Specific ion effects of incomplete ion-exchange by electric field-induced ion polarization.

Abstract

Incomplete ion-exchange results from ion interfacial reactions portray a particular scenario of interactions between ions and charged surfaces. In this study, the constant flow method was adopted to study the incomplete ion-exchange state of mono-valent cation adsorption of X+ (X+ = Cs+, Na+ and Li+) in X+/K+ exchange at the montmorillonite particle surface. The pronounced incomplete ion-exchange state and strong specific ion effects were experimentally observed. Further research found that the disparity in the activation energies for different ion exchange systems caused by electric field-induced ion polarization was responsible for the observations. Thus, a theoretical description of the incomplete ion-exchange state by taking the ion polarization into account was established and verified. Applicable new approaches to measuring the cationic diffusion coefficient in heterogeneously charged systems and the cationic actual diffuse depth in the electric double layer were also derived from the theory.