An ion-exchange membrane for the separation of radionuclides and its preparation method

Abstract

This invention discloses an ion exchange membrane for the separation of radionuclides and its preparation method, belonging to the field of membrane technology. The preparation method includes the following steps: amino-modified polysulfone resin, sodium polyacrylate-coated MOFs emulsion, organic solvent, and crosslinking agent are mixed in a weight ratio of 10-12:3-4:20-30:0.1-0.14, and the pH is adjusted to 10-10.5. The mixture is reacted for 2-3 hours, and then the pH is adjusted to neutral to obtain a casting solution. After vacuum degassing, the casting solution is scraped to obtain the ion exchange membrane. This invention prepares an ion exchange membrane for the separation and purification of nuclear wastewater through the crosslinking and coordination of amino-modified polysulfone resin and sodium polyacrylate-coated MOFs emulsion.

Description

Technical Field

[0001] This invention belongs to the field of membrane technology, specifically relating to an ion exchange membrane for the separation of radionuclides and its preparation method. Background Technology

[0002] With the rapid development of the global nuclear energy industry, the generation and treatment of nuclear wastewater has become a major issue concerning ecological environment safety and human health. Nuclear wastewater differs from ordinary industrial wastewater; it contains various radioactive nuclides, making it extremely difficult to treat, and the treatment effect directly impacts the long-term stability of the ecosystem. Nuclear wastewater refers to water bodies contaminated with radioactive nuclides, with wastewater generated during the normal operation of nuclear power plants being the primary source, accounting for the vast majority of the total. During nuclear power plant operation, to prevent reactor overheating, cooling water is continuously used to cool the reactor core. This cooling water indirectly comes into contact with radioactive materials during circulation, forming low-level radioactive wastewater. In addition, equipment flushing water, process drainage, surface drainage, and wastewater from showers and laundry used by staff at nuclear power plants also contain trace amounts of radioactive nuclides and fall under the category of nuclear wastewater. The radioactive elements contained in nuclear wastewater (e.g., radioactive elements)... 60 Co、 137 Cs, and 90 Radioactive elements (such as sr) are a major cause of the harmfulness of wastewater. These radioactive elements are highly toxic and easily migrate in water bodies. Once they enter the ecosystem, they will have serious impacts on the environment and humans. For example, when people ingest contaminated water or food, their bodies absorb these radioactive elements, which accumulate in the body, thereby damaging cell structure and interfering with normal biological functions. Therefore, effective removal of radioactive elements from radioactive wastewater is essential.

[0003] The core of nuclear wastewater treatment is to reduce the concentration of radionuclides in the water to meet discharge standards or achieve safe disposal. Currently, the mainstream treatment methods can be divided into four main categories: physical methods, chemical methods, membrane separation methods, and biological methods. Physical methods mainly separate radionuclides from nuclear wastewater through physical processes, without altering the chemical properties of the nuclides. They have the advantages of simple operation and no secondary pollution, and mainly include evaporation concentration and adsorption methods. Chemical methods convert radionuclides in nuclear wastewater into precipitates or stable compounds through chemical reactions, facilitating separation and disposal. They mainly include chemical precipitation and ion exchange methods. Biological methods utilize the adsorption, enrichment, or transformation of microorganisms and plants to remove radionuclides from nuclear wastewater. This method is green, environmentally friendly, and extremely low-cost, suitable for treating low-concentration nuclear wastewater and soil remediation, but has low treatment efficiency, long cycle time, and limited effectiveness for treating high-concentration nuclear wastewater. Membrane separation utilizes the selective permeability of membranes. Under the driving force of pressure difference, concentration difference, or potential difference, water and radionuclides selectively permeate through the membrane, thereby achieving separation. This method boasts advantages such as high efficiency, environmental friendliness, no secondary pollution, and no phase change, making it a research hotspot in nuclear wastewater treatment in recent years. Nuclear wastewater is highly radioactive, requiring membranes with high radiation resistance. Polysulfone is a resin containing an aromatic ring structure. Its main chain contains sulfone groups and ether bonds, exhibiting good heat and radiation resistance, and showing promising application prospects in the field of nuclear wastewater membrane separation. However, due to its hydrophobic structure, the membrane has poor permeability, and its hydrophobic structure makes it susceptible to organic fouling and clogging, further reducing the effectiveness of nuclear wastewater separation.

[0004] Therefore, improving the performance of polysulfone membranes in the separation of nuclear wastewater is of great significance for the treatment of nuclear wastewater. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention utilizes the crosslinking and coordination of amino-modified polysulfone resin and sodium polyacrylate-encapsulated MOF emulsion to prepare an ion exchange membrane for the separation and purification of nuclear wastewater, thereby solving the technical problems mentioned in the background art. Specifically, the technical solution of this invention includes the following: A method for preparing an ion exchange membrane for the separation of radionuclides, the method comprising the following steps: Amino-modified polysulfone resin, sodium polyacrylate-encapsulated MOFs emulsion, organic solvent, and crosslinking agent are mixed in a weight ratio of 10~12:3~4:20~30:0.1~0.14. The pH is adjusted to 10~10.5 and the mixture is reacted for 2~3 hours. The pH is then adjusted to neutral to obtain a casting solution. After vacuum degassing, the casting solution is scraped to obtain the ion exchange membrane.

