Preparation method of bismuth-based material and application thereof in treatment of iodine-containing waste liquid

Abstract

This invention discloses a method for preparing a bismuth-based material and its application in the treatment of iodine-containing wastewater. The bismuth-based material is a bismuth-based oxoacid salt material and / or a bismuth-based oxoacid salt composite material; the bismuth-based material is used to remove iodide ions and iodate ions from iodine-containing wastewater. This invention provides a method for the simultaneous and efficient removal of iodide ions based on bismuth-based oxoacid salt materials and / or bismuth-based oxoacid salt composite materials. ‑ and IO3 ‑ The proposed method for treating iodine-containing wastewater has advantages such as high treatment efficiency, large adsorption capacity, high efficiency in removing iodine-containing wastewater of different concentrations, strong resistance to interference from coexisting anions, and a wide applicable pH range. The bismuth-based material of this invention exhibits good stability, is safe to use, and poses no risk of secondary pollution.

Description

Technical Field

[0001] This invention belongs to the field of radioactive element processing technology. More specifically, this invention relates to a method for preparing bismuth-based materials and their application in the treatment of iodine-containing wastewater. Background Technology

[0002] Nuclear power plants encounter safety issues during long-term operation and produce large amounts of radioactive nuclides, including fission products of uranium and plutonium. 129 I and 131 I is widely present in spent fuel reprocessing. Because 129 I has an extremely long half-life (1.57 × 10⁻⁶). 7 (Year), which allows it to migrate significantly in the natural environment, while also being highly toxic, posing a considerable threat to the natural environment and human health. Although 131 Radioactive iodine has a half-life of only 8.02 days, but due to its high specific activity and high migration rate in nature, it is extremely likely to harm the health of human organs such as the thyroid gland. Radioactive iodine is mainly present as iodide (I-). - ), iodate (IO3) - Radioactive iodine exists in liquid environments in forms such as iodine, so there is an urgent need to achieve efficient treatment of radioactive iodine in waste liquids. Developing an iodine adsorbent that is inexpensive, efficient, safe, high-performance, and easy to separate solids and liquids is of great significance to my country's natural environmental protection and the stable development of nuclear energy.

[0003] Currently, common methods for removing iodine from water mainly include wet scrubbing and solid adsorption. Wet scrubbing, however, requires sophisticated equipment, produces toxic and corrosive wastewater, and is expensive to operate. It also presents safety concerns and environmental pollution from post-treatment wastewater. Solid adsorption, on the other hand, has gained more attention due to its lower cost, ease of operation, and convenient maintenance. This method typically utilizes solid compounds containing Ag(I) and Hg(II) to react with different forms of iodine in water, forming insoluble precipitates (AgI, AgIO3, etc.), thereby achieving the fixation and separation of iodine. Some of these materials are already capable of large-scale production to meet industrial needs. However, they still suffer from drawbacks such as slow adsorption kinetics, low adsorption capacity, poor resistance to interference, insufficient acid-base stability, and high cost of the supporting metal, limiting their practical application.

[0004] Bismuth-based compounds are considered promising iodine adsorbents due to their low toxicity, cost-effectiveness, and high affinity for iodine. However, pure bismuth compounds exhibit inert adsorption capacity for various iodine forms, making the development of novel bismuth-based adsorbents a current research focus. Summary of the Invention

[0005] One object of the present invention is to solve at least the above-mentioned problems and / or defects, and to provide at least the advantages described below.

[0006] To achieve these objectives and other advantages of the present invention, an application of a bismuth-based material in the treatment of iodine-containing wastewater is provided, the bismuth-based material comprising: a bismuth-based oxyacid salt material and / or a bismuth-based oxyacid salt composite material; wherein the bismuth-based oxyacid salt material is Bi2WO6, and the bismuth-based oxyacid salt composite material is Bi2WO6 / modified biochar.

[0007] Preferably, the bismuth-based material is used to remove iodide ions and iodate ions from iodine-containing wastewater. The specific method includes: adding the bismuth-based material to the iodine-containing wastewater containing iodide ions and / or iodate ions for adsorption, thereby completing the removal of iodide ions and / or iodate ions.

[0008] A method for preparing a bismuth-based material for treating iodine-containing wastewater, wherein the bismuth-based material is a bismuth-based oxoacid salt material, and the preparation method includes the following steps: Step 1: Dissolve Bi(NO3)3·5H2O in nitric acid solution to prepare solution A; dissolve Na2WO4·2H2O in deionized water to prepare solution B; Step 2: Under continuous stirring, add solution B dropwise to solution A, continue stirring, transfer the stirred suspension to a reaction vessel, heat the reaction, and allow it to cool naturally to room temperature to obtain the reaction product; Step 3: Wash, filter and dry the reaction product to obtain Bi2WO6, which is a bismuth-based oxyacid salt material.

[0009] Preferably, in step one, the mass-to-volume ratio of Bi(NO3)3·5H2O to nitric acid solution is 0.1~1g:5~50mL; and the molar volume ratio of nitric acid to deionized water in the nitric acid solution is 0.5~1.5mmol:10~50mL.

[0010] Preferably, in step one, the mass-to-volume ratio of Na2WO4·2H2O to deionized water is 1~2g:10~50mL.

[0011] Preferably, in step two, the mass ratio of Bi(NO3)3·5H2O in solution A to Na2WO4·2H2O in solution B is 0.1~1:1~2; stirring is continued for 1~3 hours; the reaction is heated to 150~170℃ for 18~22 hours.

[0012] Preferably, in step three, the washing is performed using deionized water 5 to 10 times; the drying temperature is 50 to 80°C, and the time is 8 to 16 hours.

[0013] Application of a bismuth-based oxoacid salt material prepared by the method described above in the treatment of iodine-containing wastewater.

[0014] Application of a bismuth-based oxoacid salt material prepared by the method described above in the removal of iodide ions and iodate ions from iodine-containing wastewater.

[0015] A method for preparing a bismuth-based material for treating iodine-containing wastewater, wherein the bismuth-based material is a bismuth-based oxoacid salt composite material, and the preparation method includes the following steps: S1. Preparation of modified biochar; S2. Dissolve Bi(NO3)3·5H2O in nitric acid solution to prepare solution A; dissolve Na2WO4·2H2O in deionized water to prepare solution B; S3. Under continuous stirring, solution B is added dropwise to solution A, stirring is continued, the stirred suspension is transferred to the reaction vessel, modified biochar and polyvinylpyrrolidone are added, the reaction is heated, and the mixture is naturally cooled to room temperature to obtain the reaction product. S4. The reaction product is washed, filtered and dried to obtain Bi2WO6 / modified biochar, i.e., bismuth-based oxyacid salt composite material.

