Role of ionic polarization and dielectric decrement in the estimation of surface potential of clay particles

Abstract

The surface potential of clay particles plays a pivotal role in soil mineral–water interfacial reactions. A new model to estimate surface potential was established taking into account dielectric decrement extracted from the Langevin equation and taking account of ion polarization under a strong electric field. The intensity of ion polarization was quantified through the effective charges of counterions, which are from 1 to 1.036 for Na+ and from 1 to 1.534 for Cs+ at the montmorillonite surface in aqueous solutions. The effective charges were overestimated because the dielectric decrement was disregarded. The surface potential decreases with increasing ion polarizability and dielectric constant. The clay–ion interaction energies were estimated from the effective charges of ions and surface potentials. We observed that the strong additional energies from ion polarization depended on the electron configuration of the counterions at charged surfaces, which not only results from the dispersion interactions, but also the strong induction interactions. The contributions of the latter to the total energy were much stronger than those of the dispersion interactions for Cs+. The strong electric field near the clay surface clearly enhanced the polarizability of Cs+. The energies of non‐valence electrons of ions at the charged surfaces were substantially understated in electrolyte solutions. The experimental adhesive forces between silica and mica surfaces in different cation species can be predicted correctly through the surface potential calculated using the new model.Highlights A model to estimate surface potential was established considering ion polarization and dielectric decrement. Ion polarizability at the clay surface was quantified in the presence of dielectric decrement. The contributions of ion polarization and dielectric decrement to surface potential were quantified. The dielectric decrement affects surface potential by influencing ion polarizability.