[0006] Furthermore, the preparation method of the amino-modified polysulfone resin includes the following steps: Bisphenol monomer, halosulfone monomer and inorganic base catalyst are mixed in a molar ratio of 1:1.2 to 1.5:1, and then pretreated at 170°C for 2 to 3 hours under nitrogen protection. The mixture is then heated to 180°C to 190°C and reacted for 3 to 3.5 hours to obtain the amino-modified polysulfone resin.

[0007] Furthermore, the bisphenol monomer includes bisphenol A.

[0008] Furthermore, the halosulfone monomer is composed of 4,4'-dichlorodiphenyl sulfone and 2-amino-4'-fluorobenzophenone in a molar ratio of 10:2~5.

[0009] Furthermore, the inorganic base catalyst includes potassium carbonate or sodium hydroxide.

[0010] Furthermore, the method for preparing the sodium polyacrylate-encapsulated MOFs includes the following steps: Organic ligands and metal salts were mixed and dispersed at a molar ratio of 1.2 to 1.5:1, and then reacted at 120°C for 24 to 26 hours to obtain NH2-MOFs. NH2-MOFs, acrylic acid, 3-buten-1-ol, and catalyst were mixed in a weight ratio of 1:20~25:3~5:1.2~1.5 and reacted at 70~80℃ for 2.5~3 hours. The pH was then adjusted to neutral by adding alkali to obtain the sodium polyacrylate-encapsulated MOFs emulsion. Furthermore, the organic ligand comprises 2-aminoterephthalic acid or 4-aminophthalic acid, and the metal salt comprises zirconium tetrachloride.

[0011] Furthermore, the catalyst is composed of potassium persulfate and sodium bisulfite in a weight ratio of 1:1.

[0012] Furthermore, the crosslinking agent includes divinyl sulfone.

[0013] Furthermore, the thickness of the scraped film is 100μm~150μm.

[0014] An ion exchange membrane prepared by a method for separating radionuclides.

[0015] This invention obtains amino-modified polysulfone resin by polymerizing bisphenol monomers and halosulfone monomers. The amino group improves the nonpolarity of the polysulfone resin, enabling it to have good interfacial compatibility with subsequent sodium polyacrylate-encapsulated MOFs, thus avoiding the impact of solubilizers on the membrane material. On the other hand, the amino group can crosslink with the hydroxyl groups on the structure of the sodium polyacrylate-encapsulated MOFs through a crosslinking agent, thereby introducing the highly hydrophilic sodium polyacrylate into the polysulfone material. This not only improves hydrophilicity and reduces the clogging caused by organic pollutants, thus increasing its water flux, but also allows the negatively charged carboxylate groups on the sodium polyacrylate structure to chelate metal ions in nuclear wastewater through ion exchange, achieving the removal of metal ions from the nuclear wastewater. The role of the metal-organic framework (MOF) material in the sodium polyacrylate-encapsulated MOF emulsion is that while increasing hydrophilicity, the excessive swelling effect of the membrane can lead to problems. This can hinder the removal of radioactive elements and, as separation progresses, cause a decrease in mechanical strength and pore structure collapse, resulting in a decline in flux over time. The introduction of MOFs addresses this by anchoring the easily absorbing and expanding molecular chains, limiting excessive chain movement. Furthermore, the ion exchange properties of MOFs themselves enhance the separation of radionuclides, thus synergistically improving the separation efficiency. Detailed Implementation

[0016] The technical solution of the present invention will be described in detail and completely below through embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] Unless otherwise stated, all raw materials and reagents used in this invention are commercially available or can be prepared by known methods.

[0018] Preparation Example 1 The preparation of amino-modified polysulfone resin is as follows: 1 mol of bisphenol A and 1.2 mol of halosulfone monomer (composed of 1 mol of 4,4'-dichlorodiphenyl sulfone and 0.2 mol of 2-amino-4'-fluorobenzophenone) were weighed and added to 1 L of N,N-dimethylformamide and stirred until dissolved and homogeneous. Then, 1 mol of potassium carbonate was added and stirred until homogeneous. Nitrogen gas was then introduced to purge air as a protective gas during the reaction. The mixture was then heated to 160 °C for 2 h for pretreatment. After pretreatment, the temperature was further increased to 180 °C for 3 h. After the reaction was completed, the mixture was allowed to cool naturally to room temperature. Then, 2 L of deionized water was added to precipitate the precipitate. The precipitate was collected by filtration and dried in a vacuum drying oven at 60 °C to remove water, thus obtaining amino-modified polysulfone resin.

[0019] Preparation Example 2 The preparation of amino-modified polysulfone resin is as follows: 1 mol of bisphenol A and 1.3 mol of halosulfone monomer (composed of 1 mol of 4,4'-dichlorodiphenyl sulfone and 0.3 mol of 2-amino-4'-fluorobenzophenone) were weighed and added to 1 L of N,N-dimethylformamide and stirred until dissolved and homogeneous. Then, 1 mol of potassium carbonate was added and stirred until homogeneous. Nitrogen gas was then introduced to purge air as a protective gas during the reaction. The mixture was then heated to 160 °C for 2 h for pretreatment. After pretreatment, the temperature was further increased to 180 °C for 3.5 h. After the reaction, the mixture was allowed to cool naturally to room temperature. Then, 2 L of deionized water was added to precipitate the precipitate. The precipitate was collected by filtration and dried in a vacuum drying oven at 60 °C to remove water, thus obtaining amino-modified polysulfone resin.

