A mercury-containing wastewater treatment agent, a preparation method and application thereof

Abstract

This invention pertains to mercury wastewater treatment technology, providing a recyclable mercury wastewater treatment agent, its preparation method, and its application. The method includes the following steps: (1) activating a polypropylene fiber membrane with a potassium permanganate-sulfuric acid solution; (2) using walnut shells and coconut shells as raw materials, grinding them into powder, mixing them, and carbonizing them at high temperature to obtain biochar; then treating them with sodium sulfate and preparing a slurry, covering the modified polypropylene fiber membrane, and drying it; (3) preparing a growth solution with ZrCl4 and terephthalic acid, and generating a zirconium-based MOF in situ on the product obtained in step (2), followed by washing and drying; (4) incubating it in a dopamine hydrochloride solution to obtain the treatment agent. This invention can achieve a treatment efficiency of over 99% for mercury wastewater with a mercury content exceeding 200 mg / L with an extremely low dosage of 1 g / L, and can maintain a treatment efficiency of 90% even after repeated use 10 times, demonstrating good industrial application value.

Description

Technical Field

[0001] This invention pertains to mercury wastewater treatment technology, specifically relating to a recyclable mercury wastewater treatment agent, its preparation method, and its application. Background Technology

[0002] Mercury, a toxic heavy metal pollutant, poses a serious threat to aquatic ecosystems and the human nervous system due to its difficulty in degradation and tendency to accumulate in organisms. The World Health Organization (WHO) has listed mercury as one of the priority pollutants for control, and various countries have successively introduced increasingly stringent emission standards. This has prompted researchers to dedicate themselves to developing efficient and stable mercury wastewater treatment technologies.

[0003] Currently, adsorption is favored for treating mercury-containing wastewater due to its ease of operation and high removal efficiency. To achieve even higher treatment capacity, existing technologies often favor particulate agents with larger specific surface areas. For example, nano-zero-valent iron (nZVI) has been widely studied for heavy metal removal due to its small particle size and high surface atomic ratio. (Zhang et al.) [1] Studies have shown that nano-zero-valent iron has a much higher removal rate of mercury ions than traditional micron-sized iron powder. Similarly, nano-manganese dioxide has also been shown to have extremely high adsorption capacity. However, this highly dispersed form also brings a fatal drawback—difficulty in recovery. Liu et al. [2] Research indicates that nanoparticles are easily lost with water flow during water treatment, not only wasting expensive adsorbents but also potentially causing secondary pollution due to the inherent ecotoxicity of nanomaterials. In practical engineering applications, this contradiction between "high activity and difficulty in recycling" severely restricts their widespread adoption in large-scale water treatment.

[0004] In contrast, while traditional membrane separation technologies have inherent advantages in solid-liquid separation and can effectively avoid adsorbent loss, their treatment capacity for mercury-contaminated wastewater is generally low. Conventional polymer membranes (such as polysulfone and polyvinylidene fluoride) mainly rely on physical sieving, and their retention rate for low concentrations of mercury ions is often unsatisfactory. Although some modified membranes attempt to enhance adsorption capacity by introducing functional groups, they often face problems such as decreased flux and poor antifouling ability. For example, Wang et al. [3] Research reports indicate that although thiol-modified membranes have a certain affinity for mercury, their treatment flux rapidly declines in a short period of time, and the membrane surface is easily covered by organic matter in the water, leading to deactivation.

[0005] In summary, current research on mercury wastewater treatment agents faces a dilemma between "high activity and difficult recovery" and "easy separation and low efficiency." How to maintain the excellent adsorption performance brought by high specific surface area while solving the recovery problem of granular agents, or overcoming the bottleneck of membrane product treatment capacity, has become a key scientific problem that urgently needs to be solved in this field. Developing novel functional materials that combine high adsorption capacity, high selectivity, and easy solid-liquid separation is an important direction for the future development of mercury pollution control technology.

