Method for removing thallium element in water by using modified zeolite

Abstract

The invention relates to the technical field of environmental engineering water treatment, in particular to a method for removing thallium element in water through modified zeolite. The invention aims to solve the technical bottlenecks that when the existing zeolite adsorbent is used for removing thallium, solid-liquid separation is difficult, and the selective adsorption capacity on trace thallium is limited. Therefore, the invention creatively provides a composite treatment method integrating magnetic separation, multistage pore channel adsorption and biological enhancement. The preparation method is characterized in that firstly, a core-shell structure composite material with magnetic Fe3O4 as a core, natural zeolite as a middle layer and an MOF material as a shell layer is prepared through a hydrothermal synthesis and coprecipitation technology, and the material has magnetic response, high specific surface area and high affinity to thallium ions; secondly, performing functional modification on the surface of the composite material, and directionally mounting a specific thallium removal biological membrane to construct an adsorption-biotransformation synergistic system;

Description

Technical Field

[0001] This invention relates to the field of environmental engineering water treatment technology, specifically to a method for removing thallium from water using modified zeolite. Background Technology

[0002] Thallium is a rare, dispersed metallic element with extremely high biotoxicity. Its compounds can enter the environment through water bodies and accumulate in organisms, causing severe damage to the nervous and digestive systems, and even death. With the development of non-ferrous metallurgy, electronics manufacturing, and other industrial activities, thallium pollution incidents in water bodies occur frequently, posing a serious threat to drinking water safety and ecological health. my country's "Surface Water Environmental Quality Standard" (GB 3838-2002) clearly stipulates that the limit for thallium in specific projects at centralized drinking water surface water sources is 0.1 µg / L, placing extremely high demands on water treatment technologies.

[0003] Currently, the removal technology for trace thallium in water mainly revolves around chemical oxidation precipitation and adsorption methods. For example, Chinese invention patent application number 201410186418.6 discloses a method for removing trace thallium from water. This method utilizes the strong oxidizing properties of ferrates to convert monovalent thallium into easily precipitable trivalent thallium, while its reduction product, ferric hydroxide, acts as an adsorption and co-precipitation agent. The process is simple and rapid. However, this method relies on the continuous addition of chemical agents, resulting in a large amount of thallium-containing sludge, and its stability in deep purification of different forms of thallium in complex water bodies needs improvement. Chinese invention patent CN118105950A focuses on developing high-performance adsorption materials. By modifying organic salts with low-carbon alcohols and combining them with natural minerals, a material with high adsorption capacity and selectivity for thallium was obtained. This material shows outstanding performance in efficient adsorption, but it still faces challenges such as difficulties in solid-liquid separation of powder materials, high recovery costs, and limited application in dynamic water flow systems. In addition, although existing zeolite materials have ion exchange capabilities, their selective adsorption capacity for trace thallium is nearing its limit, making it difficult to meet increasingly stringent emission standards.

[0004] In summary, current technology urgently needs a new material and method for thallium removal that can simultaneously achieve efficient adsorption, easy separation and recovery, and adaptability to large-scale water treatment scenarios. Against this backdrop, this invention aims to overcome the limitations of single technologies by developing an innovative thallium removal technology that integrates rapid magnetic separation, efficient mass transfer adsorption through multi-level pores, and selective enhancement via biofilm through material structural design and functional integration. This technology will provide a more economical and thorough solution to the problem of trace thallium pollution in water bodies. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing zeolite adsorbents and thallium removal technologies in terms of adsorption capacity, selectivity, and solid-liquid separation efficiency, and to provide a highly efficient, easily recyclable, and scalable method for thallium removal. Specifically, the invention aims to construct a core-shell composite material that combines a magnetic core, a zeolite intermediate layer, and a MOF shell, and couple it with a specific biomembrane to achieve a synergistic effect of rapid magnetic separation, efficient adsorption through multi-level pores, and enhanced bioselectivity, thereby achieving deep and stable removal of trace and low-concentration thallium from water.

[0006] To achieve the above objectives, the present invention provides a method for removing thallium from water using modified zeolite, comprising the following steps: S1. Preparation of magnetic MOF-zeolite core-shell composite material: Using magnetic Fe3O4 nanoparticles synthesized by coprecipitation method as the core, a layer of natural zeolite modified with silane coupling agent is coated on its surface by hydrothermal synthesis to form magnetic zeolite microspheres; then, using the magnetic zeolite microspheres as a carrier, an MOF material shell is constructed on its outermost layer by in-situ growth method to obtain a composite material with a core-shell structure. S2. Surface functionalization and biofilm formation of composite material: The composite material obtained in step S1 is immersed in a polymer solution rich in carboxyl groups for surface grafting modification; then, it is placed in an enrichment culture medium containing specific thallium-removing functional bacteria and biofilm formation is carried out under aeration or shaking conditions until a stable biofilm is formed on the surface of the composite material. The specific thallium-removing functional bacteria are microorganisms that are tolerant to and have the ability to accumulate thallium. S3. Adsorption treatment and magnetic separation: The modified zeolite composite material loaded with biofilm prepared in step S2 is added to the thallium-containing water to be treated at a dosage of 0.1-5.0 g / L. The reaction is carried out for 10-60 minutes at a pH of 6.0-9.0 and a stirring rate of 100-300 r / min. After the reaction is completed, an external magnetic field is applied to quickly separate the adsorbed saturated composite material from the water, thus completing the removal of thallium.

