to this option, cathode hydrogen is used as a combustion gas component for generating heated steam. If the production process follows option B, concentrated hydrochloric acid is obtained by using cathode hydrogen and anodic chlorine to obtain concentrated hydrochloric acid, burning this mixture, and absorbing hydrogen chloride with water (reaction 23). The resulting acid is mixed with an anode liquid stream purified from sulfate ions, where the anode liquid stream is drawn at a predetermined volumetric flow rate from a circulating anode liquid stream enriched with sulfate ions during electrolysis. A mixed solution of concentrated hydrochloric acid and anode liquid purified from sulfate ions is brought into contact with a predetermined amount of initial Li2CO3 salt and demineralized water to produce a LiCl solution of a predetermined concentration. After purification from calcium and magnesium, this solution is used to replenish the circulating anode liquid stream in the membrane electrolysis process with LiCl. According to option B, ammonia is mixed with NH3:Cl2 under conditions of a molar ratio of 2:3 to absorb anodic chlorine into demineralized water, producing a 6N hydrochloric acid solution (reaction 25). The resulting acid is mixed with an anode liquid stream purified from sulfate ions, where the anode liquid stream is drawn at a given volumetric flow rate from a circulating anode liquid stream enriched with sulfate ions during electrolysis. A mixed solution of hydrochloric acid and anode purified from sulfate ions is brought into contact with a predetermined amount of initial Li2CO3 salt to produce a LiCl solution of a predetermined concentration. After purification from calcium and magnesium, this solution is used as a replenishment solution for the circulating anode in the membrane electrolysis process. The cathode hydrogen produced by this option is used as fuel for generating heating vapor.According to option B, a LiCl solution is produced in the presence of a predetermined amount of reducing agent in the material composition to prevent contamination of the absorbent, such as ammonia, hydrazine, hydroxylamine, carbamide, and formic acid, according to the following reaction. [ka]

[0057] Aqueous pulp for anodic chlorine absorption is prepared from demineralized water, lithium carbonate obtained from spent evaporated lithium cathode liquid in the form of initial Li2CO3 salt, a suitable reducing agent, and a sulfate-free anode liquid stream drawn at a predetermined volumetric flow rate from a circulating anode liquid stream enriched with sulfate ions during electrolysis. The cathode hydrogen produced by this option is used as fuel for the generation of heating steam.

[0058] Figure 4 shows a process flowchart for producing LiOH·H2O from a material containing a lithium salt in the form of a mixture of Li2SO4 and Li2CO3. This flowchart is substantially the same as the one shown in Figure 1. The difference is that the enrichment of the spent anode liquid to a predetermined lithium concentration is performed by dissolving a predetermined amount of the initial mixed salt of Li2SO4 and Li2CO3 before the complete neutralization procedure with sulfuric acid. In other respects, the flowchart is identical.

[0059] Figure 5 shows a process flowchart for producing LiOH·H2O from a material containing a lithium salt in the form of a mixture of LiCl and Li2CO3. This flowchart is substantially the same as the one shown in Figure 2. The difference is that the spent (lithium-enriched) anode is strengthened by mixing a concentrated LiCl solution obtained by decarbonizing the initial mixture of LiCl and Li2CO3 with hydrochloric acid with a carbonate obtained by reusing spent evaporated cathode liquid. In other respects, the flowchart is identical.

[0060] Figure 6 shows a process flowchart for producing LiOH·H2O from a material containing lithium salt in the form of a mixture of Li2SO4 and LiCl. A notable feature of this technique is that two highly soluble lithium salts, lithium chloride and lithium sulfate, are simultaneously involved in the anode process, with reactions (1) and (21) occurring simultaneously at the anode, and H2SO4, Cl2, and O2 being formed simultaneously in the anode compartment. For this reason, the reliability of the film electrolysis process of the mixed salt using a platinum-plated titanium anode is ensured. Here, the cathode process remains unchanged and occurs exactly as in the case of film electrolysis of solutions of highly soluble Li2SO4 and LiCl salts.

