METHOD FOR PRODUCING HIGH PURITY LITHIUM HYDROXIDE MONOHYDRATE
20240200206 ยท 2024-06-20
Assignee
Inventors
- Aleksandr Dmitriyevich Riabtsev (Novosibirsk, RU)
- Nikolay Mikhaylovich Nemkov (Novosibirsk, RU)
- Valeriy Ivanovich Titarenko (Novosibirsk, RU)
- Andrey Aleksandrovich Kurakov (Novosibirsk, RU)
- Aleksandr Viktorovich LETUEV (Yurga, RU)
Cpc classification
C25B11/052
CHEMISTRY; METALLURGY
C25B1/34
CHEMISTRY; METALLURGY
C25B9/23
CHEMISTRY; METALLURGY
C25B15/087
CHEMISTRY; METALLURGY
International classification
C25B1/34
CHEMISTRY; METALLURGY
C25B9/23
CHEMISTRY; METALLURGY
Abstract
A method for producing high purity lithium hydroxide monohydrate from materials containing a lithium salt selected from Li2SO4, LiCl, Li2CO3 or mixtures thereof is provided. The method includes membrane electrolysis of an aqueous solution of the indicated lithium salt using a cation exchange membrane and a nickel-plated stainless steel cathode. The catholyte is withdrawn from the circulating stream and evaporated to give crystals of lithium hydroxide monohydrate, which are separated from the mother liquor, washed with water and dried to give the final high purity lithium hydroxide monohydrate. Part of the spent washing solution is fed into the catholyte evaporation process. Part of the mother liquor formed after the separation of crystals of lithium hydroxide monohydrate is returned to the catholyte evaporation process. The reverse flow of the anolyte is replenished with a concentrated lithium salt solution prepared from the original lithium salt.
Claims
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, the method comprising: performing membrane electrolysis of an aqueous solution of the lithium salt using a cation-exchange membrane as the membrane separating cathode and anode circuits of electromagnetic cells in the mode of circulation of the catholyte in the form of a solution of lithium hydroxide and anolyte in the form of a lithium salt solution, wherein a cathode for the membrane electrolysis is made of nickel-plated stainless steel and the cation-exchange membrane is selected from a membrane resistant to alkalis and acids; withdrawing a volume of the catholyte from a circulating catholyte stream and evaporating the withdrawn volume of the catholyte to obtain crystals of lithium hydroxide monohydrate in a mother liquor; separating the crystals from the mother liquor, washing the crystals with water and drying the washed crystals to obtain final high purity lithium hydroxide monohydrate; wherein the method is further characterized by the following steps: removing cathodic and anodic gases formed during the electrolysis; feeding a part of a resulting stream of spent washing solution to a catholyte evaporation process and using part of the spent washing solution fed to the catholyte evaporation process in recycling of withdrawn spent anolyte stream; returning a part of the mother liquor formed after separation of the crystals of lithium hydroxide monohydrate to the catholyte evaporation process; recycling a part of the spent catholyte stream, which is withdrawn from the evaporation process and represents a concentrated solution of lithium hydroxide with an admixture of sodium and potassium hydroxides; replenishment of a circulating anolyte stream with a concentrated solution of a lithium salt prepared from an original source of lithium salt and a solution of a lithium salt obtained as a result of the recycling the withdrawn spent anolyte stream.
2. The method according to claim 1, wherein recycling the spent catholyte stream comprises: mixing the concentrated solution of lithium hydroxide with the admixture of sodium and potassium hydroxides with a stream of an aqueous solution containing sodium, potassium and lithium bicarbonates, to obtain lithium carbonate; concentrating a resulting pulp represented by a mixture of solid phase of lithium carbonate and a carbonate solution containing Na.sub.2CO.sub.3, K.sub.2CO.sub.3, Li.sub.2CO.sub.3 by removing water; separating the solid phase of lithium carbonate from the carbonate solution liquid phase, carbonizing the carbonate solution liquid phase by directly contacting it with carbon dioxide to convert the carbonate solution into a bicarbonate suspension comprising a mixture of solid phases of sodium bicarbonate and potassium bicarbonate in a solution of sodium, potassium and lithium bicarbonates; filtering the bicarbonate suspension to separate the solid phase of sodium and potassium bicarbonates from a solution containing sodium, potassium and lithium bicarbonates, which is directed to mixing with the stream of spent catholyte withdrawn from the process of evaporation containing lithium, sodium and potassium hydroxides.
3. The method according to claim 1, wherein using part of the spent washing solution fed to the catholyte evaporation process in the recycling of the withdrawn spent anolyte stream comprises using the spent washing solution as an alkaline reagent at a step of chemical purification of the lithium salt solution from impurities and/or as a regenerating solution for converting the ion exchanger from H-form to Li-form at a step of ion exchange purification.
4. The method according to claim 3, wherein the concentrated solution of lithium salts has a direct current density of 1-4 kA/m.sup.2; the cation-exchange membrane for the membrane electrolysis is a membrane of Nafion-438, CTIEM-3, or MF-4SK-100 types; and an ion exchanger is used at the step of ion exchange purification.
