Comparative study of Zn2+, Cd2+, and Pb2+ removal from water solution using natural clinoptilolitic zeolite and commercial granulated activated carbon.: Equilibrium of adsorption

The aim of this work is to study the effectiveness of regional, low-cost natural clinoptilolitic zeolite tuff in heavy metal ions removal from aqueous solution, through comparative study with commercial granulated activated carbon. The equilibrium of adsorption of Cd2+, Pb2+, and Zn2+ on both adsorbents have been determined at 25, 35, and 45 degrees C in batch mode. The granulated activated carbon has shown around three times higher adsorption capacity for Cd2+ and Zn2+ than natural zeolite, and almost the same adsorption capacity for Pb2+ as the natural zeolite. The metal ion selectivity series Pb2+ > Cd2+ > Zn2+, on a mass basis, has been obtained on both adsorbents. The Langmuir and Freundlich model have been used to describe the adsorption equilibrium. The thermodynamic parameters were calculated from the adsorption isotherm data obtained at different temperatures. The study of the influence of the acidity of the metal ion aqueous solution has shown an increase of metal ion uptake with increase of the pH. The sorption mechanism of Cd2+, Pb2+, and Zn2+ on natural zeolite changes from ion-exchange to ion-exchange and adsorption of metal-hydroxide with increase of the pH from 2 to 6 (and 7 for Zn2+). The preliminary cost calculation, based on adsorbents maximum adsorption capacity and their price, have revealed the potential of natural zeolite as an economic alternative to the granulated activated carbon in the treatment of heavy metal polluted wastewater.