A chelating resin for highly selective removal of calcium and magnesium ions and its preparation method

Abstract

This application belongs to the field of chelating resin materials, and more specifically relates to a chelating resin for highly selectively removing calcium and magnesium ions and its preparation method. The raw materials of the highly selective calcium and magnesium ion removing chelating resin include a carrier resin, a chloromethylating agent, a hydroxymethylating agent, a catalyst, a first chelating matrix, a second chelating matrix, and a composite functional agent. The highly selective calcium and magnesium ion removing chelating resin provided in this application is used for highly selective removal of calcium and magnesium ions. The treated product has a calcium and magnesium ion concentration reduced to below 0.5 ppm, and its overall long-term stability and mechanical properties are also superior, fully meeting the higher performance requirements of the existing field for this type of chelating resin.

Description

Technical Field

[0001] This application belongs to the field of chelating resin materials, and more specifically relates to a chelating resin for highly selective removal of calcium and magnesium ions and its preparation method. Background Technology

[0002] In zero-discharge and resource-based treatment processes for high-salinity wastewater, salt recovery and resource utilization are typically achieved by separating valuable components such as magnesium sulfate and sodium sulfate from the biochemically treated and membrane-concentrated wastewater. The resulting salt solution still contains a certain concentration of calcium and magnesium ions. The presence of these divalent metal ions can adversely affect subsequent processes such as bipolar membrane treatment, leading to membrane fouling, reduced product purity, and impacting system stability. Therefore, the concentration of calcium and magnesium ions must be strictly controlled to a low level, typically below 0.5 ppm, before entering the bipolar membrane process.

[0003] In existing technologies, chelating resin adsorption is commonly used for the deep removal of calcium and magnesium ions from wastewater. Chelating resins, due to their functional groups forming stable coordination bonds with metal ions, exhibit high selectivity and adsorption capacity, making them suitable for removing low concentrations of heavy metal ions. In practical engineering applications, chelating resins are typically packed into fixed-bed adsorption columns, allowing the calcium and magnesium ion-containing salt solution to flow through the resin bed. Ion retention is achieved through ion exchange and coordination. After the resin becomes saturated, it can be regenerated through methods such as acid washing to restore its adsorption performance, thus enabling recycling.

[0004] However, in high-salt systems, especially complex solutions where sodium sulfate and magnesium sulfate coexist, existing chelating resins still face several technical challenges in practical operation. On the one hand, the selectivity of the resins for calcium and magnesium ions needs improvement. High concentrations of monovalent cations such as sodium ions compete with calcium and magnesium ions for adsorption sites, affecting the resin's adsorption efficiency and deep removal effect on the target ions. On the other hand, the regeneration performance and service life of the resins are also affected by high-salt environments and frequent regeneration operations, potentially leading to the loss of functional groups or structural degradation, resulting in unstable treatment effects and increased operating costs. Furthermore, the kinetic adsorption properties and mechanical strength of the resins also need further optimization to meet the demands of continuous and high-efficiency engineering applications. Summary of the Invention

[0005] In summary, developing a chelating resin that exhibits excellent selectivity and stability even in high-salt environments is of great significance for improving the overall efficiency of high-salt wastewater resource recovery technologies. The chelating resin for highly selective removal of calcium and magnesium ions provided in this application achieves a calcium and magnesium ion concentration reduction to below 0.5 ppm in the treated product, while also demonstrating superior long-term stability and mechanical properties, fully meeting the current high performance requirements for this type of chelating resin.

[0006] This application provides a chelating resin for highly selective removal of calcium and magnesium ions. The raw materials of the chelating resin, by weight, include: 90-120 parts of carrier resin, 100-130 parts of chloromethylating agent, 10-20 parts of hydroxymethylating agent, 10-15 parts of catalyst, 20-35 parts of first chelating matrix, 15-25 parts of second chelating matrix, and 6.5-12.5 parts of composite functional agent; the chloromethylating agent is chloromethyltrimethylsilane; the hydroxymethylating agent is paraformaldehyde; and the composite functional agent is a composition of polyepoxysuccinic acid and polyvinylpyrrolidone in a weight ratio of (4-6):(2-3).

