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Show INTRODUCTION Iron-bearing minerals (e.g., pyrite) have long been recognized as a major source of wall slagging. 1 Vhile ash particles, sampled in the furnace, show that pyrite is oxidized predominantly to magnetite (Fe304), deposit analysis shows the oxidation product to be hematite (Fe203). Furthermore, it is not obvious why iron oxide should deposit, since the melting points of both hematite and magnetite (1800 to 1900 K) are higher than typical peak gas temperatures in the furnace. This makes it necessary to understand the transformations of pyrite under combustion conditions, and to identify the iron species responsible for deposition. Drop-tube combustion studies,2-4 and experiments in entrained flow and particle jet smeltingS,6 systems have permitted observations to be made on the progress of decomposition of individual pyrite particles in controlled environments. Analysis of partially oxidized pyrite samples by advanced techniques such as Hossbauer spectroscopy,7 and particle temperature measurements by twocolor pyrometry,8,9 have been especially valuable in providing quantitative information on the amount of iron distributed in the various phases and in determining the thermal history of the particles during combustion. In this study, the existing information base on the high temperature oxidation of liberated pyrite has been integrated into a unified model to describe the various stages during pyrite oxidation. The experimental results are compared with the developed model for predicting the rates of these transformations. Calculations predict that a melt phase exists in the particle during the course of its combustion, and solidification occurs only upon completion of the oxidation reaction. To test this hypothesis, deposition tests were carried out to determine sticking coefficients of pyrite particles as a function of residence time available for combustion. In another set of experiments, the particle size evolution was determined in an entrained flow reactor. The morphology and structure of the particles at increasing levels 2 |