Patent Application
20240200206
The invention belongs to the field of chemical technology for inorganic substances, and in particular to the methods for producing high purity lithium hydroxide monohydrate from lithium salts containing materials.
It is known to produce a lithium hydroxide solution from solid carbonate-containing lithium waste by contacting the same with water, settling the resulting pulp, decanting the clarified liquid phase, followed by its filtration and recirculation of the resulting lithium-containing solution through the central chamber of the electrodialysis unit to obtain a lithium hydroxide solution in the cathode chamber, a mixed acid solution in the anode chamber, and a desalted liquid in the central chamber which is returned to the process of leaching lithium from solid carbonate-containing lithium waste [1].
The disadvantage of this method is the production of a low concentrated LiOH solution (at most 25 kg/m3) and low production efficiency of the process due to operation at a current density of at most 2 A/dm2 (0.2 kA/m2), high electrical resistance of the recycled Li2CO3 solution due to the low Li2CO3 concentration (at most 10 kg/m3) and therefore high specific energy consumption per unit of product produced.
Another known method for producing lithium hydroxide solution from lithium compounds containing materials, in particular from waste lithium-ion batteries [2], comprises extracting lithium from the waste in the form of highly soluble lithium sulfate, membrane electrolysis of the lithium sulfate solution using a Nafion 350 cation-exchange membrane separating the cathode and anode compartments. The electrolysis is carried out at a direct current density of 20 A/dm2 and a voltage of 5.3 V with constant withdrawal of the LiOH solution (catholyte) from the cathode compartment and of the Li2SO4-depleted anolyte comprising sulfuric acid formed at the anode from the anode compartment. The withdrawn anolyte stream is directed to lithium leaching process to neutralize sulfuric acid while at the same time strengthen the stream with lithium sulfate. The anolyte strengthened with Li2SO4 is returned to the electrolysis process.
This anolyte is disadvantageous in that it is limited to the production of the LiOH solution contaminated with impurities. It is not possible to produce high purity product in the form of LiOH·H2O using this method.
It is known to produce high purity lithium hydroxide by membrane electrolysis of an aqueous solution containing lithium chloride and lithium carbonate recovered from natural brine in the presence of a reducing agent [3]. The withdrawn catholyte is evaporated to crystallize LiOH·H2O. Following separation from the mother liquor, LiOH·H2O is washed with demineralized water, dried, resulting in high purity LiOH·H2O. Herewith cathodic hydrogen is used to produce a heat carrier for generating a heating steam utilized in the catholyte evaporation process, and anodic chlorine is used for oxidizing bromide ions to elemental bromine by directly contacting chlorine with the natural brine rich in bromide ions.
The disadvantages of this method include the use as a feed for electrochemical transformation of a low concentration LiCl solution that is first recovered from lithium-bearing natural brine by means of a LiCl-selective sorbent, as well as the need to use a reducing agent to eliminate the risk of formation of oxychloride species in the anode compartment during electrolysis of a low concentration LiCl solution.
A method for producing high purity lithium monohydrate from lithium carbonate containing materials [4] overcomes most of the disadvantages of the above methods. The method is based on the reproduction of an aqueous solution of highly soluble lithium sulfate fed to replenish the anolyte solution undergoing depletion in Li2SO4 and enrichment in H2SO4 which circulates in the anolyte circuit of the electrolysis unit. To this end a part of the lithium-depleted anolyte is constantly withdrawn from the anolyte circuit and brought into contact with an equivalent amount of lithium carbonate to convert the anodic sulfuric acid into lithium sulfate. This method also provides for the chemical purification of the reproduced Li2SO4 solution from Ca, Mg impurities and heavy metals via carbonate-alkaline method using a solution of LiOH and CO2 released upon neutralization of carbonates in the anolyte.
The method has a disadvantage of using cation-exchange membranes MK-40 of low mechanical and chemical stability in the membrane electrolysis process. Furthermore, the disadvantages of the method include pollution of water with liquid waste, contamination of lithium carbonate solution with sodium and potassium carbonates, as well as unsatisfactory chemical purification of the Li2SO4 solution fed to the anolyte circuit for replenishment, meaning that the membranes which become contaminated with calcium and magnesium cations shall be regularly checked for the need of acid recovery.
A method for producing lithium monohydrate from brines and an apparatus for the implementation thereof [5] overcomes the disadvantages of the above method. LiOH solution fed for evaporation, crystallization, washing and drying of LiOH·H2O is obtained from a concentrated LiCl solution subjected to chemical purification via carbonate-alkaline method followed by ion exchange purification on the Lewatit-208-TP ion exchanger in Li-form. The method also involves employing the spent catholyte stream withdrawn from the evaporation process in the form of a LiOH solution containing NaOH and KOH as a reagent for obtaining a pregnant LiCl solution, whereby sodium and potassium are removed from the process in the form of NaCl and KCl crystals. By its technical essence and the parameters achieved this method for producing lithium hydroxide monohydrate from a lithium salt containing material is the closest to the claimed method and thus was chosen as the closest prior art.
The disadvantages of the method are as follows:
The above drawbacks can be overcome through the implementation of the following technical solutions which constitute the basis of the claimed method:
The implementation of the provided 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 process, expand the range of the coproducts produced, eliminate the formation of liquid and gaseous waste and, consequently, improve the environmental performance of the production process.