[0007] Preferably, the mass ratio of the carrier resin, chloromethylating agent and hydroxymethylating agent is (10~11.5):(11~12):(1.2~1.6).

[0008] Preferably, the mass ratio of the carrier resin, chloromethylating agent and hydroxymethylating agent is (10~10.5):(11~11.5):(1.2~1.4).

[0009] Preferably, the preparation method of the carrier resin specifically includes the following steps: S1: Add styrene, crosslinking agent, initiator and pore-forming agent to a reaction vessel and mix and stir evenly to obtain an oil phase; S2: Add deionized water and dispersant to another reaction vessel, heat to 50~55℃ and stir for 5~10min to obtain an aqueous phase, then mix the aqueous phase and oil phase, mix and stir at 300~400rpm for 10~15min, then heat to 75~78℃ and keep warm for 4~4.5h, then heat to 82~85℃ and react for 5~6h, and finally mature at 90~92℃ for 2~3h; S3: After maturation, cool to room temperature, filter to obtain the product, wash with deionized water and anhydrous ethanol 2~3 times respectively, and vacuum dry to constant weight to obtain spherical carrier resin.

[0010] Preferably, the mass ratio of styrene, crosslinking agent, initiator, pore-forming agent and dispersant is (75~85):(20~25):(0.8~1.1):(40~50):(1~2).

[0011] Preferably, the mass ratio of styrene, crosslinking agent, initiator, pore-forming agent and dispersant is (75~80):(22~25):(0.9~1):(44~48):(1.2~1.5).

[0012] Preferably, the crosslinking agent is divinylbenzene and / or trivinylbenzene.

[0013] Preferably, the crosslinking agent is divinylbenzene.

[0014] Preferably, the initiator is benzoyl peroxide or dicumyl peroxide.

[0015] Preferably, the initiator is benzoyl peroxide.

[0016] Preferably, the pore-forming agent is at least one selected from n-heptane, toluene, and n-octanol.

[0017] Preferably, the pore-forming agent is n-heptane or toluene.

[0018] Preferably, the dispersant is at least one of gelatin, polyvinyl alcohol, and hydroxyethyl cellulose.

[0019] Preferably, the dispersant is gelatin or polyvinyl alcohol.

[0020] Preferably, the dispersant is gelatin.

[0021] Preferably, the catalyst is at least one of anhydrous aluminum trichloride, zinc chloride, and tin tetrachloride.

[0022] Preferably, the catalyst is anhydrous aluminum trichloride or zinc chloride.

[0023] Preferably, the catalyst is anhydrous aluminum trichloride.

[0024] Preferably, the first chelating matrix is ​​iminodiacetic acid.

[0025] Preferably, the second chelating matrix is ​​2-phosphonobutane-1,2,4-tricarboxylic acid.

[0026] Preferably, the mass ratio of the carrier resin, the first chelating matrix, and the second chelating matrix is ​​(10~11.5):(2.2~3):(1.8~2.3).

[0027] Preferably, the mass ratio of the carrier resin, the first chelating matrix, and the second chelating matrix is ​​(10~10.5):(2.4~2.8):(1.8~2.1).

[0028] The raw material system and innovative preparation process in this application achieve a comprehensive improvement in the performance of the chelating resin. The dense three-dimensional network constructed by a high proportion of crosslinking agents endows the resin with excellent mechanical strength and anti-swelling properties, ensuring its structural integrity during long-term operation. The well-developed pores created by the porogen greatly optimize the ion diffusion path and enhance adsorption kinetics. The core lies in the stepwise introduction of bifunctional groups: iminodiacetic acid groups provide high adsorption capacity and rapid ion capture ability; subsequently grafted phosphonic acid groups, with their highly specific coordination ability with calcium and magnesium ions, achieve deep and selective removal even against a high concentration of sodium ions.

