MODELING OF THE PROTON-METAL ION-EXCHANGE IN BIOSORPTION

Biosorption of the heavy metal ions Cd2+, CU2+, and Zn2+ by previously protonated nonliving biomass of the marine alga Sargassum fluitans was observed to be coupled with a release of protons. Metal ion binding experiments with continuously controlled pH were performed. The metal ion and proton binding at equilibrium were modeled as a function of pH and metal ion concentration using a modified multicomponent Langmuir sorption model. Both the exchange of metal ions for protons from functional groups in their acidic form and the sorption of metal ions on ionized groups were considered. The model is applicable to adsorption by biomass with free or protonated metal binding sites as well as to metal ion desorption with acids since the direction of the reaction depends simply on the given initial conditions. The model parameters were incorporated into the MINEQL+ equilibrium program, leading to a prediction of the equilibrium, e.g., of metal ion laden biosorbent desorption performance for given initial conditions.