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Keywords:

  • sulfide;
  • iron;
  • oxidation;
  • solid-state transformation;
  • localized corrosion

Abstract

In this study, Raman spectroscopy was used to precisely understand the mechanisms of oxidation of mackinawite (FeS). Two experimental conditions were considered: (1) oxidation in air at room temperature and (2) oxidation in acidic anoxic solutions at 80 °C. In both cases, the oxidation process began by the in situ oxidation of Fe(II) cations inside the crystal structure of mackinawite and led to Fe(III)-containing mackinawite, FeII1−3xFeIII2xS. The oxidation in air finally led to Fe(III) oxyhydroxides and elemental sulfur α-S8, but greigite (Fe3S4) was observed as an intermediate compound. In anoxic acidic solutions, the product of the oxidation was proved to depend on the Fe/S concentration ratio. For Fe/S = 3/4, greigite was the only product obtained, and this allowed us to determine unambiguously the Raman spectrum of this compound. Copyright © 2010 John Wiley & Sons, Ltd.