EA046337B1 - METHOD FOR PRODUCING HIGH-PURITY LITHIUM HYDROXIDE MONOHYDRATE - Google Patents

Description

Field of technology

The invention relates to the field of chemical technology for the production of inorganic compounds, namely to methods for producing lithium hydroxide monohydrate of high purity from materials containing lithium salts.

State of the art

There is a known method for producing a solution of lithium hydroxide from solid carbonate-containing lithium waste by contacting it with water, settling the resulting pulp, decanting the clarified liquid phase, followed by filtration and recycling the resulting lithium-containing solution through the central chamber of the electrodialyzer to obtain a solution of lithium hydroxide in the cathode chamber, in the anodic chamber a solution chamber of a mixture of acids, and a central chamber of saline liquid returned to the operation of leaching lithium from solid carbonate-containing lithium waste [1].

The disadvantage of this method is the production of a low concentrated LiOH solution (no more than 25 kg/m ³ ) and the low productivity of the process due to its operation at a current density of no higher than 2 A/dm ² (0.2 kA/m ² ), high electrical resistance of the recirculating solution Li ₂ CO ₃ due to the low concentration of Li ₂ CO ₃ (no more than 10 kg/m ³ ) and, as a consequence, high specific energy consumption per unit of product produced.

There is a known method for producing a solution of lithium hydroxide from materials containing lithium compounds, in particular from waste lithium batteries [2], including the extraction of lithium from waste in the form of highly soluble lithium sulfate, membrane electrolysis of a solution of lithium sulfate using a Nation 350 cation exchange membrane separating the cathode and anode space. Electrolysis is carried out at a direct current density of 20 A/dm ² and a voltage of 5.3 V with a constant output of a LiOH solution (catholyte) from the cathode space, and an anolyte depleted in Li ₂ SO ₄ containing the product of the anodic process - sulfuric acid - from the anode space. The withdrawn anolyte stream is sent to the lithium leaching operation, neutralizing sulfuric acid and at the same time strengthening it with lithium sulfate. The anolyte strengthened with Li ₂ SO ₄ is returned to the electrolysis operation.

The disadvantages of this anolyte include its limitation in producing a LiOH solution contaminated with impurities. It is not possible to produce a highly pure product in the form of LiOH-H ₂ O using this method.

There is a known method for producing lithium hydroxide of high purity by membrane electrolysis of an aqueous solution containing lithium chloride and lithium carbonate isolated from natural brine in the presence of a reducing agent [3]. The removed catholyte is evaporated, crystallizing LiOH-H ₂ O. After separation from the mother solution, LiOH-H ₂ O is washed with demineralized water and dried, obtaining LiOH-H2O of high purity. In this case, cathode hydrogen is used to obtain a coolant for the production of heating steam, which is used in the catholyte evaporation operation, and anodic chlorine is used to oxidize bromide ions into elemental bromine through direct contact of chlorine with bromionic natural brine.

The disadvantages of this method include the use of a low concentration LiCl solution for electrochemical conversion, previously isolated from a natural lithium-bearing brine using a sorbent selective for LiCl, and the need to use a reducing agent to eliminate the risk of formation of oxychlorides in the anode space during the electrolysis of a low concentrated LiCl solution.

The method for producing high-purity lithium monohydrate from materials containing lithium carbonate [4] eliminates most of the disadvantages of the above methods. The method is based on the reproduction of an aqueous solution of highly soluble lithium sulfate supplied to feed an anolyte solution depleted in Li ₂ SO ₄ and enriched in H ₂ SO ₄ , circulating in the anolyte circuit of the electrolysis unit. To do this, part of the lithium-depleted anolyte is constantly removed from the anolyte circuit and brought into contact with an equivalent amount of lithium carbonate, converting the anodic acid series into lithium sulfate. This method also provides for reagent purification from impurities of Ca, Mg and heavy metals of a reproduced solution of Li ₂ SO ₄ by the carbonate-alkaline method using a solution of LiOH and CO2 of the anolyte released during carbonate neutralization.

The disadvantages of this method include the use of MK-40 cation exchange membranes, which have low mechanical and chemical stability, in the membrane electrolysis operation. In addition, the disadvantages of the method include the presence of liquid production waste in water, a solution of lithium carbonate contaminated with sodium and potassium carbonates, as well as an insufficient depth of reagent purification from impurities of the Li ₂ SO ₄ solution fed to the anolyte circuit, which leads to the need periodically check the acid regeneration of membranes contaminated with calcium and magnesium cations.

The method for producing lithium monohydrate from brines and the installation for its implementation [5] eliminates these disadvantages of the previous method. The LiOH solution supplied for evaporation, crystallization, washing and drying LiOH-H ₂ O is obtained from a concentrated LiCl solution that has undergone reagent purification using the carbonate-alkaline method and then ion exchange purification on the Lewatit-208-TP ion exchanger in Li

- 1 046337 form. The method also involves using the waste catholyte stream removed from the evaporation operation in the form of a LiOH solution containing NaOH and KOH as a reagent to obtain a productive LiCl solution with the removal of sodium and potassium from the process in the form of NaCl and KCl crystals. In terms of technical essence and achieved performance, this method of producing lithium hydroxide monohydrate from a material containing lithium salt is closest to the claimed one and therefore it is adopted as a prototype.

The disadvantages of this method are:

1) Limited range of raw materials from which it is possible to obtain LiOH-H2O only with aqueous solutions of lithium chloride produced from lithium-bearing natural brines;

2) The possibility of removing sodium and potassium impurities accumulated in the catholyte only in the form of NaCl and KCl if there is a stage in the LiOH-H ₂ O production process for producing productive lithium concentrate (lithium concentrate suitable for producing LiCl-H ₂ O and LiCl) by concentration and purification from impurities of low LiCl concentrated raw material sources in the form of primary lithium concentrates produced from lithium-rich natural brines using LiCl-selective sorbents;

3) Limited range of by-products produced during the disposal of anode chlorine;

4) Lack of solutions for the utilization of cathode hydrogen.

These disadvantages can be eliminated by implementing the following technical solutions that form the basis of the proposed method:

obtaining a LiOH solution by membrane electrolysis of an aqueous solution of Li ₂ SO ₄ , an aqueous solution of LiCl or a mixed solution of Li ₂ SO ₄ and LiCl, produced from materials containing a lithium salt in the form of Li ₂ SO ₄ or LiCl or Li ₂ CO ₃ or various mixtures of these salts ;

processing the stream enriched in sodium and potassium (spent catonite) removed from the catholyte evaporation operation into solid-phase lithium carbonate and solid-phase sodium and potassium bicarbonate;

the use of stainless steel coated with a layer of nickel as a cathode, eliminating both hydrogenation of the cathode and the risk of corrosion;

use of the spent washing solution formed after washing LiOH-H ₂ O crystals as an alkaline reagent in the operations of preparing aqueous lithium salts for membrane electrolysis;

application of new solutions for the disposal of cathodic and anodic by-products of membrane electrolysis of aqueous solutions of lithium salts.

The implementation of the proposed technical solutions makes it possible to expand the range of raw materials suitable for the production of lithium hydroxide monohydrate, increase the reliability of the membrane electrolysis operation, expand the range of produced by-products, eliminate the formation of liquid and gaseous production waste and, as a consequence, improve the environmental performance of production.

The essence of the invention

The technical result is achieved by the fact that lithium sulfate or lithium chloride, or lithium carbonate or various mixtures of these salts are used as a material containing lithium salt; in the processes of membrane electrolysis of aqueous solutions of lithium salts, cathodes made of stainless steel coated with nickel are used, and in as cation exchange membranes of the brands Nafion-348, CTIEM-3, MF-4SK-100 or membranes analogues of these brands.

The technical result is achieved by the fact that the spent washing solution entering the catholyte evaporation operation is partially used in the operation of preparing for electrolysis of a lithium salt solution brought to a given concentration as an alkaline reagent, first at the stage of reagent purification of this salt solution from impurities and then as a regenerating solution for transfer ion exchanger from the H-form to the Li-form at the stage of ion exchange purification.

The technical result is achieved by the fact that the processing of a stream of spent catholyte, which is a solution of lithium hydroxide with an admixture of sodium hydroxide and potassium hydroxide, is carried out by mixing with a stream of an aqueous solution containing sodium, potassium and lithium bicarbonates, the resulting pulp, which is a mixture of the solid phase of lithium carbonate and a solution containing Na2CO3, K2CO3 and Li2CO3 is concentrated by removing a given amount of water, the solid phase of lithium carbonate is separated from the liquid phase, the liquid phase is carbonated by contact with carbon dioxide, converting the carbonate solution into a hydrocarbonate suspension, which is a mixture of solid phases of sodium bicarbonate and bicarbonate potassium in a solution of sodium, potassium and lithium bicarbonates, the resulting suspension is filtered, separating the solid phase of sodium and potassium bicarbonates from a solution containing sodium, potassium and lithium bicarbonates, which is sent for mixing with the flow of spent catholyte removed from the evaporation operation, containing lithium and sodium hydroxides and potassium.

