Multi-element modeling of heavy metals competitive removal from aqueous solution by raw and activated clay from the Aleg formation (Southern Tunisia)

The present study has been carried out for potential use of a raw clay from Gabes district (southern Tunisia) in wastewater treatment. A representative clay sample was collected from the outcropping feature of the Aidoudi area to the west of Gabes city; it followed a simple treatment to enhance its physicochemical properties. Adsorption experiments were performed by using a simple batch technique in single- and multi-element solution (Pb2+, Cd2+, Cu2+ and Zn2+). The obtained results were fitted to different adsorption models, including extended and modified Langmuir, extended Freundlich and modified Redlich-Peterson. Our results indicated that the collected clay sample is mainly a smectite with high amounts of silica, alumina and iron. Adsorptive removal of single elements revealed encouraging efficiencies for most of the studied metals, reaching nearly 100%. Our results also indicated that lead removal reached 26.78 mg/g and 45.94 mg/g for natural and activated clay samples, respectively. Competitive adsorption showed strong dependence on the initial concentration and the metal properties, with preferential removal of lead that reached 41.71 mg/g in binary systems. In most of the mixed systems, metal removal substantially decreased in the presence of competing ions. It showed preferential removal of lead over other metals, regardless of the studied mixture. Further, the use of smectitic clay from southern Tunisia showed a good potential for metal ions removal in single and multi-element systems from aqueous solutions. Thus, it could be turned out to a viable material for the treatment of metal loaded waters.