The Speciation of Americium Cations in Neat Water Implicated from DFT Studies.

The recent observed manipulatable redox potential of trivalent americium ion in the aqueous phase by modifying an electrode offers an alternative to accomplish the separation. In order to understand extensively the speciation of Am, which is the prerequisite to understanding the mechanism of the oxidation of Am, we conducted a density functional study to identify the potential species of Am in its tri-, tetra-, and pentavalent states in aqueous phase. Based on the speciation analysis, the calculations implicate a stepwise mechanism for the oxidation of hydrated Am(III), which predominantly exists in its hydrated monatomic cationic form (Am 3+ (aq)). The two sequential one-electron oxidation processes first produce AmO 2+ (aq), which may establish an equilibrium with Am 4+ (aq), and the AmO 2+ (aq) may then evolve to the dioxo americyl(V) ion. These results suggest the copresence of Am 4+ (aq) and AmO 2+ (aq), which builds a bridge for the conversion of americium ion from a monatomic ion to dioxo americyl(V).