[0061] The preparation of LiOH·H2O based on the electrochemical conversion of a mixed solution of Li2SO4 and LiCl does not require a special process to purify the anode solution from sulfate ions. In other words, the technique described in Figure 6 is a combination of the process steps in the flowcharts of Figures 1 and 2.

[0062] Figure 7 shows a process flowchart for producing LiOH·H2O from a material containing lithium salts in the form of a mixture of Li2SO4, LiCl, and Li2CO3. This flowchart differs from the flowchart for processing the mixed salt of Li2SO4 and LiCl (Figure 6) only in that the spent anode strengthening process is performed before the sulfuric acid neutralization step. In other respects, the flowcharts are identical. [Examples]

[0063] A comparative study of technical processes for producing LiOH·H2O from various lithium salts—lithium sulfate, lithium chloride, and mixtures of sulfate and lithium chloride—was conducted using a laboratory-scale apparatus comprising a membrane electrolysis unit, a unit for processing the cathode solution into LiOH·H2O, a unit for pre-treating and purifying the supplemental lithium salt solution for supply to the circulating anode solution, a unit for processing the spent evaporated cathode solution, and an anode gas utilization unit. The technical processes reproduced in the laboratory apparatus were carried out based on the flowcharts shown in Figures 1 and 2. Here, the sulfate-containing anode solution was neutralized according to the option of using slaked lime for this purpose, and the chloride-containing anode solution was fortified with lithium carbonate pre-dissolved in hydrochloric acid, utilizing the anodic chlorine as neutral calcium hypochlorite. The following lithium salts were used in the test: technical grade lithium sulfate monohydrate (composition shown in Table 1) and lithium chloride according to TU2152-017-07622236-2015 (composition shown in Table 2).

[0064] [Table 1]

[0065] [Table 2]

[0066] Calcium hydroxide, used to neutralize sulfuric acid and utilize anodic chlorine as neutral calcium hypochlorite, was obtained by precipitation from a solution of CaCl2 produced by dissolving hydrated technical-grade CaCl2·6H2O salt (using NaOH as a precipitating agent).

[0067] Table 3 shows the main comparative parameters and characteristics of the LiOH·H2O production techniques from various lithium salts using the claimed method. Table 4 shows the composition of each obtained LiOH·H2O sample.

[0068] [Table 3]

[0069] [Table 4]

[0070] As can be seen from the results, the claimed method can produce high-quality LiOH·H2O products that meet the requirements of LGO-1 GOST 8595-83 grade from the tested lithium salt. Here, the electrochemical parameters of the membrane electrolytic conversion process from a solution of highly soluble lithium salt to a LiOH solution have nearly identical characteristics.

[0071] The tests also showed that when anodic chlorine was utilized according to the options proposed in the claimed method, which includes reusing anodic chlorine for neutral calcium hypochlorite, the active chlorine content in the sample of the generated product was 62% to 63% by weight, and the water-insoluble impurity content did not exceed 4.3%. The utilization rate of anodic chlorine was 99.7%.

[0072] Furthermore, tests have shown that the neutralization of sulfuric acid in the spent sulfuric acid anode should be carried out by adding a stoichiometric amount of Ca(OH)2, however, this operation is performed in two steps to completely neutralize the H2SO4 in the anode without the need to introduce excess Ca(OH)2.

[0073] In the first step, the initial spent anode liquid is brought into contact with the spent precipitate from the second step, which is a mixture of CaSO4·2H2O and Ca(OH)2. This contact is carried out with the assurance of the conversion of all free Ca(OH)2 to CaSO4·2H2O and the extraction of the resulting CaSO4·2H2O precipitate by filtration. The filtrate containing unreacted H2SO4 residue is brought into contact with the Ca(OH)2 incorporated in stoichiometric ratios into the H2SO4 contained in the initial spent anode liquid supplied to the first neutralization step. During phase contact in the second step, a mixed precipitate of CaSO4·2H2O and Ca(OH)2 is formed, ensuring the complete neutralization of sulfuric acid. The contact between the anode liquid and Ca(OH)2 is carried out under conditions of vigorous mixing. [Examples]

[0074] To test the suitability of three cation exchange membranes, Nafion-438, CTIEM-3, and MF-4SK-100, for electrochemical conversion from Li2SO4 and LiCl solutions to LiOH solutions, a laboratory bench containing three membrane electrolysis units was used. The total test time was 219 hours of work. The following materials were tested as anodes: ruthenium oxide-coated titanium (ORTA) for the electrolysis of LiCl solutions, and platinum-plated titanium for the electrolysis of Li2SO4 solutions. The results are shown in Table 5.

