Electrode processes of plutonium ions in phosphate media

The electrolytic behaviour of plutonium ions in a mixture of phosphate and nitrate solutions was studied by flow-coulometry with column electrodes of glassy carbon(GC)-fibers and voltammetry with a GC disc electrode, and compared with that in phosphate-free media. The redox processes, PuO 2 2+ /PuO 2 + and Pu4+/Pu3+, were demonstrated to be reversible even in the phosphate media and their half wave potentials shifted more negatively due to the formation of PuO2(H2PO4)+ and Pu(HPO4)2. The rate of the irreversible reduction of PuO 2 + to Pu3+ increased in the presence of phosphoric acid and the quantitative reduction was attained with the column electrode even at +0.35 V vs. saturated KCl-Ag/AgCl. The reduction process of PuO 2 + was elucidated considering an intermediate Pu(IV)-species, PuO2+, which decomposed into Pu4+ by a post-chemical reaction. Analytical advantages of the use of phosphate media are discussed.