Removal of Pb2+ and Zn2+ using modified Chocolate B clay: a study using statistical analysis, equilibrium isotherms, and adsorption kinetics

Abstract

Abstract In this work, natural and thermally modified Chocolate B clays were used for batch adsorption of Pb2+ and Zn2+ from an aqueous solution. The materials were characterized by X-ray diffraction, X-ray fluorescence spectroscopy, nitrogen adsorption, and cation exchange capacity. The tests were performed in a finite bath following a 22 factorial design, with the variables: pH and initial concentrations of metal. Results revealed that the thermal treatment caused alterations on the Chocolate B clay structure and decreased the specific surface area. Affinities between Pb2+ or Zn2+ and Chocolate B clay were found with adsorption capacities up to 3.36 and 3.72 mg.g-1, respectively. The maximum adsorption capacities were 6.79 mg.g-1 for Pb2+ and 3.35 mg.g-1 for Zn2+ using thermally activated clay. The Langmuir and Freundlich models were used for the adsorption equilibrium analysis, and the Langmuir model provided the best fit for sorption isotherms. The adsorption kinetics was evaluated by two models: pseudo-first-order and pseudo-second-order. The pseudo-first-order kinetic model represented well the mechanism of interaction involved during Pb2+ adsorption into the pores of the clay. However, the two models represented well the mechanism of interaction of Zn2+ adsorption into the pores of the clay.

Keywords

• Chocolate B clay
• thermal activation
• lead
• zinc
• sorption
• isotherm
• kinetics