[0075] [Table 5]

[0076] As the results show, all tested membranes are suitable for membrane electrolysis of lithium sulfate and lithium chloride solutions to obtain the cathode solution in the form of a LiOH solution. Here, the membrane electrolysis parameters, such as the cell voltage and LiOH current output of the tested membranes, are substantially equivalent. The tests also showed that the energy consumption of electrolysis of LiCl solution to obtain a LiOH solution is lower, as the cell voltage of the membrane electrolysis unit during the electrolysis of sulfate solution is always higher than the voltage during the electrolysis of chloride-containing solution. This result is due to the higher electrical conductivity of Li2SO4 solution compared to LiCl solution.

[0077] The obtained data indicates that other cation exchange membranes that are chemically stable in these media can be used for the conversion of Li2SO4 and LiCl solutions, and are equivalent to those tested. [Examples]

[0078] A laboratory apparatus fabricated according to the flowchart shown in Figure 3 was used to test a technique for producing LiOH·H2O from lithium carbonate by regenerating LiCl and Li2SO4 supplied to the anodic acid circulation circuit to replenish the membrane electrolysis process of LiCl and Li2SO4 solutions from spent electrolytes where LiCl and Li2SO4 have been depleted from the electrolysis process. Here, the regeneration of the replenishment Li2SO4 solution was carried out by directly contacting a predetermined amount of Li2CO3 with the spent anodic acid in the neutralization step of the spent sulfate-containing anodic acid. The regeneration of the replenishment LiCl solution was carried out according to two options. According to the first option, anodic chlorine was absorbed into demineralized water as part of a mixture with ammonia (molar ratio of NH3:Cl2 = 2:3) to obtain a hydrochloric acid solution of a predetermined concentration, which was then contacted with a predetermined amount of Li2CO3, and the resulting solution was mixed with spent anodic acid pre-neutralized to pH 7 with lithium carbonate to obtain a LiCl-enhanced lithium chloride solution, which was used to replenish the circulating anodic acid in the membrane electrolysis process. According to the second option, anodic chlorine was absorbed into lithium carbonate pulp having a predetermined Li2CO3 content in the presence of a predetermined amount of carbamide reducing agent to obtain a LiCl solution of a predetermined concentration. This solution was then mixed with used anode liquid that had been pre-neutralized to pH=7 with lithium carbonate to obtain a LiCl-enhanced lithium chloride solution, which was used to replenish the circulating anode liquid. Technical-grade lithium carbonate manufactured by SQM (Chile) was used as the initial carbonate. Its composition is shown in Table 6.

[0079] [Table 6]

[0080] The enhanced and purified lithium salt solution generated from the spent anodic fluid was adjusted to the predetermined concentrations of Li2SO4 and LiCl in the replenishment solution by evaporation. The main parameters of the tests performed are shown in Table 7. The composition of each LiOH·H2O sample obtained is shown in Table 8. The results clearly demonstrate that the proposed method can produce LiOH·H2O from technical-grade lithium carbonate as a high-purity product that meets the requirements of LGO-1 grade.

