Salt lake brine cascade lithium extraction method based on in-situ electrolysis driving

Abstract

The invention relates to a salt lake brine cascade lithium extraction method based on in-situ electrolysis driving, and belongs to the technical field of salt lake lithium extraction. According to the invention, the surface of the nano-diamond and the surface of the polyether-ether-ketone are grafted with the polymerized sulfonic acid chain segment, so that the resistivity of the cation exchange membrane can be effectively reduced, and the surface of the nano-diamond and the surface of the polyether-ether-ketone are also grafted with the long-chain-segment high-density polymerized sulfonic acid chain segment; the polymerized sulfonic acid chain segments are distributed in a branched manner on the surface of the nano-diamond and the surface of the polyetheretherketone, the grafted sulfonic acid chain segments can be arranged in an interactive net shape or are intertwined together through physical winding, the distribution density of sulfonic acid groups is improved, the main chain polyetheretherketone and the core of the nano-diamond can provide a distribution basis for the polymerized sulfonic acid chain segments, and the anti-corrosion performance of the nano-diamond is improved. Sulfonic acid polymerization chain segments can be effectively and uniformly distributed and can be staggered with long-branched sulfonic acid polymerization chain segments to form pores formed by sulfonic acid groups, so that a basis is provided for cation penetration.

Description

Technical Field

[0001] The invention relates to a salt lake brine cascade lithium extraction method based on in-situ electrolysis drive, belonging to the technical field of salt lake lithium extraction. Background Art

[0002] Lithium exists in nature mainly in the form of solid lithium ore in pegmatites such as spodumene and lepidolite, or in the form of lithium ions in salt lake brine, underground brine and seawater. Compared with solid lithium ore, brine lithium resources are more abundant, accounting for about 91% of the earth's lithium resources. In recent years, due to the advantages of low cost and simple process of lithium extraction from brine, and the increasing depletion of solid lithium ore resources, the proportion of lithium products from brine has increased significantly, and the development and application of lithium resources has undergone a major turning point. At present, the methods for extracting lithium from salt lake brine mainly include precipitation, solvent extraction, calcination and leaching, carbonization, adsorption, membrane separation technology and electrodialysis technology. Among them, electrodialysis technology uses the selective permeability of ion exchange membranes to anions and cations to cause anions and cations to migrate in a directional manner under the action of an external DC electric field, so that the electrolytes are separated and concentrated.

[0003] Chinese patent document CN117265291A discloses a method for extracting lithium and removing sodium from a low-concentration lithium-containing leaching solution of fly ash, the method comprising alkalizing the fly ash leaching solution to form an alkalized lithium-containing leaching solution; building a multi-stage electrodialysis device; allowing the cathode electrolyte containing sodium ions to enter the cathode chambers of multiple electrodialysis units in parallel at the same time, and allowing the alkalized lithium-containing leaching solution to enter the anode chambers of multiple electrodialysis units step by step in series; the lithium-rich electrolyte formed in the cathode chambers of each electrodialysis unit is converged to a sodium removal tank, and the sodium-depleted lithium-rich electrolyte is discharged; the sodium-depleted lithium-rich electrolyte is evaporated and crystallized to obtain a sodium-depleted lithium-extracted product. The lithium product extracted from the lithium extraction method disclosed in the patent document contains a large amount of sodium ions, and the lithium product has low purity and needs subsequent purification and impurity removal. Therefore, it is necessary to provide a method for electrolytic lithium extraction of high-purity lithium products. Summary of the invention

[0004] The purpose of the present invention is to provide a salt lake brine cascade lithium extraction method based on in-situ electrolysis driven to solve the problem of low purity of lithium products obtained when lithium is currently extracted by electrolysis.

[0005] The invention provides a salt lake brine cascade lithium extraction method based on in-situ electrolysis drive, comprising the following steps: electrolyzing lithium-containing salt lake brine to make lithium ions in the salt lake brine selectively pass through a cation exchange membrane to complete the enrichment and extraction of lithium ions; the cation exchange membrane is prepared by drying a solution of polymerized sulfonic acid grafted sulfonated polyetheretherketone and polymerized sulfonic acid grafted nanodiamond; the polymerized sulfonic acid grafted sulfonated polyetheretherketone is prepared by polymerization reaction of double-bond sulfonated polyetheretherketone and sulfonic acid monomer; the double bond ... The bond-sulfonated polyetheretherketone is prepared by reacting hydroxylated sulfonated polyetheretherketone with acryloyl chloride; the polymerized sulfonic acid grafted nanodiamond is prepared by polymerizing propylene sulfonated nanodiamond with sulfonic acid monomer, the propylene sulfonated nanodiamond is prepared by reacting propylene alcoholized nanodiamond with 4-(chlorosulfonyl)benzoyl chloride, and the propylene alcoholized nanodiamond is prepared by reacting carboxylated nanodiamond with glycidyl acrylate; the sulfonic acid monomer is sodium 2,3-epoxypropanesulfonate or sodium allyl sulfonate.

[0006] Preferably, the carboxylated nanodiamond is prepared by mixing nanodiamond powder and acid solution at 70-80° C. for 48-55 hours, the acid solution is composed of concentrated nitric acid and concentrated sulfuric acid in a volume ratio of 1:3-3.5, and the mass ratio of nanodiamond powder to acid solution is 1:120-150.

[0007] Preferably, the acrylated nanodiamond is prepared by mixing carboxylated nanodiamond, glycidyl acrylate and catalyst trimethylbenzylammonium bromide at 90-100° C. for 6-8 hours, the molar ratio of carboxyl group and glycidyl acrylate of the carboxylated nanodiamond is 1:2-3, and the mass ratio of carboxylated nanodiamond and catalyst trimethylbenzylammonium bromide is 50:0.5-0.8.

[0008] Preferably, the temperature of the reaction of acrylated nanodiamond and 4-(chlorosulfonyl)benzoyl chloride is 20-25° C., and the time is 3-4 hours; during the reaction, the acrylated nanodiamond dispersion is added to the 4-(chlorosulfonyl)benzoyl chloride solution; the molar ratio of the hydroxyl group of the acrylated nanodiamond to the 4-(chlorosulfonyl)benzoyl chloride is 1:1.5-2.

[0009] Preferably, the reaction temperature of hydroxylated sulfonated polyetheretherketone and acryloyl chloride is room temperature, the reaction time is 8 to 10 hours, and the mass ratio of hydroxylated sulfonated polyetheretherketone to acryloyl chloride is 1:2 to 3.

[0010] Preferably, the hydroxylated sulfonated polyetheretherketone is prepared by mixing sulfonated polyetheretherketone and sodium borohydride in a solvent at 110-120°C for 3-4 hours, and the mass ratio of sodium borohydride to sulfonated polyetheretherketone is 1.8-2:1; the sulfonated polyetheretherketone is prepared by mixing polyetheretherketone and concentrated sulfuric acid at 55-65°C for 3-4 hours, and the amount ratio of polyetheretherketone to concentrated sulfuric acid is 20-22g:280-300mL.

[0011] Preferably, the sulfonic acid monomer is sodium 2,3-epoxypropanesulfonate, and the method for polymerizing the double-bond sulfonated polyetheretherketone and the sulfonic acid monomer is as follows: double-bond sulfonated polyetheretherketone, sodium 2,3-epoxypropanesulfonate and a solvent are mixed to obtain a reaction solution, and then a hydrogen peroxide solution with a mass fraction of 7-9% is added dropwise to the reaction solution under stirring. After the addition is completed, the mixture is heated to 80-85° C. and mixed for reaction for 5-6 hours to obtain polymerized epoxypropanesulfonic acid grafted sulfonated polyetheretherketone; the mass ratio of the double-bond sulfonated polyetheretherketone to the mass ratio of sodium 2,3-epoxypropanesulfonate is 1:3-4, and the mass ratio of the mass of sodium 2,3-epoxypropanesulfonate to the mass ratio of the hydrogen peroxide solution is 1:9-10.

[0012] Preferably, the sulfonic acid monomer is sodium 2,3-epoxypropanesulfonate, and the method for polymerizing propylene sulfonated nanodiamonds and sulfonic acid monomers is as follows: mixing a propylene sulfonated nanodiamond dispersion and a sodium 2,3-epoxypropanesulfonate solution to obtain a reaction solution, then dripping a hydrogen peroxide solution with a mass fraction of 7-9% into the reaction solution under stirring, and after the dripping is completed, heating to 80-85° C., mixing and reacting for 3-4 hours to obtain polymerized epoxypropanesulfonic acid grafted nanodiamonds; the ratio of the mass of propylene sulfonated nanodiamonds in the propylene sulfonated nanodiamond dispersion to the mass of sodium 2,3-epoxypropanesulfonate in the sodium 2,3-epoxypropanesulfonate solution is 1:2-2.5, and the ratio of the mass of sodium 2,3-epoxypropanesulfonate in the sodium 2,3-epoxypropanesulfonate solution to the mass of the hydrogen peroxide solution is 1:5-7.

