The adsorption of Al(III) from aqueous solutions onto chitosan was studied in a batch system. The isotherms and the kinetics of adsorption with respect to the initial Al(III) concentration and temperature were investigated. Langmuir and Freundlich adsorption models were applied to describe the experimental isotherms. Equilibrium data fitted very well to the Langmuir model in the entire concentration range (5-40 mg/L). The negative values of free energy (Delta G degrees) and enthalpy (Delta H degrees) for the adsorption of AI(HI) onto chitosan indicated that the adsorption process is a spontaneous and exothermic one. Two simplified kinetic models, based on pseudo first-order and pseudo second-order equations, were tested to describe the adsorption mechanism. The pseudo second-order kinetic model resulted in an activation energy of 56.4 kJ/mol. It is suggested that the overall rate of Al(III) ion adsorption is likely to be controlled by the chemical process. The values of the enthalpy (Delta H-#) and entropy (Delta S-#) of activation were 53.7 kJ/mol and -164.4 J/mol K, respectively. The free energy of activation (Delta G(#)) at 30 degrees C was 103.5 kJ/mol. (C) 2007 Elsevier B.V. All rights reserved.