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Competing oxidants with temperature-dependent oxidation efficiencies results in multiple reaction mechanisms for different temperatures and surface conditions. A combination of reactive oxygen species from H2O2 decomposition products and reactive iron species from pyrite dissolution is inferred to aggressively oxidize the receding pyrite surface. Rates measured in sealed-tube experiments at 25☌, for H2O2 concentration of 2 × 10−3 M are 8.8 × 10−9 M/m2/sec, which are higher than previous estimates. Pyrite oxidation by H2O2 increases in rate with increasing H2O2concentration, pyrite surface area, and temperature.

Elemental sulfur and/or polysulfides are inferred to be form on reacting pyrite surface based on extraction with organic solvents. Hematite was detected only in solid residue produced during high temperature experiments. X-ray diffraction patterns and images from scanning electron microscopy reveal solid residues composed primarily of hydrated ferric iron sulfates and sporadic ferric–ferrous iron sulfates. Sulfate was the only aqueous sulfur species detected in solution, with sulfite and thiosulfate below the detection limits.

No volatile sulfur species were recovered from any experiment. The dominant gaseous product was molecular oxygen. Gaseous, aqueous, and solid phases were collected and measured following sealed-tube experiments that lasted from 1 to 14 days. Oxidation of pyrite by hydrogen peroxide (H2O2) at millimolar levels has been studied from 4 to 150 ☌ in order to evaluate isotopic effects potentially associated with radiolytic oxidation of pyrite.

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