Method for extracting rubidium and cesium salts from an environmentally friendly lithium mica lithium precipitation mother liquor

Abstract

The application discloses a method for extracting rubidium and cesium salts from lithium mica lithium precipitation mother liquor, and particularly relates to the following steps: acidizing the lithium precipitation mother liquor, then alkalinizing, concentrating and filtering to remove most of potassium and sodium salts after pH reaches a requirement, and then extracting and separating rubidium and cesium, so that valuable metal elements of rubidium and cesium are comprehensively utilized, and considerable economic benefits can be generated. The application has the advantages of short technological process, simple operation, strong continuity, large processing capacity, low production cost, high total recovery rate, and the like. The wastewater is returned to a lithium precipitation workshop, and the process is internally circulated, so that the wastewater discharge is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium sink solution treatment, in particular to an environment-friendly method for extracting rubidium and cesium salts from lithium mica lithium sink solution. BACKGROUND

[0002] China is rich in rubidium and cesium resources. Rubidium and cesium resources in solid form mainly exist in lepidolite and pollucite. Rubidium and cesium resources in liquid form mainly exist in salt lakes and geothermal water in Qinghai and Tibet. No matter the initial output form is solid ore or liquid ore, the separation of rubidium and cesium can only be realized in aqueous solution. Rubidium and cesium are rare non-ferrous metals, and the world reserves are very small. Both of them are typical dispersed elements, and are rarely formed into single minerals, but are often mixed in lithium ores. At present, most of the ore extraction lithium processes use lepidolite as the main ore, and rubidium and cesium elements are separated and extracted from the lithium sink solution of lepidolite, which can produce considerable economic benefits. At present, the methods for separating and extracting rubidium and cesium mainly include precipitation method, ion exchange method and solvent extraction method. The precipitation method has long process, low recovery rate and low product purity, and is mainly used for analysis and testing or crude product purification. The ion exchange method has simple process, good selectivity and high recovery rate, but the exchange capacity of the ion exchange agent is relatively small, and it is suitable for low-concentration rubidium and cesium separation and extraction. The solvent extraction method has large treatment capacity, good separation effect and easy continuous operation, and is a kind of separation and extraction technology which is studied more and developed faster. SUMMARY

[0003] Therefore, the present application provides an environment-friendly method for extracting rubidium and cesium salts from lithium mica lithium sink solution, and the steps include:

[0004] (1) adding dibenzo-18-crown-6 ether into N,N-dimethylformamide in a reaction kettle, stirring for more than 5 min, then adding glacial acetic acid into the reaction kettle under stirring, stirring for more than 20 min after the completion of feeding, then adding concentrated nitric acid into the reaction kettle under stirring, stirring for more than 30 min after the completion of feeding, then sealing the reaction kettle, heating to 130±5℃ and keeping for more than 2 h, cooling to room temperature after the end of keeping, opening the reaction kettle, then adding palladium-carbon catalyst and hydrazine hydrate into the reaction kettle, sealing the reaction kettle again, heating to 120±3℃ and keeping for more than 1 h, then naturally cooling to room temperature, opening the reaction kettle, removing the catalyst by centrifugation, then adding 4-nitrophenyl isocyanate into the liquid under stirring after centrifugation, stirring at room temperature for more than 8 h after the completion of feeding, then removing N,N-dimethylformamide by reduced pressure distillation, and obtaining an extraction promoter;

[0005] (2) acidifying the lithium precipitation mother liquor to remove carbonate in the lithium precipitation mother liquor to obtain an acidified solution; adding alkali to the acidified solution to adjust the pH to 8-10, then concentrating, precipitating potassium and sodium salt crystals, removing the precipitates by solid-liquid separation to obtain a concentrated solution, adding alkali to the concentrated solution to adjust the pH to 10-12, adding a primary extractant to the concentrated solution to perform extraction to obtain a cesium-loaded organic phase and a primary extraction residual solution; the primary extractant is a mixture of 4-tert-butyl-2-(α-methylbenzyl) phenol, the extraction promoter and sulfonated kerosene; washing, back-extracting and crystallizing the cesium-loaded organic phase to obtain a cesium salt;

[0006] (3) adding alkali to the primary extraction residual solution to adjust the pH to 12-14, then adding a secondary extractant to perform extraction to obtain a rubidium-loaded organic phase and an extracted solution; the secondary extractant is a mixture of 4-tert-butyl-2-(α-methylbenzyl) phenol, the extraction promoter, N-butyl-N-methyl pyrrolidine bis(trifluoromethanesulfonyl) imide salt and sulfonated kerosene; washing, back-extracting and crystallizing the rubidium-loaded organic phase to obtain a rubidium salt.

[0007] Further, in the step (1), the mass ratio of the dibenzo-18-crown-6 ether to N,N-dimethylformamide is dibenzo-18-crown-6 ether:N,N-dimethylformamide = 1:50.

[0008] Further, in the step (1), the amount of the glacial acetic acid, concentrated nitric acid, palladium-carbon catalyst, hydrazine hydrate and 4-nitrophenyl isocyanate added is 1 part of dibenzo-18-crown-6 ether, 14-18 parts of glacial acetic acid, 1-2 parts of concentrated nitric acid, 0.03-0.04 parts of palladium-carbon catalyst, 4-6 parts of hydrazine hydrate and 0.8-1.6 parts of 4-nitrophenyl isocyanate by weight fraction in the reaction kettle; wherein the mass percentage of the solute in the concentrated nitric acid is 68%, and the palladium-carbon catalyst is 10% Pd / C.

[0009] Further, in the step (2), the acidification of the lithium precipitation mother liquor is to add sulfuric acid with a solute mass percentage of 98% to the lithium precipitation mother liquor to adjust the pH of the mother liquor to 1-2; the alkali is sodium hydroxide.

[0010] Further, in the step (2), the mass ratio of the components in the primary extractant is 4-tert-butyl-2-(α-methylbenzyl) phenol:extraction promoter:sulfonated kerosene = 2:0.5-0.6:1; the mass ratio of the primary extractant to the concentrated solution for extraction is primary extractant:concentrated solution = 1-2:1, and the stirring extraction is performed for 3-5 min; the back-extraction uses sulfuric acid with a solute mass percentage of 98%, and the mass ratio of the sulfuric acid to the back-extraction organic phase is back-extraction organic phase:sulfuric acid = 15:1.

