A method of reducing hexavalent uranium

Abstract

The application discloses a method for reducing hexavalent uranium, which comprises the following steps: mixing a catalyst CdSe / CdTe heterojunction nanorod with a solution containing hexavalent uranium, adjusting the pH value to be weak acidity, and performing a photocatalytic reduction reaction to obtain a solution containing tetravalent uranium. The method has the characteristics of high catalytic activity, fast catalytic speed, strong ion interference ability, and repeated cyclic use, and does not need to add a sacrificial agent into the solution containing hexavalent uranium, so that the method is economic and environmental protection, and is beneficial to production expansion.

Description

Technical Field

[0001] This invention relates to a method for reducing hexavalent uranium, and more particularly to a method for reducing hexavalent uranium using a CdSe / CdTe heterojunction as a catalyst, belonging to the field of photocatalytic reduction of uranium technology. Background Technology

[0002] Among the new clean energy sources that have been vigorously developed in recent years, the rapid development of nuclear power technology has continuously attracted public attention. However, with the development of nuclear energy, one of the major environmental impact factors is the release of uranium, primarily from the operation of nuclear power plants and during uranium mining and processing. Although uranium plays an irreplaceable role in the operation of nuclear reactors, its high toxicity to various biological species has been well documented in the literature. It has been reported that the main hazards caused by uranium are chemical toxicity and radiotoxicity. Uranium exists in several valence states in nature, with hexavalent uranium (U(VI)) and tetravalent uranium (U(IV)) being the most common in the environment. Regarding biological toxicity, it is generally agreed that the chemical toxicity of uranium is mainly related to U(VI), typically manifested as uranyl, UO2, etc. 2+ U(VI) exists in the form of U.S. VI. It is highly soluble and mobile in the environment. Once it enters a biological community, it can disrupt plant photosynthesis, damage animal cell DNA, and cause disorders in the human nervous system. Currently, the main methods for treating uranium-containing wastewater are adsorption and ion exchange. Although these methods are simple and effective, they still adsorb U(VI) onto materials and separate it from the wastewater. During desorption or post-treatment, U(VI) may still be released into the environment and migrate with the water. Furthermore, the treated materials may also cause secondary pollution.

[0003] In recent decades, photocatalysis has been widely used as an efficient, green, simple, and economical method to eliminate harmful heavy metals and organic pollutants. In photocatalysis, electrons are excited from the valence band to the conduction band under illumination and rapidly transferred to the counter electrode under an applied voltage, used to reduce heavy metal ions or oxidize organic pollutants. Photoinduced redox reactions can be used to control the valence states of various metal ions over a wide range under mild conditions. For uranium, photocatalysis converts soluble U(VI) into fixed U(IV), which then precipitates, thus achieving efficient removal of uranium from radioactive wastewater. For example, Chinese patent CN115106077A discloses the preparation and application of erbium-doped zinc oxide nanosheets based on photocatalytic reduction of uranium. This patent prepares erbium-doped zinc oxide nanosheets based on photocatalytic reduction of uranium through doping with lanthanide elements (Er), and uses them for photocatalytic treatment of uranium-containing wastewater. Although it can remove uranium in a short time and has some ion interference resistance, the use of these photocatalytic nanosheets requires the addition of a photocatalytic sacrificial agent to the uranium wastewater, increasing the cost of uranium wastewater treatment and generating waste.

[0004] For uranium, photocatalysts, which convert soluble U(VI) into fixed U(IV), offer an alternative solution to the aforementioned challenges in water-uranium separation and extraction. For example, the composite material (SCC-4) composed of CdS, CdCO3, and SnO2 exhibits a strong promoting effect of photocorrosion under illumination on the photoreduction of U(VI). CdS provides photoelectrons and holes, while CdCO3 primarily enhances the separation rate of photoelectrons and holes. Its well-matched energy level structure facilitates the separation of photoelectrons and holes, allowing photogenerated holes to accumulate in CdS and be consumed by it, while electrons accumulate on SnO2 for the photoreduction of U(VI). However, existing photocatalyst synthesis methods are complex, and the photocatalytic reduction efficiency of U(VI) is low. They typically require the assistance of co-catalysts or hole traps and oxygen-deficient conditions, which severely limits the application of this method. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a method for the photocatalytic reduction of hexavalent uranium using a CdSe / CdTe heterojunction. This method does not require the use of a photocatalytic sacrificial agent and features high photocatalytic efficiency and environmental friendliness.

