A method for stepwise lithium extraction from salt lake brine based on in-situ electrolysis drive

Abstract

The present invention relates to a method for stepwise lithium extraction from salt lake brine driven by in-situ electrolysis, belonging to the technical field of lithium extraction from salt lakes. By grafting and polymerizing sulfonic acid segments on the surface of nanodiamond and the polyether ether ketone chain segments, the resistivity of the cation exchange membrane can be effectively reduced. Long-chain high-density polymerized sulfonic acid segments are also grafted on the surface of nanodiamond and polyether ether ketone, and the polymerized sulfonic acid segments are branched on the surface of nanodiamond and polyether ether ketone. The grafted sulfonic acid segments can be arranged in an interpenetrating network or entangled together by physical entanglement to increase the distribution density of sulfonic acid groups. The main chain of polyether ether ketone and the nanodiamond core can provide a distribution basis for the polymerized sulfonic acid segments to ensure the effective and uniform distribution of the polymerized sulfonic acid segments, and can be staggered with the long-branched sulfonic acid polymerized segments to form pores composed of sulfonic acid groups, providing a basis for the passage of cations.

Description

Technical Field

[0001] The present invention relates to a method for stepwise lithium extraction from salt lake brine driven by in-situ electrolysis, belonging to the technical field of lithium extraction from salt lakes. Background Art

[0002] Lithium mainly exists in spodumene, lepidolite and other pegmatites in the form of solid lithium ore in nature, or exists in salt lake brine, underground brine and seawater in the form of lithium ions. 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 in lithium extraction from brine, and the increasing depletion of solid lithium ore resources, the proportion of lithium products from brine has increased significantly, and there has been a major turning point in the development and application direction of lithium resources. At present, the methods for lithium extraction from salt lake brine mainly include precipitation method, solvent extraction method, calcination leaching method, carbonization method, adsorption method, membrane separation technology and electrodialysis technology, etc. Among them, electrodialysis technology uses the selective permeability of ion exchange membranes to anions and cations, and under the action of an external direct current electric field, anions and cations migrate directionally, so that the electrolyte is separated and concentrated.

[0003] Chinese patent document CN117265291A discloses a method for lithium extraction and sodium removal from low-concentration lithium-containing leaching solution of fly ash. The method includes alkalizing the fly ash leaching solution to form an alkalized lithium-containing leaching solution; building a multi-stage electrodialysis device; simultaneously introducing the cathode electrolyte containing sodium ions into the cathode chambers of multiple electrodialysis units in parallel, and introducing the alkalized lithium-containing leaching solution into the anode chambers of multiple electrodialysis units step by step in series; collecting the lithium-rich electrolyte formed in the cathode chambers of each electrodialysis unit into a sodium removal tank, and discharging the sodium-removed lithium-rich electrolyte; evaporating and crystallizing the sodium-removed lithium-rich electrolyte to obtain a sodium-removed lithium extraction product. In the lithium extraction method disclosed in this patent document, a large amount of sodium ions are contained in the extracted lithium product, and the purity of the lithium product is low, and subsequent purification and impurity removal are required. Therefore, an electrolytic lithium extraction method for high-purity lithium products is needed. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for stepwise lithium extraction from salt lake brine driven by in-situ electrolysis to solve the problem of low purity of lithium products obtained by current electrolytic lithium extraction methods.

[0005] The present invention provides a method for stepwise lithium extraction from salt lake brine driven by in-situ electrolysis, comprising the following steps: electrolyzing the lithium-containing salt lake brine to enable lithium ions in the salt lake brine to selectively pass through a cation exchange membrane, thereby completing the enrichment and extraction of lithium ions; the cation exchange membrane is prepared by drying a solution of polymerized sulfonic acid grafted sulfonated polyether ether ketone and polymerized sulfonic acid grafted nanodiamond; the polymerized sulfonic acid grafted sulfonated polyether ether ketone is prepared by polymerizing double bond sulfonated polyether ether ketone and a sulfonic acid monomer, and the double bond sulfonated polyether ether ketone is prepared by reacting hydroxylated sulfonated polyether ether ketone with acryloyl chloride; the polymerized sulfonic acid grafted nanodiamond is prepared by polymerizing acrylsulfonated nanodiamond and a sulfonic acid monomer, and the acrylsulfonated nanodiamond is prepared by reacting allylated nanodiamond with 4-(chlorosulfonyl) benzoyl chloride, and the allylated nanodiamond is prepared by reacting carboxylated nanodiamond with glycidyl acrylate; the sulfonic acid monomer is sodium 2,3-epoxypropanesulfonate or sodium allylsulfonate.

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

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

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

[0009] Preferably, the reaction temperature of hydroxylated sulfonated polyether ether ketone and acryloyl chloride is room temperature and the time is 8-10 h, and the mass ratio of hydroxylated sulfonated polyether ether ketone to acryloyl chloride is 1:2-3.

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

[0011] Preferably, the sulfonic acid monomer is sodium 2,3-epoxypropanesulfonate, and the method for the polymerization reaction of the double-bond sulfonated polyether ether ketone and the sulfonic acid monomer is as follows: Mix the double-bond sulfonated polyether ether ketone, sodium 2,3-epoxypropanesulfonate and a solvent to obtain a reaction solution, and then dropwise add a hydrogen peroxide solution with a mass fraction of 7-9% to the reaction solution under stirring. After the dropping is completed, heat to 80-85 °C and carry out a mixed reaction for 5-6 h to obtain the polymerized epoxypropane sulfonic acid grafted sulfonated polyether ether ketone; the mass ratio of the double-bond sulfonated polyether ether ketone to the mass of sodium 2,3-epoxypropanesulfonate is 1:3-4, and the mass ratio of the mass of sodium 2,3-epoxypropanesulfonate to the mass of the hydrogen peroxide solution is 1:9-10.

[0012] Preferably, the sulfonic acid monomer is sodium 2,3-epoxypropanesulfonate, and the method for the polymerization reaction of the acrylsulfonated nanodiamond and the sulfonic acid monomer is as follows: Mix the acrylsulfonated nanodiamond dispersion and the sodium 2,3-epoxypropanesulfonate solution to obtain a reaction solution, and then dropwise add a hydrogen peroxide solution with a mass fraction of 7-9% to the reaction solution under stirring. After the dropping is completed, heat to 80-85 °C and carry out a mixed reaction for 3-4 h to obtain the polymerized epoxypropane sulfonic acid grafted nanodiamond; the mass ratio of the acrylsulfonated nanodiamond in the acrylsulfonated nanodiamond dispersion to the mass of sodium 2,3-epoxypropanesulfonate in the sodium 2,3-epoxypropanesulfonate solution is 1:2-2.5, and the mass 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 allylsulfonate, and the method for the polymerization reaction of the double-bond sulfonated polyether ether ketone and the sulfonic acid monomer is as follows: Mix the double-bond sulfonated polyether ether ketone, sodium allylsulfonate and a solvent to obtain a reaction solution, then add a persulfate initiator, heat to 90-95 °C, and carry out a mixed reaction for 5-6 h to obtain the polymerized propylsulfonic acid grafted sulfonated polyether ether ketone; the mass ratio of the double-bond sulfonated polyether ether ketone to the mass of sodium allylsulfonate is 1:3-4;

[0014] The method for the polymerization reaction of propylene sulfonated nanodiamond and sulfonic acid monomer is as follows: Mix the propylene sulfonated nanodiamond dispersion and the sodium allyl sulfonate solution to obtain a reaction solution, then add a persulfate initiator, heat to 90 - 95 °C, and carry out a mixing reaction for 3 - 4 h. The mass ratio of the propylene sulfonated nanodiamond in the propylene sulfonated nanodiamond dispersion to the sodium allyl sulfonate in the sodium allyl sulfonate solution is 1:2 - 2.5.

