Preparation method and application of photocatalytic material for selective technetium separation

Abstract

The invention discloses a preparation method and application of a photocatalytic material for selective technetium separation. Amorphous titanium dioxide prepared through a hydrolysis method, ZnCl2 and KCl are mixed and ground into powder, then the powder is calcined in a muffle furnace for 2-4 hours at the temperature of 250-350 DEG C, solids obtained after cooling are washed with water for multiple times and then dried, the photocatalytic material for selective technetium separation is obtained, and the molar ratio of the dosage of ZnCl2 to the dosage of KCl is 55: 45. The preparation method comprises the following steps: adding the photocatalytic material into an aqueous solution containing technetium and containing high-concentration nitrate radicals, simulating sunlight irradiation for 4-5 hours to extract pertechnetate radicals, then physically filtering and recycling a mixture of the photocatalytic material and a technetium product, finally extracting technetium through hydrogen peroxide oxidation, and secondarily filtering and regenerating the photocatalytic material for reuse. The photocatalyst material prepared by the invention is especially suitable for separating technetium from an aqueous solution containing high-concentration nitrate radicals, and overcomes the key problems of low reduction separation efficiency and low selectivity of high-technetium acid radicals caused by interference of the nitrate radicals on the separation process.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of key radionuclide separation and enrichment, and particularly relates to a preparation method and application of a photocatalytic material for selective technetium separation. BACKGROUND

[0002] 99 Technetium ( 99 Tc) is a β radionuclide with a half-life of 2.1 x 10 5 years, and a high yield (6%) in uranium ( 235 U) fission reactors, making it a focus of long-term risk management of nuclear waste. In aqueous solution, 99 Tc mainly exists in the form of high solubility and high mobility high pertechnetate ( 99 TcO4 - ) oxygen-containing anions, which not only threatens the long-term stability of nuclear waste glass solidification, but also increases the risk of migration and leakage in geological disposal. In addition to environmental challenges, 99 Tc also seriously affects the valence control and separation direction of elements such as uranium ( 235 U), neptunium ( 237 Np) and plutonium ( 94 Pu) in the key PUREX process of nuclear fuel reprocessing. However, 99 Tc can be used to produce the nuclear medicine drug "Gunk" - technetium methylene diphosphonate ( 99 Tc-MDP), which can be used to treat various bone diseases including rheumatoid arthritis and ankylosing spondylitis. Therefore, the separation of 99 Tc is the dual demand of realizing nuclear energy safety and promoting nuclear medical application.

[0003] The methods currently mainly used for separating technetium include solvent extraction and solid-phase adsorption. Solvent extraction relies on the difference in the distribution coefficient of the target substance between the organic phase and the aqueous phase. Common extractants include neutral phosphine, amide, amine and crown ether extractants. The advantages of this method are strong selectivity, high recovery rate and easy continuous operation, but a large amount of organic solvent is needed in the extraction and stripping process, which easily leads to secondary pollution and increases the burden of subsequent waste liquid treatment. In contrast, solid-phase adsorption relies on the specific action (such as coordination, ion exchange and electrostatic attraction) of the solid adsorbent on TcO4 - , has the advantages of simple equipment, safe operation and less secondary waste. However, the adsorbent generally has limited capacity, insufficient stability in complex waste liquid and is prone to form radioactive solid waste. In addition, new adsorbents with excellent performance (such as some metal-organic frameworks or ionic polymers) often have complicated synthesis steps and high cost, which restricts their large-scale application.

[0004] As a green technology, photocatalysis has shown a broad application prospect in the field of energy and environment due to its outstanding advantages such as mild reaction conditions (room temperature and atmospheric pressure), simple and safe operation, low energy consumption and strong sustainability. The photocatalytic technology has been applied in the field of heavy metal ion separation and purification treatment, which is bound to indicate that it can also be used for efficient separation of technetium. However, the reduction efficiency of pertechnetate is easily affected by the coexisting nitrate, especially high concentration of nitrate will seriously interfere with the reduction of pertechnetate. Specifically, nitrate and pertechnetate will compete for carbon dioxide radical (·CO2 - ) generated by the oxidation of formic acid (a kind of hole trapping agent), and in the reduction process, nitrate (standard reduction potential [NO3 - / N2] = +1.25 V) has more thermodynamic advantage than pertechnetate (standard reduction potential [Tc(VII) / Tc(IV)] = +0.74 V), which seriously interferes with the reduction efficiency of pertechnetate. Therefore, it is urgent to solve the problem of high concentration of nitrate interference in the photocatalytic separation of technetium to achieve green and efficient technetium separation. SUMMARY

[0005] In order to solve the problem that the existing photocatalytic method for separating technetium is seriously interfered by high concentration of nitrate, the application provides a preparation method of a photocatalytic material for selective technetium separation.

