Novel kinetics model for adsorption of pollutant from wastewaters onto zeolites. Kinetics of phenol adsorption on zeolite-type silicalite

Abstract

The kinetics of isothermal adsorption of phenol from an aqueous solution onto the zeolite-type silicalite was investigated. Zeolite-type silicalite was synthesized and its basic physico-chemical properties were determined. Isothermal adsorption kinetics curves of phenol on zeolite-type silicalite were measured at temperature range from 283 to 313 K. By applying Friedman’s differential isoconversional method it was found that the adsorption of phenol on silicalite has one rate determining step. By using the ‘model-fitting’ method it was established that the kinetic of adsorption can be described with theoretical kinetic model of the two-dimensional phase-boundary controlled reaction (model R2). The kinetic parameters, activation energy ( E a = 45 kJ mol − 1 ) and preexponetial factor ( lnA = 14.1 min −1 ) of phenol adsorption were calculated. The thermodynamic parameters, standard enthalpy (Δ H *), standard entropy (Δ S *) and standard free Gibbs energy of adsorption (Δ G *) were calculated and discussed. A novel model for the kinetics of pollutant adsorption from wastewaters onto zeolites based on the following: zeolite pores have cylindrical shape with average radius r 0 , pores in zeolite are filled simultaneously by the model ‘layer by layer’, the rate of phenol adsorption is higher than the rate of the growth of the thickness of the adsorption layer was suggested. It has been found that the adsorption kinetics can be completely described by this kinetic model.