Disproportionation of Pu(VI) and reproportionation of Pu(V), Pu(VII) in aqueous alkali solutions

Disproportionation of Pu(VI) and reproportionation of Pu(V) and Pu(VII) in aqueous NaOH solutions was studied. With an increase in the NaOH concentration in solution over 7.5 M, the equilibrium of the reaction Pu(VII) + Pu(V)⇄2Pu(VI) is gradually shifted toward formation of Pu(V) and Pu(VII) as products of Pu(VI) disproportionation, and at [NaOH] + 13 M, Pu(VI) disproportionates virtually completely. At [NaOH] + 7.5 M, the equilibrium of the above reaction is shifted toward formation of Pu(VI). Based on the experimental data, the equilibrium constants of the reaction at various alkali concentrations in the solution and the formal potentials ? f[Pu(VII)/Pu(VI)] were calculated. The data obtained showed that, with respect to reduction with water, Pu(VII) is stable in aqueous alkali solutions at NaOH concentrations exceeding 7.5 M.