[0029] Preferably, the composite functional agent is a combination of polyepoxysuccinic acid and polyvinylpyrrolidone.

[0030] Preferably, the mass ratio of the polyepoxysuccinic acid to polyvinylpyrrolidone is (4~6):(2~3).

[0031] Preferably, the mass ratio of the polyepoxysuccinic acid to polyvinylpyrrolidone is (5~5.5):(2.2~2.8).

[0032] Preferably, the mass ratio of the carrier resin to the composite functional agent is (10~11.5):(0.8~1.2).

[0033] Preferably, the mass ratio of the carrier resin to the composite functional agent is (10~10.5):(0.9~1.1).

[0034] This application introduces a crucial synergistic effect on the resin through the final addition of a composite functional agent. Polyepoxysuccinic acid preferentially adsorbs onto the surface of resin pores and active sites. Its strong scale inhibition and dispersing properties effectively suppress the deposition and scaling of slightly soluble substances such as calcium sulfate and magnesium hydroxide within the resin during long-term operation, thereby significantly improving the resin's antifouling ability and stability for recycling. Polyvinylpyrrolidone improves the hydrophilicity and pore wettability of the resin surface, reduces mass transfer resistance, accelerates the adsorption and desorption kinetics, and enhances the toughness of the resin particles. The combined effect of these two agents further optimizes the overall performance of the resin from a physical perspective without affecting chemisorption.

[0035] The preparation method of the highly selective calcium and magnesium ion removal chelating resin provided in this application includes the following steps: S1: Take the carrier resin and put it into a reaction vessel equipped with a stirring and reflux condenser. Add the chloromethylating agent, stir and swell at room temperature, and add the catalyst in three parts. After heating and stirring to react thoroughly, wash and dry to obtain the chloromethylated resin; S2: Take the prepared chloromethylated resin and mix it with the first chelating matrix and add it into the reaction vessel. Add the alkaline solution and stir. Heat and maintain the reaction. After the reaction is completed, filter out the resin to obtain the intermediate resin; S3: Take the intermediate resin, the second chelating matrix and the hydroxymethylating agent and add them into a polytetrafluoroethylene reaction vessel. Add acid solution to react and wash repeatedly with deionized water; S4: Add the composite functional agent to deionized water and stir to mix evenly to obtain a mixed solution. Immerse the resin obtained in S3 in the above mixed solution to fully adsorb and load. After completion, filter out the resin and drain it. Put the resin into a glass column for immersion transformation. After completion, rinse, vacuum dry and sieve to obtain uniform particles in the particle size range of 0.6~1.2 mm, thus obtaining the highly selective calcium and magnesium ion removal chelating resin.

[0036] Preferably, the preparation method of the highly selective calcium and magnesium ion removal chelating resin includes the following steps: S1: Take the carrier resin and put it into a reaction vessel equipped with a stirring and reflux condenser, add the chloromethylating agent, stir and swell at room temperature for 2-3 hours, then add the catalyst in three portions at 20-25 minutes intervals under ice-water bath cooling and continuous stirring at 100-200 rpm. After the addition is complete, remove the ice bath and slowly raise the temperature to 45-50°C, stir and react at 80-100 rpm for 10-12 hours. After completion, pour the reaction mixture into ice water, filter out the product resin, wash thoroughly with glacial acetic acid, methanol, and deionized water in sequence, and dry to obtain the chloromethylated resin; S2: Take the prepared chloromethylated resin and mix it with the first chelating matrix and add it into the reaction vessel, add... After adding the alkaline solution, stir at 80-100 rpm and heat to 80-85℃, maintaining the reaction for 9-10 hours. After the reaction is complete, filter out the resin to obtain the intermediate resin; S3: Add the intermediate resin, the second chelating matrix, and the hydroxymethylating agent to a polytetrafluoroethylene reactor, add acid solution, heat to 102-105℃, and react for 7-8 hours. After the reaction is complete, allow it to cool naturally to room temperature, filter out the resin, and wash repeatedly with deionized water until the effluent is clear and the pH value is close to neutral; S4: Add the composite functional agent to deionized water and stir to obtain a mixed solution. Immerse the resin obtained in S3 in the above mixed solution and stir at 50-55℃ for 5-6 hours to fully adsorb and load. After completion, filter out the resin and drain it. Pack the resin into a glass column and use 4wt% of 2 times the bed volume. NaOH solution is passed through the resin bed at a flow rate of 2 BV / h, and the resin is soaked for 4 hours. After the transformation is completed, the resin is rinsed until the pH of the effluent is 9-10. The resin is then vacuum dried and sieved to obtain uniform particles with a particle size range of 0.6-1.2 mm, which yields a chelating resin with high selectivity for removing calcium and magnesium ions.

