Chromites reduction reaction mechanisms in carbon-chromites composite agglomerates at 1773K

Abstract

Fe-Cr-C production is a very high electrical energy consuming process. When self-reducing agglomerates are used, it is expected to decrease up to 10% of this electrical energy. This paper presents the fundamental aspects of the reactions involved in reduction of chromites by use of self-reducing agglomerates. Brazilian chromite containing 41.2% Cr2O3 was mixed with petroleum coke and agglomerated with cement as the binder. The concept of "initial slag" was introduced and it was assumed that this "initial slag" is formed of fluxing agents, coke ash, silica formed, binder and dissolution of only 5% of the gangue from the chromite. This concept is important since the gangue of chromite is composed mainly by refractory oxides (MgO+Al2O3), which are difficult to dissolve into slag. The effects of "initial slag" composition, one with low liquidus temperature (∼1700 K) and the other with high liquidus temperature (∼1 750K) were investigated. The mixture was pelletized, dried and submitted at the temperature of 1 773 K until completion of the reactions and also the fractional reaction as a function of time was determined. The results showed that the pellets in which liquid slag phase was formed at high temperature presented significant better reduction behavior than the pellets in which the liquid slag phase was formed at low temperature. The microscopic analysis showed that a liquid phase was formed but the pellet did not collapse, and indicated that the coalescence of the metallic phase depended on the dissolution of the pre-reduced particles of the chromite into slag. © 2007 ISIJ.