[0006] Source of the literature: [1]Zhang, WX (2003). Nanoscale iron particles for environmental remediation: An overview. Journal of Nanoparticle Research, 5(3-4), 323-332. [2] Liu, Y., Majetich, SA, Tilton, RD, Brown, DO, & Lowry, GV (2005). TCE, HCB, and aniline removal with polyaspartate-stabilizednanoscale iron. [3] Wang, J., Chen, C., & Pan, B. (2015). Mercury removal from wastewater using porous adsorbents. Coordination Chemistry Reviews, 293-294,220-234. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a reusable mercury wastewater treatment agent with excellent treatment efficiency for mercury-containing wastewater. This agent exhibits superior treatment efficiency for wastewater with high mercury content, and its treatment efficiency remains high even after multiple reuses. The present invention provides the following technical solutions to achieve the aforementioned objective.

[0008] A method for preparing a recyclable mercury wastewater treatment agent, the method comprising the following steps: (1) The polypropylene fiber membrane was activated by potassium permanganate sulfuric acid solution to obtain a modified polypropylene fiber membrane; (2) Walnut shells and coconut shells are used as raw materials in a weight ratio of 2~4:2. They are powdered, mixed and carbonized at high temperature to obtain biochar. Then, the biochar is treated with sodium sulfate to obtain modified biochar. The modified biochar is made into a slurry, covered on a modified polypropylene fiber membrane and dried. (3) A growth solution was prepared using ZrCl4 and terephthalic acid, and a zirconium-based MOF was generated in situ on the product obtained in step (2) using the growth solution and then washed and dried. (4) The product obtained in step (3) is placed in a dopamine hydrochloride solution for incubation, and after washing and drying, the treatment agent is obtained.

[0009] Preferably, in step (1), when the polypropylene fiber membrane is activated with potassium permanganate sulfuric acid solution, the specific method is as follows: the polypropylene fiber membrane is soaked in potassium permanganate sulfuric acid solution with a potassium permanganate concentration of 60mM and treated in a water bath at 70°C for 1 hour; then it is washed with deionized water until the washing water is neutral, and then dried at 60°C to obtain the activated polypropylene fiber membrane.

[0010] Preferably, in step (2), the weight ratio of the walnut shell to the coconut shell is 2:1.

[0011] Preferably, in step (2), when grinding the walnut shells and coconut shells into powder, they are ground and passed through a 60-mesh sieve.

[0012] Preferably, in step (2), the specific method for high-temperature carbonization is as follows: under nitrogen protection, the temperature is increased to 600°C at a heating rate of 5°C / min and held for 2 hours to obtain biochar.

[0013] Preferably, in step (2), when treating with sodium sulfide, the specific method is as follows: according to the solid-liquid ratio of 1:10, the biochar is immersed in a sodium sulfide solution with a concentration of 0.1M and incubated at room temperature for 12 hours by shaking; then the mixture is filtered, and the solid phase is washed with deionized water to remove the residual sodium sulfide, and then dried at 60°C to obtain modified biochar.

[0014] Preferably, in step (2), when the modified biochar is prepared into a slurry and coated onto the modified polypropylene fiber membrane, the specific method is as follows: the obtained modified biochar is dispersed in an aqueous ethanol solution with a concentration of 50% v / v to prepare a slurry with a concentration of 2 mg / mL; finally, the slurry is vacuum filtered with a loading of 1.5 g / mL. 2 The slurry is evenly filtered onto the surface of the activated polypropylene fiber membrane.

[0015] Preferably, in step (3), the concentrations of ZrCl4 and terephthalic acid in the growth solution are both 0.15~0.20M, and the solvent is N,N-dimethylformamide; in step (4), the concentration of dopamine hydrochloride in the dopamine hydrochloride solution is 1.0~1.5g / L.

[0016] A recyclable mercury wastewater treatment agent, said treatment agent being prepared by the aforementioned preparation method.

[0017] The aforementioned treatment agent is used in the treatment of mercury wastewater. The method of application is to place the treatment agent in the mercury wastewater, and after the adsorption is saturated, to desorb it with dilute hydrochloric acid, and then to place it in the mercury wastewater for recycling.

[0018] The beneficial effects of this invention are: This invention constructs a material system capable of multi-level interception, adsorption, and synergistic capture of mercury ions based on an acrylic fiber membrane, through the combination of modified biochar, zirconium-based MOF, and a dopamine layer. This system is structurally stable and reusable. The invention reveals that using walnut shells and coconut shells as biochar raw materials is crucial for the construction of the aforementioned system, and that the zirconium-based MOF also has a significant impact.