[0037] Preferably, the acid solution is concentrated hydrochloric acid.

[0038] Preferably, the mass concentration of the concentrated hydrochloric acid is 36-38%.

[0039] Preferably, the alkaline solution is an aqueous solution of sodium hydroxide or an aqueous solution of potassium hydroxide.

[0040] Preferably, the mass concentration of the alkaline solution is 7.5~12.5%.

[0041] Preferably, the mass concentration of the alkaline solution is 10%.

[0042] The beneficial effects of this application are: 1. The chelating resin and its preparation method provided in this application, through innovative bifunctional group design and the introduction of composite reinforcing additives, bring significant beneficial effects. This resin exhibits extremely high adsorption selectivity for calcium and magnesium ions in complex high-salt systems, effectively resisting competitive interference from high-concentration monovalent ions and achieving deep purification. Simultaneously, its robust framework structure provides strong resistance to swelling and wear, and combined with the excellent scale inhibition and stabilization functions of the additives, ensures long-term performance stability and an ultra-long service life under frequent regeneration conditions. Furthermore, the optimized pore structure enhances adsorption kinetics, facilitating efficient and continuous engineering operation. Ultimately, this resin provides a reliable guarantee for the core bipolar membrane pretreatment process, significantly improving the overall efficiency of the high-salt wastewater resource recovery system.

[0043] 2. This application achieves a comprehensive improvement in the performance of chelating resins through a carefully selected raw material system and innovative preparation process. The dense three-dimensional network constructed by a high proportion of crosslinking agents endows the resin with excellent mechanical strength and anti-swelling properties, ensuring its structural integrity during long-term operation. The well-developed pores created by the porogen greatly optimize the ion diffusion path and enhance adsorption kinetics. The core lies in the stepwise introduction of bifunctional groups: iminodiacetic acid groups provide high adsorption capacity and rapid ion capture ability; subsequently grafted phosphonic acid groups, with their highly specific coordination ability with calcium and magnesium ions, achieve deep and selective removal in the context of high-concentration sodium ions. The combined effect of the raw material scheme and the highly efficient capture chain targeting the target ions effectively solve the technical problems of poor selectivity and difficulty in deep purification under high-salt environments.

[0044] 3. The composite functional agent introduced through the physical loading process in this application brings a key synergistic effect to the resin. Polyepoxysuccinic acid preferentially adsorbs onto the surface of resin pores and active sites. Its strong scale inhibition and dispersing properties can effectively inhibit the deposition and scaling of slightly soluble substances such as calcium sulfate and magnesium hydroxide inside the resin during long-term operation, thereby significantly improving the resin's anti-fouling ability and stability for recycling. Polyvinylpyrrolidone improves the hydrophilicity and pore wettability of the resin surface, reduces mass transfer resistance, accelerates the adsorption and desorption kinetics, and enhances the toughness of resin particles. The two work synergistically to further optimize the overall performance of the resin from a physical perspective without affecting chemical adsorption. Attached Figure Description

[0045] Figure 1 This is a physical image of the chelating resin for highly selective removal of calcium and magnesium ions prepared in Example 1 of this application. Detailed Implementation

[0046] Example 1 A highly selective chelating resin for removing calcium and magnesium ions comprises, by weight, 100 parts of carrier resin, 115 parts of chloromethylating agent, 13.5 parts of hydroxymethylating agent, 10 parts of catalyst, 26 parts of first chelating matrix, 20 parts of second chelating matrix, and 10.5 parts of composite functional agent.