[0016] Preferably, in step S1, the method for preparing modified biochar includes: S11. Add corn straw powder to nitric acid solution and soak at 50~70℃ for 1~3h. After filtration, washing and drying, pretreated straw powder is obtained. The pretreated straw powder is heated to 400~600℃ at a heating rate of 5~15℃ / min under nitrogen atmosphere and kept at this temperature for 1~3h. After natural cooling to room temperature, it is ground to obtain biochar. S12. Dissolve Bi(NO3)3·5H2O in nitric acid solution to prepare solution C; add biochar and polyvinylpyrrolidone to AlCl3 solution to prepare solution D; add solution C dropwise to solution D, stir at room temperature for 1-3 h, let stand for 6-24 h, filter, wash and dry to obtain pre-modified biochar; S13. The pre-modified biochar is kept at 200~300℃ for 4~8h under an argon-hydrogen atmosphere, then naturally cooled to room temperature, and ground to obtain modified biochar.

[0017] Preferably, in step S11, the mass-to-volume ratio of corn stalk powder to nitric acid solution is 1g:5~20mL; and the concentration of nitric acid solution is 1~10wt%.

[0018] Preferably, in S12, the mass-to-volume ratio of Bi(NO3)3·5H2O to nitric acid solution is 1~3g:30~80mL; in the nitric acid solution, the molar volume ratio of nitric acid to deionized water is 0.5~1.5mmol:10~50mL; the mass-to-volume ratio of biochar, polyvinylpyrrolidone, and AlCl3 solution is 10g:0.1~2g:50~200mL; and the concentration of AlCl3 solution is 5~20g / L.

[0019] Preferably, in step S13, the volume ratio of argon to hydrogen in the argon-hydrogen atmosphere is 8~9.5:0.5~2.

[0020] Preferably, in S2, the mass-to-volume ratio of Bi(NO3)3·5H2O to nitric acid solution is 0.1~1g:5~50mL; and in the nitric acid solution, the molar volume ratio of nitric acid to deionized water is 0.5~1.5mmol:10~50mL.

[0021] Preferably, in S2, the mass-to-volume ratio of Na2WO4·2H2O to deionized water is 1~2g:10~50mL.

[0022] Preferably, in step S3, the mass ratio of Bi(NO3)3·5H2O in solution A to Na2WO4·2H2O in solution B is 0.1~1:1~2; stirring is continued for 1~3 hours; the reaction is heated to 150~170℃ for 18~22 hours.

[0023] Preferably, in S3, the mass ratio of Bi(NO3)3·5H2O, modified biochar, and polyvinylpyrrolidone in solution A is 0.1~1:0.01~0.5:0.01~0.1.

[0024] Preferably, in step S4, the washing process involves washing with deionized water 5 to 10 times; the drying temperature is 50 to 80°C, and the drying time is 8 to 16 hours.

[0025] Application of a bismuth-based oxoacid salt composite material prepared by the method described above in the treatment of iodine-containing wastewater.

[0026] Application of a bismuth-based oxoacid salt composite material prepared by the method described above in the removal of iodide ions and iodate ions from iodine-containing wastewater.

[0027] The present invention has at least the following beneficial effects: (1) This invention addresses the difficulty of simultaneously and efficiently removing I from existing iodine-containing wastewater treatment technologies. - and IO3 -To address the shortcomings of slow adsorption kinetics, low adsorption capacity, weak resistance to interference from coexisting anions, and poor acid-base adaptability, a method based on bismuth-based oxoacid salt material (Bi2WO6) is proposed for the simultaneous and efficient removal of I... - and IO3 - Methods for treating iodine-containing wastewater. Bismuth-based oxoacid salts (Bi2WO6), due to their flower-like microsphere structure, assemble into flower-like nanosheets arranged in an interlaced pattern with large gaps between the sheets, resulting in a high specific surface area. Simultaneously, in aqueous solution, the surface of Bi2WO6 exposes metal cations (such as Bi...). 3+ The material contains bismuth ions (Bi) and hydroxyl groups (-OH). These surface hydroxyl groups are active adsorption sites, providing more surface adsorption sites for pollutants and thus enhancing its adsorption capacity. The material is negatively charged, exhibits chemisorption with high strength, and its adsorption capacity increases with increasing pH. It is also less susceptible to interference from other coexisting anions. Furthermore, the material contains bismuth ions (Bi... 3+ ) and iodide ions (I - The strong chemical affinity between bismuth and bismuth, along with their structural tunability and safety, demonstrates promising application prospects, making them a novel iodine adsorbent with development potential.

[0028] (2) The bismuth-based oxoacid salt material (Bi2WO6) of the present invention simultaneously removes I - and IO3 - It has outstanding capabilities and can simultaneously and efficiently adsorb and remove I- coexisting in a liquid environment. - and IO3 - This method overcomes the technical bottleneck of traditional adsorbents that can only remove single iodine species, and has significant advantages in treating wastewater containing mixed iodine forms. It features fast adsorption kinetics, high treatment efficiency, and strong resistance to I-. - and IO3 - All can rapidly reach adsorption saturation in about 10 minutes, demonstrating a fast processing rate that meets the needs of continuous and rapid treatment of iodine-containing wastewater. They exhibit large adsorption capacity and excellent treatment effect, demonstrating high-efficiency removal capability for iodine-containing wastewater of varying concentrations, with excellent iodine capture performance. They also possess strong resistance to interference from coexisting anions, exhibiting excellent performance in Cl... - SO4 2- CO3 2- PO4 3- NO3 - Under 10 times higher concentrations of plasma interference, the effect on I - and IO3 -The removal effect remains relatively stable, making it suitable for complex iodine-containing wastewater systems. It has a wide pH range, with better performance under alkaline conditions, exhibiting good removal efficiency within a pH range of 1-11. Adsorption capacity increases with increasing pH, maintaining high removal efficiency even in alkaline environments, making it suitable for complex acid-base conditions such as industrial wastewater. The material exhibits good stability and is safe to use. The Bi2WO6 material used demonstrates excellent thermal stability, showing no significant decomposition at 700-800 ℃. After iodine adsorption, the material's morphology and crystal structure remain intact, posing no risk of secondary pollution and meeting the safety requirements for wastewater treatment. The process is simple and easily industrialized. The treatment method is easy to operate, operates under mild conditions, and facilitates solid-liquid separation without requiring complex equipment. Combined with the material's low cost and environmental friendliness, it possesses excellent potential for industrial application, providing a new solution for the efficient purification of radioactive iodine-containing wastewater.