[0011] Further, in the step (3), the mass ratio of each component in the secondary extraction agent is 4-tert-butyl-2-(α-methylbenzyl) phenol: extraction promoter: N-butyl-N-methyl pyrrolidine bis(trifluoromethane sulfonate) imidate salt: sulfonated kerosene = 3: 0.6-0.7: 0.2-0.4: 2; the mass ratio of the secondary extraction agent to the primary extraction residual liquid is 10:1 for extraction by adding the secondary extraction agent to the primary extraction residual liquid, and the stirring extraction is performed for 3-5 min; and the stripping uses sulfuric acid with a solute mass percentage of 98%, and the mass ratio of the sulfuric acid to the organic phase for stripping is 15:1.

[0012] The method has the advantages that the rubidium and cesium elements in the lithium mica lithium precipitation mother liquor can be efficiently extracted, the valuable metal elements of rubidium and cesium are comprehensively utilized, the waste of resources is reduced, and considerable economic benefits can be obtained. The prior art discloses a process using only 4-tert-butyl-2-(α-methylbenzyl) phenol and sulfonated kerosene, but 4-tert-butyl-2-(α-methylbenzyl) phenol has a large extraction effect on potassium and sodium ions, thus forming an ion competition effect, and part of the extraction agent resources is occupied by potassium ions and sodium ions, thereby reducing the extraction rate of the target ions Cs + and Rb + . As compared with Example 3 and the comparative example, the addition of the extraction promoter can further improve the extraction rate of rubidium and cesium. The present application first introduces a nitro group on the diphenyl-18-crown-6 ether, then reduces and aminates the nitro group, and then introduces an active group on the amino group through 4-nitrophenyl isocyanate, thereby improving the coordination ability of the extraction promoter to Cs + and Rb + ions in the aqueous phase, improving the efficiency of the extraction promoter in forming a complex with Cs + and Rb + ions; on the other hand, the selectivity of the extraction promoter to ions reduces the coordination of potassium and sodium ions, so that the target ions and impurity ions are separated. In the extraction process, Cs + and Rb + ions are first coordinated with the extraction promoter to enter the oil phase. Since 4-tert-butyl-2-(α-methylbenzyl) phenol has a stronger coordination ability to Cs + and Rb + ions, and the formed complex is more stable, the complex of the extraction promoter and Cs + and Rb + ions in the oil phase is easily converted into the complex of 4-tert-butyl-2-(α-methylbenzyl) phenol and Cs + and Rb + ions, so that the extraction promoter can be coordinated with Cs+ ions, Rb + Ions are recycled. In addition, the addition of N-butyl-N-methylpyrrolidine bis(trifluoromethanesulfonyl)imide salt can improve the extraction of rubidium by the extractant, which may be due to the fact that N-butyl-N-methylpyrrolidine bis(trifluoromethanesulfonyl)imide salt can improve the hydrophilicity of the extraction promoter and promote the coordination of the extraction promoter to ions. The process of the present invention is short, simple to operate, has strong production continuity, large processing capacity, low production cost, high total recovery rate, and the wastewater is returned to the lithium precipitation workshop for internal circulation in the process, which can reduce the discharge of wastewater. DETAILED DESCRIPTION

[0013] The present invention will be further described below with reference to the embodiments.

[0014] Example 1

[0015] An environmentally friendly method for extracting rubidium and cesium salts from lithium-precipitated lepidolite mother liquor, comprising the following steps:

[0016] (1) Add dibenzo-18-crown-6 ether to N,N-dimethylformamide in a reactor, and add dibenzo-18-crown-6 ether to N,N-dimethylformamide in a mass ratio of dibenzo-18-crown-6 ether to N,N-dimethylformamide at 1:50; stir for 5 minutes, then add glacial acetic acid to the reactor under stirring, stir for 20 minutes after the addition is completed, then add concentrated nitric acid to the reactor under stirring, stir for 30 minutes after the addition is completed, then seal the reactor, heat to 130±5°C and keep warm for 2 hours, cool to room temperature after the end of the insulation, open the reactor, and then add palladium carbon catalyst and hydrazine hydrate to the reactor, seal the reactor again after the addition is completed, heat to 120±3°C and keep warm for 2 hours. The mixture was stirred at room temperature for 1 hour, then naturally cooled to room temperature, the reactor was opened, the catalyst was removed by centrifugation, 4-nitrobenzene isocyanate was added to the liquid after centrifugation under stirring, and after the addition was completed, the mixture was stirred at room temperature for 8 hours, and then N,N-dimethylformamide was removed by distillation under reduced pressure to obtain an extraction promoter; wherein the amount of glacial acetic acid, concentrated nitric acid, palladium-carbon catalyst, hydrazine hydrate and 4-nitrobenzene isocyanate added to the amount of dibenzo-18-crown-6 ether added to the reactor was calculated in parts by weight as follows: 1 part of dibenzo-18-crown-6 ether, 14 parts of glacial acetic acid, 1 part of concentrated nitric acid, 0.03 parts of palladium-carbon catalyst, 4 parts of hydrazine hydrate, and 0.8 parts of 4-nitrobenzene isocyanate; wherein the mass percentage of the solute in the concentrated nitric acid is 68%, and the palladium-carbon catalyst is 10% Pd / C;

[0017] (2) the lithium sink mother liquor (ingredients as shown in Table 1) is acidified to remove carbonate in the lithium sink mother liquor to obtain an acidified solution; the lithium sink mother liquor is acidified by adding 98% sulfuric acid to the lithium sink mother liquor to adjust the pH of the mother liquor to 2; sodium hydroxide is added to the acidified solution to adjust the pH to 9, and then concentrated; due to the relatively large content of potassium and sodium salt, it is easier to reach the saturation state first, so part of the potassium and sodium salt is precipitated first, which can remove most of the potassium and sodium salt on the one hand, and enrich rubidium and cesium in the lithium sink mother liquor on the other hand; solid-liquid separation is performed to remove the precipitate to obtain a concentrated solution, and then sodium hydroxide is added to adjust the pH of the concentrated solution to 11; a primary extractant is added to the concentrated solution for extraction to obtain a cesium-loaded organic phase and a primary extraction residual solution; the primary extractant is a mixture of 4-tert-butyl-2-(α-methylbenzyl) phenol, the extraction promoter and sulfonated kerosene; the mass ratio of each component in the primary extractant is 4-tert-butyl-2-(α-methylbenzyl) phenol: extraction promoter: sulfonated kerosene = 2:0.5:1; the mass ratio of the primary extractant to the concentrated solution for extraction is 1:1, and the stirring extraction time is 5 min; the cesium salt is obtained by washing, back-extracting and crystallizing the cesium-loaded organic phase; the back-extraction uses 98% sulfuric acid, and the mass ratio of the added sulfuric acid to the back-extracted organic phase is back-extracted organic phase:sulfuric acid = 15:1;

