Composite ion exchange membrane, preparation method and efficient enrichment 6 Method for lithium isotopes

Abstract

This invention discloses a composite ion exchange membrane, its preparation method, and its efficient enrichment process. 6 The method for Li isotopes relates to the field of lithium isotope separation technology; the preparation method of the composite ion exchange membrane is as follows: after pretreatment of the ion exchange membrane substrate, it is immersed in a composite impregnation solvent containing ionic liquid and crown ether solution, dried and shaped, and then coated on both sides with a coating solvent. A mesh support layer is then applied to cover both sides, and after curing, the composite ion exchange membrane is obtained; enrichment. 6 The method using Li isotopes involves treating the composite ion exchange membrane in hydrochloric acid solution, then placing it in the intermediate membrane chamber of an electrodialysis device. Anode / cathode solutions are injected into the anode and cathode chambers, respectively. A peristaltic pump connects the multi-stage electrodialysis unit in series, controlling the anode / cathode solutions at a constant circulation rate and current to achieve… 6 The efficient enrichment of Li isotopes at each stage significantly improves the single-stage separation coefficient.

Description

Technical Field

[0001] This invention relates to the field of lithium isotope separation technology, specifically to a composite ion exchange membrane, its preparation method, and efficient enrichment. 6 Methods using Li isotopes. Background Technology

[0002] 6 Li is used in fusion reactors... 6 Li(n,α)T is the core raw material for the production of tritium, but its natural abundance is only about 7.6 at, and industrial applications require enrichment to 30-90 at. Traditional lithium isotope separation methods mainly use amalgamation, but this method has serious mercury pollution problems and a separation coefficient of only 1.06, making it difficult to balance environmental protection and separation efficiency.

[0003] While existing ion exchange membrane separation technology has solved the problem of mercury pollution, it still has significant drawbacks: First, the membrane material lacks stability; ionic liquid-impregnated membranes are prone to ionic liquid loss under high current conditions, with a residual ionic liquid rate of only 63% after 5 hours, which cannot meet the requirements for long-term continuous operation. Second, it is difficult to balance the separation coefficient and lithium mobility. At low currents of 100µA to 3mA, the separation coefficient can reach 1.1 to 1.4, but the lithium mobility is <1%, resulting in excessively low yield. While high currents above 30mA can improve the mobility, they reduce the separation coefficient to 1.0, rendering the separation meaningless. Third, large-scale enrichment requires extremely long migration paths. 6 Increasing Li abundance to 90% requires simulating migration at 5800m, which involves complex equipment, large footprint, and is difficult to industrialize.

[0004] Therefore, it is necessary to develop a composite ion exchange membrane with high separation coefficient, high membrane stability, and high scalability, as well as efficient enrichment. 6 The method using Li isotopes has become a key need to overcome existing technological bottlenecks. Summary of the Invention

[0005] This invention aims to solve the existing separation 6 The Li isotope method suffers from low ionic liquid residual rate and separation coefficient, and it is difficult to meet the requirements of long-term operation.

[0006] To address the above problems, the present invention provides the following technical solution.

[0007] In a first aspect, the present invention provides a method for preparing a composite ion exchange membrane, comprising the following steps:

[0008] Step 1: After cutting, soaking and drying the ion exchange membrane substrate, a pretreated ion exchange membrane is obtained; the pretreated ion exchange membrane is immersed in a composite impregnation solvent containing ionic liquid and crown ether solution. After impregnation, it is vacuum dried and shaped to obtain an impregnated ion exchange membrane.

[0009] Step 2: Apply a coating solvent to both sides of the impregnated ion exchange membrane to form a polymer composite coating on both sides of the impregnated ion exchange membrane.

[0010] Step 3: Cover the polymer composite coating with a mesh support layer. After curing, a composite ion exchange membrane is obtained.