[0015] Preferably, during electrolysis, a cation exchange membrane, a cathode electrode, and an anode electrode are assembled into an electrolytic cell. The anode electrode material is a reticulated ruthenium-plated titanium metal electrode, and the cathode electrode material is a reticulated nickel material. Then, several electrolytic cells are connected in series in turn for cascade electrolysis to complete the extraction and enrichment of lithium in the salt lake brine.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0017] (1) In the present invention, by grafting and polymerizing sulfonic acid chain segments on the surface of the nanodiamond and the polyether ether ketone chain segment, the resistivity of the cation exchange membrane can be effectively reduced, and the conductivity of the film can be improved. In addition to the sulfonic acid groups bonded to the surface of the nanodiamond and the polyether ether ketone surface, long-chain high-density polymerized sulfonic acid chain segments are also grafted on the surface of the nanodiamond and the polyether ether ketone surface. And the polymerized sulfonic acid chain segments are distributed in a branched shape on the surface of the nanodiamond and the polyether ether ketone surface. The film material made of the two contains a large number of sulfonic acid chain segments. The grafted sulfonic acid chain segments can be arranged in an alternating network or entangled together by physical entanglement to increase the distribution density of the sulfonic acid groups. The main chain polyether ether ketone and the nanodiamond core can provide a distribution basis for the polymerized sulfonic acid chain segments to ensure the effective and uniform distribution of the polymerized sulfonic acid chain segments, and can be arranged in an alternating pattern with the long branched-chain sulfonic acid polymerized chain segments to form pores composed of sulfonic acid groups, providing a basis for the passage of cations. In addition, the main chain polyether ether ketone, the nanodiamond core, and the long branched-chain sulfonic acid polymerized chain segments are physically crosslinked with each other, which can effectively improve the strength and elongation of the film material, and can also improve the antioxidant performance of the film material.

[0018] (2) The experimental results show that using polymerized glycidyl sulfonic acid as the long branched-chain sulfonic acid polymerized chain segment can improve the mechanical properties and antioxidant performance of the film material more than using polymerized propyl sulfonic acid as the long branched-chain sulfonic acid polymerized chain segment. This may be because polymerized glycidyl sulfonic acid contains ether bonds, which have stronger rotation ability and can form hydrogen bonds, thereby improving the mechanical properties and antioxidant performance of the film.

[0019] (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 the surface of polyether ether ketone can be arranged in a staggered manner to form pores composed of sulfonic acid groups. These pores 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 absent, 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 temporary unstable structures, which will not cause a large amount of electric energy to be consumed when lithium ions pass through, so it has a high current efficiency and a high lithium ion yield. Detailed implementation mode

[0020] The following examples are intended to further illustrate the content of the present invention rather than limit the protection scope of the present invention. Example 1

[0021] The method for stepwise lithium extraction from salt lake brine based on in-situ electrolysis driving in this example includes the following steps:

[0022] (1) Vacuum dry the nanodiamond powder at 60 °C for 24 h. Put the dried nanodiamond powder and acid solution into a stirring kettle, heat to 70 °C, stir and reflux for 48 h, cool to room temperature, filter, wash the filter cake with water until the washing liquid is neutral, and dry to obtain carboxylated nanodiamond. Among them, the acid solution is composed of concentrated nitric acid and concentrated sulfuric acid with a volume ratio of 1:3, and the mass ratio of the nanodiamond powder to the acid solution is 1:120.

[0023] (2) Add carboxylated nanodiamond, glycidyl acrylate, acetone and catalyst trimethylbenzyl ammonium bromide into the reaction kettle. After stirring evenly, heat to 90 °C and stir for 6 h. Filter, wash with acetone and then wash with water, and dry to obtain allylated nanodiamond. Among them, the molar ratio of the carboxyl group of carboxylated nanodiamond to glycidyl acrylate is 1:2, and the mass ratio of carboxylated nanodiamond, acetone and catalyst trimethylbenzyl ammonium bromide is 50:80:0.5.

[0024] (3) Add 4-(chlorosulfonyl)benzoyl chloride and anhydrous dichloromethane into the reaction kettle, stir evenly to obtain a 4-(chlorosulfonyl)benzoyl chloride solution with a mass fraction of 15%; stir evenly allylated nanodiamond and anhydrous dichloromethane to obtain an allylated nanodiamond dispersion with a mass fraction of 20%; under the conditions of 5 °C and stirring, dropwise add the allylated nanodiamond dispersion into the 4-(chlorosulfonyl)benzoyl chloride solution. After the dropping is completed, add triethylamine, then raise the temperature to 20 °C, stir and react for 3 h, filter, wash the filter cake with acetone first, then wash it thoroughly with water, and dry to obtain allylsulfonated nanodiamond. Among them, the molar ratio of the hydroxyl group of allylated nanodiamond to 4-(chlorosulfonyl)benzoyl chloride is 1:1.5, and the molar ratio of 4-(chlorosulfonyl)benzoyl chloride to triethylamine is 1:1.

[0025] (4) Add a saturated aqueous solution of sodium bisulfite into the reaction kettle, then dropwise add epichlorohydrin under stirring. After the dropping is completed, stir and react at room temperature for 24 h, filter, wash, and dry to obtain sodium 3-chloro-2-hydroxypropanesulfonate; among them, the molar ratio of sodium bisulfite to epichlorohydrin in the saturated aqueous solution of sodium bisulfite is 0.1:0.1.

[0026] (5) Add sodium 3-chloro-2-hydroxypropanesulfonate and water into the reaction kettle, stir evenly and heat to 28 °C, then add sodium hydroxide, stir and react for 30 min to obtain a sodium 2,3-epoxypropanesulfonate solution. Among them, the mass ratio of sodium 3-chloro-2-hydroxypropanesulfonate to water is 20:28, and the molar ratio of sodium 3-chloro-2-hydroxypropanesulfonate to sodium hydroxide is 1:1.

[0027] (6) Disperse allylsulfonated nanodiamond in water to obtain an allylsulfonated nanodiamond dispersion with a mass fraction of 30%; then stir evenly the allylsulfonated nanodiamond dispersion and the sodium 2,3-epoxypropanesulfonate solution obtained in step (5) to obtain a reaction solution, and then dropwise add a 7% hydrogen peroxide solution to the reaction solution under stirring. After the dropping is completed, heat to 80 °C, stir and reflux for 3 h, filter, wash with water first, then wash with ethanol, then wash with hydrochloric acid, and finally wash with ethanol, and dry to obtain polyepoxypropane sulfonic acid grafted nanodiamond. Among them, the mass ratio of allylsulfonated nanodiamond in the allylsulfonated nanodiamond dispersion to sodium 2,3-epoxypropanesulfonate in the sodium 2,3-epoxypropanesulfonate solution is 1:2, and the mass ratio of sodium 2,3-epoxypropanesulfonate in the sodium 2,3-epoxypropanesulfonate solution to the hydrogen peroxide solution is 1:5.

[0028] (7) Sodium borohydride, sulfonated poly(ether ether ketone), and N,N-dimethylformamide were added to a reaction kettle, heated to 110 °C, and stirred and refluxed for 3 h. After cooling to room temperature, the reaction system was poured into dilute hydrochloric acid, filtered, washed first with water and then with ethanol, and dried to obtain hydroxyl sulfonated poly(ether ether ketone). Among them, the mass ratio of sodium borohydride, sulfonated poly(ether ether ketone), and N,N-dimethylformamide was 1.8:1:50. The preparation method of sulfonated poly(ether ether ketone) was as follows: 20 g of poly(ether ether ketone) and 280 mL of concentrated sulfuric acid were stirred and reacted at 55 °C for 3 h, then cooled to room temperature, slowly poured into a large amount of ice water, filtered, washed, and dried to obtain sulfonated poly(ether ether ketone). The structural formula of poly(ether ether ketone) was as follows:

[0029]

[0030] (8) Hydroxyl sulfonated poly(ether ether ketone) and anhydrous N,N-dimethylformamide were added to a reaction kettle, heated to 45 °C, and stirred until the hydroxyl sulfonated poly(ether ether ketone) was completely dissolved. After cooling to room temperature, a 2% (by mass) hydroxyl sulfonated poly(ether ether ketone) solution was obtained; a dichloromethane solution of acryloyl chloride with a mass fraction of 10% was added dropwise to the hydroxyl sulfonated poly(ether ether ketone) solution. After the addition was completed, triethylamine was added, and the mixture was stirred and reacted for 8 h. The reaction system was poured into water, filtered, washed first with water and then with ethanol, and dried to obtain double bond sulfonated poly(ether ether ketone). Among them, the mass ratio of hydroxyl sulfonated poly(ether ether ketone) to acryloyl chloride was 1:2, and the mass ratio of triethylamine to acryloyl chloride was 1:1.