The technical result is achieved by the fact that when using lithium sulfate as a material containing lithium salt, titanium with

- 2 046337 coated with a noble metal: platinum, ruthenium, iridium, tantalum, and from the flow of circulating anolyte, combined in Li ₂ SO ₄ and enriched in H ₂ SO ₄ , an anolyte flow of a given volume is constantly removed at a given speed, the withdrawn anolyte flow is brought into contact, either with CaO, or with Ca(OH) ₂ , or with CaCO ₃ until complete neutralization of H ₂ SO ₄ , the resulting solid phase CaSO ₄ -2H ₂ O is separated from the Li ₂ SO ₄ solution, the Li ₂ SO ₄ solution is brought into contact with a given mass amount of the outgoing salt Li ₂ SO ₄ , dissolving it and obtaining a solution of Li ₂ SO ₄ of a given concentration, a given volume of washing solution is added to the resulting solution, after which the solution is carbonated with carbon dioxide coming from the operation of neutralizing the output anolyte flow, before transfer calcium and magnesium contained in the solution into insoluble compounds CaCO ₃ and Mg(OH) ₂ 3MgCO ₃ 3H ₂ O, the resulting suspension is filtered, separating the precipitate from the Li ₂ SO ₄ solution, the reagent-purified Li ₂ SO ₄ solution is sent for ion exchange purification by passing through a layer of Lewatit-208-TP ion exchanger in Li-form or an analogue ion exchanger in Li-form, a solution of Li ₂ SO ₄ that has undergone ion exchange purification is used as a make-up solution into the circulating anolyte stream in the membrane electrolysis operation, the spent ion exchanger is regenerated in two stages : at the first stage by treatment with a 2.0 N solution of sulfuric acid, at the second stage by treatment with a 2 N solution of LiOH prepared from the spent washing solution, the spent regenerates are mixed with the spent anolyte stream before its reagent purification, which is a by-product of electrolysis of cathodic hydrogen ejected with a stream of natural gas from the cathode gas separator of the electrolysis unit, the resulting mixture of gases is sent to a steam generator as fuel for the production of heating steam, used as a coolant in the evaporation operations of solutions and catholyte, in particular.

The technical result is achieved by the fact that when used as a material containing lithium salt, lithium sulfate salt is constantly removed from the circulating flow of anolyte, depleted in Li ₂ SO ₄ and enriched in H ₂ SO ₄ , a given volume of anolyte with a given volumetric velocity is brought into contact with an air-ammonia mixture to neutralize H ₂ SO ₄ to obtain a mixed solution of Li2SO4 and (NH4) 2SO4, which is evaporated, salting out (NH4) 2SO4, the evaporated solution with the residue (NH ₄ ) ₂ SO ₄ is mixed with a given volume of spent washing solution, bringing into contact with the air stream coming from the operation of contacting the spent alkaline anolyte stream with an ammonia-air mixture to remove the remaining ammonia from the Li2SO4 solution, the air stream containing ammonia vapor is enriched with ammonia from the ammonia source and sent to the operation of neutralizing the waste anolyte stream, freed from ammonia a solution of Li ₂ SO ₄ after a given strengthening of Li ₂ SO ₄ by dissolving a given mass amount of the initial lithium sulfate salt in it and reagent and ion exchange purification from impurities is used as a make-up solution in the circulating anolyte stream in the membrane electrolysis operation.

The technical result is achieved by the fact that when using as a material containing lithium salt, lithium chloride or lithium chloride monohydrate, anodes made of titanium coated with ruthenium oxide are used in the membrane electrolysis operation, and a specified volume of anolyte is constantly removed from the circulating anolyte flow, depleted in LiCl content at a given volumetric velocity, the withdrawn anolyte stream is brought into contact with the original salt containing lithium chloride, bringing the LiCl concentration in the withdrawn anolyte stream to a given value, the LiCl-enriched stream of the withdrawn anolyte, along with reagent purification from impurities of metal cations, is purified from sulfate ions by adding a given amount of barium chloride, converting sulfate ions into an insoluble precipitate of BaSO ₄ , the liquid phase is separated from the precipitates and, after ion-exchange purification, is used as a make-up solution in the circulating anolyte stream for membrane electrolysis operations; the cathode hydrogen and anodic chlorine removed from the gas separators are mixed and subjected to flame combustion, the resulting hydrogen chloride is absorbed into demineralized water, producing concentrated 36% hydrochloric acid.

The technical result is achieved by the fact that when used as a material containing lithium salt, lithium chloride or lithium chloride monohydrate, the anodic chlorine removed from the gas separator is absorbed by an aqueous solution of ammonia, producing at a molar ratio NH ₃ :Cl ₂ = 8:3 a solution of NH ₄ Cl, and at a molar ratio of NH ₃ : Cl ₂ = 2:3, a 6N HCl solution, the resulting NH ₄ Cl solution is evaporated, NH4Cl is crystallized, the crystals are dried, and the removed hydrogen in this case is utilized in a coolant to produce heating steam.

The technical result is achieved by the fact that when used as a material containing lithium salt, lithium chloride or lithium chloride monohydrate, the anodic chlorine removed from the gas separator is completely absorbed by a NaOH solution, producing a disinfecting solution of sodium hypochlorite or 0.5 of the removed volume flow of chlorine is absorbed by a NaOH solution, producing a solution extremely saturated with sodium hypochlorite, and the other 0.5 of the output volume flow of anodic chlorine is absorbed by a suspension of Ca(OH)2, producing a solution extremely saturated with calcium hypochlorite, the resulting solutions are mixed, salting out neutral calcium hypochlorite, which is separated from the mother liquor and dried, Calcium is precipitated from the resulting mother solution, first in the form of Ca(OH)2 by adding a given amount of NaOH, and then in the form of CaCO3 by adding a given amount of Na2CO3,

- 3 046337 the precipitate containing Ca(OH)2 with an admixture of _CaCO3 is separated from a solution containing active chlorine in the form of hypochlorite ions, the solution is divided into two equal portions, one portion is mixed with a given amount of NaOH and sent for chlorination to obtain a sodium hypochlorite solution, the other a portion is mixed with a given amount of Ca(OH) ₂ and is also sent to a chlorination operation to obtain a solution of calcium hypochlorite, cathode hydrogen is utilized in a coolant to produce heating steam.

The technical result is achieved by the fact that when used as a material containing lithium salt, lithium carbonate, lithium carbonate salt is used to reproduce highly soluble salts of lithium chloride or lithium sulfate, circulating in the form of aqueous solutions in the anolyte circuit of the electrolysis unit and depleted in LiCl or Li ₂ SO ₄ in the process of membrane electrolysis, while in the case of using an aqueous solution of lithium chloride as an anolyte, titanium anodes coated with ruthenium oxide are used in the membrane electrolysis operation, while in the first option, the removed cathode hydrogen and anodic chlorine are burned after mixing to produce high-temperature vapors hydrogen chloride, hydrogen chloride vapor is cooled and absorbed by demineralized water in a stepwise countercurrent mode to obtain a stream of concentrated (36%) hydrochloric acid from the first absorption stage along the HCl vapor, the stream of the resulting concentrated hydrochloric acid is mixed with the purified stream, using BaCl ₂ in as a reagent, from the sulfate ions of the anolyte removed for purification from the sulfate ions from the circulating anolyte stream in the membrane electrolysis operation, the mixed stream of concentrated hydrochloric acid and the anolyte purified from sulfate ions is brought into contact with specified amounts of the original lithium carbonate and demineralized water, obtaining a stream a LiCl solution of a given concentration, which, after purification from calcium and magnesium impurities, is used as a make-up solution into the circulating anolyte stream in the membrane electrolysis operation; according to the second option, the removed anodic chlorine is absorbed by demineralized water in the presence of ammonia at a molar ratio of NH ₃ :Cl2=2:3 to obtain a solution of 6N hydrochloric acid, which is mixed with a stream of purified, using BaCl ₂ as a reagent, from the sulfate ions of the anolyte removed for purification from the sulfate ion from the circulating stream of anolyte in the membrane electrolysis operation, a mixed stream of a solution of hydrochloric acid and purified from sulfate ions The anolyte is brought into contact with a given amount of the initial lithium carbonate, producing a stream of LiCl salt solution, which, after purification from calcium and magnesium impurities, is used as a make-up solution in the circulating anolyte stream in the membrane electrolysis operation, and cathode hydrogen is used as fuel for the production of heating steam , according to the third option, anodic chlorine is absorbed by an aqueous slurry of lithium carbonate with a given content of Li2CO3 and in the presence of a given amount of an elemental chlorine reducing agent, the material composition of which excludes contamination of the absorbent with side cations and anions, for example, ammonia, hydrazine, hydroxylamine, urea, formic acid or reducing agents of their analogues , obtaining as an absorption product a solution of lithium chloride with a given concentration of LiCl, which is used as a make-up solution in the circulating anolyte stream in the membrane electrolysis operation, wherein the aqueous slurry for the absorption of anode chlorine is prepared from demineralized water, lithium carbonate obtained from spent catholyte, lithium carbonate in the form of the initial salt Li ₂ CO ₃ , a reducing agent and a stream purified using BaCl ₂ as a reagent, an anolyte from sulfate ions, which in turn is removed from the circulating anolyte stream at a given volume flow rate in membrane electrolysis operations, and cathode hydrogen is used as fuel for the production of heating steam.

In the case of using an aqueous solution of lithium sulfate as an anolyte in the membrane electrolysis operation, titanium anodes coated with noble metals are used: platinum, ruthenium, iridium, tantalum, and the anolyte flow of a given volume removed from the anolyte circulation circuit is combined with lithium sulfate and enriched with sulfuric acid. at a given speed, they are brought into contact with a given amount of initial lithium carbonate, obtaining a solution of lithium sulfate of a given concentration, which, after purification from impurities, is used as a make-up solution in the circulating anolyte circuit.