[0007] Preferably, in step S1, the natural zeolite is clinoptilolite or mordenite, with a silica-to-alumina ratio greater than 5; the silane coupling agent is γ-aminopropyltriethoxysilane or γ-(2,3-epoxypropoxy)propyltrimethoxysilane; the MOF material is selected from ZIF-8, MIL-101(Fe), or UiO-66; the MOF material shell has a microporous and / or mesoporous structure, and its BET specific surface area is not less than 300 m². 2 / g, preferably 500-1500m 2 / g, with a main pore size distribution range of 0.5-3.0nm, which is beneficial for size screening and confined adsorption of thallium ions and their hydrated ions.

[0008] Preferably, in step S1, the specific process of constructing a MOF material shell on its outermost layer by in-situ growth is as follows: dispersing magnetic zeolite microspheres in a precursor solution containing metal ions and organic ligands, and reacting at 60-120°C for 4-24 hours; wherein the metal ions are Zn. 2+ Fe 3+ or Zr 4+ Any one of the following; the organic ligand is any one of 2-methylimidazole, terephthalic acid, or trimesic acid.

[0009] Preferably, the magnetic MOF-zeolite core-shell composite material obtained in step S1 has a particle size distribution of 50 nm-5 μm and a specific surface area of ​​300-800 m². 2 / g, saturation magnetization greater than 20 emu / g, thickness 10-200 nm.

[0010] Preferably, in step S2, the carboxyl-rich polymer is any one of sodium alginate, polyacrylic acid, or polyethyleneimine-polyacrylic acid copolymer, with an immersion concentration of 0.5-5 wt% and an immersion time of 2-12 hours.

[0011] Preferably, in step S2, the conditions for biofilm formation are: temperature 25-35°C, pH 6.5-8.0, dissolved oxygen concentration greater than 2 mg / L, and biofilm formation period of 7-14 days.

[0012] Preferably, in step S3, the initial concentration of thallium in the thallium-containing water is 0.1-100 µg / L, and the forms include monovalent thallium ions, trivalent thallium ions, and their organic or inorganic complexes.

[0013] Preferably, the composite material has a core-shell structure, comprising, from the inside out, a magnetic Fe3O4 core, a modified natural zeolite intermediate layer, and a MOF material shell, with the outermost MOF shell surface grafted with a functional polymer and loaded with a thallium removal biofilm.

[0014] Preferably, the microorganisms contained in the biofilm are capable of converting thallium ions through extracellular adsorption, intracellular enrichment, or redox reactions, and the extracellular polymers secreted by them contain carboxyl, hydroxyl, and phosphate groups that can complex with thallium ions.

[0015] Preferably, the composite material separated in step S3 can be eluted and regenerated using a dilute acid solution. After the regenerated composite material is activated into a biofilm using a culture medium, it can be reused in the thallium removal process for at least 5 cycles. The dilute acid solution is a nitric acid or hydrochloric acid solution with a concentration of 0.1-1.0 mol / L, and the elution time is 1-4 hours. The culture medium used for biofilm activation is a thallium removal functional bacterial enrichment culture medium for biofilm attachment, and the activation time is 12-48 hours.

[0016] Source of microorganisms: Functional microorganisms can be collected from natural environments that have been contaminated with thallium for a long time or from activated sludge in industrial wastewater treatment systems. For example, bottom sediment or activated sludge near the wastewater discharge outlet of a lead-zinc mine smelter can be collected as the initial source of microorganisms.

[0017] Microbial domestication: Culture medium: Inorganic salt culture medium was used, with the following basic composition (g / L): KH2PO4 0.5, K2HPO4 0.5, NH4Cl 0.5, MgSO4·7H2O 0.2, NaCl 0.5, and trace element solution 1 mL, with sodium acetate (1.0 g / L) as the main carbon and energy source.

[0018] Acclimation process: The collected bacterial strains are inoculated into the above-mentioned culture medium. Initially, no thallium is added, and the culture is carried out at 30°C and 120 rpm with shaking for 2-3 days to allow the microorganisms to recover. Subsequently, thallium chloride (TlCl) is gradually added during subculture, with an initial concentration of 0.5 mg / L (calculated as Tl). Every 2-3 subcultures, the thallium concentration is increased by 0.5-1.0 mg / L until the bacterial community can grow stably at a thallium concentration of 5-10 mg / L and shows a significant ability to remove thallium. The entire acclimation cycle usually lasts 30 to 60 days. This process can enrich functional microorganisms that are thallium tolerant and can fix thallium ions through extracellular adsorption, intracellular enrichment, or redox reactions, such as Pseudomonas, Bacillus, and Thiobacillus, which are common in heavy metal-polluted environments.

[0019] During the acclimatization process of the functional microbial community, the growth curve of the microbial community and the removal rate of thallium can be monitored regularly to determine the optimal acclimatization endpoint; the acclimatized microbial community can be stored in glycerol tubes at 4°C for subsequent biofilm application.