[0031] (9) Double bond sulfonated poly(ether ether ketone) was added to anhydrous N,N-dimethylformamide, and after dissolution, a 2% (by mass) double bond sulfonated poly(ether ether ketone) solution was obtained; then the double bond sulfonated poly(ether ether ketone) solution and an N,N-dimethylformamide solution of 2,3-epoxypropanesulfonic acid sodium with a mass fraction of 25% were stirred evenly to obtain a reaction solution. Then, an N,N-dimethylformamide solution of hydrogen peroxide with a mass fraction of 7% was added dropwise to the reaction solution under stirring. After the addition was completed, it was heated to 80 °C, stirred and refluxed for 5 h. After cooling to room temperature, the reaction system was poured into water, filtered, washed first with water, then with acetone, then with ethanol, then with hydrochloric acid, and finally with ethanol, and dried to obtain poly(epoxypropanesulfonic acid) grafted sulfonated poly(ether ether ketone). The mass ratio of double bond sulfonated poly(ether ether ketone) to 2,3-epoxypropanesulfonic acid sodium was 1:3, and the mass ratio of 2,3-epoxypropanesulfonic acid sodium to the N,N-dimethylformamide solution of hydrogen peroxide was 1:9. Among them, the N,N-dimethylformamide solution of 2,3-epoxypropanesulfonic acid sodium was prepared by stirring and mixing 2,3-epoxypropanesulfonic acid sodium and N,N-dimethylformamide. 2,3-epoxypropanesulfonic acid sodium was obtained by removing water from the 2,3-epoxypropanesulfonic acid sodium solution prepared in step (5) by vacuum distillation.

[0032] (10) Add the polymerized epoxysulfonic acid grafted sulfonated polyether ether ketone and dimethyl sulfoxide into a stirring kettle, heat to 45 °C, and stir until the polymerized epoxysulfonic acid grafted sulfonated polyether ether ketone is completely dissolved to obtain a polymerized epoxysulfonic acid grafted sulfonated polyether ether ketone solution with a mass fraction of 8%. Then add the polymerized epoxysulfonic acid grafted nanodiamond into the polymerized epoxysulfonic acid grafted sulfonated polyether ether ketone solution, and disperse it evenly by ultrasonic waves to obtain a film-forming slurry (the mass ratio of the polymerized epoxysulfonic acid grafted sulfonated polyether ether ketone to the polymerized epoxysulfonic acid grafted nanodiamond is 100:3). Pour the film-forming slurry into a glass mold, let it stand at room temperature for 24 h, and then place it in a drying oven at 60 °C to dry to a constant weight to obtain a cation exchange membrane.

[0033] (11) Assemble the prepared cation exchange membrane, the cathode electrode and the anode electrode into an electrolytic cell. The anode electrode material is a reticulated ruthenium-plated titanium metal electrode, and the cathode electrode material is a reticulated nickel material. Then connect three electrolytic cells in series from left to right. Add lithium-containing brine into the anode chamber of the leftmost electrolytic cell, and add lithium hydroxide solution into the cathode chamber of the leftmost electrolytic cell, as well as the cathode chambers and anode chambers of the other two electrolytic cells. Turn on the power supply for electrolysis. Under the action of the electric field, 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, 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. Finally, it enters the cathode chamber from the anode chamber under the action of the electric field. Through cascade electrolysis, the extraction and enrichment of lithium in the brine are completed. Dry the lithium hydroxide solution in the cathode chamber of the rightmost electrolytic cell to obtain a lithium hydroxide product with a purity greater than 99%. Example 2

[0034] The method for stepwise lithium extraction from salt lake brine based on in-situ electrolysis driving in this example includes the following steps:

[0035] (1) Vacuum-dry the nanodiamond powder at 60 °C for 24 h. Place the dried nanodiamond powder and the acid solution in a stirring kettle, heat to 75 °C, and stir and reflux for 50 h. Cool to room temperature, filter, wash the filter cake with water until the washing liquid is neutral, and dry to obtain carboxylated nanodiamond. Among them, the acid solution is composed of concentrated nitric acid and concentrated sulfuric acid with a volume ratio of 1:3.2, and the mass ratio of the nanodiamond powder to the acid solution is 1:130.

[0036] (2) Add carboxylated nanodiamond, glycidyl acrylate, acetone, and the catalyst trimethylbenzylammonium bromide into a reaction kettle. After stirring evenly, heat to 95 °C and stir for reaction for 7 h. Filter, wash with acetone and then with water, and dry to obtain allylated nanodiamond. Among them, the molar ratio of the carboxyl group of the carboxylated nanodiamond to glycidyl acrylate is 1:2.5, and the mass ratio of the carboxylated nanodiamond, acetone, and the catalyst trimethylbenzylammonium bromide is 50:100:0.6.

[0037] (3) Add 4-(chlorosulfonyl)benzoyl chloride and anhydrous dichloromethane into a reaction kettle, stir evenly to obtain a 4-(chlorosulfonyl)benzoyl chloride solution with a mass fraction of 18%; stir evenly the allylated nanodiamond and anhydrous dichloromethane to obtain an allylated nanodiamond dispersion with a mass fraction of 22%; under the conditions of 7 °C and stirring, dropwise add the allylated nanodiamond dispersion into the 4-(chlorosulfonyl)benzoyl chloride solution. After the dropping is completed, add triethylamine, then raise the temperature to 23 °C and stir for reaction for 3.5 h. Filter, first wash the filter cake with acetone, and then wash it thoroughly with water, and dry to obtain allylsulfonated nanodiamond. Among them, the molar ratio of the hydroxyl group of the allylated 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.

[0038] (4) Add a saturated aqueous solution of sodium bisulfite into a reaction kettle, and then dropwise add epichlorohydrin under stirring. After the dropping is completed, stir for reaction at room temperature for 27 h. Filter, wash, and dry to obtain sodium 3-chloro-2-hydroxypropanesulfonate; among them, the molar ratio of sodium bisulfite to epichlorohydrin in the saturated aqueous solution of sodium bisulfite is 0.1:0.11.

[0039] (5) Add sodium 3-chloro-2-hydroxypropanesulfonate and water into a reaction kettle, stir evenly and heat to 30 °C, then add sodium hydroxide and stir for reaction for 40 min to obtain a sodium 2,3-epoxypropanesulfonate solution. Among them, 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.

[0040] (6) Sulfonate the acrylated nanodiamond and disperse it in water to obtain an acrylated nanodiamond dispersion with a mass fraction of 35%. Then, uniformly stir the acrylated nanodiamond dispersion and the sodium 2,3-epoxysulfonate solution obtained in step (5) to obtain a reaction solution. Next, while stirring, add an 8% hydrogen peroxide solution dropwise to the reaction solution. After the addition is complete, heat the solution to 82 °C and stir and reflux for 3.5 h. Then, filter the solution, wash it first with water, then with ethanol, then with hydrochloric acid, and finally with ethanol again. After drying, poly(epoxysulfonic acid)-grafted nanodiamond is obtained. Among them, the mass ratio of acrylated nanodiamond in the acrylated nanodiamond dispersion to sodium 2,3-epoxysulfonate in the sodium 2,3-epoxysulfonate solution is 1:2.2, and the mass ratio of sodium 2,3-epoxysulfonate in the sodium 2,3-epoxysulfonate solution to the hydrogen peroxide solution is 1:6.