[0020] Preparation Example 3 The preparation of amino-modified polysulfone resin is as follows: 1 mol of bisphenol A and 1.4 mol of halosulfone monomer (composed of 1 mol of 4,4'-dichlorodiphenyl sulfone and 0.4 mol of 2-amino-4'-fluorobenzophenone) were weighed and added to 1 L of N,N-dimethylformamide and stirred until dissolved and homogeneous. Then, 1 mol of sodium hydroxide was added and stirred until homogeneous. Nitrogen gas was then introduced to purge air as a protective gas during the reaction. The mixture was then heated to 160 °C for 3 h for pretreatment. After pretreatment, the temperature was further increased to 190 °C for 3.5 h. After the reaction, the mixture was allowed to cool naturally to room temperature. Then, 2 L of deionized water was added to precipitate the precipitate. The precipitate was collected by filtration and dried in a vacuum drying oven at 60 °C to remove water, thus obtaining amino-modified polysulfone resin.

[0021] Preparation Example 4 The preparation of amino-modified polysulfone resin is as follows: 1 mol of bisphenol A and 1.5 mol of halosulfone monomer (composed of 1 mol of 4,4'-dichlorodiphenyl sulfone and 0.5 mol of 2-amino-4'-fluorobenzophenone) were weighed and added to 1 L of N,N-dimethylformamide and stirred until dissolved and homogeneous. Then, 1 mol of sodium hydroxide was added and stirred until homogeneous. Nitrogen gas was then introduced to purge air as a protective gas during the reaction. The mixture was then heated to 160 °C for 3 h for pretreatment. After pretreatment, the temperature was further increased to 190 °C for 3.5 h. After the reaction, the mixture was allowed to cool naturally to room temperature. Then, 2 L of deionized water was added to precipitate the precipitate. The precipitate was collected by filtration and dried in a vacuum drying oven at 60 °C to remove water, thus obtaining amino-modified polysulfone resin.

[0022] Preparation Example 5 The preparation of polysulfone resin is as follows: 1 mol of bisphenol A and 1.5 mol of 4,4'-dichlorodiphenyl sulfone were weighed and added to 1 L of N,N-dimethylformamide and stirred until dissolved and homogeneous. Then, 1 mol of sodium hydroxide was added and stirred until homogeneous. Nitrogen gas was then introduced to purge air as a protective gas during the reaction. The mixture was then heated to 160 °C for 3 h for pretreatment. After pretreatment, the temperature was further increased to 190 °C for 3.5 h. After the reaction was completed, the mixture was allowed to cool naturally to room temperature. Then, 2 L of deionized water was added to precipitate the precipitate. The precipitate was collected by filtration and dried in a vacuum drying oven at 60 °C to remove water, thus obtaining polysulfone resin.

[0023] Preparation Example 6 The preparation of amino-modified polysulfone resin is as follows: 1 mol of bisphenol A and 1.5 mol of halosulfone monomer (composed of 0.5 mol of 4,4'-dichlorodiphenyl sulfone and 1 mol of 2-amino-4'-fluorobenzophenone) were weighed and added to 1 L of N,N-dimethylformamide and stirred until dissolved and homogeneous. Then, 1 mol of sodium hydroxide was added and stirred until homogeneous. Nitrogen gas was then introduced to purge air as a protective gas during the reaction. The mixture was then heated to 160 °C for 3 h for pretreatment. After pretreatment, the temperature was further increased to 190 °C for 3.5 h. After the reaction, the mixture was allowed to cool naturally to room temperature. Then, 2 L of deionized water was added to precipitate the precipitate. The precipitate was collected by filtration and dried in a vacuum drying oven at 60 °C to remove water, thus obtaining amino-modified polysulfone resin.

[0024] Preparation Example 7 The preparation of MOFs encapsulated with sodium polyacrylate is as follows: 0.012 mol of 2-aminoterephthalic acid and 0.01 mol of zirconium tetrachloride were added to 300 mL of N,N-dimethylformamide, followed by 4 mL of concentrated hydrochloric acid as a regulator. The mixture was then dispersed by ultrasonic treatment at 400 W for 20 min, and then transferred to a sealed reactor and heated to 120 °C for 24 h. After the reaction, the product was collected by centrifugation at 8000 r / min. The product was first washed with N,N-dimethylformamide, then with anhydrous methanol, and finally dried in a vacuum drying oven at 80 °C for 18 h to obtain NH2-MOFs. 4 g of NH2-MOFs, 80 g of acrylic acid, and 12 g of 3-buten-1-ol were weighed and added to the reactor and mixed thoroughly. Nitrogen gas was then introduced to purge the air from the reactor, and 0.08 g of catalyst (composed of potassium persulfate and sodium bisulfite in a 1:1 weight ratio) was added. The reactor was then closed and heated to 70 °C, where it was reacted for 2.5 h. After the reaction was completed, the temperature was lowered to 40°C, and then the pH was adjusted to neutral with sodium hydroxide solution to complete the preparation of the sodium polyacrylate-encapsulated MOFs emulsion.

