Evaluation of Cesium, Strontium, and Lead Sorption, Desorption, and Diffusion in Volcanic Tuffs from Frenchman Flat, Nevada Test Site: Macroscopic and Spectroscopic Investigations

摘要

The interaction of radionuclides and other contaminants with minerals and other aquifer materials controls the rate of migration of these contaminants in groundwater. The stronger these interactions, the more a radionuclide will be retarded. Processes such as sorption and diffusion often control the migration of inorganic compounds in aquifers. In addition, these processes are often controlled by the nature of ions of interest, the nature of the aquifer materials, and the specific geochemical conditions. Parameters describing sorption and diffusion of radionuclides and other inorganic ions on aquifer materials are used in transport codes to predict the potential for migration of these contaminants into the accessible environment. Sorption and diffusion studies can help reduce the uncertainty of radionuclide transport modeling on the Nevada Test Site (NTS) and other nuclear testing areas. For example, reliable sorption equilibrium constants, obtained under a variety of conditions, can be used to suggest a plausible sorption mechanism and to provide retardation parameters that can be used in transport models. In addition, these experiments, performed under a variety of conditions, can lead to models that can accommodate changing geochemical conditions. Desorption studies can probe the reversibility of reactions and test whether the reversibility assumed by equilibrium models is justified. Kinetic studies can be used to probe the time-dependent limitations of reactions and suggest whether an equilibrium or kinetic model may be more appropriate. Finally, spectroscopic studies can be used to distinguish between different sorption mechanisms, and provide further guidance with respect to model selection.