Adsorption of chromium(VI) from aqueous solution by glycine modified cross-linked chitosan resin

Abstract

THE ADSORPTION of Cr(VI) onto glycine-modified crosslinked chitosan (GMCCR) resin has been investigated. Batch experiments were performed to examine kinetics, adsorption isotherm, pH effect, and thermodynamic parameters. The effect of pH for the adsorption of Cr(VI) was studied at range from 2 to 6 and the equilibrium was accomplished within 150 minutes and maximum removal was achieved under the optimum conditions at pH 3. The result obtained from equilibrium adsorption studies are fitted Langmuir and Freundlich adsorption models and the data was found that the equilibrium data agreed very well with the Langmuir model. The maximum uptake was found to be 1.5 mmol/g (calc 1.75 mmol/g) at 250C. Thermodynamic parameters for the adsorption system were determined at 298 K, 308 K and 318 K (ΔH° =22.85 kJ·mol-1; ΔG° = -33.17 to -36.93 kJ·mol-1 and ΔS° = 188 J·K-1·mol-1). The positive values of ΔH° and ΔS° suggest an endothermic reaction and increase in randomness at the solid-liquid interface during the adsorption. The negative values of ΔG° indicating a spontaneous adsorption process. The kinetic process was described very well by a pseudo-second-order rate equation.