[0020] Biofilm attachment: The above-mentioned domesticated and mature functional bacterial groups are collected by centrifugation and resuspended in fresh inorganic salt culture medium (which may contain a low concentration of thallium, such as 0.1-0.5 mg / L, to maintain bacterial activity) to prepare a bacterial suspension; the surface-functionalized magnetic MOF-zeolite composite material is immersed in the bacterial suspension and cultured for 7-14 days at 25-35°C, pH 6.5-8.0, and continuous micro-aeration (dissolved oxygen >2 mg / L); during this period, fresh bacterial solution and nutrients are regularly replaced or replenished. When a visible slippery mucus forms on the surface of the composite material and a dense microbial aggregation structure can be observed under a microscope, it indicates that a stable thallium-removing biofilm has been successfully attached.

[0021] The following are the main technical solutions of this invention: We abandoned the approach of simply modifying zeolite or using a single MOF material, and instead constructed a hierarchically functionalized core-shell composite material consisting of a magnetic core, a zeolite intermediate layer, and a MOF shell. The magnetic Fe3O4 core ensures that solid-liquid separation can be achieved within seconds using an external magnetic field after treatment, fundamentally solving the problem of powder adsorbent recovery. The intermediate modified zeolite layer not only serves as a supporting framework, but its inherent ion exchange properties also provide initial adsorption sites. The outermost MOF shell, with its ultra-high specific surface area, adjustable pore size, and abundant unsaturated metal sites, greatly enhances the composite material's physical adsorption capacity and chemical affinity for thallium ions. This multi-level structure, combining rigidity and flexibility, achieves synergistic effects of magnetic recovery, ion exchange, and coordination adsorption.

[0022] A bio-enhancing strategy of "biofilm attachment" was introduced. After the composite material was prepared, a hydrophilic polymer layer was further grafted onto its surface, and a domesticated thallium-removing microbial biofilm was directionally attached. This biofilm is not passive; it is an active "biological processor." Microorganisms, through their secreted extracellular polymers and their own metabolism, can achieve bioadsorption, bioaccumulation, and possible valence state transformation of thallium ions. The presence of the biofilm endows the material with dynamic and selective purification capabilities. Especially for trace amounts of thallium or special complexed thallium that are difficult to completely capture by MOF physicochemical adsorption, biological action provides an important supplementary removal pathway, significantly improving the reliability and stability of deep purification.

[0023] The invention boasts excellent system integration and versatility, organically combining advanced nanocomposite material preparation, surface bioengineering, and water treatment operation units. Modified zeolite serves not only as an adsorbent but also as an ideal carrier for functionalized biofilms. The entire system operates simply, involving only conventional operations such as dosing, stirring, and magnetic separation, making it easily integrated into existing water plant processes or used to construct modular treatment units. The material's inherent magnetic separation properties make it particularly suitable for large-scale, continuous-flow water treatment scenarios, overcoming the technical pain points of traditional fixed-bed clogging and fluidized-bed separation difficulties, thus paving the way for the large-scale application of efficient thallium removal technology.

[0024] Beneficial technical effects of the present invention: 1. This invention achieves a significant increase in adsorption efficiency. By constructing a MOF-zeolite core-shell hierarchical porous structure, the specific surface area of ​​the material is increased by more than an order of magnitude compared to the original zeolite, providing a massive number of adsorption sites. The size sieving effect and coordination of thallium ions by the MOF channels, combined with the ion exchange of the zeolite, form a multiple capture mechanism for thallium. Experiments show that for raw water with thallium concentrations exceeding the standard by several to tens of times, after short-term treatment with the material of this invention, the thallium content can be reduced by 1-2 orders of magnitude, and the effluent indicators are far better than the national standard limit of 0.1 µg / L.

[0025] 2. This invention proposes a novel solid-liquid separation mode. Imbuing the composite material with strong magnetism is key to overcoming its engineering application bottlenecks. After treatment, no complex centrifugation or filtration equipment is needed; a simple magnet is sufficient to achieve complete separation of the composite material and purified water within tens of seconds. This characteristic significantly reduces operating energy consumption and equipment investment, simplifies the operation process, and makes the application of highly efficient adsorbent materials in high-flow-rate water treatment possible, solving the common problem of adsorbent recovery.

[0026] 3. This invention achieves a dual improvement in both deep purification and selectivity. The surface-loaded biofilm is the core of the technology. Functional microorganisms and their secretions can specifically recognize and enrich thallium ions, even altering their valence and form, thus overcoming the selectivity limits that may exist in pure physicochemical adsorption. This synergistic mechanism combining physicochemical adsorption and biotransformation ensures that the system maintains stable and efficient removal performance for trace thallium even under complex aquatic matrix interference, achieving deep and precise purification. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the process flow of the method described in this invention. Detailed Implementation

[0028] Before further describing specific embodiments of the present invention, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments described below; it should also be understood that the terminology used in the embodiments of the present invention is for describing specific embodiments and not for limiting the scope of protection of the present invention. Test methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the respective manufacturers.

[0029] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in this invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by those skilled in the art. In addition to the specific methods, apparatus, and materials used in the embodiments, based on the knowledge of those skilled in the art and the description of this invention, any prior art methods, apparatus, and materials similar to or identical to those described in the embodiments of this invention may be used to implement this invention.

[0030] Unless otherwise stated, the test methods, detection methods and preparation methods disclosed in this invention all adopt conventional techniques in this technical field.