[0019] In practical use, this invention can achieve a treatment efficiency of over 99% for wastewater with mercury content exceeding 200 mg / L with an extremely low dosage of 1 g / L, and can maintain a treatment efficiency of 90% even after being used repeatedly 10 times, thus having good industrial application value. Detailed Implementation

[0020] The present invention will be specifically described below through embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above-described invention are still within the scope of protection of the present invention.

[0021] Example 1

[0022] The main raw materials and reagents involved in this embodiment are as follows: Polypropylene: Shanghai Aladdin Biochemical Technology Co., Ltd., specification: P301642, melt index is 28g / 10min; Walnut shells and coconut shells: Remove the shells from walnuts and coconuts purchased from the local farmers' market; Sodium sulfide: Shanghai Aladdin Biochemical Technology Co., Ltd.; ZrCl4: Forsmann Technology (Beijing) Co., Ltd.; Terephthalic acid (H2BDC): Chengdu Desite Biotechnology Co., Ltd.; Dopamine hydrochloride: Shanghai Yuyuan Biochemical Co., Ltd.; Tris-HCl buffer: Wuhan Desheng Biochemical Technology Co., Ltd.; Trion X-100: Wuhan Saiweier Biotechnology Co., Ltd.

[0023] The preparation method of a recyclable mercury wastewater treatment agent involved in this embodiment is as follows: (1) The polypropylene fiber membrane was soaked in a potassium permanganate sulfuric acid solution with a potassium permanganate concentration of 60mM and treated in a water bath at 70°C for 1 hour; then it was washed with deionized water until the washing water was neutral, and then dried at 60°C to obtain an activated polypropylene fiber membrane.

[0024] (2) Walnut shells and coconut shells were prepared at a weight ratio of 2:1, ground separately and passed through a 60-mesh sieve, and then mixed evenly to obtain a mixed powder. The mixed powder was placed in a tube furnace and heated to 600°C at a heating rate of 5°C / min under nitrogen protection and held for 2 hours to obtain biochar. The biochar was immersed in a 0.1M sodium sulfide solution at a solid-liquid ratio of 1:10 and incubated at room temperature with shaking (100 rpm) for 12 hours. After filtration, the solid phase was washed with deionized water to remove residual sodium sulfide and then dried at 60°C to obtain modified biochar. The modified biochar was then dispersed in an ethanol aqueous solution (50% v / v) to prepare a slurry with a concentration of 2 mg / mL. Finally, the slurry was vacuum filtered with a loading of 1.5 g / mL. 2 The slurry is evenly filtered onto the surface of an activated polypropylene fiber membrane and then naturally dried to obtain a modified biochar-polypropylene fiber membrane (SBC-PP).

[0025] (3) Dissolve ZrCl4 and H2BDC in DMF, add glacial acetic acid to adjust pH=2.5 to obtain growth solution, wherein the final concentration of ZrCl4 and H4BDC is 0.15M; then immerse SBC-PP in growth solution and fix it with Teflon porous plate, and react in oven at 120℃ for 24 hours; then take out the membrane, wash it repeatedly with DMF and methanol to remove unreacted monomers; finally, vacuum dry at room temperature to obtain zirconium-based MOF-modified biochar-polypropylene fiber membrane (abbreviated as MSBC-PP).

[0026] (4) Dissolve dopamine hydrochloride and Trion X-100 in Tris-HCl buffer (pH = 8.5) to make the concentration of dopamine hydrochloride 1 g / L and the concentration of Trion X-100 0.01 v / v% to obtain a dopamine hydrochloride solution; then place the obtained MSBC-PP in the dopamine hydrochloride solution and incubate at room temperature in the dark with shaking (100 rpm) for 1 hour; after taking out the membrane, gently wash it with deionized water to remove the residual dopamine hydrochloride solution and let it air dry naturally.

[0027] Example 2

[0028] The main raw materials and reagents used in this embodiment are the same as those in Example 1.

