Salt separation ion exchange membrane for electrodialysis and preparation method of salt separation ion exchange membrane

Abstract

The preparation method comprises the following steps: immersing a cation exchange membrane into a buffer solution containing tannic acid and a zwitterionic diamine monomer, and carrying out a reaction at 0-60 DEG C for 0.5-60 h to obtain the salt-separating ion exchange membrane for electrodialysis. The uniform and stable tannic acid / diamine zwitter-ion ultrathin coating is formed on the surface of the cation exchange membrane through Michael addition or Schiff base reaction between tannic acid molecules and zwitter-ion diamine monomers under the weak alkaline condition. According to the invention, the Li < + > / Mg < 2 + > selectivity is obviously improved. The preparation process is simple, environment-friendly and high in universality, the prepared modified cation exchange membrane has excellent Li < + > / Mg < 2 + > selectivity, the anti-pollution performance of the membrane can be improved, and the modified cation exchange membrane can be used for extracting lithium from brine with the high magnesium-lithium ratio through an electrodialysis method.

Description

Technical Field

[0001] The present invention belongs to the technical field of selective electrodialysis and membrane technology, and relates to a salt-splitting ion exchange membrane for electrodialysis and a preparation method thereof. Background Art

[0002] Mg 2+ and Li + have approximate atomic radii and chemical properties, which are the main difficulties and challenges in the current lithium extraction technology from salt lakes.

[0003] Electrodialysis technology has the advantages of convenient operation, high degree of continuity, and environmental friendliness in the process. In recent years, it has received extensive attention in lithium extraction from salt lakes. Its essence is to use an electric field as a driving force to promote the selective passage of ions through the exchange membrane, so as to achieve the purpose of ion separation and enrichment. The ion exchange membrane is the core component of the electrodialysis device, and its performance directly determines the effect of lithium extraction by electrodialysis. However, the existing preparation process of the ion exchange membrane for lithium extraction by electrodialysis is complex, and the performance needs to be further improved, which restricts the industrial application of lithium extraction by electrodialysis. Summary of the Invention

[0004] In order to overcome the deficiencies of the prior art, the purpose of the present invention is to provide a salt-splitting ion exchange membrane for electrodialysis and a preparation method thereof, and the preparation method is simple, fast, and environmentally friendly in the preparation process.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A preparation method of a salt-splitting ion exchange membrane for electrodialysis, comprising the following steps:

[0007] Immerse the cation exchange membrane in a buffer solution containing tannic acid and zwitterionic diamine monomer, and react at 0-60 °C for 0.5-60 h to obtain a salt-splitting ion exchange membrane for electrodialysis.

[0008] Further, the zwitterionic diamine monomer is at least one of N-O oxide zwitterionic diamine and N,N-bis(3-aminopropyl)methylaminopropane sulfonic acid.

[0009] Further, the structural formula of the N-O oxide zwitterionic diamine is as follows:

[0010]

[0011] Further, the structural formula of the N,N-bis(3-aminopropyl)methylaminopropane sulfonic acid is as follows:

[0012]

[0013] Further, the buffer solution containing tannic acid and zwitterionic diamine monomer is prepared through the following process:

[0014] Add tannic acid and zwitterionic diamine monomer into a buffer solution and mix them evenly.

[0015] Furthermore, the buffer solution includes at least one of N,N-bis(2-hydroxyethyl)glycine buffer solution, tris(hydroxymethyl)aminomethane buffer solution and phosphate buffer solution with a pH of 7-9.

[0016] Furthermore, by mass, the ratio of tannic acid, zwitterionic diamine monomer to the buffer solution is 0.01-0.6 parts: 0.01-0.8 parts: 100 parts.

[0017] Furthermore, the reaction temperature is 25-50 °C and the time is 1-24 h.

[0018] Furthermore, the cation exchange membrane is a heterogeneous cation exchange membrane or a homogeneous cation exchange membrane.