[0031] Unless otherwise specified, all reagents and materials used in the following examples are commercially available analytical grade or chemically pure; all microbiological operations were performed under aseptic conditions; and water quality testing was conducted according to the standard "Determination of 65 Elements in Water by Inductively Coupled Plasma Mass Spectrometry" (HJ 700-2014). The following are the testing standards for other relevant indicators: BET specific surface area: GB / T 19587-2017; particle size distribution: GB / T 19077-2024; saturation magnetization: GB / T 14986-2008.

[0032] Example 1 A method for removing thallium from water using modified zeolite includes the following steps: S1. Preparation of magnetic MOF-zeolite core-shell composite materials: Clinoptilolite powder with a silica-to-alumina ratio of 8 was modified with a 5% γ-aminopropyltriethoxysilane ethanol solution for 2 hours, washed with water, and dried for later use. Fe3O4 magnetic nanoparticles with an average particle size of 100 nm were prepared by co-precipitation. The modified zeolite powder and Fe3O4 nanoparticles were mixed at a mass ratio of 3:1, and a zeolite layer was coated onto the Fe3O4 surface using a hydrothermal method (180°C, 12 h) to form magnetic zeolite microspheres. Subsequently, the magnetic zeolite microspheres were dispersed in a solution containing Zn. 2+ In a methanol solution of zinc nitrate and 2-methylimidazole, where Zn 2+ The concentration of 2-methylimidazole was 0.4 mol / L, the solid-liquid ratio was 1 g:100 mL, and the reaction was carried out at 70°C for 12 hours to construct the MOF material shell (ZIF-8 shell) via in-situ growth. After the reaction, the mixture was washed with ethanol and deionized water and dried under vacuum at 60°C to obtain the magnetic MOF-zeolite composite material (denoted as MZ-1). Characterized by laser particle size analyzer and transmission electron microscopy, its average particle size was approximately 750 nm, and its BET specific surface area was approximately 650 m² / m³. 2 / g, saturation magnetization is about 32 emu / g, and the thickness of the MOF material shell (ZIF-8 shell) is 50nm; S2. Surface functionalization of composite materials and biofilm formation: MZ-1 was immersed in a 1wt% sodium alginate solution for 4 hours, then gently washed with deionized water to remove ungrafted polymer. The composite material was then placed in an enriched culture medium containing thallium-removing functional bacteria for biofilm formation. These functional bacteria were derived from activated sludge from a lead-zinc smelter wastewater treatment system. The bacteria were obtained by gradually increasing the thallium concentration (from 0.5 mg / L to 8 mg / L) for 50 days in an inorganic salt culture medium (composition: KH₂PO₄ 0.5 g / L, K₂HPO₄ 0.5 g / L, NH₄Cl 0.5 g / L, MgSO₄·7H₂O 0.2 g / L, NaCl 0.5 g / L, trace element solution 1 mL / L, sodium acetate 1.0 g / L). The bacteria were dominated by Pseudomonas. Biofilm formation conditions were: temperature 30°C, pH... 7.2 Continuous micro-aeration (dissolved oxygen 6 mg / L), biofilm formation period of 12 days, during which the culture medium is changed every 2 days to maintain bacterial activity; after biofilm formation, a stable grayish-white biofilm forms on the surface of the composite material, and dense bacterial cells can be seen under a microscope. S3. Adsorption treatment and magnetic separation: One L each of raw water from "Zhongkengzhai" with a thallium concentration of 0.8990 µg / L and "Lanbei" with a thallium concentration of 3.2268 µg / L were taken, and 1.0 g / L of MZ-1 composite material loaded with biofilm was added to each. The mixture was reacted for 30 minutes at pH 7.5 and a stirring rate of 200 r / min. After the reaction, a strong magnet (neodymium iron boron with a surface magnetic induction intensity of 450 mT) was brought close to the container wall. Within 30 seconds, the saturated composite material was completely adsorbed onto the magnet surface, achieving solid-liquid separation. The sedimentation time of the separated water samples was different. The supernatant was taken, and the thallium concentration was determined by ICP-MS.

[0033] The detailed process flow diagram is as follows: Figure 1 As shown.

[0034] Example 2 A method for removing thallium from water using modified zeolite includes the following steps: S1. Preparation of magnetic MOF-zeolite core-shell composite materials: Mordenite powder with a silica-to-alumina ratio of 10 was modified with a 3% γ-(2,3-epoxypropoxy)propyltrimethoxysilane ethanol solution for 3 hours, followed by washing and drying. Fe3O4 magnetic nanoparticles (average particle size 80 nm) were prepared using a co-precipitation method. A modified zeolite layer was then coated onto the Fe3O4 surface using a hydrothermal method (190°C, 10 h). Subsequently, the magnetic zeolite microspheres were dispersed in a substrate containing Fe... 3+ In a solution of ferric nitrate and terephthalic acid (H2BDC) in N,N-dimethylformamide (DMF), where Fe 3+The concentration of H2BDC was 0.05 mol / L, the concentration of H2BDC was 0.1 mol / L, the solid-liquid ratio was 1 g:80 mL, and the mixture was hydrothermally reacted at 100°C for 8 hours to grow a MIL-101(Fe) shell in situ. The product was washed with DMF and ethanol and dried at 80°C to obtain a composite material (denoted as MZ-2). Characterized by laser particle size analyzer and transmission electron microscopy, its average particle size was approximately 1.2 μm, and its BET specific surface area was approximately 520 m². 2 / g, saturation magnetization is about 28 emu / g, and the shell thickness of MIL-101(Fe) is 80nm; S2. Surface functionalization of composite materials and biofilm formation: MZ-2 was immersed in a 2wt% polyacrylic acid solution for 6 hours, washed, and then placed in a culture medium containing acclimated thallium-removing functional bacteria for biofilm formation. The functional bacteria were obtained from thallium-contaminated river sediment and acclimated to the same inorganic salt culture medium for 40 days. The bacteria contained Bacillus and Thiobacillus. Biofilm formation conditions: temperature 28°C, pH 7.5, continuous shaking (120 r / min), biofilm formation period 10 days. S3. Adsorption treatment and magnetic separation: Take 1L of raw water from "Zhongkengzhai" and "Lanbei", add 0.5g / L of MZ-2 composite material loaded with biofilm, react for 45 minutes at pH 7.0 and stirring rate of 180r / min, then perform magnetic separation, and test the thallium concentration in the supernatant at different settling times.

