Synthesis Of Mesoporous Bi~0-SBA-15 For Capture And Immobilization Iodine Gas

The radioactive iodine waste gas generated during nuclear power operation and spent fuel reprocessing has become a major issue of nuclear safety,posing a serious threat to environmental safety and human health.The control of radioactive gaseous iodine is crucial for achieving the sustainable development of nuclear energy.Adsorption is considered to be one of the effective methods for capturing gaseous iodine.However,existing adsorbents have problems such as low adsorption capacity and are not easy to solidify.In addition,there is a serious problem of iodine loss during the solidification process of iodine containing waste.Therefore,developing new iodine adsorption materials with good adsorption performance and easy solidification treatment,as well as new methods for solidification with high iodine retention rate,is of great significance for the effective treatment of radioactive iodine waste gas.Based on this,this thesis aims at solving the problems of low adsorption capacity,difficulty in solidification treatment,and low iodine retention rate,and conducts research on the synthesis,capture,and solidification of new bismuth based mesoporous silica（Bi⁰-SBA-15）materials with good adsorption performance and easy solidification treatment,with the expectation of achieving effective treatment of radioactive gaseous iodine.The main research work and results are as follows:（1）Synthesis of mesoporous Bi⁰-SBA-15 material for highly efficient capture iodineBi⁰-SBA-15 material was synthesized using an improved impregnation reduction method and its adsorption performance for iodine gas was studied.The effects of acid and alkali dosage,bismuth loading amount,reductant dosage,reaction temperature,washing solution system,and calcination temperature on the microstructure and morphology of the material were discussed.The results show that the modified impregnation reduction method can uniformly and loosely load Bi⁰ onto mesoporous SBA-15 materials,and nano Bi0 particles are mainly spherical and flocculent particles.In addition,the effects of bismuth loading,iodine gas concentration,adsorption temperature,and time on the adsorption performance of iodine gas were studied.The adsorption study results show that the iodine adsorption amount of Bi⁰-SBA-15 material increases with the increase of bismuth loading amount,and decreases with the increase of adsorption temperature.Due to the uniform and loose attachment morphology of Bi⁰ nanoparticles,the active site has a high utilization rate,and the obtained Bi⁰-SBA-15 material exhibits a high iodine adsorption capacity（925 mg/g）and a fast adsorption rate（60 min）.The fitting of adsorption data shows that the adsorption process of iodine conforms to a quasi second order kinetic equation.The adsorption mechanism of Bi⁰-SBA-15 material for iodine is mainly chemical adsorption（2Bi⁰+3I₂=2Bi I₃）.The obtained Bi⁰-SBA-15 material exhibits good thermal stability,aqueous solution stability,and irradiation stability.This study shows that Bi⁰-SBA-15 is a good adsorbent for iodine gas.（2）Study on immobilization and stability of Mesoporous Bi⁰-SBA-15 after iodine captureThe curing treatment of mesoporous Bi⁰-SBA-15 material after trapping iodine was studied using Bi₂O₃ as an iodine stabilizer in N₂ atmosphere.The effects of iodine waste content,stabilizer content,sintering atmosphere,sintering temperature and time on iodine retention,phase structure,micromorphology,compactness,and chemical stability in solidified solids were studied.The results showed that the retention rate of iodine increased with the increase of the content of Bi₂O₃,and decreased with the increase of the content of iodine waste.Under the synergistic action of N₂ atmosphere and Bi₂O₃,the iodine retention rate in the solidified body can reach 92.22%,which is much higher than the iodine retention rate（18.01%）of traditional curing processes.Research on the curing mechanism shows that Bi₂O₃ can react with easily volatile Bi I₃ to form stable Bi_xO_yI,while N₂ can effectively avoid the loss of iodine caused by the reaction of Bi_xO_yI with O₂,thereby achieving a high retention rate of solidified iodine.In addition,the cured body obtained has good compactness(5.1-5.8 g·cm^-3)and chemical stability(10^-3 g·m^-2·d^-1).The research results can provide a new idea for the solidification treatment of waste containing volatile components.