[0019] A salt-splitting ion exchange membrane for electrodialysis.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) In the present invention, the co-deposition of tannic acid and zwitterionic diamine monomer is based on chemical covalent interaction. Compared with the polyelectrolyte layer-by-layer self-assembly surface modification process driven by electrostatic force, the coating obtained by the present invention has better long-term stability.

[0022] (2) The present invention uses the covalent deposition of tannic acid and zwitterionic diamine monomer to perform surface modification on the ion exchange membrane, and can form an ultrathin coating with very low resistance on the surface of various membrane materials, which has the characteristic of universality and can be applied to the modification of various cation exchange membranes.

[0023] (3) The present invention introduces a zwitterionic structure with both cationic functional groups and anionic functional groups to the surface of the cation exchange membrane. Zwitterionic modification can significantly improve the hydrophilicity of the membrane, block the direct contact between pollutants and the membrane surface, and can improve the anti-pollution performance of the membrane.

[0024] (4) The present invention uses water as a solvent, and the materials used are safe, non-toxic, the preparation process is simple and environmentally friendly, and the prepared modified cation exchange membrane has good Li + / Mg 2+ selectivity and can be used for lithium extraction from brine with a high magnesium-lithium ratio by electrodialysis.

[0025] (5) Through the Michael addition or Schiff base reaction between tannic acid molecules and zwitterionic diamine monomers under weak alkaline conditions, the present invention forms a uniform and stable tannic acid / diamine zwitterionic ultrathin coating on the surface of a conventional cation exchange membrane. The present invention overcomes the limitations of existing commercially available cation exchange membranes and significantly improves Li+ / Mg 2+ Selectivity. Moreover, the preparation process is simple, environmentally friendly, and highly universal. The modified cation exchange membrane prepared by the present invention has excellent Li + / Mg 2+ selectivity, can improve the anti-pollution property of the membrane, and can be used for lithium extraction from brine with a high magnesium-lithium ratio by electrodialysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, obtaining other drawings based on these drawings still belongs to the scope of the present invention.

[0027] Figure 1 It is a schematic diagram of the composition of the tannic acid / zwitterionic diamine modified coating in the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0028] In order to enable those skilled in the art to better understand the solutions of the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, not all of them, and are not intended to limit the scope of the present invention. In addition, in the following description, the description of well-known structures and technologies is omitted to avoid unnecessarily confusing the concepts disclosed in the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

[0029] A method for preparing a salt-splitting ion exchange membrane for electrodialysis according to the present invention includes the following steps:

[0030] S1. Prepare a buffer solution with a pH of 6 to 10;

[0031] S2. Dissolve 0.01 to 0.6 parts of tannic acid and 0.01 to 0.8 parts of zwitterionic diamine monomer in the above buffer solution to obtain a buffer solution containing tannic acid and zwitterionic diamine monomer;

[0032] S3. Immerse a commercial cation exchange membrane into the buffer solution containing tannic acid and zwitterionic diamine monomer, shake it evenly in a water bath shaker at 0 to 60 °C, and react for 0.5 to 60 h; wash it clean with deionized water to obtain a salt-splitting ion exchange membrane for electrodialysis, and store it for later use.

[0033] Preferably, the buffer solution in the above step (1) includes at least one of N,N-bis(2-hydroxyethyl)glycine (Bicine) buffer solution, tris(hydroxymethyl)aminomethane (Tris) buffer solution, and phosphate buffer solution (PBS).

[0034] As a further preference, the pH of the buffer solution in the above step (1) is 7-9.

[0035] Preferably, the buffer solution in the above step (2) includes at least one of N,N-bis(2-hydroxyethyl)glycine (Bicine) buffer solution, tris(hydroxymethyl)aminomethane (Tris) buffer solution, and phosphate buffer solution (PBS).

[0036] As a further preference, by mass, the dosage of the buffer solution in the above step (1) is 100 parts, the dosage of tannic acid is 0.05-0.4 parts, and the dosage of the zwitterionic diamine monomer is 0.05-0.6 parts.