5. The method according to claim 4, wherein when lithium sulfate is used as the material containing lithium salt, titanium coated with noble metals selected from platinum, iridium, ruthenium or tantalum, is used as an anode in the performing membrane electrolysis step, and an anolyte stream is constantly withdrawn from the circulating anolyte stream undergoing depletion in Li.sub.2SO.sub.4 and enrichment in H.sub.2SO.sub.4; neutralizing the withdrawn anolyte stream by bringing into contact with CaO, Ca(OH).sub.2, or CaCO.sub.3 until H.sub.2SO.sub.4 is completely neutralized; a resulting solid phase of CaSO.sub.4.Math.2H.sub.2O is separated from a Li.sub.2SO.sub.4 solution, the Li.sub.2SO.sub.4 solution is brought into contact with initial lithium sulfate salt to dissolve the initial lithium sulfate salt and to obtain a lithium sulfate solution; the lithium sulfate solution is added with the spent washing solution forming a mixed lithium sulfate solution followed by carbonizing the mixed solution with carbon dioxide coming from the process of neutralization of the withdrawn anolyte stream until calcium and magnesium contained in the mixed lithium sulfate solution are converted into insoluble compounds CaCO.sub.3 and Mg(OH).sub.2.Math.3MgCO.sub.3.Math.3H.sub.2O forming a suspension; the suspension is filtered to separate the insoluble compounds from the mixed lithium solution forming a chemically purified Li.sub.2SO.sub.4 solution, the chemically purified Li.sub.2SO.sub.4 solution is directed to ion exchange purification by passing the chemically purified Li.sub.2SO.sub.4 solution through a layer of ion exchanger in Li-form producing an Li.sub.2SO.sub.4 solution that has undergone ion exchange purification; the Li.sub.2SO.sub.4 solution that has undergone ion exchange purification is used as a replenishing solution for the circulating anolyte stream in the membrane electrolysis process; regenerating spent ion exchanger in two steps: the first step comprises treatment with 2.0N sulfuric acid solution, the second step comprises treatment with 2.0N LiOH solution; the spent regenerates from the ion exchange process are mixed with the spent anolyte stream before its chemical purification; cathodic hydrogen, obtained from the membrane electrolysis, is ejected with a natural gas stream from the cathode gas separator of the electrolysis unit providing a gaseous mixture, the gaseous mixture is directed to a steam generator as fuel for the generation of a heating steam used as a heat carrier in an evaporation step.
6. The method according to claim 5, wherein a volume of the anolyte constantly withdrawn from the circulating anolyte stream undergoing depletion in Li.sub.2SO.sub.4 and enrichment in H.sub.2SO.sub.4 is brought into contact with an air-ammonia mixture to neutralize H.sub.2SO.sub.4 and obtain a mixed solution of Li.sub.2SO.sub.4 and (NH.sub.4).sub.2SO.sub.4 which is evaporated to salt out (NH.sub.4).sub.2SO.sub.4 and increase the concentration of Li.sub.2SO.sub.4 in an evaporated solution; the evaporated solution with remaining (NH.sub.4).sub.2SO.sub.4 is mixed with a volume of the spent alkaline washing solution to produce a mixed solution, and the mixed solution is brought into contact with an air stream coming from the process of contacting the spent anolyte stream with the ammonia-air mixture to remove the remaining ammonia from the Li.sub.2SO.sub.4 solution producing a gaseous ammonia containing air stream and an ammonia-free Li.sub.2SO.sub.4 solution; the gaseous ammonia containing air stream is enriched with ammonia from an ammonia source and directed to the step of neutralizing the spent anolyte stream; the ammonia-free Li.sub.2SO.sub.4 solution after strengthening with Li.sub.2SO.sub.4 by dissolving therein the initial Li.sub.2SO.sub.4 salt and purification from impurities is used as a replenishing solution for the circulating anolyte stream in the membrane electrolysis process.
7. The method according to claim 4, wherein 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 volume of the anolyte is constantly withdrawn from the circulating anolyte stream undergoing depletion in LiCl providing a withdrawn anolyte stream; the withdrawn anolyte stream is brought into contact with the initial lithium chloride salt to bring the LiCl concentration in the withdrawn anolyte stream to a predetermined value providing a withdrawn anolyte stream; purifying the withdrawn LiCl-enriched anolyte stream from metal cation impurities and adding barium chloride to the withdrawn LiCl-enriched anolyte stream to convert sulfate ions into an insoluble BaSO.sub.4 precipitate producing a withdrawn LiCl-enriched anolyte stream purified from metal cation impurities and sulfate ions, a liquid phase of the withdrawn LiCl-enriched anolyte stream purified from metal cation impurities and sulfate ions is separated from precipitates and, following an ion exchange purification, is used as a replenishing solution in the circulating anolyte stream in the membrane electrolysis process; cathodic hydrogen and anodic chlorine withdrawn from gas separators are mixed and subjected to flame combustion; the resulting hydrogen chloride is absorbed by demineralized water to produce concentrated 36% hydrochloric acid.
8. The method according to claim 7, wherein the anodic chlorine withdrawn from a gas separator of the gas separators is absorbed by aqueous ammonia to produce, at a molar ratio of NH.sub.3:Cl.sub.2=8:3, a NH.sub.4Cl solution, and at a molar ratio of NH.sub.3:Cl.sub.2=2:3, a 6N HCl solution; the resulting NH.sub.4Cl solution is evaporated, NH.sub.4Cl is crystallized and dried, the cathodic hydrogen withdrawn from a gas separator of the gas separators is utilized as a heat carrier for generation of heating steam.