[0081] [Table 7]

[0082] [Table 8]

[0083] Here, the recovery rate of the converted alkali (LiOH solution) as a solid product (LiOH·H2O) largely depends on the sodium and potassium content in the initial lithium carbonate. [Examples]

[0084] A laboratory bench, an assembly for utilizing sulfate ions present in H2SO4 salt, was used to test utilization options for converting sulfuric acid contained in spent sulfate anosol to (NH4)2SO4 salt by contacting spent anode liquid with ammonia and salting out (NH4)2SO4 salt from a mixed spent solution of Li2SO4 and (NH4)2SO4 during evaporation, which increases the concentration of Li2SO4 in the anosol liquid. Figure 1 shows the technical process options for utilizing sulfuric acid contained in spent anode liquid in the form of (NH4)2SO4 salt. The results obtained are shown in Table 9.

[0085] [Table 9]

[0086] The (NH4)2SO4 salt sample obtained after a three-step countercurrent washing with demineralized water and drying at 110°C contained 99.7% by weight of the main substance in the form of (NH4)2SO4, and the lithium impurity content was less than 0.002% by weight. As a result, the ammonia utilization rate was 99.84%. [Examples]

[0087] The following composition (g / dm 3 ): LiOH-120; NaOH-8.7; KOH-0.3 (10 dm 3 The spent cathode fluid was reused in an apparatus with steady-state operating conditions according to the claimed method (Figures 1-7). The reuse yielded 1,850 g of dry Li2CO3, with a major substance content of 99.9% and a total sodium and potassium impurity content of less than 0.01%. The total weight of the dried precipitates of the obtained NaHCO3 and KHCO3 salts was 188.1 g, with a residual lithium content of less than 0.002%.

[0088] References 1. Russian Patent No. 2071819, published January 20, 1997. 2. International Publication No. 9859385, published in 1998. 3. Russian Patent No. 2157338, published October 10, 2000. 4. Russian Patent No. 21967335, published January 20, 2003. 5. Russian Patent No. 2656452, published June 5, 2018.

Claims

1. A method for producing high-purity lithium hydroxide monohydrate from an original source containing a lithium salt selected from lithium sulfate, lithium chloride, lithium chloride monohydrate, lithium carbonate, or a mixture thereof, A step of performing membrane electrolysis of an aqueous solution of a lithium salt using a cation exchange membrane as a membrane separating the cathode circuit and anode circuit of an electrolytic unit, wherein the membrane electrolysis is carried out by circulating a cathode solution in the form of a lithium hydroxide solution and an anode solution in the form of a lithium salt solution, the cathode for the membrane electrolysis is made of nickel-plated stainless steel, and the cation exchange membrane is selected from membranes that exhibit resistance to alkalis and acids, A step of drawing an arbitrary volume of the cathode solution from the cathode circuit, evaporating the drawn volume of the cathode solution to obtain lithium hydroxide monohydrate crystals, A step to obtain high-purity lithium hydroxide monohydrate by separating the lithium hydroxide monohydrate crystals to obtain a mother liquor, washing the separated lithium hydroxide monohydrate crystals with water, and drying them, wherein the water used to wash the lithium hydroxide monohydrate crystals becomes the used washing solution. This includes the following steps: A step of removing cathode gas and anode gas formed during electrolysis, wherein the cathode gas is cathode hydrogen, A step of withdrawing a portion of the anodic solution from the anode circuit and obtaining the withdrawn used anodic solution, A step of supplying a portion of the used cleaning solution to the cathode liquid evaporation process, and using a portion of the used cleaning solution supplied to the cathode liquid evaporation process for the reuse of the extracted used anode liquid, A step of returning a portion of the mother liquor obtained during the separation of the lithium hydroxide monohydrate crystals back to the cathode liquid evaporation process, A step to obtain lithium carbonate by reusing a portion of the mother liquor obtained during the separation of the lithium hydroxide monohydrate crystals, which is a concentrated solution of lithium hydroxide containing sodium hydroxide and potassium hydroxide as additives, extracted from the cathode solution evaporation process, A step of replenishing the anode in the anode circuit with a concentrated lithium salt solution prepared from the original source containing the lithium salt and a lithium salt solution obtained as a result of reusing the extracted spent anode. A method characterized by the following.