[0018] (3) sodium hydroxide is added to adjust the pH of the primary extraction residual solution to 13, and then a secondary extractant is added for extraction to obtain a rubidium-loaded organic phase and an extracted solution; the secondary extractant is a mixture of 4-tert-butyl-2-(α-methylbenzyl) phenol, the extraction promoter, N-butyl-N-methyl pyrrolidine bis(trifluoromethanesulfonyl) imide salt and sulfonated kerosene; the mass ratio of each component in the secondary extractant is 4-tert-butyl-2-(α-methylbenzyl) phenol: extraction promoter: N-butyl-N-methyl pyrrolidine bis(trifluoromethanesulfonyl) imide salt: sulfonated kerosene = 3:0.6:0.2:2; the mass ratio of the secondary extractant to the primary extraction residual solution for extraction is 10:1, and the stirring extraction time is 5 min; the rubidium salt is obtained by washing, back-extracting and crystallizing the rubidium-loaded organic phase; the back-extraction uses 98% sulfuric acid, and the mass ratio of the added sulfuric acid to the back-extracted organic phase is back-extracted organic phase:sulfuric acid = 15:1.

[0019] Example 2

[0020] An environmentally friendly method for extracting rubidium and cesium salt from lithium mica lithium sink mother liquor, the steps comprising:

[0021] (1) in the reaction kettle, diphenyl-18-crown-6 ether is added into N,N-dimethylformamide, the mass ratio of diphenyl-18-crown-6 ether to N,N-dimethylformamide is diphenyl-18-crown-6 ether: N,N-dimethylformamide = 1:50; stir for 5 min, then add glacial acetic acid into the reaction kettle under stirring, stir for 20 min after the completion of feeding, then add concentrated nitric acid into the reaction kettle under stirring, stir for 30 min after the completion of feeding, then seal the reaction kettle, heat to 130±5℃ and keep for 2 h, cool to room temperature after the end of keeping, open the reaction kettle, then add palladium-carbon catalyst and hydrazine hydrate into the reaction kettle, seal the reaction kettle again after the completion of feeding, heat to 120±3℃ and keep for 1 h, then cool to room temperature naturally, open the reaction kettle, centrifuge to remove the catalyst, then add 4-nitrophenyl isocyanate into the liquid under stirring after centrifugation, stir for 8 h at room temperature after the completion of feeding, then remove N,N-dimethylformamide by distillation under reduced pressure, to obtain an extraction promoter; wherein the amount of glacial acetic acid, concentrated nitric acid, palladium-carbon catalyst, hydrazine hydrate and 4-nitrophenyl isocyanate added is 16 parts, 1 part, 0.03 part, 5 parts and 1 part respectively, based on the amount of diphenyl-18-crown-6 ether added into the reaction kettle; wherein the mass percentage of solute in the concentrated nitric acid is 68%, and the palladium-carbon catalyst is 10% Pd / C;

[0022] (2) the lithium precipitation mother liquor (ingredients are shown in Table 1) is acidified to remove carbonate in the lithium precipitation mother liquor, to obtain an acidified liquid; the lithium precipitation mother liquor is acidified by adding 98% sulfuric acid into the lithium precipitation mother liquor to adjust the pH of the mother liquor to 2; sodium hydroxide is added into the acidified liquid to adjust the pH to 9, then concentrated; since the content of potassium and sodium salt is relatively large, it is easier to reach the saturation state first, so part of the potassium and sodium salt is precipitated first, which can remove most of the potassium and sodium salt on the one hand, and enrich rubidium and cesium in the lithium precipitation mother liquor on the other hand; the precipitate is removed by solid-liquid separation to obtain a concentrated liquid, then sodium hydroxide is added to adjust the pH of the concentrated liquid to 11, a primary extractant is added into the concentrated liquid for extraction, to obtain a cesium-loaded organic phase and a primary extraction residual liquid; the primary extractant is a mixture of 4-tert-butyl-2-(α-methylbenzyl) phenol, the extraction promoter and sulfonated kerosene; the mass ratio of each component in the primary extractant is 4-tert-butyl-2-(α-methylbenzyl) phenol: extraction promoter: sulfonated kerosene = 2:0.5:1; the mass ratio of the primary extractant to the concentrated liquid is 1:1 when the primary extractant is added into the concentrated liquid for extraction, and the stirring extraction is carried out for 5 min; the cesium salt is obtained by washing, back extraction and crystallization separation of the cesium-loaded organic phase; the back extraction uses 98% sulfuric acid, and the mass ratio of sulfuric acid to back extraction organic phase is back extraction organic phase: sulfuric acid = 15:1;

[0023] (3) adding sodium hydroxide to adjust the pH of the primary extraction residual liquid to 13, and then adding a secondary extraction agent for extraction to obtain a rubidium-loaded organic phase and an after-extraction liquid; the secondary extraction agent is a mixture of 4-tert-butyl-2-(α-methylbenzyl) phenol, the extraction promoter, N-butyl-N-methyl pyrrolidine bis(trifluoromethanesulfonyl) imide salt and sulfonated kerosene; the mass ratio of the components in the secondary extraction agent is 4-tert-butyl-2-(α-methylbenzyl) phenol: extraction promoter: N-butyl-N-methyl pyrrolidine bis(trifluoromethanesulfonyl) imide salt: sulfonated kerosene = 3:0.6:0.3:2; the mass ratio of the secondary extraction agent to the primary extraction residual liquid for extraction is secondary extraction agent: primary extraction residual liquid = 10:1, and the extraction is stirred for 5 min; the rubidium-loaded organic phase is washed, stripped, and crystallized to separate to obtain a rubidium salt; the stripping uses sulfuric acid with a solute mass percentage of 98%, and the mass ratio of the sulfuric acid to the stripped organic phase is stripped organic phase: sulfuric acid = 15:1.

