Effect of reduction on the stability of Pu(VI) hydrolysis species

The chemical speciation of aqueous plutonium species has been performed by spectrophotometry. The main focus was concentrated on the effect of Pu(V) produced by the reduction of Pu(VI) on the stability of the Pu(VI) hydrolysis species. In order to detect the trace amounts of PuO2+ ions, a liquid waveguide capillary cell with an optical path length of 100cm was connected to a spectrophotometer. As a consequence of the improved detection sensitivity, an absorption band at 569 nm being indicative of Pu(V) was observed within one day after the sample preparation from the pure Pu(VI) solution. The first hydrolysis species was (PuO2)2(OH)22+, at plutonium concentrations of 0.1-0.12 mM and at weak acidic conditions (pH 5-6). The formation constant of (PuO2)2(OH)22+ was determined to be log *β'22 = -7.34±0.22 at 0.01 M NaClO4. This dinuclear hydroxide species was unstable and disappeared within one month after the sample preparation at the present experimental condition. In the neutral pH range, the second hydrolysis species was formed and remained for over one year. The samples showed different behavior for the reduction of Pu(VI). The time dependent distribution of plutonium species and their characteristic features in the absorption spectra are reported. (orig.)