2. The mother liquor obtained in the process of separating the crystals of lithium hydroxide monohydrate is a concentrated lithium hydroxide solution extracted from the cathode evaporation process, which contains sodium hydroxide and potassium hydroxide as additives. A portion of this mother liquor is reused by mixing it with an aqueous solution stream containing sodium bicarbonate, potassium bicarbonate, and lithium bicarbonate to obtain pulp. The pulp contains a solid phase of lithium carbonate and Na ２ CO ３ _K ２ CO ３ Li ２ CO ３ The method according to claim 1, comprising: a mixture with a carbonate solution containing the above, the pulp being concentrated by removing water, the solid phase of lithium carbonate being separated from the liquid phase, the liquid phase being carbonized by directly contacting it with carbon dioxide to convert the carbonate solution into a bicarbonate suspension which is a mixture of the solid phase of sodium bicarbonate and the solid phase of potassium bicarbonate in a solution of sodium bicarbonate, potassium bicarbonate and lithium bicarbonate, the obtained suspension being filtered to separate the solid phase of sodium bicarbonate and the solid phase of potassium bicarbonate from the solution containing sodium bicarbonate, potassium bicarbonate and lithium bicarbonate, and these being mixed with a portion of the mother liquor obtained in the step of separating the crystals of lithium hydroxide monohydrate drawn from the cathode solution evaporation process containing lithium hydroxide, sodium hydroxide and potassium hydroxide.

3. The method according to claim 1, wherein the reuse of the extracted spent anode solution includes a step of chemically purifying the extracted spent anode solution and / or a step of ion exchange purifying the extracted spent anode solution, wherein the used washing solution is used as an alkaline reagent in the step of chemically purifying the extracted spent anode solution and / or is used as a regeneration solution for converting the ion exchanger from H form to Li form in the step of ion exchange purifying the extracted spent anode solution.

4. The DC current density of the extracted spent anode liquid is 1 kA / m³ ２ ~4kA / m ２ The method according to claim 3.

5. When using lithium sulfate as the original source containing the lithium salt, titanium coated with a noble metal selected from platinum, iridium, ruthenium or tantalum is used as the anode in membrane electrolysis, and the anolyte circulating in the anode circuit is Li ２ SO ４ is depleted and H ２ SO ４ is enriched, and is always withdrawn to obtain the drawn used anolyte, the drawn used anolyte is first neutralized by contacting it with lithium carbonate, and then H ２ SO ４ is completely neutralized by contacting it with CaO or Ca(OH) ２ or CaCO ３ to obtain a solid phase of CaSO ２ SO ４ in the Li ４ SO ２ solution, the obtained solid phase of CaSO ４ SO ２ is separated from the Li ２ SO ４ solution, the Li ２ SO ４ solution is contacted with the lithium sulfate salt of the original source to dissolve it in the Li ２ SO ４ solution, the obtained Li ２ SO ４ solution is added with the used washing solution, and then carbon is added. The carbon addition uses carbon dioxide derived from the process of neutralizing the drawn anolyte. The carbon addition is carried out until calcium and magnesium contained in the solution are converted into precipitates consisting of insoluble CaCO ３ and Mg(OH) ２ ·3MgCO ３ ·3H ２ O to obtain a suspension. The suspension is filtered to separate the precipitate to obtain a chemically purified Li ２ SO ４ solution, the obtained Li ２ SO ４ solution is induced to ion exchange purification by passing it through a layer of an ion exchanger in the Li form, and the ion exchange purified Li ２ SO ４ The method according to claim 4, wherein the solution is used to replenish the anode liquid in the anode circuit in the membrane electrolysis, the ion exchanger is regenerated in two steps: a first step of treatment with a 2.0 N sulfuric acid solution and a second step of treatment with a 2.0 N LiOH solution to obtain used regenerated liquid, the used regenerated liquid is mixed with the extracted used anode liquid before chemical purification, the cathode hydrogen which is the cathode gas is discharged and removed by a natural gas flow obtained from the cathode gas separator of the electrolysis unit to obtain a gaseous mixture, and the obtained gaseous mixture is introduced into a steam generator as fuel for generating heated steam to be used as a heat transfer medium in the process of evaporating the extracted cathode liquid.

