SURFACE-ACIDITY BASICITY OF ROAD STONE AGGREGATES BY ADSORPTION FROM NONAQUEOUS SOLUTIONS

The surfaces of several road stone aggregates were characterized by the adsorption of organic probe molecules (with acidic and basic functional groups) from cyclohexane. The results showed differences in the adsorption affinity and adsorption capacity of the molecules for the different mineral surfaces. In most cases it was found convenient to represent the data by a Langmuir-Freundlich type of isotherm, which defines a quasi-Gaussian energy distribution around a peak value. From the theory a range of adsorption free energies and surface coverages (site densities) were calculated, and the heterogeneity of the surfaces evaluated. Generally the interactions strengths were rationalized in terms of Lewis acid-base theory.