[0041] (7) Add sodium borohydride, sulfonated poly(ether ether ketone), and N,N-dimethylformamide to a reaction kettle, heat to 115 °C, stir and reflux for 3.5 h, and then cool to room temperature. Pour the reacted system into dilute hydrochloric acid, filter the solution, wash it first with water, then with ethanol, and after drying, hydroxy-sulfonated poly(ether ether ketone) is obtained. Among them, the mass ratio of sodium borohydride, sulfonated poly(ether ether ketone), and N,N-dimethylformamide is 1.9:1:60. The preparation method of sulfonated poly(ether ether ketone) is as follows: Stir and react 21 g of poly(ether ether ketone) and 290 mL of concentrated sulfuric acid at 60 °C for 3.5 h, then cool to room temperature, slowly pour it into a large amount of ice water, filter, wash, and dry to obtain sulfonated poly(ether ether ketone). The structural formula of poly(ether ether ketone) is as follows:

[0042]

[0043] (8) Add hydroxy-sulfonated poly(ether ether ketone) and anhydrous N,N-dimethylformamide to a reaction kettle, heat to 50 °C, stir until the hydroxy-sulfonated poly(ether ether ketone) is completely dissolved, and then cool to room temperature to obtain a hydroxy-sulfonated poly(ether ether ketone) solution with a mass fraction of 2.5%. Dropwise add a 12% solution of acryloyl chloride in dichloromethane to the hydroxy-sulfonated poly(ether ether ketone) solution. After the addition is complete, add triethylamine and stir and react for 9 h. Pour the reacted system into water, filter the solution, wash it first with water, then with ethanol, and after drying, double-bond-sulfonated poly(ether ether ketone) is obtained. Among them, the mass ratio of hydroxy-sulfonated poly(ether ether ketone) to acryloyl chloride is 1:2.5, and the mass ratio of triethylamine to acryloyl chloride is 1.3:1.

[0044] (9) The double-bond sulfonated polyether ether ketone was added to anhydrous N,N-dimethylformamide. After dissolution, a double-bond sulfonated polyether ether ketone solution with a mass fraction of 2.5% was obtained. Then, the double-bond sulfonated polyether ether ketone solution and an N,N-dimethylformamide solution of sodium 2,3-epoxypropylsulfonate with a mass fraction of 27% were stirred evenly to obtain a reaction solution. Then, an N,N-dimethylformamide solution of hydrogen peroxide with a mass fraction of 8% was added dropwise to the reaction solution under stirring. After the addition was completed, the mixture was heated to 83 °C and stirred and refluxed for 6 h. After cooling to room temperature, the reaction system was poured into water, filtered, washed first with water, then with acetone, then with ethanol, then with hydrochloric acid, and finally with ethanol. After drying, the polymerized sodium 2,3-epoxypropylsulfonate-grafted sulfonated polyether ether ketone was obtained. The mass ratio of the double-bond sulfonated polyether ether ketone to the mass of sodium 2,3-epoxypropylsulfonate was 1:3, and the mass ratio of the mass of sodium 2,3-epoxypropylsulfonate to the mass of the N,N-dimethylformamide solution of hydrogen peroxide was 1:10. Among them, the N,N-dimethylformamide solution of sodium 2,3-epoxypropylsulfonate was prepared by stirring and mixing sodium 2,3-epoxypropylsulfonate and N,N-dimethylformamide. Sodium 2,3-epoxypropylsulfonate was obtained by removing water from the sodium 2,3-epoxypropylsulfonate solution prepared in step (5) by vacuum distillation.

[0045] (10) The polymerized sodium 2,3-epoxypropylsulfonate-grafted sulfonated polyether ether ketone and dimethyl sulfoxide were added to a stirring kettle and heated to 50 °C. After stirring until the polymerized sodium 2,3-epoxypropylsulfonate-grafted sulfonated polyether ether ketone was completely dissolved, a polymerized sodium 2,3-epoxypropylsulfonate-grafted sulfonated polyether ether ketone solution with a mass fraction of 9% was obtained. Then, the polymerized sodium 2,3-epoxypropylsulfonate-grafted nanodiamond was added to the polymerized sodium 2,3-epoxypropylsulfonate-grafted sulfonated polyether ether ketone solution and ultrasonically dispersed evenly to obtain a film-forming slurry (the mass ratio of the polymerized sodium 2,3-epoxypropylsulfonate-grafted sulfonated polyether ether ketone to the polymerized sodium 2,3-epoxypropylsulfonate-grafted nanodiamond was 100:4). The film-forming slurry was poured into a glass mold, left standing at room temperature for 24 h, and then placed in a drying oven at 70 °C and dried to a constant weight to obtain a cation exchange membrane.

[0046] (11) Assemble the prepared cation exchange membrane, cathode electrode, and anode electrode into an electrolytic cell. The anode electrode material is a reticulated ruthenium-plated titanium metal electrode, and the cathode electrode material is a reticulated nickel material. Then, connect three electrolytic cells in series from left to right. Add lithium-containing brine to the anode chamber of the leftmost electrolytic cell, and add lithium hydroxide solution to the cathode chamber of the leftmost electrolytic cell, as well as the cathode chambers and anode chambers of the other two electrolytic cells. Turn on the power supply and conduct electrolysis. 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 under the action of an electric field. 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 an electric field, and then flows into the anode chamber of the rightmost electrolytic cell under the action of gravity. Finally, it enters the cathode chamber from the anode chamber under the action of an electric field. Through stepwise electrolysis, the extraction and enrichment of lithium in the brine are completed. Dry the lithium hydroxide solution in the cathode chamber of the rightmost electrolytic cell to obtain a lithium hydroxide product with a purity greater than 99%. Example 3

[0047] The method for stepwise lithium extraction from salt lake brine based on in-situ electrolysis drive in this example includes the following steps:

[0048] (1) Vacuum-dry the nanodiamond powder at 60 °C for 24 h. Place the dried nanodiamond powder and acid solution in a stirring kettle, heat to 80 °C, stir and reflux for 55 h, cool to room temperature, filter, wash the filter cake with water until the washing liquid is neutral, and dry to obtain carboxylated nanodiamond. Among them, the acid solution is composed of concentrated nitric acid and concentrated sulfuric acid with a volume ratio of 1:3.5, and the mass ratio of the nanodiamond powder to the acid solution is 1:150.

[0049] (2) Add carboxylated nanodiamond, glycidyl acrylate, acetone, and the catalyst trimethylbenzylammonium bromide to the reaction kettle. After stirring evenly, heat to 100 °C and stir for 8 h. Filter, wash with acetone and then with water, and dry to obtain allylated nanodiamond. Among them, the molar ratio of the carboxyl group of carboxylated nanodiamond to glycidyl acrylate is 1:3, and the mass ratio of carboxylated nanodiamond, acetone, and the catalyst trimethylbenzylammonium bromide is 50:120:0.8.

[0050] (3) Add 4-(chlorosulfonyl)benzoyl chloride and anhydrous dichloromethane into the reaction kettle, stir evenly to obtain a 4-(chlorosulfonyl)benzoyl chloride solution with a mass fraction of 20%; stir evenly allylated nanodiamond and anhydrous dichloromethane to obtain an allylated nanodiamond dispersion with a mass fraction of 25%; under the conditions of 8 °C and stirring, dropwise add the allylated nanodiamond dispersion into the 4-(chlorosulfonyl)benzoyl chloride solution. After the dropping is completed, add triethylamine, then raise the temperature to 25 °C, stir and react for 4 h, filter, first wash the filter cake with acetone, then wash it thoroughly with water, and dry to obtain allylsulfonated nanodiamond. Among them, the molar ratio of the hydroxyl group of allylated nanodiamond to 4-(chlorosulfonyl)benzoyl chloride is 1:2, and the molar ratio of 4-(chlorosulfonyl)benzoyl chloride to triethylamine is 1:1.2.

[0051] (4) Add a saturated aqueous solution of sodium bisulfite into the reaction kettle, then dropwise add epichlorohydrin under stirring. After the dropping is completed, stir and react at room temperature for 30 h, filter, wash, and dry to obtain sodium 3-chloro-2-hydroxypropanesulfonate; among them, the molar ratio of sodium bisulfite to epichlorohydrin in the saturated aqueous solution of sodium bisulfite is 0.1:0.12.

