Abstract for presentation at Chemeca 2007

The Mechanism of Pentlandite Oxidation under Isothermal Conditions

  • Dr Yung Ngothai, University of Adelaide, Australia
  • Fang Xia, University of Adelaide, Australia
  • Allan Pring, South Australian Museum, Australia
  • Dr Brian O'Neill, University of Adelaide, Australia
  • Joël Brugger, South Australian Museum, Australia
  • Guorong Chen, East China University, China
  • Dr Chris Colby, University of Adelaide, Australia

    • The oxidation of pentlandite was investigated isothermally under ambient pressure using the anneal-quench technique. The phase evolution during the oxidation was monitored by X-ray diffraction (XRD) and Rietveld quantitative phase analysis. The cross-sections of oxidized samples at different stages were analyzed by a scanning electron microscopy (SEM) with an energy dispersive X-ray analysis (EDX). The results suggest that the oxidation of pentlandite is a three steps process. The first step is fast, and involves the consumption of pentlandite and the evolution of intermediate phases, magnetite and Ni-rich pyrrhotite. The second step is slow, consisting of the transformation from magnetite to hematite and pyrrhotite to nickel sulfide. The third step the transformation from nickel sulfide to nickel oxide, which is very slow and rate limiting. The oxidation mechanism is independent on particle size, crucible material (quartz, zircon, alumina and platinum) and temperature (530-600°C). The results are compared with the non-isothermal studies of pentlandite oxidation in the literature. The magnetite phase was not reported in the most of the previous studies but was found in all experiments in the current study. This problem is discussed and is believed to be due to the effects of overlapping peaks in the XRD patterns. The sulfate products which are prevail in the non-isothermal studies were not found in this study.

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