RES³T - Rossendorf Expert System for Surface and Sorption Thermodynamics

Surface complex formation of K⁺, NO₃⁻, SO₄²⁻, Ca²⁺, F⁻, Co²⁺, and Cr³⁺ ions was determined on the surface of silica gel. Experimental data obtained by acid–base titration of suspensions were interpreted in terms of the triple-layer model. The value of the deprotonation constant of surface OH could be determined precisely but the protonation constant was rather uncertain. The logarithms of ion pair formation constants for K⁺, NO₃⁻, Ca²⁺, and SO₄²⁻ adsorbed in the β-plane are log K_ipM,X∼0, therefore these species can be considered inert ions in the investigated pH range. F⁻, Co²⁺, and Cr³⁺ ions were found to be strongly sorbed in the o-plane. In order to provide a good fit and to obtain parameters independent of their initial values, all possible equilibrium must be accounted for in the models.