[0024] Example 3

[0025] An environment-friendly method for extracting rubidium and cesium salts from a lithium mica lithium precipitation mother liquor, comprising the following steps:

[0026] (1) adding dibenzo-18-crown-6 ether into N,N-dimethylformamide in a reaction kettle, the mass ratio of dibenzo-18-crown-6 ether to N,N-dimethylformamide is dibenzo-18-crown-6 ether: N,N-dimethylformamide = 1:50; stirring for 5 min, then adding glacial acetic acid into the reaction kettle under stirring, stirring for 20 min after the completion of feeding, then adding concentrated nitric acid into the reaction kettle under stirring, stirring for 30 min after the completion of feeding, then sealing the reaction kettle, heating to 130±5℃ for 2 h, cooling to room temperature after the completion of heat preservation, opening the reaction kettle, then adding palladium-carbon catalyst and hydrazine hydrate into the reaction kettle, sealing the reaction kettle again after the completion of feeding, heating to 120±3℃ for 1 h, then naturally cooling to room temperature, opening the reaction kettle, removing the catalyst by centrifugation, then adding 4-nitrophenyl isocyanate into the liquid after centrifugation under stirring, stirring at room temperature for 8 h after the completion of feeding, then removing N,N-dimethylformamide by reduced pressure distillation to obtain an extraction promoter; wherein the amounts of the glacial acetic acid, concentrated nitric acid, palladium-carbon catalyst, hydrazine hydrate and 4-nitrophenyl isocyanate added are 16 parts, 2 parts, 0.04 parts, 5 parts and 1.2 parts of glacial acetic acid, concentrated nitric acid, palladium-carbon catalyst, hydrazine hydrate and 4-nitrophenyl isocyanate per 1 part of dibenzo-18-crown-6 ether added into the reaction kettle, respectively; wherein the mass percentage of the solute in the concentrated nitric acid is 68%, and the palladium-carbon catalyst is 10% Pd / C;

[0027] (2) the lithium sink mother liquor (ingredients as shown in Table 1) is acidified to remove carbonate in the lithium sink mother liquor to obtain an acidified solution; the lithium sink mother liquor is acidified by adding 98% sulfuric acid to the lithium sink mother liquor to adjust the pH of the mother liquor to 2; sodium hydroxide is added to the acidified solution to adjust the pH to 9, and then concentrated; due to the relatively large content of potassium and sodium salt, it is easier to reach the saturation state first, so part of the potassium and sodium salt is precipitated first, which can remove most of the potassium and sodium salt on the one hand, and enrich rubidium and cesium in the lithium sink mother liquor on the other hand; solid-liquid separation is performed to remove the precipitate to obtain a concentrated solution, and then sodium hydroxide is added to adjust the pH of the concentrated solution to 11; a primary extractant is added to the concentrated solution for extraction to obtain a cesium-loaded organic phase and a primary extraction residual solution; the primary extractant is a mixture of 4-tert-butyl-2-(α-methylbenzyl) phenol, the extraction promoter and sulfonated kerosene; the mass ratio of each component in the primary extractant is 4-tert-butyl-2-(α-methylbenzyl) phenol: extraction promoter: sulfonated kerosene = 2:0.6:1; the mass ratio of the primary extractant to the concentrated solution for extraction is 1:1, and the stirring extraction time is 5 min; the cesium salt is obtained by washing, back-extracting and crystallizing the cesium-loaded organic phase; the back-extraction uses 98% sulfuric acid, and the mass ratio of the added sulfuric acid to the back-extracted organic phase is back-extracted organic phase:sulfuric acid = 15:1;

[0028] (3) sodium hydroxide is added to adjust the pH of the primary extraction residual solution to 13, and then a secondary extractant is added for extraction to obtain a rubidium-loaded organic phase and an extracted solution; the secondary extractant is a mixture of 4-tert-butyl-2-(α-methylbenzyl) phenol, the extraction promoter, N-butyl-N-methyl pyrrolidine bis(trifluoromethanesulfonyl) imide salt and sulfonated kerosene; the mass ratio of each component in the secondary extractant is 4-tert-butyl-2-(α-methylbenzyl) phenol: extraction promoter: N-butyl-N-methyl pyrrolidine bis(trifluoromethanesulfonyl) imide salt: sulfonated kerosene = 3:0.7:0.3:2; the mass ratio of the secondary extractant to the primary extraction residual solution for extraction is 10:1, and the stirring extraction time is 5 min; the rubidium salt is obtained by washing, back-extracting and crystallizing the rubidium-loaded organic phase; the back-extraction uses 98% sulfuric acid, and the mass ratio of the added sulfuric acid to the back-extracted organic phase is back-extracted organic phase:sulfuric acid = 15:1.

[0029] Example 4

[0030] An environmentally friendly method for extracting rubidium and cesium salts from lithium mica lithium sink mother liquor, comprising the following steps:

[0031] (1) in the reaction kettle, diphenyl-18-crown-6 ether is added into N,N-dimethylformamide, the mass ratio of diphenyl-18-crown-6 ether to N,N-dimethylformamide is diphenyl-18-crown-6 ether: N,N-dimethylformamide = 1:50; stir for 5 min, then add glacial acetic acid into the reaction kettle under stirring, stir for 20 min after the completion of feeding, then add concentrated nitric acid into the reaction kettle under stirring, stir for 30 min after the completion of feeding, then seal the reaction kettle, heat to 130±5℃ and keep for 2 h, cool to room temperature after the end of keeping, open the reaction kettle, then add palladium-carbon catalyst and hydrazine hydrate into the reaction kettle, seal the reaction kettle again after the completion of feeding, heat to 120±3℃ and keep for 1 h, then cool to room temperature naturally, open the reaction kettle, centrifuge to remove the catalyst, then add 4-nitrophenyl isocyanate into the liquid under stirring after centrifugation, stir at room temperature for 8 h after the completion of feeding, then remove N,N-dimethylformamide by distillation under reduced pressure, to obtain an extraction promoter; wherein the amount of glacial acetic acid, concentrated nitric acid, palladium-carbon catalyst, hydrazine hydrate and 4-nitrophenyl isocyanate added is 18 parts, 2 parts, 0.04 parts, 6 parts and 1.6 parts respectively, based on the amount of diphenyl-18-crown-6 ether added into the reaction kettle; wherein the mass percentage of solute in the concentrated nitric acid is 68%, and the palladium-carbon catalyst is 10% Pd / C;