The achievement of the technical effect is provided by using lithium sulfate or lithium chloride, or lithium carbonate, or various mixtures of these salts as the lithium salt containing material; using cathodes made of nickel-plated stainless steel in the processes of membrane electrolysis of the aqueous solutions of lithium salts; and using the membranes of Nafion-348, CTIEM-3, MF-4SK-100 types or membranes equivalent thereto as the cation-exchange membranes.
The achievement of the technical effect is provided by that the spent washing solution fed to the catholyte evaporation process is partially used as an alkaline reagent in the process of pretreating the lithium salt solution brought to a predetermined concentration prior to electrolysis, first at the step of chemical purification of this salt solution from impurities and then as a regenerating solution for converting the ion exchanger from H-form into Li-form at the step of ion exchange purification.
The achievement of the technical effect is provided by that the recycling of the spent catholyte stream, which represents a lithium hydroxide solution with an admixture of sodium hydroxide and potassium hydroxide, is carried out by mixing it with the stream of an aqueous solution containing sodium, potassium and lithium bicarbonates; the resulting pulp, which represents a mixture of a solid phase of lithium carbonate and a solution containing Na2CO3, K2CO3 and Li2CO3, is concentrated by removing a predetermined amount of water; the solid phase of lithium carbonate is separated from the liquid phase, the liquid phase is carbonized by contacting it with carbon dioxide to convert the carbonate solution into a bicarbonate suspension, which represents a mixture of solid phases of sodium bicarbonate and potassium bicarbonate in a solution of sodium, potassium and lithium bicarbonates; the resulting suspension is filtered to separate the solid phase of sodium and potassium bicarbonates from the solution containing sodium, potassium and lithium bicarbonates which is directed to mixing with the spent catholyte stream withdrawn from the evaporation process containing lithium, sodium and potassium hydroxides.
The achievement of the technical effect is provided by that 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 anodes in the membrane electrolysis process, and an anolyte stream of a predetermined volume is constantly withdrawn at a predetermined rate from the circulating anolyte stream undergoing depletion in Li2SO4 and enrichment in H2SO4; the withdrawn anolyte stream is brought into contact with CaO, or with Ca(OH)2, or with CaCO3 until H2SO4 is completely neutralized; the resulting solid phase of CaSO4·2H2O is separated from the Li2SO4 solution, the Li2SO4 solution is brought into contact with a predetermined mass quantity of the initial Li2SO4 salt to dissolve it and to obtain a Li2SO4 solution of a predetermined concentration; the resulting solution is added with a predetermined volume of a washing solution followed by carbonizing the solution with carbon dioxide coming from the process of neutralization of the withdrawn anolyte stream, until the calcium and magnesium contained in the solution are converted into insoluble compounds CaCO3 and Mg(OH)2·3MgCO3·3H2O; the resulting suspension is filtered to separate the precipitate from the Li2SO4 solution, the chemically purified Li2SO4 solution is directed to ion exchange purification by passing it through a layer of Lewatit-208-TP ion exchanger in Li-form or an equivalent ion exchanger in Li-form; the Li2SO4 solution that has undergone ion exchange purification is used as a replenishing solution for the circulating anolyte stream in the membrane electrolysis process; the spent ion exchanger is regenerated in two steps: the first step consists in the treatment with 2.0N sulfuric acid solution, the second step consists in the treatment with 2N LiOH solution prepared from the spent washing solution, the spent regenerates are mixed with the spent anolyte stream before its chemical purification; cathodic hydrogen, which is a coproduct of electrolysis, is ejected with a natural gas stream from the cathode gas separator of the electrolysis unit, the resulting gaseous mixture is directed to the steam generator as the fuel for the generation of a heating steam used as a heat carrier in the processes of evaporation of solutions and, in particular, of the catholyte.
The achievement of the technical effect is provided by that when lithium sulfate is used as the lithium salt containing material, a predetermined volume of the anolyte constantly withdrawn at a predetermined volumetric rate from the circulating anolyte stream undergoing depletion in Li2SO4 and enrichment in H2SO4 is brought into contact with an air-ammonia mixture to neutralize H2SO4, to obtain a mixed solution of Li2SO4 and (NH4)2SO4 which is evaporated to salt out (NH4)2SO4; the evaporated solution with the remaining (NH4)2SO4 is mixed with a predetermined volume of the spent washing solution while bringing into contact with the air stream coming from the process of contacting the spent alkaline anolyte stream with the ammonia-air mixture to remove the remaining ammonia from the Li2SO4 solution; the gaseous ammonia containing air stream is enriched with ammonia from an ammonia source and directed to the process of neutralizing the spent anolyte stream; the ammonia-free Li2SO4 solution after a predetermined strengthening with Li2SO4 by dissolving therein a predetermined mass quantity of the initial lithium sulfate salt and chemical and ion exchange purification from impurities, is used as a replenishing solution for the circulating anolyte stream in the membrane electrolysis process.