[0025] Preparation Example 8 The preparation of MOFs encapsulated with sodium polyacrylate is as follows: 0.013 mol of 2-aminoterephthalic acid and 0.01 mol of zirconium tetrachloride were added to 300 mL of N,N-dimethylformamide, followed by 4 mL of concentrated hydrochloric acid as a regulator. The mixture was then dispersed by ultrasonic treatment at 400 W for 20 min, and then transferred to a sealed reactor and heated to 120 °C for 25 h. After the reaction, the product was collected by centrifugation at 8000 r / min. The product was first washed with N,N-dimethylformamide, then with anhydrous methanol, and finally dried in a vacuum drying oven at 80 °C for 18 h to obtain NH2-MOFs. 4 g of NH2-MOFs, 85 g of acrylic acid, and 15 g of 3-buten-1-ol were weighed and added to the reactor and mixed thoroughly. Nitrogen gas was then introduced to purge the air from the reactor, and 0.08 g of catalyst (composed of potassium persulfate and sodium bisulfite in a 1:1 weight ratio) was added. The reactor was then closed and heated to 75 °C, where it was reacted for 2.5 h. After the reaction was completed, the temperature was lowered to 40°C, and then the pH was adjusted to neutral with sodium hydroxide solution to complete the preparation of the sodium polyacrylate-encapsulated MOFs emulsion.

[0026] Preparation Example 9 The preparation of MOFs encapsulated with sodium polyacrylate is as follows: 0.014 mol of 4-aminophthalic acid and 0.01 mol of zirconium tetrachloride were added to 300 mL of N,N-dimethylformamide, followed by 4 mL of concentrated hydrochloric acid as a regulator. The mixture was then dispersed by ultrasonic treatment at 400 W for 20 min, and then transferred to a sealed reactor and heated to 120 °C for 26 h. After the reaction, the product was collected by centrifugation at 8000 r / min. The product was first washed with N,N-dimethylformamide, then with anhydrous methanol, and finally dried in a vacuum drying oven at 80 °C for 18 h to obtain NH2-MOFs. 4 g of NH2-MOFs, 95 g of acrylic acid, and 18 g of 3-buten-1-ol were weighed and added to the reactor and mixed thoroughly. Nitrogen gas was then introduced to purge the air from the reactor, and 0.09 g of catalyst (composed of potassium persulfate and sodium bisulfite in a 1:1 weight ratio) was added. The reactor was then closed and heated to 80 °C, where it was reacted for 2.5 h. After the reaction was completed, the temperature was lowered to 40°C, and then the pH was adjusted to neutral with sodium hydroxide solution to complete the preparation of the sodium polyacrylate-encapsulated MOFs emulsion.

[0027] Preparation Example 10 The preparation of MOFs encapsulated with sodium polyacrylate is as follows: 0.015 mol of 4-aminophthalic acid and 0.01 mol of zirconium tetrachloride were added to 300 mL of N,N-dimethylformamide, followed by 4 mL of concentrated hydrochloric acid as a regulator. The mixture was then dispersed by ultrasonic treatment at 400 W for 20 min, and then transferred to a sealed reactor and heated to 120 °C for 26 h. After the reaction, the product was collected by centrifugation at 8000 r / min. The product was first washed with N,N-dimethylformamide, then with anhydrous methanol, and finally dried in a vacuum drying oven at 80 °C for 18 h to obtain NH2-MOFs. 4 g of NH2-MOFs, 100 g of acrylic acid, and 20 g of 3-buten-1-ol were weighed and added to the reactor and mixed thoroughly. Nitrogen gas was then introduced to purge the air from the reactor, and 0.1 g of catalyst (composed of potassium persulfate and sodium bisulfite in a 1:1 weight ratio) was added. The reactor was then closed and heated to 80 °C, where it was reacted for 3 h. After the reaction was completed, the temperature was lowered to 40°C, and then the pH was adjusted to neutral with sodium hydroxide solution to complete the preparation of the sodium polyacrylate-encapsulated MOFs emulsion.

[0028] Preparation Example 11 The preparation of MOFs encapsulated with sodium polyacrylate is as follows: 0.015 mol of dimethylimidazole and 0.01 mol of zirconium tetrachloride were added to 300 mL of N,N-dimethylformamide, followed by 4 mL of concentrated hydrochloric acid as a regulator. The mixture was then dispersed by ultrasonic treatment at 400 W for 20 min, and then transferred to a sealed reactor and heated to 120 °C for 26 h. After the reaction, the product was collected by centrifugation at 8000 r / min. The product was first washed with N,N-dimethylformamide, then with anhydrous methanol, and finally dried in a vacuum drying oven at 80 °C for 18 h to obtain MOFs. 4 g of MOFs, 100 g of acrylic acid, and 20 g of 3-buten-1-ol were weighed and added to the reactor and mixed thoroughly. Nitrogen gas was then introduced to purge the air from the reactor, and 0.1 g of catalyst (composed of potassium persulfate and sodium bisulfite in a 1:1 weight ratio) was added. The reactor was then closed and heated to 80 °C, and the reaction was carried out at this temperature for 3 h. After the reaction was completed, the temperature was lowered to 40°C, and then the pH was adjusted to neutral with sodium hydroxide solution to complete the preparation of the sodium polyacrylate-encapsulated MOFs emulsion.