[0013] Preferably, the sulfonic acid monomer is sodium allyl sulfonate, and the method for polymerizing the double-bond sulfonated polyether ether ketone and the sulfonic acid monomer is as follows: double-bond sulfonated polyether ether ketone, sodium allyl sulfonate and a solvent are mixed to obtain a reaction solution, and then a persulfate initiator is added, heated to 90-95° C., and mixed for 5-6 hours to obtain polymerized propyl sulfonic acid grafted sulfonated polyether ether ketone; the mass ratio of the double-bond sulfonated polyether ether ketone to the mass of the sodium allyl sulfonate is 1:3-4; The method for polymerizing propylene sulfonated nanodiamonds and sulfonic acid monomers is as follows: a propylene sulfonated nanodiamond dispersion and a sodium allyl sulfonate solution are mixed to obtain a reaction solution, and then a persulfate initiator is added, heated to 90-95° C., and mixed for reaction for 3-4 hours, wherein the ratio of the mass of propylene sulfonated nanodiamonds in the propylene sulfonated nanodiamond dispersion to the mass of sodium allyl sulfonate in the sodium allyl sulfonate solution is 1:2-2.5.

[0014] Preferably, during electrolysis, the cation exchange membrane, cathode electrode and anode electrode are assembled into an electrolytic cell, the anode electrode material is a mesh ruthenium-plated titanium metal electrode, and the cathode electrode material is a mesh nickel material. Then, several electrolytic cells are connected in series in sequence to perform cascade electrolysis to complete the extraction and enrichment of lithium in the salt lake brine.

[0015] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention can effectively reduce the resistivity of the cation exchange membrane and improve the conductivity of the film by grafting polymerized sulfonic acid segments onto the surface of the nanodiamond and the polyetheretherketone segments. In addition to the sulfonic acid groups bonded to the surface of the nanodiamond and the polyetheretherketone, the surface of the nanodiamond and the polyetheretherketone are also grafted with long-chain high-density polymerized sulfonic acid segments, and the polymerized sulfonic acid segments are distributed in a branched manner on the surface of the nanodiamond and the polyetheretherketone. The film material made of the two contains a large number of sulfonic acid segments. The grafted sulfonic acid segments can be arranged in an interactive network or entangled together by physical entanglement to increase the distribution density of the sulfonic acid groups. The main chain polyetheretherketone and the nanodiamond core can provide a distribution basis for the polymerized sulfonic acid segments, ensuring that the sulfonic acid polymer segments are effectively and evenly distributed, and can be staggered with the long branched sulfonic acid polymer segments to form pores composed of sulfonic acid groups, providing a basis for the passage of cations. In addition, the main chain polyetheretherketone, nanodiamond core and long branched sulfonic acid polymer segments are physically cross-linked with each other, which can effectively improve the strength and elongation of the film material and improve the antioxidant properties of the film material.

[0016] (2) The experimental results show that the use of polymerized propylene oxide sulfonic acid as the long-chain sulfonic acid polymer segment can improve the mechanical properties and antioxidant properties of the film material more than using polymerized propyl sulfonic acid as the long-chain sulfonic acid polymer segment. This may be because polymerized propylene oxide sulfonic acid contains ether bonds, which have stronger rotation ability and can form hydrogen bonds, thereby improving the mechanical properties and antioxidant properties of the film.

[0017] (3) The cation exchange membrane provided in the present invention has a good selective separation effect on impurity ions and lithium ions in conventional brine. This may be because the long-chain high-density polymerized sulfonic acid segments grafted on the surface of nanodiamond and polyetheretherketone can be arranged in a staggered manner to form pores composed of sulfonic acid groups, which can well screen lithium ions, sodium ions, magnesium ions, calcium ions and potassium ions, thereby improving the ion recognition and separation effect. The experimental results show that when the long-chain high-density polymerized sulfonic acid segments are missing, the pores composed of sulfonic acid groups cannot be formed by staggered arrangement, resulting in poor lithium ion selective permeability of the film. In addition, the pores formed in the film of the present invention are temporarily unstable structures, which will not cause a large amount of electrical energy to be consumed when lithium ions pass through, and thus have a higher current efficiency and a higher lithium ion yield. DETAILED DESCRIPTION

[0018] The following examples are intended to further illustrate the present invention rather than to limit the scope of protection of the present invention. Example 1

[0019] The salt lake brine cascade lithium extraction method based on in-situ electrolysis driven in this embodiment comprises the following steps: (1) The nano-diamond powder is vacuum dried at 60°C for 24 hours, the dried nano-diamond powder and acid solution are placed in a stirring kettle, heated to 70°C, stirred and refluxed for 48 hours, cooled to room temperature, filtered, and the filter cake is washed with water until the washing liquid is neutral, and dried to obtain carboxylated nano-diamond. The acid solution is composed of concentrated nitric acid and concentrated sulfuric acid in a volume ratio of 1:3, and the mass ratio of the nano-diamond powder to the acid solution is 1:120.

[0020] (2) Carboxylated nanodiamond, glycidyl acrylate, acetone and catalyst trimethylbenzylammonium bromide were added to a reaction kettle, stirred evenly and heated to 90°C, stirred for 6 hours, filtered, washed with acetone and then with water, and dried to obtain acrylated nanodiamond. The molar ratio of carboxyl group and glycidyl acrylate in the carboxylated nanodiamond was 1:2, and the mass ratio of carboxylated nanodiamond, acetone and catalyst trimethylbenzylammonium bromide was 50:80:0.5.

[0021] (3) Add 4-(chlorosulfonyl)benzoyl chloride and anhydrous dichloromethane to the reaction kettle and stir evenly to obtain a 4-(chlorosulfonyl)benzoyl chloride solution with a mass fraction of 15%; stir the acrylated nanodiamond and anhydrous dichloromethane evenly to obtain a acrylated nanodiamond dispersion with a mass fraction of 20%; add the acrylated nanodiamond dispersion dropwise to the 4-(chlorosulfonyl)benzoyl chloride solution at 5°C and under stirring conditions. After the addition is completed, add triethylamine, then heat to 20°C, stir and react for 3 hours, filter, wash the filter cake with acetone first, then wash it with water, and dry it to obtain acrylated nanodiamond. Among them, the molar ratio of hydroxyl group of acrylated nanodiamond to 4-(chlorosulfonyl)benzoyl chloride is 1:1.5, and the molar ratio of 4-(chlorosulfonyl)benzoyl chloride to triethylamine is 1:1.

[0022] (4) A saturated aqueous solution of sodium bisulfite is added to a reaction kettle, and then epichlorohydrin is added dropwise under stirring. After the addition is completed, the mixture is stirred and reacted at room temperature for 24 hours, filtered, washed, and dried to obtain sodium 3-chloro-2-hydroxypropanesulfonate; wherein the ratio of the molar amount of sodium bisulfite to the molar amount of epichlorohydrin in the saturated aqueous solution of sodium bisulfite is 0.1:0.1.

[0023] (5) Sodium 3-chloro-2-hydroxypropanesulfonate and water were added to a reaction kettle, stirred evenly, and then heated to 28°C. Then, sodium hydroxide was added and stirred for 30 minutes to obtain a sodium 2,3-epoxypropanesulfonate solution, wherein the mass ratio of sodium 3-chloro-2-hydroxypropanesulfonate to water was 20:28, and the molar ratio of sodium 3-chloro-2-hydroxypropanesulfonate to sodium hydroxide was 1:1.

[0024] (6) Dispersing the propylene sulfonated nanodiamond in water to obtain a propylene sulfonated nanodiamond dispersion with a mass fraction of 30%; then stirring the propylene sulfonated nanodiamond dispersion and the sodium 2,3-epoxypropanesulfonate solution obtained in step (5) to obtain a reaction solution, and then dropping a 7% mass fraction hydrogen peroxide solution into the reaction solution under stirring. After the dropping is completed, heating to 80° C., stirring and reflux reaction for 3 hours, filtering, washing with water first, then washing with ethanol, then washing with hydrochloric acid, and finally washing with ethanol, and drying to obtain polymerized epoxypropanesulfonic acid grafted nanodiamond. Among them, the mass ratio of the propylene sulfonated nanodiamond in the propylene sulfonated nanodiamond dispersion to the mass ratio of the sodium 2,3-epoxypropanesulfonate in the sodium 2,3-epoxypropanesulfonate solution is 1:2, and the mass ratio of the sodium 2,3-epoxypropanesulfonate in the sodium 2,3-epoxypropanesulfonate solution to the mass ratio of the hydrogen peroxide solution is 1:5.

