A metal-modified ion exchange membrane, a preparation method and application thereof

Abstract

The application relates to the technical field of wastewater treatment, in particular to a metal-modified ion exchange membrane and a preparation method and application thereof. The metal-modified ion exchange membrane comprises the following steps: taking an anion exchange membrane as a base film, modifying the surface of the base film after impurity removal through pretreatment by using an amino silane coupling agent to obtain an amino silane coupling agent modified base film, and co-loading Zr 4+ , Al 3+ , Nd 3+ on the amine group active sites of the amino silane coupling agent modified base film through coordination bonds, and then forming a ZrO(OH)2, AlO(OH), Nd(OH)3 composite adsorption layer on the surface of the base film through hydroxylation to obtain the metal-modified ion exchange membrane. The ion exchange membrane is modified through the steps of "pretreatment-coupling agent modification-multimetal co-loading-hydroxylation", the bridging effect of the coupling agent is used to strengthen the binding stability of the metal components and the film base material, the multimetal synergistic effect is used to endow the film with efficient and stable fluorine adsorption performance, and the synergistic defluorination of electromigration and chemical adsorption is realized.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically to a metal-modified ion exchange membrane, its preparation method, and its application. Background Technology

[0002] Industrial processes such as semiconductor processing, fluorochemicals, and aluminum electrolysis typically generate large quantities of fluoride-containing wastewater, with fluoride ions reaching tens to hundreds of milligrams per liter. Direct discharge of this wastewater can pollute aquatic environments. Therefore, the advanced treatment of fluoride-containing wastewater has become a crucial issue in environmental protection. Current treatment technologies for fluoride-containing wastewater mainly include coagulation sedimentation, adsorption, and electrodialysis. Among these, electrodialysis has broad application prospects in advanced defluorination due to its advantages such as simple operation, low energy consumption, and no secondary pollution. The core of electrodialysis defluorination is the ion exchange membrane, whose performance directly determines the defluorination efficiency and treatment effect.

[0003] The ion exchange membranes used in current electrodialysis are mostly general-purpose membranes with poor selectivity for fluoride ions, especially in applications containing Cl-. － SO4 2－ In water bodies where coexisting anions, the separation efficiency of fluoride ions decreases significantly. Furthermore, ordinary ion exchange membranes rely solely on electric field-driven ion migration for separation, lacking the ability to specifically remove fluoride ions. Therefore, they typically fail to meet the standards for deep purification when treating low-concentration fluoride-containing wastewater. Currently, materials for deep fluoride removal largely focus on zirconium-based and aluminum-based resins, which involve loading zirconium-based or aluminum-based components onto a resin carrier. However, these resins suffer from drawbacks such as high mass transfer resistance, easy loss in dynamic water flow, and difficulty in adapting to the electric field environment of electrodialysis, making them unsuitable for direct application in electrodialysis fluoride removal systems.

[0004] Existing technologies disclose the use of resin filling or MOF physical mixing to improve the selectivity of fluoride ions. For example, patent publication number CN113731196A, entitled "A Mixed Matrix Membrane for Removing Fluoride from Water and Its Preparation Method," describes a method for preparing MOF materials by reacting calcium, aluminum, manganese, and zirconium polymetallic ions with organic acids. The MOF is then mixed into the CAP casting solution as a functional additive. After coating and solvent evaporation, a mixed matrix membrane is obtained. Fluoride removal is achieved through ion exchange between the MOF and fluoride ions. While this technology combines the advantages of adsorption and membrane separation, the preparation of MOF requires high-temperature reactions in an autoclave, making the process relatively complex and energy-intensive. Furthermore, the physical mixing of MOF and membrane substrate may affect the dispersion uniformity and bonding stability of the material with long-term use. Another example is patent publication number CN119191495A, entitled "A Packed Bed Electrodialysis Device and Method for Targeted Selective Fluoride Removal," which describes filling a dilute electrodialysis chamber with a mixed bed of resin, utilizing the synergistic effect of resin adsorption and electrodialysis to improve the selectivity of fluoride ions. This technology provides a new approach for selective defluorination, but the resin filling the dilute chamber is not integrated with the ion exchange membrane, which can easily lead to high bed mass transfer resistance, uneven water flow distribution, and may affect the long-term operational stability of the device under the long-term influence of the electric field. Therefore, this invention provides a metal-modified ion exchange membrane, its preparation method, and its applications. Summary of the Invention

[0005] To address the problems of poor selectivity, low separation efficiency, and significant interference from coexisting anions in existing electrodialysis defluorination technologies, as well as the weak binding and easy loss of active components in traditional ion exchange membranes, this invention provides a metal-modified ion exchange membrane, its preparation method, and its application. The ion exchange membrane is modified through a four-step process: pretreatment, coupling agent modification, multi-metal co-loading, and hydroxylation. The coupling agent enhances the bonding stability between the metal components and the membrane substrate, while the synergistic effect of multiple metals endows the membrane with efficient and stable fluoride adsorption performance, achieving synergistic defluorination through electromigration and chemisorption. Simultaneously, the regeneration process conditions are clearly defined to ensure the membrane's regeneration performance and long-term operational stability, providing a reliable technical solution for the advanced treatment of fluoride-containing wastewater.

[0006] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: In a first aspect, a method for preparing a metal-modified ion exchange membrane includes the following steps: Using an anion exchange membrane as the base membrane, the base membrane is pretreated to remove impurities. The surface of the pretreated base membrane is then modified with an aminosilane coupling agent, causing the siloxy groups in the aminosilane coupling agent to undergo a condensation reaction with the surface hydroxyl groups of the base membrane, thereby grafting amino active sites onto the surface of the base membrane to obtain an aminosilane coupling agent-modified base membrane. The amino active sites of the aminosilane coupling agent-modified base membrane are oriented and uniformly co-loaded with Zr through coordination bonds. 4+ Al 3+ 、Nd 3+ After hydroxylation, a ZrO(OH)2, AlO(OH), and Nd(OH)3 composite adsorption layer is formed on the surface of the base membrane, resulting in a metal-modified ion exchange membrane.

[0007] Based on the above technical solution, the present invention can be further improved as follows.

[0008] Furthermore, the Zr 4+ The Al 3+ With the Nd 3+ The molar ratio is (2~4):1:1; The metal-modified ion exchange membrane is co-loaded with Zr 4+ Al 3+ 、Nd 3+ The total metal loading was 9~13 mg / g.

[0009] Further, modifying the surface of the pretreated base film with an aminosilane coupling agent includes the following specific steps: completely immersing the base film in an aminosilane coupling agent solution and impregnating it at 25℃~30℃ for 0.8~1.5 h; removing the impregnated base film and curing it at 80±2℃ for 1~3 h, so that the siloxy groups in the aminosilane coupling agent undergo a condensation reaction with the surface hydroxyl groups of the base film, thereby grafting amino active sites onto the surface of the base film; The mass concentration of the aminosilane coupling agent solution is 1.2% to 2.5%; the pH value of the aminosilane coupling agent solution is 4.2 to 4.8.

[0010] Furthermore, the amino-silane coupling agent-modified base film has its amino-active sites oriented and uniformly co-loaded with Zr via coordination bonds. 4+ Al 3+ 、Nd 3+ The specific steps include: completely immersing the base film modified with the aminosilane coupling agent into a solution containing the Zr. 4+ The Al 3+ With the Nd 3+The substrate is immersed in a mixed solution at 35℃~45℃ for 1.5~2.5 h to allow the amino-silane coupling agent-modified base film to be oriented and uniformly co-loaded with Zr through coordination bonds at its amino-silane coupling agent active sites. 4+ Al 3+ 、Nd 3+ ; Zr in the mixed solution 4+ Al 3+ With Nd 3+ The total metal ion concentration is 0.5~1.5 mol / L, and the pH value of the mixed solution is 1.9~2.5.

