Influence of pH and ionic strength on Cd, Cu and Pb removal from water by adsorption in Na-bentonite

Abstract

This article presents a study on cadmium, copper and lead removal by means of adsorption in a natural Na-bentonite. Influence of pH and ionic strength on clay fabric and its role on cation removal are analyzed by means of Zeta potential and sedimentation tests. Batch adsorption and kinetics tests were carried out to quantify the adsorption capacity of the bentonite at monospecies and multispecies conditions, where ion competition was analyzed. Experimental results show that ionic strength strongly affects clay structure and cadmium removal, but has little influence on lead and copper removal. Adsorption kinetics was fast in all cases, which was mostly related to reaction kinetics than to diffusion kinetics. Cadmium adsorption can be explained by linear adsorption models, while copper, lead and the multispecies tests showed good agreement with both the linear and Freundlich models within the tested concentration range. The results confirm that tested Na-bentonite possesses a high capacity for the removal of Cd, Cu and Pb.