ALKALI-METAL CATALYSIS OF CARBOTHERMIC REDUCTION OF ILMENITE

The selective reduction in the solid state of iron oxide in synthetic ilmenite (FeTiO3) by graphite with and without catalysts was investigated in the temperature range 850-1200 degrees C with the use of thermogravimetric analysis. Experiments were carried out under argon atmosphere and the isothermal weight loss of samples was determined as a function of time. In uncatalysed reduction the reaction was observed to start at 860 degrees C at the contact points between reactants. Above this temperature a faster rate of reaction was observed, which was attributed to a change of mechanism to the gaseous reduction of ilmenite by regenerated CO. The catalytic effects of alkali carbonates (Cs2CO3, K2CO3, Li2CO3, Na2CO3 and Rb2CO3) on reduction were determined. The reduction data were plotted on graphs of fractional reduction versus time; the plots are sigmoidal and exhibit induction, acceleratory and decay regions. Akinetic model that: was developed on the basis of a carbon solution-loss reaction (Boudouard reaction) as the rate-controlling step was found to represent the reduction data fairly well. The addition of catalyst improves the overall rate and extent of reduction. In the presence of catalysts-despite same enhancement of the rate-the Boudouard reaction continues to dominate the overall process. For the uncatalysed process the activation energy was found to be 78-84 kcay/mole in the temperature range 1050-1150 degrees C, and for processes catalysed by Cs2CO3, Rb2CO3, Li2CO3, K2CO3 and Na2CO3 the activation energy values were 41.5, 48.6, 57.3, 57.7 and 68.2 kcal/mole, respectively. The mechanism of catalysis by Li2CO3 seems to differ from that associated with the other carbonates.