[0025] (7) Sodium borohydride, sulfonated polyetheretherketone and N,N-dimethylformamide are added to a reaction kettle, heated to 110°C, stirred and refluxed for 3 hours, cooled to room temperature, poured into dilute hydrochloric acid after the reaction, filtered, washed with water first, then washed with ethanol, and dried to obtain hydroxysulfonated polyetheretherketone. Among them, the mass ratio of sodium borohydride, sulfonated polyetheretherketone and N,N-dimethylformamide is 1.8:1:50. The preparation method of sulfonated polyetheretherketone is as follows: 20g of polyetheretherketone and 280mL of concentrated sulfuric acid are stirred and reacted at 55°C for 3 hours, then cooled to room temperature, slowly poured into a large amount of ice water, filtered, washed and dried to obtain sulfonated polyetheretherketone. The structural formula of polyetheretherketone is as follows:

[0026] (8) Add hydroxysulfonated polyetheretherketone and anhydrous N,N-dimethylformamide into a reaction kettle, heat to 45°C, stir until the hydroxysulfonated polyetheretherketone is completely dissolved, cool to room temperature, and obtain a 2% by mass hydroxysulfonated polyetheretherketone solution; add a 10% by mass acryloyl chloride solution in dichloromethane dropwise to the hydroxysulfonated polyetheretherketone solution, add triethylamine after the addition, stir and react for 8 hours, pour the system after the reaction into water, filter, wash with water first, then with ethanol, and dry to obtain double-bond sulfonated polyetheretherketone. The mass ratio of hydroxysulfonated polyetheretherketone to acryloyl chloride is 1:2, and the mass ratio of triethylamine to acryloyl chloride is 1:1.

[0027] (9) Add double-bond sulfonated polyetheretherketone into anhydrous N,N-dimethylformamide and dissolve it to obtain a 2% by mass solution of double-bond sulfonated polyetheretherketone; then stir the double-bond sulfonated polyetheretherketone solution and a 25% by mass solution of sodium 2,3-epoxypropanesulfonate in N,N-dimethylformamide to obtain a reaction solution; then add a 7% by mass solution of hydrogen peroxide in N,N-dimethylformamide to the reaction solution under stirring; after the addition is completed, heat to 80°C, stir and reflux to react for 5 hours; after cooling to room temperature, pour the reaction system into water, filter, wash with water, then with acetone, then with ethanol, then with hydrochloric acid, and finally with ethanol; and dry to obtain polymerized epoxypropanesulfonic acid grafted sulfonated polyetheretherketone. The mass ratio of double bond sulfonated polyetheretherketone to sodium 2,3-epoxypropanesulfonate is 1:3, and the mass ratio of sodium 2,3-epoxypropanesulfonate to N,N-dimethylformamide solution of hydrogen peroxide is 1:9. The N,N-dimethylformamide solution of sodium 2,3-epoxypropanesulfonate is prepared by stirring and mixing sodium 2,3-epoxypropanesulfonate and N,N-dimethylformamide, and the sodium 2,3-epoxypropanesulfonate is obtained by removing water from the sodium 2,3-epoxypropanesulfonate solution prepared in step (5) by vacuum distillation.

[0028] (10) Add poly(epoxypropanesulfonic acid) grafted sulfonated poly(ether ether ketone) and dimethyl sulfoxide into a stirring kettle, heat to 45°C, and stir until the poly(epoxypropanesulfonic acid) grafted sulfonated poly(ether ether ketone) is fully dissolved to obtain a poly(epoxypropanesulfonic acid) grafted sulfonated poly(ether ether ketone) solution with a mass fraction of 8%; then add poly(epoxypropanesulfonic acid) grafted nanodiamonds into the poly(epoxypropanesulfonic acid) grafted sulfonated poly(ether ether ketone) solution, and disperse them evenly by ultrasonication to obtain a film-forming slurry (the mass ratio of poly(epoxypropanesulfonic acid) grafted sulfonated poly(ether ether ketone) to poly(epoxypropanesulfonic acid) grafted nanodiamonds is 100:3); pour the film-forming slurry into a glass mold, let it stand at room temperature for 24 hours, and then put it into a drying oven at 60°C to dry to constant weight to obtain a cation exchange membrane.

[0029] (11) The prepared cation exchange membrane, cathode electrode and anode electrode are assembled into an electrolytic cell, wherein the anode electrode material is a mesh ruthenium-plated titanium metal electrode, and the cathode electrode material is a mesh nickel material. Then, the three electrolytic cells are connected in series from left to right, and lithium-containing brine is added to the anode chamber of the leftmost electrolytic cell, and lithium hydroxide solution is added to the cathode chamber of the leftmost electrolytic cell and the cathode chambers and anode chambers of the other two electrolytic cells. The power is turned on to perform electrolysis. Under the action of the electric field, the lithium ions in the lithium-containing brine selectively pass through the cation exchange membrane from the anode chamber of the leftmost electrolytic cell into the cathode chamber. Then, the electrolyte in the cathode chamber of the leftmost electrolytic cell flows into the anode chamber of the middle electrolytic cell under the action of gravity, and then enters the cathode chamber from the anode chamber under the action of the electric field, and then flows into the anode chamber of the rightmost electrolytic cell under the action of gravity, and finally enters the cathode chamber from the anode chamber under the action of the electric field. After cascade electrolysis, the extraction and enrichment of lithium in the brine is completed. The lithium hydroxide solution in the cathode chamber of the rightmost electrolytic cell is dried to obtain a lithium hydroxide product with a purity greater than 99%. Example 2

[0030] The salt lake brine cascade lithium extraction method based on in-situ electrolysis driven in this embodiment comprises the following steps: (1) The nano-diamond powder was vacuum dried at 60°C for 24 hours, and the dried nano-diamond powder and acid solution were placed in a stirring kettle, heated to 75°C, stirred and refluxed for 50 hours, cooled to room temperature, filtered, and the filter cake was washed with water until the washing liquid was neutral. After drying, carboxylated nano-diamond was obtained. The acid solution was composed of concentrated nitric acid and concentrated sulfuric acid in a volume ratio of 1:3.2, and the mass ratio of nano-diamond powder to acid solution was 1:130.

[0031] (2) Carboxylated nanodiamond, glycidyl acrylate, acetone and catalyst trimethylbenzylammonium bromide were added to a reaction kettle, stirred evenly and heated to 95°C, stirred and reacted for 7 hours, filtered, washed with acetone and then washed with water, and dried to obtain acrylated nanodiamond. The molar ratio of carboxyl group and glycidyl acrylate in the carboxylated nanodiamond was 1:2.5, and the mass ratio of carboxylated nanodiamond, acetone and catalyst trimethylbenzylammonium bromide was 50:100:0.6.

[0032] (3) Add 4-(chlorosulfonyl)benzoyl chloride and anhydrous dichloromethane to the reaction kettle and stir evenly to obtain a 4-(chlorosulfonyl)benzoyl chloride solution with a mass fraction of 18%; stir the acrylated nanodiamond and anhydrous dichloromethane evenly to obtain a acrylated nanodiamond dispersion with a mass fraction of 22%; add the acrylated nanodiamond dispersion dropwise to the 4-(chlorosulfonyl)benzoyl chloride solution at 7°C and stirring. After the addition is completed, add triethylamine, then heat to 23°C, stir and react for 3.5 hours, filter, wash the filter cake with acetone first, then wash it with water, and dry it to obtain acrylated nanodiamond. The molar ratio of the hydroxyl group of the acrylated nanodiamond to 4-(chlorosulfonyl)benzoyl chloride is 1:1.7, and the molar ratio of 4-(chlorosulfonyl)benzoyl chloride to triethylamine is 1:1.1.

[0033] (4) A saturated aqueous solution of sodium bisulfite is added to a reaction kettle, and then epichlorohydrin is added dropwise under stirring. After the addition is completed, the mixture is stirred and reacted at room temperature for 27 hours. The mixture is filtered, washed, and dried to obtain sodium 3-chloro-2-hydroxypropanesulfonate; wherein the ratio of the molar amount of sodium bisulfite to the molar amount of epichlorohydrin in the saturated aqueous solution of sodium bisulfite is 0.1:0.11.

[0034] (5) Sodium 3-chloro-2-hydroxypropanesulfonate and water are added to a reaction kettle, stirred evenly, and then heated to 30°C. Then, sodium hydroxide is added and stirred for 40 minutes to obtain a sodium 2,3-epoxypropanesulfonate solution, wherein the mass ratio of sodium 3-chloro-2-hydroxypropanesulfonate to water is 20:30, and the molar ratio of sodium 3-chloro-2-hydroxypropanesulfonate to sodium hydroxide is 1:1.

