A method for preparing a carboxylated cation selective separation membrane for acid recovery

Abstract

This invention discloses a method for preparing a carboxylated cation selective separation membrane for acid recovery. The method involves grafting an acyl chloride-containing monomer onto a self-polymerizing microporous polymer PN, where partial hydrolysis of the acyl chloride generates -COO. ‑ The group serves as a polymer ion exchange group, thereby obtaining a PNT polymer with strong π-π interactions and hydrogen bond self-assembly capabilities. The degree of crosslinking and the number of ion exchange groups within the membrane are further controlled by adjusting the equivalent amount of acyl chloride-containing monomers. The prepared homogeneous membrane solution is coated onto a glass plate surface. By adjusting the drying temperature, the membrane forms a dense crosslinked network while simultaneously constructing H... + Rapid transport channel. The membrane material prepared by this invention exhibits excellent mechanical properties and high H2O during electrodialysis. + The high flux and cation selectivity give this membrane material broad application potential in industrial production and practical applications.

Description

Technical Field

[0001] This invention belongs to the field of membrane technology, and specifically relates to a method for preparing a carboxylated cation exchange membrane for acid recovery. Background Technology

[0002] Acids play a vital role in various industrial fields, including waste lithium recycling, steel pickling, rare earth ion separation, electroplating, and chemicals, and are widely used as cleaning agents, corrosives, and catalysts. However, during recycling, H... + The continuous consumption of acid and the increase of impurities gradually reduce its effectiveness, eventually forming a large amount of waste acid. Waste acid typically contains various corrosive and toxic heavy metal ions. Direct discharge of untreated waste acid poses a serious threat to the ecological environment, polluting water sources and soil, and even endangering human health. The complex composition of waste acid is one of the main challenges in industrial waste acid recycling, mainly due to the coexistence of multiple acids, the presence of heavy metal ions, the mixing of organic matter, and variations in acid concentration. These factors result in significant differences in the physicochemical properties of waste acid, increasing the difficulty of separation and purification. Furthermore, different components in waste acid may react with each other, forming new compounds or precipitates. Therefore, accurate separation of H... + It is crucial for waste acid recovery. In industries such as waste lithium recycling, rare earth ion separation, electroplating, and metal processing, the main acid recovery systems include H₂O. + / Fe 2+ H + / Li + and H + / Nd 3+ wait.

[0003] Currently, waste acid recovery technologies mainly include neutralization precipitation, crystallization, distillation, solvent extraction, and membrane separation. These methods all have significant drawbacks. For example, neutralization precipitation may lead to secondary pollution; crystallization has high energy consumption; distillation has high equipment investment and maintenance costs; and solvent extraction has high operating costs and operational complexity. In contrast, membrane separation technology demonstrates significant advantages in waste acid recovery: it can efficiently separate ions and small molecules from waste acid, exhibiting high selectivity and separation efficiency, while also being energy-efficient, easy to operate, reducing dependence on chemical reagents, and lowering the risk of secondary pollution. This technology is highly adaptable, suitable for various types of waste acid, enables continuous operation, improves processing efficiency, and recovers high-purity acid to meet industrial needs.

[0004] Currently, the main method for acid recovery membrane separation is diffusion dialysis. Its basic principle is to use the concentration gradient of acid in the waste acid solution to drive the diffusion of anions from a high-concentration region to a low-concentration region. The anion exchange membrane allows anions to pass through while hindering the passage of cations or molecules, thereby achieving separation. Under the influence of the concentration gradient, anions (such as Cl-) in the waste acid diffuse from a high-concentration region to a low-concentration region. -NO3 - SO4 2- (etc.) migrates to the low-concentration side, promoting acid recovery. However, diffusion dialysis has limited treatment capacity, and the concentration of recovered acid is limited by the concentration of acid in the wastewater. Compared to diffusion dialysis, electrodialysis utilizes the selective permeability of ion exchange membranes to deacidify and concentrate waste acid under the action of an applied DC electric field. The electrodialysis process is relatively simple, has a high product recovery rate, and has no limitation on the initial concentration of waste acid. However, current cation-selective separation membranes used in electrodialysis still suffer from limitations in the relationship between ion exchange capacity and ion selectivity, as well as low cation selectivity, resulting in low purity of the recovered acid. To achieve high selectivity and high H2O... + Flux is mainly achieved through the following methods: 1) Adjusting the microphase separation structure and ion transport channel size. For example, the modified cation-selective separation membrane mentioned in patent CN118620152A regulates the ion transport channel by introducing side chains with carboxylic acids at the ends, thereby achieving H... + The effect of simultaneously improving flux and selectivity. 2) Increasing membrane crosslinking degree: Achieving high selectivity of ion separation through pore size sieving. For example, the hydrogen bond crosslinking structure formed by "AT base pairs" reported in the Journal of Membrane Science (711, 123203) is beneficial for selective permeation. 3) Surface modification of the membrane to change the surface charge level. For example, the modified cation-selective membrane mentioned in patent CN117815915A ensures H+ flux and selectivity by coating the membrane surface with a crosslinked anion exchange membrane. + It increases flux while effectively intercepting other cations, thus improving its selectivity.