[0029] Preparation Example 12 The preparation of MOFs encapsulated with sodium polyacrylate is as follows: 0.015 mol of 4-aminophthalic acid and 0.01 mol of zirconium tetrachloride were added to 300 mL of N,N-dimethylformamide, followed by 4 mL of concentrated hydrochloric acid as a regulator. The mixture was then dispersed by ultrasonic treatment at 400 W for 20 min, and then transferred to a sealed reactor and heated to 120 °C for 26 h. After the reaction, the product was collected by centrifugation at 8000 r / min. The product was first washed with N,N-dimethylformamide, then with anhydrous methanol, and finally dried in a vacuum drying oven at 80 °C for 18 h to obtain NH2-MOFs. 4 g of NH2-MOFs, 100 g of acrylic acid, and 20 g of 1-octen-3-ol were weighed and added to the reactor and mixed thoroughly. Nitrogen gas was then introduced to purge the air from the reactor, and 0.1 g of catalyst (composed of potassium persulfate and sodium bisulfite in a 1:1 weight ratio) was added. The reactor was then closed and heated to 80 °C, where it was reacted for 3 h. After the reaction was completed, the temperature was lowered to 40°C, and then the pH was adjusted to neutral with sodium hydroxide solution to complete the preparation of the sodium polyacrylate-encapsulated MOFs emulsion.

[0030] Example 1

[0031] A method for preparing an ion-exchange membrane for the separation of radionuclides, specifically including the following steps: 200g of the amino-modified polysulfone resin obtained in Preparation Example 1 was weighed and mixed with 400mL of N,N-dimethylformamide. The mixture was heated and stirred to promote dissolution. After dissolution, the temperature was lowered to 30℃ and maintained. Then, 60g of the sodium polyacrylate-encapsulated MOF emulsion obtained in Preparation Example 7 and 2g of divinyl sulfone were added and mixed and stirred evenly. Then, sodium hydroxide solution was added dropwise to adjust the pH to 10 and the reaction was carried out for 2 hours. After the reaction was completed, the pH was adjusted to neutral with dilute hydrochloric acid to obtain the casting solution. The casting solution was degassed in a vacuum environment of -0.08MPa for 20 minutes and then poured onto a glass plate. The coating thickness was controlled to 100μm using a coating machine. The membrane was then placed in deionized water at 4℃ to solidify and form a film. The membrane was then removed and soaked in deionized water at 25℃ for 48 hours (with fresh deionized water replaced every 4 hours during the soaking period) to obtain the ion exchange membrane.

[0032] Example 2

[0033] A method for preparing an ion-exchange membrane for the separation of radionuclides, specifically including the following steps: 220g of the amino-modified polysulfone resin obtained in Preparation Example 2 was weighed and mixed with 500mL of N,N-dimethylformamide. The mixture was heated and stirred to promote its dissolution. After dissolution, the temperature was lowered to 30℃ and kept warm. Then, 70g of the sodium polyacrylate-coated MOF emulsion obtained in Preparation Example 8 and 2.4g of divinyl sulfone were added and mixed evenly. Then, sodium hydroxide solution was added dropwise to adjust the pH to 10 and the reaction was carried out for 2.5h. After the reaction was completed, the pH was adjusted to neutral with dilute hydrochloric acid to obtain the casting solution. The casting solution was degassed in a vacuum environment of -0.08MPa for 20min, and then poured onto a glass plate. The coating thickness was controlled to 120μm using a coating machine. The membrane was then placed in deionized water at 4℃ to solidify and form a film. The membrane was then removed and soaked in deionized water at 25℃ for 48h (with fresh deionized water replaced every 4h during the soaking period) to obtain the ion exchange membrane.

[0034] Example 3

[0035] A method for preparing an ion-exchange membrane for the separation of radionuclides, specifically including the following steps: 240g of the amino-modified polysulfone resin obtained in Preparation Example 3 was weighed and mixed with 600mL of N,N-dimethylformamide. The mixture was heated and stirred to promote its dissolution. After dissolution, the temperature was lowered to 30℃ and kept warm. Then, 80g of the sodium polyacrylate-encapsulated MOF emulsion obtained in Preparation Example 9 and 2.8g of divinyl sulfone were added and mixed and stirred evenly. Then, sodium hydroxide solution was added dropwise to adjust the pH to 10.5 and reacted for 3h. After the reaction was completed, the pH was adjusted to neutral with dilute hydrochloric acid to obtain the casting solution. The casting solution was degassed in a vacuum environment of -0.08MPa for 20min, and then poured onto a glass plate. The coating thickness was controlled to 150μm using a coating machine. The membrane was then placed in deionized water at 4℃ to solidify and form a film. The membrane was then removed and soaked in deionized water at 25℃ for 48h (with fresh deionized water replaced every 4h during the soaking period) to obtain the ion exchange membrane.

