Cationic speciation in non-aqueous media of uranium, neptunium and plutonium in oxidation states III and IV

A Melbourne program dating from 1975 and based largely on UV-visible spectroscopy of solutions, initially in HF acidified with Lewis acids and later in oleums and acidified HSO3F and CF3SO3H, gave much information on solvent coordination of many d- and f- transition metal cations, such as Cr3+ and Co2+ and tripositive lanthanides. In a project initiated during a sabbatical leave at the Lawrence Berkeley Laboratory in 1976, stable HF solutions of U3+ were prepared and spectra were recorded for U(III) and U(IV) and, subsequently, for Np(III) and Np(IV). Recently at Melbourne we have been investigating solutions of U(III) and U(IV) in HSO3F and CF3SO3H, with U(IV) exhibiting interesting speciation, as it does in HF. Eller and colleagues at Los Alamos National Laboratory have recorded spectra for U(IV), Np(IV), Pu(III) and Pu(IV) in SbF5/HF and SbF5/HSO3F. UV-visible spectra in water, superacids and acidic chloroaluminates will be presented to propose that cationic speciation of U, Np and Pu in oxidation states (III) and (IV) occurs generally in acidic media