Sepiolite-based lithium ion imprinted polymer, preparation method and application in low-grade brine lithium ion adsorption separation

Abstract

The present application belongs to the technical field of high-value utilization of mineral resources and water treatment adsorption separation materials, and relates to a sepiolite-based lithium ion imprinting polymer, a preparation method and application in adsorption and separation of lithium ions in low-grade brine. The sepiolite is activated and pretreated, mixed with a lithium ion template, a functional monomer, a crosslinking agent and an initiator in a solvent system, and then subjected to a polymerization reaction, elution of the template ion, filtration, washing and drying to obtain the sepiolite-based lithium ion imprinting polymer. The sepiolite-based lithium ion imprinting polymer has good structural stability, lithium ion recognition selectivity and cyclic regeneration performance, and is suitable for efficient enrichment and separation of lithium ions in low-grade brine.

Description

Technical Field

[0001] This invention relates to a sepiolite-based lithium-ion imprinted polymer, its preparation method, and its application in the adsorption and separation of lithium ions in low-grade brine, belonging to the fields of chemistry and environmental technology. Background Technology

[0002] Against the backdrop of global energy transition and green sustainable development, lithium, hailed as "white oil," is a crucial raw material in new energy batteries, energy storage materials, aerospace materials, and fine chemical products. With the explosive growth of the global electric vehicle market and the increasing demand for clean energy storage, the efficient recovery and separation of lithium resources has become increasingly important. Traditional lithium extraction primarily relies on hard rock ores and brine resources from salt lakes. However, the extensive exploitation and depletion of these resources have led to severe problems such as energy consumption, groundwater depletion, and land disturbance. Therefore, low-grade brine resources, due to their large reserves and wide distribution, have become one of the important sources of lithium extraction.

[0003] Existing lithium extraction technologies mainly include precipitation, extraction, membrane separation, electrochemical methods, and adsorption. Among these, adsorption has good application potential due to its mild operating conditions, simple process, large adsorption capacity, and easy regeneration. However, low-grade brines have low lithium-ion content and contain coexisting ions such as sodium, potassium, calcium, and magnesium. Especially under high magnesium-to-lithium ratio conditions, efficient and selective separation of lithium ions is challenging. Traditional adsorption materials suffer from insufficient selectivity, limited adsorption capacity, poor structural stability, and poor regeneration performance in complex brine systems. Therefore, there is an urgent need to develop a novel lithium extraction technology with high selectivity, high adsorption capacity, and strong anti-interference ability to solve the problem of lithium extraction from low-grade brines.

[0004] Ion imprinting technology possesses a unique "key and lock" specific recognition mechanism. Lithium-ion imprinted polymers (Li-IIPs) prepared based on this technology have become a research hotspot for the efficient extraction of lithium from low-grade brine. For example, CN117624708A discloses a biomass porous carbon-based lithium-ion imprinted material and its preparation method. Using magnetic biomass porous carbon with a core-shell structure as the matrix, it is surface-activated with polyvinylpyrrolidone as a surfactant. After surface activation, it is uniformly dispersed in a solvent, and then aminated in the solvent. 2-(hydroxymethyl)-12-crown ether-4 is used as the functional monomer, and Li... +In-situ polymerization using ethylene glycol dimethacrylate as a crosslinking agent yielded biomass porous carbon-based lithium-ion imprinted materials. Ion-imprinted polymers, by introducing lithium ions as templates during polymerization, can form recognition sites within the polymer that match the size, spatial configuration, and coordination environment of lithium ions, exhibiting good specific recognition capabilities. However, traditional lithium-ion imprinted polymers suffer from problems such as particle agglomeration, high mass transfer resistance, and low utilization of effective recognition sites. These problems can be overcome by placing the recognition sites on or near the surface of a support. Adding a support material during the polymerization of ions and functional monomers allows the polymerization process to occur on the surface of the support material, offering advantages such as easy elution of template ions, large adsorption capacity, and high mass transfer efficiency. Finding suitable functional monomers for efficient lithium extraction from low-grade brine and supports with high specific surface area and good mechanical properties is crucial.

