Moringa oleifera-A solid phase extractant for the removal of copper, nickel and zinc from aqueous solutions

Moringa oleifera (MO) wood, a solid waste was used for the preparation of activated carbon (ACMO) for the removal of copper, nickel and zinc from synthetic wastewater. Effects of various operating variables namely solution pH, contact time, carbon dose, adsorbate concentration and temperature on the removal of metal ions have been studied. Thermodynamic parameters such as free energy change, enthalpy change and entropy change were calculated. The optimum pH for the adsorption for all the above mentioned metals was found to be 6. The adsorption process was found to be endothermic for Cu and exothermic for Ni and Zn. The Langmuir, Freundlich, Temkin and Dubinin Radushkevich isotherm models were used to analyze the equilibrium data at different temperatures. The data were also fitted to kinetic models such as pseudo-first-order and pseudo-second-order model. Kinetic studies showed that the adsorption followed a pseudo-second-order model. The intra-particle diffusion rate constants and effective diffusion coefficient for different temperatures were evaluated and discussed. Adsorption occurs both by film diffusion and particle diffusion mechanism. The ACMO could be regenerated using 0.1 M H2SO4, with up to 98% recovery for all the three metals. (C) 2010 Elsevier B.V. All rights reserved.