The achievement of the technical effect is provided by that when lithium chloride or lithium chloride monohydrate is used as the lithium salt containing material, titanium anodes coated with a ruthenium oxide are used in the membrane electrolysis process, and a predetermined volume of anolyte is constantly withdrawn at a predetermined volumetric rate from the circulating anolyte stream undergoing depletion in LiCl; the withdrawn anolyte stream is brought into contact with the initial salt containing lithium chloride to bring the LiCl concentration in the withdrawn anolyte stream to a predetermined value; the withdrawn LiCl-enriched anolyte stream in addition to chemical purification from metal cation impurities is also purified from sulfate ions by adding a predetermined amount of barium chloride to convert sulfate ions into an insoluble BaSO4 precipitate; the liquid phase is separated from the precipitates and, following ion exchange purification, used as a replenishing solution for the circulating anolyte stream in the membrane electrolysis process; the cathodic hydrogen and anodic chlorine withdrawn from the gas separators are mixed and subjected to flame combustion; the resulting hydrogen chloride is absorbed by demineralized water to produce a concentrated 36% hydrochloric acid.
The achievement of the technical effect is provided by that when lithium chloride or lithium chloride monohydrate is used as the lithium salt containing material, the anodic chlorine withdrawn from the gas separator is absorbed by aqueous ammonia to produce, at a molar ratio of NH3:Cl2=8:3, a NH4Cl solution, and at a molar ratio of NH3:Cl2=2:3, a 6N HCl solution; the resulting NH4Cl solution is evaporated, NH4Cl is crystallized, the crystals are dried, the withdrawn hydrogen in this case is utilized as a heat carrier for the generation of the heating steam.
The achievement of the technical effect is provided by that when lithium chloride or lithium chloride monohydrate is used as the lithium salt containing material, the anodic chlorine withdrawn from the gas separator is completely absorbed by a NaOH solution to produce a disinfecting solution of sodium hypochlorite, or 0.5 of the withdrawn volumetric flow of chlorine is absorbed by a NaOH solution to produce a solution saturated with sodium hypochlorite, and the other 0.5 of the withdrawn volumetric flow of anodic chlorine is absorbed by a Ca(OH)2 suspension to produce a solution saturated with calcium hypochlorite; the produced solutions are mixed to salt out the neutral calcium hypochlorite which is separated from the mother liquor and dried, calcium is precipitated out of the resulting mother liquor, first in the form of Ca(OH)2 by adding a predetermined amount of NaOH, and then in the form of CaCO3 by adding a predetermined amount of Na2CO3; the precipitate containing Ca(OH)2 with an admixture of CaCO3 is separated from the solution containing active chlorine in the form of hypochlorite ions; the solution is divided into two equal portions, one portion is mixed with a predetermined amount of NaOH and directed to chlorination to obtain a sodium hypochlorite solution, another portion is mixed with a predetermined amount of Ca(OH)2 and is also directed to chlorination process to obtain a calcium hypochlorite solution; the cathodic hydrogen is utilized as a heat carrier for the generation of the heating steam.
The achievement of the technical effect is provided by that when lithium carbonate is used as the lithium salt containing material, 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 undergoing depletion in LiCl or Li2SO4 during membrane electrolysis, wherein if an aqueous solution of lithium chloride is used as the anolyte, titanium anodes coated with ruthenium oxide are used in membrane electrolysis process, wherein according to the first option, the withdrawn cathodic hydrogen and anodic chlorine are combusted after mixing to produce high-temperature hydrogen chloride vapor, the 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 step along the path of the HCl vapor; the stream of the resulting concentrated hydrochloric acid is mixed with a stream of anolyte purified from sulfate ions using BaCl2 as the reagent, withdrawn for purification from sulfate ions from the circulating anolyte stream in the membrane electrolysis process; the mixed stream of the concentrated hydrochloric acid and the anolyte purified from sulfate ions is brought into contact with the predetermined amounts of the initial lithium carbonate and demineralized water to obtain a stream of LiCl solution of a predetermined concentration which, after being purified from calcium and magnesium impurities, is used as a replenishing solution for the circulating anolyte stream in the membrane electrolysis process; according to the second option, the withdrawn anodic chlorine is absorbed by demineralized water in the presence of ammonia at a mole ratio of NH3:Cl2=2:3 to obtain a 6N hydrochloric acid solution, which is mixed with a stream of anolyte purified from sulfate ions using BaCl2 as the reagent, withdrawn for purification from sulfate ions from the circulating anolyte stream in the membrane electrolysis process; the mixed stream of the hydrochloric acid solution and the anolyte purified from sulfate ions is brought into contact with a predetermined amount of the initial lithium carbonate to obtain a LiCl salt solution stream, which, after being purified from calcium and magnesium impurities, is used as a replenishing solution for the circulating anolyte stream in the membrane electrolysis process, and the cathodic hydrogen is used as a fuel for the generation of the heating steam; according to the third option, the anodic chlorine is absorbed by an aqueous pulp of lithium carbonate with a predetermined content of Li2CO3 and in the presence of a predetermined amount of a reducing agent for elemental chlorine, the material composition of which prevents the absorber from contamination with foreign cations and anions, such as ammonia, hydrazine, hydroxylamine, carbamide, formic acid, or reducing agents equivalent thereto, to obtain as the absorption product a lithium chloride solution with a predetermined LiCl concentration, which is used as a replenishing solution for the circulating anolyte stream in the membrane electrolysis process, whereby the aqueous pulp for the absorption of the anodic chlorine is prepared from demineralized water, lithium carbonate obtained from spent catholyte, lithium carbonate in the form of the initial Li2CO3 salt, a reducing agent and the anolyte stream purified from sulfate ions using BaCl2 as the reagent, which in turn is withdrawn from the circulating anolyte stream with a predetermined volumetric flow rate in the membrane electrolysis process, and the cathodic hydrogen is used as a fuel for the generation of the heating steam.
