Reduction of FeO in smelting slags by solid carbon: Re-examination of the influence of the gas-carbon reaction
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[1]
(FeO) 1 CO 5 CO2 1 Fe
[2]
CO2 1 C 5 2CO
[3]
Sarma et al. list the most likely rate-limiting steps as the following: (1) diffusion of FeO from the bulk slag to the slag-gas interface; (2) chemical reaction at the slag-gas interface; (3) diffusion of CO2 from the gas-slag interface to the gascarbon interface; and (4) chemical reaction at the gas-carbon interface. To establish the role of each of these steps in char-slag reduction kinetics, Sarma et al. carried out experiments at 1400 7C with a variety of carbonaceous materials under conditions where the geometry and chemistry of the reaction were well defined. The rate of mass transfer of FeO from the slag to the carbon was varied by changing the rotation speed of carbon rods in a slag contained in an [1]
S.R. STORY, formerly Graduate Student, Materials Science and Engineering Department, Carnegie Mellon University, is Research Scientist, BHP Laboratories, BHP Steel, Shortland, NSW 2307, Australia. B. SARMA, Development Associate, is with Applications Research and Development, Praxair Inc., Tarrytown, NY 10591. R.J. FRUEHAN and A.W. CRAMB, Professors, are with the Materials Science and Engineering Department, Carnegie Mellon University, Pittsburgh, PA 15213. G.R. BELTON, Chief Scientist, is with BHP Laboratories, BHP Steel, Shortland, NSW 2307, Australia. Manuscript submitted June 9, 1997. METALLURGICAL AND MATERIALS TRANSACTIONS B
alumina crucible. In addition, the reaction between horizontal carbon surfaces and molten slag was observed extensively using X-ray fluoroscopy. By varying the rate of liquid phase mass transfer in the rotating rod experiments, it was clearly demonstrated that liquid phase mass transfer to the gas-slag interface can have a significant effect on the observed rates. Also, comparison of measured rates with those of other studies specifically directed at the slag-gas reaction revealed that this reaction may limit the rates when transport rates of FeO in the slag are high. Simple calculations showed that the gas diffusion (step 3) will have a minor effect on the observed rate. For the previous analysis by Sarma et al.,[1] to evaluate the influence of the gas-carbon reaction, the kinetic data of Gulbrannsen et al.[4] were extrapolated from experiments which had originally been carried out at lower temperatures and reduced CO2 partial pressures. From these data, it was concluded that the gas-carbon reaction probably has only a minor effect on the overall reduction rate. However, in spite of this conclusion, during the course of the experiments, some differences were noted in the measured rates between the various carbonaceous materials (graphite, coke, and coal char). Also, Belton and Fruehan[5] have suggested that the gas-carbon reaction may play an important role in establishing the overall rate of the carbon-slag reaction. The kinetics of carbon oxidation by CO2 and H2O have recently been examined, and the details of the experiments and results are given elsewhere.[3] The experiments were carried out at temperatures (1300 7C to 1500
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