[0029] (3) The present invention uses a bismuth-based oxoacid composite material (Bi2WO6 / modified biochar) prepared based on bismuth-based oxoacid material (Bi2WO6) to simultaneously remove I - and IO3 - It has superior capabilities and can simultaneously and efficiently adsorb and remove I- coexisting in a liquid environment. - and IO3 - First, the straw is pretreated with nitric acid, which not only promotes the formation of a porous structure and increases the specific surface area of ​​the biochar, but also increases the number of active sites. Then, the biochar is impregnated and modified with aluminum chloride and bismuth nitrate, followed by heat treatment under an argon-hydrogen atmosphere to introduce more active adsorption sites. Polyvinylpyrrolidone is added to improve dispersibility and surface activity, promoting the reaction. Finally, Bi2WO6 is loaded onto the modified biochar, which effectively inhibits the aggregation of Bi2WO6 particles. Simultaneously, the interlaced arrangement of Bi2WO6 nanosheets forming a cavity structure synergistically promotes the adsorption of I... - and IO3 - Rapid adsorption and fixation, combined with abundant active sites, further enhance the efficient and selective adsorption of iodide ions and iodate ions.

[0030] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0031] Figure 1 The XRD pattern of Bi2WO6 prepared in Example 1; Figure 2 The FT-IR image of Bi2WO6 prepared in Example 1; Figure 3 (a) SEM image and (b) EDX image of Bi2WO6 prepared in Example 1; Figure 4 Zeta potential diagrams of Bi2WO6 prepared in Example 1 at different pH values; Figure 5 The TGA spectrum of Bi2WO6 prepared in Example 1; Figure 6 Bi2WO6 prepared in Example 1 was used to treat I under coexisting anions. - The amount of adsorption; Figure 7 Bi2WO6 prepared in Example 1 exhibits resistance to IO3 under coexisting anions. - The amount of adsorption; Figure 8 Bi2WO6 prepared in Example 1 was used to treat I under different pH conditions. - Adsorption; Figure 9 Bi2WO6 prepared in Example 1 reacts with IO3 under different pH conditions - Adsorption; Figure 10 Bi2WO6 prepared for Example 1 against (a)I - The adsorption kinetics curves, (b) IO3 - Adsorption kinetics curves; Figure 11 Bi2WO6 prepared for Example 1 against (a)I - Isothermal adsorption curves, (b) IO3 - Isothermal adsorption curves; Figure 12 Bi2WO6-I after iodine adsorption on Bi2WO6 prepared in Example 1 - and Bi2WO6-IO3 - XRD pattern; Figure 13 Bi2WO6 adsorbent I prepared in Example 1 - Bi2WO6-I - FT-IR plot; Figure 14 Bi2WO6 prepared in Example 1 adsorbs IO3 - Bi2WO6-IO3 - FT-IR plot; Figure 15 Bi2WO6 prepared in Example 1 adsorbed I in (a) - (b) SEM image after adsorption of I - The subsequent EDS plot; Figure 16 Bi2WO6 prepared in Example 1 adsorbs IO3 in (a) - (b) SEM image after adsorption of IO3- The subsequent EDS plot; Figure 17 XPS spectra of Bi2WO6 prepared in Example 1 before and after iodine adsorption: (a) Measurement spectrum; (b) Bi2WO6, Bi2WO6-I - and Bi2WO6-IO3 - O 1s plot; (c) Bi2WO6, Bi2WO6-I - and Bi2WO6-IO3 - I 3d diagram; (d)Bi2WO6, Bi2WO6-I - and Bi2WO6-IO3 - The Bi 4f diagram. Detailed Implementation

[0032] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0033] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0034] Example 1 A method for preparing a bismuth-based oxoacid salt material includes the following steps: Step 1: Add 0.485 g Bi(NO3)3·5H2O to 20 mL of deionized water containing 1 mmol nitric acid, sonicate for 10 min at room temperature to prepare a transparent solution, denoted as solution A; add 1.649 g Na2WO4·2H2O to 20 mL of deionized water, sonicate for 10 min to prepare a solution, denoted as solution B. Step 2: Add a magnetic stir bar to solution A and stir continuously on a magnetic stirrer. Add solution B dropwise to solution A and stir at room temperature for 2 hours. Transfer the stirred suspension to a stainless steel reactor lined with tetrafluoroethylene and heat at 160 °C for 20 hours. Allow it to cool naturally to room temperature to obtain the reaction product. Step 3: Wash the reaction product thoroughly with deionized water 8 times, then filter it, and then dry the reaction product in an oven at 60 °C for 12 h to obtain bismuth-based oxyacid salt material (Bi2WO6).

[0035] Figure 1 The XRD pattern of Bi2WO6 prepared in Example 1 shows the characteristic peaks of pure phase Bi2WO6 crystal.

[0036] Figure 2 The FT-IR image of Bi2WO6 prepared in Example 1 shows that at 3431 cm⁻¹...-1 The characteristic peak baseline at this point is attributed to the OH stretching vibration, corresponding to the hydroxyl groups (-OH) present on the surface of bismuth tungstate. 1628 cm⁻¹ -1 The vibrational peak at this location originates from weakly interacting surface groups and is caused by the bending vibration of hydroxyl groups, further confirming the presence of hydroxyl groups. (1380 cm⁻¹) -1 The absorption peak is attributed to NO3. − This may be due to residual bismuth nitrate precursor. 730 cm -1 With 581 cm -1 The strong absorption at this point corresponds to the Bi-O vibration, which may originate from the Bi-OW coordination structure formed between Bi and heteropoly anions.

[0037] Figure 3 (a) SEM image and (b) EDX image of Bi2WO6 prepared in Example 1; it can be observed that the bismuth-based oxoacid salt material is a micron-sized flower-like microsphere material with a size of about 2.5 μm. The flower-like nanosheets are arranged in an interlaced manner with large gaps between the sheets, and have a good cavity structure.

[0038] Figure 4 The image shows the zeta potential of Bi2WO6 prepared in Example 1 at different pH values; it can be seen that the material is negatively charged.

[0039] Figure 5 The TGA spectrum of Bi2WO6 prepared in Example 1 shows that the material has good thermal stability and remains stable at high temperatures of 700~800 ℃ with a mass loss of only 0.19%.

[0040] The successful synthesis of bismuth-based oxyacid acid material (Bi2WO6) was confirmed by XRD, FT-IR, SEM and EDX characterization. This material is a layered oxide crystal with a good cavity structure. Zeta potential analysis showed that the material is negatively charged in the liquid environment. TGA analysis showed that the material is still stable at high temperatures of 700~800 °C, which shows that it has good thermal stability. The above analysis provides feasibility support for subsequent adsorption experiments.