In case of using an aqueous solution of lithium sulfate as the anolyte, titanium anodes coated with noble metals: platinum, ruthenium, iridium, tantalum, are used in the membrane electrolysis process, and the anolyte stream of a predetermined volume depleted in lithium sulfate and enriched in sulfuric acid, withdrawn at a predetermined rate from the anolyte circulation circuit, is brought into contact with a predetermined amount of the initial lithium carbonate to obtain a lithium sulfate solution of a predetermined concentration, which, after purification from impurities, is used as a replenishing solution for the anolyte circulation circuit.
The achievement of the technical effect is provided by that when a mixture of lithium salts lithium sulfate and lithium carbonate is used as the lithium salt containing material, titanium coated with noble metals: platinum, ruthenium, iridium, tantalum, is used as the anodes in the membrane electrolysis process, and the anolyte stream of a predetermined volume depleted in lithium sulfate and enriched in sulfuric acid, withdrawn at a predetermined rate from the anolyte circulation circuit, is brought into contact with a predetermined amount of the initial mixture of Li2SO4 and Li2CO3 salts to obtain a lithium sulfate solution of a predetermined concentration with a residual content of H2SO4; the resulting Li2SO4 solution is freed from the residual sulfuric acid and after purification from impurities is used as a replenisher for the circulating anolyte stream in the membrane electrolysis process.
The achievement of the technical effect is provided by that when a mixture of lithium chloride and lithium carbonate salts is used as the lithium salt containing material, titanium coated with ruthenium oxide is used as the anodes in the membrane electrolysis process, and the initial mixture of lithium chloride and carbonate salts is brought into contact with a predetermined volume of hydrochloric acid of a predetermined concentration and a predetermined volumetric flow of the anolyte withdrawn from the circulating anolyte stream, depleted in LiCl during membrane electrolysis, to produce a lithium chloride solution, the resulting lithium chloride solution after purification from impurities is used as a replenishing solution for the circulating anolyte stream in the membrane electrolysis process.
The achievement of the technical effect is provided by that when a mixture of lithium salts lithium sulfate and lithium chloride is used as the lithium salt containing material, titanium coated with noble metals: platinum, ruthenium, iridium, tantalum, is used as the anodes in the membrane electrolysis process, and an anolyte stream of a predetermined volume is withdrawn at a predetermined rate from the circulating anolyte stream undergoing depletion in lithium sulfate and chloride and enrichment in H2SO4, which is either brought into contact with a predetermined amount of ammonia contained in the ammonia-air mixture, followed by concentration of the mixed sulfite solution of Li2SO4 and (NH4)2SO4 and salting out the (NH4)2SO4 salt until a Li2SO4 solution is obtained, or brought into contact with a predetermined amount of either Ca(OH)2 or CaCO3 until the H2SO4 is completely neutralized and a Li2SO4 solution is obtained, which is separated from the CaSO4·2H2O precipitate; the Li2SO4 solution obtained either way is brought into contact with a predetermined amount of the initial mixture of Li2SO4 and LiCl salts to dissolve it and to obtain a mixed solution of Li2SO4 and LiCl with a predetermined concentration of lithium, which after purification from impurities is used as a replenishing solution for the circulating anolyte stream in the membrane electrolysis process; the anodic chlorine withdrawn from the gas separator is recycled into a 36% hydrochloric acid, or into a NH4Cl salt, or into a sodium hypochlorite solution, or into a neutral calcium hypochlorite.
The achievement of the technical effect is provided by that when a mixture of lithium sulfate, lithium chloride and lithium carbonate salts is used as the lithium salt containing material, titanium coated with noble metals is used as the anodes in the membrane electrolysis process, and a predetermined volume of the anolyte is constantly withdrawn at a predetermined volumetric rate from the circulating anolyte stream undergoing depletion in Li2SO4 and LiCl and enrichment in H2SO4, which is first brought into contact with a predetermined amount of the initial mixture of Li2SO4, LiCl and Li2CO3 salts to produce a mixed solution of Li2SO4, LiCl, H2SO4 with a predetermined concentration of lithium, the resulting mixed solution is converted into a mixed solution of Li2SO4 and LiCl, which is used as a replenishing solution for the anolyte circulating stream in the membrane electrolysis process.