The technical result is achieved by the fact that when using as a material containing lithium salt, a mixture of lithium salts, lithium sulfate and lithium carbonate, titanium coated with noble metals is used as anodes in the membrane electrolysis operation: platinum, ruthenium, iridium, tantalum, and removed from of the anolyte circulation circuit, a combined lithium sulfate and sulfuric acid-enriched anolyte flow of a given volume at a given speed is brought into contact with a given amount of the initial mixture of Li ₂ SO ₄ and Li ₂ CO ₃ salts to obtain a lithium sulfate solution of a given concentration with a residual content of H ₂ SO ₄ , the resulting Li ₂ SO ₄ solution is freed from the presence of sulfuric acid residue and, after purification from impurities, is used as a feed into the circulating anolyte stream in the membrane electrolysis operation.

The technical result is achieved by the fact that when using as a material containing a lithium salt, a mixture of lithium chloride and lithium carbonate salts, titanium coated with ruthenium oxide is used as anodes in the membrane electrolysis operation, and the initial mixture of chloride and carbine salts

- 4 046337 lithium bonate is brought into contact with a given volume of hydrochloric acid of a given concentration and a given volumetric flow of anolyte removed from the flow of circulating anolyte depleted in LiCl in the process of membrane electrolysis, producing a solution of lithium chloride, the resulting solution of lithium chloride after purification from impurities is used in as a make-up solution into the circulating anolyte stream in the membrane electrolysis operation.

The technical result is achieved by the fact that when using as a material containing lithium salt, a mixture of lithium salts, lithium sulfate and lithium chloride, titanium coated with noble metals is used as anodes in the membrane electrolysis operation: platinum, ruthenium, iridium, tantalum, and from the circulating flow anolyte depleted in lithium sulfate and chloride and enriched in H ₂ SO ₄ , an anolyte stream of a given volume and at a given speed is removed, which is either brought into contact with a given amount of ammonia in the ammonia-air mixture, followed by concentration of a mixed sulfite solution of Li ₂ SO ₄ and (NH ₄ ) ₂ SO ₄ and salting out the salt (NH ₄ ) ₂ SO ₄ to obtain a solution of Li ₂ SO ₄ , or brought into contact with a given amount of either Ca(OH) ₂ or CaCO ₃ until the H ₂ SO ₄ is completely neutralized, and obtaining a Li ₂ SO ₄ solution, which is separated from the CaSO ₄ -2H ₂ O precipitate, the Li ₂ SO ₄ solution obtained in one way or another is brought into contact with a given amount of the initial mixture of Li ₂ SO ₄ and LiCl salts, dissolving it and obtaining a mixed solution of Li ₂ SO ₄ and LiCl with a given lithium concentration, which, after purification from impurities, is used as a make-up solution in the circulating anolyte stream in the membrane electrolysis operation; the anodic chlorine removed from the gas separator is processed either into 36% hydrochloric acid or Na ₄ Cl salt, either into a solution of sodium hypochlorite or neutral calcium hypochlorite.

The technical result is achieved by the fact that when using as a material containing a lithium salt, a mixture of salts from lithium sulfate, lithium chloride and lithium carbonate, titanium coated with noble metals is used as anodes in the membrane electrolysis operation, and from the circulating anolyte flow depleted in Li ₂ SO ₄ and LiCl and enriched in H ₂ SO ₄ constantly remove a given volume of anolyte at a given volumetric velocity, which is first brought into contact with a given amount of the initial mixture of salts Li ₂ SO ₄ , LiCl and Li ₂ CO ₃ , producing a mixed solution of Li ₂ SO ₄ , LiCl, H ₂ SO ₄ with a given lithium concentration, the resulting mixed solution is processed into a mixed solution of Li ₂ SO ₄ and LiCl, which is used as a make-up solution in the circulating anolyte stream in the membrane electrolysis operation.

List of drawings

Fig. 1. Technological scheme for producing LiOH-H ₂ O from a material containing lithium salt in the form of Li ₂ SO ₄ salt.

Fig. 2. Technological scheme for producing LiOH-H ₂ O from a material containing lithium salt in the form of LiCl salt.

Fig. 3. Technological scheme for producing LiOH-H ₂ O from a material containing lithium salt in the form of Li2CO3 salt.

Fig. 4. Technological scheme for producing LiOH-H ₂ O from a material containing lithium salt in the form of a mixture of Li2SO4 and Li2CO3 salts.

Fig. 5. Technological scheme for producing LiOH-H ₂ O from a material containing lithium salt in the form of a mixture of LiCl and Li ₂ CO ₃ salts.

Fig. 6. Technological scheme for producing LiOH-H ₂ O from a material containing lithium salt in the form of a mixture of Li ₂ SO ₄ and LiCl salts.

Fig. 7. Technological scheme for producing LiOH-H ₂ O from a material containing lithium salt in the form of a mixture of salts Li2SO4, LiCl and Li2CO3.

The implementation of the present invention is carried out in accordance with the technological schemes for producing lithium hydroxide monohydrate from materials containing lithium salts or mixtures thereof, presented in Fig. 1-7 and is confirmed by the examples given.

A schematic flow diagram for producing LiOH-H ₂ O from a material containing lithium salt in the form of Li ₂ SO ₄ salt is shown in Fig. 1. The technology is based on the operation of membrane electrolysis, which is used to carry out the electrochemical conversion of a Li ₂ SO ₄ solution into a LiOH solution. In this case, the process of electrochemical conversion occurs under the influence of a direct electric current and the participation of cation exchange membranes that are stable in solutions of alkalis and acids, separating the cathode and anode spaces of electrolysis units through which a LiOH solution (catholyte) and a Li ₂ SO ₄ solution (anolyte) are constantly circulating, respectively. During the circulation of solutions, electrode processes occur in them upon contact with the electrodes. In this case, electrochemical oxidation of water occurs at the anodes with the formation of gaseous oxygen and H ⁺ ions according to the reaction:

H ₂ O - 2e 2H ⁺ + N OD (1)

Accordingly, electrochemical decomposition of water occurs at the cathodes with the formation of hydrogen gas and OH ions ^- according to the reaction:

2H ₂ O + 2e 2OH + ND (2)

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In general, the process of electrochemical conversion of Li ₂ SO ₄ to LiOH can be described by the following reaction:

membrane electrolysis

L12SO4 + ZH ₂ O 2 LiOH + H ₂ + 1/202 + H2SO4 (3)

The cation exchange membrane ensures the unimpeded transfer of cations from the anode space to the cathode space. The transfer of SO ₄ ^2- ions from the anode space to the cathode and OH ^- ions from the cathode space is excluded due to the specific circumstances of cation-exchange membranes. Since the anolyte is constantly depleted in Li2SO4 and enriched in H2SO4, and the catholyte is constantly enriched in LiOH, the circulating anolyte is constantly fed with a fresh solution of Li2SO4. The optimal range of current density is the range of 2-4 kA/m ² while maintaining the lithium concentration in the circulating anolyte in the concentration range of 20-25 kg/m ³ . The optimal concentration of lithium hydroxide in the circulating catholyte is in the range of 50-80 kg/m ³ . Membranes of the brands Nafion-434, Nafion-438, Nafion-324, CTIEM-3, MF4SK-100 and other analogues of the above that are stable in alkali and acid environments can be used as cation exchange membranes. As cathodes, it is advisable to use perforated plates made of stainless steel coated with nickel, which eliminates both the risk of hydrogenation of the structural material of the cathodes with cathode hydrogen, and the risk of their corrosion during emergency stops and disconnection of the current load. The most durable anodes for electrolysis of sulfate solutions are anodes made of platinized titanium; in addition, titanium with an iridium-ruthenium oxide coating can be used as anodes. From the circulating catholyte from the Li2SO ₄ solution produced by membrane electrolysis, a stream of catholyte of a given productivity is constantly removed and sent to the operation of evaporation and crystallization of LiOH-H ₂ O. LiOH-H ₂ O crystals are usually separated from the mother evaporation solution by centrifugation, the separated crystals are washed from the remainder of the mother liquor with demineralized water, dried to obtain the product LiOH-H ₂ O corresponding to the LGO-1 grade GOST 8595-83. The mother liquor formed after evaporation and separation of the crystals is returned for evaporation. Due to the fact that the sodium and potassium salts of lithium sulfate supplied to electrolysis, contained as impurities in the composition, together with lithium pass into the composition of the catholyte and gradually accumulate in the composition of the evaporated catholyte to concentrations, the level of which does not allow the production of a product that meets the requirements of the LGO-1 brand. Therefore, from the alkaline solution returned to the catholyte evaporation operation, formed after the separation of LiOH-H ₂ O crystals, a given volume is constantly removed and sent for processing, ensuring the return of lithium to production. Processing of spent catholyte involves the separation of lithium from alkali metal impurities based on the significant difference in solubility of the compounds Li ₂ CO ₃ , LiHCO ₃ , Na ₂ CO ₃ , NaHCO ₃ , K ₂ CO ₃ , KHCO ₃ . In this case, lithium carbonate is the least soluble compound, and K ₂ CO ₃ the most soluble compound in the given series. In turn, sodium and potassium bicarbonates are much less soluble than their carbonates, and the solubility of lithium bicarbonate, on the contrary, is much higher than the solubility of lithium carbonate. At the initial stage of processing, a mixed hydrocarbonate solution is prepared, saturated in KHCO ₃ , NaHCO ₃ and LiHCO ₃ , the stream of which is mixed with the stream of the processed spent catholyte. As a result of mixing the flows, the following reactions occur with the transfer of poorly soluble lithium carbonate into a precipitate and the conversion of potassium and sodium bicarbonates into carbonates, the solubility of which is significantly higher than the solubility of the corresponding bicarbonates:

2LiOH( _P) (Na,K) + 2KHCO3 _(P) -Ml ₂ CO3 _(t ) + K ₂ CO3 _(P) (4)