[0041] Example 2 A method for preparing a bismuth-based oxyacid salt composite material includes the following steps: S1. Preparation of modified biochar, including: S11. Add 100 g of corn straw powder to 1000 mL of 5wt% nitric acid solution and impregnate at 60 ℃ for 2 h. After filtration, washing and drying, pretreated straw powder is obtained. Place the pretreated straw powder in a tube furnace and heat it to 500 ℃ at a heating rate of 10 ℃ / min under a nitrogen atmosphere and hold it at that temperature for 2 h. After naturally cooling to room temperature, grind it through a 100-mesh sieve to obtain biochar. S12. Add 2 g Bi(NO3)3·5H2O to 50 mL of deionized water containing 5 mmol nitric acid, and sonicate for 10 min at room temperature to prepare solution C; add 10 g biochar and 0.5 g polyvinylpyrrolidone to 100 mL of 10 g / L AlCl3 solution, and sonicate for 10 min to prepare solution D; add solution C dropwise to solution D, stir at room temperature for 2 h, let stand for 12 h, and then filter, wash, and dry to obtain pre-modified biochar; S13. Place the pre-modified biochar in a tube furnace and keep it at 250 ℃ for 6 h under an argon-hydrogen atmosphere (argon-hydrogen volume ratio of 9:1). Allow it to cool naturally to room temperature and grind it through a 100-mesh sieve to obtain the modified biochar. S2. Add 0.485 g Bi(NO3)3·5H2O to 20 mL of deionized water containing 1 mmol nitric acid, sonicate for 10 min at room temperature to prepare a transparent solution, denoted as solution A; add 1.649 g Na2WO4·2H2O to 20 mL of deionized water, sonicate for 10 min to prepare a solution, denoted as solution B. S3. Add a magnetic stir bar to solution A and stir continuously on a magnetic stirrer. Add solution B dropwise to solution A and stir at room temperature for 2 h. Transfer the stirred suspension to a stainless steel reactor lined with tetrafluoroethylene, add 0.1 g of modified biochar and 0.01 g of polyvinylpyrrolidone, heat at 160 ℃ for 20 h, and cool naturally to room temperature to obtain the reaction product. S4. The reaction product was washed thoroughly with deionized water 8 times, then filtered, and then dried in an oven at 60 °C for 12 h to obtain bismuth-based oxyacid salt composite material (Bi2WO6 / modified biochar).

[0042] Comparative Example 1 In this comparative example, the method for preparing biochar includes: 100 g of corn stalk powder was added to 1000 mL of 5 wt% nitric acid solution and impregnated at 60℃ for 2 h. After filtration, washing and drying, pretreated stalk powder was obtained. The pretreated stalk powder was placed in a tube furnace and heated to 500℃ at a heating rate of 10 ℃ / min under a nitrogen atmosphere and held at that temperature for 2 h. After natural cooling to room temperature, it was ground through a 100-mesh sieve to obtain biochar. The remaining steps are the same as in Example 2; Compared to Example 2, this comparative example uses unmodified biochar.

[0043] Comparative Example 2 In this comparative example, the method for preparing modified biochar includes: S11. Add 100 g of corn straw powder to 1000 mL of 5wt% nitric acid solution and impregnate at 60℃ for 2 h. After filtration, washing and drying, pretreated straw powder is obtained. Place the pretreated straw powder in a tube furnace and heat it to 500℃ at a heating rate of 10℃ / min under a nitrogen atmosphere and hold it at that temperature for 2 h. After naturally cooling to room temperature, grind it through a 100-mesh sieve to obtain biochar. S12. Prepare 50 mL of deionized water containing 5 mmol nitric acid as solution C; add 10 g biochar and 0.5 g polyvinylpyrrolidone to 100 mL of 10 g / L AlCl3 solution, and sonicate for 10 min to prepare solution D; add solution C dropwise to solution D, stir at room temperature for 2 h, let stand for 12 h, and then filter, wash, and dry to obtain pre-modified biochar; S13. Place the pre-modified biochar in a tube furnace and keep it at 250 ℃ for 6 h under an argon-hydrogen atmosphere (argon-hydrogen volume ratio of 9:1). Allow it to cool naturally to room temperature and grind it through a 100-mesh sieve to obtain the modified biochar. The remaining steps are the same as in Example 2; Compared to Example 2, the modified biochar preparation method in this comparative example does not use Bi(NO3)3·5H2O.

[0044] Comparative Example 3 In this comparative example, the method for preparing modified biochar includes: S11. Add 100 g of corn straw powder to 1000 mL of 5wt% nitric acid solution and impregnate at 60℃ for 2 h. After filtration, washing and drying, pretreated straw powder is obtained. Place the pretreated straw powder in a tube furnace and heat it to 500℃ at a heating rate of 10℃ / min under a nitrogen atmosphere and hold it at that temperature for 2 h. After naturally cooling to room temperature, grind it through a 100-mesh sieve to obtain biochar. S12. Add 2 g Bi(NO3)3·5H2O to 50 mL of deionized water containing 5 mmol nitric acid, and sonicate for 10 min at room temperature to prepare solution C; add 10 g biochar and 0.5 g polyvinylpyrrolidone to 100 mL of deionized water, and sonicate for 10 min to prepare solution D; add solution C dropwise to solution D, stir for 2 h at room temperature, let stand for 12 h, filter, wash, and dry to obtain pre-modified biochar; S13. Place the pre-modified biochar in a tube furnace and keep it at 250 ℃ for 6 h under an argon-hydrogen atmosphere (argon-hydrogen volume ratio of 9:1). Allow it to cool naturally to room temperature and grind it through a 100-mesh sieve to obtain the modified biochar. The remaining steps are the same as in Example 2; Compared to Example 2, AlCl3 is not used in the modified biochar preparation method of this comparative example.

[0045] Comparative Example 4 In this comparative example, the method for preparing modified biochar includes: S11. Add 100 g of corn straw powder to 1000 mL of 5wt% nitric acid solution and impregnate at 60℃ for 2 h. After filtration, washing and drying, pretreated straw powder is obtained. Place the pretreated straw powder in a tube furnace and heat it to 500℃ at a heating rate of 10℃ / min under a nitrogen atmosphere and hold it at that temperature for 2 h. After naturally cooling to room temperature, grind it through a 100-mesh sieve to obtain biochar. S12. Add 2 g Bi(NO3)3·5H2O to 50 mL of deionized water containing 5 mmol nitric acid, and sonicate for 10 min at room temperature to prepare solution C; add 10 g biochar to 100 mL of 10 g / L AlCl3 solution, and sonicate for 10 min to prepare solution D; add solution C dropwise to solution D, stir at room temperature for 2 h, let stand for 12 h, and then filter, wash, and dry to obtain pre-modified biochar. S13. Place the pre-modified biochar in a tube furnace and keep it at 250 ℃ for 6 h under an argon-hydrogen atmosphere (argon-hydrogen volume ratio of 9:1). Allow it to cool naturally to room temperature and grind it through a 100-mesh sieve to obtain the modified biochar. The remaining steps are the same as in Example 2; Compared to Example 2, the modified biochar preparation method in this comparative example does not use polyvinylpyrrolidone.

