Kinetics in reduction of synthetic ilmenite with carbon monoxide

In order to elucidate the kinetics and mechanism of synthetic ilmenite reduction with carbon monoxide, reduction experiments were carried out using thermogravimetric technique in the temperature range between 1173 and 1373 K. The reduction rate was analyzed in terms of the mixed-control kinetics by applying the isothermal shrinking unreacted-core model, on the basis of the observation of cross section of the partially reduced ilmenite and reduction reaction path in the Ti-Fe-O ternary phase diagram. Reaction rate constant k_c and effective diffusivity D_e determined are expressed by the following equations: k_c/m·s^-1=exp {-129.9×10³/(RT)+7.149}, D_e/m²·s^-1=exp (-4331/T-6.158), where R: gas constant (J·mol^-1·K^-1), T: temperature (K). The activation energy of the reaction was 130 kJ· mol^-1. The calculated reduction curves using the rate parameters finely reproduced the experimental data. The reduction rate increases as the reduction temperature increases. In the initial stage of reduction, the overall rate is controlled by a mass transfer step through the gas film and a chemical reaction step, while in the final stage both the diffusion step of carbon monoxide through pores of the product layer (Fe+TiO₂) and the chemical reaction sten determine the overall reaction rate.