Final Report: Understanding the Chemistry of the Actinides in High Level Waste Tank Systems: The Impact of Temperature on Hydrolysis and Complexation with Organics

The solubility of CeO2 and ThO2 in aqueous NaNO3 solutions was studied as a function of pH and ionic strength, and the concentration of the organic ligands: citrate, EDTA, and oxalate. The main findings of the study are that these organic ligands increase the solubility of CeO2 markedly via the formation of complexes. On the other hand, the solubility of ThO2 was not affected by the presence of these ligands at levels of several hundred micromolar. These results have implications for the behavior of Pu(IV), for which Ce(IV) and Th(IV) are analogues