Preparation method of potassium mercuric nitrate modified silica gel composite material for purifying gaseous radioactive iodine in spent fuel reprocessing plant

Abstract

The invention discloses a preparation method of a potassium mercuric nitrate modified silica gel composite material for purifying gaseous radioactive iodine in a spent fuel reprocessing plant, which comprises the following steps: dissolving potassium nitrate and mercuric nitrate hydrate with dilute nitric acid to obtain a clear solution; adding the clarified solution into a reaction kettle, and then putting the reaction kettle into a drying oven for hydrothermal reaction treatment; silica gel is added into the solution subjected to the hydrothermal reaction treatment to be subjected to dipping treatment; placing the silica gel subjected to dipping treatment in a drying oven for drying treatment to obtain the potassium mercuric nitrate modified silica gel composite material. The potassium mercuric nitrate modified silica gel composite material provided by the invention has the advantages of large iodine adsorption capacity, good thermal stability, nitrogen and oxygen erosion resistance and low cost, and is suitable for purification treatment of gaseous radioactive iodine in a spent fuel reprocessing plant.

Description

Technical Field

[0001] The present invention belongs to the technical fields of nuclear industry and material preparation, and more specifically, the present invention relates to a preparation method of a potassium mercuric nitrate modified silica gel composite material for purifying gaseous radioactive iodine in a spent fuel reprocessing plant. Background Art

[0002] With the large-scale development of nuclear energy in China, nuclear power plants will produce about 1000 m 3 or more of spent fuel every year, and it is estimated that the cumulative amount of spent fuel in China will reach more than 24,000 cubic meters in 2050. Therefore, the problem of spent fuel reprocessing needs to be solved urgently. China mainly adopts the wet reprocessing technology, and during this process, furnace exhaust gas, dissolution exhaust gas, cell exhaust gas, process vessel exhaust gas, waste liquid solidification exhaust gas, etc. will be generated. These exhaust gases contain a large amount of radioactive iodine-129, mainly including inorganic iodine ( 129 I 2 ) and organic iodine (CH 3 129 I). Since iodine-129 has a long half-life (1.57×10 7 a), high mobility, chemical toxicity and high affinity for the thyroid gland, it must be purified in time. At present, the treatment methods for iodine-containing exhaust gases are mainly divided into two types: wet and dry treatment. Due to the high adsorption efficiency of the solid adsorption technology and the low requirements for equipment, it has been at the forefront of the research on the purification treatment of gaseous radioactive iodine. At present, silver-based adsorption materials are mainly used at home and abroad, including silver-impregnated silica gel, silver-impregnated zeolite, silver-impregnated alumina, etc. Although they have excellent performance, due to the high price of silver, their cost is high. In addition, there are various solid adsorbents such as metal oxides, sulfur-based aerogels, metal-organic frameworks, and porous organic polymers, but they have defects such as a cumbersome synthesis process or poor structural stability in the application environment, and are not suitable for popularization and application at this stage. Therefore, the design and development of new iodine-129 purification materials have very important practical significance. Summary of the Invention

[0003] An object of the present invention is to solve at least the above problems and / or defects, and provide at least the advantages described hereinafter.

[0004] To achieve these objects and other advantages of the present invention, there is provided a preparation method of a potassium mercuric nitrate modified silica gel composite material for purifying gaseous radioactive iodine in a spent fuel reprocessing plant, including the following steps:

[0005] Step 1: Dissolve potassium nitrate and mercuric nitrate hydrate with dilute nitric acid, and stir until clear;

[0006] Step 2: Add the above clear solution to a reaction kettle for hydrothermal reaction treatment to obtain a potassium mercuric nitrate solution;

[0007] Step 3: Add silica gel into the potassium mercuric nitrate solution for impregnation treatment;

[0008] Step 4: Place the impregnated silica gel in an oven for drying treatment to obtain the potassium mercuric nitrate modified silica gel composite material.

[0009] Preferably, in Step 1, the molar concentration of dilute nitric acid is 1 - 1.5 mol / L, the stoichiometric ratio of potassium nitrate to mercuric nitrate hydrate is 2:1 - 2.5:1, and the stirring time is 10 - 30 min.

[0010] Preferably, in Step 2, the hydrothermal reaction temperature is 80 - 100 °C, and the hydrothermal reaction time is 24 - 48 h.