[0035] Example 3 A method for removing thallium from water using modified zeolite includes the following steps: S1. Same as in Example 1, to obtain MZ-1 composite material; (Note: The average particle size of MZ-1 is 750 nm, and other parameters are the same as described in Example 1.) S2. Surface functionalization of composite materials and biofilm formation: MZ-1 was immersed in a 2wt% polyacrylic acid solution for 6 hours, washed, and then placed in a culture medium containing acclimated thallium-removing bacteria for biofilm formation. The bacteria were derived from activated sludge from an electronics factory thallium-containing wastewater treatment system, with an acclimation period of 60 days, and were mainly composed of Pseudomonas and Bacillus. Biofilm formation conditions: temperature 32°C, pH 7.0, continuous aeration, and a biofilm formation period of 8 days. S3. Adsorption treatment and magnetic separation: Take 1L of raw water from "Zhongkengzhai" and "Lanbei", add 2.0g / L of MZ-1 composite material loaded with biofilm, react for 20 minutes at pH 8.0 and stirring rate of 200 r / min, then perform magnetic separation and test the thallium concentration in the supernatant at different settling times.

[0036] Example 4 Take 5g of the MZ-1 composite material of the loaded biofilm, which was saturated with adsorption and magnetically separated in Example 1, and soak it in 0.5mol / L dilute nitric acid solution for 2 hours to elute thallium. After elution, wash it with deionized water until neutral. Then, immerse the material in fresh thallium-removing functional bacterial enrichment culture medium and activate it at 30°C under micro-aeration for 24 hours to restore biofilm activity. The regenerated material is added at a dosage of 1.0g / L to treat 1L of "Lanbei" raw water with a thallium concentration of 3.2268µg / L, under the same conditions as in Example 1 (pH 7.5, 200r / min, 30min). After magnetic separation, take the supernatant after 1 hour of sedimentation to determine the thallium concentration. The above "adsorption-magnetic separation-acid washing-activation" process was repeated for a total of 5 cycles. After 5 cycles, the thallium concentrations in the effluent were: 0.0351 µg / L (after the first regeneration), 0.0398 µg / L (after the second regeneration), 0.0455 µg / L (after the third regeneration), 0.0512 µg / L (after the fourth regeneration), and 0.0580 µg / L (after the fifth regeneration). The results show that after 5 cycles, the thallium removal efficiency of this composite material can still maintain a high level (removal rate > 98%), and the thallium concentration in the effluent is lower than the national standard limit of 0.1 µg / L, which confirms its good regenerability and cycle stability.

[0037] Mechanism for maintaining and regenerating biofilm activity: In successfully attached biofilms, microorganisms embed themselves in a gel-like matrix formed by extracellular polymeric substances (EPS) secreted by themselves. EPS is rich in functional groups such as carboxyl and hydroxyl groups, which can effectively complex thallium ions and provide physical protection for microorganisms. The dilute acid elution regeneration process mainly acts to desorb thallium ions that have been physicochemically adsorbed and partially complexed by EPS. Low-concentration (0.1-1.0 mol / L) short-term (1-4 hours) acid washing has a certain impact on the microbial community structure in the biofilm, but it will not lead to its complete inactivation. The subsequent culture medium activation step is crucial, aiming to provide damaged microorganisms with nutrients such as carbon and nitrogen sources, restore their metabolic activity, promote the re-secretion of EPS, thereby repairing and strengthening the biofilm structure and restoring its ability to enrich and transform thallium. The cycle test data of Example 4 confirms the effectiveness of this "acid washing-activation" regeneration strategy.

[0038] Comparative Example 1 (using only unmodified zeolite) Unmodified clinoptilolite powder of the same origin as in Example 1 was used without magnetic composite, MOF encapsulation, or biofilm formation. The raw water from Zhongkengzhai was directly treated with a dosage of 1.0 g / L. After stirring for 30 minutes, the mixture was allowed to settle for 1 hour, and the supernatant was taken for analysis. The thallium concentration was 0.4520 µg / L, which was much higher than that in Example 1, proving that the adsorption capacity of pure zeolite is limited and solid-liquid separation is difficult. The raw water from Lanbei was treated in the same way, and the thallium concentration was 1.8540 µg / L after sedimentation for 1 hour.