[0006] The application provides a simple and efficient method for preparing a photocatalytic material, that is, a photocatalytic material for selective technetium separation is directly obtained by one-step calcination. Specifically, the amorphous titanium dioxide prepared by a hydrolysis method, ZnCl2 and KCl are mixed and ground into powder, then calcined using a muffle furnace, and calcined at 250-350℃ for 2-4 hours. After cooling, the obtained solid is washed with water for 8-10 times and dried at 60℃ for 24 hours to obtain the photocatalytic material for selective technetium separation. The photocatalytic material is anatase titanium dioxide material with low crystallinity and rich oxygen vacancies.

[0007] The specific steps of preparing the amorphous titanium dioxide by the hydrolysis method are as follows: first, anhydrous ethanol, water and ammonia water are mixed, and tetrabutyl titanate is dropped into the mixed solution, and stirred for 6 hours to obtain a hydrolysis suspension; the hydrolysis suspension is centrifuged and washed with ethanol and water alternately for 2-3 times, and the obtained solid is dried, and air-dried at 60℃ for 24 hours to obtain the amorphous titanium dioxide. Preferably, the volume ratio of anhydrous ethanol, water, ammonia water and tetrabutyl titanate is 50:0.3:0.15:5.

[0008] The molar ratio of the amount of ZnCl2 to the amount of KCl is 55:45, and the mass ratio of the total amount of ZnCl2 and KCl to the mass of amorphous titanium dioxide is (9-27):1.

[0009] In view of the previous research of the inventor, it is confirmed that low crystallinity TiO2 prepared by calcination at 250-350℃ exhibits excellent photocatalytic reduction activity on Tc(VII) / perrhenate, and TiO2 prepared by calcination at 300℃ has the best photocatalytic reduction activity. Therefore, the present application needs to find a eutectic salt with a melting point of exactly 300℃ as a reaction medium. Melting point (Tm) is a very important parameter for selecting a suitable molten salt system. In order to maintain a liquid state, the reaction temperature needs to be higher than the melting point of the molten salt system. Generally, a multi-component salt system is used to adjust the melting point, and the working temperature is reduced by lowering the eutectic point, thereby reducing the pressure of the working temperature. Among many salt systems, the zinc chloride-potassium chloride system (molar ratio 55:45) is the only choice because its eutectic point can accurately match the target temperature (300℃), and other salt systems cannot achieve this. Therefore, the salt system composed of ZnCl2 and KCl (molar ratio 55:45) is selected as the reaction medium in the preparation method of the present application. Neither zinc chloride nor potassium chloride alone can provide a stable liquid environment at 300℃. Therefore, zinc chloride and potassium chloride must be used together in the preparation method of the present application to form a low-melting-point, stable liquid reaction medium for preparing a photocatalytic material for selective technetium separation.

[0010] The photocatalytic material prepared by the above method is used for separating technetium from radioactive wastewater by a photocatalytic method, and is especially suitable for selectively separating technetium from an aqueous solution containing technetium and having a high concentration of nitrate.

[0011] The present application also provides a method for separating and recovering technetium from radioactive wastewater using the photocatalytic material prepared by the above method. Specifically, the photocatalytic material is added to an aqueous solution containing technetium and having a high concentration of nitrate (simulated radioactive wastewater), simulated sunlight is irradiated for 4-5 hours to extract pertechnetate, then the mixture of the photocatalytic material and the technetium product is physically filtered and recovered, finally the technetium is extracted by hydrogen peroxide oxidation, and the photocatalytic material is regenerated by secondary filtration for repeated use.

