The migration of uranium through Clashach Sandstone: the role of low molecular weight organics in enhancing radionuclide transport

Interaction of bentonite colloids with Cs, Eu, Th and U in presence of humic acid: A flow field-flow fractionation study

“…In case of our experiments with Th(IV) it was shown that an equilibrium model is not adequate for describing the sorption-desorption process and the addition sequence was found to play a major role. Similar observations on disequilibria depending on addition sequences have been reported for other elements in various systems in presence of HA: U(VI) migrating through well characterized Clashach Sandstone matrix (Read et al, 1998), Ni on kaolinite (Nachtegaal and Sparks, 2003), Ni on HFO (Bryce et al, 1994), Th on hematite (Reiller et al, 2005), Zr and Hf on kaolinite and silica (Takahashi et al, 1999). However, all these studies considered significantly shorter observation periods than 3 years.…”

“…However, all these studies considered significantly shorter observation periods than 3 years. Explanations for observed kinetic effects are inter alia the transformation of initially adsorbed element to a less leachable surface precipitate (Read et al, 1998) forming for example a metal hydroxide, a mixed layered double hydroxide (LDH) or a phyllosilicate phase within a matter of days or even less with a stabilization of the precipitate phase upon ageing (Nachtegaal and Sparks, 2003). Another explanation which can be found in literature is diffusion of metal ions into mineral pores or interlayer sites, finally retarding metal ion desorption from the mineral surface.…”

Approaches to surface complexation modeling of Uranium(VI) adsorption on aquifer sediments

“…For most metal and radionuclide risk assessments conducted by the U. S. government, reactive transport models utilize the distribution coefficient (constant-K d ) modeling approach to describe the retardation of metal and radionuclide contaminants in aquifers caused by adsorption reactions (USEPA, 1999;Bethke and Brady, 2000). Significant uncertainty in the calculation of retardation may be introduced when the constant-K d modeling approach is used, due to temporal or spatial variations in groundwater chemistry ( Read et al, 1998;Bethke and Brady, 2000;Glynn, 2003). One reason this may occur is because K d values are very sensitive to chemical conditions.…”

Application of Molecular Techniques To Elucidate the Influence of Cellulosic Waste on the Bacterial Community Structure at a Simulated Low-Level-Radioactive-Waste Site

“…Additionally, fermentative bacteria can then use these cellulose breakdown products as carbon and energy sources, producing a variety of fermentation products, including shortchain organic acids, alcohols, and hydrogen (20). These fermentation products may significantly influence contaminant mobility, since organic acids can chelate metals and radionuclides, potentially increasing their mobility (8,21,27,44,47). On the other hand, the work of numerous investigators has shown that these same compounds can serve as the carbon and energy sources for metal-and sulfate-reducing bacteria that reduce and precipitate the metals and radionuclides found at these sites (1,7,19,31,39,40,45,48,52,56,59).…”