[0029] The preparation method of a recyclable mercury wastewater treatment agent involved in this embodiment is as follows: (1) The polypropylene fiber membrane was soaked in a potassium permanganate sulfuric acid solution with a potassium permanganate concentration of 60mM and treated in a water bath at 70°C for 1 hour; then it was washed with deionized water until the washing water was neutral, and then dried at 60°C to obtain an activated polypropylene fiber membrane.

[0030] (2) Walnut shells and coconut shells were prepared at a weight ratio of 3:2, ground separately and passed through a 60-mesh sieve, and then mixed evenly to obtain a mixed powder. The mixed powder was placed in a tube furnace and heated to 600°C at a heating rate of 5°C / min under nitrogen protection and held for 2 hours to obtain biochar. The biochar was immersed in a 0.1M sodium sulfide solution at a solid-liquid ratio of 1:10 and incubated at room temperature (100 rpm) for 12 hours. After filtration, the solid phase was washed with deionized water to remove residual sodium sulfide and then dried at 60°C to obtain modified biochar. The modified biochar was then dispersed in an ethanol aqueous solution (50% v / v) to prepare a slurry with a concentration of 2 mg / mL. Finally, the slurry was vacuum filtered with a loading of 1.2 g / mL. 2 The slurry is evenly filtered onto the surface of an activated polypropylene fiber membrane and then naturally dried to obtain a modified biochar-polypropylene fiber membrane (SBC-PP).

[0031] (3) Dissolve ZrCl4 and H2BDC in DMF, add glacial acetic acid to adjust pH=2.5 to obtain growth solution, wherein the final concentration of ZrCl4 and H2BDC is 0.2M; then immerse SBC-PP in growth solution and fix it with Teflon porous plate, and react in oven at 120℃ for 24 hours; then take out the membrane, wash it repeatedly with DMF and methanol to remove unreacted monomers; finally, vacuum dry at room temperature to obtain zirconium-based MOF-modified biochar-polypropylene fiber membrane (abbreviated as MSBC-PP).

[0032] (4) Dissolve dopamine hydrochloride and Trion X-100 in Tris-HCl buffer (pH = 8.5) to make the concentration of dopamine hydrochloride 1.5 g / L and the concentration of Trion X-100 0.02 v / v% to obtain a dopamine hydrochloride solution; then place the obtained MSBC-PP in the dopamine hydrochloride solution and incubate at room temperature in the dark with shaking (100 rpm) for 1 hour; after taking out the membrane, gently wash it with deionized water to remove the residual dopamine hydrochloride solution and let it air dry naturally.

[0033] Example 3

[0034] The main raw materials and reagents used in this embodiment are the same as those in Example 1.

[0035] The preparation method of a recyclable mercury wastewater treatment agent involved in this embodiment is as follows: (1) The polypropylene fiber membrane was soaked in a potassium permanganate sulfuric acid solution with a potassium permanganate concentration of 60mM and treated in a water bath at 70°C for 1 hour; then it was washed with deionized water until the washing water was neutral, and then dried at 60°C to obtain an activated polypropylene fiber membrane.

[0036] (2) Walnut shells and coconut shells were prepared at a weight ratio of 1:1, ground separately and passed through a 60-mesh sieve, and then mixed evenly to obtain a mixed powder. The mixed powder was placed in a tube furnace and heated to 600°C at a heating rate of 5°C / min under nitrogen protection and held for 2 hours to obtain biochar. The biochar was immersed in a 0.1M sodium sulfide solution at a solid-liquid ratio of 1:10 and incubated at room temperature with shaking (100 rpm) for 12 hours. After filtration, the solid phase was washed with deionized water to remove residual sodium sulfide and then dried at 60°C to obtain modified biochar. The modified biochar was then dispersed in an ethanol aqueous solution (50% v / v) to prepare a slurry with a concentration of 2 mg / mL. Finally, the slurry was vacuum filtered with a loading of 1.2 g / mL. 2 The slurry is evenly filtered onto the surface of an activated polypropylene fiber membrane and then naturally dried to obtain a modified biochar-polypropylene fiber membrane (SBC-PP).