[0011] The method for preparing the composite ion exchange membrane of the present invention has, but is not limited to, the following beneficial effects compared with the prior art:

[0012] The preparation method of the composite ion exchange membrane of the present invention employs a composite impregnation solvent impregnation, a coating solvent coating, and a mesh support layer. The composite impregnation solvent, containing ionic liquid and crown ether solution, is used because the crown ether cavity size is highly compatible with lithium ions, but it is easily soluble. Therefore, the ionic liquid is introduced to utilize its high hydrophobicity and low volatility to inhibit crown ether loss and enhance the complexing properties of the crown ether to ensure sufficient filling of the composite impregnation solution. A double-sided coating is used to form a physical barrier, and by controlling the thickness, further effective resistance to crown ether ion dissolution is achieved, ensuring lithium ion migration efficiency. The mesh support layer avoids membrane deformation and damage during subsequent electrodialysis, strengthens the bond between the coating and the impregnated membrane, prevents coating detachment, and improves the stability of the composite ion exchange membrane.

[0013] Preferably, in step 1, the ion exchange membrane substrate is any one of polytetrafluoroethylene (PTFE) membrane, polyvinylidene fluoride (PVDF) membrane, porous polysulfone (PSF) membrane, polyethersulfone (PES) membrane, or polyethylene (PE) membrane; the thickness of the ion exchange membrane substrate is 160 μm to 200 μm and the porosity is ≥80%.

[0014] Specifically, a chemical-resistant membrane material with a high porosity of ≥80% is selected to ensure that the composite impregnation solvent is fully filled, providing sufficient channels for subsequent ion transport. At the same time, the thickness of 160um to 200um balances the strength of the membrane structure and the mass transfer efficiency.

[0015] Preferably, in step 1, the cutting, soaking, and drying method is as follows: the ion exchange membrane substrate is cut into small square pieces, soaked in anhydrous ethanol or a mixed solution of anhydrous ethanol and N,N-dimethylformamide (DMF) for 30 minutes, and dried at 50℃~70℃ for 18 hours.

[0016] Specifically, the solvent immersion process can remove impurities from the substrate and unclog pores. Under the drying parameters, the substrate can be shaped, which can improve the loading effect and bonding stability of functional components in the subsequent impregnation process.

[0017] Preferably, in step 1, the volume ratio of the ionic liquid to the crown ether solution in the composite impregnation solvent is (4-9):1; wherein, the ionic liquid solution is any one of N-methyl-N-propylpiperidine bis(trifluoromethanesulfonyl)imide (PP13-TFSI), trimethylpropylammonium bis(trifluoromethanesulfonyl)imide (TMPA-TFSI), or 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([HMIm][NTf2]), and the crown ether solution is any one of dibenzo-15-crown-5 (DB15C5) solution or benzo-15-crown-5 (B15C5) solution; the concentration of the crown ether solution is 0.2 mol / L to 0.4 mol / L.

[0018] Specifically, ionic liquids are used to suppress crown ether dissolution, and suitable crown ether types and concentrations are employed to enhance the complexation selectivity for lithium ions, laying a core foundation for improving the lithium isotope separation coefficient.

[0019] Preferably, in step 1, the impregnation temperature is 25℃~30℃ and the impregnation time is 24h; the vacuum drying temperature is 40℃, the vacuum degree is -0.08MPa, and the vacuum drying time is 4h.

[0020] Specifically, the impregnation and vacuum drying parameters are optimal. The mild impregnation conditions ensure uniform loading of functional components, while the precise vacuum drying parameters achieve membrane shaping and prevent loss of functional components, thereby improving the performance stability of the impregnated membrane.

[0021] Preferably, in step 2, the coating solvent is any one of perfluorosulfonic acid resin (Nafion) solvent, polyvinylidene fluoride (PVDF) solvent, or epoxy resin solvent; the concentration of the coating solvent is 5wt% to 8wt%; and the coating thickness is 8µm to 10µm.

[0022] Specifically, under the conditions of solvent type, concentration and coating thickness, a dense and appropriately thick physical barrier layer is formed, which can effectively prevent crown ethers and ionic liquids from dissolving, while avoiding excessive coating thickness from affecting lithium ion migration efficiency and balancing the stability and mass transfer of the film. The coating thickness is controlled within the optimal range of 8µm to 10µm. If the thickness is too thin, the barrier will fail, and if it is too thick, mass transfer will be impaired.

[0023] Preferably, in step 3, the material of the mesh support layer is either polyethylene (PE) or polypropylene (PP); the pore size of the mesh support layer is 150 μm and the thickness is 50 μm.

