A method for treating radioactive technetium-containing solution

Abstract

The present invention discloses a method for treating a radioactive technetium-containing aqueous solution. The method specifically comprises the following steps: adjusting the pH of the Tc(VII)-containing solution to be acidic; adding a certain amount of baked charcoal and an organic acid salt to the Tc(VII)-containing solution, stirring and shaking for a period of time to reduce Tc(VII) to Tc(IV) with poor environmental fluidity and adsorb and separate. The baked charcoal is prepared by low-temperature baking of bamboo shoot shell particles, and its specific surface area and the number of surface functional groups are increased after baking. The organic acid salt is adsorbed to undergo an oxidation-reduction reaction, which changes the electron transfer mode of the organic acid salt and strengthens its electron-donating effect, thereby reducing Tc(VII) to Tc(IV). The present invention utilizes the baked charcoal and organic acid salt obtained by waste recycling to achieve efficient reduction treatment of technetium, solves the problems of complex process and high treatment cost of the existing method, and avoids the problem of secondary pollution in the treatment process.

Description

Technical Field

[0001] The invention belongs to the field of radioactive nuclide separation, and in particular relates to a method for treating a radioactive technetium-containing solution. Background Art

[0002] With the continuous development of mankind, the world's demand for energy is growing. As a clean, economical and sustainable energy source, uranium / plutonium fission nuclear energy is one of the most ideal choices for partially replacing fossil fuel energy, providing an indispensable energy supply for my country's rapid economic growth. With the increasing amount of highly radioactive waste stored around the world, finding efficient, reliable and cost-effective methods and strategies for spent fuel reprocessing is an increasingly important international concern. Technetium (Tc), the element 43, is one of the main sources of long-term radiotoxicity in spent fuel waste liquid. Technetium-99 is β Radioactive body, half-life is 2.13×10 5 Since 1915, it is one of the main nuclides produced by the fission of heavy nuclei. It is stored because it is difficult to handle, resulting in large inventories of spent nuclear fuel and solutions containing technetium. Technetium is mainly present in the form of the pertechnetate anion TcO4 − It exists in nuclear waste liquid and has the characteristics of high solubility, high environmental mobility, and complex behavior, which leads to the risk of radioactive leakage and contamination of storage solutions containing technetium. Therefore, improving the safety of radioactive solutions containing technetium is a huge challenge. Tetravalent technetium Tc(IV) is a relatively fixed form of technetium with low environmental mobility. Therefore, reducing heptavalent technetium Tc(VII) to tetravalent technetium Tc(IV) is an effective way to improve the storage safety of technetium-containing solutions and is a promising strategy for technetium storage.

[0003] Various methods have been developed to reduce and fix Tc(VII) to improve its storage safety. Such as radiation reduction, biological reduction, electroreduction and photoreduction. However, most of these methods are difficult to implement, complicated to operate and costly. Finding a simple, convenient and low-cost method for reducing technetium remains a challenging issue. Small molecule organic acids are weak electron donors, but their electron-donating capacity in aqueous solution is limited. Recently, biochar has attracted attention because of its redox activity and its ability to participate in redox reactions. Baked charcoal is a biochar obtained by low-temperature heat treatment. It has a wide source, low price, rich oxygen-containing functional groups, can chelate with heavy metal ions, and is a natural adsorption material. As an adsorbent, it has been used in the adsorption and separation of heavy metals, but the reduction adsorption capacity of baked charcoal is weak, and its ability to reduce technetium is limited. Therefore, using baked charcoal to enhance the ability of small molecule organic acids to reduce technetium and using baked charcoal and small molecule organic acids to treat radioactive technetium-containing solutions together will be a potential simple and sustainable method. Bamboo shoot shells are a byproduct of the bamboo shoot processing industry and are often incinerated or landfilled as waste, resulting in resource loss. However, they can be used as a sustainable raw material to prepare baked charcoal. Summary of the invention

[0004] The purpose of the present invention is to provide a method for treating a radioactive technetium-containing aqueous solution. The method overcomes the problem of complex and high cost of technetium reduction process, and provides a method for reducing radioactive nuclides of technetium with simple process, convenient use and convenient operation.

[0005] The present invention adopts the following technical solution:

[0006] A method for treating a radioactive technetium-containing aqueous solution comprises the following steps:

[0007] 1) Adjusting pH: adjusting the pH of the Tc(VII)-containing solution to acidic;

[0008] 2) Technetium reduction: A certain amount of baked charcoal and organic acid salt is added to the acidic Tc(VII) solution and stirred and shaken for a period of time for adsorption reaction.