[0006] To achieve the above-mentioned technical objectives, the present invention provides a method for reducing hexavalent uranium. The method involves mixing CdSe / CdTe heterojunction nanorods with a solution containing hexavalent uranium, adjusting the pH value to a weakly acidic state, and then performing a photocatalytic reduction reaction to obtain a solution containing tetravalent uranium.

[0007] This invention utilizes a CdSe / CdTe heterojunction nanorod catalyst for the photocatalytic reduction of U(VI). It fully leverages the band structure difference of the CdSe / CdTe heterojunction to form electron-hole pairs, thereby promoting the separation of photogenerated electrons and holes. When light irradiates the heterojunction surface, photons are absorbed, exciting electrons and holes. These electrons and holes recombine at the heterojunction interface, generating free radicals. These free radicals further reduce hexavalent uranium ions. The reaction mechanism of this invention is as follows: Under light-free conditions, stirring the CdSe / CdTe heterojunction catalyst allows uranyl ions in the solution to reach adsorption-equilibrium equilibrium, temporarily detaching them from the solution. Under light irradiation, the CdSe / CdTe heterojunction catalyst generates photogenerated electrons and holes on the catalyst surface in the solution. The electrons react with oxygen in the water to form O2. - , O2 -It possesses strong reducing properties, capable of reducing U(VI) to U(IV). The method of this invention can generate U(IV), thereby extracting water-soluble uranium. This method exhibits high photocatalytic performance, high photocatalytic efficiency, and good photocatalytic stability, and is recyclable. Furthermore, because the CdSe / CdTe heterojunction prepared by this invention has a uniform nanorod structure with attached particles and a smooth surface, it can provide multiple active sites for the photocatalytic reaction. Therefore, high photocatalytic efficiency can be achieved without the use of sacrificial agents such as methanol.

[0008] As a preferred embodiment, the pH value is 4-6. This invention improves photocatalytic performance and efficiency by controlling the pH value of the photocatalytic reaction solution. The pH value of the aqueous solution affects the form of U(VI) ions, thus influencing the photoreduction process. When the pH value of the solution is too low, it causes catalyst decomposition, thereby reducing the photocatalytic ability of the CdSe / CdTe heterojunction; while when the pH value of the solution is too high, various negatively charged anions (such as UO2(OH)) are formed. + (UO2)2CO3(OH) 3- and UO2(CO3)3 4- This reduces the catalytic activity of the CdSe / CdTe heterojunction photocatalyst.

[0009] As a preferred embodiment, the mass-to-volume ratio of the CdSe / CdTe heterojunction nanorods to the solution containing hexavalent uranium is 0.05–0.1 mg:1 mL; the concentration of hexavalent uranium in the solution is not higher than 350 ppm. In this invention, if the mass-to-volume ratio of the CdSe / CdTe heterojunction nanorods to the uranium-containing aqueous solution is too small, hexavalent uranium cannot be effectively reduced, resulting in low reduction efficiency and long reduction time. If the mass-to-volume ratio of the CdSe / CdTe heterojunction nanorods to the uranium-containing aqueous solution is too large, the amount of photocatalyst recovered increases, leading to increased costs.

[0010] As a preferred embodiment, the mixing method is stirring, and the stirring time is 100-150 minutes. In this invention, if the stirring time is too short, the CdSe / CdTe heterojunction nanorods cannot reach the adsorption-desorption equilibrium; if the stirring time is too long, it will not only increase the time cost, but may also cause uranium-containing ions to desorb from the material and redisperse in the solution.

[0011] As a preferred embodiment, the stirring is carried out in a dark environment.

[0012] As a preferred embodiment, the photocatalytic reduction time is 60–120 min.

[0013] As a preferred embodiment, the diameter of the CdSe / CdTe heterojunction nanorods is 40–60 nm.

[0014] As a preferred embodiment, the CdSe / CdTe heterojunction nanorods are prepared by the following steps: hydrothermal reaction I is carried out on a solution containing tellurium salt and polyvinylpyrrolidone to obtain a tellurium nanotube substrate; the tellurium nanotube substrate and selenium powder are dispersed in a solution containing cadmium salt and hydrothermal reaction II is carried out to obtain the nanorods.