[0011] Furthermore, the formation of a ZrO(OH)2, AlO(OH), Nd(OH)3 composite adsorption layer on the surface of the base film via hydroxylation includes the following specific steps: co-loading Zr 4+ Al 3+ 、Nd 3+ The base membrane is then immersed in an alkaline solution and reacted at 45℃~55℃ for 1.5~2.5 h. Afterwards, it is washed and dried sequentially, forming a ZrO(OH)2, AlO(OH), Nd(OH)3 composite adsorption layer on the surface of the base membrane. The concentration of alkaline substances in the alkaline solution is 0.2~0.4 mol / L; the alkaline substances include sodium hydroxide, potassium hydroxide, etc.

[0012] Furthermore, the anion exchange membrane comprises a styrene-based strongly basic anion exchange membrane with an exchange capacity ≥1.2 mmol / g and a membrane thickness of 0.15~0.20 mm; The aminosilane coupling agent includes N-(β-aminoethyl)-γ-aminopropyltriethoxysilane (KH792). The Zr 4+ Derived from ZrCl4; the Al 3+ Derived from AlCl3·6H2O; the Nd 3+ It originates from NdCl3·6H2O.

[0013] Furthermore, the process also includes base membrane pretreatment: a three-stage cleaning process involving ultrasonic cleaning with deionized water, ultrasonic cleaning with 3-5 wt% hydrochloric acid solution, and ultrasonic cleaning with deionized water. After cleaning, the membrane is placed in a vacuum drying oven and dried at 60±2℃ for 4 hours until constant weight (mass deviation ≤0.001g) for later use.

[0014] Secondly, a metal-modified ion exchange membrane is provided, wherein the metal-modified ion exchange membrane is prepared by the aforementioned preparation method.

[0015] Thirdly, an electrodialysis membrane stack for selective defluorination, the electrodialysis membrane stack being provided with the aforementioned metal-modified ion exchange membrane.

[0016] Fourthly, an electrodialysis apparatus for selective defluorination, the electrodialysis apparatus comprising the aforementioned electrodialysis membrane stack for selective defluorination.

[0017] Fifthly, the metal-modified ion exchange membrane, the electrodialysis membrane stack for selective defluorination, or the electrodialysis device for selective defluorination is used for the removal of fluoride from fluoride-containing wastewater.

[0018] Note: Metal-modified ion exchange membranes can be regenerated after selective fluoride removal and reused. This means that the metal-modified ion exchange membrane can be reused after regeneration when its adsorption capacity reaches saturation (manifested as defluorination in the dilute compartment). － When the concentration decrease rate is ≤0.02 mg / (L·min), regeneration is performed using an alkaline solution circulation desorption method. The core of this method is to utilize high concentrations of OH-. － Breaking the F-bond in multi-metallic compounds to achieve F － The efficient desorption process involves the following steps: Alkali regeneration desorption: ① Preparation of regenerant: Use sodium hydroxide (purity ≥99%) as the regenerant to prepare a 0.5~1.0 mol / L NaOH regenerant; ② Circulation regeneration: Close the fluoride-containing wastewater circulation system, discharge the solutions in the dilute and concentrate chambers, and add regenerant to the dilute and concentrate storage tanks respectively (the regenerant volume is calculated according to "membrane effective area × 20 mL / cm²"). 2 For example, 100 cm 2 Add 2 L of OH to both the dilute and concentrate chambers of the membrane stack, turn on the peristaltic pump, adjust the flow rate to 7-9 L / h, and continue regeneration for 1-2 h. During regeneration, high concentrations of OH... － It competes with the -F bonds of multiple metals on the membrane surface for adsorption, disrupting the stability of Zr-F, Al-F, and Nd-F bonds, ultimately leading to the adsorption of F. － The fluoride ions are desorbed into the regenerated solution; during the regeneration process, the fluoride ion concentration in the regenerated solution is monitored using an online fluoride ion monitoring probe. － The concentration of the sample is considered stable when the concentration fluctuates by ≤0.5 mg / L over 30 minutes, indicating that desorption has reached equilibrium.

[0019] This invention uses anion exchange membranes as the base membrane and achieves functional modification of the membrane through "pretreatment – ​​coupling agent modification – multi-metal directional co-loading – hydroxylation modification". The core innovations are: ① the introduction of a coupling agent (e.g., N-(β-aminoethyl)-γ-aminopropyltriethoxysilane (KH792, diamino group)). The amino group structure provides coordination sites, achieving a strong bond between the membrane substrate and metal ions through covalent bridging, significantly improving metal loading stability compared to traditional single amino coupling agents and coupling agent-free solutions; ② the selection of zirconium (Zr) 4+ ) as the main active component, combined with aluminum (Al) 3+ ), neodymium (Nd) 3+ As a synergistic component, the coordination and binding of multi-metal ions with active groups on the membrane surface are utilized to achieve uniform and robust co-loading of multi-metal components; ③ A ZrO(OH)2-AlO(OH)-Nd(OH)3 ternary metal hydroxy oxide composite adsorption layer is constructed through hydroxylation reaction, and the specific adsorption capacity for fluoride ions is enhanced by utilizing the complementarity of different metal adsorption sites and electronic effects.

[0020] The beneficial effects of this invention are: (1) An innovative ternary metal synergistic modification strategy was proposed: Zr and Al and Nd metals were co-loaded on the surface of the ion exchange membrane and modified by hydroxylation to construct a ZrO(OH)2-AlO(OH)-Nd(OH)3 ternary metal hydroxy oxide composite adsorption layer. By utilizing the complementary adsorption sites and electronic synergistic effect, the adsorption capacity and selectivity of the membrane for fluoride ions were significantly improved, which solved the problems of poor fluoride removal and weak anti-interference of traditional commercial membranes. (2) High fluoride removal efficiency and strong processing capacity: The synergistic effect of the ternary metals in this invention significantly improves the fluoride removal efficiency of the metal-modified ion exchange membrane. － Its selective permeability and adsorption performance make it suitable for the treatment of fluoride-containing water with a wide concentration range, and it is especially suitable for the efficient treatment of high-fluoride water. (3) Excellent stability and good regeneration performance: The multi-metal complex of this invention is firmly bonded to the active groups on the surface of the membrane modified with amine groups through coordination bonds. The total metal leaching in the permeate is less than 0.005 mg / L. Compared with the functional decay and impurity shedding problems that are easy to occur in traditional commercial ion exchange membranes, the stability is significantly improved. The optimized alkaline regeneration process can achieve a regeneration rate of more than 92%. After repeated regeneration 10 times, the defluorination efficiency is still more than 75%. The service life is long and the operating cost is effectively reduced. (4) Simple operation process and wide applicability: The preparation-defluorination-regeneration process parameters of this invention are highly adjustable. By adjusting parameters such as the ratio of multiple metals, loading process, and electric field strength, it can be adapted to the water treatment needs of different fluoride concentrations and coexisting ion compositions. Compared with traditional commercial ion exchange membranes, it has a high degree of control over Cl. － SO42－ The anti-interference ability of coexisting anions is significantly improved, and it can be widely used in industrial wastewater treatment, drinking water purification and other scenarios, and is easy to promote industrially. Attached Figure Description

[0021] Figure 1 This is a process flow diagram for preparing the modified ion exchange membrane of the present invention; Figure 2 This is a schematic diagram of the electrodialysis membrane stack assembly structure of the present invention; Figure 3 This is a schematic diagram of the zirconium-aluminum-neodymium ternary metal modified ion exchange membrane structure of the present invention. Detailed Implementation

[0022] The principles and features of this invention are described below. The examples given are for illustrative purposes only and are not intended to limit the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they should be performed according to the techniques or conditions described in the literature in this field, or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased through legitimate channels.

