The effect of additives on the reduction of chromite by graphite: An isothermal kinetic study
Mixtures of chromite, graphite and various additives were reacted isothermally under argon, and the loss in mass was recorded continuously. The additives used, SiO2, Al2O3, K2CO3, Na2O2 CaO, MgO, Fe and Cr, all influence the Boudouard reaction positively. Of these, only MgO and Al2O3 revealed an inhibiting effect during the carbothermic reduction of chromite. The X-ray diffraction peaks characteristic of the additives decreased in intensity during reduction, which could indicate that the additives reacted in some way. In most of the reduction products olivine (MgO · Al2O3), Fe, Fe3C and (Cr,Fe)7C3 could be identified. It appears as though MgO plays an inhibiting role in the decomposition of the chromite spinel. A decrease in the particle size of the chromite accelerated the reduction kinetics when CaO was used as additive, but no difference in the equilibrium conversion was observed. The activation energy of 192 kJ mol-1 for the reduction reaction without any additives is of the same order of magnitude as that measured by other authors. © 1988.