[0005] However, adjusting the microphase separation of the membrane may lead to a decrease in its mechanical strength, affecting its stability and durability. Furthermore, such adjustments may require complex processes, increasing production costs and technical difficulty. Increasing the degree of membrane crosslinking inevitably leads to a decrease in ion conductivity and an increase in energy consumption. Surface modification of the membrane is also prone to detachment of the modified layer during long-term operation. Therefore, there is a need to develop a cation-selective separation membrane for acid recovery with excellent overall performance, capable of meeting the requirements for commercial applications. Summary of the Invention

[0006] To overcome the shortcomings of current technologies, this invention provides a method for preparing a carboxylated cation-selective separation membrane for acid recovery. The method utilizes a microporous polymer PN containing numerous hydrogen bonds as a precursor. Through non-covalent interactions between hydrogen bonds, an ordered structure is spontaneously formed, thereby constructing a precisely controllable ion transport channel. Simultaneously, the polymer PN is grafted with an acyl chloride-containing monomer to obtain a cross-linked intermediate membrane. The carboxylic acid groups generated from the hydrolysis of some unreacted acyl chloride groups can serve as ion exchange sites to prepare the cation-selective separation membrane. This method for preparing the acid recovery cation-selective separation membrane is simple and, as a homogeneous membrane, is compatible with existing membrane production processes, possessing significant commercial application potential.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for selective separation of carboxylated cations for acid recovery includes the following steps:

[0009] Step 1: Dissolve the self-porous polymer PN with the structural formula shown in formula (1) in an organic solvent to obtain a polymer PN solution;

[0010]

[0011] Step 2: Add acyl chloride-containing monomers to the polymer PN solution to carry out a grafting reaction to obtain a membrane solution containing polymer PNTs;

[0012] Step 3: Apply the membrane solution containing polymer PNTs onto the substrate and dry it to obtain the intermediate membrane;

[0013] Step 4: Immerse the intermediate membrane in water to detach it from the substrate. At the same time, the unreacted acyl chloride groups in the membrane rapidly hydrolyze to generate carboxylic acid groups, which serve as ion exchange groups, thus obtaining a carboxylated cation selective separation membrane for acid recovery.

[0014] Furthermore, in step 1, the degree of polymerization m of polymer PN ranges from 10. 2 -10 5 between.

[0015] Furthermore, in equation (1), R comes from a bisphenol monomer, the specific structural formula of which is shown in any one of the equations in equation (2), where * represents the connection position:

[0016]

[0017] Furthermore, the polymer PN used in this invention is prepared by reacting bisphenol monomers (such as 1,1-bi(2-naphthol), 2,2'-dihydroxybiphenyl, 3,3,3,3-tetramethyl-1,1-spirobyl (indane)-6,6-diol) with ketone monomers (such as indigo). For specific reaction methods, please refer to the literature "One-step synthesis of hydroxyl-functionalized fully carbon main chain PIMs via a Friedel-Crafts reaction for efficient gas separation" (Separation and Purification Technology 262(2021)118313).

[0018] Furthermore, in step 1, the organic solvent includes one of the common organic solvents such as tetrahydrofuran, dimethyl sulfoxide, N,N-dimethylformamide, and N-methylpyrrolidone, and the PN mass concentration in the polymer PN solution is 5-20%.

[0019] Furthermore, in step 2, the specific structural formula of the acyl chloride-containing monomer is shown in any one of formula (3):

[0020]

[0021] Furthermore, in step 2, the sites for the reaction grafting on polymer PN are -OH sites, and the molar ratio of polymer PN to the acyl chloride-containing monomer is 1:0.1-2.

