Immobilization of iodine waste at low sintering temperature: Phase evolution and microstructure transformation

•Phase evolution and microstructure transformation of the matrix were obtained.•AgI were gradually immobilized as the temperature increased.•Part of AgI were incorporated into the glassy phase and others were fixed in the matrix.•The [BO3] units transformed into that of [BO4] under the effect of temperature. The treatment of radioiodine produced from nuclear industry is a key priority. It is significant to understand the phase evolution and microstructure transformation of the matrix in the field of radioiodine immobilization. In this work, the iodine wastes (silver-coated silica gel doped with iodine waste) were immobilized by B2O3-Bi2O3-ZnO at different low sintering temperatures (500, 550, and 600 ℃, respectively). The effect of iodine content in silver-coated silica gel on the phase evolution for the sintered matrix was investigated. Based on the FT-IR results, the changing of microstructure transformation affects by temperature and composition were also studied. These results demonstrate that the simulated iodine waste was gradually immobilized in the glassy phase as the sintering temperature increased. Moreover, under the effect of sintering temperature and material composition, part of B-O-B in [BO3] unit transformed into B-O-B in [BO4], resulting in more iodine wastes were immobilized in the glassy phase. This work mainly reveals the phase evolution and microstructure transformation of the iodine waste matrix sintered at low sintering temperatures.