[0015] This invention prepares CdSe / CdTe heterojunction nanorods through a two-stage hydrothermal reaction. This method is simple, low-cost, and conducive to large-scale production applications. The CdSe / CdTe heterojunctions prepared by this method exhibit a rod-like structure with attached particles and a smooth surface. The added Te restricts the isotropy of CdSe, thus fixing the crystal phase of the prepared CdSe / CdTe heterojunction and resulting in high photocatalytic efficiency.

[0016] As a preferred embodiment, the tellurium salt is sodium tellurite.

[0017] As a preferred embodiment, the cadmium salt is at least one of cadmium nitrate and its hydrate.

[0018] As a preferred embodiment, the mass ratio of the tellurium salt to polyvinylpyrrolidone is 0.1–8:0.4–1.6.

[0019] As a preferred embodiment, the molar ratio of the tellurium nanotube substrate, selenium powder, and cadmium salt is 0.1–1:0.1–1:1. The photocatalytic reduction performance of uranyl by the CdSe / CdTe heterojunction initially increases and then decreases with increasing CdSe content. That is, as the selenium powder content increases, the photocatalytic reduction performance of uranyl by the CdSe / CdTe heterojunction initially increases and then decreases. As a preferred embodiment, the conditions for the hydrothermal reaction I are: temperature 160–200℃ and time 2–4 h; if the temperature is too low, the reaction will not proceed completely, resulting in low CdSe / CdTe heterojunction yield and many byproducts; if the temperature is too high, the reaction will be too vigorous, and the target product cannot be obtained.

[0020] As a preferred embodiment, the conditions for the hydrothermal reaction II are: a temperature of 140–180°C and a time of 8–16 hours.

[0021] As a preferred embodiment, both hydrothermal reaction I and hydrothermal reaction II involve the addition of the reducing agent hydrated hydrazine.

[0022] The CdSe / CdTe heterojunction nanorods provided by this invention are specifically prepared by the following steps:

[0023] 1) Add polyvinylpyrrolidone and sodium tellurite to ultrapure water and stir until a colorless and transparent liquid is formed. Then add acetone, ammonia, and hydrazine hydrate, and continue stirring.

[0024] 2) Transfer the reaction solution from step 1) to a polytetrafluoroethylene reactor for hydrothermal reaction I. After the reaction is complete, cool the reactor to room temperature, wash the reaction product multiple times with water and ethanol, and dry the resulting silvery-gray precipitate.

[0025] 3) Disperse cadmium nitrate tetrahydrate in ethylenediamine and stir to form a homogeneous and transparent solution. Then, disperse the product obtained in step 2) together with selenium powder in the solution, add hydrazine hydrate, and continue stirring to disperse.

[0026] 4) Transfer the solution from step 3) to a hydrothermal reactor to carry out hydrothermal reaction II. After the reaction is completed, allow the reactor to cool naturally. After the reactor has cooled, wash the reaction product with water and ethanol and then dry it.

[0027] As a preferred embodiment, the volume ratio of acetone, ammonia and hydrated hydrazine in step 1) is 15:5:2.5.

[0028] Compared with existing technologies, the beneficial technical effects of the present invention are as follows:

[0029] 1) The method for reducing hexavalent uranium provided by the present invention is to carry out photocatalytic reduction of hexavalent uranium by CdSe / CdTe heterojunction nanorods, reducing soluble hexavalent uranium in uranium-containing aqueous solution to tetravalent uranium. This method can effectively achieve the reduction, enrichment and fixation of uranium. This method does not require the addition of sacrificial agents to uranium-containing aqueous solution and has the characteristics of high catalytic efficiency, fast photocatalytic speed and economic and environmental protection.