9. The method according to claim 7, wherein either all anodic chlorine withdrawn from the gas separator is absorbed by a NaOH solution to produce a disinfecting solution of sodium hypochlorite, or half of the withdrawn volumetric flow of chlorine is absorbed by a NaOH solution to produce a solution saturated with sodium hypochlorite, and the other half of the withdrawn volumetric flow of anodic chlorine is absorbed by a Ca(OH).sub.2 suspension to produce a solution saturated with calcium hypochlorite; the produced solutions are mixed to salt out neutral calcium hypochlorite which is separated and dried; calcium is precipitated out of a resulting mother liquor, first by adding a predetermined amount of NaOH, and then by adding Na.sub.2CO.sub.3; precipitate containing Ca(OH).sub.2 with an admixture of CaCO.sub.3 is separated and directed to the preparation of Ca(OH).sub.2 suspension containing active chlorine in the form of hypochlorite ions; a remaining solution is divided into two equal portions, one portion is mixed with NaOH and directed to chlorination process to obtain a sodium hypochlorite solution, another portion is mixed with Ca(OH).sub.2 and is also directed to chlorination process to obtain a calcium hypochlorite solution.
10. The method according to claim 4, wherein when lithium carbonate is used as the lithium salt containing material, lithium carbonate salt is used for the reproduction of anolytes by converting Li.sub.2CO.sub.3 into highly soluble lithium salts lithium chloride or lithium sulfate, circulating as anolytes in the anode circuits of the electrolysis unit and undergoing depletion in LiCl or Li.sub.2SO.sub.4 during membrane electrolysis.
11. The method according to claim 4, wherein when an aqueous solution of lithium chloride is used as the anolyte, titanium anodes coated with ruthenium oxide are used in the membrane electrolysis process, wherein 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 a concentrated 36% hydrochloric acid withdrawn from a first absorption step along the path of the HCl vapor; a stream of resulting concentrated hydrochloric acid is mixed with a stream purified from sulfate ions using BaCl.sub.2 as the reagent, withdrawn for purification from sulfate ions from the circulating anolyte stream in the membrane electrolysis process producing a mixed stream of concentrated hydrochloric acid and anolyte purified from sulfate ions; the mixed stream of concentrated hydrochloric acid and anolyte purified from sulfate ions is brought into contact with an initial lithium carbonate and demineralized water to obtain a stream of LiCl solution 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.
12. The method according to claim 11, wherein anodic chlorine is absorbed by demineralized water in the presence of ammonia at a mole ratio of NH.sub.3:Cl.sub.2=2:3 to obtain a 6N hydrochloric acid solution, which is mixed with a stream of anolyte chemically purified withdrawn for purification from sulfate ions from the circulating anolyte stream in the membrane electrolysis process to produce a mixed stream of hydrochloric acid solution and the anolyte purified from sulfate ions; the mixed stream of hydrochloric acid solution and anolyte purified from sulfate ions is brought into contact with an initial lithium carbonate to obtain a LiCl 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 fuel for generation of heating steam.
13. The method according to claim 11, wherein the anodic chlorine is absorbed by an aqueous pulp of lithium carbonate and in the presence of a reducing agent for elemental chlorine, which prevents an absorber during chlorine absorption from being contaminated with foreign cations and anions and to obtain as an absorption product a lithium chloride solution, 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, whereby the aqueous pulp for the absorption of the anodic chlorine is prepared from demineralized water, lithium carbonate obtained from the spent catholyte, lithium carbonate in the form of the initial salt, a reducing agent and the anolyte stream purified from sulfate ions using as the reagent, following withdrawal of the anolyte stream for purification from sulfate ions from the circulating anolyte stream in the membrane electrolysis process, and cathodic hydrogen is used as fuel for generation of heating steam.
14. The method according to claim 4, wherein when using an aqueous solution of lithium sulfate as the anolyte, titanium coated with noble metals selected from platinum, iridium, tantalum or ruthenium, is used as an anode in the electrolysis process, and an anolyte stream depleted in lithium sulfate and enriched in sulfuric acid, withdrawn from the anolyte circulation circuit, is brought into contact with an initial lithium carbonate to obtain a lithium sulfate solution, which, after purification from impurities, is used as a replenishing solution for the anolyte circulation circuit.
15. The method according to claim 4, wherein when a mixture of lithium sulfate and lithium carbonate is used as the lithium salt containing material, an anolyte stream of a predetermined volume is constantly withdrawn from the circulating anolyte stream undergoing depletion in Li.sub.2SO.sub.4 and enrichment in H.sub.2SO.sub.4; the withdrawn anolyte stream is brought into contact with an initial mixture of Li.sub.2SO.sub.4 and Li.sub.2CO.sub.3 salts to obtain a lithium sulfate solution containing a residual amount of H.sub.2SO.sub.4; the lithium sulfate solution containing the residual amount of H2SO4 is recycled into a Li.sub.2SO.sub.4 solution for replenishing the circulating anolyte stream in the membrane electrolysis process.
16. The method according to claim 4, when a mixture of lithium chloride and lithium carbonate salts is used as the lithium salt containing material, an initial mixture of lithium chloride and lithium carbonate salts is brought into contact with a hydrochloric acid solution and a flow of the anolyte withdrawn from the circulating anolyte stream undergoing depletion in LiCl during electrolysis, to produce a lithium chloride solution of a predetermined concentration; the lithium chloride solution of the predetermined concentration, after purification from impurities, is used as a replenishing solution for the circulating anolyte stream in the membrane electrolysis process.
17. The method according to claim 4, wherein when a mixture of lithium sulfate and lithium chloride salts is used as the lithium salt containing material, titanium coated with a noble metal selected from platinum, iridium, tantalum or ruthenium, is used as an anode in the membrane electrolysis process, and an anolyte stream is withdrawn from the circulating anolyte stream undergoing depletion in lithium sulfate and chloride and enrichment in H.sub.2SO.sub.4, which is brought into contact with a predetermined amount of CaO, Ca(OH).sub.2, or CaCO.sub.3 until H.sub.2SO.sub.4 is completely neutralized producing a mixed solution of Li.sub.2SO.sub.4 and LiCl and a CaSO.sub.4.Math.2H.sub.2O; the mixed solution of Li.sub.2SO.sub.4 and LiCl is separated from the CaSO.sub.4.Math.2H.sub.2O precipitate, brought into contact with an initial mixture of Li.sub.2SO.sub.4 and LiCl salts to dissolve the initial mixture of Li.sub.2SO.sub.4 and LiCl and to obtain a mixed solution of Li.sub.2SO.sub.4 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; and cathodic hydrogen is utilized as fuel for generation of heating steam.
