Formation of AgI/Ag₃PO₄ solid solution on alumina for enhancing radioactive iodine adsorption at high temperatures

Radioiodine-131 is one of the pernicious radionuclides released during nuclear accidents, as its radioactivity can potentially affect public health and safety. To prevent radioiodine-131 from being released into the environment, the use of adsorbents that are highly efficient at high temperatures is significantly important. The radioactive gas from the nuclear core in an accident, such as the Fukushima nuclear accident, is usually released occurs under high-temperature conditions. Therefore, in this study, a 10 wt% silver phosphate-loaded alumina (Ag₃PO₄/Al₂O₃) adsorbent was prepared. Further, its performance toward radioiodine adsorption was tested at high temperatures up to 750 °C, using Al₂O₃ and traditional 10 wt% Ag/Al₂O₃ adsorbent as controls. The results of the iodine adsorption test indicated that the 10 wt% Ag₃PO₄/Al₂O₃ adsorbent showed a higher decontamination factor than did the 10 wt% Ag/Al₂O₃ adsorbent by two orders of magnitude at 650 and 750 °C. Results of the iodine desorption test revealed that the new adsorbent could be effectively used at 750 °C. The characteristic powder X-ray diffraction, nitrogen adsorption–desorption isotherm, X-ray photoelectron spectroscopy, and thermogravimetric analysis–differential scanning calorimetry data indicated that the enhanced adsorption ability at high temperatures was attributed to the formation of a solid solution between silver iodide and Ag₃PO₄.