The implementation of the provided invention is carried out in accordance with the flow diagrams of the production of lithium hydroxide monohydrate from the materials containing lithium salts or mixtures thereof, as shown in
A process flow diagram of the production of LiOH·H2O from a material containing a lithium salt in the form of the Li2SO4 salt is shown on
H2O−2e−→2H++½O2↑ (1)
Accordingly, electrochemical decomposition of water occurs at the cathodes resulting in hydrogen gas and OH− ions according to the reaction:
2H2O+2e−→2OH+H2↑ (2)
In a general form, the process of electrochemical conversion of Li2SO4 to LiOH can be described by the following reaction:
The cation-exchange membrane permits unhindered transfer of cations from the anode compartment to the cathode compartment. At that the transfer of SO42− ions from the anode compartment to the cathode compartment and of OH− ions from the cathode compartment is prevented due to the specific features of cation-exchange membranes. Since the anolyte is being constantly depleted in Li2SO4 and enriched in H2SO4, and the catholyte is being constantly enriched in LiOH, the circulating anolyte is constantly replenished with fresh Li2SO4 solution. The optimal range of the current density is 2-4 kA/m2 while maintaining the concentration of lithium in the circulating anolyte in the range of 20-25 kg/m3. The optimal concentration of lithium hydroxide in the circulating catholyte is in the range of 50-80 kg/m3. The membranes of Nafion-434, Nafion-438, Nafion-324, CTIEM-3, MF-4SK-100 types and other equivalent membranes resistant to alkalis and acids can be used as cation-exchange membranes. For the cathodes, it is advisable to use perforated plates made of nickel-plated stainless steel, which eliminates both the risk of hydrogenation of the structural material of cathodes with cathodic hydrogen and the risk of their corrosion during emergency stops and interruption of the current load. The most durable anodes in the electrolysis of sulfate solutions are the anodes made of platinized titanium; in addition, titanium with an iridium-ruthenium oxide coating can be used as the anodes. A catholyte stream of a predetermined capacity is constantly withdrawn from the circulating catholyte with the Li2SO4 solution produced by membrane electrolysis and sent to the process of evaporation and crystallization of LiOH·H2O. LiOH·H2O crystals are usually separated from the mother liquor upon evaporation by centrifugation, the separated crystals are washed from the remainder of the mother liquor with demineralized water and dried to give the LiOH·H2O product which meets the requirements of the LGO-1 GOST 8595-83 grade. The mother liquor formed after evaporation and separation of the crystals is returned to evaporation. Since sodium and potassium are contained as impurities in the lithium sulfate salt fed to electrolysis together with the lithium pass into the catholyte, they gradually accumulate in the evaporated catholyte to concentrations at a level which does not allow producing a product that meets the requirements of the LGO-1 grade. For this reason a predetermined volume is constantly withdrawn from the alkaline solution returned to the catholyte evaporation process formed after the separation of the LiOH·H2O crystals, and is directed to recycling, which ensures returning of lithium to production process. Recycling of the spent catholyte consists in separating lithium from alkali metal impurities based on a significant difference in the solubility of the compounds Li2CO3, LiHCO3, Na2CO3, NaHCO3, K2CO3, KHCO3. Herewith lithium carbonate is the least soluble compound, and K2CO3 is the most soluble compound among the given list. 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 step of recycling a mixed bicarbonate solution saturated with KHCO3, NaHCO3 and LiHCO3 is prepared, and its stream is mixed with the stream of the spent catholyte being recycled. Upon mixing of the streams the following reactions occur, resulting in the precipitation of poorly soluble lithium carbonate and the conversion of potassium and sodium bicarbonates into carbonates of a significantly higher solubility than the corresponding bicarbonates:
2LiOH(solution)(Na,K)+2KHCO3(solution)→Li2CO3(s)↓+K2CO3(solution) (4)
2LiOH(solution)(Na,K)+2NaHCO3(solution)→Li2CO3(s)↓+Na2CO3(solution) (5)
2LiOH(solution)(Na,K)+2LiHCO3(solution)→Li2CO3(s)↓+Li2CO3(solution) (6)
The mixing process is combined with the process of removing excess water coming with the spent catholyte stream. The removal of water is carried out by directly contacting the resulting suspension with a predetermined stream heated to a temperature above 100° C. As a result of the contacting the heated air with the suspension water evaporates from the suspension while the air is cooled to the temperature of the wet thermometer. In turn, the removal of water from the suspension results in an increase in the degree of conversion of Li2CO3 into solid phase. At the same time, the liquid phase is enriched with sodium and potassium coming from the spent catholyte. The resulting solid phase of Li2CO3 is separated from the carbonate solution by centrifugation and directed to the process of neutralizing the spent anolyte, and the resulting carbonate solution is converted into a bicarbonate solution by treatment with carbon dioxide according to the reactions:
K2CO3(solution)+CO2(g)+H2O(l)→2KHCO3(solution, s) (7)
Na2CO3(solution)+CO2(g)+H2O(l)→2NaHCO3(solution, s) (8)
Li2CO(solution)+CO2(g)+H2O(l)→2LiHCO3(solution) (9)
Due to the oversaturation of NaHCO3 and KHCO3 solutions due to their enrichment with sodium and potassium coming from the spent catholyte, part of the sodium and potassium bicarbonates will remain in the solid phase, while the lithium bicarbonate formed from the dissolved Li2CO3 due to its higher solubility will never remain in the solid phase. The resulting solid phase of sodium and potassium bicarbonates is separated from the bicarbonate solution by filtration. The bicarbonate solution is directed to mixing with the next batch of spent catholyte.