[0024] Specifically, the mesh support layer provides mechanical support for the membrane, preventing deformation and damage during electrodialysis. At the same time, it strengthens the adhesion between the coating and the impregnated membrane, prevents the coating from peeling off, and improves the long-term operational stability of the membrane.

[0025] Secondly, the present invention provides a composite ion exchange membrane prepared by the method described above.

[0026] Specifically, the composite ion exchange membrane prepared by the above method has the advantages of high ionic liquid retention rate, high lithium ion complexation selectivity and mechanical stability, which solves the problems of easy loss and damage of traditional membrane materials and is suitable for the working conditions of lithium isotope electrodialysis separation.

[0027] Thirdly, this invention provides a highly efficient enrichment method. 6 The method for using Li isotopes includes the following steps:

[0028] Step A: Immerse the above-mentioned composite ion exchange membrane in hydrochloric acid solution to form an H-type composite ion exchange membrane;

[0029] Step B: Place the H-type composite ion exchange membrane in the middle membrane chamber of the electrodialysis unit, inject anolyte into the anode chamber and catholyte into the cathode chamber; connect the electrodialysis device through a peristaltic pump, control the anolyte and catholyte solutions to maintain a circulating flow rate, and apply a constant current.

[0030] Step C: Employ multi-stage electrodialysis units connected in series, with consistent operating parameters for each stage, to achieve... 6 Efficient enrichment of Li isotopes at each stage.

[0031] The efficient enrichment of this invention 6 The Li isotope method, compared to existing technologies, has, but is not limited to, the following beneficial effects:

[0032] The only mature and industrially viable enrichment technology among existing technologies 6 The lithium isotope method, also known as the lithium amalgam method, requires the introduction of a large amount of the toxic substance mercury. The method of this invention achieves mercury-free separation with a higher separation coefficient than the traditional lithium amalgam method. Furthermore, existing single crown ether extraction or membrane separation methods do not adequately consider component dissolution and membrane stability. This method, however, employs a composite ion exchange membrane with high stability and lithium-ion migration efficiency for electrodialysis separation, achieving better separation results than the lithium amalgam method and single separation techniques.

[0033] Preferably, in step A, the concentration of hydrochloric acid is 0.2 mol / L to 0.4 mol / L, and the soaking time is 3-4 hours.

[0034] Specifically, within this range of hydrochloric acid concentrations and soaking times, the ion exchange membrane can be efficiently converted to the H-type, ensuring the membrane material's ability to exchange and transport lithium ions.

[0035] Preferably, in step A, the anolyte is a 0.5 mol / L natural LiCl solution; and the cathode solution is a 0.5 mol / L lithium-free NaCl solution.

[0036] Specifically, the natural LiCl solution at the anode provides raw materials for lithium isotope separation, while the lithium-free NaCl solution at the cathode ensures the ionic conductivity of the electrodialysis system. Furthermore, the concentrations of the two solutions are well-matched to avoid osmotic pressure imbalance caused by concentration differences and to stabilize the electrodialysis operation.

[0037] Preferably, in step B, the circulation flow rate is 0.8 mL / min to 1.2 mL / min, and the constant current is 100 μA to 1 mA.

[0038] Specifically, this flow rate range ensures sufficient contact between the feed liquid and the membrane, improving ion migration efficiency, while this low current range balances the separation coefficient and lithium mobility, achieving efficient separation.

[0039] Preferably, in step C, the number of stages of the electrodialysis unit is ≥2.

[0040] Specifically, through multi-level enrichment, the abundance limit of single-level separation is broken through, significantly improving... 6 The final enrichment degree of Li shortens the migration path for large-scale enrichment. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the preparation method of the composite ion exchange membrane in Embodiment 1 of the present invention;

[0042] Figure 2 This is a scanning electron microscope image of the surface microstructure of the polymer composite coating in step 2 of Example 1 of the present invention;

[0043] Figure 3 This is the efficient enrichment method of Embodiment 7 of the present invention. 6 A flowchart illustrating the Li isotope method. Detailed Implementation

[0044] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0045] The terminology used in the embodiments of this application is for the purpose of describing particular implementations only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the implementations of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0046] It should be understood that in the various embodiments of this application, the sequence number of each process does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the implementation regulations of this application.