[0005] Crown ether ligands, due to their cyclic cavities and oxygen-rich coordination structures, exhibit strong complexation effects on small-radius alkali metal ions. They are frequently studied as lithium-ion sieves; for example, CN118955774A discloses an acrylate crown ether polymer used to separate and enrich lithium ions in salt lake brine. Furthermore, introducing crown ethers into lithium-ion imprinted systems enhances the material's ability to recognize lithium ions, making them a common choice as functional monomers in lithium-ion imprinted polymerization. While crown ether derivatives typically possess high specific surface area and chemical reactivity, they still suffer from weak mechanical strength and susceptibility to caking, affecting polymer separation efficiency. Functionalizing crown ether derivatives on supports to prepare lithium-ion imprinted polymers not only leverages the single selectivity of crown ethers for lithium ions but also fully combines the adsorption and separation characteristics of the support, further improving the selectivity and lithium-ion adsorption capacity of the imprinted polymer. For carrier materials, various materials have been used as carriers for imprinted polymers, such as graphene, carbon nanotubes, and mesoporous silicon-based materials. For example, CN106756104A discloses a method for extracting lithium from seawater using silicon-based mesoporous materials. This method uses silicon-based mesoporous materials as a substrate to prepare adsorbents, and grafts crown ethers onto the silicon-based mesoporous materials to functionalize them, thereby improving their lithium selective adsorption capacity. However, carrier materials such as graphene, carbon nanotubes, and mesoporous silicon-based materials are costly, which is not conducive to the industrialization of lithium extraction from low-grade brine.

[0006] Therefore, developing low-cost, high-efficiency, and environmentally friendly materials as carriers, while simultaneously modifying crown ethers, with the synergistic effect of both enhancing adsorption, and preparing low-cost, highly selective, and adsorbent lithium-ion imprinted polymers, is of great significance for the industrialization of lithium extraction from low-grade brine. Summary of the Invention

[0007] Given the current state of the prior art, particularly the problems of low selectivity, insufficient structural stability, and limited mass transfer efficiency of existing lithium-ion adsorption materials, and the high cost of existing carrier materials, which hinders the industrialization of lithium extraction from low-grade brine, this invention addresses these issues. Through in-depth and extensive research in the field of brine lithium extraction, this invention has discovered that using sepiolite, a natural mineral raw material, as a carrier, in synergy with modified crown ethers, yields a sepiolite-based lithium-ion imprinted polymer that not only exhibits excellent selective adsorption performance and cycle stability for lithium ions but also boasts low cost, making it highly beneficial for the industrialization of lithium extraction from low-grade brine. This invention is based on these findings.

[0008] Therefore, one object of the present invention is to provide a sepiolite-based lithium-ion imprinted polymer. Using sepiolite as a carrier for crown ether derivatives, lithium-ion imprinted polymers are prepared, exhibiting excellent adsorption performance, high selectivity, and good stability.

[0009] The second objective of this invention is to provide a method for preparing the above-mentioned sepiolite-based lithium-ion imprinted polymer, which uses lithium nitrate as a template, crown ether as a recognition ligand, ethylene glycol dimethacrylate as a crosslinking agent, and azobisisobutyronitrile as an initiator to prepare the sepiolite-based lithium-ion imprinted polymer. This preparation method is easy to operate.

[0010] A third objective of this invention is to provide the application of the above-mentioned sepiolite-based lithium-ion imprinted polymer in the adsorption and separation of lithium ions in low-grade brine.

[0011] The technical solution for achieving the above-mentioned objectives can be summarized as follows:

[0012] Sepiolite-based lithium-ion imprinted polymers use acid-activated sepiolite as a carrier, with modified crown ether polymers attached to the carrier surface.

[0013] According to the present invention, preferably, the modified crown ether polymer is obtained by polymerization of propylene bromide modified crown ether as monomer and ethylene glycol dimethacrylate as crosslinking agent; more preferably, the crown ether is 2-(hydroxymethyl)-12-crown ether-4.

[0014] According to the present invention, preferably, the mass ratio of the carrier to the modified crown ether polymer is (0.3~0.6) g : (7~20) g.

[0015] According to the present invention, the preparation method of the above-mentioned sepiolite-based lithium-ion imprinted polymer includes the following steps:

[0016] (1) After grinding the sepiolite, it was immersed in an acid solution for activation treatment, washed and dried to obtain acid-activated sepiolite;

[0017] (2) 2-(hydroxymethyl)-12-crown ether-4 was modified with bromopropene under alkaline conditions to obtain a modified crown ether;

[0018] (3) In an organic solvent, acid-activated sepiolite and modified crown ether are mixed, lithium ion template is added, and crosslinking polymerization is carried out in the presence of crosslinking agent and initiator. After the lithium ion template is washed off the product, it is washed with water and dried to obtain sepiolite-based lithium ion imprinted polymer.

[0019] According to the present invention, preferably, in step (1), the acid solution is a 1 mol / L hydrochloric acid solution;

[0020] Preferably, the activation treatment involves immersing sepiolite in an acid solution, ultrasonicating, and then stirring at 50°C for 18 hours.

