Web Release Date: August 31,
Mechanistic Aspects of Pyrite Oxidation in an Oxidizing Gaseous Environment: An in Situ HATR-IR Isotope Study
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Department of Chemistry, Temple University, 1901 North 13th Street, Philadelphia, Pennsylvania 19122, Department of Plant and Soil Sciences, University of Delaware, 152 Townsend Hall, Newark, Delaware 19716, Department of Geosciences, The Pennsylvania State University, 308 Deike Building, University Park, Pennsylvania 16802, Department of Geosciences, Stony Brook University, Stony Brook, New York 11794, and Center for Environmental Molecular Science, Stony Brook University, Stony Brook, New York 11794-2100
Received for review April 7, 2005
Revised manuscript received July 1, 2005
Accepted July 13, 2005
Abstract:
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 SO42-. 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 SO42- and iron oxyhydroxide became significant products. Isotopic labeling experiments using the O2-then-H2O sequence showed that the oxygen in the SO42- 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.
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