[0023] Source of materials and equipment: Styrene-based strong basic anion exchange membrane (model AMX, exchange capacity 1.3 mmol / g, membrane thickness 0.18 mm, Asahi Kasei); cation exchange membrane (model CMX, exchange capacity 1.2 mmol / g, membrane thickness 0.17 mm, Asahi Kasei); N-(β-aminoethyl)-γ-aminopropyltriethoxysilane (KH792, purity ≥98%, Sinopharm Group); Zirconium chloride (ZrCl4, analytical grade, Sinopharm Group); Aluminum chloride (AlCl3·6H2O, analytical grade, Sinopharm Group); Neodymium chloride (NdCl3·6H2O, analytical grade, Sinopharm Group); Sodium hydroxide (purity ≥99%, Sinopharm Group); Hydrochloric acid (analytical grade, concentration 36-38%, Sinopharm Group); Sodium sulfate (analytical grade, Sinopharm Group); Fluoride ion standard solution (1000 mg / L, Sinopharm Group); Simulated fluoride-containing water A (F － Concentration 50 mg / L, containing Cl － 50 mg / L, SO4 2－ 30 mg / L); electrodialysis membrane stack (effective membrane area 100 cm²) 2DC regulated power supply (model PS-305D, Longwei); fluoride ion selective electrode (model PF-1, Leici); peristaltic pump (BT100-1F, Baoding Lange); vacuum drying oven (model DZF-6050, Shanghai Yiheng); constant temperature water bath (model HH-S4, Gongyi Yuhua); ultrasonic cleaner (model KQ-200VDE, Kunshan Shumei); inductively coupled plasma atomic emission spectrometer (ICP-OES 7300, PerkinElmer).

[0024] This embodiment relates to a method for preparing a metal-modified ion exchange membrane, comprising the following steps: Using an anion exchange membrane as the base membrane, the base membrane is pretreated to remove impurities. The surface of the pretreated base membrane is then modified with an aminosilane coupling agent, causing the siloxy groups in the aminosilane coupling agent to undergo a condensation reaction with the surface hydroxyl groups of the base membrane, thereby grafting amino active sites onto the surface of the base membrane to obtain an aminosilane coupling agent-modified base membrane. The amino active sites of the aminosilane coupling agent-modified base membrane are oriented and uniformly co-loaded with Zr through coordination bonds. 4+ Al 3+ 、Nd 3+ Subsequently, a ZrO(OH)₂, AlO(OH), and Nd(OH)₃ composite adsorption layer is formed on the surface of the base membrane through hydroxylation, resulting in a metal-modified ion exchange membrane, such as... Figure 3 As shown.

[0025] Preferably, the Zr described in this embodiment 4+ The Al 3+ With the Nd 3+ The molar ratio is (2~4):1:1, for example 2:1:1, 3:1:1, 4:1:1, etc.; The preprocessed CCP load Zr 4+ Al 3+ 、Nd 3+ The total metal loading is 9~13 mg / g, for example, 9 mg / g, 11 mg / g, 13 mg / g, etc.

[0026] Preferably, in this embodiment, modifying the surface of the base film with an aminosilane coupling agent includes the following specific steps: completely immersing the pretreated base film in an aminosilane coupling agent solution for 0.8 to 1.5 hours at 25°C to 30°C; removing the immersed base film and curing it at 80±2°C for 1 to 3 hours, such as 1 hour or 2 hours, so that the siloxy groups in the aminosilane coupling agent undergo a condensation reaction with the surface hydroxyl groups of the base film, thereby grafting amino active sites onto the surface of the base film; The mass concentration of the aminosilane coupling agent solution is 1.2% to 2.5%, for example, 1.2%, 2%, 2.5%, etc.; the pH value of the aminosilane coupling agent solution is 4.2 to 4.8.

[0027] Preferably, in this embodiment, the amino-silane coupling agent modified base film has Zr groups that are oriented and uniformly co-loaded through coordination bonds at their amino-silane active sites. 4+ Al 3+ 、Nd 3+ The specific steps include: completely immersing the base film modified with the aminosilane coupling agent into a solution containing the Zr. 4+ The Al 3+ With the Nd 3+ The substrate is immersed in a mixed solution at 35℃~45℃ for 1.5~2.5 h to allow the amino-silane coupling agent-modified base film to be oriented and uniformly co-loaded with Zr through coordination bonds at its amino-silane coupling agent active sites. 4+ Al 3 + 、Nd 3+ ; Zr in the mixed solution 4+ Al 3+ With Nd 3+ The total metal ion concentration is 0.5~1.5 mol / L, for example 0.5 mol / L, 1 mol / L, 1.5 mol / L, etc., and the pH value of the mixed solution is 1.9~2.5.

[0028] Preferably, in this embodiment, the formation of a ZrO(OH)2, AlO(OH), Nd(OH)3 composite adsorption layer on the surface of the base film via hydroxylation includes the following specific steps: co-loading Zr 4+ Al 3+ 、Nd 3+ The base membrane is then immersed in an alkaline solution and reacted at 45℃~55℃ for 1.5~2.5 h. Afterwards, it is washed and dried sequentially, forming a ZrO(OH)2, AlO(OH), Nd(OH)3 composite adsorption layer on the surface of the base membrane. The concentration of the alkaline substance in the alkaline solution is 0.2~0.4 mol / L, for example, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, etc.; the alkaline substance includes sodium hydroxide, potassium hydroxide, etc.

[0029] Preferably, the anion exchange membrane described in this embodiment comprises a styrene-based strongly basic anion exchange membrane with an exchange capacity ≥1.2 mmol / g and a membrane thickness of 0.15~0.20 mm; The aminosilane coupling agent includes N-(β-aminoethyl)-γ-aminopropyltriethoxysilane (KH792). The Zr 4+ Derived from ZrCl4; the Al 3+ Derived from AlCl3·6H2O; the Nd 3+ It originates from NdCl3·6H2O.

[0030] Preferably, this embodiment also includes base film pretreatment: sequentially performing ultrasonic cleaning with deionized water, ultrasonic cleaning with 3~5wt% hydrochloric acid solution, and ultrasonic cleaning with deionized water in three stages; after cleaning, the membrane is placed in a vacuum drying oven and dried at 60±2℃ for 4 h to constant weight (mass deviation ≤0.001g) for later use.