18. The method according to claim 17, wherein the volume of anolyte constantly withdrawn from the circulating anolyte stream undergoing depletion in Li.sub.2SO.sub.4 and LiCl after recycling is used as a replenishing mixed solution of Li.sub.2SO.sub.4 and LiCl for the circulating anolyte stream; anodic chlorine withdrawn from a gas separator of the gas separators is recycled into 36% hydrochloric acid or into NH.sub.4Cl, sodium hypochlorite solution, or neutral calcium hypochlorite.
19. The method according to claim 4, wherein when a mixture of lithium sulfate, lithium chloride, and lithium carbonate salts is used as the lithium salt containing material, a volume of the anolyte is constantly withdrawn from the circulating anolyte stream undergoing depletion in Li.sub.2SO.sub.4 and LiCl and enrichment in H.sub.2SO.sub.4, which is first brought into contact with an initial mixture of Li.sub.2SO.sub.4, LiCl and Li.sub.2CO.sub.3 salts to produce a mixed solution of a predetermined lithium concentration; the mixed solution of predetermined lithium concentration is recycled into a mixed solution of Li.sub.2SO.sub.4 and LiCl which is used as a replenishing solution for the anolyte circulating stream in the membrane electrolysis process.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0037]
[0038]
[0039]
[0040]
[0041]
[0042]
[0043]
[0044] 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
[0045] A process flow diagram of the production of LiOH.Math.H.sub.2O from a material containing a lithium salt in the form of the Li.sub.2SO.sub.4 salt is shown on
H.sub.2O?2e.sup.?.fwdarw.2H.sup.++?O.sub.2?(1)
[0046] Accordingly, electrochemical decomposition of water occurs at the cathodes resulting in hydrogen gas and OH.sup.? ions according to the reaction:
2H.sub.2O+2e.sup.?.fwdarw.2OH+H.sub.2?(2)
[0047] In a general form, the process of electrochemical conversion of Li.sub.2SO.sub.4 to LiOH can be described by the following reaction:
##STR00001##
[0048] The cation-exchange membrane permits unhindered transfer of cations from the anode compartment to the cathode compartment. At that the transfer of SO.sub.4.sup.2? ions from the anode compartment to the cathode compartment and of OH.sup.? ions from the cathode compartment is prevented due to the specific features of cation-exchange membranes. Since the anolyte is being constantly depleted in Li.sub.2SO.sub.4 and enriched in H.sub.2SO.sub.4, and the catholyte is being constantly enriched in LiOH, the circulating anolyte is constantly replenished with fresh Li.sub.2SO.sub.4 solution. The optimal range of the current density is 2-4 kA/m.sup.2 while maintaining the concentration of lithium in the circulating anolyte in the range of 20-25 kg/m.sup.3. The optimal concentration of lithium hydroxide in the circulating catholyte is in the range of 50-80 kg/m.sup.3. 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 Li.sub.2SO.sub.4 solution produced by membrane electrolysis and sent to the process of evaporation and crystallization of LiOH.Math.H.sub.2O. LiOH.Math.H.sub.2O 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.Math.H.sub.2O 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.Math.H.sub.2O 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 Li.sub.2CO.sub.3, LiHCO.sub.3, Na.sub.2CO.sub.3, NaHCO.sub.3, K.sub.2CO.sub.3, KHCO.sub.3. Herewith lithium carbonate is the least soluble compound, and K.sub.2CO.sub.3 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 KHCO.sub.3, NaHCO.sub.3 and LiHCO.sub.3 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.sub.(solution)(Na,K)+2KHCO.sub.3(solution).fwdarw.Li.sub.2CO.sub.3(s)?+K.sub.2CO.sub.3(solution) (4)
2LiOH.sub.(solution)(Na,K)+2NaHCO.sub.3(solution).fwdarw.Li.sub.2CO.sub.3(s)?+Na.sub.2CO.sub.3(solution) (5)
2LiOH.sub.(solution)(Na,K)+2LiHCO.sub.3(solution).fwdarw.Li.sub.2CO.sub.3(s)?+Li.sub.2CO.sub.3(solution) (6)
[0049] 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 Li.sub.2CO.sub.3 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 Li.sub.2CO.sub.3 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:
K.sub.2CO.sub.3(solution)+CO.sub.2(g)+H.sub.2O.sub.(l).fwdarw.2KHCO.sub.3(solution, s) (7)
Na.sub.2CO.sub.3(solution)+CO.sub.2(g)+H.sub.2O.sub.(l).fwdarw.2NaHCO.sub.3(solution, s) (8)
Li.sub.2CO.sub.(solution)+CO.sub.2(g)+H.sub.2O.sub.(l).fwdarw.2LiHCO.sub.3(solution) (9)
[0050] Due to the oversaturation of NaHCO.sub.3 and KHCO.sub.3 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 Li.sub.2CO.sub.3 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.
