Mechanism for the simultaneous removal of Sb(III) and Sb(V) from mining wastewater by phytosynthesized iron nanoparticles

Abstract

Since antimony (Sb) is a toxic metalloid cost-effective method for the simultaneous removal of the two major Sb species from mining wastewater has attracted much attention. In this study, phytosynthesized iron nanoparticles (nFe) prepared using a eucalyptus leaf extract were successfully used to simultaneously remove Sb(III) and Sb(V) via an adsorption and oxidation mechanism with removal efficiencies of 100 and 97.7% for Sb(III) and Sb(V), respectively. Advanced analysis using X-ray photoelectron spectroscopy (XPS), ion chromatography-atomic fluorescence spectroscopy (IC-AFS), and electrochemical analysis confirmed that Sb(III) was oxidized to Sb(V) by Fe(III) on the nFe surface while Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) indicated that both Sb(III) and Sb(V) were adsorbed onto nFe. Adsorption of both Sb(III) and Sb(V) best fit the Langmuir adsorption model with R2 of 0.999 and 0.989, respectively and both followed pseudo-second-order kinetics with R2 of 0.999 and 0.981, respectively. Furthermore, the adsorption rate of Sb(III) was faster than that of Sb(V) due to inner-sphere complex formation, and the Fe–O bonds in the asymmetric tetrahedron structure of Sb(III) were easier to break due to a lower energy barrier (0.863 eV). Consequently, a simultaneous removal mechanism of Sb(III) and Sb(V) was proposed. Finally, nFe was used practically to remove Sb in mining wastewater with a removal efficiency of 93.5%, demonstrating that nFe have significant potential to remove Sb in contaminated mining wastewaters.