[0031] Specifically, this embodiment describes a method for preparing a metal-modified ion exchange membrane. Figure 1 ), including the following steps: (1) Base membrane pretreatment: The anion exchange membrane was cut into standard sizes of 10 cm × 10 cm and subjected to three-stage cleaning: ① Ultrasonic cleaning with deionized water (power 200W, frequency 40kHz) for 15~30 min to remove dust and impurities physically adsorbed on the membrane surface; ② Ultrasonic cleaning with 3~5wt% hydrochloric acid solution (parameters as above) for 15~30 min. Hydrochloric acid can react with residual metal impurities on the membrane surface to generate soluble salts, and at the same time activate amino (-NH2) and quaternary ammonium (-N) groups on the membrane surface. + (CH3)3) and other active groups enhance the binding ability with coupling agents; ③ Ultrasonic cleaning with deionized water (parameters as above) for 15~30 min to thoroughly remove residual hydrochloric acid and reaction products from the membrane surface. After cleaning, place the membrane in a vacuum drying oven and dry it at 60±2℃ for 4h to constant weight (mass deviation ≤0.001g) for later use; (2) Coupling agent modification: ① Preparation of coupling agent solution: For example, N-(β-aminoethyl)-γ-aminopropyltriethoxysilane (KH792) is dissolved in anhydrous ethanol-water mixed solvent (volume ratio 9:1) to prepare a coupling agent solution with a mass concentration of 1.2wt%~2.5wt% (preferably 1.8wt%). Then, the pH value of the solution is adjusted to 4.2~4.8 with glacial acetic acid to promote the hydrolysis of siloxy groups; ② Constant temperature immersion modification: The pretreated base membrane is completely immersed in the above coupling agent solution and placed in a constant temperature water bath. It is immersed at 25℃~30℃ for 0.8~1.5 h, and stirred once every 30 min (200 rpm, 1 min) to ensure that the membrane surface is in full contact with the coupling agent solution; ③ Curing reaction: The membrane is removed, and the unbound free coupling agent on the surface is rinsed with anhydrous ethanol. It is then placed in a vacuum drying oven at 80±2℃ for 1.5 h for curing. h, which causes the siloxy groups in the coupling agent molecule to undergo a condensation reaction with the hydroxyl groups on the membrane surface, grafting a high-density layer of diamine active sites onto the membrane surface; (3) Co-loading of multiple metals: ① Preparation of a mixed solution of multiple metal salts: Zirconium chloride (ZrCl4, purity ≥99.5%) was selected as the main salt, and aluminum chloride (AlCl3·6H2O, purity ≥99%) and neodymium chloride (NdCl3·6H2O, purity ≥99%) were used as synergistic salts; the total metal ion concentration of the mixed solution was 1 mol / L, of which Zr 4+ With Al 3+ 、Nd 3+ The molar ratio is (2~4):1:1 (preferably 3:1:1); 6 mol / L hydrochloric acid solution is added dropwise to the mixed solution to adjust the pH to 1.9~2.5, with continuous stirring (200 rpm) during the adjustment process to avoid localized excessively high pH causing premature hydrolysis of metal ions to form hydroxide precipitates; ② Constant temperature immersion loading: The base membrane modified with the coupling agent is completely immersed in the above multi-metal salt mixed solution, placed in a constant temperature water bath, and immersed at 35~45℃ for 1.5~2.5 h, stirring once every 30 min (200 rpm, 1 min) to ensure sufficient contact between the membrane surface and the mixed solution. During this process, the diamine groups grafted by the coupling agent on the membrane surface can react with Zr. 4+ Al 3+ 、Nd 3+ Formation of stable coordinate bonds (-N→M) n+ M represents metal ions), achieving directional and uniform co-loading of multiple metal ions on the membrane surface, with the total metal loading controlled at 9~13 mg / g (which can be detected by inductively coupled plasma optical emission spectrometry (ICP-OES). (4) Hydroxylation modification: ① Alkali conversion reaction: After the membrane loaded with multiple metal ions is taken out, it is rinsed with deionized water to remove unbound free metal ions on the surface (rinsing until the total metal ion concentration in the rinsing solution is less than 0.1 mg / L), and then immersed in 0.2~0.4 mol / L sodium hydroxide solution and placed in a constant temperature water bath at 45~55℃ for 1.5~2.5 h; during the reaction, the metal ions loaded on the membrane surface react with OH-. － A ternary metal hydroxy oxide composite layer of ZrO(OH)2-AlO(OH)-Nd(OH)3 was formed; ② Post-treatment: After the reaction, the membrane was repeatedly rinsed with deionized water until the pH of the rinsing solution was 7.0±0.5, and then placed in a vacuum drying oven at 60±2℃ for 4 h to constant weight to obtain a zirconium-aluminum-neodymium ternary metal modified anion exchange membrane.

[0032] This embodiment also relates to a metal-modified ion exchange membrane, which is prepared by the aforementioned preparation method.

[0033] This embodiment also relates to an electrodialysis membrane stack for selective defluorination, wherein the electrodialysis membrane stack is provided with the aforementioned metal-modified ion exchange membrane, such as...Figure 2 As shown.

[0034] This embodiment also relates to an electrodialysis device for selective defluorination, the electrodialysis device including the electrodialysis membrane stack for selective defluorination.

[0035] This embodiment also relates to the use of the metal-modified ion exchange membrane, the electrodialysis membrane stack for selective defluorination, or the electrodialysis device for selective defluorination in the removal of fluoride from fluoride-containing wastewater.

[0036] Specifically, the electrodialysis-assisted fluoride removal method using metal-modified ion exchange membranes employs a synergistic effect of "electromigration-ternary metal synergistic adsorption" to achieve deep treatment of fluoride-containing wastewater. Essentially, it utilizes the ion-selective permeability and enhanced fluoride adsorption performance of zirconium-aluminum-neodymium ternary metal modified anion exchange membranes to further improve the separation efficiency of fluoride ions under an electric field. The specific steps are as follows: (1) Pretreatment preparation: The fluoride-containing wastewater to be treated is pretreated by filtration through a 5μm filter membrane to remove suspended particulate matter and avoid clogging the membrane pores; the electrodialysis membrane stack is arranged alternately in the order of "cation exchange membrane - dilute chamber - modified anion exchange membrane - concentrated chamber", and titanium-based coated electrodes (anode and cathode) are installed at both ends of the membrane stack. 0.5 mol / L sodium sulfate solution is introduced into the electrode chamber as the electrode liquid, which plays the role of conducting current and stabilizing electrode reaction; (2) Circulation balance: Add filtered fluoride-containing wastewater to the dilute chamber storage tank, and add deionized water or softened water to the concentrate chamber storage tank. Turn on the peristaltic pump and adjust the circulation flow rate of the solutions in the dilute, concentrate, and polar chambers. When the membrane stack is of small to medium scale (effective membrane area 50~200 cm²), 2 The flow rates in the dilute, concentrate, and electrode chambers are controlled at 2–10 L / h (preferably 5 L / h); when the membrane stack is a large-scale membrane stack (effective membrane area > 200 cm²), 2 The flow rate can be adjusted adaptively according to the treatment capacity, based on the principle that "the flow rate is proportional to the effective area of ​​the membrane stack" (recommended flow rate range: 10~30 L / h). Continuously circulate for 30 minutes to ensure uniform solution temperature and concentration in each chamber and hydraulic equilibrium on the membrane surface. (3) Synergistic defluorination: Turn on the DC regulated power supply and adjust the operating voltage to 10~15 V to form a stable DC electric field (electric field strength approximately 1.0~1.5 V / cm) across the membrane stack. Under the action of the electric field, fluoride ions (F...) in the defluorination chamber... － As an anion, it migrates directionally towards the anode, when F － Upon reaching the surface of the zirconium-aluminum-neodymium ternary metal modified anion exchange membrane, a triple synergistic effect occurs: ① Enhanced selective permeability of fluoride ions: In the mixed anion system, the ternary metal hydroxyl oxide layer on the surface of the metal-modified ion exchange membrane enhances the selective permeability of fluoride ions. －The specific coordination of F reduces F － The energy barrier for transmembrane transport preferentially allows F － ① Passing through the membrane into the concentration chamber; ② Multi-metal chemisorption: ZrO(OH)2, AlO(OH), and Nd(OH)3 on the membrane surface react with F... － Specific chemisorption occurs, and the -OH groups in ZrO(OH)2, AlO(OH)3 are respectively adsorbed by F. － Replacement forms Zr-F, Al-F, and Nd-F bonds to achieve F － ③ Efficient retention and fixation on the membrane surface; ③ Electron synergistic effect: Electron transfer occurs between multiple metals, which can reduce F － The binding energy with metal oxides further enhances the adsorption rate and capacity. Through the synergistic effect of electromigration and multi-metal adsorption, the adsorption capacity of F is significantly increased. － The separation efficiency of F in the concentration chamber － As the concentration gradually increases, F in the dilute chamber － The concentration continued to decrease; (4) Process monitoring and termination: Real-time monitoring of the fluoride ion concentration in the dilute and concentrated chambers using an online fluoride ion monitoring probe. － Concentration, synchronously record membrane stack current changes to ensure stable operation; when the dilute chamber F － When the concentration drops below 10 mg / L (Integrated Wastewater Discharge Standard (GB 8978-1996)) or meets the preset treatment requirements, the system automatically shuts off the DC regulated power supply and peristaltic pump to complete the defluorination process and collect the permeate water in the desalination chamber.