Since during membrane electrolysis the circulating anolyte undergoes depletion in Li2SO4 and enrichment in H2SO4, a predetermined anolyte stream is constantly withdrawn from the circulating anolyte stream and is first brought into contact with lithium carbonate obtained upon recycling of the spent catholyte to neutralize a part of the sulfuric acid according to the reactions:
H2SO4(solution)+Li2CO3(s)→Li2SO4(solution)+CO2(g)+H2O(l) (10)
During acid neutralization with lithium carbonate the spent anolyte is partially strengthened with Li2SO4. Afterwards there are two possible options for the preparation of the neutralized anolyte for electrolysis. According to the first option (option A), the spent anolyte solution after neutralization with lithium carbonate is brought into contact with calcium oxide, or calcium hydroxide, or calcium carbonate, or a mixture thereof, to convert sulfuric acid into the solid phase of CaSO4·2H2O according to the reactions:
H2SO4(solution)+CaO(s)+H2O(l)→CaSO4·2H2O(s) (11)
H2SO4(solution)+Ca(OH)2(g)→CaSO4·2H2O(s) (12)
H2SO4(solution)+CaCO3(s)+H2O(l)→CaSO4·2H2O(s)+CO2(g) (13)
After separation from the precipitate, the spent anolyte, which is a solution of Li2SO4, completely freed from sulfuric acid is brought into contact with a predetermined mass quantity of the initial Li2SO4 salt after the dissolution of which the solution will have a predetermined content of Li2SO4. Next, the resulting Li2SO4 solution is chemically purified from calcium and magnesium, if necessary. The process of chemical purification is necessary if the level of calcium and magnesium in the initial Li2SO4 salt is significant. The predetermined part of the spent washing solution (120 kg/m3 LiOH solution containing NaOH and KOH at a total level of 0.1 kg/m3) and carbon dioxide are used as the reagents. The purification process is described by the following chemical equations:
Ca(solution)+2LiOH(solution)+CO2(g)→CaCO3(s)↓+2Li(solution)++H2O(l) (14)
4Mg(solution)2++8LiOH(solution)+3 CO2(g)→Mg(OH)2·3MgCO3·3 H2O(s)↓+8Li(solution)+ (15)
The chemical purification generally allows to bring the rest of the total content of calcium and magnesium in the analyzed solution to the level of 10-15 g/m3. After separation of the precipitates the Li2SO4 solution is directed to ion exchange purification; to this end the Lewatit 208 TP ion exchanger in Li-form or its anolyte also in Li-form are used. The ion exchange purification process is described by the following reaction equations:
Sorption step
Regeneration step:
Step of converting from H-form to Li-form
Ion exchange purification allows to bring the residual total concentration of calcium and magnesium in the Li2SO4 solution to a level not exceeding 0.1 g/m3, and this solution is used as the replenishing solution for the circulating anolyte stream in the membrane electrolysis process.
According to another option (option B), the withdrawn anolyte stream is first partially neutralized with lithium carbonate obtained at the stage of recycling of the spent catholyte, then with ammonia upon directly contacting the partially neutralized spent anolyte with the air-ammonia mixture, to convert the remaining sulfuric acid into ammonium sulfate according to the reaction:
2NH3(g)+H2SO4(solution)→(NH4)2SO4(solution) (19)
The mixed solution of Li2SO4 and (NH4)2SO4 obtained by complete neutralization of the spent anolyte is evaporated by salting out (NH4)2SO4 from the mixed solution. Ammonium sulfate after washing from the mother brine and drying represents a commercial fertilizer sold on the market. The Li2SO4 solution obtained from the spent anolyte with a residual content of (NH4)2SO4 is in turn alkalized using a part of the spent washing solution formed during the washing process of the LiOH·H2O crystals.
After alkalinization, the solution is deammonized by aeration with a stream of atmospheric air. The deammonization process is described by the following chemical equation:
(NH4)2SO4(solution)+2LiOH(solution)→2NH3(g)+Li2SO4(solution)+2H2O (20)
The gaseous ammonia containing air stream is enriched with a predetermined amount of ammonia and directed to neutralize the next portion of the spent and partially neutralized anolyte.
The Li2SO4 solution subjected to the deammonization step is sent for additional strengthening by dissolving a predetermined mass quantity of the initial Li2SO4 salt and, after chemical and ion exchange purification, is used as a replenishing solution for the circulating anolyte stream.
A coproduct of membrane electrolysis, cathodic hydrogen, is ejected from the cathode gas separator with a natural gas stream. The resulting gaseous mixture is utilized as a fuel for the generation of a heating steam. The heating steam is used in evaporation processes. The juice vapor condensate formed during the evaporation processes is used as the demineralized water in the processes of washing the crystals obtained by evaporation of the solutions.
A process flow diagram of the production of LiOH·H2O from a material containing a lithium salt in the form of the LiCl or LiOH·H2O salt is shown on
Cl−−e−→½ Cl2 (21)
In this case no acid is formed and only depletion of the anolyte in LiCl occurs during electrolysis.
In a general form, the process of electrochemical conversion of LiCl salt solution to LiOH solution can be described by the following overall reaction:
The same cathodes and cation-exchange membranes are used in the conditions of membrane electrolysis of LiCl salt solution as in the conditions of electrolysis of the Li2SO4 salt solution. The main parameters of the process of membrane electrolysis of soluble salts are virtually the same. However, instead of expensive anodes made of platinized titanium or titanium coated with other noble metals usually used in the electrolysis of lithium sulfate solution, titanium anodes coated with ruthenium oxide (Oxidized Ruthenium-Titanium Anodes (ORTA)) can be successfully used in the electrolysis of lithium chloride solution, provided that the chloride anolyte is acidified to pH=2. Acidification of the chloride-containing anolyte also eliminates the risk of the formation of chlorates in the circulating anolyte. The schemes of withdrawal and processing of the catholyte into final LiOH·H2O for the electrochemical conversion of sulfate and chloride solutions of lithium are the same. Withdrawal and pretreatment for electrolysis of the spent (depleted in LiCl) anolyte are similar to the scheme and pretreatment of the sulfate anolyte, except that the pretreatment of the spent chloride anolyte does not require a neutralization process and the strengthening of the spent anolyte to a predetermined concentration of lithium is carried out by dissolving a predetermined amount of the initial LiCl salt. Since sulfate ions introduced as impurities contained in the initial lithium chloride used in the process can accumulate in the circulating anolyte stream, the chemical purification of the spent anolyte strengthened with LiCl provides for, along with purification from calcium and magnesium, purification from sulfate ions by converting them into the insoluble BaSO4 salt using BaCl2 as the precipitating agent. During the process of ion exchange purification of the lithium chloride solution strengthened with LiCl, the acid regeneration step is carried out with a 2N hydrochloric acid solution.