[0032] (2) the lithium precipitation mother liquor (ingredients are shown in Table 1) is acidified to remove carbonate in the lithium precipitation mother liquor, to obtain an acidified liquid; the lithium precipitation mother liquor is acidified by adding 98% sulfuric acid into the lithium precipitation mother liquor to adjust the pH of the mother liquor to 2; sodium hydroxide is added into the acidified liquid to adjust the pH to 9, then concentrated; since the content of potassium and sodium salt is relatively large, it is easier to reach the saturation state first, so part of the potassium and sodium salt is precipitated first, which can remove most of the potassium and sodium salt on the one hand, and enrich rubidium and cesium in the lithium precipitation mother liquor on the other hand; the precipitate is removed by solid-liquid separation to obtain a concentrated liquid, then sodium hydroxide is added to adjust the pH of the concentrated liquid to 11, a primary extractant is added into the concentrated liquid for extraction, to obtain a cesium-loaded organic phase and a primary extraction residual liquid; the primary extractant is a mixture of 4-tert-butyl-2-(α-methylbenzyl) phenol, the extraction promoter and sulfonated kerosene; the mass ratio of each component in the primary extractant is 4-tert-butyl-2-(α-methylbenzyl) phenol: extraction promoter: sulfonated kerosene = 2:0.6:1; the mass ratio of the primary extractant to the concentrated liquid is 1:1 when the primary extractant is added into the concentrated liquid for extraction, and the stirring extraction is carried out for 5 min; the cesium salt is obtained by washing, back extraction and crystallization separation of the cesium-loaded organic phase; the back extraction uses 98% sulfuric acid, and the mass ratio of sulfuric acid to back extraction organic phase is back extraction organic phase: sulfuric acid = 15:1;

[0033] (3) adding sodium hydroxide to adjust the pH of the primary extraction residual liquid to 13, then adding a secondary extraction agent for extraction, to obtain a rubidium-loaded organic phase and an extracted liquid; the secondary extraction agent is a mixture of 4-tert-butyl-2-(a-methylbenzyl) phenol, the extraction promoter, N-butyl-N-methyl pyrrolidine bis(trifluoromethanesulfonyl) imide salt and sulfonated kerosene; the mass ratio of each component in the secondary extraction agent is 4-tert-butyl-2-(a-methylbenzyl) phenol: extraction promoter: N-butyl-N-methyl pyrrolidine bis(trifluoromethanesulfonyl) imide salt: sulfonated kerosene = 3:0.7:0.4:2; the mass ratio of the secondary extraction agent to the primary extraction residual liquid for extraction is secondary extraction agent: primary extraction residual liquid = 10:1, stirring extraction for 5 min; washing, stripping and crystallization separation of the rubidium-loaded organic phase to obtain rubidium salt; the stripping uses sulfuric acid with a solute mass percentage of 98%, and the mass ratio of sulfuric acid to the stripping organic phase is stripping organic phase: sulfuric acid = 15:1.

[0034] Comparative Example 1

[0035] A method for extracting rubidium and cesium salts from a lithium mica lithium precipitation mother liquor as a comparison, the steps comprising:

[0036] (1) acidifying the lithium precipitation mother liquor (the composition is shown in Table 1) to remove carbonate in the lithium precipitation mother liquor to obtain an acidified liquid; the lithium precipitation mother liquor is acidified by adding sulfuric acid with a solute mass percentage of 98% to the lithium precipitation mother liquor to adjust the pH of the mother liquor to 2; adding sodium hydroxide to the acidified liquid to adjust the pH to 9, then concentrating, since the content of potassium and sodium salt is relatively large, it is easier to reach the saturation state first, so part of the potassium and sodium salt is precipitated first, on the one hand, most of the potassium and sodium salt can be removed, on the other hand, the rubidium and cesium in the lithium precipitation mother liquor can be enriched; removing the precipitate by solid-liquid separation to obtain a concentrated liquid, then adding sodium hydroxide to adjust the pH of the concentrated liquid to 11, adding a primary extraction agent to the concentrated liquid for extraction to obtain a cesium-loaded organic phase and a primary extraction residual liquid; the primary extraction agent is a mixture of 4-tert-butyl-2-(a-methylbenzyl) phenol and sulfonated kerosene; the mass ratio of each component in the primary extraction agent is 4-tert-butyl-2-(a-methylbenzyl) phenol: sulfonated kerosene = 2:1; the mass ratio of the primary extraction agent to the concentrated liquid for extraction is primary extraction agent: concentrated liquid = 1:1, stirring extraction for 5 min; washing, stripping and crystallization separation of the cesium-loaded organic phase to obtain cesium salt; the stripping uses sulfuric acid with a solute mass percentage of 98%, and the mass ratio of sulfuric acid to the stripping organic phase is stripping organic phase: sulfuric acid = 15:1;

[0037] (2) adding sodium hydroxide to adjust the pH of the primary extraction residual liquid to 13, then adding a secondary extraction agent for extraction to obtain a loaded rubidium organic phase and an after-extraction liquid; the secondary extraction agent is a mixture of 4-tert-butyl-2-(a-methylbenzyl) phenol, N-butyl-N-methyl pyrrolidine bis(trifluoromethane sulfonate) imide salt and sulfonated kerosene; the mass ratio of each component in the secondary extraction agent is 4-tert-butyl-2-(a-methylbenzyl) phenol:N-butyl-N-methyl pyrrolidine bis(trifluoromethane sulfonate) imide salt:sulfonated kerosene = 3:0.3:2; the mass ratio of the secondary extraction agent to the primary extraction residual liquid for extraction is secondary extraction agent:primary extraction residual liquid = 10:1, and stirring extraction is performed for 5 min; the loaded rubidium organic phase is subjected to washing, back extraction, and crystallization separation to obtain a rubidium salt; the back extraction uses sulfuric acid with a solute mass percentage of 98%, and the mass ratio of the added sulfuric acid to the back-extracted organic phase is back-extracted organic phase:sulfuric acid = 15:1.

