Silane-based coatings on the pyrite for remediation of acid mine drainage

• An environmentally friendly coating to remediate acid mine drainage is reported.
• Silane coating is successful to suppress pyrite chemical and biological oxidation.
• A mechanism of pyrite oxidation suppression by coating was clearly determined.
• The superior suppression ability is due to flexibility and hydrophobicity of coating.

Acid mine drainage (AMD) resulting from the oxidation of pyrite and other metal sulfides has caused significant environmental problems, including acidification of rivers and streams as well as leaching of toxic metals. With the goal of controlling AMD at the source, we evaluated the potential of tetraethylorthosilicate (TEOS) and n-propyltrimethoxysilane (NPS) coatings to suppress pyrite oxidation. The release of total Fe and SO42−SO42− from uncoated and coated pyrite in the presence of a chemical oxidizing agent (H2O2) or iron-oxidizing bacteria (Acidithiobacillus ferrooxidans  ) was measured. Results showed that TEOS- and NPS-based coatings reduced chemical oxidation of pyrite by as much as 59 and 96% (based on Fe release), respectively, while biological oxidation of pyrite was reduced by 69 and 95%, respectively. These results were attributed to the formation of a dense network of Fe–O–Si and Si–O–Si bonds on the pyrite surface that limited permeation of oxygen, water, and bacteria. Compared with results for TEOS-coated pyrite, higher pH and lower concentrations of total Fe and SO42−SO42− were observed for oxidation of NPS-coated pyrite, which was attributed to its crack-free morphology and the presence of hydrophobic groups on the NPS-based coating surface. The silane-based NPS coating was shown to be highly effective in suppressing pyrite oxidation, making it a promising alternative for remediation of AMD at its source.

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