Iron(II) sulfides (FeS) are common and widespread in natural systems, primarily due to natural biogeochemical cycles of iron and sulfur, but also as the likely endpoint for engineered iron-based nanomaterials when released into natural environments. Although relatively stable under reducing conditions, when exposed to oxygen during a disturbance such as excavation, natural tidal flushing, or aquifer recharge, both the Fe(II) and S(−II) are readily oxidized, forming a range of transient minerals and dissolved species on the eventual pathway to thermodynamically stable Fe(III) and sulfate. Hydrogen peroxide is known to form during this process, resulting in a system containing both Fe(II) and H<sub>2</sub>O<sub>2</sub> and therefore conducive to the Fenton reaction. The strong oxidants formed during these processes have been examined by employing a suite of probe compounds with varying reactivity, allowing estimates of the magnitude of total strong oxidant production and also the nature of the reactivity of the strong oxidant to be assessed. The solid phase Fe-transformations accompanying the FeS oxidation process has also been probed using Fe K-edge x-ray absorption spectroscopy in order to understand the nature of the intermediate and final-state mineralogy as well as to deduce the potential role of the mineral phases in driving the observed oxidation capacity of the system.

Nature and magnitude of strong oxidant formation during oxygen-mediated iron(II) monosulfide oxidation

255th National Meeting (2018)

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