Sorption of Cr(VI) anions in aqueous solution using carbonized or dried pineapple leaves

Adsorption studies of Cr(VI) were conducted on 623 K or 723 K carbonized pineapple leaves as well as the dried one. Thermo Gravimetric/Differential Thermal Analysis (TG-DTA) of raw pineapple leaves reveals two main peaks indicating the change in structure of the material with increasing temperature. Some important parameters such as pH, contact time and solution temperature were evaluated and the results show their high dependence with Cr(VI) anions uptake. The removal rate of 90.1% and the maximum adsorption capacity of 18.77 mg/g were registered for 723 K carbonized pineapple leaves. Consistent with an endothermic reaction, the mechanism was found to be chemisorption and the system was well described by the pseudo-second order kinetic model. The intraparticle diffusion model, on the other hand, indicated that the system is governed by both film diffusion and intraparticule diffusion. Adsorption isotherm data were described by both Langmuir and Freundlich models. The calculated value of Gibbs free energy suggested that the reaction is spontaneous. Moreover, the Fourier Transform Infrared Spectrometer studies point out the carboxylate ion, aliphatic group and unsaturated group like alkene as responsible for Cr(VI) binding process. The results notice that the selected materials are appropriate for removing Cr(VI) anions from wastewater. (C) 2011 Elsevier B.V. All rights reserved.