Reversibility of sorption of plutonium-239 onto hematite and goethite colloids

Laboratory batch sorption experiments were conducted to evaluate: 1) sorption of plutonium-239 (Pu-239) On different iron oxide colloids (hematite and goethite), 2) sorption kinetics of colloidal Pu(IV) and soluble Pu(V) onto these two colloids, and 3) desorption of colloidal Pu(IV) and soluble Pu(V) from Pu-239-loaded colloids as a function of time. Natural groundwater and carbonate-rich synthetic groundwater were used in this study. To examine the possible influence of bicarbonate on Pu-239 sorption, an additional set of experiments was conducted in sodium nitrate (NaNO3) solutions under carbon dioxide free environments. Our results show that colloidal Pu(IV) as well as soluble Pu(V) was rapidly adsorbed by hematite and goethite colloids in both natural and synthetic groundwater. The amount of Pu-239 adsorbed by both iron oxide colloids in synthetic groundwater was higher than in natural groundwater. The presence of carbonate did not influence the sorption of Pu-239. While sorption of soluble Pu(V) is a slow process, sorption of colloidal Pu(IV) occurs rapidly. Desorption of Pu from iron oxide colloids is much slower than the sorption processes. Our findings suggest that different sorption and desorption behaviors of Pu-239 by iron oxide colloids in groundwater may facilitate the transport of Pu-239 along potential flowpaths from the areas contaminated by radionuclide and release to the accessible environment.