A study of the reduction of hematite to magnetite using a stabilized zirconia cell
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IN previous studies of the fluidized bed reduction of iron ore by hydrogen, Sheasby and Granden t made use of a stabilized zirconia cell (SZC) inserted in the bed to obtain qualitative information on the state of the reaction. In the laboratory fluidized bed the reaction was found to be naturally staged at temperatures above 650 ~ the reduction to Fe304 was complete before the formation of FeO. Similarly, iron formation did not occur until the Fe304 was fully reduced. Use was made of the SZC to facilitate the extraction from the bed of particles with specific degrees of reduction for morphological and porosity studies. 2 The present study extends the use of the SZC to the measurement of the kinetics of the first stage of the reduction reaction, i.e. the hematite-magnetite transformation. This was done by using the SZC to measure the oxygen potential (and hence hydrogen/water ratio) at eight locations above the distributor plate. The voltage-time relationships from the eight taps gave a clear picture of the progress of the reaction and one in which small changes in the efficiency of the reduction were readily apparent. There were several advantages to studying the reaction in this way compared to the more usual techniques in which a single, or small number, of specimens are reduced in an excess of gas. In the course of a single fluidized bed reduction a full matrix of reaction conditions was achieved. Particles from hematite through to magnetite were exposed to pure hydrogen close to the distributor, changing to the equilibrium hydrogen/water mixture higher in the bed. Further, ore particles were M. V. SRINIVASAN is with The Algoma Steel Corp. Ltd., Saulte Ste. Marie, Ontario, Canada. J. S. SHEASBY is on the Faculty of Engineering Science, The University of Western Ontario, London, Ontario, Canada NGA 5B9 Manuscript submitted February 28, 1980.
extracted from the bed throughout the reduction for morphological analysis. This represents a considerable saving in time over methods in which separate experiments are required for each H2/H20 mixture, and additional experiments for each specimen for morphological analysis. A further advantage of the fluidized bed is that the time for a given stage of the reaction can be extended without changing the local reaction rate by increasing the quanitity of ore in the bed. This is of particular value in the initial stages of a reaction which can be too brief to be studied by gravimetric techniques. The hematite to magetite reaction has received considerable atention being well suited to fundamental studies 3-7 and also of practical importance in iron making. This is because the porosity formed during reduction to magnetite is retained in the subsequent reduction of wustite 8.9 and thus influences the rate of the final reduction to iron. The reduction of dense hematite particles by hydrogen is of the class of reactions known as unreacted-core shrinking model which has been considered in detail by Wen ~~and by Spitzer, Manning and Philbrook. ~ Following the latter workers the rate o
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