2LiOH _(p) (Na,K) + 2NaHCO ₃ ( _P ) -Ml ₂ CO3 _(t ) + Per ₂ CO3 _(P) (5)

2LiOH _(p) (Na,K) + 2LiHCO3 _(P) -Ml ₂ CO3 _(t ) J + and ₂ CO3 _(P ) (6)

The mixing operation is combined with the operation of removing excess water coming with the waste catholyte flow. Water is removed by direct contact of the resulting suspension with a given flow, heated to a temperature above 100°C. As a result of contact of heated air with the suspension, water evaporates from the suspension while simultaneously cooling the air to the wet-bulb temperature. In turn, removing water from the suspension leads to an increase in the degree of transition of Li ₂ CO ₃ into the solid phase. At the same time, the liquid phase is enriched with sodium and potassium introduced by the spent catholyte. The resulting solid phase Li ₂ CO ₃ is separated from the carbonate solution by centrifugation and sent to the operation of neutralizing the spent anolyte, and the resulting carbonate solution is transferred to a hydrocarbonate solution by treatment with carbon dioxide according to the reactions:

K ₂ COz ( _R ) + CO ₂ ( _G ) + H ₂ O ( _F ) -> 2 KHSOz ( _R , _T )

Na ₂ CO3 ( _P ) + CO ₂ ( _G ) + H ₂ O ( _L ) —* 2NaHCO3 ( _P , _T )

Li ₂ CO ( _P ) + CO ₂ ( _G ) + H ₂ O ( _L ) -> 2b1HCO3 ( _P ) (Ό (8) (9)

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Due to the oversaturation of NaHCO ₃ and KHCO3 solutions due to their enrichment with sodium and potassium introduced in the composition of the spent catholyte, part of the sodium and potassium bicarbonates will pass into the solid phase, while lithium bicarbonate formed from dissolved Li2CO ₃ due to its higher solubility than Li2CO3 into the solid phase will not pass the phase under any circumstances. The resulting solid phase of sodium and potassium bicarbonates is separated from the hydrocarbonate solution by filtration. The hydrocarbonate solution is sent for mixing with the next batch of spent catholyte.

Since in the process of membrane electrolysis the circulating anolyte is depleted in Li ₂ SO ₄ and enriched in H2SO4, a given anolyte flow is constantly removed from the circulating anolyte flow, which first comes into contact with lithium carbonate obtained during the processing of spent catholyte, neutralizing part of the sulfuric acid according to the reaction:

H ₂ SO ₄ (p) + 1l ₂ SO3 ( _T ) -> Li ₂ SO ₄ ( _P ) + CO ₂ ( _G ) + H ₂ O ( _L ) (10)

In the process of neutralizing the acid with lithium carbonate, the spent anolyte is partially strengthened by Li ₂ SO ₄ . Next, there are two possible options for preparing the neutralized anolyte for electrolysis. According to the first option (option A), a solution of spent anolyte after neutralization with lithium carbonate is brought into contact with calcium oxide or calcium hydroxide, or calcium carbonate or a mixture thereof, converting sulfuric acid into the solid phase CaSO ₄ -2H ₂ O according to the reactions:

H ₂ SO _{4 (P)} + CaO _(T ) + H ₂ O ( _L ) CaSO ₄ 2H ₂ O _(t) (I)

H ₂ SO _{4 (P)} + Ca (OH) _{2 (g)} -+ CaSO ₄ 2 H ₂ O _(t) (12)

H ₂ SO _{4 (P)} + CaCO3 (t) + H ₂ O _(L ) CaSO ₄ 2H ₂ O _(t) + CO _{2 (g)} (13)

After separation from the sediment, the spent anolyte, completely freed from sulfuric acid, which is a Li2SO4 solution, is brought into contact with a given mass amount of the original Li2SO4 salt, after dissolving which the solution will acquire a given level of Li2SO4 content in it. Next, the resulting Li ₂ SO ₄ solution, if necessary, is reagently purified from calcium and magnesium. A reagent purification operation is necessary if the level of calcium and magnesium in the original Li ₂ SO ₄ salt is sufficiently high. The reagents used are a given portion of the spent washing solution (LiOH solution 120 kg/m ³ containing NaOH and KOH in total at the level of 0.1 kg/m ³ ) and carbon dioxide. The cleaning process is described by the following chemical reaction equations:

Saf) + 2LiOH(p) + CO ₂ (g) - "CaCO3(t)], + 2Li( _P ) ⁺ + H ₂ O( _L ) (14)

4Mg( _P) ²⁺ + 8LiOH _(P ) + 3 CO _2(G ) -+ Mg(OH) ₂ 3MgCO ₃ 3 H ₂ O _(t) J + 8Li _(p) ⁺ (15)

As a rule, reagent purification makes it possible to bring the remaining total content of calcium and magnesium in the design solution to a level of 10-15 g/m ³ . After separating the precipitates, the Li ₂ SO ₄ solution is sent for ion exchange purification, using for these purposes the Lewatit 208 TR ion exchanger in Li-form or its anolyte, also in Li-form. The ion exchange purification process is described by the following reaction equations:

Sorption stage:

^Li (Mg ²⁺ )Ca(P) ²⁺ + Lew —> Lew = Ca ²⁺ (Mg ²⁺ )(T) + 2Li( _P )(16)

Li( _T )

Regeneration stage:

Η

Lew = Ca(Mg)( _T ) + H ₂ SO ₄ ( _P ) —► Lew + Ca ²⁺ (Mg ²⁺ )( _P )(17)

H(p)

Stage of conversion from H-form to Li-form

НLi

Lew + LiOH(p) —> Lew + H ₂ O( _L ) (18)

H(r)Li(

Ion exchange purification makes it possible to bring the residual total concentration of calcium and manium in the Li ₂ SO ₄ solution to a level not exceeding 0.1 g/m ³ and this solution is used as a feed solution in the circulating anolyte stream in the membrane electrolysis operation.

According to another option (option B), the exhaust stream of spent anolyte is first partially neutralized with lithium carbonate obtained at the stage of processing the spent catholyte, then with ammonia in the process of direct contact of the partially neutralized spent anolyte with an air-ammonia mixture, converting the remaining sulfuric acid into ammonium sulfate according to the reaction:

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ΝΗ3(γ) + H ₂ SO ₄ (p) —> (NH ₄ ) ₂ SO ₄ (p) (19)

The mixed solution of Li ₂ SO ₄ and (NH4)2SO4 obtained by complete neutralization of the spent anolyte is evaporated, salting out (NH4)2SO4 from the mixed solution. Ammonium sulfate, after washing from the mother brine and drying, is a commercial fertilizer sold on the market. In turn, the Li ₂ SO ₄ solution with a residual content of (NH4)2SO4 obtained from the spent anolyte is alkalized, using for these purposes part of the spent washing solution formed during the washing operation of LiOH-H2O crystals.

After alkalization, the solution is deammoniated by aeration with a stream of atmospheric air. The deammonization process is described by the following chemical reaction equation:

(NH ₄ ) ₂ SO ₄ (p) + 2LiOH( _P ) —> 2ΝΗ3( _Γ ) + Li ₂ SO ₄ ( _P ) + 2H ₂ O (20)

The air flow containing ammonia vapor is enriched with a given amount of ammonia and sent to neutralize the next portion of spent and partially neutralized anolyte.

The Li ₂ SO ₄ solution that has passed the deammonization stage is sent for additional strengthening by dissolving a given mass amount of the initial Li ₂ SO ₄ salt and, after reagent and ion exchange purification, is used as a make-up solution in the circulating anolyte stream.

A by-product of membrane electrolysis, cathode hydrogen, is ejected from the cathode gas separator by a stream of natural gas. The resulting gas mixture is sent as fuel to produce heating steam. Heating steam is used in evaporation operations. The juice steam condensate formed during evaporation operations is used as demineralized water during the operations of washing the crystals of the solutions obtained during evaporation.

A basic technological scheme for producing LiOH-H2O from a material containing lithium salt in the form of LiCl or LiOH-H2O salt is shown in Fig. 2. In the case under consideration, the technology is based on the operation of membrane electrolysis, which is used to carry out the electrochemical conversion of a LiCl solution into a LiOH solution. In this case, the cathodic process occurring under the conditions of membrane electrolysis of a LiCl solution is similar to the cathodic process occurring under the conditions of membrane electrolysis of a Li2SO4 solution. In turn, the anodic process under the conditions of membrane electrolysis of a LiCl solution has a significant difference since it is accompanied by the electrochemical oxidation of chloride ions with the formation of chlorine gas according to the reaction:

SG - e N C1 ₂ (21)

In this case, no acid is formed and during the electrolysis process only the anolyte is depleted in LiCl.

In general, the process of electrochemical conversion of a LiCl salt solution into a LiOH solution can be described by the following overall reaction:

membrane electrolysis

LiCl + 2 H ₂ O 2LiOH + H ₂ + Cl ₂ (22)

Under the conditions of membrane electrolysis of a LiCl salt solution, the same cathodes and cation exchange membranes are used as under the conditions of electrolysis of a Li ₂ SO ₄ salt solution. The main parameters of the process of membrane electrolysis of soluble salts are almost the same. However, while expensive anodes made of platinized type or titanium coated with other noble metals, usually used in the electrolysis of lithium sulfate solution, titanium anodes coated with ruthenium oxide (ORTA anodes) can be successfully used in the electrolysis of lithium chloride solution, provided the anolyte chloride is acidified to pH = 2 . Acidification of the chloride anolyte also eliminates the risk of chlorate formation in the circulating anolyte. The scheme for the extraction and processing of catholyte into commercial LiOH-H ₂ O during the electrochemical conversion of lithium sulfate and chloride solutions is completely the same. Conclusions and preparation for electrolysis of spent (LiCl-depleted) anolyte is similar to the scheme and preparation of sulfate anolyte, except that the preparation of spent chloride anolyte does not require a neutralization operation and the strengthening of the spent anolyte to a given lithium concentration involves dissolving a given amount of the original LiCl salt. Since sulfate ions can accumulate in the circulating anolyte flow, introduced as impurities in the composition of the initial lithium chloride used, the reagent purification of LiCl-strengthened spent anolyte involves, along with purification from calcium and magnesium, purification from sulfate ions by converting them into the insoluble salt BaSO ₄ using as a precipitating reagent BaCl ₂ . In the ion exchange purification operation of a LiCl-strengthened lithium chloride solution, the acid regeneration stage is carried out with a 2N hydrochloric acid solution.