[0011] Preferably, in Step 3, the silica gel is water-resistant silica gel, the liquid-solid ratio of the potassium mercuric nitrate solution to the silica gel is 1 - 1.5:1, and the impregnation treatment conditions are impregnation at 15 - 35 °C for 2 - 4 h.

[0012] Preferably, in Step 4, the specific drying conditions are heating at 130 - 150 °C in an air atmosphere for 24 - 48 h to obtain the potassium mercuric nitrate modified silica gel composite material for purifying gaseous radioactive iodine in a spent fuel reprocessing plant.

[0013] Preferably, the silica gel in Step 3 is pretreated by the following method:

[0014] S1: Heat and acidify the silica gel in a hydrochloric acid solution, then wash it with deionized water until neutral to obtain coarsely expanded silica gel. Then immerse the coarsely expanded silica gel in a sodium hydroxide solution for alkali etching to obtain silica gel with nano-grooves formed on its surface;

[0015] S2: Subject the silica gel obtained in S1 to corona treatment, then wash it with deionized water, soak it in absolute ethanol, then take out the silica gel, soak it in a silane coupling agent solution, and finally dry it to obtain pretreated silica gel.

[0016] Preferably, in S1, the mass concentration of the hydrochloric acid solution is 5 - 8 wt%, the dosage ratio of the silica gel to the hydrochloric acid solution is 100 g:200 - 400 mL, the heating temperature is 50 - 60 °C, the heating time is 30 - 45 min, the mass concentration of the sodium hydroxide solution is 4 - 6 wt%, the dosage ratio of the coarsely expanded silica gel to the sodium hydroxide solution is 100 g:500 - 600 mL, and the etching time is 90 - 120 s.

[0017] Preferably, in S2, the corona parameter is 20 - 40 W / min·m 2 , wash with deionized water for 5 - 10 min, soak in absolute ethanol for 5 - 20 min, the silane coupling agent solution is 0.1 - 5% KH-550 solution, and soak for 5 - 20 min.

[0018] The present invention also provides an application of a potassium mercuric nitrate modified silica gel composite material, which is used to purify gaseous radioactive iodine or non-radioactive iodine in a spent fuel reprocessing plant. The gaseous radioactive iodine or non-radioactive iodine can be organic iodine and / or inorganic iodine. The organic iodine is methyl iodide, and the inorganic iodine is elemental iodine.

[0019] Preferably, the static adsorption method is used to treat non-radioactive iodine, and the specific steps are as follows: ① Place non-radioactive iodine in a crucible at the bottom of the reactor, and then place a sand core partition above the crucible; ② Place the potassium mercuric nitrate modified silica gel composite material in a hanging basket on the sand core partition, and the mass ratio of non-radioactive iodine to the potassium mercuric nitrate modified silica gel composite material is 1:1 to 3:1; ③ Cover the end cover of the reactor, and then place it in a blast drying oven, set the adsorption temperature to 100°C, and the adsorption time to 24 h; ④ Weigh the mass of the potassium mercuric nitrate modified silica gel composite material again, and calculate the non-radioactive iodine adsorption capacity through the change in mass before and after adsorption.

[0020] The present invention has at least the following beneficial effects:

[0021] (1) The saturated adsorption capacities of the potassium mercuric nitrate modified silica gel composite material of the present invention for elemental iodine and methyl iodide under static adsorption conditions reach 0.185 g / g and 0.154 g / g respectively, and it has a strong iodine adsorption ability, showing excellent iodine capture performance;

[0022] (2) The potassium mercuric nitrate modified silica gel composite material of the present invention does not show obvious weight loss below 150°C, and after heat treatment in an oven at 200°C for 24 hours, its mass loss is extremely small and the adsorption ability does not change significantly, indicating that the material has excellent thermal stability;

[0023] (3) After being eroded by a nitrogen mixed gas, the crystal structure of the potassium mercuric nitrate modified silica gel composite material of the present invention remains unchanged, proving that it has good resistance to nitrogen and oxygen gas erosion;

[0024] (4) From an economic perspective, the manufacturing cost of the potassium mercuric nitrate modified silica gel composite material of the present invention is only one-third of that of silver-attached silica gel, showing a significant cost advantage;

[0025] (5) The present invention also pre-treats silica gel, expands pores through acidification treatment and forms surface nano-grooves through alkali etching to increase the specific surface area, and then introduces corona treatment and immersion in a silane coupling agent to enhance the loading capacity of silica gel, effectively increasing the potassium mercuric nitrate loading amount. The static saturated adsorption capacities of the composite material finally prepared from the pre-treated silica gel for non-radioactive gaseous elemental iodine and non-radioactive gaseous methyl iodide are 0.233 g / g and 0.201 g / g respectively, and the iodine adsorption ability is significantly improved.

