Reduction Kinetics of Natural Ilmenite Ore with Carbon Monoxide

Abstract

In order to elucidate the reduction kinetics and mechanism of natural ilmenite ore with carbon monoxide, reduction experiments have been carried out using thermogravimetric technique in the temperature range between 1173 and 1323 K with three kinds of natural ilmenite ores from Australia, Malaysia and China. The reduction rate was analyzed in terms of the mixed-control kinetics by applying a shrinking unreacted-core model, on the basis of the observation of cross section of partially reduced ilmenite and X-ray diffraction patterns. The determined reaction rate constant k_c and effective diffusivity D_e are expressed in the temperature range between 1173 and 1323 K by the following equations: k_c/m·s^-1&=exp{-113×10^3/(RT)+5.03} (Australian)
k_c/m·s^-1&=exp{-47.0×10^3/(RT)-3.04} (Malaysian)
k_c/m·s^-1&=exp{-71.6×10^3/(RT)+0.554} (Chinese)
D_e/m^2·s^-1&=exp(-4250/T-7.54) (Australian)
D_e/m^2·s^-1&=exp(-3860/T-7.94) (Chinese) where R: gas constant (J·mol⁻¹·K⁻¹), T: temperature (K). The activation energy of the reaction is 113, 47.0, 71.6 kJ·mol⁻¹ for Australian, Malaysian and Chinese natural ilmenite ore, respectively. The calculated reduction curves using the rate parameters reproduced the experimental data well. The reduction rate increases with increasing reduction temperature. With respect to the rate-determining step for Australian and Chinese ilmenite ores, the relative contribution of resistance of a mass transfer step through gas film is smaller than that for synthetic ilmenite, while the relative contribution of resistance of a diffusion step of carbon monoxide through pores of the product layer is larger than that for synthetic ilmenite. As for Malaysian ilmenite ore, the overall rate is mainly controlled by a chemical reaction step.