Equilibrium and kinetics studies of fluoride ions adsorption on CeO2/Al2O3 composites pretreated with non-thermal plasma

The removal of fluoride from aqueous solution using the original and non-thermal plasma (NTP) modified CeO2/Al2O3 composites was systematically studied. The adsorption was investigated in batch adsorption system, including both equilibrium and kinetics. Equilibrium adsorption data were analyzed using Langmuir, Freundlich and Dubinin-Radushkevich isotherm models. In order to understand the mechanism of adsorption, thermodynamic parameters such as Delta G(theta), Delta S-theta, Delta H-theta and E-a were calculated. Results showed that the adsorption data were found to be well described by Langmuir model. The pseudo-first-order, pseudo-second-order and intraparticle diffusion models were applied to test the kinetic data, and the results revealed that the pseudo-second-order kinetic reaction as the surface reaction was dominated and controlled adsorption stage. The thermodynamic parameters were changed using NTP modified adsorbents. For the Delta S-theta increased from 78.42 J/mol K to 93.42 J/mol K, the E-a decreased from 57.52 kJ/mol to 54.60 kJ/mol and the Delta G(theta) (363 K) decreased from -6.82 kJ/mol to -8.06 kJ/mol. The negative value of Delta G(theta) indicates that the adsorption occurs via a spontaneous process, the decrease in the value of E-a indicates that the adsorption of fluoride on NIP modified adsorbents is more favourable. (C) 2011 Elsevier B.V. All rights reserved.