OXIDATION-STATE DETERMINATION OF PLUTONIUM AQUO IONS USING X-RAY-ABSORPTION SPECTROSCOPY

Four oxidation states (III, IV, V, and VI) of Pu may coexist under env ironmentally relevant conditions. An efficient method to determine the states actually present in various matrices would enhance the ability to model the fate and transport of plutonium in process streams and i n the environment. This communication establishes that the L-3 X-ray a bsorption near-edge structure (XANES) spectra of Pu are primarily dete rmined by the valence state and the presence or absence of the trans d ioxo moiety, consistent with previous U and Np XANES studies. The edge energies were observed to shift progressively to higher energy with i ncreasing valence, with an average 1.68 eV increase per formal oxidati on state increase. Ih addition, the general spectral shape of the (III ) and (IV) species is clearly different from the dioxo-containing (V) and (VI) species, with the first maximum much larger and sharper for t he (III) and (IV) spectra than for the (V) and (VI) spectra. (C) 1998 Elsevier Science Ltd. All rights reserved.