Biosorption of palladium(II) and platinum(IV) from aqueous solution using tannin from Indian almond (Terminalia catappa L.) leaf biomass: Kinetic and equilibrium studies

A feasibility study was performed on Indian almond leaf biomass (Terminalia catappa L.) to remove palladium (Pd(II)) and platinum (Pt(IV)) ions from aqueous solution by biosorption. The biosorption characteristics of Pd(II) and Pt(IV) ions were investigated in terms of equilibrium, kinetics and thermodynamics. Optimum biosorption conditions were determined as a function of pH, biomass dosage, contact time, and temperature. Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) models were applied to describe the biosorption isotherm. The Langmuir model fitted the equilibrium data better than the Freundlich isotherm. Palladium is more preferable with T. catappa L than platinum. The maximum biosorption capacity (q(m)) of T. catappa L biomass for Pd(II) and Pt(IV) ions were 41.86 and 22.50, respectively. The mean free energy values evaluated from the D-R model indicated that the biosorption of Pd(II) and Pt(IV) onto T. catappa L biomass took place by chemical ion-exchange. The calculated thermodynamic parameters Delta G(0), Delta H-0 and Delta S-0 indicate that the biosorption of Pt(II) and Pd(II) ions onto T. catappa L biomass is feasible, spontaneous and exothermic. Biosorption kinetics using pseudo-first-order and pseudo-second-order kinetic models were also examined. Experimental data was found to be in good agreement with pseudo-second-order kinetics. (C) 2012 Elsevier B.V. All rights reserved.