[0046] Comparative Example 5 In this comparative example, the method for preparing modified biochar includes: S11. Place corn stalk powder in a tube furnace, heat it to 500 ℃ at a heating rate of 10 ℃ / min under a nitrogen atmosphere and hold it at that temperature for 2 h. Let it cool naturally to room temperature and grind it through a 100-mesh sieve to obtain biochar. S12. Add 2 g Bi(NO3)3·5H2O to 50 mL of deionized water containing 5 mmol nitric acid, and sonicate for 10 min at room temperature to prepare solution C; add 10 g biochar and 0.5 g polyvinylpyrrolidone to 100 mL of 10 g / L AlCl3 solution, and sonicate for 10 min to prepare solution D; add solution C dropwise to solution D, stir at room temperature for 2 h, let stand for 12 h, and then filter, wash, and dry to obtain pre-modified biochar; S13. Place the pre-modified biochar in a tube furnace and keep it at 250 ℃ for 6 h under an argon-hydrogen atmosphere (argon-hydrogen volume ratio of 9:1). Allow it to cool naturally to room temperature and grind it through a 100-mesh sieve to obtain the modified biochar. The remaining steps are the same as in Example 2; Compared to Example 2, the modified biochar preparation method in this comparative example does not involve nitric acid pretreatment.

[0047] Application Example 1 Application of a bismuth-based oxoacid salt material in the treatment of iodine-containing wastewater (1) Coexisting anion pairs I - Adsorption effect Weigh out 8 mg of bismuth-based oxoacid salt material from five groups, maintaining a solid-liquid ratio of 1:1, and add 8 mL of I₂ solution containing coexisting anions and iodide ions in a molar ratio of 10:1. − Solution (200 ppm, pH=10) with Cl − Solution, SO4 2− Solution, CO3 2− Solution and PO4 3− The solution was placed on a shaker and shaken for 2 hours. After shaking, the supernatant was collected, filtered through a 0.22 μm aqueous MCE membrane, diluted, and the iodine ion concentration was measured using a UV spectrophotometer to obtain the material's response to I... - The adsorption capacity is calculated using the following formula: Where, q e Representing I − The adsorption capacity is V, the solution volume is m, the material mass is C0, and the initial concentration of iodide ions in the solution before adsorption is C. e This represents the concentration of iodide ions in the solution after adsorption equilibrium.

[0048] (2) Coexisting anion pairs IO3 - Adsorption effect Weigh out 8 mg of bismuth-based oxoacid salt material from five groups, maintaining a solid-liquid ratio of 1:1, and add 8 mL of IO3 solution with a molar ratio of coexisting anion to iodate ion of 10:1. - Solution (500 ppm, pH=10) with Cl − Solution, SO4 2− Solution, CO3 2− Solution and NO3 − The solution was placed on a shaker and shaken for 2 hours. After shaking, the supernatant was collected, filtered through a 0.22 μm aqueous MCE membrane, diluted, and the iodate ion concentration was determined using a UV spectrophotometer to obtain the iodide concentration for IO3-. - The adsorption capacity is calculated using the following formula: Where, q e Represents IO3 - The adsorption capacity is V, the solution volume is m, the material mass is C0, and the initial concentration of iodate ions in the solution before adsorption is C. e This represents the concentration of iodate ions in the solution after adsorption equilibrium.

[0049] (3) Effects of different pH values ​​on I - and IO3 - adsorption Weigh out 8 mg of bismuth-based oxoacid salt material for 6 groups, maintain a solid-liquid ratio of 1:1, and add 8 mL of I solution with pH values ​​of 1, 3, 5, 7, 9, and 11 respectively. - Solution (200 ppm) or IO3 - The solution (500 ppm) was placed in a shaker and shaken for 2 h. After shaking, the supernatant was collected, filtered through a 0.22 μm aqueous MCE membrane, diluted, and the iodine concentration was determined using a UV spectrophotometer to obtain the iodine concentration relative to I. - or IO3 - The adsorption capacity is calculated using the following formula: Where, q e V represents the adsorption capacity, V represents the solution volume, m represents the material mass, and C0 represents the I content in the solution before adsorption. - or IO3 - The initial concentration, C e Represents I in the solution after adsorption equilibrium - or IO3 - The concentration.

[0050] (4) to I - and IO3 - Adsorption kinetics The solid-liquid ratio was controlled at 1:1. 8 mg of the prepared bismuth-based oxoacid salt material was weighed and added to 8 mL of I...- Solution (500 ppm, pH=10) or IO3 - In a solution (800 ppm, pH=10), after mixing, the mixture was placed on a shaker and samples were taken at specific time points of 3, 5, 10, 20, 30, 60, 90, 120, 180, 240, 300, 360, and 420 min for adsorption kinetic experiments. After each sampling, the supernatant was collected, filtered through a 0.22 μm aqueous MCE membrane, diluted, and I was measured using a UV spectrophotometer. - and IO3 - Concentration, to obtain the effect of I - and IO3 - The adsorption capacity is calculated using the following formula: Where, q e V represents the adsorption capacity, V represents the solution volume, m represents the material mass, and C0 represents the I content in the solution before adsorption. - or IO3 - The initial concentration, C e Represents I in the solution after adsorption equilibrium - or IO3 - The concentration.

[0051] (5) to I - or IO3 - Isothermal adsorption method The solid-liquid ratio was controlled at 1:1. 8 mg of the prepared bismuth-based oxoacid salt material was weighed and added to 8 mL of a solution of a certain concentration of I... - (100~2000 mg / L, pH=10) and IO3 - In a solution of (100~2100 mg / L, pH=10), the mixture was placed in a shaker and shaken for 2 h for isothermal adsorption experiments. After the experiments, the supernatant was collected, filtered through a 0.22 μm aqueous MCE membrane, diluted, and the iodine concentration was determined using a UV spectrophotometer to obtain the iodine concentration for I. - and IO3 - The adsorption capacity is calculated using the following formula: Where, q e V represents the adsorption capacity, V represents the solution volume, m represents the material mass, and C0 represents the I content in the solution before adsorption. - or IO3 - The initial concentration, C e Represents I in the solution after adsorption equilibrium - or IO3 - The concentration.

