CEEES - Examining the influence of redox speciation on plutonium subsurface transport: Laboratory and field lysimeter experiments
Although the sorption of actinides onto mineral surfaces is known to be one of the primary mechanisms that controls actinide mobility in the near-field of a geologic repository and far-field subsurface environments, existing models provide limited capability for predicting complex biogeochemical behavior. This is primarily due to the lack of mechanistic knowledge of sorption reactions and detailed characterization of surface species. In this work, sorption of plutonium and other f-elements to various mineral surfaces has been examined with an emphasis on understanding and quantifying aqueous and surface mediated redox reactions. The results of batch sorption, isothermal titration nanocalorimetery, potentiomentric titrations, and x-ray absorption spectroscopy are combined to develop self-consistent thermodynamic surface complexation models. Results of studies with Eu(III), Np(V), Pu(IV), and Pu(V) indicate that sorption generally increases with temperature and is driven by entropy. The influence of temperature and degree of sorption generally increases with increasing effective charge and degree of hydration of the actinide ions. These data indicate that sorption of actinides is controlled by formation of inner sphere complexes and displacement of hydrating waters. Conceptual and quantitative models of these lab based studies have previously been applied to a set of field lysimeter experiments and show that Pu transport is governed by redox reactions, sorption, and plant uptake. To gain some experimental control and allow for a wider range of variables, a new field lysimeter experiment has been designed, constructed, and deployed at the Savannah River Site. Data from the historical lysimeters and an overview of the current lysimeter experiment (RadFLEx: Radiological Field Lysimeter Experiemnt) will be discussed.
Ph.D. Environmental Engineering and Science, Clemson University, 2004 M.S. Environmental Engineering and Science, Clemson University, 2001 B.S. Chemistry, University of Montevallo, 1999