Reduction kinetics of MgO-doped calcium ferrites under CO-N2 atmosphere

The effect of magnesia on calcium ferrite (CaO center dot Fe2O3) reduction by CO was examined by isothermal thermogravimetry. Samples of calcium ferrite added with 0, 2, 4, and 8 wt.% magnesia (abbreviated as CF, CF2M, CF4M, and CF8M) were prepared. Phase composition was analyzed by X-ray diffraction, and the results indicated that CF2M and CF4M are reduced to lower reduction degree and with lower apparent activation energy than CF; and CF8M with more MgO center dot Fe2O3 is reduced to a lower degree and with more difficulty compared with CF. Reduction rate analysis revealed that CF, CF2M, CF4M, and CF8M reductions are all typical two-step reactions with the order of CF -> CWF (CaO center dot FeO center dot Fe2O3) -> Fe. The apparent reduction activation energies of CF, CF2M, CF4M, and CF8M are 46.89, 37.30, 17.30, and 29.20 kJ/mol, respectively. Sharp analysis depicted that CF2M, CF4M, and CF8M reductions are all described by 2D Avrami-Erofeev (A-E) equation (A(2)) in the whole process, while CF reduction is first expressed by A(2) and then by 3D A-E equation (A(3)). Different from shrinking core model, a new kinetic model for powdery samples reduction was proposed to illustrate the relationship among reduction rates, reduction routes, and model functions.