[0052] Langmuir isotherm model: Freundlich isotherm model: Allocation coefficient: Where, q m (mg / g) indicates the effect of bismuth-based oxoacid salts on I - and IO3 - Maximum adsorption capacity; K L and K F Representing Langmuir and Freundrich intensity constants respectively; C e (mg / L) represents I after adsorption - and IO3 - The remaining concentration. Distribution coefficient (K) d () is to evaluate the effect of bismuth-based oxoacid salt materials on I - and IO3 - The key parameter of adsorption capacity.

[0053] Figure 6 Bi2WO6 prepared in Example 1, with coexisting anions and I - The molar ratio of I at 10:1 - Adsorption; same I - Under concentration conditions, in Cl − SO4 2− CO3 2− and PO4 3− Under interference, Bi2WO6 affects I - The adsorption capacity remained essentially unchanged, demonstrating the effectiveness of Bi2WO6 in adsorbing I... - At that time, it has the ability to react with Cl − SO4 2− CO3 2− and PO4 3− It has good anti-interference ability with coexisting anions.

[0054] Figure 7 Bi2WO6 prepared in Example 1 coexists with anion and IO3 - The molar ratio of 10:1 for IO3 - Adsorption; same IO3 - Under concentration conditions, in Cl − SO4 2− CO3 2− and NO3 − Under interference, Bi2WO6 affects IO3 - The adsorption capacity remained essentially unchanged, demonstrating that Bi2WO6 effectively adsorbed IO3. - At that time, it has the ability to react with Cl −SO4 2− CO3 2− and NO3 − It has good anti-interference ability with coexisting anions.

[0055] Figure 8 Bi2WO6 prepared in Example 1 was used to treat I under different pH conditions. - Adsorption; in the same I - Under certain concentration conditions, as pH increases, Bi2WO6 has an effect on I... - The adsorption amount gradually increases.

[0056] Figure 9 Bi2WO6 prepared in Example 1 reacts with IO3 under different pH conditions - Adsorption; in the same IO3 - Under certain concentration conditions, as pH increases, Bi2WO6's effect on IO3... - The adsorption capacity first decreases and then increases.

[0057] Figure 10 Bi2WO6 prepared for Example 1 against (a)I - The adsorption kinetics curves, (b) IO3 - Adsorption kinetics curves of Bi2WO6 for I - and IO3 - Both exhibit rapid adsorption kinetics, reaching adsorption saturation in approximately 10 minutes. At a concentration of 500 ppm, both show strong adsorption for I... - The maximum adsorption capacity was 141 mg / g, and it was effective against IO3 at a concentration of 800 ppm. - The maximum adsorption capacity is 216 mg / g.

[0058] Figure 11 Bi2WO6 prepared for Example 1 against (a)I - Isothermal adsorption curves, (b) IO3 - Isothermal adsorption curves of Bi₂WO₆ for I₂ under high concentration conditions; - and IO3 - Maximum adsorption capacity q m The concentrations reached 314 mg / g and 329 mg / g respectively, demonstrating excellent iodine capture performance.

[0059] Table 1 Through coexisting anion competitive adsorption experiments, adsorption experiments under different pH conditions, and adsorption kinetic experiments, it was demonstrated that the bismuth-based oxoacid salt material (Bi2WO6) effectively attracts iodine species (I) in liquid. − and IO3 −It has the advantages of high adsorption capacity and fast adsorption kinetics; in Cl − SO4 2− CO3 2− The interference of coexisting anions on I in the liquid state − and IO3 − The adsorption and removal of I⁻ and IO₃⁻ remained effective, exhibiting good resistance to interference from coexisting anions. It also demonstrated good pH adaptability, maintaining high adsorption capacity for I⁻ and IO₃⁻ even under alkaline conditions as pH increased. Isothermal adsorption experiments were conducted, and the experimental data were fitted using both Langmuir and Freundlich isothermal adsorption models (parameters are shown in Table 1). For I⁻… − The adsorption of Langmuir model yields the coefficient of determination ( ). R The result (²=0.9827) is significantly higher than that of the Freundlich model ( R (²=0.9649), from which it can be inferred that I − The adsorption behavior on the Bi2WO6 surface tends towards a monolayer adsorption mechanism, primarily adsorbing onto the active sites on the surface. As for IO3... − Adsorption, Langmuir model ( R The model with a length of 2² = 0.9837 also showed a better fit than the Freundlich model. R (²=0.9533), examples show that it adsorbs IO3. − The process is still dominated by monolayer adsorption.

[0060] Figure 12 Bi2WO6-I after iodine adsorption - and Bi2WO6-IO3 - XRD pattern; Curve 1 (adsorption I) - (After), Curve 2 (Adsorption of IO3) - The characteristic peak position of the latter peak is basically the same as that of the original peak, but compared to the former peak... Figure 1 Both showed reduced intensity and slightly broadened peak shape.

[0061] Figure 13 Bi2WO6-I - The FT-IR plot; the peak changes shown in the curve reflect the following mechanism: according to the hard and soft acid-base theory (HSAB), I - Belongs to Lewis bases, Bi in Bi2WO6 3+ Both are Lewis acids, and they readily undergo coordination interactions. Simultaneously, surface hydroxyl groups participate in this process, resulting in an OH peak (3431 cm⁻¹). -1 1628 cm -1 ) strength Figure 2 The significant reduction indicates that the hydroxyl sites were consumed, possibly due to the interaction between surface hydroxyl groups and I.- Ion exchange, or the direct formation of hydrogen bonds or coordination between hydroxyl groups and I−. 1112 cm -1 and 976 cm -1 The peak position reflects the W=O and Bi-O vibrations, compared to Figure 2 Its peak position and intensity both shifted significantly, thus indicating that I - After coordination with Bi, the vibrational environment of the W=O bond and the Bi-O bond is indirectly disturbed (e.g., bond length and bond strength change), indicating that I - Confirmed with the surface metal sites of bismuth tungstate (Bi 3+ Coordination occurs.

[0062] Figure 14 Bi2WO6-IO3 - FT-IR plot; adsorbed IO3 − Subsequently, the peak change mechanism of the curve: According to the hard and soft acid-base theory (HSAB), IO3 − It belongs to Lewis bases, while Bi in Bi2WO6 3+ Both are Lewis acids, and their interaction can be strong through coordination. Simultaneously, surface hydroxyl groups also participate in the interaction, as evidenced by the OH peak (3431 cm⁻¹). -1 1628 cm -1 ) strength Figure 2 The significant decrease indicates that IO3 − It interacts with surface hydroxyl groups, examples include IO3. − It binds to hydroxyl protons through electrostatic attraction, or forms coordination with hydroxyl oxygen. 1112 cm -1 With 976 cm -1 Peak shape and Figure 2 The difference is significant, reflecting IO3 − Medium oxygen and Bi 3+ After coordination, the vibrational environment of W=O and Bi−O bonds changes, thus confirming the presence of IO3. − With bismuth tungstate surface metal sites (Bi 3+ Coordination behavior of ).