6. When lithium sulfate is used as the original source containing the lithium salt, the anodic solution circulating in the anode circuit is Li ２ SO ４ Depletion and H ２ SO ４ Enriched by and always drawn out to obtain the drawn-out spent anode liquid, the drawn-out spent anode liquid is brought into contact with an air-ammonia mixture and H ２ SO ４ It neutralizes Li ２ SO ４ and (NH ４ ) ２ SO ４ A mixed solution of Li₂SO₄ and (NH₄)₂SO₄ is obtained, the mixed solution of Li₂SO₄ and (NH₄)₂SO₄ is evaporated to salt out (NH₄)₂SO₄, and a concentrated solution of Li₂SO₄ containing (NH₄)₂SO₄ as an impurity is obtained, the concentrated solution of Li₂SO₄ containing (NH₄)₂SO₄ as an impurity is mixed with an arbitrary volume of used washing solution to obtain a mixed solution, the mixed solution is brought into contact with an airflow resulting from the process of contacting the used anode liquid with the air-ammonia mixture, and the remaining ammonia is removed from the concentrated solution of Li₂SO₄ to obtain ammonia-free Li₂SO₄. ２ SO ４ A solution and an airflow containing gaseous ammonia are obtained, and the ammonia in the airflow containing gaseous ammonia is enriched with ammonia from an ammonia source, H ２ SO ４ This process induces a neutralization of Li derived from the original source. ２ SO ４ By dissolving it there, the Li that does not contain ammonia ２ SO ４ Solution Li ２ SO ４ The method according to claim 4, further strengthened, purified from impurities, and used to replenish the anodic acid in the anode circuit in the film electrolysis.

7. When lithium chloride or lithium chloride monohydrate is used as the original supply source, a titanium anode coated with ruthenium oxide is used for the film electrolysis, the anolyte circulating in the anode circuit is depleted of LiCl, and the spent anolyte is always drawn out to obtain the drawn-out spent anolyte, the drawn-out spent anolyte is brought into contact with LiCl from the original supply source, the LiCl concentration in the drawn-out spent anolyte is set to a predetermined value to obtain a LiCl-enriched anolyte, and in order to chemically purify the drawn-out LiCl-enriched anolyte from metal cation impurities and sulfate ions, barium chloride is added to the LiCl-enriched anolyte to make the sulfate ions insoluble in the liquid phase BaSO₄ ４ Convert the liquid phase to a precipitate, and the insoluble BaSO4 is converted to a liquid phase. ４ The method according to claim 4, wherein the precipitate is separated and subjected to ion exchange purification, and then used to replenish the anode solution in the anode circuit in the membrane electrolysis, the cathode gas is cathode hydrogen and the anode gas is anode chlorine, which are extracted using the cathode gas separator and anode gas separator of the electrolysis unit, respectively, the cathode hydrogen and the anode chlorine are mixed and subjected to flame combustion to obtain hydrogen chloride, and the obtained hydrogen chloride is absorbed into desalinated water to produce 36% concentrated hydrochloric acid.

8. The anodic chlorine extracted from the anode gas separator is absorbed into ammonia water, and NH ３ : Cl ２ Under the condition that the molar ratio is 8:3, NH ４ Cl solution, NH ３ : Cl ２ A 6N HCl solution was prepared under conditions of a molar ratio of 2:3, and the obtained NH ４ Evaporate the Cl solution, then NH ４ The method according to claim 7, wherein Cl is crystallized and dried, and the cathode hydrogen extracted from the cathode gas separator is used as a heat transfer medium for generating heated steam.

