Cs, Sr, and Ba Sorption on Clays and Fe-Oxides

摘要

Technical guidance for performance assessment (PA) of low-level radioactive waste211u001e(LLRW) sites is currently dependent upon experimental retardation factors (K(sub 211u001eD)'s) to predict radionuclide transport. Accurate predictions of waste transport 211u001eor retardation will require mechanistic models of radionuclide sorption so as to 211u001ebe applicable to a wide range of soil/groundwater environments. To that end, we 211u001ehave investigated Cs(sup +), Sr(sup +), and Ba(sup 2+) sorption on several clay 211u001eand Fe-oxide minerals. Relative metal binding strengths for montmorillonite clay 211u001edecrease from Ba(sup 2+) to Sr(sup +), which is similar to that sorption trend 211u001enoticed for kaolinite. Molecular dynamics simulations for kaolinite suggest that 211u001eCs(sup +) is sorbed at aluminol (010) edge sites as an inner-sphere complex and 211u001eweakly sorbed as an outer-sphere complex on (001) basal surfaces. Sorption is 211u001ethought to occur on similar sites for smectite clays, however, the basal plane 211u001eresidual charge and its increased basal plane exposure should have a greater 211u001einfluence on metal sorption. On the other hand, phase transformation kinetics 211u001e(e.g., ferrihydrite to goethite) is a very important control of metal sorption 211u001eand resorption for Fe-oxides/hydroxides. These results provide a basis for 211u001eunderstanding and predicting metal sorption on complex soil minerals.