Kinetic models of competitive adsorption of cadmium–iron mixture on montmorillonite

Abstract

In this work, montmorillonite (MNT) extracted from Algerian clay is used to remove cadmium and iron that are found simultaneously in wastewaters. The effects of pH, initial adsorbate concentration (C0 ), and adsorbent concentration (CB ), on competitive adsorption of both metals were studied in batch system. MNT was analyzed by infrared, scanning electron microscopy with energy dispersive X-ray analysis, and Brunauer–Emmett–Teller. The kinetic models tested are: Boyd’s, Weber and Morris external models, Urano and Tachikawa, Weber and Morris internal models, Elovich, pseudo-first and pseudo-second-order models. These models were compared based on: root mean square error, mean relative error deviation, mean absolute error, coefficient of correlation, accuracy, and bias factors. The competitive sorption of both metals is controlled by diffusion in pores and mésopores, and follows the Weber and Morris internal model. The statistical coefficients for this model are the most significant based on Bf values. Also, the estimated error coefficients show that kinetics of Cd and Fe fit well Elovich and pseudo-second-order models, respectively. The maximum uptakes are respectively 76 and 55 mg g–1 after 120 min. Raw MNT showed remarkable efficiency for the simultaneous sorption of cadmium and iron, especially for Cd. So, it could be suggested as a low cost adsorbent for effluents charged with cadmium.