Experimental study of phase equilibria in the Al-Fe-Zn-O system in air
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1/1/04
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Experimental Study of Phase Equilibria in the Al-Fe-Zn-O System in Air ROBERT HANSSON, PETER C. HAYES, and EVGUENI JAK The phase equilibria in the Al-Fe-Zn-O system in the range 1250 °C to 1695 °C in air have been experimentally studied using equilibration and quenching techniques followed by electron probe X-ray microanalysis. The phase diagram of the binary Al2O3-ZnO system and isothermal sections of the Al2O3-“Fe2O3”-ZnO system at 1250 °C, 1400 °C, and 1550 °C have been constructed and reported for the first time. The extents of solid solutions in the corundum (Al,Fe)2O3, hematite (Fe,Al)2O3, Al2O3*Fe2O3 phase (Al,Fe)2O3, spinel (Al,Fe,Zn)O4, and zincite (Al,Zn,Fe)O primary phase fields have been measured. Corundum, hematite, and Al2O3*Fe2O3 phases dissolve less than 1 mol pct zinc oxide. The limiting compositions of Al2O3*Fe2O3 phase measured in this study at 1400 °C are slightly nonstoichiometric, containing more Al2O3 then previously reported. Spinel forms an extensive solid solution in the Al2O3-“Fe2O3”-ZnO system in air with increasing temperature. Zincite was found to dissolve up to 7 mole pct of aluminum in the presence of iron at 1550 °C in air. A meta-stable Al2O3-rich phase of the approximate composition Al8FeZnO14x was observed at all of the conditions investigated. Aluminum dissolved in the zincite in the presence of iron appears to suppress the transformation from a round to platelike morphology.
I. INTRODUCTION
THE Imperial Smelting Process (ISP) commercially achieves the extraction of zinc and lead from complex zinc/lead sulfide concentrates and secondary zinc containing materials. First, the material is sintered, resulting in oxidation of metal sulfides and the formation of agglomerated fine-grained primary and secondary feed. The oxidized sinter containing only trace amounts of sulfur is then charged together with coke into the Imperial Smelting Furnace (ISF). Numerous transformations of the sintered material including heating, softening, melting, and reduction occur in different parts of the ISF. The reduction of zinc/lead oxides in the sinter is more efficient if the material retains a high mechanical strength at the high temperatures in the shaft of the blast furnace.[1] The physical properties of the sintered material at high temperature are directly related to the presence and morphology of the zincite phase. Zincite, the main zinc-containing phase in the sinter, remains solid up to high temperatures during the reduction process in the ISF. Previous studies have indicated that the zincite phase can be present as rounded or platelike crystals.[2] Only rounded zincite has been observed during studies on the Fe-Zn-O system at metallic iron saturation.[3] Platelike zincite was found to form at temperatures between 1200 °C and 1300 °C in air.[4] The framework formed upon formation of platelike zincite crystals is found to give superior high-temperature softening characteristics.[5,6,7] The conditions for the formation of rounded and platelike zincite phase have yet
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