Reactions of antimony compounds with fluorine gas by thermogravimetric and differential thermal analyses and X-ray diffraction analysis

Antimony is one of the key fission products in the reprocessing of spent nuclear fuel by the fluoride volatility method because of the high volatility of antimony fluorides. Since the fluorination reaction of antimony compounds is not well understood, the reaction behavior of antimony compounds with F₂ was investigated by thermogravimetric and differential thermal analyses and X-ray diffraction analysis in this study. The target antimony compounds were antimony metal, SbF₃, Sb₂O₃, Sb₂O₄, and Sb₂O₅. The fluorination reaction of antimony metal started at 150 °C, and the fluorination product was SbF₃. SbF₃ volatilized completely by the reaction with F₂ above 190 °C; it was considered that volatile SbF₅ was formed by the reaction with F₂. In the series of fluorination of the antimony oxides, Sb₂O₃, Sb₂O₄, and Sb₂O₅, they started to react with F₂ and volatilize at 330 °C as SbF₅. During the fluorination of Sb₂O₃, Sb₂O₄ was formed temporarily in the course of the reaction. Oxygen released from the fluorination reaction of a part of Sb₂O₃ would oxidize remained Sb₂O₃ to Sb₂O₄. The reaction mechanism for the fluorination of antimony compounds obtained in this study is applicable to evaluate the transfer of antimony in the reprocessing process of the fluoride volatility method.