International Journal of Hydrogen Energy, Vol.44, No.50, 27615-27625, 2019
The effect of H-2 pressure on the reduction kinetics of hematite at low temperatures
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 degrees C and at H-2 pressures of 3, 6 and 8 MPa, respectively. Complementary experiments were performed in an open system at atmospheric H-2 pressure and 270 degrees 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 consec- utively in open systems (p(H-2) approximate to 0.1 MPa), in closed systems at elevated H-2 pressure both reduction products are observed simultaneously. At 200 degrees C the reaction rates are about one order of magnitude lower than at 270 degrees 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(H-2) from 3 to 6 MPa and by 2.0 between 6 and 8 MPa. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.