X-ray absorption spectroscopic study of trivalent and tetravalent actinides in solution at varying pH values

We perform X-ray absorption spectroscopy (XAS) investigations to monitor the stabilization of redox trivalent and tetravalent actinide ions in solution at acidic conditions in a pH range from 0 to 3 after treatment with holding reductants, hydroxylamine hydrochloride (NH2OHHCl) and Rongalite (sodium hydroxymethanesulfinate, CH3NaO3S). X-ray absorption near edge structure (XANES) measurements clearly demonstrate the stability of the actinide species for several hours under the given experimental conditions. Hence, Structural parameters can be accurately derived by extended X-ray absorption fine structure (EXAFS) investigations. The coordination structure of oxygen atoms belonging to water ligands Surrounding the actinide ions does not change with increasing pH value (approximately 11 O atoms at 2.42 angstrom in the case of U(IV) at pH 1, 9 O atoms at 2.52 angstrom for Np(III) at pH 1.5, and 10 O atoms at 2.49 angstrom for Pu(III) up to pH 3), indicating that hydrolysis reactions are suppressed under the given chemical conditions.