[0022] Furthermore, in step 2, the grafting reaction temperature is 50℃-120℃, and the reaction time is 12h-48h.

[0023] Furthermore, in step 3, the drying temperature is between 40℃ and 100℃.

[0024] Furthermore, in step 4, the membrane is soaked for 1-3 hours.

[0025] The method for preparing a carboxylated cation selective separation membrane for acid recovery provided by this invention employs a homogeneous membrane casting process, resulting in a membrane with high uniformity and excellent mechanical properties. Simultaneously, it avoids the introduction of a surface modification layer, thereby significantly improving various performance indicators of the membrane. Its beneficial effects are specifically reflected in the following aspects:

[0026] (1) Unlike traditional microporous materials, self-polymerizing microporous polymers (PNs) are polymers with intrinsic porosity formed due to the inability of rigid chain segments to stack effectively. The micropore size and shape of PNs are tunable, allowing for the construction of more precise ion-selective transport channels. Specifically, the π-π stacking effect between benzene rings in PNs drives the ordered assembly of molecules, forming nanostructures or supramolecular structures, which enhances the interaction forces between polymer chains, thereby forming continuous ion transport channels. Simultaneously, PNs possesses good mechanical strength and chemical stability, maintaining structural stability under complex operating conditions. The tunable pore size provides a large specific surface area, thus improving ion transport efficiency. Furthermore, PNs themselves have an ether-free main chain structure, exhibiting good antioxidant and acid-base stability, ensuring the membrane's lifespan.

[0027] (2) The polymer PN contains abundant -OH and -NH- sites, which can serve as modification sites, laying the foundation for improving membrane separation performance. High-density hydrogen bonds significantly enhance the interaction forces between polymer PN chains, driving the polymer chains to form stable structures during self-assembly, thereby maintaining an ordered arrangement. Simultaneously, the structures formed by self-assembly often possess specific functionalities, such as selective permeability. In the separation of H... + During the process with metal ions, the smaller H... + Ion transport channels can be easily formed through the self-assembly of polymer PN molecules, while larger metal ions are hindered from transmembrane transport due to size sieving mechanisms, thus enabling H... + Selective separation from metal ions.

[0028] (3) While traditional sulfonic acid groups, as ion exchange groups, possess excellent ion conductivity, they also have some drawbacks. For example, their high dissociation in water can lead to excessive membrane swelling, and they are prone to degradation and failure in strong acid environments. Furthermore, sulfonic acid groups have low selectivity for specific ions, affecting separation efficiency. To address these issues, this invention selects monomers containing acyl chlorides to react with -OH sites. On one hand, the structure and size of the membrane pores are precisely controlled through cross-linking, thereby enhancing the membrane's selective separation capability. On the other hand, unreacted acyl chloride groups are hydrolyzed to generate carboxylic acid groups, forming new ion exchange sites, lowering the transmembrane energy barrier, and thus reducing membrane surface resistance and energy consumption. Simultaneously, carboxylic acid groups can interact with specific cations through electrostatic and coordination interactions, further improving the selectivity for target ions. Choosing carboxylic acid groups as ion exchange sites is problematic because their weak acidity makes them less dissociable under low pH conditions, hindering ion exchange. This characteristic may prevent metal ions from effectively exchanging through carboxylic acid groups, thus impeding their transmembrane transport and improving membrane selectivity. However, since PNT membranes themselves have a microporous structure, and H...+ The size is small, which ensures H + The flux, thereby achieving H + Precise separation of metal ions. Furthermore, the carboxylic acid group exhibits good stability in a variety of chemical environments, maintaining its function under both acidic and alkaline conditions.

[0029] (4) The ion exchange membrane of the present invention is prepared by homogeneous membrane casting, which is an efficient, flexible and simple membrane preparation technology that can achieve uniformity and consistency of the membrane. During the preparation process, the physical and chemical properties of the membrane can be precisely controlled by controlling the casting speed, coating thickness and drying conditions. For example, by controlling the molding temperature of the PNT membrane material, the directional self-assembly of hydrogen bonds can be adjusted, thereby affecting the structure and performance of the membrane. In addition, the casting method supports large-scale production, is compatible with existing processes, and allows for post-processing to further improve the membrane performance. Attached Figure Description

[0030] Figure 1 This is an analysis of the H NMR results of the polymer PN prepared in Example 1 of the present invention.