[0012] Compared with the prior art, the present application has the following advantages: (1) The present application prepares a new type of photocatalytic material by targeted defect engineering modification of titanium dioxide through a simple one-step calcination method. The concentration of surface oxygen defects is introduced and regulated through defect engineering, and the oxygen vacancies formed have a dual synergistic function: on the one hand, as an electron capture site, the separation efficiency of photo-generated electron-hole pairs is improved, thereby improving the photocatalytic reduction efficiency of technetium; on the other hand, the oxygen vacancies can be used as active sites to regulate the nitrate reduction path, guide the specific catalytic conversion of nitrate, and effectively avoid the interference of nitrate on the reduction process of technetium. The photocatalytic material has abundant stable oxygen vacancies and excellent carrier separation efficiency, and under certain conditions, it can quickly realize the selective separation of high pertechnetate under simulated sunlight. The key problem of low reduction efficiency and selectivity of high pertechnetate due to the serious interference of nitrate in the treatment of radioactive wastewater by existing photocatalytic technology is solved.

[0013] (2) The present application realizes green, efficient and high-selectivity photocatalytic reduction and separation of technetium in radioactive wastewater, so as to ensure the safe disposal of radioactive wastewater and reduce environmental risk, and promote the application of separated technetium in nuclear medicine drugs.

[0014] Other advantages, objects and features of the present application will be partly embodied in the following description, and partly understood by those skilled in the art through research and practice of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 X-ray diffraction pattern of the photocatalytic material prepared in Example 2 of the present application.

[0016] Figure 2 UV-visible spectrum of the photocatalytic material prepared in Example 2 of the present application.

[0017] Figure 3 Scanning electron microscope image of the photocatalytic material prepared in Example 2 of the present application.

[0018] Figure 4 X-ray photoelectron spectrogram of commercial titanium dioxide, titanium dioxide prepared in Comparative Example 1 and photocatalytic material prepared in Example 2.

[0019] Figure 5 Performance of photocatalytic selective separation of perrhenate (non-radioactive substitute of technetium) of photocatalytic materials prepared at different calcination temperatures.

[0020] Figure 6 Performance of selective separation of perrhenate of different types of photocatalytic materials under simulated high-concentration nitrate conditions.

[0021] Figure 7To implement the photocatalytic selectivity separation of perrhenate of the photocatalytic material of Example 2 under different concentrations of nitrate. DETAILED DESCRIPTION

[0022] The preferred embodiments of the present application are described below in conjunction with the accompanying drawings, it should be understood that the preferred embodiments described here are only used to illustrate and explain the present application, and are not used to limit the present application.

[0023] Example 1 A photocatalytic material for selective technetium separation is prepared as follows: (1) Take 50 mL of anhydrous ethanol, 0.3 mL of deionized water and 0.15 mL of ammonia water into a reaction container, then drop 5 mL of butyl titanate, seal and stir the reaction at 600 rpm for 6 hours to obtain a hydrolysis suspension; centrifugal separation of the hydrolysis suspension, the solid product is washed with ethanol and water alternately for 2-3 times and then air dried, and air dried at 60℃ for 24 hours to obtain an amorphous titanium dioxide material.

[0024] (2) Take 0.2 g of amorphous titanium dioxide, 3.72 g of zinc chloride and 1.67 g of potassium chloride, mix and grind into powder; then calcine in a muffle furnace, with a heating rate of 5 ℃ / min to 270℃, keep for 2 hours, then naturally cool to room temperature, wash the solid with water for 8-10 times and then air dry, air dry at 60℃ for 24 hours to obtain the photocatalytic material for selective technetium separation.

[0025] In the above method, the calcination temperature in step (2) is changed to 300℃ and 330℃ respectively, and other reaction conditions remain unchanged, different photocatalytic materials can be prepared.

[0026] Example 2 A method for preparing a photocatalytic material for selective technetium separation: Step (1) is the same as Example 1; Step (2): Take 0.4 g of amorphous titanium dioxide, 3.72 g of zinc chloride and 1.67 g of potassium chloride, mix and grind into powder; then calcine in a muffle furnace, with a heating rate of 5 ℃ / min to 300℃, keep for 3 hours, then naturally cool to room temperature, wash the solid with water for 8-10 times and then air dry, air dry at 60℃ for 24 hours to obtain the photocatalytic material for selective technetium separation.

[0027] Example 3 Step (1) is the same as Example 1; Step (2): Take 0.6 g of amorphous titanium dioxide, 3.72 g of zinc chloride, and 1.67 g of potassium chloride, mix and grind into powder; then place in a muffle furnace and calcine at a temperature increasing rate of 5 ℃ / min to 330 ℃, keep for 4 hours, then naturally cool to room temperature, wash the solid with water for 8-10 times, and then dry with air blowing at 60 ℃ for 24 hours to obtain the photocatalytic material for selective technetium separation.

