Redox Behavior of Pu(III/IV) in Dilute to Concentrated Saline Systems

摘要

Plutonium is the main concern in the context of nuclearwaste disposal as well as at several U.S. Department ofEnergy (DOE) contaminated sites due to its high abundancy,long half-life and high radio toxicity. The migrationbehavior of Pu depends highly on its oxidation statedistribution that may vary between +3 and +6 underenvironmentally-relevant conditions. In the case ofunderground disposal of transuranic waste in the WasteIsolation Pilot Plant (WIPP) salt repository, anoxic andreducing conditions are established by the reactivity of zerovalentiron that limit the oxidation state of Pu to the trivalentand tetravalent states. Pu(Ⅳ) forms sparingly solublePuO_2(am,hyd)(or PuO_2·xH_2O(s)), which defines [Pu] < 10~(–10)M above pH = 6 in the absence of strong complexingligands. Pu(Ⅲ) is more soluble up to the alkaline to hyperalkalinepH range where eventually oxidation to Pu(Ⅳ) ispredicted. Establishing the long-term stability and relativeimportance of Pu(Ⅲ) and Pu(Ⅳ) phases under repositoryrelevantconditions is a key goal of this research.