Equilibrium parameters for the single- and multicomponent biosorption of Cr(VI) and Fe(III) ions on R. arrhizus in a packed column

In this study, simultaneous biosorption of Cr(VI) and Fe(III) on free Rhizopus arrhizus in a packed column operated in a continuous mode was investigated and compared to the single metal ion situation. The breakthrough curves were measured as a function of feed flow rate and different combinations of metal ion concentrations in the feed solutions. Column competitive biosorption data were evaluated in terms of the maximum (equilibrium) capacity of the column, the amount of metal loading on the R. arrhizus surface, the adsorption yield, and the total adsorption yield. Since the maximum column capacity and the adsorption yield decreased with increasing concentrations of the other metal ion, the combined action of Cr(VI) and Fe(III) on R. arrhizus was generally found to be antagonistic. In the single-ion situation, the adsorption isotherms were developed for optimum conditions and it was seen that the adsorption equilibrium data fit the non-competitive Freundlich model. For the multicomponent adsorption equilibrium, the competitive adsorption isotherms were also developed. The empirical Freundlich model for binary metal mixtures represented satisfactorily most of the column adsorption equilibrium data of Cr(VI) and Fe(III) on R. arrhizus.