[0037] (3) Dissolve ZrCl4 and H2BDC in DMF, add glacial acetic acid to adjust pH=2.5 to obtain growth solution, wherein the final concentration of ZrCl4 and H4BDC is 0.2M; then immerse SBC-PP in growth solution and fix it with Teflon porous plate, and react in oven at 120℃ for 24 hours; then take out the membrane, wash it repeatedly with DMF and methanol to remove unreacted monomers; finally, vacuum dry at room temperature to obtain zirconium-based MOF-modified biochar-polypropylene fiber membrane (abbreviated as MSBC-PP).

[0038] (4) Dissolve dopamine hydrochloride and Trion X-100 in Tris-HCl buffer (pH = 8.5) to make the concentration of dopamine hydrochloride 1.2 g / L and the concentration of Trion X-100 0.015 v / v% to obtain a dopamine hydrochloride solution; then place the obtained MSBC-PP in the dopamine hydrochloride solution and incubate at room temperature in the dark with shaking (100 rpm) for 1 hour; after taking out the membrane, gently wash it with deionized water to remove the residual dopamine hydrochloride solution and let it air dry naturally.

[0039] Comparative Example 1 In the preparation of biochar, only walnut shells were used as raw materials, and the rest was the same as in Example 1.

[0040] Comparative Example 2 In preparing biochar, the weight ratio of walnut shells to coconut shells was 3:1, and the rest was the same as in Example 1.

[0041] Comparative Example 3 Compared with Example 1, this comparative example does not perform step (4) and uses the obtained MSBC-PP as the final product.

[0042] Comparative Example 4 Compared to Example 1, this comparative example replaces the zirconium-based MOF in step (3) with an iron-based MOF. The specific technical solution is as follows: Ferric nitrate nonahydrate: Shanghai Aladdin Biochemical Technology Co., Ltd.; other raw materials and reagents are the same as in Example 1.

[0043] (1) The polypropylene fiber membrane was soaked in a potassium permanganate sulfuric acid solution with a potassium permanganate concentration of 60mM and treated in a water bath at 70°C for 1 hour; then it was washed with deionized water until the washing water was neutral, and then dried at 60°C to obtain an activated polypropylene fiber membrane.

[0044] (2) Walnut shells and coconut shells were prepared at a weight ratio of 2:1, ground separately and passed through a 60-mesh sieve, and then mixed evenly to obtain a mixed powder. The mixed powder was placed in a tube furnace and heated to 600°C at a heating rate of 5°C / min under nitrogen protection and held for 2 hours to obtain biochar. The biochar was immersed in a 0.1M sodium sulfide solution at a solid-liquid ratio of 1:10 and incubated at room temperature with shaking (100 rpm) for 12 hours. After filtration, the solid phase was washed with deionized water to remove residual sodium sulfide and then dried at 60°C to obtain modified biochar. The modified biochar was then dispersed in an ethanol aqueous solution (50% v / v) to prepare a slurry with a concentration of 2 mg / mL. Finally, the slurry was vacuum filtered with a loading of 1.5 g / mL. 2The slurry is evenly filtered onto the surface of an activated polypropylene fiber membrane and then naturally dried to obtain a modified biochar-polypropylene fiber membrane (SBC-PP).

[0045] (3) Dissolve ferric nitrate nonahydrate and H2BDC in DMF, add glacial acetic acid to adjust pH=3.5 to obtain growth solution, wherein the final concentration of ferric nitrate nonahydrate and H2BDC is 0.15M; add 2.5% deionized water by volume of DMF as structure directing agent; then immerse SBC-PP in growth solution and fix it with Teflon porous plate, and react in oven at 100℃ for 12 hours; then take out the membrane, wash it repeatedly with DMF and ethanol to remove unreacted monomers; finally, vacuum dry at room temperature to obtain iron-based MOF-modified biochar-polypropylene fiber membrane (abbreviated as Fe-MSBC-PP).

