Mechanistic Aspects of Pyrite Oxidation in an Oxidizing Gaseous Environment:  An in Situ HATR−IR Isotope Study

The reaction of FeS2 (pyrite) with gaseous H2O, O2, and H2O/O2 was investigated using horizontal attenuated total reflection Fourier transform infrared spectroscopy (HATR-FTIR). Spectra were interpreted with the aid of hybrid molecular orbital/density functional theory calculations of sulfate-iron h...

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Bibliographic Details
Published in:Environmental science & technology 2005-10, Vol.39 (19), p.7576-7584
Main Authors: Usher, Courtney R, Paul, Kristian W, Narayansamy, Jayakumar, Kubicki, James D, Sparks, Donald L, Schoonen, Martin A. A, Strongin, Daniel R
Format: Article
Language:English
Subjects:
Chemical reactions
Earth sciences
Earth, ocean, space
Electrons
Exact sciences and technology
Fourier transforms
Gases
Iron - chemistry
Iron alloys
Isotope Labeling
Mineralogy
Non silicates
Oxidation-Reduction
Oxygen
Oxygen - chemistry
Spectroscopy, Fourier Transform Infrared - methods
Spectrum analysis
Sulfides - chemistry
Sulfur
Water - chemistry
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Summary:The reaction of FeS2 (pyrite) with gaseous H2O, O2, and H2O/O2 was investigated using horizontal attenuated total reflection Fourier transform infrared spectroscopy (HATR-FTIR). Spectra were interpreted with the aid of hybrid molecular orbital/density functional theory calculations of sulfate-iron hydroxide clusters. Reaction of pyrite in gaseous H2O led primarily to the formation of iron hydroxide on pyrite. Exposure of the pyrite to gaseous O2 after exposure to H2O vapor led to the formation of sulfur oxyanions that included SO4 2-. Isotopic labeling experiments showed that after this exposure sequence the oxygen in the sulfate product was primarily derived from the H2O reactant. If, however, pyrite was exposed to gaseous O2 prior to pure H2O vapor, both SO4 2- and iron oxyhydroxide became significant products. Isotopic labeling experiments using the O2-then-H2O sequence showed that the oxygen in the SO4 2- product was derived from both H2O and O2. The results indicate that H2O and O2 exhibit a competitive adsorption on pyrite, with H2O blocking surface sites for O2 adsorption. The extent of oxygen incorporation from either the H2O or the O2 component into the surface-bound sulfur oxyanion product appears to be a strong function of the relative concentration ratio of the reactant H2O and O2.
ISSN:0013-936X
1520-5851
DOI:10.1021/es0506657