[0038] Comparative Example 2

[0039] A method for extracting rubidium and cesium salts from a lithium mica lithium precipitation mother liquor as a comparison, the steps comprising:

[0040] (1) acidifying the lithium precipitation mother liquor (the components are shown in Table 1) to remove carbonate in the lithium precipitation mother liquor to obtain an after-acidification liquid; the lithium precipitation mother liquor is acidified by adding sulfuric acid with a solute mass percentage of 98% to the lithium precipitation mother liquor to adjust the pH of the mother liquor to 2; sodium hydroxide is added to the after-acidification liquid to adjust the pH to 9, and then concentrated; due to the relatively large content of potassium and sodium salts, it is easier to reach a saturated state first, so part of the potassium and sodium salts are precipitated first, which can remove most of the potassium and sodium salts on the one hand, and enrich rubidium and cesium in the lithium precipitation mother liquor on the other hand; solid-liquid separation is performed to remove the precipitates to obtain a concentrated liquid, and then sodium hydroxide is added to adjust the pH of the concentrated liquid to 11; a primary extraction agent is added to the concentrated liquid for extraction to obtain a loaded cesium organic phase and a primary extraction residual liquid; the primary extraction agent is a mixture of 4-tert-butyl-2-(a-methylbenzyl) phenol, dibenzo-18-crown-6 ether and sulfonated kerosene; the mass ratio of each component in the primary extraction agent is 4-tert-butyl-2-(a-methylbenzyl) phenol:dibenzo-18-crown-6 ether:sulfonated kerosene = 2:0.6:1; the mass ratio of the primary extraction agent to the concentrated liquid for extraction is primary extraction agent:concentrated liquid = 1:1, and stirring extraction is performed for 5 min; the loaded cesium organic phase is subjected to washing, back extraction, and crystallization separation to obtain a cesium salt; the back extraction uses sulfuric acid with a solute mass percentage of 98%, and the mass ratio of the added sulfuric acid to the back-extracted organic phase is back-extracted organic phase:sulfuric acid = 15:1;

[0041] (2) adding sodium hydroxide to adjust the pH of the primary extraction residual liquid to 13, then adding a secondary extraction agent for extraction to obtain a rubidium-loaded organic phase and an after-extraction liquid; the secondary extraction agent is a mixture of 4-tert-butyl-2-(α-methylbenzyl) phenol, dibenzo-18-crown-6 ether, N-butyl-N-methyl pyrrolidine bis(trifluoromethanesulfonyl) imide salt and sulfonated kerosene; the mass ratio of each component in the secondary extraction agent is 4-tert-butyl-2-(α-methylbenzyl) phenol:dibenzo-18-crown-6 ether:N-butyl-N-methyl pyrrolidine bis(trifluoromethanesulfonyl) imide salt:sulfonated kerosene = 3:0.7:0.3:2; the mass ratio of the secondary extraction agent to the primary extraction residual liquid for extraction is secondary extraction agent:primary extraction residual liquid = 10:1, and the extraction is stirred for 5 min; the rubidium-loaded organic phase is washed, back-extracted and crystallized to separate to obtain a rubidium salt; the back-extraction uses sulfuric acid with a solute mass percentage of 98%, and the mass ratio of sulfuric acid to back-extraction organic phase is back-extraction organic phase:sulfuric acid = 15:1.

[0042] Comparative Example 3

[0043] A method for extracting rubidium and cesium salts from a lithium mica lithium precipitation mother liquor as a comparison, the steps comprising:

[0044] (1) adding dibenzo-18-crown-6 ether into N,N-dimethylformamide in a reaction kettle, the mass ratio of dibenzo-18-crown-6 ether to N,N-dimethylformamide is dibenzo-18-crown-6 ether:N,N-dimethylformamide = 1:50; stirring for 5 min, then adding glacial acetic acid into the reaction kettle under stirring, stirring for 20 min after the completion of feeding, then adding concentrated nitric acid into the reaction kettle under stirring, stirring for 30 min after the completion of feeding, then sealing the reaction kettle, heating to 130±5℃ for 2 h, cooling to room temperature after the completion of heat preservation, opening the reaction kettle, then adding palladium-carbon catalyst and hydrazine hydrate into the reaction kettle, sealing the reaction kettle again after the completion of feeding, heating to 120±3℃ for 1 h, then naturally cooling to room temperature, opening the reaction kettle, centrifuging to remove the catalyst, and removing N,N-dimethylformamide by reduced pressure distillation after centrifugation to obtain the extraction promoter of the present comparative example; wherein the amounts of glacial acetic acid, concentrated nitric acid, palladium-carbon catalyst and hydrazine hydrate added are 16 parts, 2 parts, 0.04 parts and 5 parts of dibenzo-18-crown-6 ether, respectively, in terms of weight fraction; wherein the mass percentage of the solute in the concentrated nitric acid is 68%, and the palladium-carbon catalyst is 10% Pd / C;

[0045] (2) the lithium sink mother liquor (ingredients as shown in Table 1) is acidified to remove carbonate in the lithium sink mother liquor to obtain an acidified solution; the lithium sink mother liquor is acidified by adding 98% sulfuric acid to the lithium sink mother liquor to adjust the pH of the mother liquor to 2; sodium hydroxide is added to the acidified solution to adjust the pH to 9, and then concentrated; due to the relatively large content of potassium and sodium salt, it is easier to reach the saturation state first, so part of the potassium and sodium salt is precipitated first, which can remove most of the potassium and sodium salt on the one hand, and enrich rubidium and cesium in the lithium sink mother liquor on the other hand; solid-liquid separation is performed to remove the precipitate to obtain a concentrated solution, and then sodium hydroxide is added to adjust the pH of the concentrated solution to 11; a primary extractant is added to the concentrated solution for extraction to obtain a cesium-loaded organic phase and a primary extraction residual liquid; the primary extractant is a mixture of 4-tert-butyl-2-(α-methylbenzyl) phenol, the extraction promoter and sulfonated kerosene; the mass ratio of each component in the primary extractant is 4-tert-butyl-2-(α-methylbenzyl) phenol: extraction promoter: sulfonated kerosene = 2:0.6:1; the mass ratio of the primary extractant to the concentrated solution for extraction is 1:1, and the stirring extraction time is 5 min; the cesium salt is obtained by washing, back-extracting and crystallizing the cesium-loaded organic phase; the back-extraction uses 98% sulfuric acid, and the mass ratio of the added sulfuric acid to the back-extracted organic phase is back-extracted organic phase:sulfuric acid = 15:1;

[0046] (3) sodium hydroxide is added to adjust the pH of the primary extraction residual liquid to 13, and then a secondary extractant is added for extraction to obtain a rubidium-loaded organic phase and an extracted solution; the secondary extractant is a mixture of 4-tert-butyl-2-(α-methylbenzyl) phenol, the extraction promoter, N-butyl-N-methyl pyrrolidine bis(trifluoromethanesulfonyl) imide salt and sulfonated kerosene; the mass ratio of each component in the secondary extractant is 4-tert-butyl-2-(α-methylbenzyl) phenol: extraction promoter: N-butyl-N-methyl pyrrolidine bis(trifluoromethanesulfonyl) imide salt: sulfonated kerosene = 3:0.7:0.3:2; the mass ratio of the secondary extractant to the primary extraction residual liquid for extraction is 10:1, and the stirring extraction time is 5 min; the rubidium salt is obtained by washing, back-extracting and crystallizing the rubidium-loaded organic phase; the back-extraction uses 98% sulfuric acid, and the mass ratio of the added sulfuric acid to the back-extracted organic phase is back-extracted organic phase:sulfuric acid = 15:1.

