Kinetics of solid state silica fluxed reduction of chromite with coal

Solid state reduction of an Australian chromite with black coal and silica addition was studied thermogravimetrically in the temperature range 1000-1400 degreesC under an argon atmosphere. Reduction was found to occur in two stages. In the first stage, reduction is initiated by the nucleation of metallic iron, and the rate is likely to be controlled by the diffusion of cations in the outer zone of the chromite particles. The Zhuravlev-Lesokhin-Tempel'man equation was determined to fit closest to the experimental data, giving an activation energy of 194 kJ mol(-1). The second stage involves the reduction of chromium, iron, and some silicon ions through the slag. The rate of reduction is proposed to be controlled by dissolution of the chromite into the slag with an activation energy of 256 kJ mol(-1). Silica addition was found to enhance significantly the rate and degree of reduction at 1300 and 1400 degreesC. I&S/1424 (C) 2000 IoM Communications Ltd.