[0028] Comparative Example 1 On the basis of Example 2, in step (2), omit zinc chloride and potassium chloride, and place the amorphous titanium dioxide alone in a muffle furnace for calcination, with the same calcination conditions, to obtain a titanium dioxide photocatalytic material.

[0029] The X-ray diffraction test result of the photocatalytic material prepared in Example 2 is shown in FIG. 2. Figure 1 As shown in FIG. 2, the crystal phase is mainly anatase phase, which indicates that the photocatalytic material is a low-crystalline anatase titanium dioxide material.

[0030] The ultraviolet-visible spectrum of the photocatalytic material prepared in Example 2 is shown in FIG. 3. Figure 2 As shown in FIG. 3, the light absorption threshold is about 385 nm, and the photocatalytic material presents an irregular block structure. Figure 3 FIG. 4 is a scanning electron microscope image of the photocatalytic material, which shows that the average particle size is about 200-500 nm.

[0031] Figure 4 FIG. 5 is an X-ray photoelectron spectrogram of commercial titanium dioxide (P25), the titanium dioxide prepared in Comparative Example 1, and the photocatalytic material prepared in Example 2. As can be seen, compared with the commercial titanium dioxide (P25) and the titanium dioxide directly calcined in the muffle furnace in Comparative Example 1, the photocatalytic material prepared in Example 2 has abundant oxygen vacancies.

[0032] Application Example 1 The application experiment of the titanium dioxide photocatalytic material prepared in Example 1 at different calcination temperatures in separating rhenium (non-radioactive substitute of technetium) in high-concentration nitrate is as follows: (1) First, prepare a simulated solution containing 10 ppm of perrhenate and 1.4 mol / L of sodium nitrate, and add 4% (volume ratio of formic acid to solution) formic acid to adjust the pH of the solution to 3. Place the photocatalytic materials obtained by calcination at different temperatures (270 ℃, 300 ℃, and 330 ℃) in Example 1 in the simulated solution, and the concentration of the photocatalytic material is 0.6 g / L. Use ultrasonic waves to completely disperse the materials, and maintain the temperature of the whole experiment at 25 ℃. After irradiation under simulated sunlight for 240 minutes, take the clear rhenium-containing sample solution. -1 -1

[0033] ​​(2) The remaining amount of soluble rhenium in the sample solution (C t / C0x 100%) was detected by inductively coupled plasma optical emission spectrometry (ICP-OES), and the separation efficiency of perrhenate was calculated, wherein C t and C0 represent the concentration of rhenium at a certain time and the initial time, respectively. Figure 5 As shown in the results, the preparation method of the present application can obtain a good photocatalytic removal efficiency at different calcination temperatures, and the product obtained by calcination at 300°C has the best photocatalytic performance.

[0034] Application Example 2 Commercial titanium dioxide, titanium dioxide prepared in Comparative Example 1, and the photocatalytic material prepared in Example 2 were used for photocatalytic separation of rhenium in high-concentration nitrate.

[0035] Experimental steps for photocatalytic reduction and separation of perrhenate: (1) The simulated solution was the same as above. Commercial P25, the titanium dioxide directly calcined in the muffle furnace in Comparative Example 1, and the photocatalytic material of the present application in Example 2 were placed in the solution, and the concentration of the photocatalytic material was 0.6 g / L -1 The suspension was completely dispersed by ultrasonic waves, the whole experiment was carried out at 25°C, and the sample solution containing rhenium was finally obtained after irradiation for 240 minutes. (2) The remaining amount of soluble rhenium in the sample solution (C t / C0x 100%) was detected by inductively coupled plasma optical emission spectrometry (ICP-OES), and the separation efficiency of perrhenate was calculated, wherein C t and C0 represent the concentration of rhenium at a certain time and the initial time, respectively. Figure 6 is a data graph of the separation efficiency of perrhenate after irradiation for 240 minutes. As can be seen, the separation efficiency of perrhenate by photocatalytic reduction of commercial P25, the titanium dioxide in Comparative Example 1, and the photocatalytic material in Example 2 is 25.6%, 32.3%, and 72.1%, respectively, which indicates that the photocatalytic material prepared in the present application has a significantly higher reduction efficiency of perrhenate than the other two titanium dioxide materials, and can selectively and efficiently reduce and separate perrhenate.

