Structure of uranium sorption complexes at monmorillonite edge sites

Extended X-ray absorption fine structure (EXAFS) spectroscopy at the uranium L_III-edge was used for determining the structural environment of aqueous uranyl surbed onto montmorillonite. The study reveals that uranyl uptake at pH~5-~7 and at an initial uranyl concentration of 5x10^-5M takes place at amphoteric surface hydroxyl sites as inner-sphere complex. The measured bond distances sites between uranium and the equatorial oxygen atoms are in the range of 2.34 A the presence of a U-Al backscattering pair was determined. This backscattering pair indicates that the binding of the uranyl unit to amphoteric surface hydroxyl sites occurs preferred as a bidentate inner-sphere complex on aluminol groups.