[0031] Figure 2 This is a photograph of the cation-selective separation membrane prepared in Example 1 of the present invention.

[0032] Figure 3 This is a diagram of the ion selectivity testing device used in the embodiments of the present invention.

[0033] Figure 4 It refers to the surface resistance of the membrane materials prepared in Examples 1 to 4 of this invention.

[0034] Figure 5 The H of the membrane materials prepared in Examples 1-4 of this invention + / Fe 2+ Selective test results.

[0035] Figure 6 The H of the membrane materials prepared in Examples 1-4 of this invention + / Li + Selective test results.

[0036] Figure 7 The H of the membrane materials prepared in Examples 1-4 of this invention + / Nd 3+ Selective test results. Detailed Implementation

[0037] The technical solutions of the present invention are further illustrated below through embodiments. These technical solutions are only intended to make the present invention easier for researchers in the art to understand, and are not intended to limit the scope of protection of the present invention. All divergences and variations made using the present invention are within the scope of protection of the present invention.

[0038] I. Preparation of carboxylated cation selective separation membranes

[0039] Example 1

[0040] The preparation steps of the carboxylated cation selective separation membrane for acid recovery provided in this embodiment are as follows:

[0041] Preparation of polymer PN: 28.6 g of 1,1-bi(2-naphthol) was measured into a round-bottom three-necked flask, followed by the addition of 150 mL of dichloromethane. The flask was placed in an ice bath circulation system, a stirrer was inserted, and stirring was started until the solid was completely dissolved. 18.6 g of indigo was added, followed by the dropwise addition of 15 mL of trifluoroacetic acid. Stirring continued until the indigo was completely dissolved, forming a pale red homogeneous solution. The condensation circulation temperature was set to -10°C. After the temperature stabilized, 150 mL of trifluoromethanesulfonic acid was slowly added dropwise to the three-necked flask. After reacting for 24 hours, the viscosity of the system increased sharply. The reactants were slowly poured into pure water to obtain crude PN. This product was dried and dissolved in the organic solvent DMSO. The resulting solution was then poured back into pure water to precipitate the polymer. This process was repeated three times. The precipitated polymer was then dried to obtain the final polymer PN. The degree of polymerization m ranges from 10. 2 -10 5 between.

[0042] Preparation of membrane solution containing polymer PNT: Take 1g of polymer PN and place it in a 20mL round-bottom flask. Add a magnetic spool to the round-bottom flask and place it in an oil bath. Add 9g of organic solvent (DMSO) to the flask and raise the temperature of the oil bath to 80℃ until the polymer PN is completely dissolved. Add 0.1g of acyl chloride monomer (TMC) and react for 48h. Stop the reaction and store the solution.

[0043] A membrane solution containing polymer PNT was obtained. The structure of the polymer PNT is shown below, where y = 0.1.

[0044]

[0045] Preparation of the intermediate membrane: Take 3 mL of membrane solution containing polymer PNT, pour it evenly onto a glass plate, and dry it at 80℃ for 12 h to form a membrane, thus obtaining the intermediate membrane.

[0046] Hydrolysis: The intermediate membrane was immersed in water for 1 hour to detach it from the substrate. Simultaneously, unreacted acyl chloride groups in the membrane hydrolyzed to generate carboxylic acid groups, which serve as ion exchange groups, thus obtaining a carboxylated cation-selective separation membrane for acid recovery. A photograph of the cation exchange membrane prepared in this example is shown below. Figure 1 As shown.

[0047] Example 2

[0048] The preparation steps of the carboxylated cation selective separation membrane for acid recovery provided in this embodiment are as follows:

[0049] Preparation of polymer PN: The same preparation method as in Example 1 was used.

[0050] Preparation of the membrane solution containing polymer PNTs: The same preparation method as in Example 1 was used, except that the amount of acyl chloride monomer added was adjusted to 0.3g.

[0051] Preparation of the intermediate membrane: The same preparation method as in Example 1 was used.

[0052] Hydrolysis: The same preparation method as in Example 1 was used.

[0053] Example 3

[0054] The preparation steps of the carboxylated cation selective separation membrane for acid recovery provided in this embodiment are as follows:

[0055] Preparation of polymer PN: The same preparation method as in Example 1 was used.