[0036] Application Example 3 The photocatalytic material in Example 2 was used to separate perrhenate in different concentrations of nitrate, and the experimental steps were as follows: (1) The composition of the simulated solution was the same as above, and sodium nitrate was used to adjust the concentration of nitrate in the simulated solution to obtain simulated solutions with nitrate concentrations of 0, 0.007, 0.14, 0.35, 1.4, and 3 mol / L. The photocatalytic material in Example 2 was added to different simulated solutions, and the concentration of the photocatalytic material was 0.6 g / L-1 The material is completely dispersed by ultrasonic waves, the whole experiment temperature is maintained at 25 DEG C, irradiated under simulated sunlight for 240 minutes, and finally the clear rhenium-containing sample solution is obtained.

[0037] (2) The residual amount of soluble rhenium in the sample solution is detected by inductively coupled plasma optical emission spectrometry (ICP-OES), and the separation efficiency of high rhenate is calculated. Figure 7 As shown in the results, in the range of 0-1.4 mol L -1 The present application can effectively avoid the interference of nitrate on the photocatalytic reduction of high rhenate.

[0038] As can be known from the above, the prepared photocatalytic material is applied to the nuclear waste liquid environment with high concentration of nitrate, can realize high-selectivity and high-efficiency photocatalytic reduction and separation of technetium, and thus solves the bottleneck problem faced by the prior art.

[0039] The above is only a preferred embodiment of the present application, and does not limit the present application in any form. Although the present application has been disclosed as above with a preferred embodiment, it is not intended to limit the present application. Any skilled person in the art can make some changes or modifications to the above disclosed technical content without departing from the technical solution of the present application, and any simple modification, equivalent change and modification of the above embodiment according to the technical essence of the present application are still within the scope of the present application.

Claims

1. A method for preparing a photocatalytic material for selective technetium separation, characterized in that, Amorphous titanium dioxide, ZnCl2, and KCl prepared by hydrolysis were mixed and ground into powder. The powder was then calcined at 250-350℃ for 2-4 hours. After cooling, the resulting solid was washed several times with water and dried to obtain a photocatalytic material for selective technetium separation.

2. The method for preparing the photocatalytic material for selective technetium separation as described in claim 1, characterized in that, The molar ratio of ZnCl2 to KCl is 55:

45.

3. The method for preparing the photocatalytic material for selective technetium separation as described in claim 2, characterized in that, The total amount of ZnCl2 and KCl used is in a mass ratio of (9~27):1 with that of amorphous titanium dioxide.

4. The method for preparing the photocatalytic material for selective technetium separation as described in claim 3, characterized in that, The method for preparing the amorphous titanium dioxide is as follows: first, anhydrous ethanol, water and ammonia are mixed, and tetrabutyl titanate is added dropwise to the mixture. The mixture is stirred for 6 hours to obtain a hydrolyzed suspension. The hydrolyzed suspension was centrifuged, washed alternately with ethanol and water, and the resulting solid was dried to obtain amorphous titanium dioxide.

5. The method for preparing the photocatalytic material for selective technetium separation as described in claim 4, characterized in that, The volume ratio of anhydrous ethanol, water, ammonia and tetrabutyl titanate is 50:0.3:0.15:

5.

6. The method for preparing the photocatalytic material for selective technetium separation as described in claim 1, characterized in that, After cooling, the resulting solid was washed with water 8 to 10 times and then dried at 60°C for 24 hours.

7. A photocatalytic material for selective technetium separation, characterized in that, It is prepared by the preparation method described in any one of claims 1-6.

8. The application of a photocatalytic material for selective technetium separation as described in claim 7, characterized in that, Used for separating technetium from radioactive wastewater.

9. The application of the photocatalytic material for selective technetium separation as described in claim 8, characterized in that, Used to separate technetium from radioactive wastewater containing nitrate.

10. The application of the photocatalytic material for selective technetium separation as described in claim 8, characterized in that, The photocatalytic material is added to an aqueous solution containing technetium and a high concentration of nitrate ions, and then subjected to simulated sunlight irradiation for 4-5 hours to extract pertechnetate ions. The mixture of the photocatalytic material and technetium products is then physically filtered to recover the product. Finally, technetium is extracted by oxidation with hydrogen peroxide, and the photocatalytic material is regenerated by secondary filtration for reuse.

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