Kinetic and thermodynamic studies of sorption of lead and cadmium from aqueous solution by Moringa oleifera pod wastes

Equilibrium sorption of Pb(II) and Cd(II) from aqueous solution by Moringa oleifera pods waste was conducted under batch conditions. Effects of operating variables such as initial concentration, contact time, adsorbent dose, pH and temperature on the sorption of these heavy metals have been studied. The optimum pH for the adsorption was found to be 5.0 and the adsorption process was found to be exothermic for both metal ions. The competitive adsorption characteristics of the combinations of binary mixtures of aqueous metal ion species, Pb2+ (aq) and Cd2+ (aq), on the adsorbent were also investigated. The Langmuir, Freundlich, Temkin and Dubinin Radushkevich adsorption isotherm models were used to analyse the equilibrium data. Kinetics data evaluation showed that the adsorption followed a pseudo-second order model. A solution of 0.05 M HCl has been found to be sufficient for the regeneration of spent adsorbent with up to 90% recovery for the two metal ions.