[0037] Specifically, the regeneration method for metal-modified ion exchange membranes involves regenerating the membrane when its adsorption capacity reaches saturation (manifested as a dilute chamber F). － When the concentration decrease rate is ≤0.02 mg / (L·min), regeneration is performed using an alkaline solution circulation desorption method. The core of this method is to utilize high concentrations of OH-. － Breaking the F-bond in multi-metallic compounds to achieve F － The efficient desorption process involves the following steps: (1) Alkali regeneration and desorption: ① Preparation of regenerated solution: Sodium hydroxide (purity ≥99%) is selected as the regenerator, and a 0.5~1.0 mol / L NaOH regenerated solution is prepared; ② Circulation regeneration: The fluoride-containing wastewater circulation system is shut down, the solutions in the dilute and concentrated chambers are discharged, and the regenerated solution is added to the dilute and concentrated chamber storage tanks respectively (the volume of the regenerated solution is calculated according to "membrane effective area × 20 mL / cm²"). 2 For example, 100 cm 2 Add 2 L of OH to both the dilute and concentrate chambers of the membrane stack, turn on the peristaltic pump, adjust the flow rate to 7-9 L / h, and continue regeneration for 1-2 h. During regeneration, high concentrations of OH... －It competes with the -F bonds of multiple metals on the membrane surface for adsorption, disrupting the stability of Zr-F, Al-F, and Nd-F bonds, ultimately leading to the adsorption of F. － The fluoride ions are desorbed into the regenerated solution; during the regeneration process, the fluoride ion concentration in the regenerated solution is monitored using an online fluoride ion monitoring probe. － The concentration of the sample is considered stable when the concentration fluctuates by ≤0.5 mg / L over 30 minutes, indicating that desorption has reached equilibrium. 2) Regeneration solution reuse: After desorption is completed, the regeneration solution is discharged and sealed and stored in the dark. It can be reused 5 to 10 times. Before each reuse, the concentration of NaOH in the regeneration solution is tested and concentrated alkali solution is added to the set concentration (0.5 to 1.0 mol / L). 3) Rinse with clean water: Drain the regenerant from the dilute and concentrate chambers, and add deionized water or softened water to the dilute and concentrate chambers. The total amount of rinsing solution should be calculated as "effective membrane stack area × 20 mL / cm²". 2 "Adapt; turn on the peristaltic pump and flush at a flow rate of 5~30 L / h until the total flushing time is sufficient for complete replacement of the flushing solution 2~5 times to complete regeneration. The metal-modified ion exchange membrane can be reused in the electrodialysis defluorination process. The used cleaning water can be used for the preparation of regenerated alkali solution or treated and reused."

[0038] In summary, this invention uses an ion exchange membrane as the core carrier, differing from existing technologies that employ resin filling or MOF physical mixing. By introducing an aminosilane coupling agent to construct a covalently bonded bridging layer, it achieves a directional and robust co-loading of zirconium, aluminum, and neodymium multi-metals with the membrane surface. Hydroxylation then constructs an integrated composite adsorption layer, ultimately achieving a dual fluoride removal effect through electromigration and synergistic adsorption of multi-metals. This not only avoids the problems of uneven dispersion of functional materials and high mass transfer resistance in physical mixing but also solves the defects of traditional metal-modified ion exchange membranes, such as weak binding of active components and insufficient synergy between adsorption and mass transfer, forming a significantly differentiated technical solution. Specific embodiments are further illustrated below.

[0039] Example 1 This embodiment relates to a method for preparing a metal-modified ion exchange membrane, which includes the following steps: (1) Base membrane pretreatment: The AMX anion exchange membrane was cut into 10 cm × 10 cm squares and subjected to three stages of ultrasonic cleaning: ① ultrasonic cleaning with deionized water (power 200W, frequency 40kHz) for 20 min; ② ultrasonic cleaning with 5wt% hydrochloric acid solution (parameters as above) for 25 min; ③ ultrasonic cleaning with deionized water (parameters as above) for 20 min. After cleaning, it was placed in a vacuum drying oven at 60℃ and dried for 4 h until constant weight. (2) Coupling agent modification: ① Preparation of coupling agent solution: Dissolve KH792 in anhydrous ethanol-water mixed solvent (volume ratio 9:1) to prepare a coupling agent solution with a mass concentration of 1.8wt%; adjust the pH to 4.5 with glacial acetic acid, and stir continuously (200 r / min) for 10 min until the solution is homogeneous; ② Constant temperature immersion modification: Immerse the pretreated base film in the coupling agent solution, immerse in a constant temperature water bath at 28℃ for 1.2 h, and stir once every 30 min (200 r / min, 1 min); ③ Curing reaction: Take out the film, rinse the surface with anhydrous ethanol 3 times, and place it in an 80℃ vacuum drying oven for curing for 1.5 h to obtain the base film modified with coupling agent; (3) Zr-Al-Nd multi-metal co-loading: ① Preparation of mixed solution: total metal ion concentration 1 mol / L, Zr 4+ :Al 3+ :Nd 3+ The molar ratio was 3:1:1. Weigh 13.98 g ZrCl4 (0.06 mol), 4.83 g AlCl3·6H2O (0.02 mol), and 7.17 g NdCl3·6H2O (0.02 mol), add 100 mL of deionized water to dissolve, and add 6 mol / L hydrochloric acid dropwise to adjust the pH to 2.0. Stir continuously (200 r / min) for 10 min until the solution is homogeneous and transparent. ② Constant temperature impregnation: Immerse the pretreated base membrane in the mixed solution and impregnate in a 40℃ constant temperature water bath for 2 h, stirring every 30 min (200 r / min, 1 min). After impregnation, rinse with deionized water until the free metal ion concentration is <0.1 mg / L. ICP-OES analysis showed a total metal loading of 10.2 mg / g.

[0040] (4) Hydroxylation modification: The loaded membrane was immersed in 0.35 mol / L NaOH solution and reacted in a constant temperature water bath at 50℃ for 2.5h. After the reaction, it was rinsed until pH=7.2 and dried under vacuum at 60℃ for 4h to constant weight to obtain zirconium-aluminum-neodymium ternary metal modified anion exchange membrane.

[0041] This embodiment involves electrodialysis for fluoride removal, including the following steps: ① Membrane stack assembly: Simulated fluoride-containing water A is pretreated by filtration through a 5μm filter membrane to remove suspended particulate matter; five pairs of membrane stacks are assembled in the order of "CMX cation exchange membrane - dilute chamber - ternary AMX metal-modified ion exchange membrane - concentrate chamber", with 0.5 mol / L sodium sulfate solution introduced into each chamber; 10 L of filtered simulated fluoride-containing water A is added to the dilute chamber, and 10 L of deionized water is added to the concentrate chamber; ② Circulation balancing: The peristaltic pump is turned on, and the flow rate of each chamber is 5 L / h, circulating for 30 min; ③ Synergistic fluoride removal: The DC regulated power supply is turned on, the operating voltage is adjusted to 12 V, and the initial current is 0.98 A; the dilute and concentrate chambers F are monitored in real time using an online fluoride ion monitoring probe. －Concentration was monitored, and membrane stack current changes were recorded synchronously to ensure stable operation. Monitoring data at 0, 30, 60, 90, and 120 min were as follows: 0 min (dilute chamber 49.9 mg / L, concentrated chamber 0 mg / L, defluorination efficiency 0%), 30 min (dilute chamber 18.3 mg / L, concentrated chamber 28.8 mg / L, defluorination efficiency 63.3%), 60 min (dilute chamber 13.2 mg / L, concentrated chamber 33.1 mg / L, defluorination efficiency 73.5%), 90 min (dilute chamber 11.1 mg / L, concentrated chamber 35.2 mg / L, defluorination efficiency 77.8%), 120 min (dilute chamber 9.6 mg / L, concentrated chamber 37.5 mg / L, defluorination efficiency 80.8%). ④ Termination: After 120 min, the dilute chamber F... － When the concentration drops to 9.6 mg / L, which is lower than the limit of 10 mg / L in the "Integrated Wastewater Discharge Standard" (GB 8978-1996), the system automatically shuts off the DC regulated power supply and peristaltic pump, completes the defluorination process, and collects the permeate water in the desalination chamber.