[0037] Preferably, the temperature of the shaking water bath in the above step (3) is 25-50 °C and the reaction is carried out for 1-24 h. The higher the water bath temperature, the more conducive it is to accelerating the reaction rate between tannic acid and the zwitterionic diamine monomer, but the energy consumption will increase; the longer the reaction time, the more conducive it is to increasing the deposition amount of tannic acid and the zwitterionic diamine monomer on the surface of the cation exchange membrane, but the time cost will increase.

[0038] As a further preference, the temperature of the shaking water bath in the above step (3) is 30-40 °C and the reaction is carried out for 12-24 h.

[0039] The conventional cation exchange membrane can use a commercial heterogeneous cation exchange membrane or a homogeneous cation exchange membrane.

[0040] The zwitterionic diamine monomer is at least one of N-oxide zwitterionic diamine (DNMAO) and N,N-bis(3-aminopropyl)methylaminopropanesulfonic acid (Z-DNMA).

[0041] Among them, the structural formula of N-oxide zwitterionic diamine (DNMAO) is as follows:

[0042]

[0043] The structural formula of N,N-bis(3-aminopropyl)methylaminopropanesulfonic acid (Z-DNMA) is as follows:

[0044]

[0045] The principle of the present invention is as follows: A large number of ortho-phenolic hydroxyl groups in the tannic acid molecule will be oxidized to form an ortho-benzoquinone structure under neutral to weakly alkaline conditions. Ortho-benzoquinone has high chemical reactivity and is prone to undergo Michael addition or Schiff base reaction with the amino group in the zwitterionic diamine monomer to form covalent bonds, thereby forming a uniform and stable tannic acid / diamine zwitterionic ultra-thin coating on the surface of the cation exchange membrane substrate (for the composition of the tannic acid / zwitterionic diamine modified coating, see Figure 1 ). The positively charged functional groups in the zwitterionic structure can effectively repel divalent Mg 2+ , and have relatively little influence on monovalent Li + ; at the same time, the negatively charged functional groups in the zwitterionic structure can promote the transmembrane transport of monovalent Li + . Therefore, the modified cation exchange membrane can exhibit good Li + / Mg 2+ selectivity when applied in electrodialysis. Therefore, the present invention can effectively solve the problem of low Li + / Mg 2+ selectivity of existing commercial cation exchange membranes.

[0046] The following are specific examples.

[0047] Example 1

[0048] A preparation method of an ion exchange membrane for electrodialysis with good Li + / Mg 2+ separation performance, comprising the following steps:

[0049] (1) Synthesis of zwitterionic diamine monomer N-O oxide zwitterionic diamine (DNMAO): Weigh 10 g of N,N-bis(3-aminopropyl)methylamine (DNMA) and dissolve it in 45 mL of deionized water. Then, under the condition of an ice-water bath, slowly add 30 mL of an 8% by mass H 2 O 2 solution dropwise to the above DNMA aqueous solution and continuously stir. Continuously stir the mixed solution after adding hydrogen peroxide at room temperature in the air for 12 h. Secondly, extract it 3 times with dichloromethane to remove the residual reactant DNMA. Finally, freeze-dry the obtained aqueous solution to obtain a light yellow viscous liquid, that is, the N-O oxide zwitterionic diamine (DNMAO) monomer, and the molecular structure is as follows:

[0050]

[0051] (2) Prepare an N,N-diethanolaminoacetic acid (Bicine) buffer solution with a concentration of 50 mmol / L and a pH of 8;

[0052] (3) Dissolve 0.2 parts by mass of tannic acid and 0.2 parts of N - O - oxide zwitterionic diamine (DNMAO) in 100 parts of the above - mentioned Bicine buffer solution to obtain a buffer solution containing tannic acid and DNMAO zwitterionic diamine monomer;

[0053] (4) Immerse the homogeneous cation - exchange membrane of Shandong Tianwei Membrane Technology Co., Ltd. into the buffer solution containing tannic acid and DNMAO zwitterionic diamine monomer, and shake it uniformly in a water - bath shaker at 40 °C for 16 h; wash the obtained modified membrane with deionized water to obtain a salt - separating ion - exchange membrane for electrodialysis, and store it for standby.

