Pure and Applied Chemistry

Standard redox potentials, E⁰s, and redox processes of U, Np and Pu ions in acidic aqueous solutions are reviewed and evaluated critically. The E⁰s of reversible redox processes, MO₂²⁺/MO₂⁺ and M⁴⁺/M³⁺ (M: U, Np or Pu) adopted are those proposed mainly by Riglet et al. on the basis of the precise correction of formal potentials, E^0's, according to the improved theoretical approach to estimate the activity coefficient. Electrode processes of the U, Np and Pu ions are discussed in terms of current-potential curves, measured so far by polarography, voltammetry or flow coulometry. Special attention is payed to the irreversible MO₂⁺/M⁴⁺ reactions. Disproportionation reactions of MO₂⁺ are also discussed. New substances are introduced as intermediates during reductions of MO₂⁺ to M⁴⁺ or disproportionations of MO₂⁺.