Plutonium (IV) complexation by nitrate in acid solutions of ionic strengths from 2 to 19 molal

Titrations of Pu(IV) with HNO{sub 3} in a series of aqueous HClO{sub 4} solutions ranging in ionic strength from 2 to 19 molal were followed using absorption spectrophotometry. The Pu 5f-5f spectra in the visible and near IR range change with complex formation. At each ionic strength, a series of spectra were obtained by varying nitrate concentration. Each series was deconvoluted into spectra f Pu{sup 4+}(aq), Pu(NO{sub 3}){sup 3+} and Pu(NO{sub 3}){sub 2}{sup 2+} complexes, and simultaneously their formation constants were determined. When corrected for the incomplete dissociation of nitric acid, the ionic strength dependence of each formation constant can be described by two parameters, {beta}{sup 0} and {Delta}{var_epsilon} using the formulae of specific ion interaction theory. The difficulties with extending this analysis to higher nitrate coordination numbers are discussed