[0054] Example 2

[0055] A preparation method of an ion - exchange membrane for electrodialysis with good Li + / Mg 2+ separation performance, comprising the following steps:

[0056] (1) Synthesis of zwitterionic diamine monomer N,N - bis(3 - aminopropyl)methylaminopropanesulfonic acid (Z - DNMA): First, dissolve 5.8 g of N,N - bis(3 - aminopropyl)methylamine (DNMA) in 80 mL of dichloromethane, and then add 80 mL of dichloromethane containing 19.2 g of di - tert - butyl dicarbonate. Stir at room temperature for 12 h for amino protection. After extraction with deionized water and evaporation to remove dichloromethane, intermediate 1 (DNMA - Boc) is obtained. Then, slowly add 20 mL of chloroform solution containing 1.7 g of 1,3 - propane sultone dropwise to 20 mL of chloroform solution containing 4.0 g of intermediate 1. Stir the mixture at 40 °C for 10 h. After that, wash the product with deionized water and evaporate to remove chloroform to obtain intermediate 2 (Z - DNMA - Boc). Finally, deprotect intermediate 2 in 4.0 mol / L hydrochloric acid solution at room temperature. Wash the product with acetonitrile to remove impurities and freeze - dry it to obtain the final target compound N,N - bis(3 - aminopropyl)methylaminopropanesulfonic acid (Z - DNMA), and its molecular structure is as follows:

[0057]

[0058] (2) Prepare a phosphate - buffered saline (PBS) with a concentration of pH 8.0;

[0059] (3) Dissolve 0.2 parts by mass of tannic acid and 0.2 parts of N,N - bis(3 - aminopropyl)methylaminopropanesulfonic acid (Z - DNMA) in 100 parts of the above - mentioned PBS buffer solution to obtain a buffer solution containing tannic acid and Z - DNMA zwitterionic diamine monomer;

[0060] (4) Immerse the homogeneous cation exchange membrane of Shandong Tianwei Membrane Technology Co., Ltd. into a buffer solution containing tannic acid and the zwitterionic diamine monomer Z-DNMA, and shake it evenly in a water bath shaker at 40 °C for 12 h; wash the obtained modified membrane with deionized water to obtain a salt-splitting ion exchange membrane for electrodialysis, and store it for standby.

[0061] Example 3

[0062] A preparation method of an ion exchange membrane for electrodialysis with good Li + / Mg 2+ separation performance, comprising the following steps:

[0063] (1) Synthesis of the zwitterionic diamine monomer N,N-bis(3-aminopropyl)methylaminopropanesulfonic acid (Z-DNMA): First, dissolve 5.8 g of N,N-bis(3-aminopropyl)methylamine (DNMA) in 80 mL of dichloromethane, and then add 80 mL of dichloromethane containing 19.2 g of di-tert-butyl dicarbonate. Stir at room temperature for 12 h for amino protection. After extraction with deionized water and evaporation of dichloromethane, the intermediate product 1 (DNMA-Boc) is obtained. Then, slowly drop 20 mL of a chloroform solution containing 1.7 g of 1,3-propanesultone into 20 mL of a chloroform solution containing 4.0 g of intermediate product 1. Stir the mixture at 40 °C for 10 h. After that, wash the product with deionized water and evaporate the chloroform to obtain the intermediate product 2 (Z-DNMA-Boc). Finally, deprotect the intermediate product 2 in a 4.0 mol / L hydrochloric acid aqueous solution at room temperature. Wash the product with acetonitrile to remove impurities and freeze-dry it to obtain the final target compound N,N-bis(3-aminopropyl)methylaminopropanesulfonic acid (Z-DNMA).

