Surface oxidation of pyrite under ambient atmospheric and aqueous (pH=2 to 10) conditions: Electronic structure and mineralogy from X-ray absorption spectroscopy

EC Todd, DM Sherman*, JA Purton

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

113 Citations (Scopus)

Abstract

The nature of the surface oxidation phase on pyrite, FeS2, reacted in aqueous electrolytes at pH = 2 to 10 and with air under ambient atmospheric conditions was studied using synchrotron-based oxygen K edge, sulfur L-III edge, and iron L-II,L-III edge X-ray absorption spectroscopy. We demonstrate that O K edge X-ray absorption spectra provide a sensitive probe of sulfide surface oxidation that is complementary to X-ray photoelectron spectroscopy. Using total electron yield detection, the top 20 to 50 Angstrom of the pyrite surface is characterized. In air, pyrite oxidizes to form predominantly ferric sulfate. In aqueous air-saturated solutions, the surface oxidation products of pyrite vary with pH, with a marked transition occurring around pH 4. Below pH = 4, a ferric (hydroxy)sulfate is the main oxidation product on the pyrite surface. At higher pH, we find iron(III) oxyhydroxide in addition to ferric (hydroxy)sulfate on the surface. Under the most alkaline conditions, the 0 K edge spectrum closely resembles that of goethite, FeOOH, and the surface is oxidized to the extent that no FeS2 can be detected in the X-ray absorption spectra. In a 1.667 x 10(-3) mol/L Fe3+ solution with ferric iron present as FeCl3 in NaCl, the oxidation of pyrite is autocatalyzed, and formation of the surface iron(III) oxyhydroxide phase is promoted at low pH. Copyright (C) 2003 Elsevier Science Ltd.

Original languageEnglish
Article numberPII S0016-7037(02)00957-2
Pages (from-to)881-893
Number of pages13
JournalGeochimica et Cosmochimica Acta
Volume67
Issue number5
Publication statusPublished - Mar 2003
EventTopical Symposium on Advances in Oxide and Sulfide Mineral Surface Geochemistry - HOT SPRINGS, United Kingdom
Duration: 1 Jan 2001 → …

Keywords

  • TRANSITION-METAL OXIDES
  • CARBONATE-BUFFERED SOLUTION
  • EDGE STRUCTURES
  • PHOTOELECTRON-SPECTROSCOPY
  • FRACTURED PYRITE
  • K-EDGE
  • SPECTRA
  • STATES
  • SULFUR
  • XPS

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