Analytical chemical study on actinoids ions by column electrolysis

The overall feature of the oxidation-reduction behavior of U, Np or Pu ions in acidic aqueous media has been elucidated based on the results of the electrolysis at a column electrode with the following advantages: 1) coulometric electrolysis can be attained extremely rapidly, 2) quantitative electrolysis proceeds with considerably small overpotential even if the electrode reaction is totally irreversible, and 3) the electrolysis is carried out in a flow-system. These advantages are favorable to the preparation of unstable species such as Np3+, Pu3+ or PuO2+ for the subsequent investigation of their chemical behavior. A detailed discussion was made on the irreversible electrode reduction of AnO2+ and the oxidation of An4+ (An: U, Np or Pu). PuO2+ was found as an intermediate species in the reduction of PuO2+. Based on the above fundamental results, rapid methods were developed for the coulometric determination of Pu, and for the speciation of Np or U and Pu in their mixtures. A chemical method was also proposed for the analysis of the oxidation state of U in UO2 pellets employing dissolution with strong phosphoric acid followed by detection using the column electrode. The reduction product of UO22+ in weakly acidic media, U4+, was found to be deposited on the glassy carbon electrode as a hydroxide or an oxide. This phenomenon was utilized for the collection and determination of trace U by column electrolysis. (author)