[0052] (5) Add sodium 3-chloro-2-hydroxypropanesulfonate and water into the reaction kettle, stir evenly and heat to 32 °C, then add sodium hydroxide, stir and react for 45 min to obtain a sodium 2,3-epoxypropanesulfonate solution. Among them, the mass ratio of sodium 3-chloro-2-hydroxypropanesulfonate to water is 20:32, and the molar ratio of sodium 3-chloro-2-hydroxypropanesulfonate to sodium hydroxide is 1:1.

[0053] (6) Disperse allylsulfonated nanodiamond in water to obtain an allylsulfonated nanodiamond dispersion with a mass fraction of 40%; then stir evenly the allylsulfonated nanodiamond dispersion and the sodium 2,3-epoxypropanesulfonate solution obtained in step (5) to obtain a reaction solution, and then dropwise add a 9% hydrogen peroxide solution to the reaction solution under stirring. After the dropping is completed, heat to 85 °C, stir and reflux for 4 h, filter, first wash with water, then wash with ethanol, then wash with hydrochloric acid, and finally wash with ethanol, and dry to obtain polyepoxypropane sulfonic acid grafted nanodiamond. Among them, the mass ratio of allylsulfonated nanodiamond in the allylsulfonated nanodiamond dispersion to sodium 2,3-epoxypropanesulfonate in the sodium 2,3-epoxypropanesulfonate solution is 1:2.5, and the mass ratio of sodium 2,3-epoxypropanesulfonate in the sodium 2,3-epoxypropanesulfonate solution to the hydrogen peroxide solution is 1:7.

[0054] (7) Sodium borohydride, sulfonated poly(ether ether ketone), and N,N-dimethylformamide were added to a reaction kettle, heated to 120 °C, and stirred and refluxed for 4 h. After cooling to room temperature, the reaction system was poured into dilute hydrochloric acid, filtered, washed first with water and then with ethanol, and dried to obtain hydroxyl-sulfonated poly(ether ether ketone). Among them, the mass ratio of sodium borohydride, sulfonated poly(ether ether ketone), and N,N-dimethylformamide was 2:1:70. The preparation method of sulfonated poly(ether ether ketone) was as follows: 22 g of poly(ether ether ketone) and 300 mL of concentrated sulfuric acid were stirred and reacted at 65 °C for 4 h, then cooled to room temperature and slowly poured into a large amount of ice water. After filtration, washing, and drying, sulfonated poly(ether ether ketone) was obtained. The structural formula of poly(ether ether ketone) was as follows:

[0055]

[0056] (8) Hydroxyl-sulfonated poly(ether ether ketone) and anhydrous N,N-dimethylformamide were added to a reaction kettle, heated to 60 °C, and stirred until the hydroxyl-sulfonated poly(ether ether ketone) was completely dissolved. After cooling to room temperature, a 3% (mass fraction) hydroxyl-sulfonated poly(ether ether ketone) solution was obtained; a dichloromethane solution of acryloyl chloride with a mass fraction of 5% was added dropwise to the hydroxyl-sulfonated poly(ether ether ketone) solution. After the addition was completed, triethylamine was added, and the mixture was stirred and reacted for 10 h. The reaction system was poured into water, filtered, washed first with water and then with ethanol, and dried to obtain double-bond-sulfonated poly(ether ether ketone). Among them, the mass ratio of hydroxyl-sulfonated poly(ether ether ketone) to acryloyl chloride was 1:3, and the mass ratio of triethylamine to acryloyl chloride was 1.5:1.

[0057] (9) Double-bond-sulfonated poly(ether ether ketone) was added to anhydrous N,N-dimethylformamide, and after dissolution, a 3% (mass fraction) double-bond-sulfonated poly(ether ether ketone) solution was obtained; then the double-bond-sulfonated poly(ether ether ketone) solution and an N,N-dimethylformamide solution of 2,3-epoxypropanesulfonate with a mass fraction of 30% were stirred evenly to obtain a reaction solution. Then, an N,N-dimethylformamide solution of hydrogen peroxide with a mass fraction of 9% was added dropwise to the reaction solution under stirring. After the addition was completed, it was heated to 85 °C and stirred and refluxed for 6 h. After cooling to room temperature, the reaction system was poured into water, filtered, washed first with water, then with acetone, then with ethanol, then with hydrochloric acid, and finally with ethanol, and dried to obtain poly(epoxypropanesulfonic acid)-grafted sulfonated poly(ether ether ketone). The mass ratio of double-bond-sulfonated poly(ether ether ketone) to 2,3-epoxypropanesulfonate was 1:4, and the mass ratio of 2,3-epoxypropanesulfonate to the N,N-dimethylformamide solution of hydrogen peroxide was 1:10. Among them, the N,N-dimethylformamide solution of 2,3-epoxypropanesulfonate was prepared by stirring and mixing 2,3-epoxypropanesulfonate and N,N-dimethylformamide. 2,3-epoxypropanesulfonate was obtained by removing water from the 2,3-epoxypropanesulfonate solution prepared in step (5) by vacuum distillation.

[0058] (10) Add the polymerized epoxysulfonic acid grafted sulfonated polyether ether ketone and dimethyl sulfoxide into a stirring kettle, heat to 60 °C, and stir until the polymerized epoxysulfonic acid grafted sulfonated polyether ether ketone is completely dissolved to obtain a polymerized epoxysulfonic acid grafted sulfonated polyether ether ketone solution with a mass fraction of 12%. Then add the polymerized epoxysulfonic acid grafted nanodiamond into the polymerized epoxysulfonic acid grafted sulfonated polyether ether ketone solution, and disperse it evenly by ultrasonic wave to obtain a film-forming slurry (the mass ratio of the polymerized epoxysulfonic acid grafted sulfonated polyether ether ketone to the polymerized epoxysulfonic acid grafted nanodiamond is 100:5). Pour the film-forming slurry into a glass mold, let it stand at room temperature for 24 h, and then put it into a drying oven at 80 °C to dry to constant weight to obtain a cation exchange membrane.

[0059] (11) Assemble the obtained cation exchange membrane, the cathode electrode and the anode electrode into an electrolytic cell. The anode electrode material is a reticulated ruthenium-plated titanium metal electrode, and the cathode electrode material is a reticulated nickel material. Then connect three electrolytic cells in series from left to right. Add lithium-containing brine into the anode chamber of the leftmost electrolytic cell, and add lithium hydroxide solution into the cathode chamber of the leftmost electrolytic cell and the cathode chambers and anode chambers of the other two electrolytic cells. Turn on the power supply for electrolysis. Under the action of the electric field, 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 in the middle electrolytic cell under the action of gravity, then enters the cathode 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. Finally, it enters the cathode chamber from the anode chamber under the action of the electric field. Through stepwise electrolysis, the extraction and enrichment of lithium in the brine are completed. Dry the lithium hydroxide solution in the cathode chamber of the rightmost electrolytic cell to obtain a lithium hydroxide product with a purity greater than 99%. Example 4

[0060] The method for stepwise lithium extraction from salt lake brine based on in-situ electrolysis drive in this example includes the following steps:

[0061] (1) This step is the same as step (1) of Example 1.

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

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

[0064] (4) Sulfonate the propylene-functionalized nanodiamond in water to obtain a 30% (by mass) dispersion of sulfonated propylene-functionalized nanodiamond in water. Then, uniformly stir the dispersion of sulfonated propylene-functionalized nanodiamond and the solution of sodium allylsulfonate (the mass fraction of the sodium allylsulfonate solution is 30%) to obtain a reaction solution. Then, while stirring, add a 15% (by mass) solution of sodium persulfate dropwise to the reaction solution. After the addition is complete, heat the mixture to 90 °C and stir and reflux for 3 h. Filter the mixture, first wash it with water, then with ethanol, then with hydrochloric acid, and finally with ethanol. After drying, polypropylenesulfonic acid-grafted nanodiamond is obtained. Among them, the mass ratio of the sulfonated propylene-functionalized nanodiamond in the sulfonated propylene-functionalized nanodiamond dispersion to the mass of sodium allylsulfonate in the sodium allylsulfonate solution is 1:2, and the mass of sodium persulfate in the sodium persulfate solution is 8% of the mass of sodium allylsulfonate in the sodium allylsulfonate solution.