[0047] The chloromethylating agent is chloromethyltrimethylsilane, industrial grade, manufactured by Shandong Yukang Chemical Co., Ltd., China; the hydroxymethylating agent is paraformaldehyde, industrial grade, manufactured by Metawell (Shandong), China.

[0048] The preparation method of the carrier resin, by mass, specifically includes the following steps: S1: In a reaction vessel, accurately weigh and mix 75 parts of styrene, 23 parts of crosslinking agent, 0.9 parts of initiator and 46 parts of pore-forming agent, mix and stir evenly to obtain an oil phase; S2: In another reaction vessel, add 250 parts of deionized water and 1.4 parts of dispersant, heat to 52℃ and stir for 8 min to obtain an aqueous phase, then mix the aqueous phase and oil phase, mix and stir at 300 rpm for 12 min, then heat to 75℃ and keep for 4 h, then heat to 82℃ and react for 6 h, and finally mature at 90℃ for 3 h; S3: After maturation, cool to room temperature, filter to obtain the product, wash three times with deionized water and anhydrous ethanol respectively, and vacuum dry to constant weight to obtain spherical carrier resin.

[0049] The crosslinking agent is divinylbenzene; the initiator is benzoyl peroxide; the pore-forming agent is n-heptane; the dispersant is gelatin; and the catalyst is anhydrous aluminum trichloride.

[0050] The first chelating matrix is ​​iminodiacetic acid; the second chelating matrix is ​​2-phosphonobutane-1,2,4-tricarboxylic acid.

[0051] The composite functional agent is a combination of polyepoxysuccinic acid and polyvinylpyrrolidone K30 in a mass ratio of 5.2:2.8. The polyepoxysuccinic acid is industrial grade and manufactured by Shandong Wanhua Tianhe New Materials Co., Ltd., China.

[0052] A method for preparing a highly selective calcium and magnesium ion removal chelating resin includes the following steps: S1: The carrier resin is added to a reaction vessel equipped with a stirrer and a reflux condenser, a chloromethylating agent is added, and the mixture is stirred and swollen at room temperature for 3 hours. Then, the catalyst is added in three portions at 24-minute intervals under ice-water bath cooling and continuous stirring at 150 rpm. After the addition is complete, the ice bath is removed, the temperature is slowly raised to 50°C, and the mixture is stirred at 100 rpm for 11 hours. After the reaction is completed, the reaction mixture is poured into ice water, the product resin is filtered out, and the resin is thoroughly washed with glacial acetic acid, methanol, and deionized water in sequence and then dried to obtain the chloromethylated resin; S2: The prepared chloromethylated resin is mixed with the first chelating matrix and added to a reaction vessel. An alkaline solution (solid-liquid ratio = 1:7) is added and the mixture is then refluxed at 90°C. Stir at rpm and heat to 80℃, maintain reaction for 10h. After the reaction is complete, filter out the resin to obtain intermediate resin; S3: Add intermediate resin, second chelating matrix and hydroxymethylating agent to polytetrafluoroethylene reactor, add acid solution (solid-liquid ratio = 1:5), heat to 103℃ and react for 8h. After the reaction is complete, cool naturally to room temperature, filter out the resin, and wash repeatedly with deionized water until the effluent is clear and the pH value is close to neutral; S4: Add composite functional agent to deionized water (solid-liquid ratio = 1:6) and stir to mix evenly to obtain a mixed solution. Immerse the resin obtained in S3 in the above mixed solution and stir at 50℃ for 5.5h to fully adsorb and load. After completion, filter out the resin and drain it. Pack the resin into a glass column and pass 4wt% NaOH solution with 2 times the bed volume through the resin bed at a flow rate of 2 BV / h. Soak and transform for 4h. After completion, rinse until the pH of the effluent is in the range of 9 to 10. Vacuum dry and sieve to obtain uniform particles in the range of 0.6~1.2 mm particle size.