[0056] Preparation of the membrane solution containing polymer PNTs: The same preparation method as in Example 1 was used, except that the amount of acyl chloride monomer added was adjusted to 0.5g.

[0057] Preparation of the intermediate membrane: The same preparation method as in Example 1 was used.

[0058] Hydrolysis: The same preparation method as in Example 1 was used.

[0059] Example 4

[0060] The preparation steps of the carboxylated cation selective separation membrane for acid recovery provided in this embodiment are as follows:

[0061] Preparation of polymer PN: The same preparation method as in Example 1 was used.

[0062] Preparation of the membrane solution containing polymer PNTs: The same preparation method as in Example 1 was used, except that the amount of acyl chloride monomer added was adjusted to 0.7g.

[0063] Preparation of the intermediate membrane: The same preparation method as in Example 1 was used.

[0064] Hydrolysis: The same preparation method as in Example 1 was used.

[0065] II. Membrane flux and ion selectivity testing

[0066] Utilize Figure 3 The device shown is at 10 mA cm -2 Current density tests were conducted on the HL of the cation-selective separation membranes obtained in Examples 1-4. + / Fe 2+ Ion selectivity (with a commercially available mono / divalent selective cation exchange membrane CIMS tested under the same conditions as a control), H + / Li + Ion selectivity and H + / Nd 3+ Ion selectivity. The specific method is as follows: Take 0.3M Na₂SO₄, 0.01M HCl, 1M HCl / 0.267M MCl₂. X A mixture (where M is the corresponding metal for ion selectivity testing, and x is the valence state of the metal ion) was placed in the electrode chamber, concentration chamber, and desalination chamber, respectively. After the water pump filled each chamber and there were no air bubbles, a constant current density was applied across the membrane, and the start time of energization was recorded. Under the influence of the electric field, cations in the desalination chamber migrated from the desalination chamber to the concentration chamber. Due to the ion selectivity of the membrane, H+... + A large amount of ions permeate while other ions permeate less, and the final H in the concentration chamber is measured. + Concentration and metal ion concentration; ion flux is calculated based on the concentration.

[0067]

[0068] C in the figure t Let C0 be the ion concentration at the end of t hours of operation in the concentration chamber, and C0 be the initial ion concentration in the concentration chamber. m The effective area of ​​the membrane during the test is given by t, the running time is given by V, the final volume of the concentration chamber is given by H. + The ratio of flux to metal ion flux is the selectivity value. The H1 of the cation-selective separation membranes obtained in Examples 1-4... + / Fe 2+ Ion selectivity, H + / Li + Ion selectivity and H + / Nd 3+ The ion selectivity test results are as follows: Figure 5 , Figure 6 , Figure 7 As shown.

[0069] Analysis of the NMR results of Example 1 and the surface resistivity test results of Examples 1-4 confirmed the successful synthesis of the proposed target membrane material structure and the effective introduction of carboxylic acid groups, verifying the feasibility of the proposed route. Furthermore, the prepared membrane is a homogeneous membrane, avoiding the drawbacks of traditional surface-modified membranes and mixed matrix membranes, such as high energy consumption, low stability, low flux, and short lifetime. The preparation method of this membrane is simple, the conditions are easy to control, and it has been successfully scaled up for production. It possesses excellent mechanical properties, meeting the requirements for industrial applications.

[0070] The self-polymerizing microporous polymer PN exhibits stable structure and properties. The π-π stacking between benzene rings enhances the interaction forces between PN polymer chains, thereby improving the stability and mechanical strength of its microporous structure. Furthermore, the π-π stacking of benzene rings promotes the self-assembly behavior of PN polymer, forming an ordered microporous structure, which is a prerequisite for achieving selective separation. Due to the abundant -OH sites on the PN polymer backbone, the formation of hydrogen bonds in the polymer can be adjusted by controlling the temperature during film formation, further ordering the polymer molecules.

