Sorption of Uranium (VI) on Model Minerals Kaolinite (Kga-1 & Kga-1B) & Ferrihydrite

Uranium (VI) sorption on geological materials is influenced by a large number of factors including pH, ionic strength, partial pressure of carbon dioxide, adsorbent loading, total amount of U present, and the presence of inorganic and organic ligands. Ferrihydrite (also referred to as hydrous ferric oxide - HFO), is widely used as a model sorbent for anions and cations, and is thought to be an important U-sorbing phase in the near-surface environment. The Ferrihydrite used for sorption experiments was precipitated by raising the pH of a Fe(III) / HNO3 solution to 6.0, and then aged for 65 hours at 25oC in a stirred jacketed vessel. Kaolinite standards KGa-1 and KGa-1B were obtained from the Clay Minerals Society (CMS) Source Clays Repository in Columbia, USA. KGa-1 has been extensively characterised, however KGa-1B was also used which replaced the exhausted stock of KGa-1. Uranium sorption on mixed substrates containing both Kaolinite and Ferrihydrite was also studied. In terms of the amount of U sorbed per gram of adsorbent, U uptake on Kaolinite KGa-1 and KGa-1B was much weaker than U uptake on Ferrihydrite under similar experimental conditions.