Removal of chromium (VI) from aqueous solutions by grafted chitosan

Chitosan was deposited on cotton gauze at different add-ons (0.02, 0.05 and 0.10 g chitosan/g cotton) by UV-curing in order to improve its stability in water. Chitosan-cotton gauzes were employed in the adsorption of hexavalent chromium ions, Cr (VI) from aqueous solutions at pH of 3.0 and temperature of 20°C. In this study, kinetic model (Lagergren's pseudo-first-order or Ho's pseudo-second-order) and isotherm adsorption (Langmuir, Freundlich, Dubinin-Radushkevich and BET) were determined. Results showed that the adsorption of chromium occurred by a kinetics of pseudo-second-order with an adsorption isotherm type II. The most probable energy of adsorption, from Dubinin-Radushkevich isotherm model, foresees that a physisorption was achieved by hydrogen bond interactions between chromium ions and protonated amino groups. In addition, the adsorption capacity of chromium ions on grafted chitosan (56 - 103 mg Cr (VI) /g chitosan) was higher than that reported in literature for pure chitosan (8 - 24 mg Cr (VI) /g chitosan). In this way, it was demonstrated that a higher adsorption can be reached with lower amount of chitosan by UV-curing. Finally, the specific surface area occupied by chromium ions was estimated by means of the adsorption capacity of BET model.