Determination of Formation Constants, Solubilities, and Ionic Speciation of Uranium, Plutonium and Thorium in Aqueous and Saturated Salt Solutions for Modelling Safety Aspects of Ilw Repositories

Abstract

ABSTRACTThe solubility products of uranyl hydroxide and uranyl carbonate and the formation constants of the complexes present in the solution have been determined at 25ºC and I=0.1 mol dm−3by potentiometry and solubility experiments. The uranyl complexes U02(OH)2'(UO2)2(OH)22+,(UO2)3(OH)5+, UO2CO3', UO2(CO3)22−and UO2(CO3)34−were identified. For the system uranyl-hydroxide the results were verified by analysis of conductance measurements. A similar investigation was carriedout for thorium. Using Pu(IV)-chloride complexes as an example the potential of differential pulse voltarnmetry is demonstrated for the determination of small formation constants.