9. Either absorb the entire volumetric flow rate of anodic chlorine extracted from the anode gas separator into a NaOH solution to produce a sodium hypochlorite disinfectant solution, or absorb half of the volumetric flow rate of the extracted anodic chlorine into a NaOH solution to produce a sodium hypochlorite saturated solution, and use Ca(OH) to obtain a solution containing the remaining half of the volumetric flow rate of the anodic chlorine. ２ Absorbed into a suspension to produce a solution saturated with calcium hypochlorite, the produced solution is mixed to salt out neutral calcium hypochlorite, this is separated from the liquid phase and dried, a predetermined amount of NaOH is first added to the liquid phase, and then Na ２ CO ３ By adding Ca(OH) ２ CaCO ３ A precipitate containing the mixture is obtained, and the Ca(OH) ２ CaCO ３ The precipitate contained as a mixture with is separated from the liquid phase and contains Ca(OH) in the form of hypochlorite ions, which are active chlorine. ２ The suspension is prepared, the solution is divided into two equal parts, one part is mixed with NaOH and proceeded to the chlorination process to obtain a sodium hypochlorite solution, and the other part is mixed with Ca(OH) ２ The method according to claim 7, wherein the mixture is similarly introduced into a chlorination process to obtain a calcium hypochlorite solution.

10. When lithium carbonate is used as the original source, Li ２ CO ３ By converting lithium carbonate into highly soluble lithium chloride or lithium sulfate contained in the anodic solution within the anode circuit of the electrolytic unit, lithium carbonate is used to reuse the extracted used anodic solution, and during membrane electrolysis, LiCl or Li is converted from the anodic solution. ２ SO ４ The method according to claim 4, wherein depletion is carried out.

11. When an aqueous solution of lithium chloride is used as the anode liquid, a titanium anode coated with ruthenium oxide is used for the film electrolysis, the cathode gas is cathode hydrogen, the anode gas is anode chlorine, and the cathode hydrogen and anode chlorine are mixed and burned to generate high-temperature hydrogen chloride vapor, the hydrogen chloride vapor is cooled and absorbed into demineralized water in a stepwise countercurrent manner, and a 36% concentrated hydrochloric acid stream is obtained from the first absorption step along the HCl vapor path, and the obtained concentrated hydrochloric acid stream and BaCl ２ The method according to claim 4, wherein the spent anode solution purified from sulfate ions is mixed with concentrated hydrochloric acid as a reagent to obtain a mixed flow of concentrated hydrochloric acid and the spent anode solution purified from sulfate ions, the mixed flow is brought into contact with lithium carbonate and desalinated water from the original supply source to obtain a LiCl solution flow, and after purifying this from calcium and magnesium impurities, it is used to replenish the anode solution in the anode circuit in the membrane electrolysis.

12. NH ３ : Cl ２ The method according to claim 11, wherein the anodic chlorine is absorbed into desalinated water in the presence of ammonia in a molar ratio of 2:3 to obtain a 6N hydrochloric acid solution, which is mixed with the extracted spent anode liquid chemically purified from sulfate ions to obtain a mixed flow of the hydrochloric acid solution and the anode liquid purified from sulfate ions, the mixed flow of the hydrochloric acid solution and the anode liquid purified from sulfate ions is brought into contact with lithium carbonate from the original supply source to obtain a LiCl solution flow, which is purified from calcium and magnesium impurities and then used to replenish the anode liquid in the anode circuit in the membrane electrolysis, and the cathode hydrogen is used as fuel for generating heating steam.

13. In the presence of an elemental chlorine reducing agent, a lithium carbonate aqueous pulp having a material composition that prevents contamination by foreign cations and anions during chlorine absorption is used to absorb the anodic chlorine, thereby obtaining a lithium chloride solution as an absorption product. After purifying the lithium chloride solution from calcium and magnesium impurities, it is used to replenish the anode solution in the anode circuit in the membrane electrolysis. Here, the aqueous pulp for absorbing the anodic chlorine consists of desalinated water, lithium carbonate obtained from the mother liquor derived from the process of separating the lithium hydroxide monohydrate crystals, lithium carbonate from the original source containing lithium salts, the reducing agent, and BaCl ２ The method according to claim 11, wherein the reagent is prepared from the spent anode solution extracted from sulfate ions, and the cathode hydrogen is used as fuel for generating heated steam.

