LAUSR

This study investigated the applicability of natural Egyptian Na-montmorillonite (Na-MMT) to remove Pb2+, Cd2+ and Ni2+ under acidic conditions that mimic industrial wastewater acidity. Cation exchange capacity of Na-MMT was found 91 meq/100 g and the specific surface area 42 m2 g−1. The adsorbent was characterized using X-ray fluorescence, scanning electron micrograph that showed significant morphological changes after adsorption and Fourier transform infrared spectroscopy, which confirmed that the adsorption occurred mainly in the lattice region. Removal efficiency was evaluated as a function of pH, contact time, initial concentration, and adsorbent mass. Acidic pH value was chosen for the following experiments. Langmuir and Freundlich isotherm models were applied. Freundlich model showed better fitting suggesting heterogeneous adsorption scenario. Freundlich capacity values decreased in the order of Pb2+ (3.71 mg g−1) > Cd2+ (2.45 mg g−1) > Ni2+ (1.76 mg g−1). Kinetic data were accurately fitted to pseudo-second-order, indicating the adsorption occurrence in the interior surface of Na-MMT and the contribution of internal diffusion mechanism was significant. Intraparticle diffusion model gave multi-linear curves so more than one-step controlled the adsorption process. Under temperature range 290–328 K, thermodynamic parameters revealed that adsorption of Pb2+ and Cd2+ was spontaneous but Ni2+ non-spontaneous. Adsorption was exothermic for Pb2+ and Ni2+ but endothermic for Cd2+. Arrhenius activation energy values were 5.78, 8.51 and 11.45 kJ mol−1 for Pb2+, Cd2+ and Ni2+ respectively stating the physical adsorption. Na-MMT reusability was confirmed by regeneration experiments. Application study showed excellent efficiency of Na-MMT within range (23.4–81.2%) removal for Pb2+, Cd2+ and Ni2+ from textile dyeing and tannery wastewater. Copyright © 2017 Curtin University of Technology and John Wiley & Sons, Ltd.