Removal of lead and cadmium ions from aqueous solution by polyvinyl alcohol-modified kaolinite clay: A novel nano-clay adsorbent

Abstract

Kaolinite clay was modified with polyvinyl alcohol (PVA) to obtain a PVA-nano-clay adsorbent. X-Ray diffraction measurements of the adsorbent showed no observable change in the d-spacing of its crystal lattice. Scanning electron microscopy of the PVA-modified nano-clay adsorbent indicated the presence of irregular crystal structures. Infrared spectroscopy suggested that the PVA-nano-clay adsorbent basically possessed outer -OH functional groups. This adsorbent was found to have an adsorption capacity of 56.18 mg/g for Pb2+ ions and 41.67 mg/g for Cd2+ ions. The adsorption data obtained was well explained by the Diffuse Layer Model (DLM), which implies that the adsorption of both metal ions onto the modified adsorbent was via an inner-sphere surface complexation mechanism. The ΔH0 values for the adsorption of both metal ions onto the PVA-nano-clay were -12.48 kJ/mol for Pb2+ ions and -13.49 kJ/mol for Cd2+ ions, with both ions exhibiting negative adsorption entropies. Data-fitting indicated that both the PVA-nano-clay and the unmodified adsorbent possessed homogeneous and heterogeneous adsorption sites. Virtually complete desorption (ca. 99%) of both metal ions occurred from PVA-nano-clay within 3 min.