The equations developed by us for the triple layer surface complexation approach, taking into account energetic heterogeneity of surface oxygen, are applied here to study the heterogeneity influences on the adsorption of cadmium ions at the NaClO4/silica aqueous solution interface. The model of surface heterogeneity made it possible to fit in a quantitative way the data obtained in the four independent experiments: surface charge measurements (titration), measurements of electrophoretic mobility and monitoring radiometrically cation of inert electrolyte adsorption, together with cadmium ion adsorption at different pH values. Particularly the studies of cadmium ion adsorption show that the energetic heterogeneity of the silica surface oxygen should be taken into account. (C) 2002 Elsevier Science B.V. All rights reserved.