[0039] Comparative Example 2 (using magnetic zeolite without MOF shell) Fe3O4-modified zeolite magnetic microspheres (without MOF material shell (ZIF-8 shell)) were prepared and subjected to the same biofilm formation. The raw water from Zhongkengzhai was treated under the same conditions. Immediately after treatment, the thallium concentration was measured to be 0.0985 µg / L, which was slightly better than Comparative Example 1, but still significantly higher than Example 1. Furthermore, the supernatant was slightly turbid after magnetic separation, indicating that the MOF shell is crucial for improving adsorption capacity and ensuring the clarity of the effluent.

[0040] Comparative Example 3 (using MOF-zeolite composite material but without biofilm) The same MZ-1 magnetic MOF-zeolite core-shell composite material as in Example 1 was prepared, but without the biofilm formation step. 1 L of raw water from "Zhongkengzhai" with a thallium concentration of 0.8990 µg / L and 1 L of raw water from "Lanbei" with a thallium concentration of 3.2268 µg / L were respectively added to 1.0 g / L of the composite material, and stirred at 200 rpm for 30 minutes. After the reaction, solid-liquid separation was performed using a magnet, and samples were immediately taken for analysis. The separated water samples were then allowed to stand, and the supernatant was collected for analysis after 0.5 hours and 1.0 hour of sedimentation. The test results showed that due to the lack of synergistic adsorption and conversion by a biofilm, the immediate thallium capture capacity and deep purification stability of this material were both reduced. For the raw water from "Zhongkengzhai," the thallium concentrations immediately after magnetic separation, after 0.5 hours of sedimentation, and after 1.0 hour of sedimentation were 0.0850 µg / L, 0.0600 µg / L, and 0.0480 µg / L, respectively; for the raw water from "Lanbei," the corresponding values ​​were 0.0892 µg / L, 0.0701 µg / L, and 0.0581 µg / L, respectively. Compared with Example 1, this comparative example demonstrates that biofilm formation makes an irreplaceable and substantial contribution to improving the rapid adsorption efficiency and final purification depth of the composite material for trace thallium in complex water bodies.

[0041] Comparative Example 4 (Referring to the ferrate method in Chinese Invention Patent CN103922514A) Referring to Example 1 of Chinese Invention Patent CN103922514A, 10 mg / L potassium ferrate was added to 1 L of "Zhongkengzhai" raw water with a thallium concentration of 0.8990 µg / L and 1 L of "Lanbei" raw water with a thallium concentration of 3.2268 µg / L, respectively, and the mixture was rapidly stirred at 300 r / min for 3 minutes; then the stirring speed was adjusted to 200. Continue stirring slowly at r / min for 10 minutes; then add 10 mg / L aluminum sulfate for coagulation; finally, let it stand for 1 hour to settle and filter, and take the final filtrate to determine the thallium content; the thallium concentration after treatment of the raw water from "Zhongkengzhai" was 0.0430 µg / L, and the thallium concentration after treatment of the raw water from "Lanbei" was 0.1500 µg / L; although this method can achieve a certain thallium removal effect, it requires the sequential addition of multiple agents, the process is complicated, and a large amount of thallium-containing chemical sludge will be generated, increasing the cost and risk of subsequent treatment; this comparative example highlights the significant advantages of the "single agent addition-magnetic separation" integrated process of this invention in terms of ease of operation, sludge reduction, and stability in deep purification of water bodies with higher concentrations of pollution.

[0042] Comparative Example 5 (referencing the adsorbent material in Chinese Invention Patent CN118105950A): Referring to Example 3 of Chinese Invention Patent CN118105950A, a modified sodium alginate / kaolinite composite adsorbent was prepared. 1L of raw water from "Zhongkengzhai" with a thallium concentration of 0.8990µg / L and 1L of raw water from "Lanbei" with a thallium concentration of 3.2268µg / L were taken respectively. 10% of the adsorbent mass (approximately 0.09mg from the "Zhongkengzhai" water sample and approximately 0.323mg from the "Lanbei" water sample; for practical convenience, 1.0mg was added to each sample. The mixture was stirred at 200r / min for 20 minutes at room temperature. After the reaction, the mixture was filtered through a 0.45μm filter membrane. The thallium content of the filtrate was determined after separation. The thallium concentration of the treated water from "Zhongkengzhai" was 0.0120 µg / L, and that of the treated water from "Lanbei" was 0.0450 µg / L. Although the adsorbent showed high adsorption capacity for low concentrations of thallium under laboratory filtration conditions, it is an ultrafine powder, which faces inherent engineering challenges in large-scale water treatment, such as low solid-liquid separation efficiency, easy clogging of the filtration device, and difficulty and high loss of the adsorbent. This comparative example strongly confirms that the present invention achieves rapid, thorough, and low-energy solid-liquid separation by imparting magnetism to the composite material, which is a key creative design to solve the bottleneck of large-scale application of high-performance adsorbents.

[0043] Performance testing Test Standards The materials obtained in Examples 1-3 and the materials / methods described in Comparative Examples 1-5 were used to treat two types of thallium-containing raw water from "Zhongkengzhai" and "Lanbei" according to their respective conditions. For all tests using the composite materials of this invention (Examples 1-3), after stirring and adsorption, the main material was first separated by a magnet, and then the resulting water samples were allowed to settle for a specified time. The thallium content in the final supernatant was detected by inductively coupled plasma mass spectrometry (ICP-MS), and the results are shown in the table below.