[0026] Other advantages, objects, and features of the present invention will be partially reflected by the following description and partially understood by those skilled in the art through the research and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Appearance picture of the finished product of potassium mercuric nitrate modified silica gel composite material prepared for Example 1;

[0028] Figure 2 Powder X-ray diffraction pattern of the finished product of potassium mercuric nitrate modified silica gel composite material prepared for Example 1;

[0029] Figure 3 Thermal analysis pattern of the finished product of potassium mercuric nitrate modified silica gel composite material prepared for Example 1;

[0030] Figure 4 Powder X-ray diffraction pattern and static saturation adsorption capacity pattern of the finished product of potassium mercuric nitrate modified silica gel composite material prepared for Example 1 after being eroded by nitrogen and oxygen gases. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] The following further describes the present invention in detail with reference to the accompanying drawings, so that those skilled in the art can implement it according to the description in the specification.

[0032] It should be understood that the terms such as "having", "comprising", and "including" used herein do not exclude the presence or addition of one or more other elements or their combinations.

[0033] Example 1

[0034] This example provides a preparation method of a potassium mercuric nitrate modified silica gel composite material for purifying gaseous radioactive iodine in a spent fuel reprocessing plant, including the following steps:

[0035] Step 1: Dissolve 44.069 g of potassium nitrate and 74.747 g of mercuric nitrate hydrate in 130 mL of a dilute nitric acid solution with a molar concentration of 1.2 mol / L, and stir for 10 min to obtain a clear solution;

[0036] Step 2: Hydrothermally treat the clear solution obtained in Step 1, with a hydrothermal reaction temperature of 100 °C and a hydrothermal reaction time of 24 h, to obtain a potassium mercuric nitrate solution;

[0037] Step 3: Immerse 100 g of water-resistant silica gel into the potassium mercuric nitrate solution obtained after the hydrothermal reaction treatment in Step 2, and perform impregnation treatment for 2 h;

[0038] Step 4: Place the silica gel after the impregnation treatment in Step 3 in a forced-air drying oven and dry it at 130 °C in an air atmosphere for 24 h to obtain a mercury nitrate-modified silica gel composite material for purifying gaseous radioactive iodine in a spent fuel reprocessing plant.

[0039] Figure 1 This is a photograph of the appearance of the finished product of the potassium mercury nitrate-modified silica gel composite material. As can be seen from the figure, the sample is white spherical particles with a particle size of 3 - 5 mm; Figure 2 This is the powder X-ray diffraction pattern of the finished product of the potassium mercury nitrate-modified silica gel composite material. As can be seen from the figure, only the characteristic diffraction peaks of potassium mercury nitrate (K 2 Hg(NO 3 ) 4 ) are detected in the sample; Figure 3 This is the thermal analysis pattern of the finished product of the potassium mercury nitrate-modified silica gel composite material. As can be seen from the figure, no obvious weight loss occurs in the sample at 150 °C, indicating that it has good thermal stability; Figure 4 This is the powder X-ray diffraction pattern and the static saturation adsorption capacity pattern of the finished product of the potassium mercury nitrate-modified silica gel composite material after being eroded by nitrogen and oxygen gases. As can be seen from the figure, after being eroded by nitrogen and oxygen gases, no obvious change occurs in the crystal structure of the sample, and the static saturation adsorption capacity does not decrease significantly either, indicating that it has good resistance to nitrogen and oxygen gas erosion.