[0046] (4) Dissolve dopamine hydrochloride and Trion X-100 in Tris-HCl buffer (pH=8.5) to make the concentration of dopamine hydrochloride 1g / L and the concentration of Trion X-100 0.01v / v% to obtain a dopamine hydrochloride solution; then place the obtained Fe-MSBC-PP in the dopamine hydrochloride solution and incubate at room temperature in the dark with shaking (100rpm) for 1 hour; after taking out the membrane, gently wash it with deionized water to remove the residual dopamine hydrochloride solution and air dry it to obtain the final product.

[0047] Test Example 1 Mercury treatment tests were conducted on the products obtained in Examples 1-3 and Comparative Examples 1-4. Wastewater from a wastewater treatment plant in Chengdu was used as the simulated wastewater, containing mercury (207 mg / L), lead (37 mg / L), and cadmium (45 mg / L). To facilitate the testing of mercury treatment effectiveness, simulated wastewater with the aforementioned mercury concentration was prepared by mixing 1 L of purified water with 0.3347 g of mercuric nitrate.

[0048] Take 0.1g of each of the products obtained in Examples 1-3 and Comparative Examples 1-4, add them to 100ml of simulated wastewater, shake at room temperature (100rpm) for 4 hours and take samples; use a syringe to extract 5mL of sample solution and immediately inject it into a clean centrifuge tube through a 0.45μm aqueous filter membrane; use ICP-OES to determine the concentration of Hg in the sample solution and calculate the removal efficiency. The test results are shown in Table 1. ×100%.

[0049] Table 1

[0050] As shown in Table 1, the products obtained in Examples 1-3 of this invention have a high removal efficiency for mercury. This is because this invention constructs a multi-stage interception and synergistic capture system for mercury ions. Specifically, this invention selects walnut shells and coconut shells as biochar raw materials, utilizing their ash elements such as K, Ca, and Mg to form slightly soluble sulfide precipitates after sulfidation, which can assist adsorption. Mercury is captured by forming covalent bonds between thiol groups and mercury ions. In addition, this invention introduces zirconium-based MOF to further increase the specific surface area, which can also undergo Lewis acid-base coordination with mercury ions, enhancing the capture of mercury ions. Finally, this invention uses a dopamine layer to form a stable five-membered chelate with some mercury ions, prolonging the contact time of mercury ions and facilitating the capture of mercury ions by the modified biochar and MOF. As shown in Comparative Example 1, the Hg removal rate decreased significantly when only walnut shells were used as raw materials. Simultaneously, the removal rate obtained in Comparative Example 2 also showed a significant decrease. This indicates that walnut shells and coconut shells have a synergistic effect on mercury removal, with the amount of coconut shells added having a significant impact. The underlying reason may be that walnut shells contain a large amount of polyphenols (such as tannins) and hemicellulose. These substances, upon pyrolysis, generate an exceptionally rich number of oxygen-containing functional groups (-OH, -COOH). These oxygen-rich surfaces can undergo more complete nucleophilic substitution reactions with Na2S, generating high-density thiol groups (-SH) and thioether bonds (-S-). In contrast, the carbonized coconut shells have relatively fewer surface functional groups, but a high degree of aromatization, providing excellent mechanical strength and chemical stability to the entire composite membrane, ensuring that the loaded MOF and modified biochar do not detach under severe oscillation and water flow impact. As can be seen from Comparative Example 4, replacing the MOF material also has a significant impact on the mercury removal efficiency. This may be because the iron-based MOF nucleates relatively too quickly, which shields the modified biochar and thus reduces the removal efficiency.

[0051] Test Example 2 This test case, based on Test Case 1, tests the durability of the products obtained in each group. The test procedure is as follows: After the simulated wastewater is treated for the first time, each group of products is immersed in 0.1M hydrochloric acid solution for 2 hours, then rinsed with deionized water to remove the hydrochloric acid, and dried under vacuum at room temperature; then the experiment is carried out according to the method of Test Case 1; each group repeats the above cycle 5 and 10 times respectively, and the mercury removal rate of each group of products after 5 and 10 cycles is examined. The test results are shown in Table 2.

[0052] Table 2

[0053] As shown in Table 2, Comparative Example 3 showed good removal efficiency in the initial treatment of mercury-containing simulated wastewater, but its mercury removal efficiency decreased significantly after several repeated uses. This was because the biochar and MOF materials in the untreated product were prone to detachment. Meanwhile, the data in Table 1 showed that the addition of the dopamine layer could also produce a good synergistic effect with the biochar and MOF materials.