Utilization of the coproducts of membrane electrolysis, hydrogen (cathodic gas) and chlorine (anodic gas), can be dome in multiple ways. According to option A, hydrogen and chlorine withdrawn from the gas separator are mixed and subjected to high-temperature combustion to produce hydrogen chloride gas according to the reaction:
The resulting stream of high-temperature hydrogen chloride is subjected to forced cooling and directed to a stepwise countercurrent absorption using demineralized water as the initial absorbent, which can be represented by a by-product of the evaporation processes, juice vapor condensate. Option B involves the use of cathodic hydrogen as a fuel for the generation of the heating steam used in the solution evaporation processes. According to this option chlorine can be utilized as the NH4Cl salt by evaporating the NH4Cl solution obtained by water absorption of the gaseous mixture of NH3 and Cl2 at a molar ratio of NH3:Cl2=8:3 according to the reaction:
8 NH3(g)+3 Cl2(g)→6 NH4Cl(solution)+N2(g), (24)
or as a 6N HCl solution obtained by aqueous absorption of the gaseous mixture of NH3 and Cl2 at a molar ratio of NH3:Cl2=2:3 according to the reaction:
2 NH3(g)+3 Cl2(g)→6 HCl(solution)+N2(g), (25)
or as a sodium hypochlorite solution (disinfecting and antiseptic solution) by absorbing chlorine with an aqueous solution of NaOH according to the reaction:
Cl2(g)+2 NaOH(solution)→NaOCl(solution)+NaCl(solution)+H2O(l), (26)
or as neutral calcium hypochlorite by drying this Ca(OCl)2 salt, isolated upon an exchange reaction between sodium hypochlorite solution saturated with NaOCl obtained by absorbing half of the anodic chlorine by a concentrated NaOH solution according to the reaction:
Cl2(g)+NaOH(solution)→NaOCl(solution)+α̨NaCl(s)↓+(1−α̨)NaCl(solution)+H2O(l) (27)
and the solution saturated with Ca(OCl)2 obtained by the absorption of the half of the anodic chlorine by calcium hydroxide pulp according to the reaction:
2 Cl2(g)+2Ca(OH)2(s, solution)→Ca(OCl)2(solution)+CaCl2(solution)+2 H2O(l) (28)
The main amount of calcium is precipitated from the mother liquor containing active chlorine, obtained upon conducting the exchange reaction and containing Ca2+, Na+, Cl−, OCl− ions, by introducing a predetermined amount of NaOH into the solution, according to the reaction:
Ca2+(solution)+2NaOH(solution)→Ca(OH)2(solution)↓+2Na+(solution) (29)
The residual amount of calcium is removed from the solution by adding a predetermined amount of Na2CO3, according to the reaction:
Ca2+(solution)+Na2CO3(solution)→CaCO3(g)↓+2Na+(solution) (30)
The resulting Ca(OH)2 precipitate with an admixture of CaCO3 is directed to the process of chlorination of the Ca(OH)2 pulp. The solution formed after calcium precipitation and containing active chlorine in equal proportions is returned to the process of chlorination of NaOH solution and Ca(OH)2 pulp.
A process flow diagram of the production of LiOH·H2O from a material containing a lithium salt in the form of the Li2CO3 salt is shown on
3 Cl2(g)+3Li2CO3(s)+2NH3(g)→6 LiCl(solution)+N2(g)+3CO2(g)+3 H2O(l) (31)
The aqueous pulp for the absorption of anodic chlorine is prepared from demineralized water, lithium carbonate obtained from the spent evaporated lithium catholyte in the form of initial Li2CO3 salt, an appropriate reducing agent, and an anolyte stream purified from sulfate ions which in turn is withdrawn from the circulating anolyte stream enriched in sulfate ions during electrolysis at a predetermined volumetric rate. Cathodic hydrogen according to this option is used as a fuel for the generation of the heating steam.
A process flow diagram of the production of LiOH·H2O from a material containing a lithium salt in the form of a mixture of Li2SO4 and Li2CO3 is shown on
A process flow diagram of the production of LiOH·H2O from materials containing a lithium salt in the form of a mixture of LiCl and Li2CO3 is shown on
A process flow diagram of the production of LiOH·H2O from materials containing a lithium salt in the form of a mixture of Li2SO4 and LiCl is shown on
Preparation of LiOH·H2O based on the electrochemical conversion of mixed solutions of Li2SO4 and LiCl does not require a special process for purifying the anolyte from sulfate ions. Otherwise, the technology described on
A process flow diagram of the production of LiOH·H2O from materials containing a lithium salt in the form of a mixture of Li2SO4, LiCl and Li2CO3 is shown on
A laboratory scale apparatus containing a membrane electrolysis unit, a unit for processing catholyte into LiOH·H2O, a unit for pretreating and purifying the replenishing lithium salt solution for feeding into the circulating anolyte, a unit for processing the spent evaporated catholyte, and an anodic gas utilization unit was used to carry out comparative tests of technological processes for producing LiOH·H2O from various lithium salts: lithium sulfate, lithium chloride, a mixture of sulfate and lithium chloride. The technological processes reproduced on the laboratory apparatus were carried out on the basis of the flow diagram shown on
Calcium hydroxide used for neutralizing sulfuric acid and utilizing anodic chlorine as neutral calcium hypochlorite was obtained by precipitation (with NaOH as the precipitant) from a solution of CaCl2 produced by dissolving hydrated technical grade CaCl2·6H2O salt.