The utilization of hydrogen (cathode gas) and chlorine (anode gas), which are by-products of membrane electrolysis, can be multivariate. According to option A, hydrogen and chlorine removed from the gas separator are mixed and high-temperature combustion is carried out to produce gaseous hydrogen chloride according to the reaction:

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T=1200°C

H ₂₍₁ ) + C1 ₂ (g) 2HC1 ₍₁ ) (23)

The resulting stream of high-temperature hydrogen chloride is subjected to forced cooling and sent to countercurrent stepwise absorption using demineralized water as the initial absorbent, which can be used as a by-product of evaporation operations - juice steam condensate. Option B involves using cathode hydrogen as fuel for the production of heating steam used in solution evaporation operations. In this embodiment, chlorine can be utilized either into NH4Cl salt by evaporation of an NH4Cl solution obtained by aqueous absorption of a gas mixture of NH3 and Cl ₂ at a molar ratio of NH3:Cl2 = 8:3 according to the reaction:

ΝΗ ₃₍ γ) + 3 С1 _2(g) 6 NH ₄ C1( _P ) + Ν _2(γ) , (24) or in a 6N HCl solution obtained by aqueous absorption of a gas mixture of NH3 and Cl ₂ at the molar ratio NH3:Cl2 =2:3 by reaction:

or into a sodium hypochlorite solution (disinfecting and disinfecting solution) by absorbing chlorine with an aqueous solution of NaOH according to the reaction:

or into neutral calcium hypochlorite by drying the given salt Sca(OC1) ₂ , isolated as a result of an exchange reaction between a solution of sodium hypochlorite extremely saturated in NaOCl, obtained by absorbing half of the anodic chlorine with a concentrated solution of NaOH according to the reaction:

C1 _2(g) + NaOH(p)—> NaOCI(p) + aNaCI(i)^+(1-a)NaCI(i>) + H ₂ O( _L ) (27) and extremely saturated with Ca(0O ) ₂ obtained by absorbing half of the anodic chlorine into a calcium hydroxide pulp according to the reaction:

From a mother solution containing active chlorine, obtained as a result of an exchange reaction and containing Ca ²⁺ , Na ⁺ , Cl ^- , OCl ^- ions, the main amount of calcium is precipitated by introducing a given amount of NaOH into the solution, according to the reaction:

The residual amount of calcium from the solution is removed by adding a given amount of Na ₂ CO ₃ according to the reaction:

The resulting precipitate of Ca(OH) ₂ with an admixture of CaCO ₃ is sent to the operation of chlorination of the Ca(OH) ₂ pulp. The solution formed after the precipitation of calcium and containing active chlorine in equal parts is returned to the operation of chlorination of the NaOH solution and the Ca(OH) ₂ pulp.

A schematic flow diagram for producing LiOH-H ₂ O from a material containing lithium salt in the form of LiCO ₃ salt is shown in Fig. 3. As follows from the presented scheme, the use of LiCO ₃ salt for the production of LiOH-H ₂ O comes down to the use of this salt as a reagent for the reproduction of a lithium-depleted anolyte in the membrane electrolysis operation, either circulating or in the form of a solution of Li ₂ SO ₄ (option A), or in the form of a LiCl solution (options B, C). In this case, according to option A, the strengthening of the spent anolyte for lithium is carried out simultaneously with the complete neutralization of sulfuric acid by mixing it with a given amount of the original lithium carbonate salt, including lithium carbonate obtained by processing the spent evaporated catholyte; cathode hydrogen in this option is used as a component of the flue gas for the production of heating steam. In the case of organizing production according to option B, cathodic hydrogen and anodic chlorine are used to produce concentrated hydrochloric acid by burning their mixture and aqueous absorption of hydrogen chloride (reaction 23). The produced acid is mixed with a stream of anolyte purified from sulfate ions, which in turn is removed at a given volumetric flow rate from the stream of circulating anolyte enriched with sulfate ions during the electrolysis process. A mixed solution of concentrated hydrochloric acid and anolyte purified from sulfate ions is brought into contact with a given amount of the original salt Li2CO3 and demineralized water, producing a LiCl solution of a given concentration, which, after purification from calcium and magnesium, is used as a feed solution of LiCl into the circulating anolyte stream in the membrane operation electrolysis. According to option B, anode chlorine mixed with ammonia at a molar ratio of NH ₃ :Cl ₂ = 2:3 is absorbed by demineralized water, producing a 6N solution of hydrochloric acid (reaction 25). The produced HCl solution is mixed with a stream of anolyte purified from sulfate ions, which in turn is removed at a given volumetric flow rate from the stream of circulating anolyte enriched with sulfate ions during the electrolysis process. A mixed solution of hydrochloric acid and anolyte purified from sulfate ions is brought into contact with a given amount of the original salt Li ₂ CO3, producing a LiCl solution of a given concentration, which, after purification from calcium and magnesium, is used as a make-up solution in the circulating anolyte at

- 9 046337 membrane electrolysis operations, cathode hydrogen in this embodiment is used as fuel for the production of heating steam. According to option B, in the presence of a given amount, the material composition of which eliminates contamination of the absorbent, for example, ammonia, hydrazine, hydromylamine, urea, formic acid, is restored, producing a LiCl solution according to the reaction:

The aqueous slurry for the absorption of anodic chlorine is prepared from demineralized water, lithium carbonate obtained from spent evaporated lithium catholyte in the form of the original salt Li2CO ₃ , an appropriate reducing agent and an anolyte stream purified from sulfate ions, which in turn is removed from the circulating stream at a given volumetric flow rate anolyte enriched with sulfate ions during electrolysis. In this embodiment, cathode hydrogen is used as fuel for the production of heating steam.

A basic technological scheme for producing LiOH-H2O from a material containing lithium salt in the form of a mixture of Li ₂ SO ₄ and Li ₂ CO ₃ is shown in Fig. 4. This technological scheme practically repeats the technological scheme presented in Fig. 1. The difference is that the strengthening (lithium enrichment) of the spent anolyte to a given concentration of lithium in it is carried out by dissolving a given amount of the initial mixed salt Li ₂ SO ₄ and Li ₂ CO ₃ before the technological operation of complete neutralization of sulfuric acid. Otherwise, the technological schemes are identical.

A schematic flow diagram for the production of LiOH-H ₂ O from materials containing lithium salt in the form of a mixture of LiCl and Li ₂ CO ₃ is shown in Fig. 5. This technological scheme practically repeats the technological scheme presented in Fig. 2. The difference is that the strengthening of the spent (enriched in lithium) anolyte is carried out by mixing with a concentrated solution of LiCl obtained by decarbonization with hydrochloric acid of the original mixed salt of LiCl and Li ₂ CO ₃ and the carbonate obtained by processing the spent evaporated catholyte. Otherwise, the technological schemes are identical.

A basic technological scheme for producing LiOH-H ₂ O from materials containing lithium salt in the form of a mixture of Li ₂ SO ₄ and LiCl is shown in Fig. 6. A distinctive feature of this technology is that two highly soluble lithium salts simultaneously participate in the anodic process: lithium chloride and lithium sulfate; reactions (1) and (21) simultaneously occur on the anodes with the formation of H ₂ SO ₄ and Cl ₂ in the anode space simultaneously and _O2 . In this regard, the reliability of the mixed salt membrane electrolysis process is ensured by anodes made of platinized titanium. The cathodic process remains unchanged, proceeding exactly as during membrane electrolysis of solutions of highly soluble salts Li ₂ SO ₄ and LiCl.

The production of LiOH-H ₂ O based on the electrochemical conversion of mixed solutions of Li ₂ SO ₄ and LiCl does not require a special operation to purify the anolyte from sulfate ions. Otherwise, the technology described in Fig. 6 is a combination of process steps included in the process flow diagrams of FIG. 1 and fig. 2.

A basic technological scheme for producing LiOH-H ₂ O from materials containing lithium salt in the form of a mixture of Li ₂ SO ₄ , LiCl and Li ₂ CO ₃ is shown in Fig. 7. This technological scheme differs from the technological scheme for processing the mixed salt Li ₂ SO ₄ and LiCl (Fig. 6) only in that the technological operation of strengthening the spent anolyte is carried out before the technological operation of neutralizing sulfuric acid. Otherwise the schemes are identical.

Example 1.

On a laboratory installation, including a membrane electrolysis unit, a unit for processing catholyte into LiOH-H ₂ O, a unit for preparing and purifying the lithium salt feed solution for feeding into the circulating anolyte, a unit for processing spent evaporated catholyte, and an anode gas recovery unit, comparative tests of technological processes for producing LiOH were carried out -H ₂ O from various lithium salts: lithium sulfate, lithium chloride, a mixture of lithium sulfate and lithium chloride. The technological processes reproduced in the laboratory installation were based on the technological diagram presented in Fig. 1, 2. In this case, the neutralization of the sulfate anolyte was carried out using slaked lime for this purpose, the strengthening of the chloride anolyte was carried out with lithium carbonate, previously dissolved in hydrochloric acid, and the anodic chlorine was utilized in neutral calcium hypochlorite. The following lithium salts were used for testing: technical lithium sulfate monohydrate (composition is presented in Table 1) and lithium chloride TU2152-017-07622236-2015 (composition is presented in Table 2).

