Biosorption of Heavy Metal Ions: Ion-Exchange versus Adsorption and the Heterogeneity of Binding Sites

Abstract

Surface heterogeneity-related effects have been studied in the context of biosorption systems designed for the removal of bivalent heavy metal ions from aqueous systems. The research was focused on incorporating these effects into the concept of the ion-exchange (IE) constant. Cases of both correlated and uncorrelated values of the affinity constants towards metal ions and protons were considered. When strong correlations were assumed, the dispersion of the IE constant was smaller (or, in the limiting case, the same) in comparison to the dispersions of the affinity constants. In contrast, when no correlation was assumed, the dispersion of the IE constant was greater than those corresponding to any of the affinity constants. The dispersion of the IE constant could be additionally enhanced by the existence of multi-dentate binding modes related to the metal ions.