Kinetics of reduction of ferric iron in Fe 2 O 3 -CaO-SiO 2 -Al 2 O 3 slags under argon, CO-CO 2 , or H 2 -H 2 O
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INTRODUCTION
THERE have been numerous studies of the kinetics of gas-slag reactions involving reactive gases such as CO and CO2.[1] Most previous studies were conducted with fairly reduced slags with oxygen potentials close to the values required for the formation of metallic iron. However, very little has been published for less-reduced or oxidized slags, particularly slags of low iron oxide content. New bathsmelting processes for iron ore commonly use slags of low iron oxide content and may involve gas-slag reactions with the slag being less reduced or even oxidized locally when a feed rich in Fe2O3 is used. In view of growing interest in new bath-smelting processes, the present study aimed to fill this “knowledge gap.” The behavior of the oxidized slags (high in ferric-toferrous ratios) in gas-slag reactions differs from that of the more-reduced slags. For example, when an oxidized slag is exposed to argon, the dissociation of ferric oxide, 2(Fe2O3)slag ⫽ 4(FeO)slag ⫹ O2
[1]
may take place spontaneously. This reaction is commonly referred to as evolution of oxygen, since the oxygen is released from the slag not due to reducing gases, but due
D. XIE, Senior Research Scientyist, is with CSIRO Division of Minerals, Clayton South, Victoria 3169, Australia. Contact e-mail: dongsheng.xie@ csiro.au G.R. BELTON, former Scientific Director, Metallurgy, BHP Research, Newcastle Laboratories, Wallsend, NSW 2287, Australia, and former Conjoint Professor, Department of Chemical Engineering, University of Newcastle, Callaghan, NSW 2308, Australia, is deceased. This article is based on a presentation made in the “Geoffrey Belton Memorial Symposium” held in January 2000, in Sydney, Australia, under the joint sponsorship of ISS and TMS. The original symposium appeared in the October 2000 Vol. 31B issue. METALLURGICAL AND MATERIALS TRANSACTIONS B
to the existence of an oxygen-potential gradient between the slag and the gas. As such, this reaction is of fundamental importance for oxidized slags and serves as a background reaction for redox reactions involving reactive gases. The possible involvement of oxygen evolution in redox reactions was first noticed by Kukhtin and Smirnov[2,3] in their studies on the reduction of Fe2O3 in a 40CaO-40SiO220Al2O3 (by weight) slag by 4 to 50 pct CO-Ar at around 1400 °C. They found that the reaction rates were linearly dependent on pCO. However, extrapolation of the observed rates to pCO ⫽ 0 did not pass through the origin, suggesting continued reduction in argon. These predicted reduction rates under argon were attributed to the dissociation of Fe2O3 under argon. However, no measurement was made of the rate of this reaction. Oxygen evolution from oxidized slags was also observed in a recent study on the rates of dissolution of Fe2O3 and FeO pellets into a 40CaO-40SiO2-20Al2O3 (wt pct) slag at 1450 °C by Ozturk and Fruehan.[4] For a slag bath with no external stirring, the rates of dissolution of Fe2O3 pellets were found to be faster than those of FeO pellets due to the oxygen evolution, whi
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