[0009] In the above method, the concentration of technetium in the Tc(VII) solution in step 1) is 20-100 mg / L, and the pH of the Tc(VII) solution is adjusted to 1-5.

[0010] In the above method, the amount of baked charcoal added in step 2) is 0.01-0.1 g of baked charcoal per 10 mL of Tc(VII) solution, and the concentration of the organic acid salt is 1-5 mmol / L; the reaction temperature is controlled at 20-40°C, the reaction time is 12-24 h, and the stirring speed is 130 rpm. The organic acid salt is any one of sodium tartrate, sodium oxalate, sodium lactate, and sodium succinate.

[0011] The specific steps for preparing the baked charcoal in step 2) of the above method are as follows:

[0012] (1) Granulation: Wash, dry and crush the bamboo shoot shells into 40-100 mesh particles, sieve and place in a drying container for later use;

[0013] (2) Baking: placing the bamboo shoot shell particles obtained in step (1) in a tubular furnace, introducing an inert atmosphere, baking at 200-500° C. for 0.5-2 h, and then naturally cooling to room temperature to obtain carbon particles; the inert atmosphere is any one of argon, nitrogen, and carbon dioxide.

[0014] (3) Grinding: The carbon particles obtained in step (2) are fully ground for 3-30 min, and the ground particles are washed and dried at 40-60° C. to obtain baked carbon.

[0015] The above method is used in the reduction of radioactive nuclide technetium.

[0016] Beneficial effects of the present invention:

[0017] 1. The biomass raw material for preparing the baked charcoal in the present invention is agricultural and forestry waste, which has a wide source, low cost, and can realize waste utilization; the prepared baked charcoal has been baked and ground, has rich surface functional groups and fully exposed active sites, does not require additional additives and complicated steps, and the preparation method is simple.

[0018] 2. The oxygen-containing functional groups on the surface of the baked charcoal become the adsorption and reduction sites of the radioactive nuclide heptavalent technetium, reducing and fixing Tc(VII) to Tc(IV) and providing complexation sites; when organic acid is added, the baked charcoal changes the electron transfer mode of the organic acid salt by adsorbing small molecule organic acid salts and enhances its electron donating effect, which greatly improves the reduction ability of Tc(VII). The performance of the two when used together is better than that of either alone. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a graph showing the change in removal rate of technetium by the roasted charcoal, small molecule organic acid and roasted charcoal prepared in the present invention over time.

[0020] Figure 2 The Fourier transform infrared spectra characterize the baked charcoal and the original biomass prepared under different conditions in the present invention. DETAILED DESCRIPTION

[0021] The present invention will be further described below in conjunction with implementation cases, which will help to better understand the present invention, but the present invention is not limited to the following embodiments.

[0022] Example 1

[0023] A method for treating a radioactive technetium-containing aqueous solution comprises the following steps:

[0024] The pH of the 40 mg / L Tc(VII) solution was adjusted to 3, and 5 mmol / L sodium oxalate was added. 0.02 g of baked carbon was added to 10 mL of the mixed solution. The above system was oscillated at 130 rpm at 30°C for 12 h for adsorption reaction. The concentration of Tc(VII) in the adsorption solution was measured. After the adsorption was completed, the concentration of Tc(VII) in the solution decreased from 40 mg / L to 18.097 mg / L. After reduction by baked carbon, the concentration of Tc(IV) increased from 0 mg / L to 14.302 mg / L.

[0025] The preparation steps of baked charcoal are as follows:

[0026] (1) Granulation: Wash, dry and crush the bamboo shoot shells into granules, pass through a 60-mesh sieve and place in a drying container for later use;

[0027] (2) Baking: The obtained bamboo shoot shell particles are placed in a tubular furnace, carbon dioxide gas is introduced, and the particles are baked at 200°C for 2 hours, then naturally cooled to room temperature, washed to neutrality, and then fully dried to obtain carbon particles.

[0028] (3) Grinding: The prepared carbon particles are fully ground for 10 min, washed and dried to obtain baked carbon.

[0029] Example 2

[0030] A method for treating a radioactive technetium-containing aqueous solution, characterized by the following steps:

[0031] The pH of the 50 mg / L Tc(VII) solution was adjusted to 1, and 1 mM sodium oxalate was added. 0.02 g of baked carbon was added to 10 mL of the mixed solution. The system was oscillated at 130 rpm at 30°C for 12 hours, and the concentration of Tc(VII) remaining in the adsorbed solution was measured. After the adsorption was completed, the concentration of Tc(VII) in the solution decreased from 50 mg / L to 29.568 mg / L. After reduction by baked carbon, the concentration of Tc(IV) increased from 0 mg / L to 19.332 mg / L.

