Coupled experimental and thermodynamic modeling studies for metallurgical smelting and coal combustion slag systems
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I. INTRODUCTION
THE chemistry of a large variety of slags and sinters in different metallurgical smelting processes can be represented by the PbO-ZnO-Al2O3-FeO-Fe2O3-CaO-SiO2 system. The major components of coal ash slags produced in power generation plants can be described by the FeO-Fe2O3-CaO-SiO2Al2O3 system. Despite the importance of these seven- and five-component systems, the phase equilibria and thermodynamics are not well described, even in the lower order subsystems. Reliable characterization of these systems is necessary to optimize and improve the control of bath fluxing and operating temperatures, avoid slagging and fouling during coal combustion, reduce operating costs, and develop novel commercial pyrometallurgical extraction processes. The experimental difficulties associated with high-temperature equilibration of these melts appear to be the principal reasons for this lack of information on phase equilibria and thermodynamic properties. To address this issue, an extensive research program, aimed at the characterization of phase equilibria and thermodynamic properties of the metallurgical and power generation commercial slags, was undertaken over a period of several years. The research approach combines experimental E. JAK, Senior Research Fellow, B. ZHAO, Postdoctoral Research Fellow, and P.C. HAYES, Associate Professor, are with the Department of Mining, Minerals and Materials Engineering, The University of Queensland, St Lucia, Queensland, 4072, Australia. S. DEGTEROV, Senior Research Scientist, and A.D. PELTON, Professor, are with the Centre for Research in Computational Thermochemistry, Ecole Polytechnique de Montreal, Montreal, PQ, Canada H3C 3A7. This article is based on a presentation made at “The Milton Blander Symposium on Thermodynamic Predictions and Applications” at the TMS Annual Meeting in San Diego, California, on March 1–2, 1999, under the auspices of the TMS Extraction and Processing Division and the ASM Thermodynamics and Phase Equilibrium Committee. METALLURGICAL AND MATERIALS TRANSACTIONS B
investigations with computer-aided thermodynamic modeling. This approach has enabled the phase relations and thermodynamic properties to be characterized over the wide range of compositions, temperatures, and oxygen pressures of importance to metallurgical and power generation production.
II. RESEARCH METHODOLOGY A. Experimental Method The experimental technique used involved the preparation of a synthetic slag of predetermined composition. The slag was equilibrated at a fixed temperature in a controlled gas atmosphere and quenched. On rapid cooling, the silica-containing liquid phase converts to glass so that the phase assemblage that exists at a high temperature is “frozen.” The compositions of the solid and liquid phases were then measured by electron-probe X-ray microanalysis (EPMA). The details of the experimental method have been described in a number of publications by the authors.[1–10] An important advantage of this technique is the elimination of the inaccuracies associated with s
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