[0036] Example 4

[0037] A method for preparing an ion-exchange membrane for the separation of radionuclides, specifically including the following steps: 240g of the amino-modified polysulfone resin obtained in Preparation Example 4 was weighed and mixed with 600mL of N,N-dimethylformamide. The mixture was heated and stirred to promote its dissolution. After dissolution, the temperature was lowered to 30°C and maintained. Then, 80g of the sodium polyacrylate-encapsulated MOF emulsion obtained in Preparation Example 10 and 2.8g of divinyl sulfone were added and mixed and stirred evenly. Then, sodium hydroxide solution was added dropwise to adjust the pH to 10.5 and reacted for 3 hours. After the reaction was completed, the pH was adjusted to neutral with dilute hydrochloric acid to obtain the casting solution. The casting solution was degassed in a vacuum environment of -0.08MPa for 20 minutes and then poured onto a glass plate. The coating thickness was controlled to 150μm using a coating machine. The membrane was then placed in deionized water at 4°C to solidify and form a film. The membrane was then removed and soaked in deionized water at 25°C for 48 hours (with fresh deionized water replaced every 4 hours during the soaking period) to obtain the ion exchange membrane.

[0038] Comparative Example 1 A method for preparing an ion-exchange membrane for the separation of radionuclides, specifically including the following steps: 240g of the polysulfone resin obtained in Preparation Example 5 was weighed and mixed with 600mL of N,N-dimethylformamide. The mixture was heated and stirred to promote dissolution. After dissolution, the temperature was lowered to 30°C and maintained. Then, 80g of the sodium polyacrylate-encapsulated MOF emulsion obtained in Preparation Example 10 and 2.8g of divinyl sulfone were added and mixed evenly. Sodium hydroxide solution was then added dropwise to adjust the pH to 10.5 and reacted for 3 hours. After the reaction, the pH was adjusted to neutral with dilute hydrochloric acid to obtain the casting solution. The casting solution was degassed in a vacuum environment of -0.08MPa for 20 minutes and then poured onto a glass plate. The coating thickness was controlled to 150μm using a coating machine. The membrane was then placed in deionized water at 4°C to solidify and form a film. The membrane was then removed and soaked in deionized water at 25°C for 48 hours (with fresh deionized water replaced every 4 hours during the soaking period) to obtain the ion exchange membrane.

[0039] Comparative Example 2 A method for preparing an ion-exchange membrane for the separation of radionuclides, specifically including the following steps: 240g of the amino-modified polysulfone resin obtained in Preparation Example 6 was weighed and mixed with 600mL of N,N-dimethylformamide. The mixture was heated and stirred to promote its dissolution. After dissolution, the temperature was lowered to 30°C and maintained. Then, 80g of the sodium polyacrylate-coated MOF emulsion obtained in Preparation Example 10 and 2.8g of divinyl sulfone were added and mixed and stirred evenly. Then, sodium hydroxide solution was added dropwise to adjust the pH to 10.5 and reacted for 3 hours. After the reaction was completed, the pH was adjusted to neutral with dilute hydrochloric acid to obtain the casting solution. The casting solution was degassed in a vacuum environment of -0.08MPa for 20 minutes and then poured onto a glass plate. The coating thickness was controlled to 150μm using a coating machine. The membrane was then placed in deionized water at 4°C to solidify and form a film. The membrane was then removed and soaked in deionized water at 25°C for 48 hours (with fresh deionized water replaced every 4 hours during the soaking period) to obtain the ion exchange membrane.

[0040] Comparative Example 3 A method for preparing an ion-exchange membrane for the separation of radionuclides, specifically including the following steps: 240g of the amino-modified polysulfone resin obtained in Preparation Example 4 was weighed and mixed with 600mL of N,N-dimethylformamide. The mixture was heated and stirred to promote dissolution. After dissolution, the temperature was lowered to 30°C and maintained. Then, 80g of the sodium polyacrylate-coated MOF emulsion obtained in Preparation Example 11 and 2.8g of divinyl sulfone were added and mixed and stirred evenly. Then, sodium hydroxide solution was added dropwise to adjust the pH to 10.5 and reacted for 3 hours. After the reaction was completed, the pH was adjusted to neutral with dilute hydrochloric acid to obtain the casting solution. The casting solution was degassed in a vacuum environment of -0.08MPa for 20 minutes and then poured onto a glass plate. The coating thickness was controlled to 150μm using a coating machine. The membrane was then placed in deionized water at 4°C to solidify and form a film. The membrane was then removed and soaked in deionized water at 25°C for 48 hours (with fresh deionized water replaced every 4 hours during the soaking period) to obtain the ion exchange membrane.