[0051] Since during membrane electrolysis the circulating anolyte undergoes depletion in Li.sub.2SO.sub.4 and enrichment in H.sub.2SO.sub.4, 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:
H.sub.2SO.sub.4(solution)+Li.sub.2CO.sub.3(s).fwdarw.Li.sub.2SO.sub.4(solution)+CO.sub.2(g)+H.sub.2O.sub.(l) (10)
[0052] During acid neutralization with lithium carbonate the spent anolyte is partially strengthened with Li.sub.2SO.sub.4. 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 CaSO.sub.4.Math.2H.sub.2O according to the reactions:
H.sub.2SO.sub.4(solution)+CaO.sub.(s)+H.sub.2O.sub.(l).fwdarw.CaSO.sub.4.Math.2H.sub.2O.sub.(s) (11)
H.sub.2SO.sub.4(solution)+Ca(OH).sub.2(g).fwdarw.CaSO.sub.4.Math.2H.sub.2O.sub.(s) (12)
H.sub.2SO.sub.4(solution)+CaCO.sub.3(s)+H.sub.2O.sub.(l).fwdarw.CaSO.sub.4.Math.2H.sub.2O.sub.(s)+CO.sub.2(g) (13)
[0053] After separation from the precipitate, the spent anolyte, which is a solution of Li.sub.2SO.sub.4, completely freed from sulfuric acid is brought into contact with a predetermined mass quantity of the initial Li.sub.2SO.sub.4 salt after the dissolution of which the solution will have a predetermined content of Li.sub.2SO.sub.4. Next, the resulting Li.sub.2SO.sub.4 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 Li.sub.2SO.sub.4 salt is significant. The predetermined part of the spent washing solution (120 kg/m.sup.3 LiOH solution containing NaOH and KOH at a total level of 0.1 kg/m.sup.3) and carbon dioxide are used as the reagents. The purification process is described by the following chemical equations:
Ca.sub.(solution)+2LiOH.sub.(solution)+CO.sub.2(g).fwdarw.CaCO.sub.3(s)?+2Li.sub.(solution).sup.++H.sub.2O.sub.(l) (14)
4Mg.sub.(solution).sup.2++8LiOH.sub.(solution)+3 CO.sub.2(g).fwdarw.Mg(OH).sub.2.Math.3MgCO.sub.3.Math.3 H.sub.2O.sub.(s)?+8Li.sub.(solution).sup.+(15)
[0054] 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/m.sup.3. After separation of the precipitates the Li.sub.2SO.sub.4 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:
[0055] Sorption step
##STR00002##
[0056] Regeneration step:
##STR00003##
[0057] Step of converting from H-form to Li-form
##STR00004##
[0058] Ion exchange purification allows to bring the residual total concentration of calcium and magnesium in the Li.sub.2SO.sub.4 solution to a level not exceeding 0.1 g/m.sup.3, and this solution is used as the replenishing solution for the circulating anolyte stream in the membrane electrolysis process.
[0059] 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:
2NH.sub.3(g)+H.sub.2SO.sub.4(solution).fwdarw.(NH.sub.4).sub.2SO.sub.4(solution) (19)
[0060] The mixed solution of Li.sub.2SO.sub.4 and (NH.sub.4).sub.2SO.sub.4 obtained by complete neutralization of the spent anolyte is evaporated by salting out (NH.sub.4).sub.2SO.sub.4 from the mixed solution. Ammonium sulfate after washing from the mother brine and drying represents a commercial fertilizer sold on the market. The Li.sub.2SO.sub.4 solution obtained from the spent anolyte with a residual content of (NH.sub.4).sub.2SO.sub.4 is in turn alkalized using a part of the spent washing solution formed during the washing process of the LiOH.Math.H.sub.2O crystals.
[0061] After alkalinization, the solution is deammonized by aeration with a stream of atmospheric air. The deammonization process is described by the following chemical equation:
(NH.sub.4).sub.2SO.sub.4(solution)+2LiOH.sub.(solution).fwdarw.2NH.sub.3(g)+Li.sub.2SO.sub.4(solution)+2H.sub.2O (20)
[0062] 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.
[0063] The Li.sub.2SO.sub.4 solution subjected to the deammonization step is sent for additional strengthening by dissolving a predetermined mass quantity of the initial Li.sub.2SO.sub.4 salt and, after chemical and ion exchange purification, is used as a replenishing solution for the circulating anolyte stream.
[0064] 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.
[0065] A process flow diagram of the production of LiOH.Math.H.sub.2O from a material containing a lithium salt in the form of the LiCl or LiOH.Math.H.sub.2O salt is shown on
Cl.sup.??e.sup.?.fwdarw.? Cl.sub.2 (21)
[0066] In this case no acid is formed and only depletion of the anolyte in LiCl occurs during electrolysis.
[0067] In a general form, the process of electrochemical conversion of LiCl salt solution to LiOH solution can be described by the following overall reaction:
##STR00005##
[0068] 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 Li.sub.2SO.sub.4 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.Math.H.sub.2O 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 BaSO.sub.4 salt using BaCl.sub.2 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.