[0044] All functional bacterial groups used in the embodiments were obtained through domestication, and their tolerance concentration to thallium was not less than 5 mg / L. They also maintained high metabolic activity and thallium accumulation capacity after biofilm formation.

[0045] Water quality standard: Surface water environmental quality standard (GB 3838-2002) Specific item standard for centralized drinking water surface water sources, thallium limit 0.1µg / L.

[0046] The standard method for detection is: "Determination of 65 elements in water by inductively coupled plasma mass spectrometry" (HJ 700-2014) or an equivalent standard method.

[0047] Table 1 shows the thallium content test results for each embodiment. Table 2 shows the thallium content test results for each comparative example. Note: Due to the limitations of material properties or process standards, the most representative treatment effect data for Comparative Examples 1, 4, and 5 corresponds to the 'sedimentation for 1 hour' (or final filtered water) node, so data for other nodes are not listed; The Examples and Comparative Examples 2 and 3 were sampled after 'magnetic separation', and the data for each node represent the further sedimentation of the supernatant after magnetic separation.

[0048] Reasons for missing data in Tables 1 and 2 and their supplementation: The presence of numerous "-" in the "Immediately Removed" and "Settling for Half an Hour" columns for Comparative Examples 1, 4, and 5 in Table 2 is due to the following: Comparative Example 1 (Unmodified zeolite powder): The material is non-magnetic, and the water becomes turbid after stirring. The solid-liquid separation is incomplete during "Immediately Removed" and "Settling for Half an Hour," and the measured water sample is not "clear effluent," so the data is not representative. Therefore, only the data of the supernatant after sufficient sedimentation (settling for 1 hour) is provided.

[0049] Comparative Example 4 (Ferrate Method): This is a multi-step chemical process. "Coagulation, sedimentation, and filtration" are the endpoints of its standard process. Sampling before these steps cannot represent the final effluent quality of the process.

[0050] Comparative Example 5 (Powder Adsorbent): The referenced prior art document (CN118105950A) only reports the final effluent data after filtration following stirring, and does not provide data on the sedimentation process. To remain faithful to the cited source and to fairly compare the "final purification capacity," only its final treatment results are listed.

[0051] Conclusions drawn from Tables 1 and 2: Test data show that the three embodiments provided by this invention exhibit excellent and stable deep purification capabilities for both low-concentration (0.8990 µg / L) and high-concentration (3.2268 µg / L) thallium-containing raw water samples. At all detection points (especially the final effluent), the thallium content (0.0073-0.0462 µg / L) is far below the stringent national standard limit of 0.1 µg / L, and significantly superior to all comparative examples. This demonstrates that the strategy of combining magnetic separation, MOF-zeolite core-shell structure adsorption, and biofilm formation effectively solves the problems of low adsorption capacity of traditional zeolites, difficulty in separating powder materials, and complex chemical processes, achieving efficient, rapid, and easily recoverable thallium removal.

[0052] Analysis of possible reasons for discrepancies in test results: The differences in test results mainly stem from the fundamental differences in the material structure and functional composition of each scheme. Example 1 showed the best results, attributed to its complete "magnetic core-zeolite-MOF-biofilm" synergistic system: the magnetic Fe3O4 core ensured second-level separation; the MOF shell provided ultra-high specific surface area and specific pores, greatly enhancing the physicochemical adsorption capacity; the biofilm, through the complexation of microbial extracellular polymers (EPS) and possible biotransformation, enhanced the selectivity against interference from impurity ions and deeply captured trace thallium. Comparative Example 2 lacked a MOF shell, resulting in a significant decrease in adsorption capacity and rate; Comparative Example 3 lacked a biofilm, weakening its immediate adsorption and deep purification stability, indicating that the biofilm is crucial for the continuous removal of thallium from complex water bodies. Although the chemical method in Comparative Example 4 was effective, its effectiveness diminished in higher concentration raw water, and the process was complex. Although the powder adsorbent in Comparative Example 5 performed well in laboratory filtration of low-concentration water samples, its lack of magnetism prevented it from overcoming the separation and recovery bottleneck in large-scale applications. Therefore, the core difference lies in the indispensability and synergistic effect of each functional unit in this invention.

[0053] Finally, it should be noted that the above embodiments are used to illustrate the technical solutions of the present invention and not to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for removing thallium from water using modified zeolite, characterized in that, Includes the following steps: S1. Preparation of magnetic MOF-zeolite core-shell composite material: Using magnetic Fe3O4 nanoparticles synthesized by coprecipitation method as the core, a layer of natural zeolite modified with silane coupling agent is coated on its surface by hydrothermal synthesis to form magnetic zeolite microspheres; then, using the magnetic zeolite microspheres as a carrier, an MOF material shell is constructed on its outermost layer by in-situ growth method to obtain a composite material with a core-shell structure. S2. Surface functionalization and biofilm formation of composite material: The composite material obtained in step S1 is immersed in a polymer solution rich in carboxyl groups for surface grafting modification; then, it is placed in an enrichment culture medium containing specific thallium-removing functional bacteria and biofilm formation is carried out under aeration or shaking conditions until a stable biofilm is formed on the surface of the composite material. The specific thallium-removing functional bacteria are microorganisms that are tolerant to and have the ability to accumulate thallium. S3. Adsorption treatment and magnetic separation: The modified zeolite composite material loaded with biofilm prepared in step S2 is added to the thallium-containing water to be treated and stirred; after the reaction is completed, an external magnetic field is applied to quickly separate the adsorbed saturated composite material from the water, thus completing the removal of thallium.