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Table 1

Composition of technical Li2SO4-H2O

Indicator name Content, % May Mass fraction of L12SO4 TLO 98.10 L13PO4 1.90 Na 0.020 TO 0.003 Sa 0.0064 Mg 0.0002 Fe 0.0005 water 10.5 Cl + Fe not detected

table 2

Composition of technical LiCl-H2O_______

Indicator name Content, % May Na+K θ,ι Ca+Mg 0.03 Fe 0.005 Al 0.01 Pb 0.003 PO ₄ 0.007 so ₄ ο,ι OH 0.03

Calcium hydroxide, used to neutralize sulfuric acid and utilize anode chlorine into neutral calcium hypochlorite, was obtained by precipitation (precipitant - NaOH) from a CaCl ₂ solution produced by dissolving the hydrated technical salt CaCl ₂ 6H ₂ O.

The main comparative parameters and indicators of technologies for producing LiOH-H ₂ O from various lithium salts using a given method are presented in table. 3. The compositions of the resulting LiOH-H2O samples are presented in Table. 4.

Table 3 Comparative indicators of technological processes for obtaining LiOH-H ₂ O from various lithium salts _______________________________ according to the stated method______________________________

Main indicators of obtaining Li OH H ₂ O The solution used to feed the anolyte L12SO4 solution LiCl L12SO4 + LiCl Current density, A/dm ³ thirty thirty thirty Current efficiency LiOH, % 59.8 60.6 60.1 Membrane brand CTIEM-3 CTIEM-3 CTIEM-3 Cathode material Nickel plated stainless steel Nickel plated stainless steel Nickel plated stainless steel Anode material titanium platinized titanium coated with ruthenium oxide (ORTA) titanium platinized Material quantitative composition of anolyte, g/dm ³ L12SO4 - 205.6 H ₂ SO ₄ -38.7 LiCl - 217.6 pH= 1.5 Li ₂ SO ₄ - 147.9 LiCl - 102.3 H2SO4 - 20.5 Concentration of LiOH in catholyte, g/dm ³ 48.8 49.4 49.1 Chlorine current output, % - 97.0 96.8 Composition of spent catholyte during evaporation and crystallization operations, g/dm ³ LiOH- 120 (NaOH + KOH) - 8.7 LiOH- 120 (NaOH + KOH) 9.1 LiOH- 120 (NaOH + KOH) 8.2 Yield of LiOH into a commercial product from the LiOH conversion solution 96.7 90.1 97.4 The degree of separation of lithium and alkaline (Na + K) during the processing of spent catholyte, evaporation and crystallization operations 99.97 99.90 99.93

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Table 4

Compositions of LiOH-H2O samples obtained from various lithium salts using the claimed method

Indicator name Composition %, mass of LiOH H ₂ O samples obtained from lithium salts Li ₂ SO ₄ H ₂ O LiCl H ₂ O Li ₂ SO ₄ H ₂ O and LiCl H ₂ O LiOH 56.72 56.70 56.73 Carbonates( ^CO2 ') 0.36 0.32 0.30 Na+K less than 0.002 less than 0.002 less than 0.002 Ca+Mg less than 0.001 less than 0.001 less than 0.001 Al less than 0.003 less than 0.003 less than 0.003 Fe less than 0.0005 less than 0.0005 less than 0.0005 Si less than 0.001 less than 0.001 less than 0.001 Pb less than 0.0005 less than 0.0005 less than 0.0005 Cl less than 0.005 less than 0.015 less than 0.010 So ₄ 0.015 less than 0.01 less than 0.01 Ρθ4 less than 0.005 less than 0.0005 less than 0.0005

As follows from the results obtained, the inventive method makes it possible to produce a high-quality product LiOH-H2O, corresponding to the LGO-1 grade GOST 8595-83 from tested lithium salts. At the same time, the electrochemical indicators of conversion operations by membrane electrolysis obtained from highly soluble lithium salts and solutions of these salts into a LiOH solution have almost similar indicators.

The tests also showed that when recycling anode chlorine according to the option proposed in the claimed method, which describes the processing of anode chlorine into neutral calcium hypochlorite, the content of active chlorine in the produced product samples is 62-63 wt.% with a content of water-insoluble impurities not exceeding the figure is 4.3%. The degree of utilization of anode chlorine is 99.7%.

In turn, tests have shown that the neutralization of sulfuric acid in spent sulfuric acid anolytes should be carried out by adding a stoichiometric amount of Ca(OH) ₂ , provided that this operation is carried out in two stages to completely neutralize H ₂ SO ₄ in the anolyte without the need to introduce excess Ca(OH) ₂ .

In this case, at the first stage there is contact of the initial spent anolyte with the spent sludge of the second stage, which is a mixture of CaSO ₄ 2H ₂ O and Ca(OH) ₂ with a guaranteed conversion of all free Ca(OH) ₂ into CaSO ₄ 2H ₂ O and withdrawal the resulting precipitate CaSO ₄ ·2H ₂ O by filtration. The filtrate containing the unreacted H2SO4 residue is brought into contact with Ca(OH) ₂ taken in a stoichiometric ratio to the H2SO4 contained in the original spent anolyte entering the first stage of neutralization. During phase contact at the second stage, a mixed precipitate of CaSO ₄ ·2H ₂ O and Ca(OH) ₂ is formed and complete neutralization of sulfuric acid is ensured. The contact of the anolyte with Ca(OH) ₂ is carried out under conditions of intense stirring.

Example 2.

On a laboratory bench, including three membrane electrolyzers, cation exchange membranes Nafion-438, CTIEM-3 and MF-4SK-100 were tested for their suitability for the electrochemical conversion of Li ₂ SO ₄ and LiCl solutions into a LiOH solution. The total test period was 219 working hours. The anodes tested were: during the electrolysis of LiCl solutions, titanium coated with ruthenium oxide (ORTA), and during the electrolysis of Li ₂ SO ₄ solutions, platinized titanium. The results obtained are presented in table. 5.

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Table 5

Results of testing various cation exchange membranes in relation to the electrochemical conversion of solutions of Li ₂ SO ₄ and LiCl into a solution of LiOH___________________

Basic indicators Solution used for conversion Aqueous solution L12SO4 Aqueous LiCl solution Nafion-438 stshm-z MF-4SK- 100 Nafion438 STShM-3 MF-4SK- 100 Current density, A/dm ² 30.0 30.0 30.0 35.0 35.0 35.0 Electrolyzer cell voltage - start of testing 4.9 5.0 5.0 3.3 4.0 4.0 Anolyte composition, g/dm ³ L12SO4 -200 H2SO4 -60 Li ₂ SO ₄ -200 H2SO4 -60 L12SO4 -200 H2SO4 -60 LiCl - 220 pH - 2.0 LiCl - 220 pH - 2.0 LiCl220 pH-2.0 Catholyte composition, g/dm ³ LiOH-65 NaOH-0.060 LiOH-65 NaOH-0.061 LiOH-65 NaOH-0.062 LiOH-70 NaOH0.31 LiOH-70 NaOH0.30 LiOH-70 NaOH0.31 Anolyte temperature, °C 65-70 65-70 65-70 80-85 80-85 80-85 Linear speed of movement of electrolytes in gas separators (gas purifiers), m/h 36 36 36 36 36 36 Alkali current output start of testing 60.5 60.0 59.6 60.5 60.0 59.7 end of testing 60.7 60.0 59.6 60.4 60.0 59.6

As follows from the results obtained, all membranes tested are suitable for membrane electrolysis of lithium sulfate and chloride solutions to produce catholyte in the form of a LiOH solution. At the same time, such indicators of membrane electrolysis as the voltage on the electrochemical cell and the current output of LiOH for the tested membranes are practically comparable; tests also showed that the electrolysis of LiCl solutions to obtain a LiOH solution is less energy-consuming, since the voltage on the cells of membrane electrolyzers during the electrolysis of a sulfate solution is always higher than during electrolysis of a chloride solution. This established fact is explained by the higher electrical conductivity of Li ₂ SO ₄ solutions in comparison with LiCl solutions.

Based on the data obtained, it can be argued that for the conversion of Li ₂ SO ₄ and LiCl solutions, other cation exchange membranes can be used - analogues of the tested ones, chemically stable in these environments.

Example 3.

In a laboratory installation made in accordance with the technological diagram presented in Fig. 3 tested the technology for producing LiOH-H ₂ O from lithium carbonate by using it to reproduce LiCl and Li ₂ SO ₄ supplied to the circulating anolyte circuit of membrane electrolysis operations of LiCl and Li ₂ SO ₄ solutions from LiCl-depleted solutions removed from the electrolysis operation and Li ₂ SO ₄ spent electrolytes. In this case, the reproduction of the Li ₂ SO ₄ make-up solution was carried out by direct contact of a given amount of Li ₂ CO ₃ with the spent anolyte at the stage of neutralization of the spent sulfate anolyte. Reproduction of the LiCl make-up solution was carried out using two options. According to the first option, anodic chlorine was absorbed as part of a mixture with ammonia (molar ratio NH3:Cl2 = 2:3) by demineralized water to obtain a solution of hydrochloric acid of a given concentration, which was brought into contact with a given amount of Li2CO3, the resulting solution was mixed with spent anolyte, previously neutralized to pH=7 with lithium carbonate, producing a LiCl-strengthened solution of lithium chloride, fed into the circulating anolyte during the membrane electrolysis operation. According to the second option, anodic chlorine was absorbed by a lithium carbonate pulp with a given content of Li ₂ CO ₃ in the presence of a given amount of urea reducing agent, obtaining a LiCl solution of a given concentration, which was mixed with a spent anolyte, previously neutralized to pH = 7 with lithium carbonate, obtaining a LiCl-fortified chloride solution lithium, fed into the circulating anolyte. Technical lithium carbonate produced by SQM (Chile) was used as the starting carbonate, the composition of which is presented in table. 6.