[0069] 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:
##STR00006##
[0070] 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 NH.sub.4Cl salt by evaporating the NH.sub.4Cl solution obtained by water absorption of the gaseous mixture of NH.sub.3 and Cl.sub.2 at a molar ratio of NH.sub.3:Cl.sub.2=8:3 according to the reaction:
8 NH.sub.3(g)+3 Cl.sub.2(g).fwdarw.6 NH.sub.4Cl.sub.(solution)+N.sub.2(g), (24)
[0071] or as a 6N HCl solution obtained by aqueous absorption of the gaseous mixture of NH.sub.3 and Cl.sub.2 at a molar ratio of NH.sub.3:Cl.sub.2=2:3 according to the reaction:
2 NH.sub.3(g)+3 Cl.sub.2(g).fwdarw.6 HCl.sub.(solution)+N.sub.2(g), (25)
[0072] or as a sodium hypochlorite solution (disinfecting and antiseptic solution) by absorbing chlorine with an aqueous solution of NaOH according to the reaction:
Cl.sub.2(g)+2 NaOH.sub.(solution).fwdarw.NaOCl.sub.(solution)+NaCl.sub.(solution)+H.sub.2O.sub.(l), (26)
[0073] or as neutral calcium hypochlorite by drying this Ca(OCl).sub.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:
Cl.sub.2(g)+NaOH.sub.(solution).fwdarw.NaOCl.sub.(solution)+??NaCl.sub.(s)?+(1???)NaCl.sub.(solution)+H.sub.2O.sub.(l) (27)
[0074] and the solution saturated with Ca(OCl).sub.2 obtained by the absorption of the half of the anodic chlorine by calcium hydroxide pulp according to the reaction:
2 Cl.sub.2(g)+2Ca(OH).sub.2(s, solution).fwdarw.Ca(OCl).sub.2(solution)+CaCl.sub.2(solution)+2 H.sub.2O.sub.(l) (28)
[0075] The main amount of calcium is precipitated from the mother liquor containing active chlorine, obtained upon conducting the exchange reaction and containing Ca.sup.2+, Na.sup.+, Cl.sup.?, OCl.sup.? ions, by introducing a predetermined amount of NaOH into the solution, according to the reaction:
Ca.sup.2+.sub.(solution)+2NaOH.sub.(solution).fwdarw.Ca(OH).sub.2(solution)?+2Na.sup.+.sub.(solution) (29)
[0076] The residual amount of calcium is removed from the solution by adding a predetermined amount of Na.sub.2CO.sub.3, according to the reaction:
Ca.sup.2+.sub.(solution)+Na.sub.2CO.sub.3(solution).fwdarw.CaCO.sub.3(g)?+2Na.sup.+.sub.(solution) (30)
[0077] The resulting Ca(OH).sub.2 precipitate with an admixture of CaCO.sub.3 is directed to the process of chlorination of the Ca(OH).sub.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).sub.2 pulp.
[0078] A process flow diagram of the production of LiOH.Math.H.sub.2O from a material containing a lithium salt in the form of the Li.sub.2CO.sub.3 salt is shown on
3 Cl.sub.2(g)+3Li.sub.2CO.sub.3(s)+2NH.sub.3(g).fwdarw.6 LiCl.sub.(solution)+N.sub.2(g)+3CO.sub.2(g)+3 H.sub.2O.sub.(l) (31)
[0079] 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 Li.sub.2CO.sub.3 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.
[0080] A process flow diagram of the production of LiOH.Math.H.sub.2O from a material containing a lithium salt in the form of a mixture of Li.sub.2SO.sub.4 and Li.sub.2CO.sub.3 is shown on
[0081] A process flow diagram of the production of LiOH.Math.H.sub.2O from materials containing a lithium salt in the form of a mixture of LiCl and Li.sub.2CO.sub.3 is shown on
[0082] A process flow diagram of the production of LiOH.Math.H.sub.2O from materials containing a lithium salt in the form of a mixture of Li.sub.2SO.sub.4 and LiCl is shown on
[0083] Preparation of LiOH.Math.H.sub.2O based on the electrochemical conversion of mixed solutions of Li.sub.2SO.sub.4 and LiCl does not require a special process for purifying the anolyte from sulfate ions. Otherwise, the technology described on
[0084] A process flow diagram of the production of LiOH.Math.H.sub.2O from materials containing a lithium salt in the form of a mixture of Li.sub.2SO.sub.4, LiCl and Li.sub.2CO.sub.3 is shown on
EXAMPLE 1
[0085] A laboratory scale apparatus containing a membrane electrolysis unit, a unit for processing catholyte into LiOH.Math.H.sub.2O, 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.Math.H.sub.2O 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
TABLE-US-00001 TABLE 1 Composition of technical grade Li.sub.2SO.sub.4 .Math. H.sub.2O Parameter name Content, wt. % Mass fraction of Li.sub.2SO.sub.4 .Math. H.sub.2O 98.10 Li.sub.3PO.sub.4 1.90 Na 0.020 K 0.003 Ca 0.0064 Mg 0.0002 Fe 0.0005 water 10.5 Cl + Fe not detected
TABLE-US-00002 TABLE 2 Composition of technical grade LiCl .Math. H.sub.2O Parameter name Content, wt. % Na + K 0.1 Ca + Mg 0.03 Fe 0.005 Al 0.01 Pb 0.003 PO.sub.4 0.007 SO.sub.4 0.1 OH 0.03
[0086] 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 CaCl.sub.2 produced by dissolving hydrated technical grade CaCl.sub.2.Math.6H.sub.2O salt.
[0087] The main comparative parameters and characteristics of LiOH.Math.H.sub.2O production technologies from various lithium salts according to the claimed method are shown in Table 3. The compositions of the respective resulting LiOH.Math.H.sub.2O samples are shown in Table 4.
