Validity of Egyptian Na‐montmorillonite for adsorption of Pb 2+ , Cd 2+ and Ni 2+ under acidic conditions: characterization, isotherm, kinetics, thermodynamics and application study

• Published in: Asia-Pacific journal of chemical engineering 2017-03, Vol.12 (2), p.292-306
• Main Authors: Taha, A.A., Shreadah, M.A., Heiba, Hany Fathy, Ahmed, A.M.
• Format: Article
• Language: English
• ISSN: 1932-2135; 1932-2143
• DOI: 10.1002/apj.2072

This study investigated the applicability of natural Egyptian Na‐montmorillonite (Na‐MMT) to remove Pb 2+ , Cd 2+ and Ni 2+ 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 m 2  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 Pb 2+ (3.71 mg g −1 ) > Cd 2+ (2.45 mg g −1 ) > Ni 2+ (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 Pb 2+ and Cd 2+ was spontaneous but Ni 2+ non‐spontaneous. Adsorption was exothermic for Pb 2+ and Ni 2+ but endothermic for Cd 2+ . Arrhenius activation energy values were 5.78, 8.51 and 11.45 kJ mol −1 for Pb 2+ , Cd 2+ and Ni 2+ 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 Pb 2+ , Cd 2+ and Ni 2+ from textile dyeing and tannery wastewater. Copyright © 2017 Curtin University of Technology and John Wiley & Sons, Ltd.