Kinetic and equilibrium studies of phenol adsorption by natural and modified forms of the clinoptilolite

The contribution presents results of investigation of phenol adsorption by the raw, HDTMA- and NaOH- modified clinoptilolite. The experimental data on the sorption kinetic process are modelled using the particle and the film diffusion models with calculation of a rate constant of intraparticle mass transfer. Two main stages may be divided in the kinetic sorption process: (1) initial rapid sorption (amount of phenol sorbed 85-90%) extending over the first 60 min and (2) stage of slow approach to equilibrium covering about 8 h. Equilibrium isotherms for phenol adsorption are modelled using the Langmuir. Freundlich and Dubinin-Radushkevich equations. The Freundlich isotherm describes in a greater degree phenol sorption from aqueous solutions of low phenol concentrations, while the Langmuir isotherm fits better to sorption at high initial concentrations. (C) 2009 Elsevier B.V. All rights reserved.