[0041] Comparative Example 4 A method for preparing an ion-exchange membrane for the separation of radionuclides, specifically including the following steps: 240g of the amino-modified polysulfone resin obtained in Preparation Example 4 was weighed and mixed with 600mL of N,N-dimethylformamide. The mixture was heated and stirred to promote its dissolution. After dissolution, the temperature was lowered to 30°C and maintained. Then, 80g of the sodium polyacrylate-encapsulated MOF emulsion obtained in Preparation Example 12 and 2.8g of divinyl sulfone were added and mixed evenly. Sodium hydroxide solution was then added dropwise to adjust the pH to 10.5 and reacted for 3 hours. After the reaction, the pH was adjusted to neutral with dilute hydrochloric acid to obtain the casting solution. The casting solution was degassed in a vacuum environment of -0.08MPa for 20 minutes and then poured onto a glass plate. The coating thickness was controlled to 150μm using a coating machine. The membrane was then placed in deionized water at 4°C to solidify and form a film. The membrane was then removed and soaked in deionized water at 25°C for 48 hours (with fresh deionized water replaced every 4 hours during the soaking period) to obtain the ion exchange membrane.

[0042] Comparative Example 5 A method for preparing an ion-exchange membrane for the separation of radionuclides, specifically including the following steps: 240g of the amino-modified polysulfone resin obtained in Preparation Example 4 was weighed and mixed with 600mL of N,N-dimethylformamide. The mixture was heated and stirred to promote its dissolution. After dissolution, the temperature was lowered to 30°C and kept warm. Then, 80g of the sodium polyacrylate-encapsulated MOF emulsion obtained in Preparation Example 10 and 5g of divinyl sulfone were added and mixed and stirred evenly. Then, sodium hydroxide solution was added dropwise to adjust the pH to 10.5 and reacted for 3 hours. It was found that the casting solution solidified prematurely and could not be coated to prepare the ion exchange membrane. This may be because although increasing the amount of divinyl sulfone can improve the crosslinking strength, excessive use in this system may make the crosslinking activity too strong. The casting solution may therefore undergo crosslinking and solidification and cannot proceed with the subsequent membrane preparation steps.

[0043] Comparative Example 6 A method for preparing an ion-exchange membrane for the separation of radionuclides, specifically including the following steps: 240g of the amino-modified polysulfone resin obtained in Preparation Example 4 was weighed and mixed with 600mL of N,N-dimethylformamide. The mixture was heated and stirred to promote its dissolution. After dissolution, the temperature was lowered to 30°C and maintained. Then, 80g of the sodium polyacrylate-coated MOF emulsion obtained in Preparation Example 10 and 2.8g of divinyl sulfone were added and mixed and stirred evenly. Then, sodium hydroxide solution was added dropwise to adjust the pH to 10.5 and reacted for 3 hours. After the reaction was completed, the pH was adjusted to neutral with dilute hydrochloric acid to obtain the casting solution. The casting solution was degassed in a vacuum environment of -0.08MPa for 20 minutes and then poured onto a glass plate. The coating thickness was controlled to 200μm using a coating machine. The membrane was then placed in deionized water at 4°C to solidify and form a film. The membrane was then removed and soaked in deionized water at 25°C for 48 hours (with fresh deionized water replaced every 4 hours during the soaking period) to obtain the ion exchange membrane.

[0044] The ion exchange membranes obtained in Examples 1-4, Comparative Examples 1-4, and Comparative Example 6 were pre-pressurized in deionized water at 0.2 MPa and 25 °C for half an hour, and then the pressure was adjusted to 0.1 MPa for pure water flux testing. The results are shown in Table 1 below.

[0045] Table 1

[0046] The ion exchange membranes obtained in Examples 1-4, Comparative Examples 1-4, and Comparative Example 6 were pre-pressurized in deionized water at 0.2 MPa and 25 °C for half an hour. Then, the pressure was adjusted to 0.1 MPa, and a simulated radionuclide waste liquid containing 100 mg / L of uranium ions was prepared. The retention effect of the ion exchange membrane on uranium ions after the first hour and the fifth hour of operation was calculated according to the retention rate = (uranium ion concentration in the initial waste liquid - uranium ion concentration in the permeate after permeation) / uranium ion concentration in the initial waste liquid × 100%. The results are shown in Table 2 below.

[0047] Table 2

[0048] The ion exchange membranes obtained in Examples 1-4, Comparative Examples 1-4, and Comparative Example 6 were subjected to tensile property tests using a universal testing machine at a tensile rate of 100 mm / min. The results are shown in Table 3 below.

[0049] Table 3

[0050] The following conclusions can be drawn from Tables 1-3 above: (1) As can be seen from Examples 1 to 4, the ion exchange membrane prepared by the present invention not only has good water flux and good radionuclide separation effect, but also has good mechanical properties, which is beneficial to extending service life.

[0051] (2) Comparative Example 1 shows that the water flux and nuclide separation effect of the prepared ion exchange membrane are both poor. This may be because the polysulfone in this system does not have an active amino group, which may not only lead to poor compatibility with the sodium polyacrylate structure, but also make it difficult to crosslink with the sodium polyacrylate structure, resulting in poor hydrophilic modification, low water flux and poor separation effect.