[0047] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass described in the embodiments of this application can be a mass unit known in the chemical industry, such as μg, mg, g, or kg.

[0048] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0049] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application are available on the market or can be prepared by existing methods.

[0050] Example 1

[0051] This embodiment discloses a composite ion exchange membrane. Please refer to [link / reference]. Figure 1 The preparation is carried out in the following steps:

[0052] Step 1: Cut a PTFE membrane with a thickness of 180 μm and a porosity of 85% into 5 cm × 5 cm square sheets, then soak them in anhydrous ethanol for 30 min, and then transfer them to an oven to dry at 60 °C for 2 h to obtain a pretreated PTFE membrane; completely immerse the pretreated PTFE membrane in a composite impregnation solvent of PP13-TFSI and 0.2 mol / L DB15C5 with a volume ratio of 9:1, impregnate at 25 °C for 24 h, then remove it and transfer it to an oven to dry and set in a vacuum environment of 40 °C and -0.08 MPa for 4 h to obtain an impregnated PTFE membrane;

[0053] Step 2: Spray Nafion solvent with a concentration of 5wt% onto both sides of the impregnated PTFE membrane to form a polymer composite coating with a thickness of 8µm.

[0054] Step 3: Use a polyethylene mesh support layer with a pore size of 150 μm and a thickness of 50 μm to cover the polymer composite coating on both sides, and then heat at 80°C for 48 hours to cure, to obtain a composite ion exchange membrane.

[0055] Example 2

[0056] Compared with Example 1, the only difference is that in step 1, the PTFE membrane with a thickness of 180 μm and a porosity of 85% is replaced with a PE membrane with a thickness of 180 μm and a porosity of 82%; the other steps and conditions are exactly the same as in Example 1, and a composite ion exchange membrane is finally obtained.

[0057] Example 3

[0058] Compared with Example 1, the only difference is that in step 1, anhydrous ethanol is replaced with a mixture of DMF and anhydrous ethanol in a volume ratio of 1:1, and the drying temperature is increased from 50°C to 70°C; the other steps and conditions are exactly the same as in Example 1, and a composite ion exchange membrane is finally obtained.

[0059] Example 4

[0060] Compared with Example 1, the only difference is that in step 1, the composite impregnation solvent of PP13-TFSI and DB15C5 with a volume ratio of 9:1 is replaced with the composite impregnation solvent of TMPA-TFSI and 0.3mol / L B15C5 with a volume ratio of 8:2, and the impregnation temperature is increased from 25°C to 30°C; the other steps and conditions are exactly the same as in Example 1, and a composite ion exchange membrane is finally obtained.

[0061] Example 5

[0062] Compared with Example 2, the only difference is that in step 1, anhydrous ethanol is replaced with a mixture of DMF and anhydrous ethanol in a volume ratio of 1:1, and the drying temperature is increased from 50°C to 60°C; the other steps and conditions are exactly the same as in Example 2, and a composite ion exchange membrane is finally obtained.

[0063] Example 6

[0064] Compared with Example 2, the only difference is that in step 2, the 5 wt% Nafion solvent is replaced with the 8 wt% PVDF solvent, and the coating thickness is increased from 8 μm to 10 μm; the other steps and conditions are exactly the same as in Example 2, and a composite ion exchange membrane is finally obtained.

[0065] Comparative Example 1

[0066] This comparative example discloses a pretreated PTFE membrane, which is prepared according to the following steps:

[0067] Step 1: Cut a PTFE membrane with a thickness of 180 μm and a porosity of 85% into 5 cm × 5 cm square sheets, then soak them in anhydrous ethanol for 30 min, and then transfer them to an oven to dry at 60 °C for 2 h to obtain a pretreated PTFE membrane.

[0068] Comparative Example 2

[0069] This comparative example discloses an impregnated PTFE membrane, which is prepared according to the following steps:

[0070] Step 1: Cut a PTFE membrane with a thickness of 180 μm and a porosity of 85% into 5 cm × 5 cm square sheets, then soak them in anhydrous ethanol for 30 min, and then transfer them to an oven to dry at 60 °C for 2 h to obtain a pretreated PTFE membrane; completely immerse the pretreated ion exchange membrane in a composite impregnation solvent of PP13-TFSI and 0.2 mol / L DB15C5 with a volume ratio of 9:1, impregnate at 25 °C for 24 h, then remove it and transfer it to an oven to dry and set in a vacuum environment of 40 °C and -0.08 MPa for 4 h to obtain an impregnated PTFE membrane.