[0032] The preparation steps of baked charcoal are as follows:

[0033] (1) Granulation: Wash, dry and crush the bamboo shoot shells into granules, pass through an 80-mesh sieve and place in a drying container for later use;

[0034] (2) Baking: The obtained bamboo shoot shell particles are placed in a tubular furnace, carbon dioxide gas is introduced, and the particles are baked at 350° C. for 1.5 hours and then naturally cooled to room temperature. The particles are washed to neutrality and then fully dried to obtain carbon particles.

[0035] (3) Grinding: The prepared carbon particles are fully ground for 10 min, washed and dried to obtain baked carbon.

[0036] Example 3

[0037] A method for treating a radioactive technetium-containing aqueous solution, characterized by the following steps:

[0038] The pH of the 50 mg / L Tc(VII) solution was adjusted to 5, and 3 mM sodium tartrate was added. 0.02 g of baked carbon was added to 10 mL of the mixed solution. The system was oscillated at 130 rpm at 30°C for 12 hours, and the concentration of Tc(VII) remaining in the adsorbed solution was measured. After the adsorption was completed, the concentration of Tc(VII) in the solution decreased from 50 mg / L to 28.503 mg / L. After reduction by baked carbon, the concentration of Tc(IV) increased from 0 mg / L to 19.923 mg / L.

[0039] The preparation steps of baked charcoal are as follows:

[0040] (1) Granulation: Wash, dry and crush the bamboo shoot shells into granules, pass through an 80-mesh sieve and place in a drying container for later use;

[0041] (2) Baking: The obtained bamboo shoot shell particles are placed in a tubular furnace, carbon dioxide gas is introduced, and the particles are baked at 500° C. for 0.5 hours, then naturally cooled to room temperature, washed to neutrality, and fully dried to obtain carbon particles.

[0042] (3) Grinding: The prepared carbon particles are fully ground for 10 min, washed and dried to obtain baked carbon.

[0043] Example 4

[0044] The pH of the 50 mg / L Tc(VII) solution was adjusted to 4, and 3 mM sodium lactate was added. 0.02 g of the baked carbon prepared in Example 1 was added to 10 mL of the mixed solution. The results are shown in the attached Figure 1 The above system was oscillated and adsorbed at 30°C and 130 rpm for 12 h, and the residual Tc concentration in the adsorbed solution was measured. It can be seen that in the presence of sodium lactate, the concentration of heptavalent technetium continued to decrease within 24 hours, while the concentration of tetravalent technetium, which was not initially present, increased over time.

[0045] Example 5

[0046] The baked charcoal and original biomass prepared in Examples 1, 2, and 3 were characterized by Fourier transform infrared spectrometer. The characterization results are shown in the attached figure. Figure 2 The charcoal is relatively stable at 3336, 1723, and 1622 cm -1 The peak intensity at increases, indicating that the baked carbon surface has more abundant surface functional groups and active sites.

[0047] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A method for treating a radioactive technetium-containing aqueous solution, characterized in that: The following steps are involved: 1) Adjust pH: adjust the pH of the Tc(VII) solution to acidic; 2) Technetium reduction: a certain amount of baked carbon and organic acid salt is added to an acidic Tc(VII) solution and stirred and shaken for a period of time for adsorption reaction; In the step 1), the concentration of technetium in the Tc(VII) solution is 20-100 mg / L, and the pH of the Tc(VII) solution is controlled at 1-5; In the step 2), the amount of baked charcoal added is 0.01-0.1 g of baked charcoal per 10 mL of Tc(VII) solution; the concentration of the organic acid salt is 1-5 mmol / L, the reaction temperature is controlled at 20-40° C., and the oscillation adsorption reaction time is 12-24 h; The organic acid salt in step 2) is any one of sodium tartrate, sodium oxalate, sodium lactate and sodium succinate; The specific preparation steps of the baked charcoal in step 2) are as follows: (1) Granulation: Wash, dry and crush the bamboo shoot shells into 40-100 mesh particles, sieve and place in a drying container for later use; (2) Baking: placing the bamboo shoot shell particles obtained in step (1) in a tube furnace, introducing an inert atmosphere, baking at 200-500° C. for 0.5-2 h, then naturally cooling to room temperature, washing to neutrality, and then fully drying to obtain carbon particles; (3) Grinding: The carbon particles obtained in step (2) are fully ground for 3-30 min, and the ground particles are washed and dried at 40-60° C. to obtain baked carbon.

2. The method according to claim 1, characterized in that: The inert atmosphere is any one of argon, nitrogen and carbon dioxide.

3. Use of the method for treating a radioactive technetium-containing aqueous solution according to claim 1 in the reduction of radioactive technetium.

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