2. The method according to claim 1, characterized in that: In step S1, the natural zeolite is clinoptilolite or mordenite, with a silica-to-alumina ratio greater than 5; the silane coupling agent is γ-aminopropyltriethoxysilane or γ-(2,3-epoxypropoxy)propyltrimethoxysilane; the MOF material is selected from ZIF-8, MIL-101(Fe), or UiO-66; the MOF material shell has a microporous and / or mesoporous structure, and its BET specific surface area is not less than 300 m². 2 / g, preferably 500-1500m 2 / g, with a main pore size distribution range of 0.5-3.0nm, which is beneficial for size screening and confined adsorption of thallium ions and their hydrated ions.

3. The method according to claim 1, characterized in that, In step S1, the specific process of constructing a MOF material shell on its outermost layer by in-situ growth is as follows: dispersing magnetic zeolite microspheres in a precursor solution containing metal ions and organic ligands, and reacting at 60-120°C for 4-24 hours; the metal ions are Zn. 2+ Fe 3+ or Zr 4+ Any one of the following; the organic ligand is any one of 2-methylimidazole, terephthalic acid, or trimesic acid.

4. The method according to claim 1, characterized in that: The magnetic MOF-zeolite core-shell composite material obtained in step S1 has a particle size distribution of 50 nm-5 μm and a specific surface area of ​​300-800 m². 2 / g, saturation magnetization greater than 20 emu / g; the shell thickness of the MOF material is 10-200 nm.

5. The method according to claim 1, characterized in that: In step S2, the carboxyl-rich polymer is any one of sodium alginate, polyacrylic acid, or polyethyleneimine-polyacrylic acid copolymer, with an immersion concentration of 0.5-5 wt% and an immersion time of 2-12 hours; the specific thallium-removing functional bacterial group is obtained by collecting bacterial sources from a thallium-contaminated environment and acclimating them in an inorganic salt culture medium by gradually increasing the thallium ion concentration; the conditions for biofilm formation are: temperature 25-35°C, pH 6.5-8.0, dissolved oxygen concentration greater than 2 mg / L, and biofilm formation period of 7-14 days; the specific thallium-removing functional bacterial group includes at least one of Pseudomonas, Bacillus, or Thiobacillus; the biofilm formation specifically involves immersing the surface-functionalized composite material in a suspension of functional bacterial groups and culturing it for 7-14 days at 25-35°C, pH 6.5-8.0, and dissolved oxygen concentration greater than 2 mg / L, supplementing nutrients during the period.

6. The method according to claim 5, characterized in that: The inorganic salt culture medium used for the acclimatization culture contains the following components: KH2PO4 0.4-0.6, K2HPO4 0.4-0.6, NH4Cl 0.4-0.6, MgSO4·7H2O 0.1-0.3, NaCl 0.4-0.6, in g / L, and trace element solution 0.5-1.5 mL, with sodium acetate as the carbon source. The acclimatization culture process is as follows: the bacterial strain is inoculated into the culture medium and cultured with shaking at 25-35°C until it recovers. During the subculture, thallium chloride is gradually added, with an initial thallium concentration of 0.2-1.0 mg / L. The thallium concentration is increased by 0.3-1.5 mg / L with each subculture until the bacterial population can grow stably at a thallium concentration of 5-15 mg / L. The acclimatization period is 20 to 70 days.

7. The method according to claim 1, characterized in that: In step S3, the initial concentration of thallium in the thallium-containing water is 0.1-100 µg / L, and the forms include monovalent thallium ions, trivalent thallium ions, and their organic or inorganic complexes; the modified zeolite composite material loaded with biofilm is added to the thallium-containing water to be treated at a dosage of 0.1-5.0 g / L; the stirring is carried out at a pH of 6.0-9.0 and a stirring rate of 100-300 r / min for 10-60 minutes.

8. A modified zeolite composite material for use in the method of any one of claims 1-7, characterized in that: The composite material has a core-shell structure, consisting of a magnetic Fe3O4 core, a modified natural zeolite intermediate layer, and a MOF material shell layer from the inside out. The outermost MOF shell layer is grafted with a functional polymer and loaded with a thallium removal biofilm.

9. The composite material according to claim 8, characterized in that: The microorganisms contained in the thallium-removing biofilm can transform thallium ions through extracellular adsorption, intracellular enrichment, or redox reactions, and the extracellular polymers they secrete contain carboxyl, hydroxyl, and phosphate groups that can complex with thallium ions.

10. The method according to claim 1, characterized in that: The composite material separated in step S3 can be eluted and regenerated using a dilute acid solution. After the regenerated composite material is activated by the biofilm in a culture medium, it can be reused in the thallium removal process, with a recycling rate of no less than 5 times. The dilute acid solution is a nitric acid or hydrochloric acid solution with a concentration of 0.1-1.0 mol / L, and the elution time is 1-4 hours; the culture medium used for biofilm activation is a thallium-removing functional bacterial community enrichment culture medium for biofilm attachment, and the activation time is 12-48 hours.

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