[0042] This embodiment involves a regeneration process, including the following steps: ① After membrane adsorption saturation, drain the residual solution from the dilute and concentrated chambers; add 2 L of 0.8 mol / L NaOH regeneration solution to each chamber, turn on the peristaltic pump (8 L / h), and regenerate for 1.5 h; stop regeneration after the fluoride ion desorption in the regeneration solution reaches equilibrium. The regeneration solutions are combined and sealed for storage, and can be reused 10 times. Before each reuse, the NaOH concentration is determined by acid-base titration, and 10 mol / L concentrated NaOH solution is added to bring the concentration to 0.8 mol / L; ② Rinse with clean water: drain the regeneration solution, add 2 L of deionized water to each chamber, rinse at a flow rate of 10 L / h for 30 min, then rinse at a flow rate of 5 L / h for 60 min, and then collect all the rinsing water (total 4 L), which can be used for the preparation of regeneration solution or for reuse after treatment. After regeneration, the device can be used for the next round of fluoride-containing wastewater treatment.

[0043] Performance test results: The regeneration rate of the metal-modified ion exchange membrane in this embodiment was 95.2% (regeneration rate test method: fluoride adsorption capacity of the regenerated membrane / fluoride adsorption capacity of the fresh membrane × 100%); the defluorination efficiency after 10 regeneration-defluorination cycles was 80.8%, 79.9%, 79.5%, 79.0%, 78.6%, 78.2%, 77.9%, 77.5%, 77.3%, and 77.2% respectively; the total metal leaching in the permeate was 0.002 mg / L.

[0044] Example 2 Materials and equipment used: Same as in Example 1; Simulated fluoride-containing water A: Same as in Example 1; Base film pretreatment: Same as in Example 1; Coupling agent modification: Same as in Example 1; Multi-metal co-loading (optimized ratio): ① Preparation of mixed solution: total metal ion concentration 1 mol / L, Zr 4+ :Al 3 + :Nd 3+ The molar ratio was 4:1:1. Weigh 18.66g ZrCl4, 4.83g AlCl3·6H2O, and 7.17g NdCl3·6H2O, add 100mL deionized water to dissolve, and adjust the pH to 2.0 by adding 6 mol / L hydrochloric acid dropwise. Stir continuously (200 r / min) for 10 min. ② Constant temperature impregnation: Same as Example 1 (40℃, 2 h, stirring at 200 r / min). After impregnation, rinse until free metal ions <0.1 mg / L. ICP-OES analysis showed a total metal loading of 12.5 mg / g. Hydroxylation modification: Same as in Example 1 (0.35 mol / L NaOH, 50℃, 2.5 h). After the reaction, wash until pH=7.2, and vacuum dry at 60℃ for 4 h to constant weight.

[0045] Electrodialysis defluorination procedure: Same as in Example 1 (operating voltage 12 V, flow rate 5 L / h). Defluorination test data: 30 min (dilute chamber 14.1 mg / L, concentrated chamber 31.5 mg / L, defluorination efficiency 71.8%), 60 min (dilute chamber 4.89 mg / L, concentrated chamber 39.8 mg / L, defluorination efficiency 90.2%), 90 min (dilute chamber 2.54 mg / L, concentrated chamber 41.2 mg / L, defluorination efficiency 94.9%), 120 min (dilute chamber 1.7 mg / L, concentrated chamber 41.6 mg / L, defluorination efficiency 96.6%).

[0046] Regeneration steps: Same as in Example 1.

[0047] Performance test results: The regeneration rate of the metal-modified ion exchange membrane in this embodiment was 95.8% (testing method is the same as in Example 1); the defluorination efficiency after 10 regeneration-defluorination cycles was 96.6%, 95.8%, 94.5%, 93.2%, 91.8%, 90.5%, 88.9%, 85.7%, 80.2%, and 78.6% respectively; the total metal leaching in the permeate was 0.002 mg / L.

[0048] The results show that increasing Zr 4+ After refining, the defluorination efficiency was further improved, and the adsorption selectivity was better. However, the defluorination efficiency decreased significantly after multiple regeneration cycles, and the advantage over Example 1 was smaller. Therefore, considering the material cost, this formulation is suitable for treating wastewater with higher fluoride content (fluoride ion concentration > 50 mg / L). For the treatment of medium and low concentration fluoride wastewater, the metal-loaded formulation in Example 1 should still be preferred.

[0049] Example 3 Materials and equipment used: same as in Example 1; simulated fluoride-containing water A: same as in Example 1.

[0050] Base film pretreatment: Same as in Example 1; Coupling agent modification (concentration optimization): ① Preparation of coupling agent solution: Dissolve KH792 in anhydrous ethanol-water mixed solvent (volume ratio 9:1) to prepare a coupling agent solution with a mass concentration of 2.5wt%; adjust the pH to 4.5 with glacial acetic acid, and stir continuously (200 r / min) for 10 min until the solution is homogeneous; ② Constant temperature impregnation modification and curing: Same as Example 1 (impregnation at 28℃ for 1.2 h, curing at 80℃ for 1.5 h); Multi-metal co-loading: ① Mixed solution preparation: Same as Example 1 (Zr 4+ :Al 3+ :Nd 3+ =3:1:1, total metal ion concentration 1 mol / L, pH=2.0); ② Constant temperature impregnation: Same as Example 1 (40℃, 2.0 h, 200 r / min stirring). After impregnation, rinse until free metal ions <0.1 mg / L, and ICP-OES detection shows total metal loading of 10.5 mg / g; Hydroxylation modification: Same as in Example 1; Electrodialysis defluorination procedure: Same as in Example 1. Defluorination test data: 30 min (dilute chamber 18.0 mg / L, concentrated chamber 28.9 mg / L, defluorination efficiency 63.9%), 60 min (dilute chamber 12.8 mg / L, concentrated chamber 33.2 mg / L, defluorination efficiency 74.3%), 90 min (dilute chamber 10.8 mg / L, concentrated chamber 35.5 mg / L, defluorination efficiency 78.4%), 120 min (dilute chamber 9.2 mg / L, concentrated chamber 37.5 mg / L, defluorination efficiency 81.6%).

[0051] Regeneration steps: Same as in Example 1.

[0052] Performance test results: The regeneration rate of the metal-modified ion exchange membrane in this embodiment was 95.5% (the test method was the same as in Example 1); the defluorination efficiency after 10 regeneration-defluorination cycles was 81.6%, 80.5%, 79.8%, 79.2%, 78.5%, 77.9%, 77.3%, 76.8%, 76.0%, and 75.5% respectively; the total metal leaching in the permeate was 0.002 mg / L.

[0053] The results showed that increasing the coupling agent concentration to 2.5 wt% only slightly increased the metal loading and the initial defluorination efficiency was only slightly improved (0.8%) compared to Example 1. However, the stability after regeneration decreased slightly, proving that the 1.8 wt% coupling agent solution concentration in Example 1 could achieve good results. Further increasing the coupling agent concentration did not substantially improve the membrane performance and would increase the cost.