[0071] The polymer composite coatings obtained in step 2 of Examples 1 to 6 were scanned by electron microscopy (SEM) to obtain corresponding microstructure images. The SEM results of Example 1 and other examples are listed in Table 1 below:

[0072] Table 1

[0073]

[0074] Analysis of the results in Table 1 shows that the composite coatings in Examples 1-6 all exhibit uniform coverage. Taking Example 1 as an example, the SEM image of the surface morphology of the obtained polymer composite coating is shown below. Figure 2 As shown, for Figure 2 Observations show that the particle size on the membrane surface is generally consistent, with no obvious extreme differences between ultra-large agglomerates or ultra-small dispersed particles; the polymer composite coating is uniformly covered overall, with only a few minor bright spots that are normal micro-fluctuations.

[0075] Example 7

[0076] This embodiment discloses a high-efficiency enrichment method. 6 For methods involving Li isotopes, please refer to Figure 3 It includes the following steps:

[0077] Step 1: Immerse the composite ion exchange membrane of Example 1 in a 0.2 mol / L HCl solution for 3 hours to form an H-type composite ion exchange membrane;

[0078] Step 2: Place the H-type composite ion exchange membrane in the intermediate membrane chamber of the electrodialysis unit, and inject 50 mL of a 0.5 mol / L natural LiCl solution into the anode chamber. 6 With a Li abundance of 7.6 at%, 50 mL of a 0.5 mol / L lithium-free NaCl solution was injected into the cathode chamber; the electrodialysis device was connected via a peristaltic pump, and the anolyte and cathode solutions were controlled at a circulation rate of 1 mL / min, while a constant current of 0.5 mA was applied, and the process was continued for 2 hours.

[0079] Step 3: Use a six-stage electrodialysis unit connected in series, with the operating parameters of each stage consistent with those described above, to achieve... 6 Efficient enrichment of Li isotopes at each stage.

[0080] Example 8

[0081] Compared with Example 7, the only difference is that the composite ion exchange membrane of Example 1 is replaced with the composite ion exchange membrane of Example 2; all other steps and conditions remain exactly the same as in Example 7, ultimately achieving... 6 Efficient enrichment of Li isotopes at each stage.

[0082] Example 9

[0083] Compared with Example 7, the only difference is that the composite ion exchange membrane of Example 1 is replaced with the composite ion exchange membrane of Example 3; all other steps and conditions remain exactly the same as in Example 7, ultimately achieving... 6 Efficient enrichment of Li isotopes at each stage.

[0084] Example 10

[0085] Compared with Example 7, the only difference is that the composite ion exchange membrane of Example 1 is replaced with the composite ion exchange membrane of Example 4; all other steps and conditions remain exactly the same as in Example 7, ultimately achieving... 6 Efficient enrichment of Li isotopes at each stage.

[0086] Example 11

[0087] Compared with Example 7, the only difference is that the composite ion exchange membrane of Example 1 is replaced with the composite ion exchange membrane of Example 5; all other steps and conditions remain exactly the same as in Example 7, ultimately achieving... 6 Efficient enrichment of Li isotopes at each stage.

[0088] Example 12

[0089] Compared with Example 7, the only difference is that the composite ion exchange membrane of Example 1 is replaced with the composite ion exchange membrane of Example 6; all other steps and conditions remain exactly the same as in Example 7, ultimately achieving... 6 Efficient enrichment of Li isotopes at each stage.

[0090] Example 13

[0091] Compared with Example 7, the only difference is that in step 1, the 0.2 mol / L HCl solution is replaced with a 0.4 mol / L HCl solution, and the soaking time is increased from 3 hours to 4 hours; all other steps and conditions remain exactly the same as in Example 7, ultimately achieving... 6 Efficient enrichment of Li isotopes at each stage.