[0053] The acid solution is concentrated hydrochloric acid with a mass concentration of 36%. The alkali solution is an aqueous solution of sodium hydroxide with a mass concentration of 10%.

[0054] The physical sample of the highly selective calcium and magnesium ion removal chelating resin prepared in this embodiment is shown below. Figure 1 As shown.

[0055] Example 2 This embodiment differs from Embodiment 1 only in the amount of raw materials used, as follows: by mass, the raw materials include: 115 parts of carrier resin, 110 parts of chloromethylating agent, 12 parts of hydroxymethylating agent, 10 parts of catalyst, 26 parts of first chelating matrix, 20 parts of second chelating matrix, and 10.5 parts of composite functional agent. The rest of the implementation method is the same as in Embodiment 1, resulting in a chelating resin with high selectivity for removing calcium and magnesium ions.

[0056] Example 3 This embodiment differs from Embodiment 1 only in the amount of raw materials used, as follows: by mass, the raw materials include: 105 parts of carrier resin, 120 parts of chloromethylating agent, 14.8 parts of hydroxymethylating agent, 10 parts of catalyst, 26 parts of first chelating matrix, 20 parts of second chelating matrix, and 10.5 parts of composite functional agent. The rest of the implementation method is the same as in Embodiment 1, resulting in a chelating resin with high selectivity for removing calcium and magnesium ions.

[0057] Comparative Example 1 The only difference between this comparative example and Example 1 is the amount of raw materials used, as follows: by mass, the raw materials include: 100 parts of carrier resin, 115 parts of chloromethylating agent, 13.5 parts of hydroxymethylating agent, 10 parts of catalyst, 26 parts of first chelating matrix, 20 parts of second chelating matrix, and 2.5 parts of composite functional agent. The rest of the implementation method is the same as that of Example 1, and a chelating resin with high selectivity for removing calcium and magnesium ions is obtained.

[0058] Comparative Example 2 The only difference between this comparative example and Example 1 is the amount of raw materials used, as follows: by mass, the raw materials include: 100 parts of carrier resin, 115 parts of chloromethylating agent, 5.5 parts of hydroxymethylating agent, 10 parts of catalyst, 26 parts of first chelating matrix, 10.5 parts of second chelating matrix, and 10.5 parts of composite functional agent. The rest of the implementation method is the same as that of Example 1, and a chelating resin with high selectivity for removing calcium and magnesium ions is obtained.

[0059] Comparative Example 3 The only difference between this comparative example and Example 1 is the amount of raw materials used, as follows: by mass, the raw materials include: 100 parts of carrier resin, 80 parts of chloromethylating agent, 25.5 parts of hydroxymethylating agent, 10 parts of catalyst, 17.5 parts of first chelating matrix, 20 parts of second chelating matrix, and 10.5 parts of composite functional agent. The rest of the implementation method is the same as that of Example 1, and a chelating resin with high selectivity for removing calcium and magnesium ions is obtained.

[0060] Comparative Example 4 The only difference between this comparative example and Example 1 is the amount of raw materials used, as follows: by mass, the raw materials include: 100 parts of carrier resin, 115 parts of chloromethylating agent, 18.5 parts of hydroxymethylating agent, 10 parts of catalyst, 12 parts of first chelating matrix, 25 parts of second chelating matrix, and 6.5 parts of composite functional agent. The rest of the implementation method is the same as that of Example 1, and a chelating resin with high selectivity for removing calcium and magnesium ions is obtained.