[0054] Example 4 Materials and equipment used: Same as in Example 1; Simulated fluoride-containing water B (high fluoride water body, F － Concentration 100 mg / L, containing Cl － 80 mg / L, SO4 2－ 50 mg / L); Base film pretreatment: Same as in Example 1; Coupling agent modification: Same as in Example 1; Multi-metal co-loading: Same as Example 2; Hydroxylation modification: Same as in Example 1; Electrodialysis fluoride removal implementation steps: ① Membrane stack assembly: Pre-treat simulated fluoride-containing water B through a 5μm filter membrane to remove suspended particulate matter; assemble 5 pairs of membrane stacks in the order of "CMX cation exchange membrane - dilute chamber - ternary AMX metal-modified ion exchange membrane - concentrate chamber", and connect the electrode chambers to 0.5 mol / L sodium sulfate solution; add 10 L of filtered simulated fluoride-containing water B to the dilute chamber and 10 L of deionized water to the concentrate chamber; ② Circulation balancing: Turn on the peristaltic pump, with a flow rate of 5 L / h in each chamber, and circulate for 30 min; ③ Synergistic fluoride removal: Turn on the DC regulated power supply, adjust the operating voltage to 14 V, and the initial current to 1.2 A; monitor the fluoride ion concentration in the dilute and concentrate chambers in real time using an online fluoride ion monitoring probe. － Concentration was monitored, and membrane stack current changes were recorded synchronously to ensure stable operation. Monitoring data at 0, 60, 120, and 180 min were as follows: 0 min (dilute chamber 99.8 mg / L, concentrated chamber 0 mg / L, defluorination efficiency 0%), 60 min (dilute chamber 42.5 mg / L, concentrated chamber 52.3 mg / L, defluorination efficiency 57.4%), 120 min (dilute chamber 18.3 mg / L, concentrated chamber 76.5 mg / L, defluorination efficiency 81.7%), 180 min (dilute chamber 9.2 mg / L, concentrated chamber 85.6 mg / L, defluorination efficiency 90.8%). ④ Termination: After 180 min, the dilute chamber F... － When the concentration drops to 9.2 mg / L, which is lower than the limit of 10 mg / L in the "Integrated Wastewater Discharge Standard" (GB 8978-1996), the system automatically shuts off the DC regulated power supply and peristaltic pump, completes the defluorination process, and collects the permeate water in the desalination chamber.

[0055] Regeneration steps: Same as in Example 1.

[0056] Performance test results: The regeneration rate of the metal-modified ion exchange membrane in this embodiment was 95.3%. The defluorination efficiency after 10 regeneration-defluorination cycles was 90.8%, 89.9%, 88.7%, 87.5%, 86.2%, 84.8%, 82.5%, 80.1%, 78.2%, and 76.3%, respectively. The total metal leaching in the permeate was 0.002 mg / L.

[0057] Comparative Example 1: Fluoride Removal via Electrodialysis Using Pure AMX Anion Exchange Membrane Materials and equipment used: same as in Example 1; simulated fluoride-containing water A: same as in Example 1; unmodified AMX anion exchange membrane was used directly, and the experiment was carried out according to the electrodialysis defluorination procedure in Example 1, with an operating voltage of 12 V and a flow rate of 5 L / h.

[0058] Defluorination test data: 0 min (dilute chamber 49.9 mg / L, concentrated chamber 0 mg / L, defluorination efficiency 0%), 30 min (dilute chamber 42.5 mg / L, concentrated chamber 6.8 mg / L, defluorination efficiency 14.8%), 60 min (dilute chamber 38.9 mg / L, concentrated chamber 9.5 mg / L, defluorination efficiency 22.0%), 90 min (dilute chamber 36.5 mg / L, concentrated chamber 11.2 mg / L, defluorination efficiency 26.8%), 120 min (dilute chamber 35.1 mg / L, concentrated chamber 12.3 mg / L, defluorination efficiency 29.7%).

[0059] Performance testing: No obvious fluoride adsorption performance; only electromigration is used to remove a small amount of fluoride. After 120 minutes, the defluorination chamber F... － The concentration is still far above the emission standards, and for Cl... － SO4 2－ Non-selective, coexisting anions and F － Synchronous migration results in extremely low separation efficiency.

[0060] Comparative Example 2: Defluorination using Zr-Al binary metal modified ion exchange membrane Materials and equipment used: Same as in Example 1; Simulated fluoride-containing water A: Same as in Example 1; Base film pretreatment: Same as in Example 1; Coupling agent modification: Same as in Example 1; Multi-metal co-loading: ① Preparation of mixed solution: Total metal ion concentration 1 mol / L, Zr 4+ :Al 3+① Molar ratio 3:1; ② Constant temperature impregnation: Same as Example 1 (40℃, 2 h, stirring at 200 r / min). After impregnation, rinse until free metal ions <0.1 mg / L, and the total metal loading was detected by ICP-OES as 9.8 mg / g; ② Hydroxylation modification: Same as Example 1 (0.35mol / L NaOH, 50℃, 2.5 h), after the reaction, rinse until pH=7.2, and vacuum dry at 60℃ for 4 h to constant weight.

[0061] Electrodialysis defluorination procedure: Same as in Example 1 (operating voltage 12 V, flow rate 5 L / h). Defluorination test data: 0 min (dilute compartment 49.9 mg / L, concentrated compartment 0 mg / L, defluorination efficiency 0%), 30 min (dilute compartment 25.8 mg / L, concentrated compartment 22.3 mg / L, defluorination efficiency 48.3%), 60 min (dilute compartment 20.5 mg / L, concentrated compartment 27.1 mg / L, defluorination efficiency 58.9%), 90 min (dilute compartment 18.2 mg / L, concentrated compartment 29.5 mg / L, defluorination efficiency 63.5%), 120 min (dilute compartment 16.9 mg / L, concentrated compartment 30.8 mg / L, defluorination efficiency 66.1%).

[0062] Regeneration steps: Same as in Example 1. Performance test results: The regeneration rate was 88.5%. After repeating the regeneration-defluorination cycle 10 times, the defluorination efficiency dropped to 62.3%, and the total metal leaching in the permeate was 0.008 mg / L.

[0063] Comparative Example 3: Defluorination using Al-Nd binary metal modified ion exchange membrane Materials and equipment used: Same as in Example 1; Simulated fluoride-containing water A: Same as in Example 1; Base film pretreatment: Same as in Example 1; Coupling agent modification: Same as in Example 1; Multi-metal co-loading: ① Preparation of mixed solution: Total metal ion concentration 1 mol / L, Al 3+ :Nd 3+ ① Molar ratio 1:1; ② Constant temperature impregnation: Same as Example 1 (40℃, 2 h, stirring at 200 r / min). After impregnation, rinse until free metal ions <0.1 mg / L, and the total metal loading is 8.5 mg / g as determined by ICP-OES; ② Hydroxylation modification: Same as Example 1 (0.35 mol / L NaOH, 50℃, 2.5 h). After the reaction, rinse until pH=7.2, and vacuum dry at 60℃ for 4 h to constant weight.

[0064] Electrodialysis defluorination implementation steps: Same as in Example 1 (operating voltage 12 V, flow rate 5 L / h).

[0065] Defluorination test data: 0 min (dilute chamber 49.9 mg / L, concentrated chamber 0 mg / L, defluorination efficiency 0%), 30 min (dilute chamber 32.5 mg / L, concentrated chamber 15.8 mg / L, defluorination efficiency 34.9%), 60 min (dilute chamber 28.9 mg / L, concentrated chamber 19.2 mg / L, defluorination efficiency 42.1%), 90 min (dilute chamber 26.8 mg / L, concentrated chamber 20.5 mg / L, defluorination efficiency 46.3%), 120 min (dilute chamber 25.5 mg / L, concentrated chamber 21.3 mg / L, defluorination efficiency 48.9%).

[0066] Regeneration steps: Same as in Example 1. Performance test results: The regeneration rate was 82.3%. After repeating the regeneration-defluorination cycle 10 times, the defluorination efficiency dropped to 51.5%, and the total metal leaching in the permeate was 0.012 mg / L.