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

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

[0067] (7) Add the double-bond-sulfonated poly(ether ether ketone) to anhydrous N,N-dimethylformamide and dissolve it to obtain a 2% (by mass) solution of double-bond-sulfonated poly(ether ether ketone). Then, uniformly stir the solution of double-bond-sulfonated poly(ether ether ketone) and the N,N-dimethylformamide solution of sodium allylsulfonate with a mass fraction of 25% to obtain a reaction solution. Then, while stirring, add a 15% (by mass) N,N-dimethylformamide solution of sodium persulfate dropwise to the reaction solution. After the addition is complete, heat the mixture to 90 °C and stir and reflux for 5 h. After cooling to room temperature, pour the reaction system into water, filter it, first wash it with water, then with acetone, then with ethanol, then with hydrochloric acid, and finally with ethanol. After drying, polypropylenesulfonic acid-grafted sulfonated poly(ether ether ketone) is obtained. The mass ratio of the double-bond-sulfonated poly(ether ether ketone) to the mass of sodium allylsulfonate is 1:3, and the mass of sodium persulfate is 8% of the mass of sodium allylsulfonate.

[0068] (8) Add the polypropylenesulfonic acid-grafted sulfonated poly(ether ether ketone) and dimethyl sulfoxide to a stirring kettle, heat it to 45 °C, and stir until the polypropylenesulfonic acid-grafted sulfonated poly(ether ether ketone) is completely dissolved to obtain a solution of polypropylenesulfonic acid-grafted sulfonated poly(ether ether ketone). Then, add the polypropylenesulfonic acid-grafted nanodiamond to the solution of polypropylenesulfonic acid-grafted sulfonated poly(ether ether ketone) and ultrasonically disperse it uniformly to obtain a film-forming slurry (the mass ratio of the polypropylenesulfonic acid-grafted sulfonated poly(ether ether ketone) to the polypropylenesulfonic acid-grafted nanodiamond is 100:3). Pour the film-forming slurry into a glass mold, let it stand at room temperature for 24 h, and then place it in a drying oven at 60 °C and dry it to a constant weight to obtain a cation exchange membrane.

[0069] (9) This step is the same as step (11) of Example 1. Example 5

[0070] The method for stepwise lithium extraction from salt lake brine based on in-situ electrolysis drive in this example includes the following steps:

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

[0072] (2) This step is the same as step (2) of Example 1.

[0073] (3) This step is the same as step (3) of Example 1.

[0074] (4) Disperse propene-sulfonated nanodiamond in water to obtain a propene-sulfonated nanodiamond dispersion with a mass fraction of 35%; then stir the propene-sulfonated nanodiamond dispersion and a sodium allyl sulfonate solution (the mass fraction of the sodium allyl sulfonate solution is 35%) evenly to obtain a reaction solution. Then, while stirring, dropwise add a sodium persulfate solution with a mass fraction of 17% to the reaction solution. After the addition is completed, heat to 92 °C, stir and reflux for 3.5 h, filter, wash first with water, then with ethanol, then with hydrochloric acid, and finally with ethanol. After drying, polypropylsulfonic acid grafted nanodiamond is obtained. Among them, the mass ratio of propene-sulfonated nanodiamond in the propene-sulfonated nanodiamond dispersion to 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.

[0075] (5) This step is the same as step (7) of Example 1.

[0076] (6) This step is the same as step (8) of Example 1.

[0077] (7) Add double-bond sulfonated polyether ether ketone to anhydrous N,N-dimethylformamide. After dissolution, a double-bond sulfonated polyether ether ketone solution with a mass fraction of 2.5% is obtained; then stir the double-bond sulfonated polyether ether ketone solution and an N,N-dimethylformamide solution of sodium allyl sulfonate with a mass fraction of 26% evenly to obtain a reaction solution. Then, while stirring, dropwise add an N,N-dimethylformamide solution of sodium persulfate with a mass fraction of 18% to the reaction solution. After the addition is completed, heat to 93 °C, stir and reflux for 5.5 h. After cooling to room temperature, pour the reacted system into water, filter, wash first with water, then with acetone, then with ethanol, then with hydrochloric acid, and finally with ethanol. After drying, polypropylsulfonic acid grafted sulfonated polyether ether ketone is obtained. The mass ratio of double-bond sulfonated polyether ether ketone to sodium allyl sulfonate is 1:3.5, and the mass of sodium persulfate is 8% of the mass of sodium allyl sulfonate.

[0078] (8) Add grafted polypropylsulfonic acid sulfonated polyether ether ketone and dimethyl sulfoxide into a stirring kettle, heat to 50 °C, and stir until the grafted polypropylsulfonic acid sulfonated polyether ether ketone is completely dissolved to obtain a grafted polypropylsulfonic acid sulfonated polyether ether ketone solution; then add grafted polypropylsulfonic acid nanodiamond into the grafted polypropylsulfonic acid sulfonated polyether ether ketone solution, and disperse it evenly by ultrasonic wave to obtain a film-forming slurry (the mass ratio of grafted polypropylsulfonic acid sulfonated polyether ether ketone to grafted polypropylsulfonic acid nanodiamond is 100:4); pour the film-forming slurry into a glass mold, let it stand at room temperature for 24 h, and then put it into a drying oven at 70 °C to dry to constant weight to obtain a cation exchange membrane.

[0079] (9) This step is the same as step (11) of Example 1. Example 6

[0080] The method for stepwise lithium extraction from salt lake brine based on in-situ electrolysis driving in this example includes the following steps:

[0081] (1) This step is the same as step (1) of Example 1.

[0082] (2) This step is the same as step (2) of Example 1.

[0083] (3) This step is the same as step (3) of Example 1.

[0084] (4) Disperse acrylsulfonic acid-functionalized nanodiamond in water to obtain an acrylsulfonic acid-functionalized nanodiamond dispersion with a mass fraction of 40%; then stir the acrylsulfonic acid-functionalized nanodiamond dispersion and sodium allylsulfonate solution (the mass fraction of the sodium allylsulfonate solution is 40%) evenly to obtain a reaction solution, and then dropwise add a 20% sodium persulfate solution to the reaction solution under stirring. After the addition is completed, heat to 95 °C, stir and reflux for 4 h, filter, wash with water first, then wash with ethanol, then wash with hydrochloric acid, and finally wash with ethanol, and dry to obtain grafted polypropylsulfonic acid nanodiamond. Among them, the mass ratio of acrylsulfonic acid-functionalized nanodiamond in the acrylsulfonic acid-functionalized nanodiamond dispersion to sodium allylsulfonate in the sodium allylsulfonate solution is 1:2.5, and the mass of sodium persulfate in the sodium persulfate solution is 8% of the mass of sodium allylsulfonate in the sodium allylsulfonate solution.

[0085] (5) This step is the same as step (7) of Example 1.

[0086] (6) This step is the same as step (8) of Example 1.

[0087] (7) The double-bond sulfonated polyether ether ketone was added to anhydrous N,N-dimethylformamide. After dissolution, a double-bond sulfonated polyether ether ketone solution with a mass fraction of 3% was obtained. Then, the double-bond sulfonated polyether ether ketone solution and an N,N-dimethylformamide solution of sodium allylsulfonate with a mass fraction of 30% were stirred evenly to obtain a reaction solution. Then, while stirring, an N,N-dimethylformamide solution of sodium persulfate with a mass fraction of 20% was added dropwise to the reaction solution. After the addition was completed, the mixture was heated to 95 °C and stirred and refluxed for 6 h. After cooling to room temperature, the reaction system was poured into water, filtered, washed first with water, then with acetone, then with ethanol, then with hydrochloric acid, and finally with ethanol. After drying, polyallyl sulfonic acid grafted sulfonated polyether ether ketone was obtained. The mass ratio of the double-bond sulfonated polyether ether ketone to the mass of sodium allylsulfonate was 1:4, and the mass of sodium persulfate was 8% of the mass of sodium allylsulfonate.

