Adsorption of Pb (II) by sawdust and neem bark from aqueous solutions

This study reports a systematic evaluation sawdust and neem bark as low-cost natural adsorbent for removal of Pb(II) from aqueous solutions. Studies were carried out to investigate the effect of pH, initial metal ion concentration, adsorbent dosage level, and equilibrium contact time for the adsorption process. The optimum pH for Pb(II) adsorption was found to be 5 and equilibrium was achieved within 1 h of contact time for both adsorbents. Maximum adsorption of the metal ion was obtained at an adsorbent dosage of 7.5 g/L, which may be considered as optimum adsorbent dosage level. At optimum conditions of pH, contact time and adsorbent dosage level removal efficiency of 94.5% +/- 0.3 for Pb(II) adsorption was observed for sawdust, which was found to be 86.7% +/- 0.5% for neem bark. Kinetic data were best described by pseudo-second-order model. Diffusion studies showed that the adsorption process is based on surface adsorption as well as intraparticle diffusion for both adsorbents. The equilibrium adsorption data were fitted well with Freundlich isotherm models. The sorption energy calculated from Dubinin-Radushkevich isotherm indicated that the adsorption process is chemical in nature. The maximum adsorption capacities (q(max)) of sawdust and neem bark in terms of monolayer adsorption were compared with that reported in literature. The thermodynamic equilibrium constant and the Gibbs free energy were determined and the results indicated the spontaneous adsorption process. FTIR studies were carried out to understand the type of junctional groups in sawdust and neem bark responsible for (C) 2008 American Institute of Chemical Engineers.