[0061] Comparative Example 5 The only difference between this comparative example and Example 1 is that the composite functional agent is a combination of polyepoxysuccinic acid and polyvinylpyrrolidone in a mass ratio of 7:1. The rest of the implementation method is the same as that in Example 1, resulting in a chelating resin with high selectivity for removing calcium and magnesium ions.

[0062] Comparative Example 6 The only difference between this comparative example and Example 1 is that the composite functional agent is a combination of polyepoxysuccinic acid and polyvinylpyrrolidone in a mass ratio of 3:5. The rest of the implementation method is the same as that of Example 1, resulting in a chelating resin with high selectivity for removing calcium and magnesium ions.

[0063] Test case (1) Static adsorption selectivity: simulated high-salt wastewater, a mixed solution containing Na2SO4 (100 g / L), MgSO4 (100 mg / L) and CaCl2 (100 mg / L) was prepared, and the pH was adjusted to 7.0±0.2 with NaOH or H2SO4; in a constant temperature shaker at 25℃, 1g of sample resin and 100mL of the above mixed solution were weighed into an Erlenmeyer flask and shaken at 150 rpm for 24h until adsorption equilibrium was reached. Then the concentrations of calcium and magnesium ions in the filtrate were measured and the results were recorded in Table 1.

[0064] (2) Static saturated adsorption capacity: CaCl2 and MgSO4 solutions with concentration ranges of 0.5~20 mmol / L were prepared respectively. The background ionic strength was adjusted with Na2SO4 to be similar to that of high-salt wastewater. At 25℃, 0.1g of sample resin was mixed with 50 mL of single metal ion solutions of different concentrations and oscillated at constant temperature for 24h until equilibrium was reached. The equilibrium concentration was measured, the adsorption capacity was calculated, and the Langmuir isotherm model was used to fit the data to obtain the theoretical maximum saturated adsorption capacity. The results are recorded in Table 1.

[0065] (3) Resin stability: Take the same batch of resin and repeat the following steps: pass simulated wastewater until complete breakthrough, elute with 2 BV and 4 wt% HCl at a flow rate of 5 BV / h, then convert with 2 BV and 4 wt% NaOH, and finally wash with water until neutral. After 20 complete cycles, obtain the resin's stability against Ca²⁺. + The saturated adsorption capacity retention rate was recorded in Table 1.

[0066] (4) Resin mechanical strength: Take a chelated resin sample with a known number of spherical particles, place it in a roller mill flask containing ceramic balls, test at a speed of 55 rpm for 30 min, after which the sample is transferred to a standard sieve, rinsed with water, and the complete spherical particles are separated and counted. The spherical rate after grinding = (number of spherical particles after grinding / number of spherical particles before grinding) × 100%. The average of the results of 10 tests is recorded in Table 1.

[0067] Table 1 Performance Test Results

[0068] As can be seen from the results in Table 1, Examples 1-3 achieved better performance results compared to Comparative Examples 1-6. The technical solutions specified in this application used in Examples 1-3, through innovative bifunctional group design and the introduction of composite reinforcing additives, exhibited extremely high adsorption selectivity for calcium and magnesium ions in high-salt complex systems, effectively resisting competitive interference from high-concentration monovalent ions and achieving deep purification. Furthermore, the composite functional agents introduced through the physical loading process brought crucial synergistic effects to the resin, and the combined effect of both resulted in a better overall performance. In contrast, Comparative Examples 1-6, due to the use of different non-specific technical solutions, showed a significant decrease in their corresponding technical effects in the chelating resin system, leading to a weakening of the overall performance of the final product.