14. The method according to claim 4, wherein, when an aqueous solution of lithium sulfate is used as the anode liquid, titanium coated with a noble metal selected from platinum, iridium, tantalum, or ruthenium is used as the anode in the film electrolysis, the anode liquid circulating in the anode circuit undergoes depletion of lithium sulfate and enrichment of sulfuric acid, and is drawn out from the anode circuit to obtain the drawn-out spent anode liquid, the drawn-out spent anode liquid is further brought into contact with lithium carbonate to obtain a lithium sulfate solution, and this is purified from impurities and then used to replenish the anode liquid in the anode circuit.

15. When using a mixture of lithium sulfate and lithium carbonate, which are lithium salts, as the original source containing the lithium salt, the anolyte circulating in the anode circuit becomes depleted in Li ２ SO ４ and enriched in H ２ SO ４ and is always withdrawn to obtain the drawn used anolyte. The drawn used anolyte stream is contacted with Li ２ SO ４ salt and Li ２ CO ３ salt to obtain a lithium sulfate solution containing a residual amount of H ２ SO ４ . The lithium sulfate solution containing the residual amount of H ２ SO ４ is reused as a Li ２ SO ４ solution suitable for replenishing the anolyte in the anode circuit in the membrane electrolysis. The method according to claim 4

16. The method according to claim 4, wherein, when a mixture of lithium chloride and lithium carbonate is used as the original source containing the lithium salt, the lithium chloride and lithium carbonate derived from the original source are brought into contact with a hydrochloric acid solution and the extracted spent anode liquid that has been depleted of LiCl to produce a lithium chloride solution of a predetermined concentration, and the obtained lithium chloride solution is purified from impurities and then used to replenish the anode liquid in the anode circuit in the membrane electrolysis.

17. When a mixture of lithium sulfate and lithium chloride is used as the original source containing the lithium salt, titanium coated with a noble metal selected from platinum, iridium, tantalum, or ruthenium is used as the anode in the film electrolysis, and the anodic solution circulating in the anode circuit is Li ２ SO ４ Depletion and H ２ SO ４ Enriched by and always drawn out in order to obtain the used anode liquid that has been drawn out, H ２ SO ４ Until the used anode solution is completely neutralized, a predetermined amount of CaO or Ca(OH) is added. ２ or CaCO ３ Li ２ SO ４ A mixed solution of LiCl and CaSO2 ４ ・2H ２ O precipitate is obtained, Li ２ SO ４ The mixed solution of and LiCl is described as CaSO2 ４ ・2H ２ O Separated from the precipitate, Li derived from the original source ２ SO ４ A mixture of salt and LiCl salt is brought into contact and dissolved, and Li containing a predetermined concentration of lithium ２ SO ４ The method according to claim 4, wherein another mixed solution of and LiCl is obtained, purified from impurities, and then used to replenish the anode solution in the anode circuit in the membrane electrolysis, and the cathode hydrogen is used as heating vapor.

18. The used anode solution that has been removed after reuse is used to replenish the anode circuit with Li ２ SO ４ and used as a LiCl replenishment mixed solution, wherein the anode gas is anodic chlorine drawn from the anode gas separator of the electrolytic unit, and the anodic chlorine is 36% hydrochloric acid or NH ４ The method according to claim 17, wherein the solution is reused as Cl or sodium hypochlorite solution or neutral calcium hypochlorite.

19. When a mixture of lithium sulfate, lithium chloride, and lithium carbonate is used as the original source containing the lithium salt, the anode liquid circulating in the anode circuit is Li ２ SO ４ Depletion and H ２ SO ４ Enriched by Li, and always drawn to obtain the extracted spent anode liquid, the extracted spent anode liquid is supplied from the original source Li ２ SO ４ , LiCl and Li ２ CO ３ A mixture of Li is brought into contact with the mixture to produce a mixed solution of a predetermined lithium concentration, and the mixed solution of the predetermined lithium concentration is used to replenish the anode solution in the anode circuit of the membrane electrolysis. ２ SO ４ The method according to claim 4, wherein the mixture of LiCl is reused.

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