Adsorption of cadmium (Ii) onto oxidized activated carbon derived from mahogany (swietenia macrophylla king) pericarp: Equilibrium, thermodynamics, and kinetics

Abstract

The thermodynamics and kinetics of the adsorption of Cd(II) ions onto oxidized activated carbon derived from mahogany pericarp were studied. The activated carbon was prepared via initial carbonization and activation by phosphoric acid, followed by oxidization using different concentrations of nitric acid (HNO3; 2.5 M, 5.0 M, and 10.0 M). With increasing concentration of HNO3, the number of carboxylic acid groups increased while the number of phenolic groups decreased. Adsorption equilibrium studies revealed that the maximum adsorption capacity for Cd(II) increased with the increasing degree of oxidation of carbon material. The adsorption of Cd2+ ions onto the oxidized carbon was best described by the Freundlich model. Results of kinetic studies showed that the adsorption of Cd(II) ions onto the oxidized activated carbon is limited by film diffusion; for the unmodified carbon, Cd(II) adsorption was limited by intraparticle diffusion. The adsorption process onto the oxidized activated carbon materials was determined to be spontaneous, at the temperature range studied (25–50 °C).