Claims

1. A chelating resin for highly selectively removing calcium and magnesium ions, characterized in that, The raw materials of the chelating resin, by weight, include: 90-120 parts of carrier resin, 100-130 parts of chloromethylating agent, 10-20 parts of hydroxymethylating agent, 10-15 parts of catalyst, 20-35 parts of first chelating matrix, 15-25 parts of second chelating matrix, and 6.5-12.5 parts of composite functional agent; The chloromethylating agent is chloromethyltrimethylsilane; the hydroxymethylating agent is paraformaldehyde; the first chelating matrix is ​​iminodiacetic acid; the second chelating matrix is ​​2-phosphonobutane-1,2,4-tricarboxylic acid; The composite functional agent is a combination of polyepoxysuccinic acid and polyvinylpyrrolidone, with a mass ratio of (4~6):(2~3). The preparation method of the highly selective calcium and magnesium ion removal chelating resin is as follows: S1: Take the carrier resin and put it into a reaction vessel equipped with a stirring and reflux condenser. Add the chloromethylating agent, stir and swell at room temperature, and add the catalyst in three parts. After heating and stirring to react thoroughly, wash and dry to obtain the chloromethylated resin; S2: Take the prepared chloromethylated resin and mix it with the first chelating matrix and add it into the reaction vessel. Add the alkaline solution and stir. Heat and maintain the reaction. After the reaction is completed, filter out the resin to obtain the intermediate resin; S3: Take the intermediate resin, the second chelating matrix and the hydroxymethylating agent and add them into a polytetrafluoroethylene reaction vessel. Add acid solution to react and wash repeatedly with deionized water; S4: Add the composite functional agent to deionized water and stir to mix evenly to obtain a mixed solution. Immerse the resin obtained in S3 in the above mixed solution to fully adsorb and load. After completion, filter out the resin and drain it. Put the resin into a glass column for immersion transformation. After completion, rinse, vacuum dry and sieve to obtain uniform particles in the particle size range of 0.6~1.2 mm, which is the highly selective calcium and magnesium ion removal chelating resin.

2. The chelating resin for highly selective removal of calcium and magnesium ions according to claim 1, characterized in that, The mass ratio of the carrier resin, chloromethylating agent and hydroxymethylating agent is (10~11.5):(11~12):(1.2~1.6).

3. The chelating resin for highly selective removal of calcium and magnesium ions according to claim 2, characterized in that, The preparation method of the carrier resin specifically includes the following steps: S1: Add styrene, crosslinking agent, initiator and pore-forming agent to a reaction vessel and mix and stir evenly to obtain an oil phase; S2: Add deionized water and dispersant to another reaction vessel, heat to 50~55℃ and stir for 5~10min to obtain an aqueous phase, then mix the aqueous phase and oil phase, mix and stir at 300~400rpm for 10~15min, then heat to 75~78℃ and keep warm for 4~4.5h, then heat to 82~85℃ and react for 5~6h, and finally mature at 90~92℃ for 2~3h; S3: After maturation, cool to room temperature, filter to obtain the product, wash with deionized water and anhydrous ethanol 2~3 times respectively, and vacuum dry to constant weight to obtain spherical carrier resin.

4. The chelating resin for highly selective removal of calcium and magnesium ions according to claim 3, characterized in that, The mass ratio of styrene, crosslinking agent, initiator, pore-forming agent and dispersant is (75~85):(20~25):(0.8~1.1):(40~50):(1~2).

5. The chelating resin for highly selective removal of calcium and magnesium ions according to claim 4, characterized in that, The crosslinking agent is divinylbenzene and / or trivinylbenzene.

6. The chelating resin for highly selective removal of calcium and magnesium ions according to claim 5, characterized in that, The pore-forming agent is at least one of n-heptane, toluene, and n-octanol.

7. The chelating resin for highly selective removal of calcium and magnesium ions according to claim 6, characterized in that, The dispersant is at least one of gelatin, polyvinyl alcohol, and hydroxyethyl cellulose.

8. The chelating resin for highly selective removal of calcium and magnesium ions according to claim 7, characterized in that, The catalyst is at least one of anhydrous aluminum trichloride, zinc chloride, and tin tetrachloride.

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