Biosorption of Pb (II) Ions from Aqueous Solution Using Dry and Immobilized Biomass of Rhizopus arrhizus

The biosorption of Pb(II) ions by dry and immobilized cells of Rhizopus arrhizus was studied in the aqueous solutions. The effect of contact time (0 – 42 h), pH (2 - 8), initial concentration (50 – 1500 mg/ L) of Pb(II) ions on biosorption were investigated in batch systems. The biosorption rate was established in about 48 h and the adsorbed heavy metal ions did not change further with time. The maximum biosorption capacities of dry and immobilized cells of Rhizopus arrhizus biomass were 95.94% and 95.94% respectively at 500 mg/L of Pb(II) ions. The Pb(II) adsorption data were analyzed using the first and the second order kinetic models. The experimental results suggest that the second – order equation is the most appropriate equation to predict the biosorption capacity by dry and immobilized cells of Rhizopus arrhizus. Langmuir and Freundlich isotherms were used to evaluate the data and the regression constants were derived. Biosorption equilibrium data were best described by Freundlich isotherm model followed by Langmuir model. The free energy change (∆G°) obtained for the biosorption of Pb(II) ions at the temperature of 303, 308, 313, 318 and 323 K was – 1076, - 1094, - 1111, - 1129 and – 1147 kJ/mol (dry Rhizopus arrhizus) and – 789, - 802, - 815, - 828 and - 841 kJ /mol (immobilized Rhizopus arrhizus) respectively at pH – 5. The high negative value of change in Gibbs free energy indicates the spontaneity and feasibility of the biosorption of Pb(II) by kJ/mol dry and immobilized Rhizopus arrhizus.