[0021] According to the present invention, preferably, in step (2), the molar ratio of 2-(hydroxymethyl)-12-crown ether-4 and bromopropene is 1:1.2;

[0022] Preferably, the modification reaction is carried out in an N,N-dimethylformamide solution with an alkaline pH of 11-13, under a nitrogen atmosphere at 30°C with stirring, for a reaction time of 6 hours.

[0023] Preferably, after the modification reaction is completed, the pH is adjusted to 7 with acid, and the modified crown ether is obtained by dichloromethane extraction.

[0024] According to the present invention, preferably, in step (3), the lithium-ion template is lithium nitrate, the organic solvent is methanol, the crosslinking agent is ethylene glycol dimethacrylate, and the initiator is azobisisobutyronitrile;

[0025] Preferably, the molar ratio of lithium ions to crosslinking agent is 1:(10~30); the modified crown ether and crosslinking agent are total monomers, and the molar amount of initiator is 1% of the total monomer molar amount;

[0026] Preferably, the molar ratio of modified crown ether to acid-activated sepiolite is 2.86 mmol: (0.3~0.6) g;

[0027] Preferably, the eluent used for elution is a 1 mol / L hydrochloric acid solution.

[0028] According to the present invention, the above-mentioned sepiolite-based lithium-ion imprinted polymer is used for the adsorption and separation of lithium ions in low-grade brine.

[0029] According to the present invention, preferably, the specific adsorption separation method is as follows: under the conditions of temperature 25~45℃ and pH 2.0~12.0, sepiolite-based lithium-ion imprinted polymer is added to low-grade brine containing lithium ions for lithium ion adsorption separation, and the dosage is 0.5~1.5g of sepiolite-based lithium-ion imprinted polymer per liter of low-grade brine.

[0030] The advantages of this invention are as follows:

[0031] 1. This invention uses bromide-modified crown ether as a lithium ion recognition monomer, which can form a relatively stable coordination structure with lithium ions, thereby constructing recognition sites that match lithium ions and improving the selective adsorption performance of the material for lithium ions.

[0032] 2. This invention uses sepiolite as an inorganic carrier, which can improve the mechanical stability, specific surface area and mass transfer performance of the imprinted polymer, and increase the number of adsorption sites.

[0033] 3. This invention adjusts the amount of sepiolite added, screens out the optimal amount of sepiolite added, and then further optimizes the amount of crosslinking agent added to achieve a better balance between material structural stability and adsorption performance.

[0034] 4. The sepiolite-based lithium-ion imprinted polymer of the present invention has good adsorption capacity and adsorption selectivity for lithium ions in low-grade brine, and has good regeneration and recycling performance. Attached Figure Description

[0035] Figure 1 SEM images of the acid-modified sepiolite and different sepiolite-based lithium-ion imprinted polymers of the present invention.

[0036] Figure 2 The diagram shows the adsorption performance of the sepiolite-based lithium-ion imprinted polymer of the present invention.

[0037] Figure 3 The graph shows the lithium-ion adsorption performance of the sepiolite-based lithium-ion imprinted polymer after cyclic adsorption-desorption. Detailed Implementation

[0038] This invention provides a sepiolite-based lithium-ion imprinted polymer, its preparation method, and its application in the adsorption and separation of lithium ions in low-grade brine. Using sepiolite, a natural mineral raw material, as a carrier, and in synergy with modified crown ether, the resulting sepiolite-based lithium-ion imprinted polymer exhibits good selective adsorption performance and cycle stability for lithium ions. The preparation method is also convenient.

[0039] Sepiolite is a silicate mineral with a one-dimensional fibrous structure, characterized by high abundance, low cost, wide availability, and environmental friendliness. Its unique structure and chemical composition endow it with a large specific surface area, abundant pore structure, and good mechanical stability, and its surface contains numerous active groups. This invention uses sepiolite as a carrier for modified crown ethers to prepare lithium-ion imprinted polymers for lithium ion adsorption. On one hand, its open nanoscale pore structure aligned with the fiber direction provides directionality, guiding lithium ions along the fiber axis for directional transfer, reducing energy loss and random diffusion during mass transfer. This provides an efficient diffusion path for lithium ions, reducing mass transfer resistance, and allowing lithium ions to quickly enter the material and contact the modified crown ether imprinted sites, thus increasing the adsorption rate. On the other hand, sepiolite's high specific surface area provides numerous loading sites for the modified crown ether, increasing the density of imprinted sites and thereby improving the lithium ion adsorption capacity. Furthermore, the structural stability of sepiolite ensures the continuity of the energy transfer process, preventing material structural collapse or performance degradation. The confined space of sepiolite and the coordination effect of modified crown ethers can synergistically enhance the selectivity for lithium ions. Therefore, using sepiolite as an inorganic framework to construct sepiolite-based lithium-ion imprinted polymers helps to improve the structural stability, dispersibility, and adsorption-mass transfer performance of the materials.