[0088] (8) The polyallyl sulfonic acid grafted sulfonated polyether ether ketone and dimethyl sulfoxide were added to a stirring kettle and heated to 60 °C. After stirring until the polyallyl sulfonic acid grafted sulfonated polyether ether ketone was completely dissolved, a polyallyl sulfonic acid grafted sulfonated polyether ether ketone solution was obtained. Then, the polyallyl sulfonic acid grafted nanodiamond was added to the polyallyl sulfonic acid grafted sulfonated polyether ether ketone solution and ultrasonically dispersed evenly to obtain a film-forming slurry (the mass ratio of the polyallyl sulfonic acid grafted sulfonated polyether ether ketone to the polyallyl sulfonic acid grafted nanodiamond was 100:5). The film-forming slurry was poured into a glass mold, left standing at room temperature for 24 h, and then placed in an 80 °C drying oven and dried to a constant weight to obtain a cation exchange membrane.

[0089] (9) This step is the same as step (11) of Example 1.

[0090] Comparative Example 1

[0091] The difference between the method for stepwise lithium extraction from salt lake brine based on in-situ electrolysis drive in this comparative example and the method for stepwise lithium extraction from salt lake brine based on in-situ electrolysis drive in Example 1 is only that the preparation method of the cation exchange membrane used in the method for stepwise lithium extraction from salt lake brine based on in-situ electrolysis drive in this comparative example is as follows: The sulfonated polyether ether ketone and dimethyl sulfoxide in step (7) of Example 1 were added to a stirring kettle and heated to 45 °C. After stirring until the sulfonated polyether ether ketone was completely dissolved, a film-forming slurry was obtained. The film-forming slurry was poured into a glass mold, left standing at room temperature for 24 h, and then placed in a 60 °C drying oven and dried to a constant weight to obtain a cation exchange membrane.

[0092] Comparative Example 2

[0093] The difference between the in-situ electrolysis-driven stepwise lithium extraction method from salt lake brine in this comparative example and the in-situ electrolysis-driven stepwise lithium extraction method in Example 1 lies only in that the preparation method of the cation exchange membrane used in the in-situ electrolysis-driven stepwise lithium extraction method in this comparative example is as follows: Add sulfonated polyether ether ketone and dimethyl sulfoxide from step (7) of Example 1 into a stirring kettle, heat to 45 °C, and stir until the sulfonated polyether ether ketone is fully dissolved to obtain a sulfonated polyether ether ketone solution; then add grafted nano-diamond of polyglycidyl methacrylate sulfonic acid into the sulfonated polyether ether ketone solution, and disperse it evenly by ultrasonic wave to obtain a film-forming slurry (the mass ratio of sulfonated polyether ether ketone to grafted nano-diamond of polyglycidyl methacrylate sulfonic acid is 100:3); Pour the film-forming slurry into a glass mold, let it stand at room temperature for 24 h, and then place it in a drying oven at 60 °C to dry to constant weight to obtain the cation exchange membrane.

[0094] Comparative Example 3

[0095] The difference between the in-situ electrolysis-driven stepwise lithium extraction method from salt lake brine in this comparative example and the in-situ electrolysis-driven stepwise lithium extraction method in Example 1 lies only in that the preparation method of the cation exchange membrane used in the in-situ electrolysis-driven stepwise lithium extraction method in this comparative example is as follows: Add grafted sulfonated polyether ether ketone of polyglycidyl methacrylate sulfonic acid and dimethyl sulfoxide into a stirring kettle, heat to 45 °C, and stir until the grafted sulfonated polyether ether ketone of polyglycidyl methacrylate sulfonic acid is fully dissolved to obtain a grafted sulfonated polyether ether ketone of polyglycidyl methacrylate sulfonic acid solution; then add the acrylsulfonated nano-diamond prepared in step (3) of Example 1 into the grafted sulfonated polyether ether ketone of polyglycidyl methacrylate sulfonic acid solution, and disperse it evenly by ultrasonic wave to obtain a film-forming slurry (the mass ratio of grafted sulfonated polyether ether ketone of polyglycidyl methacrylate sulfonic acid to acrylsulfonated nano-diamond is 100:3); Pour the film-forming slurry into a glass mold, let it stand at room temperature for 24 h, and then place it in a drying oven at 60 °C to dry to constant weight to obtain the cation exchange membrane.

[0096] Experimental Example 1

[0097] To evaluate the comprehensive service performance of the cation exchange membranes prepared in each example and comparative example, the surface resistance, tensile strength, elongation at break, and antioxidant property of the cation exchange membranes prepared in each example and comparative example were respectively tested. The antioxidant property is expressed by the percentage of weight loss after the cation exchange membrane is immersed in the test solution (the test solution is composed 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 antioxidant property of the cation exchange membranes prepared in each example and comparative example are shown in Table 1.

[0098] Table 1 Surface resistance, tensile strength, elongation at break, and antioxidant property of the cation exchange membrane

[0099] Cation exchange membrane <![CDATA[Sheet Resistance (Ω·cm 2 )]]> Tensile strength (MPa) Elongation at break (%) Antioxidant property (%) 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

[0100] As can be seen from the experimental results in Table 1, grafting and polymerizing sulfonic acid segments onto the surface of nanodiamond and the polyetheretherketone chain segments can effectively reduce the resistivity of the cation exchange membrane and improve the conductivity of the thin film. This is because in addition to the sulfonic acid groups bonded to the surface of nanodiamond and polyetheretherketone, long-chain and high-density polymerized sulfonic acid segments are also grafted onto the surfaces of nanodiamond and polyetheretherketone. Moreover, the polymerized sulfonic acid segments are branched on the surfaces of nanodiamond and polyetheretherketone. The thin film material made from the two contains a large number of sulfonic acid segments, and the grafted sulfonic acid segments can be arranged in an alternating network or intertwined through physical entanglement, improving the distribution density of sulfonic acid groups. The main chain of polyetheretherketone and the nanodiamond core can provide a distribution basis for the polymerized sulfonic acid segments, ensuring the effective and uniform distribution of the polymerized sulfonic acid segments, and can be arranged alternately with the long-branched sulfonic acid polymerized segments to form pores composed of sulfonic acid groups, providing a basis for the passage of cations. In addition, the main chain of polyetheretherketone, the nanodiamond core, and the long-branched sulfonic acid polymerized segments are physically crosslinked with each other, which can effectively improve the strength and elongation of the thin film material, and can also improve the antioxidant performance of the thin film material. As can be seen from Examples 1-3 and Examples 4-6, using polyglycidyl sulfonate as the long-branched sulfonic acid polymerized segment can improve the mechanical properties and antioxidant performance of the thin film material more than using polypropyl sulfonate as the long-branched sulfonic acid polymerized segment. This may be because polyglycidyl sulfonate contains ether bonds, which have stronger rotation ability and can form hydrogen bonds, thereby improving the mechanical properties and antioxidant performance of the thin film.