[0064] (2) Prepare a tris(hydroxymethyl)aminomethane (Tris) buffer solution with a concentration of 10 mmol / L and a pH of 7;

[0065] (3) Dissolve 0.05 part of tannic acid and 0.05 part of N,N-bis(3-aminopropyl)methylaminopropanesulfonic acid (Z-DNMA) in 100 parts of the above Tris buffer solution by mass to obtain a buffer solution containing tannic acid and the zwitterionic diamine monomer Z-DNMA;

[0066] (4) Immerse the homogeneous cation exchange membrane of Shandong Tianwei Membrane Technology Co., Ltd. into a buffer solution containing tannic acid and the zwitterionic diamine monomer Z-DNMA, and shake it evenly in a water bath shaker at 60 °C for 1 h; wash the obtained modified membrane with deionized water to obtain a salt-splitting ion exchange membrane for electrodialysis, and store it for standby.

[0067] Example 4

[0068] A preparation method of an ion exchange membrane for electrodialysis with good Li + / Mg 2+ separation performance, comprising the following steps:

[0069] (1) Synthesis of zwitterionic diamine monomer N,N-bis(3-aminopropyl)methanaminopropanesulfonic acid (Z-DNMA): First, dissolve 5.8 g of N,N-bis(3-aminopropyl)methylamine (DNMA) in 80 mL of dichloromethane, and then add 80 mL of dichloromethane containing 19.2 g of di-tert-butyl dicarbonate. Stir at room temperature for 12 h for amino protection. After extraction with deionized water and evaporation of dichloromethane, intermediate 1 (DNMA-Boc) is obtained. Then, slowly drop 20 mL of chloroform solution containing 1.7 g of 1,3-propanesultone into 20 mL of chloroform solution containing 4.0 g of intermediate 1. Stir the mixture at 40 °C for 10 h. After that, wash the product with deionized water and evaporate chloroform to obtain intermediate 2 (Z-DNMA-Boc). Finally, deprotect intermediate 2 in 4.0 mol / L hydrochloric acid solution at room temperature. Wash the product with acetonitrile to remove impurities and freeze-dry to obtain the final target compound N,N-bis(3-aminopropyl)methanaminopropanesulfonic acid (Z-DNMA).

[0070] (2) Prepare phosphate buffer solution (PBS) with a pH of 8.0;

[0071] (3) Dissolve 0.4 part of tannic acid and 0.6 part of N,N-bis(3-aminopropyl)methanaminopropanesulfonic acid (Z-DNMA) in 100 parts of the above PBS buffer solution by mass to obtain a buffer solution containing tannic acid and Z-DNMA zwitterionic diamine monomer;

[0072] (4) Immerse the homogeneous cation exchange membrane of Shandong Tianwei Membrane Technology Co., Ltd. into the buffer solution containing tannic acid and Z-DNMA zwitterionic diamine monomer, shake it evenly in a water bath shaker at 30 °C, and react for 24 h; wash the obtained modified membrane with deionized water to obtain a salt-separating ion exchange membrane for electrodialysis, and store it for later use.

[0073] Example 5

[0074] (1) The same as Example 1;

[0075] (2) Prepare phosphate buffer solution (PBS) with a pH of 6.0;

[0076] (3) Dissolve 0.01 part of tannic acid and 0.01 part of N-oxide zwitterionic diamine (DNMAO) in 100 parts of the above phosphate buffer solution (PBS) by mass to obtain a buffer solution containing tannic acid and DNMAO zwitterionic diamine monomer;

[0077] (4) Immerse the homogeneous cation exchange membrane of Shandong Tianwei Membrane Technology Co., Ltd. into a buffer solution containing tannic acid and DNMAO zwitterionic diamine monomer, and shake it uniformly in a water bath shaker at 50 °C for 0.5 h; clean the obtained modified membrane with deionized water to obtain a salt-splitting ion exchange membrane for electrodialysis, and store it for later use.

