High carbon ferro-chromium by self-reducing process: Fundamentals

Fe-Cr-C production is a very high electrical energy consuming process. When self-reducing agglomerates are used, it is expected to reduce up to 10% of this electrical energy. This paper presents the fundamental aspects of the reactions involved for reduction of chromites from 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 by fluxing agents, coke ash, silica, binder and only dissolution of 5% of the gangue from the chromite. This concept is important since the gangue of chromite is composed mainly of refractory oxides (MgO+ Al₂O₃), which are difficult to dissolve into slag. The effects of "initial slag" composition, one with low liquidus temperature (~1700K) and other with high liquidus temperature (~1750K) were investigated. The mixture was pelletized, dried and submitted to a temperature of 1773K until completion of the reaction. The reaction fraction as a function of time was determined. The results show that pellets containing components with liquid slag phase formed at higher temperature presented significant better reduction behavior than pellet with the liquid slag phase formed at lower temperature. The scanning electron microscopy analysis showed that a liquid phase was formed but the pellet did not collapse and indicated that the coalescence of the metallic phase depends on the dissolution of the pre-reduced particles of the chromite into slag.