Specific ion adsorption at the mineral—water interface: Cesium adsorption on chlorite

Abstract Specific ion adsorption from CsCl and Cs 2 CO 3 aqueous solutions onto clinochlore chlorite has been observed and monitored in real-time with the atomic force microscope. Cesium ions adsorb in an island-like pattern with a c(1 × 1) R60° unit mesh and appear to bind with negatively charged surface sites arising from Si 4+ /Al 3+ substitution in the chlorite structure. Furthermore, cesium adsorption appears to have a fluxional nature with removal of adsorbed atoms from the surface with successive scans of the microscope tip. We interpret these findings as implying the imaging of the highly exchangeable adsorption sites of chlorite. X-ray photoelectron spectroscopy of chlorite indicates a leached layer with high amounts of silicon and aluminum oxides. Evidence for adsorption seen with the atomic force microscope is verified by the presence of cesium peaks in photoelectron spectra of chlorite exposed to cesium solutions. Peak shift is indicative of a CsOH bond at the surface of chlorite.