Simultaneous removal of Sb(III) and Sb(V) from mining wastewater by reduced graphene oxide/bimetallic nanoparticles

Antimony (Sb) contamination is a significant environmental issue in mining impacted areas, where the use of nanomaterials to remove such metalloid species has attracted much research attention. In this study, the simultaneous removal of Sb(III) and Sb(V) was investigated using a reduced graphene oxide/Fe/Ni (rGO-Fe/Ni NPs) composite. Compared to rGO alone the composite exhibited enhanced removal efficiency. For rGO-Fe/Ni NPs the maximum Sb(III) and Sb(V) adsorption capacities were 2.00 and 1.41 mg·g^-1, respectively, compared to 1.70 and 1.02 mg·g^-1 for Sb(III) and Sb(V), respectively, when using rGO only. This indicated that Fe/Ni enhanced the simultaneous removal of Sb(III) and Sb(V). Advanced characterization via SEM and XPS before and after exposure to Sb indicated that both Sb(III) and Sb(V) were adsorbed on to the surface of rGO-Fe/Ni NPs, followed by oxidation of Sb(III) to Sb(V). Adsorption and oxidation kinetics both conformed to pseudo-second order models, where the mechanism for the simultaneous removal of Sb(III) and Sb(V) by rGO-Fe/Ni NPs involved a combination of both adsorption and oxidation. Moreover, the practical adsorption capacity of rGO-Fe/Ni was not limited to Sb, since in a real mining wastewater; containing a mixture of metal(loid)s, while rGO-Fe/Ni exhibited a Sb adsorption capacity of 1.59 mg·g^-1, it also exhibited similar adsorption capacities for As (2.61 mg·g^-1), Pb (2.41 mg·g^-1), and Cd (1.25 mg·g^-1). The composite was also highly reusable with a removal efficiency for Sb(III) as high as 72.7% after 4 cycles of use. Thus, rGO-Fe/Ni NPs has significant potential for the practical removal of Sb species and other heavy metal(loid)s in mining impacted wastewaters.