[0092] Example 14

[0093] Compared with Example 7, the only difference is that in step 2, the circulation flow rate is reduced from 1 mL / min to 0.8 mL / min, while the constant current is increased from 0.5 mA to 0.8 mA and the continuous running time is increased from 2 h to 2.5 h; all other steps and conditions remain exactly the same as in Example 7, ultimately achieving... 6 Efficient enrichment of Li isotopes at each stage.

[0094] Example 15

[0095] Compared with Example 7, the only difference is that in step 1, the 0.2 mol / L HCl solution is replaced with a 0.3 mol / L HCl solution, and the soaking time is increased from 3 hours to 4 hours; all other steps and conditions remain exactly the same as in Example 7, ultimately achieving... 6 Efficient enrichment of Li isotopes at each stage.

[0096] Example 16

[0097] Compared with Example 7, the only difference is that in step 2, the circulation flow rate is reduced from 1 mL / min to 1.2 mL / min, while the constant current is increased from 0.5 mA to 0.8 mA and the continuous running time is increased from 2 h to 2.5 h; all other steps and conditions remain exactly the same as in Example 7, ultimately achieving... 6 Efficient enrichment of Li isotopes at each stage.

[0098] Comparative Example 3

[0099] The only difference between this comparative example and Example 7 is that the composite ion exchange membrane in Example 1 is replaced with the pretreated PTFE membrane in Comparative Example 1; all other steps and conditions remain exactly the same as in Example 7, ultimately achieving... 6 The gradual enrichment of Li isotopes.

[0100] Comparative Example 4

[0101] The only difference between this comparative example and Example 7 is that the composite ion exchange membrane of Example 1 is replaced with the impregnated PTFE membrane of Comparative Example 2; all other steps and conditions remain exactly the same as in Example 7, ultimately achieving... 6 The gradual enrichment of Li isotopes.

[0102] Enrichment of Examples 7-16 and Comparative Examples 3-4 6 The Li isotope method was used to measure the ionic liquid residue rate in the composite ion exchange membrane, the single-stage separation coefficient, and the concentration of ionic liquid in the enriched solution after 5 hours of enrichment. 6 Li abundance was detected using the following method:

[0103] Ionic liquid residue rate: Based on the hydrophobic properties and UV characteristic absorption of the ionic liquids (such as PP13-TFSI, [HMIm][NTf2]) loaded in the composite ion exchange membrane, the mass of the remaining ionic liquid in the membrane after 5 hours of electrodialysis was quantitatively detected by reversed-phase HPLC external standard method, and the residue rate was calculated (residue rate = mass of ionic liquid in the membrane after 5 hours of operation / initial loaded mass × 100%), reflecting the membrane's stability in immobilizing functional components;

[0104] Single-stage separation coefficient: The single-stage separation coefficient (α) is the cathode chamber ( 6 Li-enriched phase) and anode chamber (raw material phase) 6 Li / 7 The ratio of Li abundance ratios, where α > 1 indicates 6 Li enriches at the cathode, and the higher the value, the better the single-stage separation effect; the isotope abundance calculation based on MC-ICP-MS detection requires no additional experiments;

[0105] 6 Li abundance: After a single-stage electrodialysis cycle, the cathode chamber solution was... 6 Li enrichment solution, the concentration of Li in the enrichment solution was determined by MC-ICP-MS. 6 Li, 7 The ionic strength of Li is calculated. 6 The absolute abundance of Li (at%) reflects the separation and enrichment effect of single-stage electrodialysis on lithium isotopes.

[0106] The test results are listed in Table 2, as follows:

[0107] Table 2

[0108]

[0109] Analysis of the data in Table 2 shows that, compared to Comparative Examples 3-4, Examples 7-16 exhibited enrichment. 6 In the Li isotope method, the ionic liquid residue rate is significantly higher, and the separation coefficient is larger. 6 The Li abundance was significantly higher, indicating that the composite ion exchange membrane of this invention is used for the efficient enrichment of Li in this invention. 6 The Li isotope method has better separation results.

[0110] The foregoing has described several embodiments of the present invention in detail, but these descriptions are merely preferred embodiments and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.