[0047] Comparative Example 4

[0048] A method for extracting rubidium and cesium salt from a lithium sink mother liquor of lepidolite, comprising the following steps:

[0049] (1) in the reaction kettle, diphenyl-18-crown-6 ether is added into N,N-dimethylformamide, the mass ratio of diphenyl-18-crown-6 ether to N,N-dimethylformamide is diphenyl-18-crown-6 ether: N,N-dimethylformamide = 1:50; stir for 5 min, then add glacial acetic acid into the reaction kettle under stirring, stir for 20 min after the completion of feeding, then add concentrated nitric acid into the reaction kettle under stirring, stir for 30 min after the completion of feeding, then seal the reaction kettle, heat to 130±5℃ and keep for 2 h, cool to room temperature after the end of keeping, open the reaction kettle, then add palladium-carbon catalyst and hydrazine hydrate into the reaction kettle, seal the reaction kettle again after the completion of feeding, heat to 120±3℃ and keep for 1 h, then cool to room temperature naturally, open the reaction kettle, centrifuge to remove the catalyst, then add 4-nitrophenyl isocyanate into the liquid under stirring after centrifugation, stir at room temperature for 8 h after the completion of feeding, then remove N,N-dimethylformamide by distillation under reduced pressure, to obtain an extraction promoter; wherein the amount of glacial acetic acid, concentrated nitric acid, palladium-carbon catalyst, hydrazine hydrate and 4-nitrophenyl isocyanate added is 16 parts, 2 parts, 0.04 parts, 5 parts and 1.2 parts respectively, based on the amount of diphenyl-18-crown-6 ether added into the reaction kettle; wherein the mass percentage of solute in the concentrated nitric acid is 68%, and the palladium-carbon catalyst is 10% Pd / C;

[0050] (2) the lithium precipitation mother liquor (ingredients are shown in Table 1) is acidified to remove carbonate in the lithium precipitation mother liquor, to obtain an acidified liquid; the lithium precipitation mother liquor is acidified by adding 98% sulfuric acid into the lithium precipitation mother liquor to adjust the pH of the mother liquor to 2; sodium hydroxide is added into the acidified liquid to adjust the pH to 9, then concentrated; since the content of potassium and sodium salt is relatively large, it is easier to reach the saturation state first, so part of the potassium and sodium salt is precipitated first, which can remove most of the potassium and sodium salt on the one hand, and enrich rubidium and cesium in the lithium precipitation mother liquor on the other hand; the precipitate is removed by solid-liquid separation to obtain a concentrated liquid, then sodium hydroxide is added to adjust the pH of the concentrated liquid to 11, a primary extractant is added into the concentrated liquid for extraction, to obtain a cesium-loaded organic phase and a primary extraction residual liquid; the primary extractant is a mixture of 4-tert-butyl-2-(α-methylbenzyl) phenol, the extraction promoter and sulfonated kerosene; the mass ratio of each component in the primary extractant is 4-tert-butyl-2-(α-methylbenzyl) phenol: extraction promoter: sulfonated kerosene = 2:0.6:1; the mass ratio of the primary extractant to the concentrated liquid is 1:1 when the primary extractant is added into the concentrated liquid for extraction, and the stirring extraction is carried out for 5 min; the cesium salt is obtained by washing, back extraction and crystallization separation of the cesium-loaded organic phase; the back extraction uses 98% sulfuric acid, and the mass ratio of sulfuric acid to back extraction organic phase is back extraction organic phase: sulfuric acid = 15:1;

[0051] (3) adding sodium hydroxide to adjust the pH of the first extraction residual liquid to 13, and then adding a secondary extraction agent for extraction to obtain a loaded rubidium organic phase and an after-extraction liquid; the secondary extraction agent is a mixture of 4-tert-butyl-2-(α-methylbenzyl) phenol, the extraction promoter and sulfonated kerosene; the mass ratio of each component in the secondary extraction agent is 4-tert-butyl-2-(α-methylbenzyl) phenol: extraction promoter: sulfonated kerosene = 3:0.7:2; the mass ratio of the secondary extraction agent to the first extraction residual liquid for extraction is secondary extraction agent: first extraction residual liquid = 10:1, and the stirring extraction is performed for 5 min; the loaded rubidium organic phase is washed, stripped, and crystallized and separated to obtain a rubidium salt; the stripping uses sulfuric acid with a solute mass percentage of 98%, and the mass ratio of sulfuric acid to the stripping organic phase is stripping organic phase: sulfuric acid = 15:1.

[0052] Example 5

[0053] The extraction rates of cesium and rubidium in the loaded cesium organic phase and the loaded rubidium organic phase obtained by the method described in each example and the comparative example are tested, and the results are shown in Table 2.

[0054] As shown in Table 2, the method described in the application can efficiently extract rubidium and cesium elements in the lithium mica lithium precipitation mother liquor, comprehensively utilizes the valuable metal elements of rubidium and cesium, reduces the waste of resources, and can produce considerable economic benefits. At present, the existing technology discloses a process of simply using 4-tert-butyl-2-(α-methylbenzyl) phenol and sulfonated kerosene. However, because 4-tert-butyl-2-(α-methylbenzyl) phenol has a relatively large extraction effect on potassium and sodium ions, the ion competition effect is formed, and part of the extraction agent resources is occupied by potassium ions and sodium ions, thereby reducing the extraction rate of the target ions Cs + and Rb + . As compared with Example 3 and the comparative example, by adding the extraction promoter described in the application, the extraction rates of rubidium and cesium can be further improved. The application first introduces a nitro group on the dibenzo-18-crown-6 ether, then reduces and aminates the nitro group, and then introduces an active group on the amino group through 4-nitrophenyl isocyanate, thereby improving the coordination ability of the extraction promoter to Cs + and Rb + ions in the aqueous phase, improving the efficiency of the extraction promoter to form a complex with Cs + and Rb + ions; on the other hand, the selectivity of the extraction promoter to ions is utilized to reduce the coordination of potassium and sodium ions, so as to separate the target ions and impurity ions. In the extraction process, Cs + and Rb + ions are first coordinated with the extraction promoter to enter the oil phase, and then 4-tert-butyl-2-(α-methylbenzyl) phenol is coordinated with Cs+ Cs + Cs + Cs + Cs + Cs + Cs + Cs + Cs