[0030] 2) This invention prepares a photocatalyst for the reduction of hexavalent uranium through two hydrothermal reactions. The operation is simple and the cost is low, which is conducive to large-scale production and application. At the same time, the CdSe / CdTe heterojunction structure is uniform, and it has high catalytic activity, fast catalytic speed, strong ion interference ability and can be repeatedly recycled when used for the reduction of hexavalent uranium. Attached Figure Description

[0031] Figure 1 High-resolution transmission electron microscopy (TEM) images of the CdSe / CdTe heterojunction nanorod catalyst prepared in this invention. Figure 1As shown, the CdSe / CdTe heterojunction catalyst exhibits a rod-like structure with particles attached and a smooth surface. Compared to pure CdSe nanorods, its surface is rougher, and it has a larger aspect ratio than the composite CdSe / CdTe heterojunction material. This indicates that the addition of Te restricts the isotropy of CdSe, causing it to grow in as unidirectional a direction as possible. The interface of this heterojunction shows stripe spacings of 0.181 nm, 0.187 nm, and 0.329 nm, corresponding to the (201), (200), and (101) crystal planes of CdSe, and spacings of 0.193 nm and 0.226 nm, corresponding to the (311) and (220) crystal planes of CdTe. This indicates that CdSe / CdTe has been successfully composited.

[0032] Figure 2 Figure 1 shows the photocatalytic reduction performance of CdSe / CdTe heterojunction nanorod catalysts at different pH values. Figure A shows the change in the residual uranyl ions in the solution over time, and Figure B shows the change in the uranyl degradation rate over time.

[0033] Figure 3 Figure 1 shows the performance of CdSe / CdTe heterojunction nanorods with different ratios in photocatalytic reduction of uranium at pH 5. Figure A shows the change in the residual uranyl ion concentration in the solution over time, and Figure B shows the change in the uranyl degradation rate over time. Different CdSe / CdTe ratios result in different photocatalytic reduction efficiencies for uranium. It can be clearly seen from the figures that CST-8 has the highest k-value, indicating the best photocatalytic performance when the CdSe content in the CdSe / CdTe heterojunction is 80%. (CST-X represents composite materials with different ratios of CdSe and CdTe, where X = 2, 4, 5, 6, 8, and 9 represent the percentage of CdSe in the composite material as 20%, 40%, 50%, 60%, 80%, and 90%, respectively.)

[0034] Figure 4 The graph shows the performance of photocatalytic reduction of uranium when the amount of CdSe / CdTe heterojunction nanorod catalyst is between 0 mg and 10 mg.

[0035] Figure 5 Comparison of U(VI) removal rates of CdSe / CdTe heterojunction nanorod catalysts in the presence of competing anions. Detailed Implementation

[0036] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0037] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0038] Unless otherwise specified, all reagents and raw materials used in this invention are commercially available products or products that can be prepared by known methods.

[0039] Example 1

[0040] Preparation of CdSe / CdTe heterojunction nanorod catalysts includes the following steps:

[0041] 1) At room temperature, add 1.5g of polyvinylpyrrolidone and 0.138g of sodium tellurite to ultrapure water and stir until a colorless and transparent liquid is formed. Then add 15mL of acetone, 5mL of ammonia, and 2.5mL of hydrazine hydrate, and continue stirring.

[0042] 2) Transfer the reaction solution from step 1) to a polytetrafluoroethylene reactor for hydrothermal reaction I at a temperature of 180°C for 4 hours. After the reaction is complete, cool the reactor to room temperature, wash the reaction product multiple times with water and ethanol, and dry the obtained silver-gray precipitated tellurium nanotube substrate at a temperature of 60°C under vacuum for 12 hours.

[0043] 3) Disperse 0.5 mmol of cadmium nitrate tetrahydrate in 15 mL of ethylenediamine and stir to form a homogeneous and transparent solution. Then, disperse 0.1 mmol of the product obtained in step 2) together with 0.4 mmol of selenium powder in the solution, add 1 mL of hydrazine hydrate, and continue stirring to disperse.

[0044] 4) Transfer the solution from step 3) to a hydrothermal reactor and carry out hydrothermal reaction II at a temperature of 140℃ for 12 hours. After the reaction, allow the reactor to cool naturally. Once cooled, wash the reaction product with water and ethanol, and then dry it at a temperature of 60℃ under vacuum for 12 hours to obtain CdSe / CdTe heterojunction nanorods with a CdSe content of 80%, denoted as CST-8.

[0045] By adjusting the molar ratio of the product obtained in step 2) to the selenium powder, CdSe / CdTe heterostructure nanorods with different CdSe contents can be obtained, denoted as CST-X (where X = 2, 4, 5, 6, 8, 9 represent the percentage content of CdSe in the composite material as 20%, 40%, 50%, 60%, 80%, 90%).

