Ion Adsorption on Charged Surfaces

Abstract

AbstractA model, based on ion pair formation, for the adsorption of ions on charged surfaces is developed. This approach results in a two‐layer system analogous to the Stern‐Gouy model. Relations between the charge density, the fraction of the ions in the diffuse double layer, the concentration of the ions in the bulk solution, and a formation constant K are derived. The K describes the equilibrium reaction across the boundary between the two layers without defining the exact position of the boundary. Dowex‐50 resin, which has a high charge density and consequently a relatively small fraction of ions in the diffuse double layer, was used to test the above model. The following ratios of K's were calculated from data obtained from adsorption experiments in dilute solutions: KRb/KNa = 1.71, KRb/KK = 1.26, KK/KNa = 1.37, (K′Sr)½/KNa = 3.31 (eq. per liter)½, (K′Sr)½/KLi = 5.88 (eq. per liter)½, (K′Sr)½/KH = 4.00 (eq. per liter)½, KNa/KLi = 1.89, KNa/KH = 1.35, KSr/K′Ca = 1.56.