IONIC-STRENGTH AND ELECTROSTATIC EFFECTS IN BIOSORPTION OF DIVALENT METAL-IONS AND PROTONS

This study is concerned with passive biosorption of metal ions by biom ass of the brown alga Sargassum, a process that may eventually be used for the treatment of industrial wastewaters, This work provides a mat hematical model for predicting the equilibrium of proton and metal ion binding as a function of metal ion concentration, pH, and ionic stren gth. Since the presence of sodium significantly influenced Cd binding, it is recommended to use models that incorporate ionic strength effec ts. Although swelling of the biomass particle was observed, a simple D onnan model that assumed a rigid particle already yielded good predict ion of the experimental data. A combined Donnan-Biosorption-Isotherm e quation was derived that allowed for direct calculation of cation bind ing without iterations. Only one parameter, the binding constant, had to be determined each for Cd and Ca. The intrinsic binding constant wa s several orders of magnitude lower than the apparent one. Using the p arameters (amount of binding sites, proton binding constant, and speci fic particle volume) obtained from pH titrations in an earlier study, it was possible to predict the effect of pH, ionic strength, and Ca co ncentration on Cd binding.