[0040] Example 2

[0041] This example provides a preparation method of a potassium mercury nitrate-modified silica gel composite material for purifying gaseous radioactive iodine in a spent fuel reprocessing plant, including the following steps:

[0042] Step 1: Dissolve 44.069 g of potassium nitrate and 74.747 g of mercury nitrate hydrate in 130 mL of a dilute nitric acid solution with a molar concentration of 1.2 mol / L, and stir for 10 min to obtain a clear solution;

[0043] Step 2: Hydrothermally treat the clear solution obtained in Step 1. The hydrothermal reaction temperature is 100 °C, and the hydrothermal reaction time is 24 h to obtain a potassium mercury nitrate solution;

[0044] Step 3: Pretreat the silica gel. The method is as follows:

[0045] S1: Add 100 g of silica gel to 200 mL of an 8 wt% hydrochloric acid solution, heat and acidify it at 60 °C for 30 min, then wash it with deionized water until neutral to obtain coarsely pore-expanded silica gel. Then immerse 100 g of the coarsely pore-expanded silica gel in 500 mL of a 6 wt% sodium hydroxide solution for alkali etching for 100 s to obtain silica gel with nano-grooves formed on its surface;

[0046] S2: Corona-treat the silica gel obtained in S1. The corona parameters are 30 W / min·m2 , then wash with deionized water for 10 min, soak in absolute ethanol for 15 min, then take out the silica gel, soak it in a 2.5% KH-550 silane coupling agent solution, and finally dry to obtain pretreated silica gel.

[0047] Step 4: Immerse 100 g of pretreated silica gel into the potassium mercuric nitrate solution obtained from the hydrothermal reaction treatment in Step 2, and carry out impregnation treatment for 2 h;

[0048] Step 5: Place the modified silica gel after the impregnation treatment in Step 4 in a forced air drying oven, and carry out drying treatment at 130 °C in an air atmosphere for 24 h to prepare a potassium mercuric nitrate modified silica gel composite material for purifying gaseous radioactive iodine in a spent fuel reprocessing plant.

[0049] Application Example 1

[0050] Test the static adsorption capacity of the potassium mercuric nitrate modified silica gel prepared in Example 1 for non-radioactive gaseous elemental iodine.

[0051] The experimental process is as follows: ① Weigh 3.0012 g of non-radioactive elemental iodine and place it in a crucible at the bottom of the reactor, and then place a sintered glass partition above the crucible; ② Weigh 3.0169 g of the potassium mercuric nitrate modified silica gel composite material (M 1 ), and place it in a hanging basket on the sintered glass partition; ③ Cover the top lid of the reactor, place it in a forced air drying oven, set the adsorption temperature to 100 °C, and the adsorption time to 24 h; ④ Weigh the mass of the potassium mercuric nitrate modified silica gel composite material again (M 2 ), and calculate the adsorption capacity of non-radioactive gaseous elemental iodine through the change in mass before and after adsorption, that is:

[0052]

[0053] Experimental result: Calculate that the static saturated adsorption capacity of the potassium mercuric nitrate modified silica gel composite material prepared in Example 1 for non-radioactive gaseous elemental iodine is 0.185 g / g.

[0054] After the potassium mercuric nitrate modified silica gel composite material is eroded by nitrogen and oxygen gases, carry out the adsorption experiment according to the above method, and calculate that the static saturated adsorption capacity of elemental iodine after being eroded by nitrogen and oxygen gases is 0.186 g / g.

[0055] Application Example 2

[0056] Test the static adsorption capacity of the potassium mercuric nitrate modified silica gel composite material prepared in Example 1 for non-radioactive gaseous methyl iodide.

[0057] The experimental process is as follows: ① Measure 3 mL of methyl iodide solution and add it to a crucible at the bottom of the reactor, and then place a sintered glass partition above the crucible; ② Weigh 3.007 g of the potassium mercuric nitrate modified silica gel composite material (M1 ) and place it in a hanging basket on the core baffle; ③ Cover the top lid of the reactor, place it in a forced-air drying oven, set the adsorption temperature to 100 °C, and the adsorption time to 24 h. ④ Weigh the mass of the potassium mercuric nitrate modified silica gel composite material again (M 2 ), and calculate the adsorption capacity of non-radioactive gaseous methyl iodide through the change in mass before and after adsorption, that is:

[0058]

[0059] Experimental results: The calculated static saturation adsorption capacity of the potassium mercuric nitrate modified silica gel composite material prepared in Example 1 for non-radioactive gaseous methyl iodide is 0.154 g / g.

[0060] After the potassium mercuric nitrate modified silica gel composite material is eroded by nitrogen and oxygen gases, conduct the adsorption experiment according to the above method again. The calculated static saturation adsorption capacity of methyl iodide after being eroded by nitrogen and oxygen gases is 0.155 g / g.

