Application of ionic liquid as a medium for treating waste contaminated with UF4

Abstract

We confirmed that UF4 was dissolved completely in BMICl by heating at 100°C in air. The UV-visible absorption spectrum of the resulting dissolution solution suggested that UF4 was dissolved in BMICl and oxidized to uranyl(VI) species by O2, and that the uranyl(VI) species with the mixed ligands of F- and Cl- were formed. We also found that the steel waste contaminated with UF4 was decontaminated below the temporarily proposed clearance level (1.0Bq/g) within 3h by soaking BMICl at 100°C, and that in such decontamination treatments using BMICl, the FeF3 on the surface of contaminated steel was dissolved more easily than the base metal part of the steel. This suggested that the secondary waste generations in the decontamination using BMICl would be less than that in the acid decontamination method. In the cyclic voltammogram of BMICl solution when dissolving UF 4, uncoupled reduction and oxidation peaks were observed around -0.93 and 0.18 V. The reduction peak was considered to correspond to the reduction of uranyl(VI) + e--! uranyl(V) followed by further reduction to UO2. © Atomic Energy Society of Japan.