[0040] The sepiolite-based lithium-ion imprinted polymer of the present invention uses acid-activated sepiolite as a carrier, and a modified crown ether polymer is attached to the surface of the carrier.

[0041] In one or more preferred embodiments, the modified crown ether polymer is obtained by polymerization of propylene bromide modified crown ether as monomer and ethylene glycol dimethacrylate as crosslinking agent; preferably, the crown ether is 2-(hydroxymethyl)-12-crown ether-4.

[0042] According to the present invention, sepiolite-based lithium-ion imprinted polymers with different proportions can be prepared by controlling the amount of sepiolite and crosslinking agent added.

[0043] In one or more preferred embodiments, the mass ratio of the carrier to the modified crown ether polymer is (0.3~0.6) g: (7~20) g, preferably (0.4~0.6): 13.5, and most preferably 0.5: 13.5.

[0044] According to the present invention, sepiolite-based lithium-ion imprinted polymers are preferably prepared using lithium nitrate as a template, crown ether as a recognition ligand, ethylene glycol dimethacrylate as a crosslinking agent, and azobisisobutyronitrile as an initiator.

[0045] In one or more preferred embodiments, the preparation method of the above-mentioned sepiolite-based lithium-ion imprinted polymer includes the following steps:

[0046] (1) After grinding the sepiolite, it was immersed in an acid solution for activation treatment, washed and dried to obtain acid-activated sepiolite;

[0047] (2) 2-(hydroxymethyl)-12-crown ether-4 was modified with bromopropene under alkaline conditions to obtain a modified crown ether;

[0048] (3) In an organic solvent, acid-activated sepiolite and modified crown ether are mixed, lithium ion template is added, and crosslinking polymerization is carried out in the presence of crosslinking agent and initiator. After the lithium ion template is washed off the product, it is washed with water and dried to obtain sepiolite-based lithium ion imprinted polymer.

[0049] According to the present invention, sepiolite is acidified to remove impurities on its surface and in its pores, improve the pore structure, increase the specific surface area and surface active sites such as silanol groups, so that the surface of sepiolite has more active sites that can participate in subsequent reactions, which is conducive to the uniform formation of imprinted polymers on the surface of sepiolite and improves the structural stability and recognition and adsorption performance of composite materials.

[0050] In one or more preferred embodiments, the acid solution in step (1) is a 1 mol / L hydrochloric acid solution;

[0051] Preferably, the activation treatment involves immersing sepiolite in an acid solution, ultrasonicating, and then stirring at 50°C for 18 hours.

[0052] According to the present invention, 2-(hydroxymethyl)-12-crown ether-4 is modified with bromopropene to introduce polymerizable unsaturated double bonds into the crown ether molecule, thereby enabling the crown ether molecule to participate in free radical polymerization. The modified crown ether retains its specific coordination recognition ability for lithium ions and can also participate in free radical polymerization reactions as a functional monomer. It can also copolymerize with a crosslinking agent to form a stable polymer network, fix the crown ether recognition sites, and improve the structural stability of the imprinted polymer, the uniformity of the recognition sites, and the selective recognition and adsorption performance of lithium ions.

[0053] In one or more preferred embodiments, in step (2), the molar ratio of 2-(hydroxymethyl)-12-crown ether-4 and bromopropene is 1:1.2;

[0054] Preferably, the modification reaction is carried out in an N,N-dimethylformamide solution with an alkaline pH of 11-13, under a nitrogen atmosphere at 30°C with stirring, for a reaction time of 6 hours.

[0055] Preferably, after the modification reaction is completed, the pH is adjusted to 7 with acid, and the modified crown ether is obtained by dichloromethane extraction.

[0056] According to the present invention, using lithium nitrate as a template, ethylene glycol dimethacrylate as a crosslinking agent, and azobisisobutyronitrile as an initiator, the modified crown ether is polymerized in situ on the surface of acid-activated sepiolite, so that the modified crown ether polymer is attached to the surface of acid-activated sepiolite.

[0057] In one or more preferred embodiments, in step (3), the lithium-ion template is lithium nitrate, the organic solvent is methanol, the crosslinking agent is ethylene glycol dimethacrylate, and the initiator is azobisisobutyronitrile;

[0058] Preferably, the molar ratio of lithium ions to crosslinking agent is 1:(10~30); the modified crown ether and crosslinking agent are total monomers, and the molar amount of initiator is 1% of the total monomer molar amount;

[0059] Preferably, the molar ratio of modified crown ether to acid-activated sepiolite is 2.86 mmol:(0.3~0.6) g, more preferably 2.86 mmol:(0.4~0.6) g, and most preferably 2.86 mmol:0.5 g;

[0060] Preferably, the eluent used for elution is a 1 mol / L hydrochloric acid solution.

