Aqueous Solution Structure at the Cleaved Mica Surface: Influence of K+, H3O+, and Cs+ Adsorption

Monte Carlo simulations of the interface between the cleaved surface of muscovite mica and aqueous solution containing K+, Cs+, and/or H3O+ ions compensating negative charge of muscovite and Cl- ions at ambient conditions are reported. Simulation results reveal that, in dependence on surface concentration, K+ is preferentially adsorbed above ditrigonal cavity centers or substituted tetrahedrons similar to 1.7 angstrom or similar to 2.15 angstrom from the surface, respectively, whereas Cs+ is preferentially adsorbed above ditrigonal cavity centers similar to 2.0-2.2 angstrom from the surface. Adsorption of K+ and Cs+ in excess of the surface concentration compensating the negative charge of muscovite leads to a coadsorption of Cl- as an outer sphere complex on the solution side of the Stern layer. This study also suggests that H3O+ is the only species adsorbing as close as similar to 1.3 angstrom from the mica surface in contact with deionized water and contributing to the first adsorbed layer observed recently with X-ray reflectivity. On the basis of available experimental and the presented simulated electron density profiles, it is concluded that KCl (or CsCl) solution concentrations of 0.01 and 0.5 M in contact with muscovite result in an adsorption of 0-0.5 and 1-1.375 of K+ (or similar to 0.5 and similar to 1.25 of Cs+) ions per unit cell area, respectively.