The effect of H2 pressure on the reduction kinetics of hematite at low temperatures

Abstract

Two novel experimental approaches to study the reduction kinetics of hematite (Fe2O3) by hydrogen at low temperatures are presented. Experiments were carried out in batch reactors at 200 °C and at H2 pressures of 3, 6 and 8 MPa, respectively. Complementary experiments were performed in an open system at atmospheric H2 pressure and 270 °C. Here the reaction product water in the effluent gas was quantified in short intervals by gas chromatography (Thermal Conductivity Detector; TCD). The mineralogical changes over time were assessed by X-ray powder diffraction with Rietveld analysis, scanning electron microscopy and the measurement of magnetic hysteresis loops.While the phase conversions of hematite → magnetite → Fe(0) are occurring consecutively in open systems (p(H2)≈0.1 MPa), in closed systems at elevated H2 pressure both reduction products are observed simultaneously. At 200 °C the reaction rates are about one order of magnitude lower than at 270 °C. The conversion rate of magnetite → Fe(0) is highly sensitive to the hydrogen pressure with a rate increase by a factor of 2.5 upon an increase of p(H2) from 3 to 6 MPa and by 2.0 between 6 and 8 MPa.