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Table 6

Composition of technical lithium carbonate used

Substance (element) L12CO3 C1 Na TO Sa Mg SO4 FezCh unrast. remainder LOI Content % May. 99.0 0.020 0.120 0.050 0.04 0.011 0.100 0.030 0.020 0.700

The strengthened and purified lithium salt solutions produced from waste anolyte streams were brought to the specified concentrations of Li2SO4 and LiCl in the make-up solutions by evaporation. The main indicators of the tests performed are presented in table. 7. The compositions of the LiOH-H2O samples produced in this case are presented in Table 8. As follows from the results obtained, it clearly follows that LiOH-H2O is obtained from technical lithium carbonate using the proposed method in the form of a high-purity product corresponding to LGO-1.

Table 7

Main indicators of obtaining LiOH-H2O from Li2CO ₃ through membrane electrolysis of highly soluble lithium salts

Basic indicators Production of LiOH H2O from L12CO3 through membrane electrolysis of highly soluble lithium salts salt solution L12SO4 LiCl salt solution Current density, A/dm ² 30.0 30.0 Anolyte composition, g/dm ³ L12SO4 - 204 H2SO4 - 63 LiCl - 222 Catholyte composition, g/dm ³ LiOH - 48.3 NaOH-0.13 LiOH - 48.7 NaOH-0.14 Temperature of electrolytes, °C 67 86 LiOH current output, % 60.0 60.7 Yield of LiOH into commercial product from LiOH conversion solution, % 95.9 95.9 Membrane brand CTIEM-3 CTIEM-3 Anode brand titanium platinized titanium coated with ruthenium oxide (ORTA) Concentration of HC1 produced from anodic chlorine, g/ ^dm3 - 219.1 Concentration of LiCl solution produced from L12CO3 and HC1, g/dm ³ - 255.1 Concentration of LiCl solution produced by the absorption of anodic chlorine by lithium carbonate pulp, in the presence of a reducing agent, g/dm ³ - 253.4 Concentration of lithium salt in a purified LiCl solution supplied as makeup to the circulating anolyte, g/ ^dm3 (Li ₂ SO ₄ ) 311 (LiCl) 328

Table 8

Compositions of LiOH-H2O samples obtained from Li2CO ₃ through membrane electrolysis of highly soluble lithium salts

Indicator name Composition, % wt of LiOH H2O samples obtained from L12CO3 through membrane electrolysis of solutions of highly soluble lithium salts L12SO4 LiCl LiOH 56.71 56.70 carbonates ( ^CO2 ') 0.34 0.31 Na+K less than 0.002 less than 0.002 Ca + Mg less than 0.001 less than 0.001 Al less than 0.003 less than 0.003 Fe less than 0.0005 less than 0.0005 Si less than 0.001 less than 0.001 Pb less than 0.0005 less than 0.0005 Cl less than 0.001 0.013 so ₄ 0.014 less than 0.010 PO ₄ not detected not detected

In this case, the yield of conversion alkali (LiOH solution) into the solid product (LiOH-H2O) significantly depends on the sodium and potassium content in the original lithium carbonate.

Example 4.

On a laboratory bench, which is a unit for recycling sulfate ions contained in the H2SO4 salt, a utilization option was tested by converting the sulfuric acid contained in the spent sulfate anolyte into salt (NH ₄ )2SO ₄ upon contact of the spent anolyte with ammonia and salting out the salt (NH ₄ ) ₂ SO ₄ from a mixed waste solution of Li ₂ SO ₄ and (NH ₄ ) ₂ SO ₄ at its

-

Claims (14)

