Spectroscopic study on the mononuclear hydrolysis species of Pu(VI) under oxidation conditions

The formation constants of mononuclear hydrolysis species of Pu(VI) were determined by absorption spectroscopy under carefully designed experimental conditions. In order to exclude the formation of polynuclear hydrolysis species, the concentration of plutonium was diluted below 50 μM. To maintain the oxidation state of Pu(VI), NaOCl was applied as an oxidant. The trace amount of Pu(V) was monitored by the measurement of redox potential and absorption spectroscopy by using a liquid waveguide capillary cell with the optical path length of 100 cm. The determined molar absorption coefficients (ε, M-1 cm-1) were 272±26 and 436±33 for PuO2(OH)+ and PuO2(OH)2(aq) species, respectively. The formation constants of mononuclear hydrolysis species of Pu(VI) at ionic strength of 0.01 M NaClO4 were determined as follows: log*β1' (for PuO2(OH)+) = -5.8±0.3, log*β2' (for PuO2(OH)2(aq)) = -13.4±0.2 and log*β3' (for PuO2(OH)3-) = -24.3±0.8. (orig.)