Abstract:
Uranium adsorption to Hanford sediment was studied for various pH, total inorganic carbon concentrations, and total U(VI) concentrations. Both batch and transport studies were done in an attempt to understand the adsorptive trend of U(VI) on Hanford sediment, and the changes in adsorption as both pH and total inorganic carbon concentrations were varied independently. Results from batch experiments were modeled with both linear and nonlinear adsorption isotherms to determine the overall affects of increasing total U to sediment ratios for each set of experimental conditions. For equilibrium conditions, a two-site, two-species surface complexation
model described by Waite et al. (1994) was used in FITEQL to fit the adsorption trend seen in results. The model results followed a trend similar to the data, but were not completely accurate. This may be due to inadequate knowledge of the exact number of surface sites available for the adsorption of U as the sediment chemistry is changed during the equilibration process prior to running each experiment. U transport results were fit with the two-site nonequilibrium convection dispersion equation in the code CXTFIT. This model fit only the pH 9, 10mM inorganic carbon data, suggesting that the two site model does not consider all of the relevant processes. With the modeling and experimental results obtained, it is evident that a thorough understanding of not only the aqueous species, but improved understanding of the surface species are needed to create an accurate model for U adsorption.