[0063] Figure 15 For Bi2WO6 in (a) adsorption I - (b) SEM image after adsorption of I - EDS image after adsorption; Bi2WO6 in I - Its morphology and structure remained unchanged afterward, consistent with before, and its physical structure was not destroyed.

[0064] Figure 16 Bi2WO6 adsorbs IO3 in (a) - (b) SEM image after adsorption of IO3 -EDS image after adsorption; Bi2WO6 adsorbing IO3 - Its morphology and structure remained unchanged afterward, consistent with before, and its physical structure was not destroyed.

[0065] Figure 17 XPS spectra of Bi2WO6 before and after iodine adsorption: (a) Measurement spectrum; (b) Bi2WO6, Bi2WO6-I - and Bi2WO6-IO3 - O 1s plot; (c) Bi2WO6, Bi2WO6-I - and Bi2WO6-IO3 - I 3d diagram; (d)Bi2WO6, Bi2WO6-I - and Bi2WO6-IO3 - Bi 4f plot; binding energy calibrated using C 1s (284.8 eV). Adsorption I - and IO3 - Subsequently, the peaks at approximately 532.6 eV and 530 eV should be attributed to the OH bonds and Bi-O bonds in Bi2WO6, respectively. Figure 17 b); Adsorption I - Afterwards, approximately 630.3 eV and 618.8 eV correspond to I, respectively. - I 3d 3 / 2 and I 3d 5 / 2 Adsorb IO3 - Subsequently, the peaks at 635.4 eV and 624 eV belong to IO3, respectively. - Middle I 5+ I 3d ions 3 / 2 and I 3d 5 / 2 However, I appears at 630.3 eV and 618.8 eV. - The strong peak indicates that under acidic conditions, some IO3... - Can be converted to I - This further corroborates the relationship between the hydroxyl groups on the material surface and I. - Ion exchange occurs ( Figure 17 c).

[0066] I - The adsorption mechanism can be attributed to the following aspects: 1. Coordination between hard and soft acids and bases. According to the HSAB theory, hard acids preferentially bind to hard bases, and soft acids preferentially bind to soft bases. 3+ It is an interfacial acid between hard and soft acids, therefore, Bi 3+ It readily reacts with iodides (I - ) and other soft donors and iodate (IO3) - Hard donor reactions, such as coordination, occur, thereby achieving I -Highly efficient adsorption, this is I - The core pathway of adsorption. 2. Ion exchange or coordination involving surface hydroxyl groups (OH). - It can undergo ion exchange with hydroxyl groups on the material surface, or directly form hydrogen bonds / coordination structures with hydroxyl groups, resulting in the consumption of a large number of hydroxyl sites, as shown by the characteristic peak of OH in the infrared spectrum (3431 cm⁻¹). -1 1628 cm -1 The intensity is thus significantly reduced. Furthermore, indirect structural perturbations induced by coordination are also evident. After I coordinates with Bi, the vibrational environment (such as bond length and bond strength) of the W=O bonds and Bi-O bonds within the material changes, leading to changes in the corresponding infrared characteristic peaks (1112, 976 cm⁻¹). -1 The occurrence of peak position shift and intensity change further confirms the occurrence of coordination.

[0067] For IO3 - The adsorption mechanism of IO3 is manifested as: 1. Coordination between hard and soft acids and bases. According to the HSAB theory, IO3... - It is a Lewis base and can react with interfacial acids (Bi) that lie between hard and soft acids. 3+ This allows for coordination, thereby enabling the control of IO3. - The removal of [something] also disturbs the vibrational states of W=O and Bi-O bonds, resulting in significant differences in infrared peak shapes. Hydroxyl groups on the material surface also participate in the interaction. 2, IO3 - Hydroxyl protons can be bound by electrostatic attraction or coordinate with hydroxyl oxygen, leading to a reduction in the number of surface hydroxyl groups and a subsequent decrease in the intensity of the OH characteristic peak. This is similar to the effect of I... - Adsorption exhibits common characteristics. 3. In addition, some IO3... - Under acidic conditions, a form transformation occurs. The newly formed I... - Then, according to the aforementioned I - The adsorption pathway is fixed by the material adsorption, as shown in the XPS spectrum at IO3. - I was detected after adsorption - The strong characteristic peaks in this example demonstrate the existence of the transformation process, which enhances the overall removal efficiency.

[0068] In summary, the above results confirm that bismuth-based oxoacid salt materials (Bi2WO6) can be used for the simultaneous and efficient removal of I... - and IO3 - This invention provides a novel processing method and application. The adsorption of two iodine species by this material is primarily chemisorption, encompassing ion exchange / hydrogen bonding interactions of surface hydroxyl groups and Bi... 3+ The material exhibits synergistic effects with iodine species through coordination, electrostatic interactions, and the physical adsorption advantages resulting from its high specific surface area. These multiple mechanisms work together to enhance the material's ability to attract iodine in alkaline environments. - With IO3 -All exhibit excellent adsorption performance and good anti-interference ability.

[0069] Application Example 2 Application of a bismuth-based oxyacid salt composite material in the treatment of iodine-containing wastewater The experiment was conducted according to the method of Application Example 1. Table 2 shows the results of the Bi2WO6 prepared in Example 1 and the bismuth-based oxoacid salt composite material prepared in Example 2 in the presence of coexisting anions and I... - When the ratio is 10:1, it affects I - The adsorption capacity; Table 3 shows the adsorption capacity of Bi2WO6 prepared in Example 1 and the bismuth-based oxoacid salt composite material prepared in Example 2 in the presence of coexisting anions and IO3. - When the ratio is 10:1 for IO3 - The adsorption capacity. It can be seen that the bismuth-based oxyacid salt composite material has good anti-interference ability against coexisting anions, and under different anion coexistence conditions, Example 2 shows that it has a better resistance to I... - and IO3 - The adsorption capacity of all of them is better than that of Example 1.

[0070] Table 2 Table 3 The bismuth-based oxoacid salt composite material prepared in Example 2 is effective against I. - and IO3 - It exhibits rapid adsorption kinetics, reaching adsorption saturation in approximately 10 minutes. At a concentration of 500 ppm, it exhibits strong adsorption for I... - The maximum adsorption capacity was 283 mg / g, and it was effective against IO3 at a concentration of 800 ppm. - The maximum adsorption capacity was 435 mg / g, which is superior to the bismuth-based oxoacid salt material prepared in Example 1.

