Interaction of magnesia-carbon refractory with ferrous oxide under flash ironmaking conditions

Abstract

A novel flash ironmaking technology (FIT) that greatly reduces energy consumption and greenhouse gas emissions compared with blast furnace (BF) ironmaking has been developed at the University of Utah. In this technology, a falling stream of iron ore concentrate is directly converted to metallic iron by reducing gases such as hydrogen, natural gas or coal gas in a flash furnace. In this work, the interaction of magnesia-carbon (MgO–C) refractory with ferrous oxide (FeO) under the conditions of the novel FIT has been investigated. Oxidation of carbon from the MgO–C refractory occurred and magnesiowustite (MgxFe1-xO) solid solution was formed as a result of the interaction between magnesia (MgO) in the refractory and ferrous oxide (FeO). A solid-state diffusion based kinetics model was developed to describe the growth of the magnesiowustite (MgxFe1-xO) formed. Experiments were carried out with ferrous oxide (FeO) and MgO–C refractory in the temperature range 1200–1400 °C under flash ironmaking atmospheres. Reacted samples from FeO–MgO–C experiments were analyzed using Scanning Electron Microscopy-Energy Dispersive X-Ray spectroscopy (SEM-EDX) and Electron Probe Micro-Analyzer (EPMA) and the formation of the magnesiowustite solid solution under flash ironmaking conditions was confirmed. Using the kinetics model and the composition profiles determined with EPMA, the values of interdiffusion coefficient (DFe−Mg) were determined as a function of the magnesiowustite composition. Also, an average value of the interdiffusion coefficient (D‾Fe−Mg) was calculated such that it reasonably reproduced the concentration profile of the cations over the entire composition range. The values of D‾Fe−Mg calculated in this work agreed closely with those obtained independently from experiments on the interaction between MgO–C and metallic Fe, thereby validating the interaction mechanism and the proposed kinetics model. The solid-state diffusion was a thermally activated process and the activation energy (Ea) for D‾Fe−Mg was calculated as 398 kJ/mol.