[0046] Methods for reducing hexavalent uranium:

[0047] In a quartz photocatalytic reactor, 10 mg of the series of CST-X heterojunction nanorod photocatalysts prepared above were added to 100 mL of 30 ppm UO2 without electron sacrificial agents. 2+ In the aqueous solution, nitric acid or sodium hydroxide was added to adjust the pH to 5. A 300W xenon lamp was used as a simulated light source, and the solution was vigorously stirred in the dark for 120 minutes to reach adsorption-desorption equilibrium. Then, the solution was continuously stirred for 90 minutes under simulated sunlight. During the illumination process, 1 mL of the reaction solution was filtered at regular intervals using a 0.22 μm cellulose acetate syringe membrane. The U(VI) content in the filtrate was determined at 652 nm using UV-Vis spectrophotometry with azoarsine III as the colorimetric reagent. The performance of the photocatalytic reduction of uranium is shown in [the table below]. Figure 3 .

[0048] Example 2

[0049] The CdSe / CdTe heterojunction nanorod photocatalyst used in this embodiment is the same as that in Example 1, except that the pH is adjusted to 4.

[0050] Example 3

[0051] The CdSe / CdTe heterojunction nanorod photocatalyst used in this embodiment is the same as that in Example 1, except that the pH is adjusted to 6.

[0052] Example 4

[0053] The CdSe / CdTe heterojunction nanorod photocatalyst used in this embodiment is the same as that in Example 1, except that the amount of CdSe / CdTe heterojunction nanorods added is 5 mg.

[0054] Example 5

[0055] The CdSe / CdTe heterojunction nanorod photocatalyst used in this embodiment is the same as that in Example 1, except that the amount of CdSe / CdTe heterojunction nanorod photocatalyst added is 8 mg.

[0056] Comparative Example 1

[0057] This comparative example does not include a CdSe / CdTe heterojunction nanorod photocatalyst, and all other conditions are the same as in Example 1.

[0058] Comparative Example 2

[0059] The CdSe / CdTe heterojunction nanorod photocatalyst used in this comparative example is the same as that in Example 1, except that the pH is adjusted to 3.

[0060] Comparative Example 3

[0061] The CdSe / CdTe heterojunction nanorod photocatalyst used in this comparative example is the same as that in Example 1, except that the pH is adjusted to 7.

[0062] Comparative Example 4

[0063] The CdSe / CdTe heterojunction nanorod photocatalyst used in this comparative example is the same as that in Example 1, except that the pH is adjusted to 8.

[0064] Comparative Example 5

[0065] The CdSe / CdTe heterojunction nanorod photocatalyst used in this comparative example is the same as that in Example 1, except that the pH is adjusted to 9.

[0066] Comparative Example 6

[0067] The CdSe / CdTe heterojunction nanorod photocatalyst used in this comparative example is the same as that in Example 1, except that the amount of CdSe / CdTe heterojunction nanorods added is 2 mg.

[0068] Comparative Example 7

[0069] The CdSe / CdTe heterojunction nanorod photocatalyst used in this comparative example is the same as that in Example 1, except that the amount of CdSe / CdTe heterojunction nanorods added is 4 mg.

[0070] The effects of photocatalytic reduction of uranium in Examples 1-5 and Comparative Examples 1-7 are shown in the figure. Figure 2 and Figure 4 As can be seen from the diagram:

[0071] The pH value of aqueous solutions affects the form in which U(VI) ions exist, thus influencing the photoreduction process. Therefore, this invention comparatively studies the U(VI) photoreduction capability of CdSe / CdTe heterojunctions at different pH values. Figure 2 As shown, CST-8 exhibits optimal photoreduction performance at pH 5. However, the photocatalytic removal capacity decreases with solution acidification or alkalization. This may be due to the following reasons: (I) catalyst decomposition in excessively acidic solutions; (II) when the pH is above 5, U(VI) ions in the solution can form hydrate ions (such as (UO2)(OH)). + (UO2)2(OH)2 2+ (UO2)3(OH) 5+ Furthermore, as the pH value exceeds 7, various negatively charged anions (such as UO2(OH)) will be formed. + (UO2)2CO3(OH) 3- and UO2(CO3)3 4-This further reduces the catalytic ability of the photocatalyst.