Claims

1. A method for preparing a composite ion exchange membrane, characterized in that, Includes the following steps: Step 1: After cutting, soaking and drying the ion exchange membrane substrate, a pretreated ion exchange membrane is obtained; the pretreated ion exchange membrane is immersed in a composite impregnation solvent containing ionic liquid and crown ether solution. After impregnation, it is vacuum dried and shaped to obtain an impregnated ion exchange membrane. Step 2: Apply a coating solvent to both sides of the impregnated ion exchange membrane to form a polymer composite coating on both sides of the impregnated ion exchange membrane. Step 3: Cover the polymer composite coating with a mesh support layer. After curing, a composite ion exchange membrane is obtained. In step 1, the ionic liquid solution is any one of N-methyl-N-propylpiperidine bis(trifluoromethanesulfonyl)imide, trimethylpropylammonium bis(trifluoromethanesulfonyl)imide, or 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide; in step 2, the coating solvent is any one of perfluorosulfonic acid resin solvent, polyvinylidene fluoride solvent, or epoxy resin solvent; in step 3, the mesh support layer is made of any one of polyethylene or polypropylene.

2. The method for preparing the composite ion exchange membrane according to claim 1, characterized in that, In step 1, the ion exchange membrane substrate is any one of polytetrafluoroethylene membrane, polyvinylidene fluoride membrane, porous polysulfone membrane, polyethersulfone membrane, or polyethylene membrane; the thickness of the ion exchange membrane substrate is 160 μm to 200 μm and the porosity is ≥80%.

3. The method for preparing the composite ion exchange membrane according to claim 1, characterized in that, In step 1, the cutting, soaking, and drying methods are as follows: the ion exchange membrane substrate is cut into small square pieces, soaked in anhydrous ethanol or a mixed solution of anhydrous ethanol and N,N-dimethylformamide for 30 minutes, and dried at 50℃~70℃ for 18 hours.

4. The method for preparing the composite ion exchange membrane according to claim 1, characterized in that, In step 1, the volume ratio of the ionic liquid to the crown ether solution in the composite impregnation solvent is 4 to 9:1; wherein the crown ether solution is either a dibenzo-15-crown-5 solution or a benzo-15-crown-5 solution; and the concentration of the crown ether solution is 0.2 mol / L to 0.4 mol / L.

5. The method for preparing the composite ion exchange membrane according to claim 1, characterized in that, In step 1, the impregnation temperature is 25℃~30℃ and the impregnation time is 24h; the vacuum drying temperature is 40℃, the vacuum degree is -0.08MPa, and the vacuum drying time is 4h.

6. The method for preparing the composite ion exchange membrane according to claim 1, characterized in that, The concentration of the coating solvent is 5wt% to 8wt%; the coating thickness is 8 to 10µm.

7. The method for preparing the composite ion exchange membrane according to claim 1, characterized in that, The mesh support layer has a pore size of 150 μm and a thickness of 50 μm.

8. A composite ion exchange membrane prepared by the method of any one of claims 1-7.

9. A highly efficient enrichment method 6 The method using Li isotopes is characterized by... Includes the following steps: Step A: Immerse the composite ion exchange membrane described in claim 8 in hydrochloric acid solution to form an H-type composite ion exchange membrane; Step B: Place the H-type composite ion exchange membrane in the middle membrane chamber of the electrodialysis unit, inject anolyte into the anode chamber and catholyte into the cathode chamber; connect the electrodialysis device through a peristaltic pump, control the anolyte and catholyte solutions to maintain a circulating flow rate, and apply a constant current. Step C: Employ multi-stage electrodialysis units connected in series, with consistent operating parameters for each stage, to achieve... 6 Efficient enrichment of Li isotopes at each stage.

10. The efficient enrichment method according to claim 9 6 The method using Li isotopes is characterized by... In step A, the concentration of hydrochloric acid is 0.2 mol / L to 0.4 mol / L, and the soaking time is 3 h to 4 h; the anolyte is a 0.5 mol / L natural LiCl solution; the cathode solution is a 0.5 mol / L lithium-free NaCl solution; in step B, the circulation flow rate is 0.8 mL / min to 1.2 mL / min, and the constant current is 100 uA to 1 mA; in step C, the number of stages in the electrodialysis unit is ≥2.

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