Sythesis Of SiO₂ Based Composite Aerogels And Study On The Adsorption And Immobilization Of Cerium Ions

Nuclear technology has rapid development in recent decades. While making use of nuclear energy, it also produced a large number of high-level liquid waste (HLLW) which contains so much long half-life、high radiation toxicity of plutonium and actinides that they must be disposed safely and permanently. This paper mainly talks about the absorption and immobilization of plutonium from HLLW, we can change the radioactive waste from liquid to solid directly, reducing waste volume and disposal costs effectively, and avoid secondary pollution at the same time. Therefore, it is important to develop specific materials with enormous surface area、high porosity and pore volume, which would be able to form a stable and solid structure after heat treatment.In this paper, SiO2-ZrO2 aerogels and SiO2-ZrO2-calcium alginate aerogels with three-dimensional porous structure are prepared by Sol-Gel process with phase separation method. The aerogels are characterized by the analysis of SEM, XRD, FT-IR and BET, and the static adsorption performance of the simulated plutonium (Cerium) on aerogels is investigated under different conditions. By changing the addition ratio of raw ingredients, the surface and porous structure of the aerogels can be adjusted as well. The result shows that SiO2-ZrO2 aerogels have well-organized mesopore (7.97nm) structure, high surface area (309.1m2/g) and pore volume (1.23cm3/g), the maximum adsorption capacity can reach 177.6mg/g at 25℃. The surface area, average pore size and pore volume of SiO2-ZrO2-calcium alginate aerogels is 390.81m2/g,10.38nm and 1.33cm3/g, the maximum adsorption capacity reaches 269.2mg/g at 25℃. Both of the two adsorption methods are highly consistent with Langmuir isotherm model and pseudo-second-order adsorption kinetics.Cerium was immobilized in glass and glass-ceramic. For glass waste forms, there are no characteristic peaks of CeO2, all Ce(Ⅳ) could be immobilized by the network structure of glasses. For glass-ceramic waste forms, Ce entered into Ca sites of Ca2SiO4 and Zr sites of ZrO2,Ca2SiO4 and ZrO2 are coated by SiO2, all Ce(Ⅳ) could be immobilized in the waste forms by 1450℃ heat treatment.