Uranium VI adsorption on model minerals: controlling factors and surface complexation modeling

Abstract

Uranium VI sorption on ferrihydrite and kaolinite is influenced by a large number of factors, including pH, ionic strength, partial pressure of CO2, adsorbent loading, total amount of U present, and the presence of ligands such as phosphate and humic acid. The effect of complexing ligands may be to enhance or reduce U uptake. The adsorption model being used for ferrihydrite is a surface complexation model with a diffuse double layer, and both strong and weak sites for U sorption. In terms of the amount of U sorbed per gram of adsorbent, U uptake on kaolinites KGa-1 and KGa-1B is much weaker than U uptake on ferrihydrite under similar experimental conditions. Titanium-rich impurity phases play a major role in the sorption of U by these standard kaolinites. Trace impurities and mineral coatings such as ferrihydrite can play a dominant role in determining U sorption in both environmental and model systems. © 1998 Elsevier Inc.