TABLE-US-00003 TABLE 3 Comparative characteristics of technological processes for producing LiOH .Math. H.sub.2O from various lithium salts according to the claimed method The main parameters of the The solution used to replenish the anolyte LiOH .Math. H.sub.2O production Li.sub.2SO.sub.4 solution LiCl Li.sub.2SO.sub.4 + LiCl Current density, A/dm.sup.3 30 30 30 LiOH current output, % 59.8 60.6 60.1 Membrane type CTIEM-3 CTIEM-3 CTIEM-3 Cathode material nickel-plated nickel-plated nickel-plated stainless steel stainless steel stainless steel Anode material platinized titanium titanium coated platinized titanium with ruthenium oxide (ORTA) Material quantitative Li.sub.2SO.sub.4 - 205.6 LiCl - 217.6 Li.sub.2SO.sub.4 - 147.9 composition of the anolyte, H.sub.2SO.sub.4 - 38.7 pH = 1.5 LiCl - 102.3 g/dm.sup.3 H.sub.2SO.sub.4 - 20.5 Concentration of LiOH in the 48.8 49.4 49.1 catholyte, g/dm.sup.3 Chlorine current output, % 97.0 96.8 Composition of the spent LiOH- 120 LiOH- 120 LiOH- 120 catholyte from the evaporation (NaOH + KOH) - 8.7 (NaOH + KOH) - 9.1 (NaOH + KOH) - 8.2 and crystallization process, g/dm.sup.3 Recovery of LiOH in the final 96.7 90.1 97.4 product from LiOH conversion solution The degree of separation of 99.97 99.90 99.93 lithium and alkali (Na + K) during the recycling of spent catholyte from the evaporation and crystallization process
TABLE-US-00004 TABLE 4 Compositions of LiOH .Math. H.sub.2O samples obtained from various lithium salts by the claimed method Parameter Composition, wt. %, of LiOH .Math. H.sub.2O samples obtained from lithium salts name Li.sub.2SO.sub.4 .Math. H.sub.2O LiCl .Math. H.sub.2O Li.sub.2SO.sub.4 .Math. H.sub.2O and LiCl .Math. H.sub.2O LiOH 56.72 56.70 56.73 Carbonates (CO.sub.3.sup.2?) 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.sub.4 0.015 less than 0.01 less than 0.01 PO.sub.4 less than 0.005 less than 0.0005 less than 0.0005
[0088] As follows from the results, the claimed method allows producing a high-quality LiOH.Math.H.sub.2O 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.
[0089] 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%.
[0090] 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).sub.2, provided that this operation is carried out in two steps to completely neutralize H.sub.2SO.sub.4 in the anolyte without the need to introduce excess Ca(OH).sub.2.
[0091] Herewith at the first step contacting of the initial spent anolyte with the spent precipitate from the second step, which is a mixture of CaSO.sub.4.Math.2 H.sub.2O and Ca(OH).sub.2, takes place with guaranteed conversion of all free Ca(OH).sub.2 into CaSO.sub.4.Math.2 H.sub.2O and the withdrawal of the resulting CaSO.sub.4.Math.2 H.sub.2O precipitate by filtration. The filtrate containing the unreacted H.sub.2SO.sub.4 residue is brought into contact with Ca(OH).sub.2 taken in a stoichiometric ratio to the H.sub.2SO.sub.4 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 CaSO.sub.4.Math.2 H.sub.2O and Ca(OH).sub.2 is formed and complete neutralization of sulfuric acid is ensured. The contacting of the anolyte with Ca(OH).sub.2 is carried out under conditions of vigorous mixing.
EXAMPLE 2
[0092] 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 Li.sub.2SO.sub.4 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 solutionstitanium coated with ruthenium oxide (ORTA), for the electrolysis of Li.sub.2SO.sub.4 solutionsplatinized titanium. The results are shown in Table 5.
TABLE-US-00005 TABLE 5 The results of testing various cation-exchange membranes with respect to electrochemical conversion of Li.sub.2SO.sub.4 and LiCl solutions into a LiOH solution Solution used for conversion Aqueous Li.sub.2SO.sub.4 solution Aqueous LiCl solution Main parameters Nafion-438 CTIEM-3 MF-4SK-100 Nafion-438 CTIEM-3 MF-4SK-100 Current density, 30.0 30.0 30.0 35.0 35.0 35.0 A/dm.sup.2 Cell voltage - 4.9 5.0 5.0 3.3 4.0 4.0 the beginning of testing Composition of the Li.sub.2SO.sub.4 -200 Li.sub.2SO.sub.4 -200 Li.sub.2SO.sub.4 -200 LiCl - 220 LiCl - 220 LiCl - 220 anolyte, g/dm3 H.sub.2SO.sub.4 -60 H.sub.2SO.sub.4 -60 H.sub.2SO.sub.4 -60 pH - 2.0 pH - 2.0 pH - 2.0 Catholyte LiOH-65 LiOH-65 LiOH-65 LiOH-70 LiOH-70 LiOH-70 composition, g/dm.sup.3 NaOH- 0.060 NaOH- 0.061 NaOH- 0.062 NaOH- 0.31 NaOH- 0.30 NaOH- 0.31 Anolyte 65-70 65-70 65-70 80-85 80-85 80-85 temperature, ? C. Linear travel speed 36 36 36 36 36 36 of electrolytes in gas separators (gas purifiers), m/h Alkali current output the beginning of 60.5 60.0 59.6 60.5 60.0 59.7 testing the end of testing 60.7 60.0 59.6 60.4 60.0 59.6
[0093] 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 Li.sub.2SO.sub.4 solutions in comparison to LiCl solutions.
[0094] It follows from the obtained data that other cation-exchange membranes can be used for the conversion of Li.sub.2SO.sub.4 and LiCl solutions, equivalent to the tested ones and chemically stable in these media.