[0054] The results of Test Example 1 and Test Example 2 show that the product obtained by the present invention has excellent removal efficiency for mercury in wastewater and is reusable, thus having good industrial application value.

Claims

1. A method for preparing a recyclable mercury wastewater treatment agent, characterized in that, The preparation method includes the following steps: (1) The polypropylene fiber membrane was activated by potassium permanganate sulfuric acid solution to obtain a modified polypropylene fiber membrane; (2) Walnut shells and coconut shells are used as raw materials in a weight ratio of 2~4:

2. They are powdered, mixed and carbonized at high temperature to obtain biochar. Then, the biochar is treated with sodium sulfate to obtain modified biochar. The modified biochar is made into a slurry, covered on a modified polypropylene fiber membrane and dried. (3) A growth solution was prepared using ZrCl4 and terephthalic acid, and a zirconium-based MOF was generated in situ on the product obtained in step (2) using the growth solution and then washed and dried. (4) The product obtained in step (3) is placed in a dopamine hydrochloride solution for incubation, and after washing and drying, the treatment agent is obtained.

2. The method for preparing a recyclable mercury wastewater treatment agent according to claim 1, characterized in that, In step (1), when the polypropylene fiber membrane is activated with potassium permanganate sulfuric acid solution, the specific method is as follows: the polypropylene fiber membrane is soaked in potassium permanganate sulfuric acid solution with a potassium permanganate concentration of 60mM and treated in a water bath at 70°C for 1 hour; then it is washed with deionized water until the washing water is neutral, and then dried at 60°C to obtain the activated polypropylene fiber membrane.

3. The method for preparing a recyclable mercury wastewater treatment agent according to claim 1, characterized in that, In step (2), the weight ratio of the walnut shell to the coconut shell is 2:

1.

4. The method for preparing a recyclable mercury wastewater treatment agent according to claim 3, characterized in that, In step (2), when grinding the walnut shells and coconut shells into powder, they are ground and passed through a 60-mesh sieve.

5. The method for preparing a recyclable mercury wastewater treatment agent according to claim 4, characterized in that, In step (2), the specific method for high-temperature carbonization is as follows: under nitrogen protection, the temperature is increased to 600℃ at a rate of 5℃ / min and held for 2 hours to obtain biochar.

6. A method for preparing a recyclable mercury wastewater treatment agent according to claim 1 or 5, characterized in that, In step (2), when treating with sodium sulfide, the specific method is as follows: according to the solid-liquid ratio of 1:10, the biochar is immersed in a sodium sulfide solution with a concentration of 0.1M and incubated at room temperature for 12 hours by shaking; then the mixture is filtered, and the solid phase is washed with deionized water to remove the residual sodium sulfide, and then dried at 60°C to obtain modified biochar.

7. The method for preparing a recyclable mercury wastewater treatment agent according to claim 6, characterized in that, In step (2), when the modified biochar is prepared into a slurry and coated onto the modified polypropylene fiber membrane, the specific method used is as follows: the obtained modified biochar is dispersed in an aqueous ethanol solution with a concentration of 50% v / v to prepare a slurry with a concentration of 2 mg / mL; finally, the slurry is vacuum filtered with a loading of 1.5 g / mL. 2 The slurry is evenly filtered onto the surface of the activated polypropylene fiber membrane.

8. A method for preparing a recyclable mercury wastewater treatment agent according to claim 1 or 7, characterized in that, In step (3), the concentrations of ZrCl4 and terephthalic acid in the growth solution are both 0.15~0.20M, and the solvent is N,N-dimethylformamide; in step (4), the concentration of dopamine hydrochloride in the dopamine hydrochloride solution is 1.0~1.5g / L.

9. A recyclable mercury wastewater treatment agent, characterized in that, The treatment agent is prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the treatment agent according to claim 9 in mercury wastewater treatment, characterized in that, The application method involves placing the treatment agent in mercury wastewater, and after adsorption saturation, desorbing it with dilute hydrochloric acid, and then recycling it back into the mercury wastewater.

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