[0061] According to a preferred embodiment of the method for preparing sepiolite-based lithium-ion imprinted polymers of the present invention, the method includes the following steps:

[0062] (1) After grinding the sepiolite, it was immersed in an acid solution, sonicated, stirred at 50°C for 18 hours, centrifuged, washed with deionized water until neutral, and dried in an oven at 105°C for 10 hours to obtain acid-activated sepiolite.

[0063] (2) Take N,N-dimethylformamide solution into a three-necked flask, add 2-(hydroxymethyl)-12-crown ether-4 under alkaline conditions, stir for 15 min under nitrogen atmosphere, add bromopropene solution, reflux and stir at 30℃ for 6 h to obtain modified crown ether;

[0064] (3) Take the modified crown ether in an organic solvent, add the lithium ion template, stir to dissolve, add the acid-activated sepiolite, purge with nitrogen, add the crosslinking agent and initiator, reflux and stir at 65°C for 24 h, wash with methanol after the reaction is complete to obtain the crude product; immerse the crude product in the eluent to elute the lithium ion template, wash with deionized water until neutral, freeze dry to obtain the sepiolite-based lithium ion imprinted polymer.

[0065] According to the present invention, the above-mentioned sepiolite-based lithium-ion imprinted polymer is used for the adsorption and separation of lithium ions in low-grade brine.

[0066] In one or more preferred embodiments, the specific adsorption separation method is as follows: under the conditions of temperature 25~45℃ and pH 2.0~12.0, sepiolite-based lithium-ion imprinted polymer is added to a lithium-ion solution for lithium-ion adsorption and separation. The dosage is 0.5~1.5g of sepiolite-based lithium-ion imprinted polymer per liter of wastewater. The reaction is carried out in a water bath with shaking for 0~2h at a shaking speed of 160r / min.

[0067] The present invention will be further described below with reference to specific embodiments and accompanying drawings. These embodiments are merely descriptions of preferred embodiments of the present invention, but do not limit the content described below.

[0068] Example 1

[0069] A method for preparing a sepiolite-based lithium-ion imprinted polymer includes the following steps:

[0070] (1) Take 2g of sepiolite, grind it, immerse it in 100mL of 1mol / L hydrochloric acid solution, sonicate for 15min, stir at 50℃ for 18h, centrifuge, wash with deionized water until neutral, and dry in an oven at 105℃ for 10h to obtain acid-activated sepiolite.

[0071] (2) Take 60 mL of N,N-dimethylformamide solution into a three-necked flask, adjust the pH to 11~13 with sodium hydroxide, add 0.5 mL of 2-(hydroxymethyl)-12-crown ether-4, stir for 15 min under a nitrogen atmosphere, add 0.3 mL of bromopropene, reflux and stir at 30 °C for 6 h, after the reaction, add 1 mol / L hydrochloric acid to adjust the pH to 7, add an appropriate amount of dichloromethane for extraction, and obtain the modified crown ether by rotary evaporation.

[0072] (3) Take the modified crown ether obtained in step (2) into 60 ml of methanol, add 0.22 g of lithium nitrate as a template, stir at room temperature for 30 min, add 0.5 g of acid-activated sepiolite, purge with nitrogen, add 12 mL of crosslinking agent ethylene glycol dimethacrylate and 0.13 g of initiator azobisisobutyronitrile, reflux and stir at 65 °C for 24 h, the molar ratio of lithium ions to crosslinking agent is 1:20, and the amount of initiator is 1% of the total monomer. After the reaction is complete, wash with methanol to obtain the crude product. Immerse the crude product in 1 mol / L hydrochloric acid solution and elute repeatedly until the lithium ions are completely eluted. Wash with deionized water until neutral, freeze dry to obtain sepiolite-based lithium ion imprinted polymer.

[0073] Example 2

[0074] The preparation method of the sepiolite-based lithium-ion imprinted polymer described in Example 1 differs from the following:

[0075] In step (3), the amount of acid-activated sepiolite added is 0.3g, and the amounts used in the remaining reactions are exactly the same as in Example 1.

[0076] Example 3

[0077] The preparation method of the sepiolite-based lithium-ion imprinted polymer described in Example 1 differs from the following:

[0078] In step (3), the amount of acid-activated sepiolite added is 0.4g, and the amounts used in the remaining reactions are exactly the same as in Example 1.

