Interaction of ferrous oxide with alumina refractory under flash ironmaking conditions

A novel flash ironmaking technology (FIT) has been developed at the University of Utah based on the direct reduction of iron ore concentrate by a reducing gas such as hydrogen, natural gas, coal gas or a mixture thereof. In this work, the interaction of ferrous oxide (FeO) with alumina (Al2O3) refractory under flash ironmaking conditions has been studied. A thermodynamic basis for the interaction process has been developed by considering the Fe-Al-O system and a kinetic model based on solid-state diffusion is formulated to describe the growth of the hercynite (FeAl2O4) spinel formed as a result of the interaction between FeO and Al2O3. Experiments were conducted with FeO powders and pure Al2O3 refractory in the temperature range 1200-1400 degrees C under gas atmospheres relevant to FIT. The analyses of reacted samples using XRD, SEM-EDX and EPMA techniques confirmed the formation of the hercynite (FeAl2O4) spinel under FIT conditions and results showed that the proposed kinetic model appropriately describes the growth of the hercynite spinel layer, which obeyed the parabolic rate law at all the three temperatures. Furthermore, using the kinetic model, expressions for the parabolic rate-constants (k(1)) and the effective diffusivity ((D-eff) over bar) were obtained and their respective values at the experimental temperatures were determined. The values of (D-eff) over bar calculated in this study agreed closely with those obtained independently by the authors from experiments on Fe-Al2O3 interaction thereby corroborating the interaction mechanism and the associated reaction scheme. The solid-state diffusion was temperature-dependent, with an activation energy value of 268 kJ/mol.