IONIC-STRENGTH AND ELECTROSTATIC EFFECTS IN BIOSORPTION OF PROTONS

New biosorbent materials are being developed for removal of heavy meta ls from effluents. This study investigates the effect of ionic strengt h on titrations of protonated Sargassum seaweed biomass and of alginat e, a constituent molecule mainly responsible for the binding of cation s in Sargassum. The results indicate a significant influence of electr ostatic effects on the protonation behavior. The main objective of thi s work was to examine the capability of an adapted Donnan model to pre dict pH titrations of negatively charged biomass particles at differen t ionic strengths. The model, applicable for wider ranges of ionic str ength and charge density in the biomass than other Donnan models in th e recent literature, yielded good agreement of model predictions and e xperimental data. Swelling of the sorbent was found to increase with p H. While incorporating a linear relationship between swelling and pH i mproved the model predictions, it was not necessary in order to obtain reasonable predictions. The model required only three parameters: the total number of binding sites, the equilibrium constant K-CH for prot on binding, and only one additional parameter to model the influence o f ionic strength, even when swelling was considered. Plots of the degr ee of dissociation versus (pH-pNa) as a criterion for the rigidity of the particle were found to be valid only under conditions where the co ncentration factor lambda is high.