Suppression of Pyrite Oxidation by Iron 8-Hydroxyquinoline

Abstract

One of the important approaches to prevent pyrite (FeS₂) oxidation and subsequent formation of acid mine drainage (AMD) is to create a surface coating on pyrite. In this study, a coating of iron 8-hydroxyquinoline was formed by leaching pyrite with a 0.10 M H₂O₂/0.0034 M 8-hydroxyquinoline solution; stability of the coated pyrite was tested under various pH and temperature conditions. The results showed that iron 8-hydroxyquinoline coating could significantly suppress further pyrite oxidation by both chemical (H₂O₂) and biological (e.g., Thiobacillus ferrooxidans) processes. At pH from 3.0 to 5.0 and temperature from 10–40°C, the amount of SO₄ ²⁻ leached out by 0.10 M H₂O₂ from the coated pyrite samples was 54.8–70.1% less than that from the uncoated controls. The oxidation of pyrite followed a pseudo–zero-order kinetics under the constant concentration of H₂O₂. In the presence of microorganisms, sulfate leached out of the uncoated pyrite in 1 year accounted for 5.32% of the total pyrite in the system, with a concurrent pH drop to 2.35 under the ambient room temperatures. In contrast, the amount leached out from the coated samples was only 0.15% of the total pyrite and the final pH was 5.48. Thus, the coating decreased the leachability of pyrite by 97% in the inoculated systems. In comparison to the more widely studied iron phosphate coating, the advantage of iron 8-hydroxyquinoline coating was that it inhibited both chemical and biological pyrite oxidation, whereas iron phosphate coating could only inhibit chemical pyrite oxidation.