Adsorption of heavy metals on a complex Al-Si-O bearing mineral system: Insights from theory and experiments

Abstract

The adsorption behaviour of heavy metalliC ions such as Co (II), Pb (II) and Zn (II) on an Al-Si-O mineral system mostly comprising of pyrophyllite and diaspore was explored via experimentation and first principle calculations. The characterization studies involving X-ray Diffraction (XRD), Electron Probe Micro-Analysis (EPMA), Scanning Electron Microscope attached with Energy Dispersive Spectroscopy (SEM-EDS) in addition to the quantitative mineralogical analysis under reflected light microscope revealed the presence of pyrophyllite {Al2Si4O10(OH)(2)} as the major mineral followed by the phases like diaspore {alpha-AlO(OH}, corundum (Al2O3), kaolinite (Al2Si2O5(OH)(4)) and muscovite {KAl2(AlSi3O10)(F,OH)(2)) in the decreasing order of abundance. The adsorption data fitted well to the Langmuir isotherm with Co (II) having the maximum monolayer capacity of 9.23 mg/g while the pseudo second order model could explain the sorption behaviour for all the metallic ions. The adsorption capacities of the metallic salts followed the order Co (II) > Pb (II) > Zn (II). Density Functional Theory (DFT) based calculations validated the experimental trend of adsorption capacities indicating that Co atom is able to coordinate on the constituent mineral surfaces in a much stronger manner compared to the other two metal atoms. While corundum (001) plane was found to the best adsorbing plane among all the mineral planes considered over here, the interaction of the metal atoms on the edge surface of pyrophyllite (010) was stronger compared to that on its basal plane (001). (C) 2017 Elsevier B.V. All rights reserved.