[0078] Example 6

[0079] (1) Same as Example 1;

[0080] (2) Prepare an N,N-diethanolaminoacetic acid (Bicine) buffer solution with a concentration of 50 mmol / L and a pH of 10;

[0081] (3) Dissolve 0.6 parts of tannic acid and 0.8 parts of N-oxide zwitterionic diamine (DNMAO) in 100 parts of the above Bicine buffer solution by mass to obtain a buffer solution containing tannic acid and DNMAO zwitterionic diamine monomer;

[0082] (4) Immerse the homogeneous cation exchange membrane of Shandong Tianwei Membrane Technology Co., Ltd. into a buffer solution containing tannic acid and DNMAO zwitterionic diamine monomer, and shake it uniformly in a water bath shaker at 25 °C for 60 h; clean the obtained modified membrane with deionized water to obtain a salt-splitting ion exchange membrane for electrodialysis, and store it for later use.

[0083] Example 7

[0084] (1) Same as Example 1;

[0085] (2) Prepare an N,N-diethanolaminoacetic acid (Bicine) buffer solution with a concentration of 50 mmol / L and a pH of 9;

[0086] (3) Dissolve 0.1 part of tannic acid and 0.1 part of N-oxide zwitterionic diamine (DNMAO) in 100 parts of the above Bicine buffer solution by mass to obtain a buffer solution containing tannic acid and DNMAO zwitterionic diamine monomer;

[0087] (4) Immerse the homogeneous cation exchange membrane of Shandong Tianwei Membrane Technology Co., Ltd. into a buffer solution containing tannic acid and DNMAO zwitterionic diamine monomer, and shake it uniformly in a water bath shaker at 0 °C for 16 h; clean the obtained modified membrane with deionized water to obtain a salt-splitting ion exchange membrane for electrodialysis, and store it for later use.

[0088] Comparative Example 1

[0089] Commercially available homogeneous cation exchange membrane, without being modified by tannic acid / zwitterionic diamine coating.

[0090] The modified cation exchange membranes prepared in the above Examples 1 to 7 were used together with Comparative Example 1 to conduct an electrodialysis lithium extraction experiment, and the tests were carried out according to the conditions shown in Table 1 below, and the results are shown in Table 2.

[0091] Table 1

[0092]

[0093] Table 2

[0094]

[0095] Compared with Comparative Example 1, the Li + flux of the cation exchange membrane modified with tannic acid / zwitterionic diamine coating decreased slightly, and the Li + / Mg 2+ selectivity was significantly improved. The original homogeneous cation exchange membrane in Comparative Example 1 had a high negative charge density and a rich pore structure, showing the highest Li + flux, but it could not effectively inhibit the penetration of divalent Mg 2+ , so the selectivity was only 2.16. The Li + / Mg 2+ selectivity of Examples 1 and 2 was increased to 12.74 and 14.35 respectively. When N-oxide zwitterionic diamine (DNMAO) or N,N-bis(3-aminopropyl)methylaminopropanesulfonic acid (Z-DNMA) was introduced onto the surface of the cation exchange membrane, the positively charged quaternary ammonium groups in the zwitterionic structural unit led to a significant increase in the positive charge density on the surface of the separation layer, and there was a stronger electrostatic repulsion between it and divalent Mg 2+ than that between Li + , thus effectively inhibiting the transport of Mg 2+ , and significantly improving the Li + / Mg 2+ selectivity. At the same time, the introduction of the tannic acid / zwitterionic diamine ultrathin coating made the surface of the separation layer denser, resulting in a decrease in the Li + flux.

[0096] Comparing Examples 2, 3 and 4, it shows that the dosage of tannic acid and zwitterionic diamine and the reaction time have an important influence on the Li + / Mg 2+ selectivity. Too low dosages of tannic acid and zwitterionic diamine and too short reaction time are difficult to form a uniform and effective zwitterionic coating on the surface of the cation membrane, affecting the density and uniform distribution of the positively charged quaternary ammonium groups on the surface of the separation layer, which is not conducive to the full play of the Li + / Mg 2+ selectivity.

