Adsorption of lead by kaolinite, montmorillonite, goethite and ferrihydrite: performance and mechanisms based on quantitative analysis

Abstract

This work elucidated the performance and mechanisms of Pb 2+ adsorption by kaolinite, montmorillonite, goethite and ferrihydrite using batch experiments. The contributions of various adsorption mechanisms were quantified using a stepwise extraction method. Several characterizations (scanning electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, point of zero charge analysis and X-ray fluorescence) were utilized to analyse the physicochemical properties and the potential adsorption mechanisms. The results indicated that the adsorption processes of montmorillonite and goethite approached equilibrium within 20 min, while 60 min were required for the adsorption processes of kaolinite and ferrihydrite. The adsorption processes of Pb 2+ by the four minerals best fit the pseudo-second order model. The adsorption capacities of the four minerals for Pb 2+ followed the order: montmorillonite > goethite > ferrihydrite > kaolinite, and the maximum adsorption capacities were 69.20, 46.95, 34.32 and 18.62 mg g –1 , respectively. The stepwise extraction test showed that the adsorption mechanism of Pb 2+ was dominated by ion exchange for montmorillonite, precipitation and complexation for goethite and complexation for kaolinite and ferrihydrite.