[0079] Example 4

[0080] The preparation method of the sepiolite-based lithium-ion imprinted polymer described in Example 1 differs from the following:

[0081] In step (3), the amount of acid-activated sepiolite added is 0.6g, and the amounts used in the remaining reactions are exactly the same as in Example 1.

[0082] Example 5

[0083] The preparation method of the sepiolite-based lithium-ion imprinted polymer described in Example 1 differs from the following:

[0084] In step (3), the molar ratio of lithium ions to crosslinking agent is 1:10, and the remaining reactions are carried out in the same amounts as in Example 1.

[0085] Example 6

[0086] The preparation method of the sepiolite-based lithium-ion imprinted polymer described in Example 1 differs from the following:

[0087] In step (3), the molar ratio of lithium ions to crosslinking agent is 1:30, and the remaining reactions are carried out in the same amounts as in Example 1.

[0088] Experimental Example 1

[0089] The sepiolite-based lithium-ion imprinted polymer synthesized as described above is used for lithium-ion adsorption. The specific application method is as follows:

[0090] Prepare a 200 mg / L lithium nitrate solution, take 20 mL and place it in an Erlenmeyer flask, add 0.02 g of sepiolite-based lithium-ion imprinted polymer (using Examples 1-4 as one group of experiments, and Examples 1 and 5-6 as another group of experiments), place it in a constant temperature water bath shaker, and shake at a speed of 160 r / min and a reaction temperature of 25 °C for 0-2 h.

[0091] The adsorption effects of adsorbents with different amounts of sepiolite in Examples 1-4 on lithium ions are shown in Table 1. The adsorption effects of adsorbents with different amounts of crosslinking agent in Examples 1 and 5-6 on lithium ions are shown in Table 2.

[0092] Table 1. Adsorption effect of adsorbents with different amounts of sepiolite on lithium ions.

[0093]

[0094] Table 2. Adsorption effect of adsorbents with different amounts of crosslinking agent on lithium ions.

[0095]

[0096] Table 1 shows that different amounts of sepiolite have a significant impact on the adsorption performance of the material. As the amount of sepiolite added increases from 0.3 g to 0.5 g, the adsorption capacity gradually increases; however, when the amount of sepiolite added continues to increase to 0.6 g, the adsorption capacity decreases. This indicates that an appropriate amount of sepiolite is beneficial for improving the material structure and site exposure, while excessive sepiolite may lead to uneven polymerization and affect the adsorption performance.

[0097] Table 2 shows that when the amount of crosslinking agent is low, the degree of polymer crosslinking is insufficient, making it difficult to effectively fix the recognition sites formed by template ions and functional monomers. As the amount of crosslinking agent increases, the adsorption capacity increases to 20.39 mg / g, the spatial configuration of the imprinted sites is better maintained, the stability and recognition ability of the material are enhanced, and the adsorption capacity is improved. When the amount of crosslinking agent continues to increase, the excessive degree of crosslinking makes the polymer network too dense, reducing the channels and active sites, which restricts the mass transfer and binding of lithium ions, resulting in a decrease in adsorption capacity.

[0098] Experimental Example 2

[0099] The selectivity coefficients of the sepiolite-based lithium-ion imprinted polymer Sep-Li-IIP-2 prepared in Example 1 for different metal ions are shown in Table 3.

[0100] Table 3 Selectivity coefficients of Sep-Li-IIP-2 for different metal ions

[0101]

[0102] As shown in Table 3, the sepiolite-based lithium-ion imprinted polymer prepared in this invention exhibits good performance against Li... + Relative to Na + K + Mg 2+ and Ca 2+The material exhibits a high selectivity coefficient, indicating its significant preferential recognition and adsorption capacity for lithium ions in the presence of multiple coexisting ions. The results demonstrate that the material forms imprinted sites with size and coordination matching characteristics for lithium ions. Because coexisting ions differ from Li⁺ in ionic radius, charge number, and coordination behavior, they are difficult to match well with the imprinted sites, thus the material preferentially adsorbs Li⁺. The introduction of sepiolite improves the pore structure and mass transfer performance of the material, making the imprinted sites more readily contactable with lithium ions in solution, thereby further improving the material's recognition efficiency in complex ionic systems. These results demonstrate that the sepiolite-based lithium-ion imprinted polymer prepared in this invention can achieve effective selective separation of lithium ions in low-grade brine systems.

