THE INFLUENCE OF FILM DIFFUSION ON CADMIUM BIOSORPTION BY MARINE BIOMASS

The sorption of cadmium by biomass of brown marine alga Sargassum fluitans has been studied in a standard mixed batch reactor at steady-state and transient conditions. Steady-state sorption data over the temperature range of 7 degrees C to 60 degrees C indicated a higher cadmium uptake at elevated temperatures. Overall adsorption rates also slightly increased with increasing temperature in the range of 20 degrees C to 60 degrees C. Assuming only a single external mass transfer resistance to adsorption external mass transfer coefficients were determined. Experimental data were compared to a single resistance model for several variable system parameters such as agitation, particle size and sorbent loadings under transient batch conditions. The biosorption system operated at the optimal pH 4.5 with 20 mM Na-acetate buffer. The model reflected the experimental data well only at high sorbent and low metal concentrations, which generally represents batch sorber conditions. Under these conditions, film diffusion appeared to be the rate-controlling step in adsorption. However, at low sorbent concentrations the model could not represent the sorption system behavior due to the likely predominant influence of intraparticle diffusion.