[0067] Comparative Example 4: Defluorination using Zr-Nd binary metal modified ion exchange membrane Materials and equipment used: Same as in Example 1; Simulated fluoride-containing water A: Same as in Example 1; Base film pretreatment: Same as in Example 1; Coupling agent modification: Same as in Example 1; Multi-metal co-loading: ① Preparation of mixed solution: Total metal ion concentration 1 mol / L, Zr 4 ⁺:Nd³⁺ molar ratio 3:1; ②Implantation at constant temperature: Same as Example 1 (40℃, 2 h, stirring at 200 r / min). After impregnation, rinse until free metal ions <0.1 mg / L, and the total metal loading was detected by ICP-OES as 9.5 mg / g; Hydroxylation modification: Same as Example 1 (0.35mol / L NaOH, 50℃, 2.5 h), after the reaction, rinse until pH=7.2, and vacuum dry at 60℃ for 4 h to constant weight.

[0068] Electrodialysis defluorination procedure: Same as in Example 1 (operating voltage 12 V, flow rate 5 L / h). Defluorination test data: 0 min (dilute compartment 49.9 mg / L, concentrated compartment 0 mg / L, defluorination efficiency 0%), 30 min (dilute compartment 23.5 mg / L, concentrated compartment 24.1 mg / L, defluorination efficiency 52.9%), 60 min (dilute compartment 18.9 mg / L, concentrated compartment 28.5 mg / L, defluorination efficiency 62.1%), 90 min (dilute compartment 16.5 mg / L, concentrated compartment 30.2 mg / L, defluorination efficiency 66.9%), 120 min (dilute compartment 15.2 mg / L, concentrated compartment 31.8 mg / L, defluorination efficiency 69.5%).

[0069] Regeneration steps: Same as in Example 1. Performance test results: The regeneration rate was 90.2%. After repeating the regeneration-defluorination cycle 10 times, the defluorination efficiency dropped to 65.8%, and the total metal leaching in the permeate was 0.006 mg / L.

[0070] Compared with binary metal modified membranes and pure membranes, the Zr-Al-Nd ternary metal modified ion exchange membrane of this invention has significant advantages in terms of fluoride removal efficiency, adsorption selectivity, regeneration rate, and metal loading stability. This fully demonstrates that the synergistic effect of ternary metals is the core of improving the membrane's fluoride removal performance. Furthermore, the process design of coupling agent modification greatly improves the bonding stability between the metal components and the membrane substrate and reduces the amount of metal leaching.

[0071] In summary, this invention uses anion exchange membranes as the base membrane and achieves functional modification of the membrane through "pretreatment – ​​coupling agent modification – multi-metal directional co-loading – hydroxylation modification". The core innovations are: ① the introduction of a coupling agent (e.g., N-(β-aminoethyl)-γ-aminopropyltriethoxysilane (KH792, diamino group)), whose amino structure provides coordination sites, achieving a strong bond between the membrane substrate and metal ions through covalent bridging, significantly improving metal loading stability compared to traditional single amino coupling agents and coupling agent-free solutions; ② the selection of zirconium (Zr) 4+ ) as the main active component, combined with aluminum (Al) 3+ ), neodymium (Nd) 3+ As a synergistic component, the coordination and binding of multi-metal ions with active groups on the membrane surface are utilized to achieve uniform and robust co-loading of multi-metal components; ③ A ZrO(OH)2-AlO(OH)-Nd(OH)3 ternary metal hydroxy oxide composite adsorption layer is constructed through hydroxylation reaction, and the specific adsorption capacity for fluoride ions is enhanced by utilizing the complementarity of different metal adsorption sites and electronic effects.

[0072] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a metal-modified ion exchange membrane, characterized in that, Includes the following steps: Using an anion exchange membrane as the base membrane, the base membrane is pretreated to remove impurities. The surface of the pretreated base membrane is then modified with an aminosilane coupling agent, causing the siloxy groups in the aminosilane coupling agent to undergo a condensation reaction with the surface hydroxyl groups of the base membrane, thereby grafting amino active sites onto the surface of the base membrane to obtain an aminosilane coupling agent-modified base membrane. The amino active sites of the aminosilane coupling agent-modified base membrane are oriented and uniformly co-loaded with Zr through coordination bonds. 4+ Al 3+ 、Nd 3+ After hydroxylation, a ZrO(OH)2, AlO(OH), and Nd(OH)3 composite adsorption layer is formed on the surface of the base membrane, resulting in a metal-modified ion exchange membrane.

2. The method for preparing a metal-modified ion exchange membrane according to claim 1, characterized in that, The Zr 4+ The Al 3+ With the Nd 3+ The molar ratio is (2~4):1:1; The metal-modified ion exchange membrane is co-loaded with Zr 4+ Al 3+ 、Nd 3+ The total metal loading was 9~13 mg / g.

3. The method for preparing a metal-modified ion exchange membrane according to claim 1, characterized in that, Modifying the surface of the pretreated base film with an aminosilane coupling agent includes the following specific steps: completely immersing the base film in an aminosilane coupling agent solution and impregnating it at 25℃~30℃ for 0.8~1.5 h; removing the impregnated base film and curing it at 80±2℃ for 1~3 h, so that the siloxy groups in the aminosilane coupling agent undergo a condensation reaction with the surface hydroxyl groups of the base film, thereby grafting amino active sites onto the surface of the base film; The mass concentration of the aminosilane coupling agent solution is 1.2% to 2.5%; the pH value of the aminosilane coupling agent solution is 4.2 to 4.

8.

4. The method for preparing a metal-modified ion exchange membrane according to claim 2, characterized in that, The amino-silane coupling agent-modified base film has its amino-active sites oriented and uniformly co-loaded with Zr via coordination bonds. 4+ Al 3+ 、Nd 3+ The specific steps include: completely immersing the base film modified with the aminosilane coupling agent into a solution containing Zr. 4+ Al 3+ With Nd 3+ The substrate is immersed in a mixed solution at 35℃~45℃ for 1.5~2.5 h to allow the amino-silane coupling agent-modified base film to have its amino-active sites oriented and uniformly co-loaded with Zr through coordination bonds. 4+ Al 3+ 、Nd 3+ ; Zr in the mixed solution 4+ Al 3+ With Nd 3+ The total metal ion concentration is 0.5~1.5 mol / L, and the pH value of the mixed solution is 1.9~2.

5.

5. The method for preparing a metal-modified ion exchange membrane according to claim 4, characterized in that, The formation of a ZrO(OH)2, AlO(OH), Nd(OH)3 composite adsorption layer on the surface of the base film by hydroxylation includes the following specific steps: co-loading Zr 4 + Al 3+ 、Nd 3+ The base membrane is then immersed in an alkaline solution and reacted at 45℃~55℃ for 1.5~2.5 h. Afterwards, it is washed and dried sequentially, forming a ZrO(OH)2, AlO(OH), Nd(OH)3 composite adsorption layer on the surface of the base membrane. The concentration of alkaline substances in the alkaline solution is 0.2~0.4 mol / L.

6. The method for preparing a metal-modified ion exchange membrane according to any one of claims 1 to 5, characterized in that, The anion exchange membrane includes a styrene-based strongly basic anion exchange membrane; The aminosilane coupling agent includes N-(β-aminoethyl)-γ-aminopropyltriethoxysilane.

7. A metal-modified ion exchange membrane, characterized in that, The metal-modified ion exchange membrane is prepared by the preparation method according to any one of claims 1 to 6.

8. An electrodialysis membrane stack for selective defluorination, characterized in that, The electrodialysis membrane stack is provided with the metal-modified ion exchange membrane as described in claim 7.

9. An electrodialysis apparatus for selective defluorination, characterized in that, The electrodialysis apparatus includes the electrodialysis membrane stack for selective defluorination as described in claim 8.

10. The metal-modified ion exchange membrane of claim 7, the electrodialysis membrane stack for selective defluorination of claim 8, or the electrodialysis device for selective defluorination of claim 9 is used for the removal of fluoride from fluoride-containing wastewater.

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