INTERACTION OF CADMIUM WITH PHOSPHATE ON GOETHITE

Interactions between different ions are of importance in understanding chemical processes in natural systems, In this study simultaneous ads orption of phosphate and cadmium on goethite is studied in detail, The charge distribution (CD)-multisite complexation (MUSIC) model has bee n successful in describing extended data sets of cadmium adsorption an d phosphate adsorption on goethite, in this study, the parameters of t his model for these two data sets were combined to describe a new data set of simultaneous adsorption of cadmium and phosphate on goethite, Attention is focused on the surface speciation of cadmium. With the ex tra information that can be obtained from the interaction experiments, the cadmium adsorption model is refined. For a perfect description of the data, the singly coordinated surface groups at the 110 face of go ethite were assumed to form both monodentate and bidentate surface spe cies with cadmium. The CD-MUSIC model is able to describe data sets of both simultaneous and single adsorption of cadmium and phosphate with the same parameters. The model calculations confirmed the idea that o nly singly coordinated surface groups are reactive for specific ion bi nding. (C) 1997 Academic Press.