[0035] (6) Dispersing the propylene sulfonated nanodiamond in water to obtain a propylene sulfonated nanodiamond dispersion with a mass fraction of 35%; then stirring the propylene sulfonated nanodiamond dispersion and the sodium 2,3-epoxypropanesulfonate solution obtained in step (5) to obtain a reaction solution, and then dropping a hydrogen peroxide solution with a mass fraction of 8% into the reaction solution under stirring. After the dropping is completed, heating to 82° C., stirring and reflux reaction for 3.5 hours, filtering, washing with water first, then washing with ethanol, then washing with hydrochloric acid, and finally washing with ethanol, and drying to obtain polymerized epoxypropanesulfonic acid grafted nanodiamond. The ratio of the mass of the propylene sulfonated nanodiamond in the propylene sulfonated nanodiamond dispersion to the mass of the sodium 2,3-epoxypropanesulfonate in the sodium 2,3-epoxypropanesulfonate solution is 1:2.2, and the ratio of the mass of the sodium 2,3-epoxypropanesulfonate in the sodium 2,3-epoxypropanesulfonate solution to the mass of the hydrogen peroxide solution is 1:6.

[0036] (7) Sodium borohydride, sulfonated polyetheretherketone and N,N-dimethylformamide are added to a reaction kettle, heated to 115°C, stirred and refluxed for reaction for 3.5 hours, cooled to room temperature, poured into dilute hydrochloric acid after reaction, filtered, washed with water first, then with ethanol, and dried to obtain hydroxy sulfonated polyetheretherketone. Among them, the mass ratio of sodium borohydride, sulfonated polyetheretherketone and N,N-dimethylformamide is 1.9:1:60. The preparation method of sulfonated polyetheretherketone is as follows: 21g polyetheretherketone and 290mL concentrated sulfuric acid are stirred and reacted at 60°C for 3.5 hours, then cooled to room temperature, slowly poured into a large amount of ice water, filtered, washed and dried to obtain sulfonated polyetheretherketone. The structural formula of polyetheretherketone is as follows:

[0037] (8) Add hydroxysulfonated polyetheretherketone and anhydrous N,N-dimethylformamide into a reaction kettle, heat to 50°C, stir until the hydroxysulfonated polyetheretherketone is completely dissolved, cool to room temperature, and obtain a 2.5% by mass hydroxysulfonated polyetheretherketone solution; add a 12% by mass acryloyl chloride solution in dichloromethane dropwise to the hydroxysulfonated polyetheretherketone solution, add triethylamine after the addition, stir and react for 9 hours, pour the system after the reaction into water, filter, wash with water first, then with ethanol, and dry to obtain double-bond sulfonated polyetheretherketone. The mass ratio of hydroxysulfonated polyetheretherketone to acryloyl chloride is 1:2.5, and the mass ratio of triethylamine to acryloyl chloride is 1.3:1.

[0038] (9) Add double-bond sulfonated polyetheretherketone into anhydrous N,N-dimethylformamide and dissolve it to obtain a 2.5% by mass double-bond sulfonated polyetheretherketone solution; then stir the double-bond sulfonated polyetheretherketone solution and a 27% by mass solution of sodium 2,3-epoxypropanesulfonate in N,N-dimethylformamide to obtain a reaction solution; then add 8% by mass hydrogen peroxide in N,N-dimethylformamide to the reaction solution under stirring; after the addition is completed, heat to 83°C, stir and reflux to react for 6 hours; after cooling to room temperature, pour the reaction system into water, filter, wash with water, then with acetone, then with ethanol, then with hydrochloric acid, and finally with ethanol; and dry to obtain polymerized epoxypropanesulfonic acid grafted sulfonated polyetheretherketone. The mass ratio of double bond sulfonated polyetheretherketone to sodium 2,3-epoxypropanesulfonate is 1:3, and the mass ratio of sodium 2,3-epoxypropanesulfonate to N,N-dimethylformamide solution of hydrogen peroxide is 1:10. The N,N-dimethylformamide solution of sodium 2,3-epoxypropanesulfonate is prepared by stirring and mixing sodium 2,3-epoxypropanesulfonate and N,N-dimethylformamide, and the sodium 2,3-epoxypropanesulfonate is obtained by removing water from the sodium 2,3-epoxypropanesulfonate solution prepared in step (5) by vacuum distillation.

[0039] (10) Add poly(epoxypropanesulfonic acid) grafted sulfonated poly(ether ether ketone) and dimethyl sulfoxide into a stirring kettle, heat to 50°C, and stir until the poly(epoxypropanesulfonic acid) grafted sulfonated poly(ether ether ketone) is fully dissolved to obtain a poly(epoxypropanesulfonic acid) grafted sulfonated poly(ether ether ketone) solution with a mass fraction of 9%; then add poly(epoxypropanesulfonic acid) grafted nanodiamonds into the poly(epoxypropanesulfonic acid) grafted sulfonated poly(ether ether ketone) solution, and disperse them evenly by ultrasonication to obtain a film-forming slurry (the mass ratio of poly(epoxypropanesulfonic acid) grafted sulfonated poly(ether ether ketone) to poly(epoxypropanesulfonic acid) grafted nanodiamonds is 100:4); pour the film-forming slurry into a glass mold, let it stand at room temperature for 24 hours, and then put it into a drying oven at 70°C to dry to constant weight to obtain a cation exchange membrane.

[0040] (11) The prepared cation exchange membrane, cathode electrode and anode electrode are assembled into an electrolytic cell, wherein the anode electrode material is a mesh ruthenium-plated titanium metal electrode, and the cathode electrode material is a mesh nickel material. Then, the three electrolytic cells are connected in series from left to right, and lithium-containing brine is added to the anode chamber of the leftmost electrolytic cell, and lithium hydroxide solution is added to the cathode chamber of the leftmost electrolytic cell and the cathode chambers and anode chambers of the other two electrolytic cells. The power is turned on to perform electrolysis. Under the action of the electric field, the lithium ions in the lithium-containing brine selectively pass through the cation exchange membrane from the anode chamber of the leftmost electrolytic cell into the cathode chamber. Then, the electrolyte in the cathode chamber of the leftmost electrolytic cell flows into the anode chamber of the middle electrolytic cell under the action of gravity, and then enters the cathode chamber from the anode chamber under the action of the electric field, and then flows into the anode chamber of the rightmost electrolytic cell under the action of gravity, and finally enters the cathode chamber from the anode chamber under the action of the electric field. After cascade electrolysis, the extraction and enrichment of lithium in the brine is completed. The lithium hydroxide solution in the cathode chamber of the rightmost electrolytic cell is dried to obtain a lithium hydroxide product with a purity greater than 99%. Example 3

[0041] The salt lake brine cascade lithium extraction method based on in-situ electrolysis driven in this embodiment comprises the following steps: (1) The nano-diamond powder was vacuum dried at 60°C for 24 hours, and the dried nano-diamond powder and acid solution were placed in a stirring kettle, heated to 80°C, stirred and refluxed for 55 hours, cooled to room temperature, filtered, and the filter cake was washed with water until the washing liquid was neutral. After drying, carboxylated nano-diamond was obtained. The acid solution was composed of concentrated nitric acid and concentrated sulfuric acid in a volume ratio of 1:3.5, and the mass ratio of nano-diamond powder to acid solution was 1:150.

[0042] (2) Carboxylated nanodiamond, glycidyl acrylate, acetone and catalyst trimethylbenzylammonium bromide were added to a reaction kettle, stirred evenly and heated to 100°C, stirred and reacted for 8 hours, filtered, washed with acetone and then washed with water, and dried to obtain acrylated nanodiamond. The molar ratio of carboxyl group and glycidyl acrylate in the carboxylated nanodiamond was 1:3, and the mass ratio of carboxylated nanodiamond, acetone and catalyst trimethylbenzylammonium bromide was 50:120:0.8.

[0043] (3) Add 4-(chlorosulfonyl)benzoyl chloride and anhydrous dichloromethane to the reaction kettle and stir evenly to obtain a 20% mass fraction 4-(chlorosulfonyl)benzoyl chloride solution; stir the acrylated nanodiamond and anhydrous dichloromethane evenly to obtain a 25% mass fraction acrylated nanodiamond dispersion; add the acrylated nanodiamond dispersion dropwise to the 4-(chlorosulfonyl)benzoyl chloride solution at 8°C and under stirring conditions. After the addition is completed, add triethylamine, then heat to 25°C, stir and react for 4 hours, filter, wash the filter cake with acetone first, then wash it with water, and dry it to obtain acrylated nanodiamond. The molar ratio of the hydroxyl group of the acrylated nanodiamond to 4-(chlorosulfonyl)benzoyl chloride is 1:2, and the molar ratio of 4-(chlorosulfonyl)benzoyl chloride to triethylamine is 1:1.2.

[0044] (4) A saturated aqueous solution of sodium bisulfite is added to a reaction kettle, and then epichlorohydrin is added dropwise under stirring. After the addition is completed, the mixture is stirred and reacted at room temperature for 30 hours. The mixture is filtered, washed, and dried to obtain sodium 3-chloro-2-hydroxypropanesulfonate; wherein the ratio of the molar amount of sodium bisulfite to the molar amount of epichlorohydrin in the saturated aqueous solution of sodium bisulfite is 0.1:0.12.

