Spectroscopic Study of the Hydrolysis of PuO22+ in Aqueous Solution

Abstract

The hydrolysis of Pu(VI) is investigated under Ar atmosphere in the pH range between 4.5 and 9.0 at 22°C in 0.1 M NaC104 solution in contact with an initial solid phase, PuO2CO3(s). Under the given conditions, PuO2CO3(s) is changed to PuO2(OH)2(s). The estimated equilibrium partial pressure for the transformation: PuO2CO3(s) + H2O(1) ⇌ puo2(oh)2(s) + CO2(g) can reach PCO2 ~ 10 3.6atm. In contrast to earlier investigations in oversaturated solution, no polynuclear species formation is observed. Two mononuclear complexes, puo2OH+in near neutral and PuO2(OH)2(aq) in weak alkaline solution, are found to be the dominating hydrolysis species of Pu(VI). The stability constants of the two species, evaluated from UV/VIS spectroscopic measurements, are found to be: log β11= 8.10±0.15 and log βl2= 14.25±0.18, respectively. The first equilibrium constant is in good agreement with the corresponding value for the formation of UO2OH+, log β11= 8.4±0.3, indicating a close similarity in hydrolysis between the two actinide ions. © R. Oldenbourg Verlag, München 1995