The Action of Oxidizing Agents on Neptunium(VI) in Acid Solutions

In solutions with pH 1.5–2.5, terbium(IV) stabilized by anions of unsaturated phosphotungstate KPWO , slowly oxidizes NpO ·5HO. During oxidation, the resulting Np(VII) cation retains the Np(VI) configuration; i.e., it remains a pentagonal bipyramid. Therefore, the oxidation potential of the Np(VII)/(VI) pair is higher than the potential of the pair in which Np(VII) obtained by acidifying the Np(VII) anion retains the octahedral configuration. The high potential of Np(VII) with the pentagonal bipyramidal structure makes Np(VII) unstable. It was impossible to obtain it using strong oxidizing agents such as persulfate, perxenate, and xenon difluoride. Probably, pulse radiolysis will be an effective method for oxidizing Np(VI) in deaerated solutions at pH 1.5–3, containing persulfate or XeO.