[0045] (5) Sodium 3-chloro-2-hydroxypropanesulfonate and water were added to a reaction kettle, stirred evenly, and then heated to 32°C. Then, sodium hydroxide was added and stirred for 45 minutes to obtain a sodium 2,3-epoxypropanesulfonate solution, wherein the mass ratio of sodium 3-chloro-2-hydroxypropanesulfonate to water was 20:32, and the molar ratio of sodium 3-chloro-2-hydroxypropanesulfonate to sodium hydroxide was 1:1.

[0046] (6) Dispersing the propylene sulfonated nanodiamond in water to obtain a propylene sulfonated nanodiamond dispersion with a mass fraction of 40%; then stirring the propylene sulfonated nanodiamond dispersion and the sodium 2,3-epoxypropanesulfonate solution obtained in step (5) to obtain a reaction solution, and then dropping a 9% mass fraction hydrogen peroxide solution into the reaction solution under stirring. After the dropping is completed, heating to 85° C., stirring and reflux reaction for 4 hours, filtering, washing with water first, then washing with ethanol, then washing with hydrochloric acid, and finally washing with ethanol, and drying to obtain polymerized epoxypropanesulfonic acid grafted nanodiamond. Among them, the mass ratio of the propylene sulfonated nanodiamond in the propylene sulfonated nanodiamond dispersion to the mass ratio of the sodium 2,3-epoxypropanesulfonate in the sodium 2,3-epoxypropanesulfonate solution is 1:2.5, and the mass ratio of the sodium 2,3-epoxypropanesulfonate in the sodium 2,3-epoxypropanesulfonate solution to the mass ratio of the hydrogen peroxide solution is 1:7.

[0047] (7) Sodium borohydride, sulfonated polyetheretherketone and N,N-dimethylformamide are added to a reaction kettle, heated to 120°C, stirred and refluxed for 4 hours, cooled to room temperature, poured into dilute hydrochloric acid after the reaction, filtered, washed with water first, then with ethanol, and dried to obtain hydroxysulfonated polyetheretherketone. Among them, the mass ratio of sodium borohydride, sulfonated polyetheretherketone and N,N-dimethylformamide is 2:1:70. The preparation method of sulfonated polyetheretherketone is as follows: 22g of polyetheretherketone and 300mL of concentrated sulfuric acid are stirred and reacted at 65°C for 4 hours, then cooled to room temperature, slowly poured into a large amount of ice water, filtered, washed and dried to obtain sulfonated polyetheretherketone. The structural formula of polyetheretherketone is as follows:

[0048] (8) Add hydroxysulfonated polyetheretherketone and anhydrous N,N-dimethylformamide into a reaction kettle, heat to 60°C, stir until the hydroxysulfonated polyetheretherketone is completely dissolved, cool to room temperature, and obtain a 3% by mass hydroxysulfonated polyetheretherketone solution; add a 5% by mass acryloyl chloride solution in dichloromethane dropwise to the hydroxysulfonated polyetheretherketone solution, add triethylamine after the addition, stir and react for 10 hours, pour the system after the reaction into water, filter, wash with water first, then with ethanol, and dry to obtain double-bond sulfonated polyetheretherketone. The mass ratio of hydroxysulfonated polyetheretherketone to acryloyl chloride is 1:3, and the mass ratio of triethylamine to acryloyl chloride is 1.5:1.

[0049] (9) Add double-bond sulfonated polyetheretherketone into anhydrous N,N-dimethylformamide and dissolve it to obtain a 3% by mass solution of double-bond sulfonated polyetheretherketone; then stir the double-bond sulfonated polyetheretherketone solution and a 30% by mass solution of sodium 2,3-epoxypropanesulfonate in N,N-dimethylformamide to obtain a reaction solution; then add a 9% by mass solution of hydrogen peroxide in N,N-dimethylformamide to the reaction solution under stirring; after the addition is completed, heat to 85°C, stir and reflux to react for 6 hours; after cooling to room temperature, pour the reaction system into water, filter, wash with water, then with acetone, then with ethanol, then with hydrochloric acid, and finally with ethanol; and dry to obtain polymerized epoxypropanesulfonic acid grafted sulfonated polyetheretherketone. The mass ratio of double bond sulfonated polyetheretherketone to sodium 2,3-epoxypropanesulfonate is 1:4, and the mass ratio of sodium 2,3-epoxypropanesulfonate to N,N-dimethylformamide solution of hydrogen peroxide is 1:10. The N,N-dimethylformamide solution of sodium 2,3-epoxypropanesulfonate is prepared by stirring and mixing sodium 2,3-epoxypropanesulfonate and N,N-dimethylformamide, and the sodium 2,3-epoxypropanesulfonate is obtained by removing water from the sodium 2,3-epoxypropanesulfonate solution prepared in step (5) by vacuum distillation.

[0050] (10) Add poly(epoxypropanesulfonic acid) grafted sulfonated poly(ether ether ketone) and dimethyl sulfoxide into a stirring kettle, heat to 60°C, and stir until the poly(epoxypropanesulfonic acid) grafted sulfonated poly(ether ether ketone) is fully dissolved to obtain a poly(epoxypropanesulfonic acid) grafted sulfonated poly(ether ether ketone) solution with a mass fraction of 12%; then add poly(epoxypropanesulfonic acid) grafted nanodiamonds into the poly(epoxypropanesulfonic acid) grafted sulfonated poly(ether ether ketone) solution, and disperse them evenly by ultrasonication to obtain a film-forming slurry (the mass ratio of poly(epoxypropanesulfonic acid) grafted sulfonated poly(ether ether ketone) to poly(epoxypropanesulfonic acid) grafted nanodiamonds is 100:5); pour the film-forming slurry into a glass mold, let it stand at room temperature for 24 hours, and then put it into a drying oven at 80°C to dry to constant weight to obtain a cation exchange membrane.

[0051] (11) The prepared cation exchange membrane, cathode electrode and anode electrode are assembled into an electrolytic cell, wherein the anode electrode material is a mesh ruthenium-plated titanium metal electrode, and the cathode electrode material is a mesh nickel material. Then, the three electrolytic cells are connected in series from left to right, and lithium-containing brine is added to the anode chamber of the leftmost electrolytic cell, and lithium hydroxide solution is added to the cathode chamber of the leftmost electrolytic cell and the cathode chambers and anode chambers of the other two electrolytic cells. The power is turned on to perform electrolysis. Under the action of the electric field, the lithium ions in the lithium-containing brine selectively pass through the cation exchange membrane from the anode chamber of the leftmost electrolytic cell into the cathode chamber. Then, the electrolyte in the cathode chamber of the leftmost electrolytic cell flows into the anode chamber of the middle electrolytic cell under the action of gravity, and then enters the cathode chamber from the anode chamber under the action of the electric field, and then flows into the anode chamber of the rightmost electrolytic cell under the action of gravity, and finally enters the cathode chamber from the anode chamber under the action of the electric field. After cascade electrolysis, the extraction and enrichment of lithium in the brine is completed. The lithium hydroxide solution in the cathode chamber of the rightmost electrolytic cell is dried to obtain a lithium hydroxide product with a purity greater than 99%. Example 4

[0052] The salt lake brine cascade lithium extraction method based on in-situ electrolysis driven in this embodiment comprises the following steps: (1) This step is the same as step (1) of Example 1.

[0053] (2) This step is the same as step (2) in Example 1.

[0054] (3) This step is the same as step (3) in Example 1.

[0055] (4) Dispersing the propylene sulfonated nanodiamond in water to obtain a propylene sulfonated nanodiamond dispersion with a mass fraction of 30%; then stirring the propylene sulfonated nanodiamond dispersion and the sodium allyl sulfonate solution (the mass fraction of the sodium allyl sulfonate solution is 30%) to obtain a reaction solution, and then dropping a sodium persulfate solution with a mass fraction of 15% into the reaction solution under stirring. After the dropping is completed, heating to 90°C, stirring and reflux reaction for 3 hours, filtering, washing with water first, then washing with ethanol, then washing with hydrochloric acid, and finally washing with ethanol, and drying to obtain polymerized propyl sulfonic acid grafted nanodiamond. Among them, the mass ratio of the propylene sulfonated nanodiamond in the propylene sulfonated nanodiamond dispersion to the mass ratio of the sodium allyl sulfonate in the sodium allyl sulfonate solution is 1:2, and the mass of the sodium persulfate in the sodium persulfate solution is 8% of the mass of the sodium allyl sulfonate in the sodium allyl sulfonate solution.

[0056] (5) This step is the same as step (7) in Example 1.

[0057] (6) This step is the same as step (8) in Example 1.