[0071] Polymer PN itself does not possess ion-exchange groups for ion transmembrane transport, but it can introduce ion-exchange groups through the abundant -OH groups on its main chain. Acyl chloride monomers undergo acylation reactions with hydroxyl sites, and the high-density hydroxyl environment promotes the formation of a cross-linked network, thereby making the membrane's spatial structure more compact and increasing the steric hindrance for ion transmembrane transport. In acid recovery processes, steric hindrance significantly affects the small size of H+. + The impact is relatively small, therefore H can be guaranteed. + The flux is increased. Simultaneously, some acyl chloride groups that did not participate in the acylation reaction undergo hydrolysis to produce carboxyl groups, achieving carboxylation of the PN polymer and introducing carboxylic acid groups as ion exchange groups. Since carboxylic acids are weak acids, their dissociation is weak under low pH conditions. Therefore, during acid recovery, other metal cations have difficulty achieving ion exchange through carboxylic acid groups, further reducing the flux of metal cations and improving selectivity.

[0072] Analysis of the membrane surface resistivity of Examples 1-4 revealed a significant decrease in resistivity with increasing acyl chloride monomer content. This indicates that a higher amount of acyl chloride monomer results in more carboxyl groups generated during hydrolysis, leading to a higher degree of carboxylation in the polymer PN, thus causing a decrease in membrane surface resistivity. Ht analysis of Examples 1-4 and commercial membrane CIMS... + Separation experiments with metal ions showed that as the amount of acyl chloride-containing monomer added increased, H... + With Li + The selectivity of H decreased + with Fe 2+ The selectivity also generally showed a downward trend. Examples 1-4 of Nd... 3+The concentration was below the instrument's detection limit and could not be measured, but this was sufficient to demonstrate its excellent selectivity. Comparison of the selectivity of different metal ions revealed that the larger the ion hydration radius, the higher the selectivity, further proving the size sieving effect of Examples 1-4. Meanwhile, the H in different examples... + The flux remained at a high level, further demonstrating the existence of the ordered intrinsic micropores and hydrogen bond network of polymer PNTs, which is conducive to H + Transmembrane transport.

[0073] The proposed method for preparing a cation-selective separation membrane for acid recovery is simple in process and boasts superior performance. It enables efficient production in a short time, facilitating industrialization and large-scale application. Compared with commercial cation-selective CIMS membranes, this method not only effectively solves the problem of precise separation of hydrogen and metal ions but also achieves high selectivity and high throughput by replacing the introduction of sulfonic acid groups. Simultaneously, this technology significantly improves acid recovery efficiency, reduces energy consumption, promotes efficient resource utilization, and has a significant positive impact on environmental protection and resource recycling, contributing to the achievement of sustainable development goals.

Claims

1. A method for preparing a carboxylated cation selective separation membrane for acid recovery, characterized in that, Includes the following steps: Step 1: Dissolve the self-porous polymer PN with the structural formula shown in formula (1) in an organic solvent to obtain a polymer PN solution; In equation (1), the structural form of R is shown in any one of equation (2), where * represents the connection position: Step 2: Add acyl chloride-containing monomers to the polymer PN solution to carry out a grafting reaction to obtain a membrane solution containing polymer PNTs; Step 3: Apply the membrane solution containing polymer PNTs onto the substrate and dry it to obtain the intermediate membrane; Step 4: Immerse the intermediate membrane in water to detach it from the substrate. At the same time, the unreacted acyl chloride groups in the membrane hydrolyze to generate carboxylic acid groups, which serve as ion exchange groups, thus obtaining a carboxylated cation selective separation membrane for acid recovery.

2. The preparation method according to claim 1, characterized in that: In step 1, the degree of polymerization m of polymer PN is in the range of 10. 2 -10 5 between.

3. The preparation method according to claim 1, characterized in that: In step 2, the specific structural formula of the acyl chloride-containing monomer is shown in any one of formula (3):

4. The preparation method according to claim 1, characterized in that: In step 1, the PN mass concentration in the polymer PN solution is 5-20%.

5. The preparation method according to claim 1, characterized in that: In step 2, the sites for the reaction grafting on polymer PN are -OH sites, and the molar ratio of polymer PN to the acyl chloride-containing monomer is 1:0.1~2.

6. The preparation method according to claim 1, characterized in that: In step 2, the grafting reaction temperature is 50℃-120℃, and the reaction time is 12h-48h.

7. The preparation method according to claim 1, characterized in that: In step 3, the drying temperature is between 40℃ and 100℃.

8. The preparation method according to claim 1, characterized in that: In step 4, the membrane is soaked for 1-3 hours.

9. A carboxylated cation selective separation membrane for acid recovery prepared by the preparation method according to any one of claims 1 to 8.

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