Experimental Study on the Phase Diagram of the Fe-O-S System
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INTRODUCTION
THE Fe-O-S system is important not only for many metallurgical processes, including primary steel and base metals production, but also in sulfide mineralogy.[1] In zinc sulfide roasting, the formation of the stable Fe-O-S melt has been suggested to cause problematic build-up of deposits and agglomeration.[2] In primary copper production from sulfide ores, the Fe-O-S system is the starting point to understand oxygen-sulfur interaction in all industrial sulfide mattes and represents the limiting case—zero-pct copper or nickel-matte.[3] Despite the important role of the system, the knowledge of the phase equilibria has been limited and still has high uncertainties. Information on the phase equilibria of the system is needed for achieving improvements of the current operations and the development of new processes. Several studies on the phase equilibria in the Fe-O-S system at different temperatures and different experimental methods used were found in the open literature. The eutectic points of the Fe-O-S system at 1188 K (915 °C) and liquidus have been determined by Naldrett[4] in closed silica ampoules. Experiments under inert gas atmosphere in iron crucibles to establish the liquidus surface in equilibrium with metallic iron have been performed by Hilty and Crafts[5] and Ueda et al.[6] In both studies, the quenched samples were analyzed using bulk chemical analysis. Ueda et al.[6] also carried out experiments on the iron oxide equilibrium by equilibrating the sample in alumina crucible and measured the
HANNU JOHTO, Doctoral Candidate, and PEKKA TASKINEN, Professor, are with the Metallurgical Thermodynamics and Modelling Research Group, School of Chemical Technology, Aalto University, Espoo, Finland. Contact e-mail: hannu.johto@aalto.fi HECTOR M. HENAO, formerly with the PYROSEARCH, School of Chemical Engineering, The University of Queensland, Brisbane, QLD, Australia, is now Senior Research Fellow with The School of Mechanical and Mining Engineering, The University of Queensland, Brisbane, QLD, Australia. EVGUENI JAK, Professor, is with PYROSEARCH, School of Chemical Engineering, The University of Queensland. Manuscript submitted April 2, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS B
oxygen partial pressure above the sample during all the experiments with an oxygen-concentration cell. Under controlled oxygen pressure, compositions of liquid in iron and iron oxide saturation have been determined by chemical analysis in iron crucibles by Bog and Rosenqvist,[7] Hayashi and Iguci,[8] and Lee et al.[9] The results of other studies[7, 8] are in good agreement with the results of the studies of Hilty and Crafts,[5] but the compositions measured by Lee et al.[9] in the samples containing also silver show the iron–liquid region extending to higher sulfur contents than in the previous study,[5] when the influence of silver in the samples has assumed to be negligible. In the current study, the phase equilibria of the Fe-O-S system at selected temperatures have been determined using alternative, equilibration/quenchi
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