[0058] (7) Add the double bond sulfonated polyether ether ketone into anhydrous N, N-dimethylformamide and dissolve it to obtain a 2% double bond sulfonated polyether ether ketone solution; then stir the double bond sulfonated polyether ether ketone solution and the 25% sodium allyl sulfonate solution in N, N-dimethylformamide to obtain a reaction solution, and then add a 15% sodium persulfate solution in N, N-dimethylformamide to the reaction solution under stirring. After the addition is completed, heat to 90°C, stir and reflux for 5 hours, cool to room temperature, pour the reaction system into water, filter, wash with water, then with acetone, then with ethanol, then with hydrochloric acid, and finally with ethanol, and dry to obtain polymerized propyl sulfonic acid grafted sulfonated polyether ether ketone. The mass ratio of the double bond sulfonated polyether ether ketone to the mass of sodium allyl sulfonate is 1:3, and the mass of sodium persulfate is 8% of the mass of sodium allyl sulfonate.

[0059] (8) Add polypropylsulfonic acid grafted sulfonated polyetheretherketone and dimethyl sulfoxide into a stirring kettle, heat to 45°C, and stir until the polypropylsulfonic acid grafted sulfonated polyetheretherketone is fully dissolved to obtain a polypropylsulfonic acid grafted sulfonated polyetheretherketone solution; then add polypropylsulfonic acid grafted nanodiamond into the polypropylsulfonic acid grafted sulfonated polyetheretherketone solution, and disperse it evenly by ultrasonication to obtain a film-forming slurry (the mass ratio of polypropylsulfonic acid grafted sulfonated polyetheretherketone to polypropylsulfonic acid grafted nanodiamond is 100:3); pour the film-forming slurry into a glass mold, let it stand at room temperature for 24 hours, and then put it into a 60°C drying oven to dry to constant weight to obtain a cation exchange membrane.

[0060] (9) This step is the same as step (11) of Example 1. Example 5

[0061] The salt lake brine cascade lithium extraction method based on in-situ electrolysis driven in this embodiment comprises the following steps: (1) This step is the same as step (1) of Example 1.

[0062] (2) This step is the same as step (2) in Example 1.

[0063] (3) This step is the same as step (3) in Example 1.

[0064] (4) Dispersing the propylene sulfonated nanodiamond in water to obtain a propylene sulfonated nanodiamond dispersion with a mass fraction of 35%; then stirring the propylene sulfonated nanodiamond dispersion and the sodium allyl sulfonate solution (the mass fraction of the sodium allyl sulfonate solution is 35%) to obtain a reaction solution, and then dropping a sodium persulfate solution with a mass fraction of 17% into the reaction solution under stirring. After the dropping is completed, heating to 92°C, stirring and reflux reaction for 3.5 hours, filtering, washing with water first, then washing with ethanol, then washing with hydrochloric acid, and finally washing with ethanol, and drying to obtain polymerized propyl sulfonic acid grafted nanodiamond. Among them, the ratio of the mass of propylene sulfonated nanodiamond in the propylene sulfonated nanodiamond dispersion to the mass of sodium allyl sulfonate in the sodium allyl sulfonate solution is 1:2.3, and the mass of sodium persulfate in the sodium persulfate solution is 8% of the mass of sodium allyl sulfonate in the sodium allyl sulfonate solution.

[0065] (5) This step is the same as step (7) in Example 1.

[0066] (6) This step is the same as step (8) in Example 1.

[0067] (7) Add the double bond sulfonated polyether ether ketone into anhydrous N, N-dimethylformamide and dissolve it to obtain a double bond sulfonated polyether ether ketone solution with a mass fraction of 2.5%; then stir the double bond sulfonated polyether ether ketone solution and the N, N-dimethylformamide solution with a mass fraction of 26% of sodium allyl sulfonate to obtain a reaction solution, and then add the N, N-dimethylformamide solution with a mass fraction of 18% of sodium persulfate to the reaction solution under stirring. After the addition is completed, heat it to 93°C, stir and reflux for reaction for 5.5 hours, cool it to room temperature, pour the reaction system into water, filter it, wash it with water, then with acetone, then with ethanol, then with hydrochloric acid, and finally with ethanol, and dry it to obtain the polymerized propyl sulfonic acid grafted sulfonated polyether ether ketone. The mass ratio of the double bond sulfonated polyether ether ketone to the mass of sodium allyl sulfonate is 1:3.5, and the mass of sodium persulfate is 8% of the mass of sodium allyl sulfonate.

[0068] (8) Add polypropylsulfonic acid grafted sulfonated polyetheretherketone and dimethyl sulfoxide into a stirring kettle, heat to 50°C, and stir until the polypropylsulfonic acid grafted sulfonated polyetheretherketone is fully dissolved to obtain a polypropylsulfonic acid grafted sulfonated polyetheretherketone solution; then add polypropylsulfonic acid grafted nanodiamond into the polypropylsulfonic acid grafted sulfonated polyetheretherketone solution, and disperse it evenly by ultrasonication to obtain a film-forming slurry (the mass ratio of polypropylsulfonic acid grafted sulfonated polyetheretherketone to polypropylsulfonic acid grafted nanodiamond is 100:4); pour the film-forming slurry into a glass mold, let it stand at room temperature for 24 hours, and then put it into a 70°C drying oven to dry to constant weight to obtain a cation exchange membrane.

[0069] (9) This step is the same as step (11) of Example 1. Example 6

[0070] The salt lake brine cascade lithium extraction method based on in-situ electrolysis driven in this embodiment comprises the following steps: (1) This step is the same as step (1) of Example 1.

[0071] (2) This step is the same as step (2) in Example 1.

[0072] (3) This step is the same as step (3) in Example 1.

[0073] (4) Dispersing the propylene sulfonated nanodiamond in water to obtain a propylene sulfonated nanodiamond dispersion with a mass fraction of 40%; then stirring the propylene sulfonated nanodiamond dispersion and the sodium allyl sulfonate solution (the mass fraction of the sodium allyl sulfonate solution is 40%) to obtain a reaction solution, and then dropping a 20% sodium persulfate solution into the reaction solution under stirring. After the dropping is completed, heating to 95°C, stirring and reflux reaction for 4 hours, filtering, washing with water first, then washing with ethanol, then washing with hydrochloric acid, and finally washing with ethanol, and drying to obtain polymerized propyl sulfonic acid grafted nanodiamond. Among them, the mass ratio of the propylene sulfonated nanodiamond in the propylene sulfonated nanodiamond dispersion to the mass ratio of the sodium allyl sulfonate in the sodium allyl sulfonate solution is 1:2.5, and the mass of the sodium persulfate in the sodium persulfate solution is 8% of the mass of the sodium allyl sulfonate in the sodium allyl sulfonate solution.

[0074] (5) This step is the same as step (7) in Example 1.

[0075] (6) This step is the same as step (8) in Example 1.

[0076] (7) Add the double bond sulfonated polyether ether ketone into anhydrous N, N-dimethylformamide and dissolve it to obtain a 3% double bond sulfonated polyether ether ketone solution; then stir the double bond sulfonated polyether ether ketone solution and the 30% sodium allyl sulfonate solution in N, N-dimethylformamide to obtain a reaction solution, and then add a 20% sodium persulfate solution in N, N-dimethylformamide to the reaction solution under stirring. After the addition is completed, heat to 95°C, stir and reflux for 6 hours, cool to room temperature, pour the reaction system into water, filter, wash with water, then with acetone, then with ethanol, then with hydrochloric acid, and finally with ethanol, and dry to obtain polymerized propyl sulfonic acid grafted sulfonated polyether ether ketone. The mass ratio of the double bond sulfonated polyether ether ketone to the mass of sodium allyl sulfonate is 1:4, and the mass of sodium persulfate is 8% of the mass of sodium allyl sulfonate.

[0077] (8) Add polypropylsulfonic acid grafted sulfonated polyetheretherketone and dimethyl sulfoxide into a stirring kettle, heat to 60°C, and stir until the polypropylsulfonic acid grafted sulfonated polyetheretherketone is fully dissolved to obtain a polypropylsulfonic acid grafted sulfonated polyetheretherketone solution; then add polypropylsulfonic acid grafted nanodiamond into the polypropylsulfonic acid grafted sulfonated polyetheretherketone solution, and disperse it evenly by ultrasonication to obtain a film-forming slurry (the mass ratio of polypropylsulfonic acid grafted sulfonated polyetheretherketone to polypropylsulfonic acid grafted nanodiamond is 100:5); pour the film-forming slurry into a glass mold, let it stand at room temperature for 24 hours, and then put it into a drying oven at 80°C to dry to constant weight to obtain a cation exchange membrane.

[0078] (9) This step is the same as step (11) of Example 1.

[0079] Comparative Example 1 The difference between the method for cascade lithium extraction from salt lake brine based on in-situ electrolysis driven in this comparative example and the method for cascade lithium extraction from salt lake brine based on in-situ electrolysis driven in Example 1 is that the preparation method of the cation exchange membrane used in the method for cascade lithium extraction from salt lake brine based on in-situ electrolysis driven in this comparative example is as follows: add the sulfonated polyetheretherketone and dimethyl sulfoxide in step (7) of Example 1 into a stirring kettle, heat to 45°C, and stir until the sulfonated polyetheretherketone is fully dissolved to obtain a film-forming slurry; pour the film-forming slurry into a glass mold, let it stand at room temperature for 24 hours, and then put it into a 60°C drying oven to dry to constant weight to obtain a cation exchange membrane.

