The properties of mineral-water interfaces are fundamentally affected by the presence of ions. At the mineral-water interface, ions form an electrical double layer (EDL) that extends from the solid into the aqueous bulk and balances the charges that exist at the mineral surface. The knowledge surrounding the EDL is limited by the atomic scale understanding of complex interfacial systems. Better understanding of the properties at these interfaces, especially ion mobility, is a determinant factor for many applications such as environmental monitoring or nuclear waste disposal.<br/><br/>Static and dynamical properties of monovalent and divalent ion-pairs (NaCl, KCl, and CaCl<sub>2</sub>) forming an electrical double layer at the fully hydroxylated quartz-(001) and quartz-(101)/liquid interface have been investigated by means of non-equilibrium molecular dynamics simulations, under various electric field intensities and direction. The simulations showed that diffusion coefficients strongly depend on the orientation of the applied electric field, with strong response in parallel electric field. Results also indicated the differences in structure and diffusion with a perpendicular applied field are more subtle, but we observed an induced a field as a response of the complete relocation of ions. This led to differences in diffusion at the interface, also strongly correlated to the silanol density and orientation.

Mobility of ions on humid mineral surfaces: New insights from non-equilibirum molecular dynamics

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