Application of ionic liquid as a medium for treating waste contaminated with NF(4)

Most of the metal or bed material wastes generated from uranium enrichment facilities or uranium refining and conversion plants are contaminated by uranium fluoride compounds such as UF4. These wastes are mainly classified as medium-level wastes and their direct disposal is not economical unless uranium is recovered. It is desirable to recover as much uranium as possible from these wastes. Additionally, if these wastes are decontaminated up to a level regarded as nonradioactive waste, the decontaminated parts can be reused. Wet chemical decontamination processes using inorganic or organic acids have been developed as effective decontamination methods of metal wastes.1'2) However, relatively large amounts of secondary wastes including spent acid solutions are generated because the base metal part of the wastes is dissolved by acid in the dissolution of the contaminated parts. It has also been reported that uranium of spent adsorbents can be recovered by electrolysis in sodium chloride molten salt.3) However, this method must be done at a high temperature (672 deg C). Decontamination methods carried out under milder conditions are preferable. Room-temperature ionic liquids (ILs), materials that are liquid around room temperature and consist only of ions, have been studied widely as media for various reactions, because they have attractive properties such as thermal stability, nonfiammability, high ionic conductivity, low melting point, and wide electrochemical potential windows.4,5) Some research groups have investigated the solubility of metal oxides in ILs and the extraction behavior of metal