The main comparative parameters and characteristics of LiOH·H2O production technologies from various lithium salts according to the claimed method are shown in Table 3. The compositions of the respective resulting LiOH·H2O samples are shown in Table 4.
As follows from the results, the claimed method allows producing a high-quality LiOH·H2O product which meets the requirements of the LGO-1 GOST 8595-83 grade from the tested lithium salts. Herewith the electrochemical parameters of membrane electrolysis conversion processes of solutions of highly soluble lithium salts into a LiOH solution have almost similar characteristics.
The tests also showed that when anodic chlorine is utilized according to the option proposed in the claimed method, which involves recycling the anodic chlorine into neutral calcium hypochlorite, the content of active chlorine in the samples of the produced product is 62-63 wt. % with the content of water-insoluble impurities not exceeding 4.3%. The degree of utilization of the anodic chlorine is 99.7%.
The tests in turn showed 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 steps to completely neutralize H2SO4 in the anolyte without the need to introduce excess Ca(OH)2.
Herewith at the first step contacting of the initial spent anolyte with the spent precipitate from the second step, which is a mixture of CaSO4·2 H2O and Ca(OH)2, takes place with guaranteed conversion of all free Ca(OH)2 into CaSO4·2 H2O and the withdrawal of the resulting CaSO4·2 H2O precipitate 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 initial spent anolyte fed to the first neutralization step. During contacting of the phases at the second step a mixed precipitate of CaSO4·2 H2O and Ca(OH)2 is formed and complete neutralization of sulfuric acid is ensured. The contacting of the anolyte with Ca(OH)2 is carried out under conditions of vigorous mixing.
A laboratory bench including three membrane electrolysis units was used for the testing of the three cation-exchange membranes, Nafion-438, CTIEM-3, and MF-4SK-100, for their suitability for the electrochemical conversion of Li2SO4 and LiCl solutions into a LiOH solution. The total test period was 219 work hours. The following were tested as the anodes: for the electrolysis of LiCl solutions—titanium coated with ruthenium oxide (ORTA), for the electrolysis of Li2SO4 solutions—platinized titanium. The results are shown in Table 5.
As follows from the results, all tested membranes are suitable for membrane electrolysis of sulfate and chloride lithium solutions to obtain a catholyte in the form of a LiOH solution. Herewith such parameters of membrane electrolysis as the cell voltage and the LiOH current output for the tested membranes are virtually commensurate. The 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 electrolysis units during the electrolysis of a sulfate solution is always higher than during the electrolysis of a chloride-containing solution. This finding is attributed to the higher electrical conductivity of Li2SO4 solutions in comparison to LiCl solutions.
It follows from the obtained data that other cation-exchange membranes can be used for the conversion of Li2SO4 and LiCl solutions, equivalent to the tested ones and chemically stable in these media.
A laboratory apparatus made in accordance with the flow diagram shown on
The strengthened and purified salt solutions of lithium produced from spent anolyte streams were adjusted to the predetermined concentrations of Li2SO4 and LiCl in replenishing solutions by evaporation. The main parameters of the tests performed are shown in table 7. The compositions of the respective resulting LiOH·H2O samples are shown in table 8. It can clearly be seen from the results obtained that the proposed method allows producing LiOH·H2O as a product of high purity meeting the requirements of the LGO-1 grade from the technical grade lithium carbonate.
Herewith the recovery of conversion alkali (LiOH solution) as a solid product (LiOH·H2O) significantly depends on the content of sodium and potassium in the initial lithium carbonate.
A laboratory bench represented by an assembly for the utilization of sulfate ions present in the H2SO4 salt was used for the testing the utilization option by converting the sulfuric acid contained in the spent sulfate anolyte into a (NH4)2SO4 salt by contacting the spent anolyte with ammonia and salting out the (NH4)2SO4 salt from a mixed spent solution of Li2SO4 and (NH4)2SO4 during its evaporation accompanied by increasing the concentration of Li2SO4 in the anolyte. The option of the technological process for the utilization of sulfuric acid contained in the spent anolyte in the form of (NH4)2SO4 salt is shown on
The resulting samples of the (NH4)2SO4 salt after 3-step countercurrent washing with demineralized water and drying at 110° C. contained the main substance in the form of (NH4)2SO4 at 99.7% wt. with the content of lithium impurities of less than 0.002 wt. %. Herewith the degree of ammonia utilization was 99.84%.
The spent catholyte stream of 10 dm3 having the following composition (g/dm3): LiOH—120; NaOH—8.7; KOH—0.3, was recycled according to the claimed method (
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021108817 | Mar 2021 | RU | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/RU2022/050104 | 3/30/2022 | WO |