[0103] Experimental Example 3

[0104] SEM images of acid-modified sepiolite and samples prepared under different sepiolite addition conditions are shown below. Figure 1 As shown in Figure a, where a represents acid-modified sepiolite, and b-d represent the products when the acid-modified sepiolite addition amounts are 0.4g, 0.5g, and 0.6g, respectively. Figure a shows that the acid-modified sepiolite exhibits a distinct fibrous bundle or needle-like structure with a relatively smooth surface and uniform length, displaying the typical natural fibrous morphology of sepiolite, indicating that the acid modification treatment did not destroy the basic skeletal structure of sepiolite. After polymerization, the surface morphology of the samples changed significantly, with a large number of spherical or clustered polymer particles adhering to the sepiolite surface, indicating that the imprinted polymer was successfully loaded onto the sepiolite surface (Figures b and d). Figure b shows that when the sepiolite addition amount is 0.4g, many polymer spherical particles are formed on the sample surface, with significant particle accumulation and severe local agglomeration. The sepiolite fiber skeleton is not clearly defined after being coated by the polymer, indicating that at low sepiolite addition amounts, the dispersion and loading effect on the polymer is limited, which is not conducive to the full exposure of recognition sites and the mass transfer process. As shown in Figure c, when the sepiolite content is 0.5 g, the overall morphology of the sample is relatively uniform, the polymer particle size is relatively consistent, the degree of agglomeration is reduced, the composite structure is relatively loose, and the bonding between sepiolite and polymer is good. This indicates that sepiolite can effectively serve as a framework and dispersion carrier, promoting uniform loading of the imprinted polymer and forming a more suitable surface structure. This morphological feature is beneficial to increasing the exposure of effective adsorption sites and improving the diffusion and mass transfer of lithium ions within the material. When the sepiolite content is 0.6 g (Figure d), more exposed sepiolite fiber bundles are observed, and the polymer adhesion is uneven in some areas, resulting in poor composite continuity. This indicates that as the sepiolite content further increases, the proportion of sepiolite in the system becomes too high, affecting the uniform growth of the polymer on the carrier surface, leading to insufficient local coating or uneven distribution of the recognition layer, thus reducing the number and accessibility of effective imprinted sites.

[0105] Test Example 4

[0106] The adsorption capacity of the sepiolite-based lithium-ion imprinted polymers prepared in Examples 1-4 over time was tested, such as... Figure 2 As shown. By Figure 2 It can be seen that the adsorption capacity of different lithium-ion imprinted polymers gradually increases with time and eventually tends to equilibrium. However, there are significant differences in the adsorption rate and final equilibrium adsorption capacity of samples under different sepiolite addition amounts. Among them, the adsorbent with a sepiolite addition of 0.5g exhibits the fastest adsorption rate in the initial stage of adsorption, reaching a high adsorption capacity in a short time and tending to adsorption equilibrium first, while also having the highest equilibrium adsorption capacity. This indicates that the diffusion process of lithium ions from the bulk solution to the adsorbent surface and further to the internal recognition sites is smoother in this adsorbent, with lower internal mass transfer resistance and higher accessibility to recognition sites, thus exhibiting superior adsorption kinetics performance. Adsorbents with sepiolite additions of 0.3g and 0.4g also show certain rapid adsorption characteristics, but their overall adsorption rate and final adsorption capacity are lower than those of the 0.5g adsorbent. This indicates that when the sepiolite addition amount is low, the supporting and dispersing effect of sepiolite on the imprinted polymer is insufficient, and the polymer is prone to accumulation or agglomeration, thereby affecting the diffusion mass transfer efficiency of lithium ions to the recognition sites. When the amount of sepiolite added increased to 0.6 g, the adsorption rate of the sample decreased significantly, and the equilibrium adsorption capacity was also low. This indicates that when the amount of sepiolite added is too high, the proportion of inorganic framework in the system is too large, which may lead to insufficient formation of the polymer imprinted layer or uneven distribution of recognition sites, thereby increasing the diffusion resistance of lithium ions and hindering the adsorption process. Therefore, the introduction of an appropriate amount of sepiolite helps to improve the pore structure and surface morphology of the composite material, increase the exposure of imprinted sites, and shorten the mass transfer path of lithium ions during the adsorption process. Among them, when the amount of sepiolite added is 0.5 g, the material exhibits the fastest adsorption rate and the highest equilibrium adsorption capacity, indicating that the material has the best mass transfer performance and adsorption kinetics characteristics under this condition.

