Adsorption of basic dye from aqueous solutions by modified sepiolite: Equilibrium, kinetics and thermodynamics study

The adsorption behavior of crystal violet (CV+) from aqueous solution onto a manganese oxide-coated (MCS) sepiolite sample was investigated as a function of parameters such as initial CV+ concentration, contact time and temperature. The Langmuir and Freundlich adsorption models were applied to describe the equilibrium isotherms. The Langmuir monolayer adsorption capacity of MCS was estimated as 319 mg/g. The pseudo-first-order. pseudo-second-order kinetic and the intraparticle diffusion models were used to describe the kinetic data and rate constants were evaluated. The values of the energy (E-a), enthalpy (Delta H-not equal) and entropy of activation (Delta S-not equal) were 56.45 kJ/mol, 53.90 kJ/mol and - 117.26J/(mol K), respectively, at pH 6.5. The quite high adsorption capacity and high adsorption rate of MCS will provide an important advantage for use of this material in basic dye solutions. (C) 2009 Elsevier B.V. All rights reserved.