Kinetics of CO-CO 2 reaction with CaO-SiO 2 -FeOx melts
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INTRODUCTION
with a much greater contact area with slag, compared to that of carbon particles. The latter mechanism has been proved by direct observations of reaction through slag, by methods such as X-ray fluoroscopy.[8–15] Having considered the role of intermediate gas layer, separating FeOx containing slag from carbon bearing particles or droplets, there is general agreement[13–18] that the overall reaction involves the following individual steps in sequence:
THE reaction of iron oxide dissolved in liquid slag with solid carbon or carbon from a metal bath has been paid considerable attention for its application in various metallurgical processes. In the new generation of iron making processes, for example, Corex and AISI, iron is produced by reduction of iron oxide in slag and carbon, both in solid form and dissolved in the iron bath. Modern electric arc furnaces employ the reaction to induce slag foaming, thereby increasing efficiency of the furnace.[1,2,3] With a different purpose, iron oxide is reduced by injected carbon in the “slag cleaning” stage of copper making processes. By this means, reduction of magnetite in the slag lowers the slag viscosity, and consequently, physical entrapment of copper matte in the slag is reduced.[4,5] Driven by such important applications, many studies have been carried out on the reduction of iron oxide in the liquid state by carbon. Depending on the initial and final oxidation state of iron, the overall reaction can be expressed as
(3) diffusion of CO2 away from the slag-gas interface toward the gas-carbon interface; (4) chemical reaction at the carbon-gas interface,
Fe2O3 C(C) 2FeO CO
CO2 C 2CO
[1]
[2]
There is a general agreement that the reaction initiates by direct contact of carbon and slag. However, the role of generated CO in the continuation of reaction has been a matter of argument for years. In their study of the rate of FeO reduction, Sugata et al.[6] concluded that the reaction proceeds mainly by direct contact between carbon and the slag. This conclusion has been confirmed by Bafghi et al.[7] who studied the kinetics of FeO reduction by graphite, while simultaneously removing CO by vacuum. On the other hand, it has been argued by Davies et al.[8] that the reaction area between carbon and slag is not large enough to offer significant reaction rate compared to the measured rates for the reaction. The suggested alternate reaction mechanism is generation and maintenance of a gas layer, composed of mainly CO and CO2 around carbon particles. The continuation of reaction may occur by CO reduction, MANSOOR BARATI, Doctoral Student, and KENNETH S. COLEY, Associate Professor, are with the Department of Materials Science and Engineering, McMaster University, Hamilton, ON, Canada L8S 4L7. Contact e-mail: [email protected] Manuscript submitted June 1, 2004. METALLURGICAL AND MATERIALS TRANSACTIONS B
(Fe2, O2 ) CO Fe CO2 3
2
(2Fe , 3O
) CO 2(Fe
2
2
,O
) CO2
[3] [4]
[5]
(5) diffusion of CO away from the gas-carbon interface to the
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