[0107] Experimental Example 5

[0108] The sepiolite-based lithium-ion imprinted polymer Sep-Li-IIP-2 prepared in Example 1 was used for a regeneration experiment. The regeneration solution was 1M HCl. The adsorption-saturated sepiolite-based lithium-ion imprinted polymer Sep-Li-IIP-2 underwent five lithium-ion adsorption-desorption processes. The adsorption effect of each adsorption process was as follows: Figure 3 As shown. By Figure 3It is evident that the sepiolite-based lithium-ion imprinted polymer prepared in this invention maintains a high lithium-ion adsorption capacity after five adsorption-desorption cycles, retaining an adsorption performance of over 90%, indicating that the material possesses excellent recyclability and structural stability. Hydrochloric acid solution effectively removes adsorbed lithium ions without damaging the polymer cross-linking network and its specific recognition structure. The sepiolite, acting as a supporting inorganic framework, enhances the material's mechanical strength and mitigates structural collapse and site loss during repeated use, thus enabling the material to maintain good adsorption performance even after multiple cycles.

[0109] The above results demonstrate that the sepiolite-based lithium-ion imprinted polymer of the present invention not only has a high selective adsorption capacity for lithium ions, but also has good reusability, which can effectively reduce material consumption and operating costs in the adsorption and separation process, and can be applied to a certain extent to the extraction of lithium resources from low-grade brine.

Claims

1. A sepiolite-based lithium-ion imprinted polymer, characterized in that, This sepiolite-based lithium-ion imprinted polymer uses acid-activated sepiolite as a carrier, with a modified crown ether polymer attached to the carrier surface.

2. The sepiolite-based lithium-ion imprinted polymer according to claim 1, characterized in that, The modified crown ether polymer is obtained by polymerization of propylene bromide modified crown ether as monomer and ethylene glycol dimethacrylate as crosslinking agent; preferably, the crown ether is 2-(hydroxymethyl)-12-crown ether-4.

3. The sepiolite-based lithium-ion imprinted polymer according to claim 1, characterized in that, The mass ratio of the carrier to the modified crown ether polymer is (0.3~0.6) g : (7~20) g.

4. A method for preparing the sepiolite-based lithium-ion imprinted polymer according to any one of claims 1-3, comprising the following steps: (1) After grinding the sepiolite, it was immersed in an acid solution for activation treatment, washed and dried to obtain acid-activated sepiolite; (2) 2-(hydroxymethyl)-12-crown ether-4 was modified with bromopropene under alkaline conditions to obtain a modified crown ether; (3) In an organic solvent, acid-activated sepiolite and modified crown ether are mixed, lithium ion template is added, and crosslinking polymerization is carried out in the presence of crosslinking agent and initiator. After the lithium ion template is washed off the product, it is washed with water and dried to obtain sepiolite-based lithium ion imprinted polymer.

5. The method for preparing the sepiolite-based lithium-ion imprinted polymer according to claim 4, characterized in that, In step (1), the acid solution is a 1 mol / L hydrochloric acid solution; Preferably, the activation treatment involves immersing sepiolite in an acid solution, ultrasonicating, and then stirring at 50°C for 18 hours.

6. The method for preparing the sepiolite-based lithium-ion imprinted polymer according to claim 4, characterized in that, In step (2), the molar ratio of 2-(hydroxymethyl)-12-crown ether-4 to bromopropene is 1:1.2; Preferably, the modification reaction is carried out in an N,N-dimethylformamide solution with an alkaline pH of 11-13, under a nitrogen atmosphere at 30°C with stirring, for a reaction time of 6 hours. Preferably, after the modification reaction is completed, the pH is adjusted to 7 with acid, and the modified crown ether is obtained by dichloromethane extraction.

7. The method for preparing the sepiolite-based lithium-ion imprinted polymer according to claim 4, characterized in that, In step (3), the lithium-ion template is lithium nitrate, the organic solvent is methanol, the crosslinking agent is ethylene glycol dimethacrylate, and the initiator is azobisisobutyronitrile.

8. The method for preparing the sepiolite-based lithium-ion imprinted polymer according to claim 4, characterized in that, The molar ratio of lithium ions to crosslinking agent is 1:(10~30); the modified crown ether and crosslinking agent are the total monomers, and the molar amount of initiator is 1% of the total monomer molar amount; Preferably, the molar ratio of modified crown ether to acid-activated sepiolite is 2.86 mmol: (0.3~0.6) g; Preferably, the eluent used for elution is a 1 mol / L hydrochloric acid solution.

9. The application of the sepiolite-based lithium-ion imprinted polymer according to any one of claims 1-3, characterized in that, Used for the adsorption and separation of lithium ions in low-grade brine.

10. The application according to claim 1, characterized in that, The specific adsorption and separation method is as follows: under the conditions of temperature 25~45℃ and pH 2.0~12.0, sepiolite-based lithium-ion imprinted polymer is added to low-grade brine containing lithium ions for lithium ion adsorption and separation. The dosage is 0.5~1.5g of sepiolite-based lithium-ion imprinted polymer per liter of low-grade brine.

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