Reduction of FeO in smelting slags by solid carbon: Experimental results
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INTRODUCTION
IN the new genre of bath smelting processes, the production of iron is achieved by the reduction of an iron oxide containing slag by coal char and carbon dissolved in molten iron. v,2,31 The kinetics of the reducing reactions are a possible limiting factor to the production capacity of these processes. Smelting slags contain low levels of FeO provided there is ample interfacial area for reduction. The relationship between the ore feed rate and the reaction of coal char with slag is a critical aspect of the smelting process. The slag-coal char reaction can be responsible for half of the hot metal production rate. The fundamental aspects of this reaction are a key to understanding the reduction kinetics and the production capacity of the bath smelting process. A survey of the existing literature on the reduction rates and the mechanism of this reaction indicates that few conclusive studies have been conducted for slags containing less than 10 wt pct FeO. Problems of slag containment and difficulties in the interpretation of experimental data for reactions involving the interaction of four phases are cited as possible reasons for the lack of extensive investigations. There are insufficient experimental data on the reaction rate between slags, containing 1 to 10 wt pct FeO, and solid
B. SARMA, formerly Graduate Student, Department of Metallurgical Engineering and Materials Science, Carnegie Mellon University, is Development Associate, Applications Research and Development, Praxair, Inc., Tarrytown, NY 10591. A.W. CRAMB and R.J. FRUEHAN, Professors, are with the Department of Metallurgical Engineering and Materials Science, Carnegie Mellon University, Pittsburgh, PA 15213. Manuscript submitted July 6, 1993. METALLURGICAL AND MATERIALS TRANSACTIONS B
carbon. The objectives of this study were to determine the kinetics and mechanism of this reaction. This article discusses the experimental results obtained for the reaction of carbonaceous materials such as graphite, coke, and coal char with liquid slags, containing 2 to 10 wt pct FeO, which are similar to those found in the bath smelting process.
A. Theory The overall reaction of an iron oxide containing slag with solid carbon is represented by Reaction [1]. (FeO)~ + (1 + x) C~s~ = [Fe - C J + C O ~
[1]
where (FeO) indicates that FeO is dissolved in the slag and [Fe-Cx] indicates that carbon is dissolved in the iron product which is an iron-carbon alloy of variable carbon content. Reaction [1] is a four-phase reaction, and after the reaction is initiated, a gas film separates the molten slag from the solid carbon.i6,8-1o.~31The reaction then proceeds with the aid of gaseous intermediates, via reactions involving three or less phases. The overall reaction is a combination of the following reactions which occur, at different interfaces, in a sequential manner. (FeO).~ + CO~ = F%~ + CO2~,
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