evaporation with simultaneous concentration of anolyte using Li2SO4. A variant of the technological process for recycling sulfuric acid contained in the spent anolyte into salt (NH4)2SO4 is presented in Fig. 1. The results obtained are presented in table. 9. Table 9 Main indicators of the process of processing anodic sulfuric acid in the composition of spent sulfate__________________________ anolyte into salt (NH4)2SO4____________________ Basic indicators Quantitative values of indicators Composition of spent sulfate anolyte, g/dm ³ Li ₂ SO ₄ - 201.3 H ₂ SO ₄ - 60.4 Composition of spent anolyte, after contact with ammonia, g/dm ³ Li ₂ SO ₄ - 201.8 (NH ₄ ) ₂ SO ₄ - 81.3 Composition of lithium ammonium sulfate solution after evaporation and salting out (NH ₄ )2SO ₄ , g/dm ³ Li ₂ SO ₄ - 261.3 (NH ₄ ) ₂ SO ₄ - 9.4 Composition of the sulfate solution after alkalization and aeration, g/dm ³ Li ₂ SO ₄ - 269.1 (NH ₄ ) ₂ SO ₄ < 0.05 The resulting salt samples (NH ₄ )2SO ₄ after 3-stage countercurrent washing with demineralized water and drying at 110°C contained the main substance in the form of (NH ₄ )2SO ₄ - 99.7 wt.% with a lithium impurity content of less than 0.002 wt. % At the same time, the degree of ammonia utilization was 99.84%. Example 5. Waste catholyte stream with a volume of 10 dm ³ composition (g/dm ³ ): LiOH - 120; NaOH - 8.7; KOH - 0.3 was processed according to the claimed method (Fig. 1-7) in a plant brought to operation in steady state. As a result of processing, 1850 g of dry Li ₂ CO ₃ was obtained with a content of the main substance of 99.9% and a total content of sodium and potassium impurities of less than 0.01%. The total mass of the resulting dry precipitate of NaHCO3 and KHCO3 salts was 188.1 g with a residual lithium content of less than 0.002%. Information sources. 1. Patent RU No. 2071819, publ. 01/20/97. 2. Application No. Zealnd WO No. 9859385, publ. 1998. 3. Patent RU No. 2157338, publ. 10.10. 2000. 4. Patent RU No. 21967335, publ. 01/20/2003. 5. Patent RU No. 2656452, publ. 06/05/2018. CLAIM 1. A method for producing high-purity lithium hydroxide monohydrate from materials containing a lithium salt selected from lithium sulfate, lithium chloride, lithium chloride monohydrate, lithium carbonate or mixtures thereof, comprising: membrane electrolysis of an aqueous solution of lithium salt using as a membrane separating the cathode and anode circuits of electromagnetic cells, a cation exchange membrane in the circulation mode of catholyte in the form of a solution of lithium hydroxide and anolyte in the form of a solution of lithium salt, where the cathode for membrane electrolysis is made of stainless steel coated nickel, and said cation exchange membrane is selected from a membrane that is stable in alkali and acid environments; removing the volume of catholyte from the flow of circulating catholyte and evaporating the withdrawn volume of catholyte to obtain crystals of lithium hydroxide monohydrate; separating the resulting lithium hydroxide monohydrate crystals from the mother liquor, washing with water and drying to obtain a final high purity lithium hydroxide monohydrate; where the method is further characterized by the stages: removal of cathode and anode gases formed during electrolysis; supplying part of the flow of the resulting spent wash solution to the catholyte evaporation operation and using part of the spent wash solution supplied to the catholyte evaporation operation in processing the exhaust stream of spent anolyte; returning part of the mother liquor formed after separation of lithium hydroxide monohydrate crystals to the catholyte evaporation operation; processing part of the waste catholyte stream removed from the evaporation stage and representing a concentrated solution of lithium hydroxide with an admixture of sodium and potassium hydroxides to produce lithium carbonate, which is used in processing the waste anolyte output stream; feeding the circulating anolyte stream with a concentrated solution of lithium salt prepared from the original source of lithium salt and the lithium salt solution obtained by processing the exhaust stream of spent anolyte. 2. The method according to claim 1, characterized in that the processing of the waste catholyte stream removed from the evaporation operation, which is a concentrated solution of lithium hydroxide with - 15 046337 with a mixture of sodium and potassium hydroxides, is carried out by mixing it with a flow of an aqueous solution containing sodium, potassium and lithium bicarbonates, the resulting pulp, which is a mixture of the solid phase of lithium carbonate and a carbonate solution containing Na2CO ₃ , K2CO3, Li2CO ₃ , is concentrated , removing water, the solid phase of lithium carbonate is separated from the liquid phase, the liquid phase is carbonated by direct contact with carbon dioxide, transferring the carbonate solution into a hydrocarbonate suspension, which is a mixture of solid phases of sodium bicarbonate and potassium bicarbonate in a solution of sodium, potassium and lithium bicarbonates, formed the suspension is filtered, separating the solid phase of sodium and potassium bicarbonates from a solution containing sodium, potassium and lithium bicarbonates, which is sent for mixing with the flow of spent catholyte removed from the evaporation operation, containing lithium, sodium and potassium hydroxides. 3. The method according to claim 1, characterized in that the use of part of the spent washing solution entering the catholyte evaporation operation in the processing of the exhaust stream of spent anolyte includes the use of the spent washing solution as an alkaline reagent at the stage of reagent purification of a lithium salt solution from impurities and as a regenerating solution for converting the ion exchanger from the H-form to the Li-form at the stage of ion exchange purification. 4. The method according to claim 3, characterized in that the direct current density of aqueous solutions of lithium salts is 1-4 kA/ ^m2 , cation exchange membranes for membrane electrolysis are Nafion-438, CTIEM-3, MF-4SK-100 membranes, At the stage of ion exchange purification, Lewatit 208 TR ion exchanger is used. 5. The method according to claim 4, characterized in that when using lithium sulfate as a material containing lithium salt, titanium coated with noble metals selected from platinum, iridium, ruthenium or tantalum is used as anodes in the process of membrane electrolysis, and from the flow of circulating anolyte, depleted in Li ₂ SO ₄ content and enriched in H2SO4, the anolyte flow is constantly removed, and the withdrawn anolyte flow is brought into contact with either CaO or Ca(OH) ₂ or CaCO ₃ until the H2SO4 is completely neutralized, the resulting solid the CaSO4-2H2O phase is separated from the Li ₂ SO ₄ solution, and the Li ₂ SO ₄ solution is brought into contact with the original lithium sulfate salt, dissolving it and obtaining a lithium sulfate solution, the spent washing solution from the washing stage is added to the resulting solution, after which the solution is carbonized carbon dioxide coming from the operation of neutralizing H2SO4 of the output anolyte stream, to convert the calcium and magnesium contained in the solution into insoluble compounds CaCO ₃ and Mg(OH) ₂ 3MgCO ₃ 3H ₂ O, the resulting suspension is filtered, separating the precipitate from the Li ₂ SO solution ₄ , after which the reagently purified Li ₂ SO ₄ solution is sent for ion exchange purification by passing through a layer of Lewatit 208-TP ion exchanger in Li-form, the Li ₂ SO ₄ solution that has undergone ion exchange purification is used as a make-up solution into the circulating anolyte stream in the membrane electrolysis operation , the spent ion exchanger is regenerated in two stages: at the first stage by treatment with a 2.0N solution of sulfuric acid, at the second stage by treatment with a 2.0N solution of LiOH, the spent regenerates of the ion exchange operation are mixed with the spent anolyte stream before its reagent purification, which is a by-product membrane electrolysis, cathode hydrogen is ejected with a stream of natural gas from the cathode gas separator of the electrolysis unit, and the resulting mixture of gases is sent to a steam generator as fuel for the production of heating steam, used as a coolant in the evaporation of solutions and catholyte. 6. The method according to claim 4, characterized in that the anolyte stream, constantly removed from the circulating anolyte stream, depleted in Li ₂ SO ₄ and enriched in H ₂ SO ₄ , is brought into contact with an air-ammonia mixture to neutralize H ₂ SO ₄ and obtain mixed solution of Li ₂ SO ₄ and (NH ₄ ) ₂ SO ₄ , which is evaporated by salting out (NH ₄ ) ₂ SO ₄ and concentrating the evaporated solution over Li ₂ SO ₄ , and the evaporated solution with the residue (NH ₄ ) ₂ SO ₄ is mixed with spent washing solution from the washing stage and bringing the mixed solution into contact with the air flow coming from the operation of contacting the spent anolyte flow with the ammonia-air mixture and removing the remainder of ammonia from the Li2SO4 solution, and the air flow containing ammonia vapor is enriched with ammonia from an ammonia source and sent to the operation of neutralizing the waste anolyte stream, while the Li2SO4 solution freed from ammonia after strengthening with Li ₂ SO ₄ by dissolving the original Li ₂ SO ₄ salt in it and removing impurities is used as a make-up solution into the circulating anolyte stream in the membrane electrolysis operation. 7. The method according to claim 4, characterized in that when using as a material containing a lithium salt, lithium chloride or lithium chloride monohydrate, anodes made of titanium coated with ruthenium oxide and from a circulating anolyte stream depleted in content are used in the membrane electrolysis operation LiCl is constantly removed from the anolyte, and the withdrawn anolyte stream is brought into contact with the original lithium chloride salt, bringing the LiCl concentration in the withdrawn anolyte stream to a given value; the LiCl-enriched flow of the withdrawn anolyte is purified by reagent purification from impurities of metal cations, and also purified from sulfate ions by adding barium chloride, converting sulfate ions into an insoluble precipitate BaSO ₄ , the liquid phase is separated from the sediments and after ion exchange - 16 046337 wastewater is used as a feed solution into the circulating anolyte stream in the membrane electrolysis operation, and the cathode hydrogen and anodic chlorine removed from the gas separators are mixed and subjected to flame combustion, and the resulting hydrogen chloride is absorbed by demineralized water, producing concentrated 36% hydrochloric acid. 8. The method according to claim 4, characterized in that the anodic chlorine removed from the gas separator is absorbed by an aqueous solution of ammonia, producing an NH ₄ Cl solution at a molar ratio of NH ₃ :Cl2=8:3, and at a molar ratio NH ₃ :Cl2=2: 3 6N HCl solution, the resulting NH ₄ Cl solution is evaporated, NH ₄ Cl is crystallized and dried, and the cathode hydrogen removed from the gas separator is utilized in the coolant to produce heating steam. 9. The method according to claim 4, characterized in that either all the anodic chlorine removed from the gas separator is absorbed by a NaOH solution, producing a disinfecting solution of sodium hypochlorite, or half the volume of the output chlorine flow is absorbed by a NaOH solution, producing a solution extremely saturated in sodium hypochlorite, and the other half of the volume the output stream of anodic chlorine is absorbed by a suspension of Ca(OH) ₂ , producing a solution extremely saturated in calcium hypochlorite, the resulting solutions are mixed, salting out neutral calcium hypochlorite, which is separated from the mother solution and dried, calcium is precipitated from the resulting mother solution, first by adding NaOH, and then by adding Na ₂ CO ₃ , a precipitate containing Ca(OH) ₂ with an admixture of CaCO ₃ , is separated from the solution and sent for the preparation of a Ca(OH) ₂ suspension containing active chlorine in the form of hypochlorite ions, the solution is divided into two equal portions, one portion is mixed with NaOH and sent to the chlorination operation to obtain a sodium hypochlorite solution, another portion is mixed with Ca(OH) ₂ and also sent to the chlorination operation to obtain a calcium hypochlorite solution. 10. The method according to claim 4, characterized in that when used as a material containing lithium salt, lithium carbonate, lithium carbonate salt is used for the reproduction of anolytes by converting Li ₂ CO ₃ into highly soluble lithium salts, which are lithium chloride or sulfate lithium, circulating as anolytes in the anode circuits of the electrolysis unit and depleted in the process of membrane electrolysis in LiCl or Li ₂ SO ₄ . 11. The method according to claim 4, characterized in that when an aqueous solution of lithium chloride is used as an anolyte in the membrane electrolysis operation, titanium anodes coated with ruthenium oxide are used, while cathode hydrogen and anodic chlorine, after mixing, are burned to produce high-temperature hydrogen chloride vapors , and hydrogen chloride vapors are cooled and absorbed by demineralized water in a stepwise countercurrent mode to obtain a stream of concentrated 36% hydrochloric acid, removed from the first absorption stage along the HCl vapors, the stream of the resulting concentrated hydrochloric acid is mixed with the purified one, using BaCl ₂ as a reagent , from sulfate ions, a stream removed for purification from sulfate ions from the circulating anolyte stream in the membrane electrolysis operation, a mixed stream of concentrated hydrochloric acid and anolyte purified from sulfate ions is brought into contact with the original lithium carbonate and demineralized water, obtaining a stream of LiCl solution, which, after purification from calcium and magnesium impurities, is used as a make-up solution in the circulating anolyte stream in the membrane electrolysis operation. 12. The method according to claim 4, characterized in that anodic chlorine is absorbed by demineralized water in the presence of ammonia at a molar ratio of NH ₃ : Cl ₂ = 2: 3 to obtain a solution of 6N hydrochloric acid, which is mixed with a stream of reagently purified anolyte, taken out for purification from sulfate ions from the circulating anolyte stream in the membrane electrolysis operation, a mixed stream of hydrochloric acid solution and anolyte purified from sulfate ions is brought into contact with the original lithium carbonate, obtaining a stream of LiCl solution, which, after purification from calcium and magnesium impurities, is used as a make-up solution into the circulating anolyte stream in the membrane electrolysis operation, and cathode hydrogen is used as fuel to produce heating steam. 13. The method according to claim 4, characterized in that the anodic chlorine is absorbed by an aqueous slurry of lithium carbonate and in the presence of an elemental chlorine reducing agent, the composition of which eliminates contamination of the absorbent with side cations and anions during the chlorine absorption process, obtaining a lithium chloride solution as an absorption product, which after purification from impurities, calcium and magnesium are used as a make-up solution in the circulating anolyte stream in the membrane electrolysis operation, and the aqueous slurry for the absorption of anode chlorine is prepared from demineralized water, lithium carbonate obtained from spent catholyte, lithium carbonate in the form of the original salt, reducing agent and a stream of anolyte purified from sulfate ions in a membrane electrolysis operation, and cathode hydrogen is used as fuel for the production of heating steam. 14. The method according to claim 4, characterized in that when an aqueous solution of lithium sulfate is used as an anolyte, titanium coated with noble metals selected from platinum, iridium, tantalum and ruthenium, removed from the circulation circuit, is used as anodes in the electrolysis operation An anolyte stream depleted in lithium sulfate and enriched in sulfuric acid is brought into contact with the original lithium carbonate, obtaining a lithium sulfate solution, which, after purification from impurities, is used as a make-up solution in the anolyte circulating circuit. -