Ruthenium speciation in radioactive wastes and state-of-the-art strategies for its recovery: A review

Ruthenium, mainly 106Ru, is one of the notorious fission products present in the radioactive wastes. In view of its complex chemistry, it gets partitioned into various processing streams during the radioactive waste management steps. Also, due to the volatile nature of its tetraoxide, RuO4, it gets deposited in the process pipelines and stacks. Attempts have been made by various researchers, over the years, to separate radio-ruthenium from radioactive feeds including the acidic high level liquid waste (HLLW) as well as the alkaline low level liquid waste (LLLW) or intermediate level liquid wastes (ILLW). Solvent extraction, precipitation, ion-exchange, etc are some of the commonly employed techniques used for the separation of radio-ruthenium from radioactive feeds. The present review article gives a state-of-the-art of the separation of radio-ruthenium from radioactive waste feeds based on Ruthenium speciation in the system. Most of the published literature involves synthetic feeds rather than actual radioactive wastes. Nevertheless, the published data gives very important information on how to separate radio-ruthenium from different types of radioactive feeds. The aqueous chemistry of Ruthenium is quite complex due to the co-existence of different ionic species of different oxidation states. In view of this, this review article begins with a brief summary on the aqueous chemistry of Ruthenium in acidic as well as alkaline feeds and subsequently its separation from these solutions were discussed using various techniques under the light of its speciation.