[0097] Comparing Comparative Example 5, Example 6 and Example 7 shows that the dosages of tannic acid and zwitterionic diamine and the reaction conditions have important effects on the Li + flux and the Li + / Mg 2+ selectivity. Selecting appropriate reactant dosages and reaction conditions is beneficial to simultaneously achieving a large Li + flux and a high Li + / Mg 2+ selectivity.

[0098] In terms of comprehensive performance, the above Example 2 is more ideal, having the best Li + / Mg 2+ selectivity and retaining a considerable degree of Li + flux.

[0099] Through the Michael addition or Schiff base reaction between tannic acid molecules and zwitterionic diamine monomers under weak alkaline conditions, the present invention forms a uniform and stable tannic acid / diamine zwitterionic ultra-thin coating on the surface of a conventional cation exchange membrane. The present invention overcomes the limitations of commercially available cation exchange membranes and significantly improves the Li + / Mg 2+ selectivity. The preparation process is simple, environmentally friendly and highly universal. The modified cation exchange membrane prepared by the present invention has excellent Li + / Mg 2+ selectivity and can improve the anti-pollution property of the membrane, and can be used for lithium extraction from brine with a high magnesium-lithium ratio by electrodialysis.

[0100] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications or equivalent substitutions can still be made to the specific embodiments of the present invention, and any modification or equivalent substitution without departing from the spirit and scope of the present invention shall be covered by the protection scope of the claims of the present invention.

Claims

1. A method for preparing a salt-separating ion exchange membrane for electrodialysis, characterized in that: The following steps are involved: The cation exchange membrane is immersed in a buffer solution containing tannic acid and zwitterionic diamine monomers, and reacted at 0-60° C. for 0.5-60 hours to obtain a salt-separating ion exchange membrane for electrodialysis.

2. The method for preparing a salt-separating ion exchange membrane for electrodialysis according to claim 1, characterized in that: The zwitterionic diamine monomer is at least one of NO compound zwitterionic diamine and N,N-bis(3-aminopropyl)methylamine propane sulfonic acid.

3. The method for preparing a salt-separating ion exchange membrane for electrodialysis according to claim 2, characterized in that: The structural formula of the NO compound zwitterionic diamine is as follows:

4. The method for preparing a salt-separating ion exchange membrane for electrodialysis according to claim 2, characterized in that: The structural formula of N,N-bis(3-aminopropyl)methylaminepropanesulfonic acid is as follows:

5. The method for preparing a salt-separating ion exchange membrane for electrodialysis according to claim 1, characterized in that: The buffer containing tannic acid and zwitterionic diamine monomers was prepared by the following process: Add tannic acid and zwitterionic diamine monomers into the buffer solution and mix well.

6. The method for preparing a salt-separating ion exchange membrane for electrodialysis according to claim 5, characterized in that: The buffer solution includes at least one of N,N-bis(2-hydroxyethyl)glycine buffer, tris(hydroxymethylaminomethane) buffer and phosphate buffer with a pH of 7-9.

7. The method for preparing a salt-separating ion exchange membrane for electrodialysis according to claim 5, characterized in that: Calculated by mass, the ratio of tannic acid, zwitterionic diamine monomer and buffer solution is 0.01-0.6 parts: 0.01-0.8 parts: 100 parts.

8. The method for preparing a salt-separating ion exchange membrane for electrodialysis according to claim 1, characterized in that: The reaction temperature is 25-50°C and the reaction time is 1-24 hours.

9. The method for preparing a salt-separating ion exchange membrane for electrodialysis according to claim 1, characterized in that: The cation exchange membrane is a heterogeneous cation exchange membrane or a homogeneous cation exchange membrane.

10. A salt-separating ion exchange membrane for electrodialysis prepared according to the method according to any one of claims 1 to 9.

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