[0101] Experimental Example 2

[0102] In order to investigate the selective permeation performance and actual use effect of the cation exchange membranes prepared in each example and comparative example on lithium ions, the cation exchange membranes, cathode electrodes, and anode electrodes prepared in each example and comparative example were assembled into an electrolytic cell. The anode electrode material was a reticulated ruthenium-plated titanium metal electrode, and the cathode electrode material was a reticulated nickel material. Lithium-containing brine was added to the anode chamber, and lithium hydroxide solution was added to the cathode chamber. The power supply was turned on for electrolysis. The electrolysis temperature was 45°C, and the current density was 1.5 kA / m 2, the lithium-containing brine consists 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 the lithium hydroxide solution is 10 wt%. After the electrolysis is completed, the selectivity coefficient is calculated according to the concentrations of various metal cations in the liquid in the cathode chamber before and after electrolysis. And according to the concentration and volume of lithium ions in the liquid in the cathode chamber before and after electrolysis and the concentration and volume of lithium ions in the anode chamber before and after electrolysis, the recovery rate of lithium ions in the cathode chamber is calculated. The recovery rate is equal to the percentage of the increase in lithium ions in the cathode chamber before and after electrolysis to the decrease in lithium ions in the anode chamber before and after electrolysis. At the same time, according to the power consumption and the increase in metal cations in the cathode chamber before and after electrolysis, the current efficiency is calculated. The current efficiency is equal to the percentage of the increase in metal cations in the cathode chamber before and after electrolysis to the theoretical increase in metal cations in the cathode chamber corresponding to the power consumption. The selective permeation performance and actual use effect of the cation exchange membrane for lithium ions are shown in Table 2. X(Li + / Na + ) in Table 2 represents the selectivity coefficient of the cation exchange membrane for lithium ions and sodium ions.

[0103] Table 2 Selective Permeation Performance and Actual Use Effect of Cation Exchange Membrane for Lithium Ions

[0104] Cation exchange membrane <![CDATA[X(Li + / Na + )]]> <![CDATA[X(Li + / Mg 2+ )]]> <![CDATA[X(Li + / Ca 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

[0105] 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 brines. This may be because the long-chain high-density polymer sulfonic acid segments grafted on the surface of nano-diamond and the surface of polyether ether ketone can be arranged in a staggered manner to form pores composed of sulfonic acid groups. These pores 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, the long-chain high-density polymer sulfonic acid segments are lacking, and it is impossible to form pores composed of sulfonic acid groups through 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 temporary unstable structures and will not cause a large amount of electric energy to be consumed when lithium ions pass through, so it has a high current efficiency and a high lithium ion recovery rate.

Claims

1. A method for stepwise lithium extraction from salt lake brine based on in-situ electrolysis drive, characterized in that, It includes the following steps: Electrolyze the lithium-containing salt lake brine to enable the lithium ions in the salt lake brine to selectively pass through the cation exchange membrane, thereby completing the enrichment and extraction of lithium ions; the cation exchange membrane is prepared by drying a solution of polymerized sulfonic acid grafted sulfonated polyether ether ketone and polymerized sulfonic acid grafted nanodiamond; the polymerized sulfonic acid grafted sulfonated polyether ether ketone is prepared by polymerizing double-bonded sulfonated polyether ether ketone and a sulfonic acid monomer, and the double-bonded sulfonated polyether ether ketone is prepared by reacting hydroxylated sulfonated polyether ether ketone with acryloyl chloride; the polymerized sulfonic acid grafted nanodiamond is prepared by polymerizing acrylsulfonated nanodiamond and a sulfonic acid monomer, and the acrylsulfonated nanodiamond is prepared by reacting allylated nanodiamond with 4-(chlorosulfonyl)benzoyl chloride, and the allylated nanodiamond is prepared by reacting carboxylated nanodiamond with glycidyl acrylate; the sulfonic acid monomers are all sodium 2,3-epoxysulfonate.

2. The method for stepwise lithium extraction from salt lake brine based on in-situ electrolysis drive according to claim 1, wherein The carboxylated nanodiamond is prepared by mixing and reacting nanodiamond powder with an acid solution at 70-80 °C for 48-55 h. The acid solution is composed of concentrated nitric acid and concentrated sulfuric acid with a volume ratio of 1:3-3.5, and the mass ratio of nanodiamond powder to the acid solution is 1:120-150.

3. The method for stepwise lithium extraction from salt lake brine based on in-situ electrolysis drive as claimed in claim 1, wherein The allylated nanodiamond is prepared by mixing and reacting carboxylated nanodiamond, glycidyl acrylate and a catalyst trimethylbenzylammonium bromide at 90-100 °C for 6-8 h. The molar ratio of the carboxyl group of carboxylated nanodiamond to glycidyl acrylate is 1:2-3, and the mass ratio of carboxylated nanodiamond to the catalyst trimethylbenzylammonium bromide is 50:0.5-0.

8.

4. The method for stepwise lithium extraction from salt lake brine based on in-situ electrolysis drive according to claim 1, wherein The reaction temperature of allylated nanodiamond and 4-(chlorosulfonyl)benzoyl chloride is 20-25 °C, and the reaction time is 3-4 h; during the reaction, the allylated nanodiamond dispersion is added to the 4-(chlorosulfonyl)benzoyl chloride solution; the molar ratio of the hydroxyl group of allylated nanodiamond to 4-(chlorosulfonyl)benzoyl chloride is 1:1.5-2.

5. The method for stepwise lithium extraction from salt lake brine based on in-situ electrolysis drive according to claim 1, characterized in that The reaction temperature of hydroxylated sulfonated polyether ether ketone and acryloyl chloride is room temperature, and the reaction time is 8-10 h. The mass ratio of hydroxylated sulfonated polyether ether ketone to acryloyl chloride is 1:2-3.

6. The method for stepwise lithium extraction from salt lake brine based on in-situ electrolysis drive according to claim 1, wherein The hydroxylated sulfonated polyether ether ketone is prepared by mixing and reacting sulfonated polyether ether ketone with sodium borohydride in a solvent at 110-120 °C for 3-4 h. The mass ratio of sodium borohydride to sulfonated polyether ether ketone is 1.8-2:1; the sulfonated polyether ether ketone is prepared by mixing and reacting polyether ether ketone with concentrated sulfuric acid at 55-65 °C for 3-4 h. The dosage ratio of polyether ether ketone to concentrated sulfuric acid is 20-22 g:280-300 mL.

7. The method for stepwise lithium extraction from salt lake brine based on in-situ electrolysis drive according to any one of claims 1-6, characterized in that, The method for the polymerization reaction of the double-bond sulfonated polyether ether ketone and the sulfonic acid monomer is as follows: Mix the double-bond sulfonated polyether ether ketone, sodium 2,3-epoxypropanesulfonate and the solvent to obtain a reaction solution, and then dropwise add a hydrogen peroxide solution with a mass fraction of 7-9% to the reaction solution under stirring. After the dropping is completed, heat to 80-85 °C and carry out a mixed reaction for 5-6 h to obtain a polymerized epoxypropanesulfonic acid grafted sulfonated polyether ether ketone; the mass ratio of the double-bond sulfonated polyether ether ketone to the mass of sodium 2,3-epoxypropanesulfonate is 1:3-4, and the mass ratio of the mass of sodium 2,3-epoxypropanesulfonate to the mass of the hydrogen peroxide solution is 1:9-10.

8. The method for stepwise lithium extraction from salt lake brine based on in-situ electrolysis drive according to any one of claims 1-6, characterized in that, The method for the polymerization reaction of the acrylsulfonated nanodiamond and the sulfonic acid monomer is as follows: Mix the acrylsulfonated nanodiamond dispersion and the sodium 2,3-epoxypropanesulfonate solution to obtain a reaction solution, and then dropwise add a hydrogen peroxide solution with a mass fraction of 7-9% to the reaction solution under stirring. After the dropping is completed, heat to 80-85 °C and carry out a mixed reaction for 3-4 h to obtain a polymerized epoxypropanesulfonic acid grafted nanodiamond; the mass ratio of the acrylsulfonated nanodiamond in the acrylsulfonated nanodiamond dispersion to the mass of sodium 2,3-epoxypropanesulfonate in the sodium 2,3-epoxypropanesulfonate solution is 1:2-2.5, and the mass 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.

9. The method for stepwise lithium extraction from salt lake brine based on in-situ electrolysis drive according to any one of claims 1-6, characterized in that, During electrolysis, a cation exchange membrane, a cathode electrode and an anode electrode are assembled into an electrolytic cell. The anode electrode material is a reticulated ruthenium-plated titanium metal electrode, and the cathode electrode material is a reticulated nickel material. Then, a number of electrolytic cells are connected in series in turn for cascade electrolysis to complete the extraction and enrichment of lithium in the salt lake brine.

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