[0072] Figure 4 This demonstrates the difference in U(VI) photoreduction ability of CdSe / CdTe heterojunction at dosages of 0–10 mg. The figure shows that when no CdSe / CdTe heterojunction is used or at a low dosage, U(VI) in the solution is essentially not reduced. With increasing CdSe / CdTe heterojunction dosage, the reaction significantly increases, and at a dosage of 8 mg, U(VI) in the solution is almost completely reduced.

[0073] Comparative experiment on the removal rate of U(VI) of CdSe / CdTe heterojunction nanorod catalysts in the presence of competing anions:

[0074] In a quartz photocatalytic reactor, 10 mg of the CdSe / CdTe heterojunction nanorod photocatalyst prepared above was added to 100 mL of 30 ppm UO2 without electron sacrificial agents. 2+ In an aqueous solution, 0.5 mmol / L of interfering agent M(NO3)n, 0.5 mM of Na2CO3, and 0.5 mM of NaCl were added. Nitric acid and sodium hydroxide were added to adjust the pH to 5. A 300W xenon lamp was used as a simulated light source, and the solution was vigorously stirred for 120 min in the dark to reach adsorption-desorption equilibrium. Then, the solution was continuously stirred for 90 min under simulated sunlight. During the illumination process, 1 mL of the reaction solution was filtered at regular intervals using a 0.22 μm cellulose acetate syringe membrane. The filtrate containing U(VI) was determined at 652 nm using UV-Vis spectrophotometry with azoarsine III as the colorimetric reagent. M(NO3)n n M is K + Na + Fe 3+ Zn 2+ Cu 2+ Mg 2+ Al 3+ Ni 2+ Ca 2+ Cr 2+ The interference resistance of the catalyst to photocatalytic reduction of uranium was tested.

[0075] Depend on Figure 5 It is evident that the catalyst still exhibits excellent performance in photocatalytic reduction of uranium in solutions containing interfering ions, with even the lowest catalytic efficiency exceeding 90%.

Claims

1. A method of reducing hexavalent uranium, characterized by: The CdSe / CdTe heterojunction nanorod is mixed with a solution containing hexavalent uranium, and then the pH value is adjusted to weak acidity to carry out photocatalytic reduction reaction to obtain a solution containing tetravalent uranium; the CdSe / CdTe heterojunction nanorod is prepared by the following steps: hydrothermal reaction I is carried out on a solution containing tellurium salt and polyvinylpyrrolidone to obtain a tellurium nanotube substrate; the tellurium nanotube substrate is dispersed in a solution containing selenium powder and cadmium salt, and then hydrothermal reaction II is carried out to obtain the CdSe / CdTe heterojunction nanorod. The mass ratio of the tellurium salt to the polyvinylpyrrolidone is 0.1-8:0.4-1.

6. The molar ratio of the tellurium nanotube substrate, the selenium powder and the cadmium salt is 0.1-1:0.1-1:

1. The reducing agent hydrazine hydrate is added in the hydrothermal reaction I and the hydrothermal reaction II.

2. A method of reducing hexavalent uranium according to claim 1, characterized in that: The pH value is 4-6.

3. A method of reducing hexavalent uranium according to claim 1 or 2, c h a r a c t e r i s e d in that: The mass-volume ratio of the CdSe / CdTe heterojunction nanorod to the solution containing hexavalent uranium is 0.05-0.1 mg:1 mL. The concentration of hexavalent uranium in the solution containing hexavalent uranium is not higher than 350 ppm.

4. The method of reducing hexavalent uranium of claim 1, wherein: The mixing mode is stirring, and the stirring time is 100-150 min.

5. The method of reducing hexavalent uranium of claim 1, wherein: The photocatalytic reduction time is 60-120 min.

6. The method of reducing hexavalent uranium of claim 3, wherein: The diameter of the CdSe / CdTe heterojunction nanorod is 40-60 nm.

7. The method for reducing hexavalent uranium according to claim 6, characterized in that: The tellurium salt is sodium tellurite; The cadmium salt is at least one of cadmium nitrate and its hydrate.

8. The method for reducing hexavalent uranium according to claim 6, characterized in that: The temperature of the hydrothermal reaction I is 160-200 ℃, and the time is 2-4 h; The temperature of the hydrothermal reaction II is 140-180 ℃, and the time is 8-16 h.

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