EXAMPLE 3
[0095] A laboratory apparatus made in accordance with the flow diagram shown on
TABLE-US-00006 TABLE 6 Composition of the technical grade lithium carbonate used Substance (element) insoluble Li.sub.2CO.sub.3 Cl Na K Ca Mg SO.sub.4 Fe.sub.2O.sub.3 residue LOI Content, 99.0 0.020 0.120 0.050 0.04 0.011 0.100 0.030 0.020 0.700 wt. %
[0096] The strengthened and purified salt solutions of lithium produced from spent anolyte streams were adjusted to the predetermined concentrations of Li.sub.2SO.sub.4 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.Math.H.sub.2O samples are shown in table 8. It can clearly be seen from the results obtained that the proposed method allows producing LiOH.Math.H.sub.2O as a product of high purity meeting the requirements of the LGO-1 grade from the technical grade lithium carbonate.
TABLE-US-00007 TABLE 7 The main parameters of the production of LiOH .Math. H.sub.2O from Li.sub.2CO.sub.3 by means of membrane electrolysis of highly soluble lithium salts Production of LiOH .Math. H.sub.2O from Li.sub.2CO.sub.3 by means of membrane electrolysis of highly soluble lithium salts Main parameters Li.sub.2SO.sub.4 salt solution LiCl salt solution Current density, A/dm.sup.2 30.0 30.0 Composition of the anolyte, g/dm.sup.3 Li.sub.2SO.sub.4 - 204 LiCl - 222 H.sub.2SO.sub.4 - 63 Composition of the catholyte, g/dm.sup.3 LiOH - 48.3 LiOH - 48.7 NaOH - 0.13 NaOH - 0.14 Temperature of electrolytes, ? C. 67 86 LiOH current output, % 60.0 60.7 Recovery of LiOH in the final product 95.9 95.9 from LiOH conversion solution, % Membrane type CTIEM-3 CTIEM-3 Anode type platinized titanium titanium coated with ruthenium oxide (ORTA) Concentration of HCl produced from 219.1 anodic chlorine, g/dm.sup.3 Concentration of the LiCl solution 255.1 produced from Li.sub.2CO.sub.3 and HCl, g/dm.sup.3 Concentration of the LiCl solution 253.4 produced by the absorption of anodic chlorine by the lithium carbonate pulp, in the presence of a reducing agent, g/dm.sup.3 Concentration of lithium salt in the (Li.sub.2SO.sub.4) (LiCl) purified LiCl solution fed to replenish 311 328 the circulating anolyte, g/dm.sup.3
TABLE-US-00008 TABLE 8 Compositions of LiOH .Math. H.sub.2O samples produced from Li.sub.2CO.sub.3 by means of membrane electrolysis of highly soluble lithium salts Composition, wt. %, of LiOH .Math. H.sub.2O samples produced from Li.sub.2CO.sub.3 by means of membrane electrolysis of highly soluble lithium salts solutions Parameter name Li.sub.2SO.sub.4 LiCl LiOH 56.71 56.70 carbonates (CO.sub.3.sup.2?) 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.sub.4 0.014 less than 0.010 PO.sub.4 not detected not detected
[0097] Herewith the recovery of conversion alkali (LiOH solution) as a solid product (LiOH.Math.H.sub.2O) significantly depends on the content of sodium and potassium in the initial lithium carbonate.
EXAMPLE 4
[0098] A laboratory bench represented by an assembly for the utilization of sulfate ions present in the H.sub.2SO.sub.4 salt was used for the testing the utilization option by converting the sulfuric acid contained in the spent sulfate anolyte into a (NH.sub.4).sub.2SO.sub.4 salt by contacting the spent anolyte with ammonia and salting out the (NH.sub.4).sub.2SO.sub.4 salt from a mixed spent solution of Li.sub.2SO.sub.4 and (NH.sub.4).sub.2SO.sub.4 during its evaporation accompanied by increasing the concentration of Li.sub.2SO.sub.4 in the anolyte. The option of the technological process for the utilization of sulfuric acid contained in the spent anolyte in the form of (NH.sub.4).sub.2SO.sub.4 salt is shown on
TABLE-US-00009 TABLE 9 The main parameters of the process of recycling the anodic sulfuric acid contained in the spent sulfate anolyte into (NH.sub.4).sub.2SO.sub.4 salts Values of Main parameters parameters Composition of the spent sulfate anolyte, Li.sub.2SO.sub.4 - 201.3 g/dm.sub.3 H.sub.2SO.sub.4 - 60.4 Composition of the spent anolyte following Li.sub.2SO.sub.4 - 201.8 contacting with ammonia, g/dm.sup.3 (NH.sub.4).sub.2SO.sub.4 - 81.3 Composition of lithium ammonium sulfate Li.sub.2SO.sub.4 - 261.3 solution following evaporation and salting out (NH.sub.4).sub.2SO.sub.4 - 9.4 of (NH.sub.4).sub.2SO.sub.4, g/dm.sup.3 Composition of the sulfate solution after Li.sub.2SO.sub.4 - 269.1 alkalinization and aeration, g/dm.sup.3 (NH.sub.4).sub.2SO.sub.4 < 0.05
[0099] The resulting samples of the (NH.sub.4).sub.2SO.sub.4 salt after 3-step countercurrent washing with demineralized water and drying at 110? C. contained the main substance in the form of (NH.sub.4).sub.2SO.sub.4 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%.
EXAMPLE 5
[0100] The spent catholyte stream of 10 dm.sup.3 having the following composition (g/dm.sup.3): LiOH120; NaOH8.7; KOH0.3, was recycled according to the claimed method (
REFERENCES
[0101] 1. RU patent No. 2071819, published on 20 Jan. 1997 [0102] 2. WO application Zealand No. 9859385, published on 1998 [0103] 3. RU patent No. 2157338, published on 10 Oct. 2000 [0104] 4. RU patent No. 21967335, published on 20 Jan. 2003 [0105] 5. RU patent No. 2656452, published on 5 Jun. 2018