[0080] Comparative Example 2 The difference between the method for cascade lithium extraction from salt lake brine based on in-situ electrolysis driven in this comparative example and the method for cascade lithium extraction from salt lake brine based on in-situ electrolysis driven in Example 1 is that the preparation method of the cation exchange membrane used in the method for cascade lithium extraction from salt lake brine based on in-situ electrolysis driven in this comparative example is as follows: the sulfonated polyetheretherketone and dimethyl sulfoxide in step (7) of Example 1 are added to a stirring kettle, heated to 45°C, and stirred until the sulfonated polyetheretherketone is fully dissolved to obtain a sulfonated polyetheretherketone solution; then, poly(propylene oxide sulfonic acid) grafted nanodiamonds are added to the sulfonated polyetheretherketone solution, and ultrasonically dispersed uniformly to obtain a film-forming slurry (the mass ratio of sulfonated polyetheretherketone to poly(propylene oxide sulfonic acid) grafted nanodiamonds is 100:3); the film-forming slurry is poured into a glass mold, allowed to stand at room temperature for 24 hours, and then placed in a 60°C drying oven to dry to constant weight to obtain a cation exchange membrane.

[0081] Comparative Example 3 The difference between the method for cascade lithium extraction from salt lake brine based on in-situ electrolysis driven in this comparative example and the method for cascade lithium extraction from salt lake brine based on in-situ electrolysis driven in Example 1 is that the preparation method of the cation exchange membrane used in the method for cascade lithium extraction from salt lake brine based on in-situ electrolysis driven in this comparative example is as follows: add poly(epoxypropanesulfonic acid) grafted sulfonated poly(ether ether ketone) and dimethyl sulfoxide into a stirring kettle, heat to 45°C, stir until the poly(epoxypropanesulfonic acid) grafted sulfonated poly(ether ether ketone) is fully dissolved, and obtain a polymerized The propylene sulfonate nanodiamond prepared in step (3) of Example 1 is added to the polymerized propylene sulfonate grafted sulfonated polyether ether ketone solution, and ultrasonically dispersed to obtain a film-forming slurry (the mass ratio of the polymerized propylene sulfonate grafted sulfonated polyether ether ketone to the propylene sulfonate nanodiamond is 100:3); the film-forming slurry is poured into a glass mold, allowed to stand at room temperature for 24 hours, and then placed in a 60°C drying oven to dry to constant weight to obtain a cation exchange membrane.

[0082] Experimental Example 1 In order to evaluate the comprehensive performance of the cation exchange membranes prepared in the embodiments and comparative examples, the surface resistance, tensile strength, elongation at break and oxidation resistance of the cation exchange membranes prepared in the embodiments and comparative examples were tested respectively. The oxidation resistance is expressed by the weight loss percentage after the cation exchange membrane is placed in a test liquid (the test liquid consists of water, hydrogen peroxide and ferrous sulfate, the concentration of hydrogen peroxide is 4%, and the concentration of ferrous sulfate is 4 mg / kg) at 80°C for a set time. The test results of the surface resistance, tensile strength, elongation at break and oxidation resistance of the cation exchange membranes prepared in the embodiments and comparative examples are shown in Table 1.

[0083] Table 1 Surface resistance, tensile strength, elongation at break and oxidation resistance of cation exchange membranes Cation exchange membrane <![CDATA[Sheet resistance (Ω·cm 2 )]]> Tensile strength(MPa) Elongation at break (%) Antioxidant(%) Example 1 2.7 42 53 5.7 Example 2 1.9 46 54 5.4 Example 3 2.3 44 51 5.6 Example 4 4.6 41 43 8.2 Example 5 4.9 38 45 8.6 Example 6 4.5 39 46 8.5 Comparative Example 1 7.2 36 45 14.8 Comparative Example 2 8.5 35 42 15.2 Comparative Example 3 10.4 32 41 16.4 It can be seen from the experimental results in Table 1 that grafting polymerized sulfonic acid segments onto the surface of nanodiamond and polyetheretherketone segments can effectively reduce the resistivity of the cation exchange membrane and improve the conductivity of the film. This is because in addition to the sulfonic acid groups bonded to the surface of the nanodiamond and the surface of polyetheretherketone, the surface of the nanodiamond and the surface of polyetheretherketone are also grafted with long-chain high-density polymerized sulfonic acid segments, and the polymerized sulfonic acid segments are distributed in a branched manner on the surface of the nanodiamond and the surface of polyetheretherketone. The film material made of the two contains a large number of sulfonic acid segments, and the grafted sulfonic acid segments can be arranged in an interactive network or entangled together by physical entanglement, thereby increasing the distribution density of the sulfonic acid groups. The main chain polyetheretherketone and the nanodiamond core can provide a distribution basis for the polymerized sulfonic acid segments, ensuring that the sulfonic acid polymer segments are effectively and evenly distributed, and can be staggered with the long branched sulfonic acid polymer segments to form pores composed of sulfonic acid groups, providing a basis for the passage of cations. In addition, the main chain polyetheretherketone, nanodiamond core and long branched sulfonic acid polymer segments are physically cross-linked with each other, which can effectively improve the strength and elongation of the film material, and can improve the anti-oxidation performance of the film material. It can be seen from Examples 1-3 and Examples 4-6 that the use of polymerized epoxypropanesulfonic acid as the long branched sulfonic acid polymer segment can further improve the mechanical properties and anti-oxidation performance of the film material than the use of polymerized propylsulfonic acid as the long branched sulfonic acid polymer segment. This may be because the polymerized epoxypropanesulfonic acid contains ether bonds, which have stronger rotation ability and can form hydrogen bonds, thereby improving the mechanical properties and anti-oxidation performance of the film.

[0084] Experimental Example 2 In order to investigate the selective permeability of the cation exchange membranes prepared in the embodiments and comparative examples to lithium ions and the actual use effect, the cation exchange membranes, cathode electrodes and anode electrodes prepared in the embodiments and comparative examples were assembled into an electrolytic cell, the anode electrode material was a mesh ruthenium-plated titanium metal electrode, the cathode electrode material was a mesh nickel material, lithium-containing brine was added to the anode chamber, lithium hydroxide solution was added to the cathode chamber, the power was turned on, and electrolysis was carried out, the electrolysis temperature was 45°C, and the current density was 1.5 kA / m 2, the lithium-containing brine is composed of lithium chloride, sodium chloride, magnesium chloride, calcium chloride, potassium chloride and water. The concentrations of lithium chloride, sodium chloride, magnesium chloride, calcium chloride and potassium chloride are all 0.05 mol / L, and the concentration of lithium hydroxide solution is 10wt%. After the electrolysis is completed, the selectivity coefficient is calculated based on the concentration of each metal cation in the liquid in the cathode chamber before and after the electrolysis. And according to the concentration and volume of lithium ions in the liquid in the cathode chamber before and after the electrolysis and the concentration and volume of lithium ions in the anode chamber before and after the electrolysis, the yield of lithium ions in the cathode chamber is calculated. The yield is equal to the percentage of the increase in lithium ions in the cathode chamber before and after the electrolysis to the decrease in lithium ions in the anode chamber before and after the electrolysis. At the same time, according to the power consumption and the increase in metal cations in the cathode chamber before and after the electrolysis, the current efficiency is calculated. The current efficiency is equal to the increase in metal cations in the cathode chamber before and after the electrolysis to the percentage of the theoretical increase in metal cations in the cathode chamber corresponding to the power consumption. The selective permeability performance and actual use effect of the cation exchange membrane for lithium ions are shown in Table 2. X(Li in Table 2 + / Na + ) represents the selectivity coefficient of the cation exchange membrane for lithium ions and sodium ions.

