Subsolidus Phase Equilibria of the Fe-Ni-O System
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UCTION
THE ternary Fe-Ni-O, quaternary Fe-Ni-X-O, and Fe-Ni-X-Si-O (X=Mg, Al, Cr) systems have great importance in the production of nickel metal, nickel alloys, high-temperature steels, and corrosion-resistant steels. For example, in the case of nickel metal production from nickel laterite ores through the Caron[1] process, the ores are processed through reduction roasting followed by ammoniacal leaching. The resulting liquor is refined and subsequently precipitated to form an intermediate product before final gaseous reduction to nickel metal products. The reduction roasting process is carried out at a temperature of approximately 750 °C; however, the ores are also exposed to higher temperatures (in excess of 1200 °C), e.g., when the ores are in the vicinity of the burner flame. The nickel laterite ore itself contains two principal types of material, limonitic (oxides/hydroxides) ore, where the major component is Fe with other minor elements such as Ni, Mg, Al, Cr, and Si; and saprolitic (silicates) ore with Mg and Si as the major elements and Ni, Fe, Al, and Cr as the minor elements.[2,3] Therefore, detailed thermodynamic information on the phase equilibria in the Fe-Ni-X-O and Fe-Ni-X-Si-O (X=Mg, Al, Cr) systems, including the information on the nickel distribution between the phases present, is M.A. RHAMDHANI, formerly with the Pyrometallurgy Research Centre, The University of Queensland, is Lecturer, Faculty of Engineering and Industrial Sciences, Swinburne University of Technology, John St, Hawthorn, VIC 3122, Australia. Contact e-mail: [email protected] P.C. HAYES, Professor, and E. JAK, Associate Professor, are with the Pyrometallurgy Research Centre, School of Engineering, The University of Queensland, Brisbane, QLD 4072, Australia. Manuscript submitted May 11, 2008. Article published online September 23, 2008. 690—VOLUME 39B, OCTOBER 2008
vital for the control of the reduction roasting process and for achieving maximum nickel extraction. In particular, when a mixture of the two ore types are used in the process, the optimum conditions (e.g., temperature and effective oxygen partial pressure) for nickel extraction are different for the two materials. There are only limited data on the phase equilibria of the preceding systems, even in the lower order system, such as in Fe-Ni-O system, where a majority of the studies have only focused on the phase equilibria at 1000 °C. In this article, experimental studies on the phase equilibria of the Fe-Ni-O system in air and at various oxygen partial pressures are presented. The current work provides new phase equilibria data in the system and also provides the basis for further experimental studies and development of thermodynamic models of higher order complex, especially Fe-Ni-X-O (X=Mg, Al, Cr) systems, important to the improved extraction of Ni from nickel laterite ores. A. Previous Fe-Ni-O Phase Equilibria Studies The phase equilibria of the Fe-Ni-O have been extensively investigated.[4–21] Reviews of the Fe-Ni-O phase equilibria were reported by Raghavan[4] and
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