Hydrophobic modification of pyrite with a composite of sodium oleate and SiO2 nanoparticles to inhibit its oxidation for controlling acid mine drainage

The formation of acidic mine drainage (AMD) is mainly due to the oxidation of pyrite in the presence of water. In this study, the environmentally friendly Sodium oleate (SO) was used as hydrophobic agent and SiO2 nanoparticles were added as a filler material to modify pyrite. Na-oleate and nano-SiO2 nanoparticles form a hydrophobic passivation film directly on the pyrite surface in a very simple process.Excellent antioxidant capacity was achieved with the addition of 6% SO and 1 wt% SiO2 at a reaction temperature of 70 °C. Chemical leaching experiments and electrochemical experiments were used to characterise the antioxidant properties of this hydrophobic passivated film. The results showed that the pH of the leachate could be maintained above 5.7, a 2.6 increase over raw pyrite. In addition, the reduction rate of SO42- and total Fe concentration could reach over 83.69% and 97.91%, respectively. SO-SiO2-treated pyrite exhibits lower oxidation rates in electrochemistry and an increased contact angle of 70.1° compared to pristine pyrite. Finally, this paper details the mechanism of the action of SO-SiO2 on the surface of pyrite by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis. The results show that sodium oleate can combine with iron ions to form iron oleate wrapped on the surface of pyrite, while silica nanoparticles attach to pyrite by physical adsorption, filling the pores on the surface of hydrophobic film layer and effectively protecting pyrite from oxidation.