[0061] Comparative Example 1

[0062] Step 1: Dissolve 44.069 g of potassium nitrate and 74.747 g of mercuric nitrate hydrate in 130 mL of dilute nitric acid solution with a molar concentration of 1.2 mol / L, and stir for 10 min to obtain a clear solution;

[0063] Step 2: Immerse 100 g of water-resistant silica gel into the clear solution obtained in Step 1 and conduct impregnation treatment for 2 h;

[0064] Step 3: Place the silica gel after impregnation treatment in Step 2 in a forced-air drying oven and conduct drying treatment at 130 °C in an air atmosphere for 24 h to prepare mercury and potassium co-modified silica gel.

[0065] Perform X-ray diffraction analysis on the product. The crystal structure of the sample prepared in Comparative Example 1 has changed, indicating that the potassium mercuric nitrate modified silica gel composite material cannot be synthesized by the method of Comparative Example 1.

[0066] Comparative Example 2

[0067] The difference between this comparative example and Example 2 is that S1 is not carried out, and the remaining steps are the same as those in Example 2.

[0068] Comparative Example 3

[0069] The difference between this comparative example and Example 2 is that S2 is not carried out, and the remaining steps are the same as those in Example 2.

[0070] Use the materials prepared in Example 2 and Comparative Examples 1 - 3 respectively, and then conduct iodine adsorption tests with the prepared materials according to the methods of Application Examples 1 - 2 respectively.

[0071] Experimental results: The static saturated adsorption capacity of the material prepared in Example 2 for non-radioactive gaseous elemental iodine was calculated to be 0.233 g / g, and the static saturated adsorption capacity for non-radioactive gaseous methyl iodide was 0.201 g / g; the static saturated adsorption capacity of the material prepared in Comparative Example 1 for non-radioactive gaseous elemental iodine was 0.015 g / g, and the static saturated adsorption capacity for non-radioactive gaseous methyl iodide was 0.023 g / g; the static saturated adsorption capacity of the material prepared in Comparative Example 2 for non-radioactive gaseous elemental iodine was 0.164 g / g, and the static saturated adsorption capacity for non-radioactive gaseous methyl iodide was 0.138 g / g; the static saturated adsorption capacity of the material prepared in Comparative Example 3 for non-radioactive gaseous elemental iodine was 0.205 g / g, and the static saturated adsorption capacity for non-radioactive gaseous methyl iodide was 0.173 g / g. It can be seen that on the basis of Example 1, in Example 2, due to the pretreatment of silica gel, the pore size was enlarged by acidification treatment and alkali etching, increasing the specific surface area of silica gel. Through corona treatment and immersion in silane coupling agent, the loading capacity of silica gel was enhanced. Both can effectively improve the loading amount of potassium mercuric nitrate on silica gel, and thus enhance the iodine adsorption capacity; while in Comparative Example 1, since the material could not be successfully prepared, the iodine adsorption amount was extremely low; in Comparative Example 2, due to the lack of pore size enlargement by acidification treatment and alkali etching, the subsequent corona treatment and silane coupling agent pretreatment would instead reduce the loading amount of potassium mercuric nitrate to some extent, and thus the iodine adsorption capacity decreased; in Comparative Example 3, due to only pore size enlargement by acidification treatment and alkali etching, the improvement of its iodine adsorption amount was less than that of Example 2.

[0072] Although the specific implementation modes of the present invention have been described in detail above, this does not mean that the present invention is limited to the application scope listed in the specification and implementation modes. The present invention can be fully applied to other fields that conform to its basic principles. For those skilled in the art, it is very easy to implement other modifications and changes. Therefore, without departing from the core concept defined by the claims of the present invention and their equivalent scope, the present invention is not limited to specific details or examples.

Claims

1. A method for preparing a potassium mercuric nitrate modified silica gel composite material for purifying gaseous radioactive iodine in a spent fuel reprocessing plant, characterized in that: The following steps are involved: Step 1: Dissolve potassium nitrate and mercuric nitrate hydrate with dilute nitric acid and stir until clear; Step 2: adding the clarified solution into a reactor for hydrothermal reaction to obtain a potassium mercuric nitrate solution; Step 3, adding silica gel into potassium mercuric nitrate solution for immersion treatment; Step 4: placing the impregnated silica gel in an oven for drying to obtain the potassium mercuric nitrate modified silica gel composite material.