[0052] (3) Comparative Example 2 shows that although the prepared ion exchange membrane has a certain water flux and separation effect in the early stage, its mechanical properties are poor. However, as time goes on, the water flux and separation effect also deteriorate. This may be because 2-amino-4'-fluorobenzophenone is a monofluorinated monomer with only one reaction site. It is a monofunctional end-capping agent. If the amount used in this system is too high, it may cause the chain end to be quickly sealed during the polymerization process, and the chain growth will terminate prematurely. Although the hydrophilicity increases to a certain extent, the polymerization is uneven due to the premature termination of chain growth, resulting in poor mechanical properties of the membrane. During long-term operation, the pore structure of the membrane may easily collapse, which in turn leads to a deterioration in water flux and separation effect.

[0053] (4) Comparative Example 3 shows that the water flux, radionuclide separation effect and mechanical strength of the prepared ion exchange membrane are all poor. This may be because the steric hindrance of the methyl group of the dimethylimidazolium used to prepare MOFs in this system is not conducive to the synthesis of MOFs materials to be bound to polyacrylic acid by intermolecular forces such as hydrogen bonds. This may lead to uneven encapsulation of MOFs and low encapsulation amount, which in turn affects the performance of the ion exchange membrane.

[0054] (5) Comparative Example 4 shows that the water flux and radionuclide separation effect of the prepared ion exchange membrane are poor. This may be because the 1-octen-3-ol hydrophobic alkyl carbon chain in this system is long, which will cause hydrophobic aggregation and wrap the internal carboxylate structure, reducing its ionization and hydration, resulting in a decrease in hydrophilicity and thus a lower water flux, which is not conducive to the separation of radionuclides.

[0055] (6) Comparative Example 6 shows that although the mechanical strength of the ion exchange membrane was further improved, the water flux and the separation of radionuclides were poor. This may be because, on the one hand, water permeates through the membrane in a permeable flow. The thicker the membrane, the longer the pores that water molecules need to pass through, the longer the water permeation path, the greater the mass transfer resistance, and the lower the flux. On the other hand, when the membrane is immersed in cold water for a gel bath, the surface layer solidifies first while the internal solvent exchange may be delayed. The surface layer forms a thicker and denser skin layer, which directly blocks the water permeation channels. Due to the slow diffusion of the solvent inside, irregular pores such as closed pores and blind pores are easily formed. As a result, the membrane appears to be very thick and strong, but the water flux is poor.

[0056] The embodiments described above provide a detailed explanation of the technical solutions and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Various changes and modifications can be made to the present invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed.

Claims

1. A method for preparing an ion-exchange membrane for the separation of radionuclides, characterized in that, The preparation method includes the following steps: Amino-modified polysulfone resin, sodium polyacrylate-encapsulated MOFs emulsion, organic solvent, and crosslinking agent are mixed in a weight ratio of 10~12:3~4:20~30:0.1~0.

14. The pH is adjusted to 10~10.5 and the mixture is reacted for 2~3 hours. The pH is then adjusted to neutral to obtain a casting solution. After vacuum degassing, the casting solution is scraped to obtain the ion exchange membrane.

2. The method for preparing an ion exchange membrane for the separation of radionuclides according to claim 1, characterized in that, The preparation method of the amino-modified polysulfone resin includes the following steps: Bisphenol monomer, halosulfone monomer and inorganic base catalyst are mixed in a molar ratio of 1:1.2 to 1.5:1, and then pretreated at 170°C for 2 to 3 hours under nitrogen protection. The mixture is then heated to 180°C to 190°C and reacted for 3 to 3.5 hours to obtain the amino-modified polysulfone resin.

3. The method for preparing an ion exchange membrane for the separation of radionuclides according to claim 2, characterized in that, The bisphenol monomer includes bisphenol A.

4. The method for preparing an ion exchange membrane for the separation of radionuclides according to claim 2, characterized in that, The halosulfone monomer is composed of 4,4'-dichlorodiphenyl sulfone and 2-amino-4'-fluorobenzophenone in a molar ratio of 10:2~5.

5. The method for preparing an ion exchange membrane for the separation of radionuclides according to claim 1, characterized in that, The method for preparing the sodium polyacrylate-encapsulated MOFs includes the following steps: Organic ligands and metal salts were mixed and dispersed at a molar ratio of 1.2 to 1.5:1, and then reacted at 120°C for 24 to 26 hours to obtain NH2-MOFs. NH2-MOFs, acrylic acid, 3-buten-1-ol and catalyst are mixed in a weight ratio of 1:20~25:3~5:1.2~1.5 and reacted at 70℃~80℃ for 2.5~3h. Then, alkali is added to adjust the pH to neutral to obtain the sodium polyacrylate-encapsulated MOFs emulsion.

6. The method for preparing an ion exchange membrane for the separation of radionuclides according to claim 5, characterized in that, The organic ligand includes 2-aminoterephthalic acid or 4-aminophthalic acid, and the metal salt includes zirconium tetrachloride.

7. The method for preparing an ion exchange membrane for the separation of radionuclides according to claim 1, characterized in that, The crosslinking agent includes divinyl sulfone.

8. The method for preparing an ion exchange membrane for the separation of radionuclides according to claim 1, characterized in that, The thickness of the scraped film is 100μm~150μm.

9. An ion exchange membrane prepared by the method for preparing an ion exchange membrane for the separation of radionuclides as described in any one of claims 1 to 8.

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