[0055] Table 1

[0056] Component Li Na K Rb Cs SO4 2- ]]> CO3 2- ]]> Content (g / L) 2.56 32.98 5.03 2.51 0.54 180.21 3.45

[0057] Table 2

[0058] Test group Extraction rate of Cs Extraction rate of Rb Example 1 93.65％ 90.24％ Example 2 93.71％ 91.08％ Example 3 93.76％ 91.15％ Example 4 93.72％ 91.11％ Comparative Example 1 84.19％ 77.34％ Comparative Example 2 86.90％ 83.86％ Comparative Example 3 90.33％ 88.67％ Comparative Example 4 93.74％ 88.09％

[0059] The above detailed description of the technical solutions provided by the present application, for the general technical personnel in the field, according to the idea of the embodiment of the present application, in the specific implementation and application range will have the change, the above, the content of the specification should not be understood as a limitation of the present application.

Claims

1. A method for extracting rubidium and cesium salts from an environmentally friendly lithium mica lithium sinking mother liquor, characterized by the steps of The method comprises the following steps: (1) adding dibenzo-18-crown-6 ether into N,N-dimethylformamide in a reaction kettle, stirring for more than 5 min, then adding glacial acetic acid into the reaction kettle under stirring, stirring for more than 20 min after the completion of feeding, then adding concentrated nitric acid into the reaction kettle under stirring, stirring for more than 30 min after the completion of feeding, then sealing the reaction kettle, heating to 130±5℃ and keeping for more than 2 h, cooling to room temperature after the completion of keeping, opening the reaction kettle, then adding palladium-carbon catalyst and hydrazine hydrate into the reaction kettle, sealing the reaction kettle again, heating to 120±3℃ and keeping for more than 1 h, then naturally cooling to room temperature, opening the reaction kettle, removing the catalyst by centrifugation, then adding 4-nitrophenyl isocyanate into the liquid after centrifugation under stirring, stirring at room temperature for more than 8 h after the completion of feeding, then removing N,N-dimethylformamide by distillation under reduced pressure, and obtaining an extraction promoter; (2) acidifying the lithium precipitation mother liquor to remove carbonate in the lithium precipitation mother liquor, and obtaining an acidified liquid; adding a base into the acidified liquid to adjust the pH to 8-10, then concentrating, precipitating potassium and sodium salt crystals, removing the precipitates by solid-liquid separation, obtaining a concentrated liquid, then adding a base to adjust the pH of the concentrated liquid to 10-12, adding a primary extraction agent into the concentrated liquid to perform extraction, and obtaining a cesium-loaded organic phase and a primary extraction residual liquid; the primary extraction agent is a mixture of 4-tert-butyl-2-(α-methylbenzyl) phenol, the extraction promoter and sulfonated kerosene; washing, stripping and crystallization separation are performed on the cesium-loaded organic phase to obtain cesium salt; (3) adding a base to adjust the pH of the primary extraction residual liquid to 12-14, then adding a secondary extraction agent to perform extraction, and obtaining a rubidium-loaded organic phase and an extracted liquid; the secondary extraction agent is a mixture of 4-tert-butyl-2-(α-methylbenzyl) phenol, the extraction promoter, N-butyl-N-methyl pyrrolidine bis(trifluoromethanesulfonyl) imide salt and sulfonated kerosene; washing, stripping and crystallization separation are performed on the rubidium-loaded organic phase to obtain rubidium salt.

2. The method for extracting rubidium and cesium salts from an environmentally friendly lithium mica lithium sinking mother liquor according to claim 1, characterized in that, In the step (1), the mass ratio of dibenzo-18-crown-6 ether to N,N-dimethylformamide is 1:

50.

3. The method for extracting rubidium and cesium salts from an environmentally friendly lithium mica lithium sinking mother liquor according to claim 1, characterized in that, In the step (1), the amounts of the glacial acetic acid, the concentrated nitric acid, the palladium-carbon catalyst, the hydrazine hydrate and the 4-nitrophenyl isocyanate added into the reaction kettle are 14-18 parts, 1-2 parts, 0.03-0.04 parts, 4-6 parts and 0.8-1.6 parts, respectively, based on the amount of dibenzo-18-crown-6 ether added into the reaction kettle, and the mass percentage of solute in the concentrated nitric acid is 68%.

4. The method for extracting rubidium and cesium salts from an environmentally friendly lithium mica lithium sinking mother liquor according to claim 1, characterized in that, In the step (2), the acidification of the lithium precipitation mother liquor is to add sulfuric acid with a solute mass percentage of 98% into the lithium precipitation mother liquor to adjust the pH of the mother liquor to 1-2, and the base is sodium hydroxide.

5. The method for extracting rubidium and cesium salts from an environmentally friendly lithium mica lithium sinking mother liquor according to claim 1, characterized in that, In the step (2), the mass ratio of the components in the primary extractant is 4-tert-butyl-2-(α-methylbenzyl) phenol: extraction promoter: sulfonated kerosene = 2:0.5-0.6:1; the mass ratio of the primary extractant to the concentrated solution for extraction is 1-2:1, and the stirring extraction is performed for 3-5 min; the back extraction is performed by using 98% sulfuric acid as the solute, and the mass ratio of the sulfuric acid to the organic phase for back extraction is 15:

1.

6. The method for extracting rubidium and cesium salts from an environmentally friendly lithium mica lithium sinking mother liquor according to claim 1, characterized in that, In the step (3), the mass ratio of the components in the secondary extractant is 4-tert-butyl-2-(α-methylbenzyl) phenol: extraction promoter: N-butyl-N-methyl pyrrolidine bis(trifluoromethane sulfonate) imide salt: sulfonated kerosene = 3:0.6-0.7:0.2-0.4:2; the mass ratio of the secondary extractant to the residual solution of the primary extraction for extraction is 10:1, and the stirring extraction is performed for 3-5 min; the back extraction is performed by using 98% sulfuric acid as the solute, and the mass ratio of the sulfuric acid to the organic phase for back extraction is 15:1.