Particle concentration effect and adsorption reversibility

The adsorption of zinc, copper and cadmium ions onto pure goethite particles in buffered aquatic systems was studied as a function of particle concentration C-p. The dependence of the adsorption isotherms on the particle concentration is most obvious in the Zn-goethite system, less obvious in the Cu,goethite system, and undetectable in the Cd-goethite system. This result is in agreement with the observation that an increase in C-p,causes the biggest decrease in adsorption reversibility in the Zn-goethite system, a smaller decrease in reversibility in the Cu-goethite system and almost no changes in adsorption hysteresis in the Cd-goethite system. The results of experiments, designed to eliminate several typical sources of experimental artefact, agree with the prediction of the metastable-equilibrium adsorption theory (G. Pan, P.S. Liss, J. Colloid Interface Sci. 201 (1998) 71). (C) 1999 Elsevier Science B.V. All rights reserved.