[0085] Table 2 Selective permeability of cation exchange membranes for lithium ions and actual use results Cation exchange membrane <![CDATA[X(Li + / That + )]]> <![CDATA[X(Li + / Mg 2+ )]]> <![CDATA[X(Li + / That 2+ )]]> <![CDATA[X(Li + / K + )]]> Yield (%) Current efficiency(%) Example 1 7.6 3.4 5.3 7.9 99.5 79.5 Example 2 7.9 3.5 5.6 8.2 99.8 81.2 Example 3 7.3 3.2 5.5 8.1 99.6 80.4 Example 4 5.7 2.6 4.2 6.1 96.3 67.3 Example 5 5.3 2.8 4.6 5.8 96.6 68.4 Example 6 5.6 2.5 4.3 5.7 96.1 65.7 Comparative Example 1 0.6 0.5 0.7 0.7 93.2 56.2 Comparative Example 2 0.7 0.4 0.6 0.8 94.1 55.4 Comparative Example 3 0.5 0.3 0.5 0.4 95.9 55.8 As can be seen from Table 2, the cation exchange membrane provided in the embodiment of the present invention has a good selective separation effect on impurity ions and lithium ions in conventional brine. This may be because the long-chain high-density polymerized sulfonic acid segments grafted on the surface of the nanodiamond and the surface of the polyetheretherketone can be arranged in a staggered manner to form pores composed of sulfonic acid groups, which can well screen lithium ions, sodium ions, magnesium ions, calcium ions and potassium ions, thereby improving the ion recognition and separation effect. However, in Comparative Examples 1-3, there is a lack of long-chain high-density polymerized sulfonic acid segments, and pores composed of sulfonic acid groups cannot be formed by staggered arrangement, resulting in poor lithium ion selective permeability of the film. In addition, the pores formed in the film of the present invention are temporarily unstable structures, which will not cause a large amount of electrical energy to be consumed when lithium ions pass through, and thus have a higher current efficiency and a higher lithium ion yield.

Claims

1. A method for cascade lithium extraction from salt lake brine based on in-situ electrolysis, characterized in that: The following steps are involved: The lithium-containing salt lake brine is electrolyzed so that the lithium ions in the salt lake brine can selectively pass through the cation exchange membrane to complete the enrichment and extraction of lithium ions; the cation exchange membrane is prepared by drying a solution of polymerized sulfonic acid grafted sulfonated polyetheretherketone and polymerized sulfonic acid grafted nanodiamond; the polymerized sulfonic acid grafted sulfonated polyetheretherketone is prepared by polymerization reaction of double-bond sulfonated polyetheretherketone and sulfonic acid monomer, and the double-bond sulfonated polyetheretherketone is prepared by reaction of hydroxylated sulfonated polyetheretherketone and acryloyl chloride; the polymerized sulfonic acid grafted nanodiamond is prepared by polymerization reaction of propylene sulfonated nanodiamond and sulfonic acid monomer, the propylene sulfonated nanodiamond is prepared by reaction of propylene alcoholized nanodiamond and 4-(chlorosulfonyl)benzoyl chloride, and the propylene alcoholized nanodiamond is prepared by reaction of carboxylated nanodiamond and glycidyl acrylate; the sulfonic acid monomer is sodium 2,3-epoxypropanesulfonate or sodium allyl sulfonate.

2. The method for cascade lithium extraction from salt lake brine based on in-situ electrolysis as claimed in claim 1, characterized in that: The carboxylated nano-diamond is prepared by mixing nano-diamond powder and acid solution at 70-80°C for 48-55h, wherein the acid solution is composed of concentrated nitric acid and concentrated sulfuric acid in a volume ratio of 1:3-3.5, and the mass ratio of the nano-diamond powder to the acid solution is 1:120-150.

3. The method for cascade lithium extraction from salt lake brine based on in-situ electrolysis as claimed in claim 1, characterized in that: The acrylated nanodiamond is prepared by mixing carboxylated nanodiamond, glycidyl acrylate and catalyst trimethylbenzylammonium bromide for reaction at 90-100° C. for 6-8 hours, the molar ratio of carboxyl group and glycidyl acrylate of the carboxylated nanodiamond is 1:2-3, and the mass ratio of carboxylated nanodiamond and catalyst trimethylbenzylammonium bromide is 50:0.5-0.

8.

4. The method for cascade lithium extraction from salt lake brine based on in-situ electrolysis as claimed in claim 1, characterized in that: The temperature of the reaction between acrylated nanodiamond and 4-(chlorosulfonyl)benzoyl chloride is 20-25°C, and the time is 3-4 hours. During the reaction, the acrylated nanodiamond dispersion is added into the 4-(chlorosulfonyl)benzoyl chloride solution. The molar ratio of the hydroxyl group of the acrylated nanodiamond to the 4-(chlorosulfonyl)benzoyl chloride is 1:1.5-2.

5. The method for cascade lithium extraction from salt lake brine based on in-situ electrolysis as claimed in claim 1, characterized in that: The reaction temperature of hydroxylated sulfonated polyetheretherketone and acryloyl chloride is room temperature, the reaction time is 8-10 hours, and the mass ratio of hydroxylated sulfonated polyetheretherketone and acryloyl chloride is 1:2-3.

6. The method for cascade lithium extraction from salt lake brine based on in-situ electrolysis as claimed in claim 1, characterized in that: The hydroxylated sulfonated polyetheretherketone is prepared by mixing the sulfonated polyetheretherketone and sodium borohydride in a solvent at 110-120°C for 3-4 hours, and the mass ratio of sodium borohydride to sulfonated polyetheretherketone is 1.8-2:1; the sulfonated polyetheretherketone is prepared by mixing the polyetheretherketone and concentrated sulfuric acid at 55-65°C for 3-4 hours, and the dosage ratio of the polyetheretherketone to the concentrated sulfuric acid is 20-22g:280-300mL.

7. The method for cascade lithium extraction from salt lake brine based on in-situ electrolysis as claimed in any one of claims 1 to 6, characterized in that: The sulfonic acid monomer is sodium 2,3-epoxypropanesulfonate, and the method for polymerizing the double-bond sulfonated polyetheretherketone and the sulfonic acid monomer is as follows: double-bond sulfonated polyetheretherketone, sodium 2,3-epoxypropanesulfonate and a solvent are mixed to obtain a reaction solution, and then a hydrogen peroxide solution with a mass fraction of 7-9% is added dropwise to the reaction solution under stirring. After the addition is completed, the mixture is heated to 80-85° C. and mixed for reaction for 5-6 hours to obtain polymerized epoxypropanesulfonic acid grafted sulfonated polyetheretherketone; the mass ratio of the double-bond sulfonated polyetheretherketone to the mass ratio of the sodium 2,3-epoxypropanesulfonate is 1:3-4, and the mass ratio of the sodium 2,3-epoxypropanesulfonate to the mass ratio of the hydrogen peroxide solution is 1:9-10.

8. The method for cascade lithium extraction from salt lake brine based on in-situ electrolysis as claimed in any one of claims 1 to 6, characterized in that: The sulfonic acid monomer is sodium 2,3-epoxypropanesulfonate, and the method for polymerizing propylene sulfonated nanodiamond and the sulfonic acid monomer is as follows: a propylene sulfonated nanodiamond dispersion and a sodium 2,3-epoxypropanesulfonate solution are mixed to obtain a reaction solution, and then a hydrogen peroxide solution with a mass fraction of 7-9% is added dropwise to the reaction solution under stirring. After the addition is completed, the reaction solution is heated to 80-85° C. and mixed for reaction for 3-4 hours to obtain polymerized epoxypropanesulfonic acid grafted nanodiamonds; the ratio of the mass of the propylene sulfonated nanodiamond in the propylene sulfonated nanodiamond dispersion to the mass of the sodium 2,3-epoxypropanesulfonate in the sodium 2,3-epoxypropanesulfonate solution is 1:2-2.5, and the ratio of the mass of the sodium 2,3-epoxypropanesulfonate in the sodium 2,3-epoxypropanesulfonate solution to the mass of the hydrogen peroxide solution is 1:5-7.

9. The method for cascade lithium extraction from salt lake brine based on in-situ electrolysis as claimed in any one of claims 1 to 6, characterized in that: The sulfonic acid monomer is sodium allyl sulfonate, and the method for polymerizing the double-bond sulfonated polyether ether ketone and the sulfonic acid monomer is as follows: double-bond sulfonated polyether ether ketone, sodium allyl sulfonate and a solvent are mixed to obtain a reaction solution, and then a persulfate initiator is added, heated to 90-95° C., and mixed for 5-6 hours to obtain a polymerized propyl sulfonic acid grafted sulfonated polyether ether ketone; the mass ratio of the double-bond sulfonated polyether ether ketone to the mass of the sodium allyl sulfonate is 1:3-4; The method for polymerizing propylene sulfonated nanodiamonds and sulfonic acid monomers is as follows: a propylene sulfonated nanodiamond dispersion and a sodium allyl sulfonate solution are mixed to obtain a reaction solution, and then a persulfate initiator is added, heated to 90-95° C., and mixed for reaction for 3-4 hours, wherein the ratio of the mass of propylene sulfonated nanodiamonds in the propylene sulfonated nanodiamond dispersion to the mass of sodium allyl sulfonate in the sodium allyl sulfonate solution is 1:2-2.

5.

10. The method for cascade lithium extraction from salt lake brine based on in-situ electrolysis as claimed in any one of claims 1 to 6, characterized in that: During electrolysis, the cation exchange membrane, cathode electrode and anode electrode are assembled into an electrolytic cell. The anode electrode material is a mesh ruthenium-plated titanium metal electrode, and the cathode electrode material is a mesh nickel material. Then, several electrolytic cells are connected in series in sequence to carry out cascade electrolysis to complete the extraction and enrichment of lithium in the salt lake brine.

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