Adsorption of Cr(VI) using thermally activated weed Salvinia cucullata

Cr(VI) removal studies were carried out by using activated carbon obtained from waste weed, Salvinia cucullata. Effects of various parameters, such as pH, contact time, temperature, adsorbate concentration, adsorbent dose and particle size of the adsorbent on percentage of adsorption were studied. The adsorption studies were carried out at an agitation speed of 600 rpm to minimize the film diffusion. The adsorption kinetics followed dual rate; it was fast during a first stage and then it was reduced. The equilibrium was achieved in 12 h. The kinetics increased with decrease in pH. Adsorbate and adsorbent concentration also influenced the kinetics. The adsorption process was endothermic in nature. The reaction kinetics followed pseudo-second-order kinetic equation. Empirical rate equation developed, which explained the effect of various adsorption parameters, was studied. Theoretical numbers of stages were calculated based on the results. Intra-particle diffusion was found to be the rate-controlling step. Optimization studies were also carried out to establish the upper and lower breakthrough points. (C) 2007 Elsevier B.V. All rights reserved.