Abstract
The EXAFS samples were Kunipia F-type smectite exchanged with Cs at a concentration of 2 mol/kgclay at pH 3.9 and 9.8. The K-edge absorption spectra were collected in the transmission mode at the SPring-8 (8.0 GeV), Japan. The molecular dynamics (MD) simulations were performed on beidellite. The system consisted of two 2: 1 sheets and two inter-layer spaces including water molecules. The total number of atoms in the system was 2, 672 and 4, 112 at hydration 2.5 and 7.5 H2O, respectively. The force field consisted of four types of potential: Coulomb, van der Waals, Short-range repulsion, and covalent. The Cs-O distances in wet-paste samples were 3.12-3.19 and 3.60-3.74 Å for the first and second shells, respectively. The coordination numbers were 60 and 3-40 atoms. In air-dried samples, the Cs-O distances were 3.08-3.18 and 3.55-3.73Å. The coordination numbers were 50 and 5-60 atoms. The adsorption sites were identified as three types of stagnation points of the moving Cs atoms in inter-layer water. In air-dried samples, Cs atoms were predicted to be located over a hexagonal cavity of 2: 1 sheets or over a corner oxygen atom of a tetrahedron. In contrast, in wet-paste samples, Cs atoms hovered over a side of the tetrahedron as well as a hexagonal cavity.
