Abstract for presentation at Chemeca 2005

Phase evolution during the oxidation of monosulfide solid solution under isothermal conditions

  • Mr Haipeng Wang, The University of Adelaide, Australia
  • Prof Allan Pring, South Australian Museum, Australia
  • Yung Ngothai, The University of Adelaide, Australia
  • A/Prof Brian O'Neill, The University of Adelaide, Australia

    • The oxidation of mss was investigated under isothermal condition in a dry air atmosphere. The oxidation products of mss vary in our tested samples depending on their stoichiometry. Apart from the common oxidation products hematite and trigonal nickel pyrrhotite (Ni17S18), mikasaite (Fe2(SO4)3) was observed during the oxidation of Fe7.9S8, and pentlandite for Fe6.15Ni1.54S8. Iron in mss was preferentially oxidized to hematite, leaving a nickel enriched pyrrhotite core. Nickel in the mss samples was less active than iron and eventually exist in the form of pure nickel pyrrhotite. For iron-nickel mss, X-ray diffraction evidences show that mss underwent gradually topotactic structure transformation from hexagonal (P6/mmc) to trigonal (P3 2) during the oxidation. The transformation was related to the enrichment of nickel in mss.
    This study also demonstrated that increasing sulphur content in mss accelerates the oxidation rate of mss. Also, the oxidation of mss samples showed a decrease in reaction rate as Ni: Fe atomic ratio decreased.

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