2. The method for preparing the potassium mercuric nitrate modified silica gel composite material for purifying gaseous radioactive iodine in a spent fuel reprocessing plant according to claim 1, characterized in that: In the step 1, the molar concentration of dilute nitric acid is 1-1.5 mol / L, the stoichiometric ratio of potassium nitrate to mercuric nitrate hydrate is 2:1-2.5:1, and the stirring time is 10-30 min.

3. The method for preparing the potassium mercuric nitrate modified silica gel composite material for purifying gaseous radioactive iodine in a spent fuel reprocessing plant according to claim 1, characterized in that: In the step 2, the hydrothermal reaction temperature is 80-100° C., and the hydrothermal reaction time is 24-48 hours.

4. The method for preparing the potassium mercuric nitrate modified silica gel composite material for purifying gaseous radioactive iodine in a spent fuel reprocessing plant according to claim 1, characterized in that: In the step 3, the silica gel is water-resistant silica gel, the liquid-to-solid ratio of the potassium mercuric nitrate solution to the silica gel is 1-1.5:1, and the immersion treatment condition is immersion treatment at 15-35° C. for 2-4 hours.

5. The method for preparing the potassium mercuric nitrate modified silica gel composite material for purifying gaseous radioactive iodine in a spent fuel reprocessing plant according to claim 1, characterized in that: In the step 4, the specific drying conditions are heating at 130-150° C. in an air atmosphere for 24-48 hours to obtain a potassium mercuric nitrate-modified silica gel composite material for purifying gaseous radioactive iodine in a spent fuel reprocessing plant.

6. The method for preparing the potassium mercuric nitrate modified silica gel composite material for purifying gaseous radioactive iodine in a spent fuel reprocessing plant according to claim 1, characterized in that: The silica gel in step 3 is pretreated by: S1, heating and acidifying the silica gel in a hydrochloric acid solution, then washing with deionized water until neutral, to obtain a roughly expanded silica gel, and then immersing the roughly expanded silica gel in a sodium hydroxide solution for alkaline etching, to obtain a silica gel with nanogrooves formed on the surface; S2. The silica gel obtained in S1 is subjected to corona treatment, then washed with deionized water, and then soaked in anhydrous ethanol. The silica gel is then taken out, soaked in a silane coupling agent solution, and finally dried to obtain pretreated silica gel.

7. An application of a potassium mercuric nitrate modified silica gel composite material obtained by the preparation method according to any one of claims 1 to 6, characterized in that: The potassium mercuric nitrate modified silica gel composite material is used to purify gaseous radioactive iodine or non-radioactive iodine in a spent fuel reprocessing plant. The gaseous radioactive iodine or non-radioactive iodine can be organic iodine and / or inorganic iodine. The organic iodine is methyl iodide, and the inorganic iodine is elemental iodine.

8. The use of the potassium mercuric nitrate modified silica gel composite material for purifying gaseous radioactive iodine in a spent fuel reprocessing plant as claimed in claim 7, characterized in that: The static adsorption method is used to treat non-radioactive iodine, and the specific steps are as follows: ① Place the non-radioactive iodine in a crucible at the bottom of the reactor, and then place a sand core partition above the crucible; ② Place the potassium mercuric nitrate modified silica gel composite material in a hanging basket on the sand core partition; ③ Cover the reactor end cover and then place it in a forced air drying oven for adsorption; ④ Weigh the mass of the potassium mercuric nitrate modified silica gel composite material again, and calculate the non-radioactive iodine adsorption capacity by the change in mass before and after adsorption.

9. The use of the potassium mercuric nitrate modified silica gel composite material for purifying gaseous radioactive iodine in a spent fuel reprocessing plant as claimed in claim 7, characterized in that: In step ②, the mass ratio of non-radioactive iodine to potassium mercuric nitrate modified silica gel composite material is 1:1 to 3:

1.

10. The use of the potassium mercuric nitrate modified silica gel composite material for purifying gaseous radioactive iodine in a spent fuel reprocessing plant as claimed in claim 7, characterized in that: In step ③, the adsorption temperature was set to 100°C and the adsorption time was set to 24h.

Images