[0071] Table 4 shows the Bi2WO6 prepared in Example 1 and the bismuth-based oxoacid composite material prepared in Example 2 at different initial I... - (or IO3) - The amount of adsorption in the solution of concentration I. It can be seen that as I... - and IO3 - As the initial concentration increased, the adsorption capacity gradually increased; at different initial concentrations, the adsorption capacity of Example 2 was higher than that of Example 1.

[0072] Table 4 The Bi2WO6 prepared in Example 1, the bismuth-based oxoacid composite material prepared in Example 2, and the bismuth-based oxoacid composite materials prepared in Comparative Examples 1-5 were subjected to I... - and IO3- Adsorption test: The solid-liquid ratio was controlled at 1:1. 8 mg of adsorbent material was weighed and added to 8 mL of I... - Solution (500 ppm, pH=10) or IO3 - In a solution (500 ppm, pH=10), after mixing, the mixture was placed on a shaker and shaken for 2 h. After the shaken mixture was removed, the supernatant was filtered through a 0.22 μm aqueous MCE membrane, diluted, and then I was measured using a UV spectrophotometer. - and IO3 - Concentration, to obtain the effect of I - and IO3 - The adsorption amount is shown in Table 5.

[0073] Table 5 In summary, the above results confirm that bismuth-based oxoacid salt composite materials (Bi2WO6 / modified biochar) can be used for the simultaneous and efficient removal of I₂. - and IO3 - The material exhibits superior adsorption performance for both iodine species and has good anti-interference ability.

[0074] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. The application of a bismuth-based material in the treatment of iodine-containing wastewater, characterized in that, The bismuth-based material is a bismuth-based oxyacid salt material and / or a bismuth-based oxyacid salt composite material; wherein the bismuth-based oxyacid salt material is Bi2WO6, and the bismuth-based oxyacid salt composite material is Bi2WO6 / modified biochar.

2. The application as described in claim 1, characterized in that, The bismuth-based material is used to remove iodide ions and iodate ions from iodine-containing wastewater.

3. A method for preparing a bismuth-based material for treating iodine-containing wastewater, characterized in that, The bismuth-based material is a bismuth-based oxyacid salt material, and its preparation method includes the following steps: Step 1: Dissolve Bi(NO3)3·5H2O in nitric acid solution to prepare solution A; dissolve Na2WO4·2H2O in deionized water to prepare solution B; Step 2: Under continuous stirring, add solution B dropwise to solution A, continue stirring, transfer the stirred suspension to a reaction vessel, heat the reaction, and allow it to cool naturally to room temperature to obtain the reaction product; Step 3: Wash, filter and dry the reaction product to obtain Bi2WO6, which is a bismuth-based oxyacid salt material.

4. The method for preparing bismuth-based materials for treating iodine-containing wastewater as described in claim 3, characterized in that, In step one, the mass-to-volume ratio of Bi(NO3)3·5H2O to nitric acid solution is 0.1~1g:5~50mL; in the nitric acid solution, the molar volume ratio of nitric acid to deionized water is 0.5~1.5mmol:10~50mL; and the mass-to-volume ratio of Na2WO4·2H2O to deionized water is 1~2g:10~50mL.

5. The method for preparing bismuth-based materials for treating iodine-containing wastewater as described in claim 3, characterized in that, In step two, the mass ratio of Bi(NO3)3·5H2O in solution A to Na2WO4·2H2O in solution B is 0.1~1:1~2; stirring continues for 1~3 hours; the reaction is heated to 150~170℃ for 18~22 hours.

6. The method for preparing bismuth-based materials for treating iodine-containing wastewater as described in claim 3, characterized in that, In step three, the washing process involves washing with deionized water 5 to 10 times; the drying temperature is 50 to 80°C, and the drying time is 8 to 16 hours.

7. A method for preparing a bismuth-based material for treating iodine-containing wastewater, characterized in that, The bismuth-based material is a bismuth-based oxoacid salt composite material, and its preparation method includes the following steps: S1. Preparation of modified biochar; S2. Dissolve Bi(NO3)3·5H2O in nitric acid solution to prepare solution A; dissolve Na2WO4·2H2O in deionized water to prepare solution B; S3. Under continuous stirring, solution B is added dropwise to solution A, stirring is continued, the stirred suspension is transferred to the reaction vessel, modified biochar and polyvinylpyrrolidone are added, the reaction is heated, and the mixture is naturally cooled to room temperature to obtain the reaction product. S4. The reaction product is washed, filtered and dried to obtain Bi2WO6 / modified biochar, i.e., bismuth-based oxyacid salt composite material.

8. The method for preparing bismuth-based materials for treating iodine-containing wastewater as described in claim 7, characterized in that, The method for preparing modified biochar in S1 includes: S11. Add corn straw powder to nitric acid solution and soak at 50~70℃ for 1~3h. After filtration, washing and drying, pretreated straw powder is obtained. The pretreated straw powder is heated to 400~600℃ at a heating rate of 5~15℃ / min under nitrogen atmosphere and kept at this temperature for 1~3h. After natural cooling to room temperature, it is ground to obtain biochar. S12. Dissolve Bi(NO3)3·5H2O in nitric acid solution to prepare solution C; add biochar and polyvinylpyrrolidone to AlCl3 solution to prepare solution D; add solution C dropwise to solution D, stir at room temperature for 1-3 h, let stand for 6-24 h, filter, wash and dry to obtain pre-modified biochar; S13. The pre-modified biochar is kept at 200~300℃ for 4~8h under an argon-hydrogen atmosphere, then naturally cooled to room temperature, and ground to obtain modified biochar.

9. The method for preparing bismuth-based materials for treating iodine-containing wastewater as described in claim 8, characterized in that, In step S11, the mass-to-volume ratio of corn stalk powder to nitric acid solution is 1 g: 5-20 mL; the concentration of the nitric acid solution is 1-10 wt%. In S12, the mass-to-volume ratio of Bi(NO3)3·5H2O to nitric acid solution is 1~3g:30~80mL; in the nitric acid solution, the molar volume ratio of nitric acid to deionized water is 0.5~1.5mmol:10~50mL; the mass-to-volume ratio of biochar, polyvinylpyrrolidone, and AlCl3 solution is 10g:0.1~2g:50~200mL; and the concentration of AlCl3 solution is 5~20g / L. In S13, the volume ratio of argon to hydrogen in the argon-hydrogen atmosphere is 8~9.5:0.5~2.

10. The method for preparing bismuth-based materials for treating iodine-containing wastewater as described in claim 7, characterized in that, In S3, the mass ratio of Bi(NO3)3·5H2O, modified biochar, and polyvinylpyrrolidone in solution A is 0.1~1:0.01~0.5:0.01~0.1.

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