Thermodynamic analysis of adsorption models of phenol in liquid phase on different activated carbons

Abstract

This paper studies the thermodynamic aspects of the processes of adsorption of phenol from dilute aqueous solutions on different commercial carbons, evaluating how to optimize the removal of this persistent contaminant. Two powdered activated carbons from two different companies were used: Tetrahedron Carbon (Andes Chemistry Lab., Mendoza, Argentina), and Norit (Norit Americas Inc., USA). Both specific surface areas were measured by means of the BET method. The adsorbate was high purity solid phenol (Fluka ® ≥ 99.5%). Experimental isotherms were determined at 293 K, 303 K and 313 K. The Freundlich and Sips theoretical models were used to fit the experimental data. Freundlich isotherm slightly diverges with the experimental results for higher equilibrium concentrations. Thermodynamic parameters were calculated and correlated with the adsorption behaviours. The values of the thermodynamic parameters obtained indicate an exothermic and spontaneous process for both carbons, and mainly for Norit. This is due to the fact that there might be chemically activated regions on the surface of the Norit carbon, which give rise to combined mechanisms of physisorption and chemisorption.