A comprehensive investigation of the continuous oxidation of pyrrhotite by micromolar hydrogen peroxide in near neutral and acidic solutions.

Pyrrhotite oxidation poses a big threat to water environment duo to its high potential for generating pollutants. Hydrogen peroxide, commonly found in natural water at micromolar concentrations, possesses much more aggressive oxidation ability than oxygen and can complicate the pyrrhotite oxidation process. Here, the effects of micromolar HO on the biotic and abiotic oxidation of pyrrhotite were examined at pH 1.93 and 6.45, respectively. Pyrrhotite oxidation was much more severe in acidic solutions compared to near neutral solutions. Jarosite with a high Fe/S molar ratio was widely detected in the precipitate collected in acidic solutions, and the introduction of external HO influenced the crystallinity of jarosite. A layer of iron-deficient iron-sulfur oxide formed on the surface of pyrrhotite prevents its continuous oxidation, and the presence of Acidithiobacillus ferrooxidans enhanced this situation by promoting the release of Fe from the pyrrhotite. Additionally, the presence of external micromolar HO also determined the elemental state on pyrrhotite surface, as it found that the contribution of Fe and S (S and S) species on pyrrhotite surface increased with the increase of HO concentration in the solutions, especially in the presence of Acidithiobacillus ferrooxidans.