Kinetics of reduction of iron oxides by H2 -: Part I:: Low temperature reduction of hematite

This study deals with the reduction of Fe2O3 by H-2 in the temperature range of 220-680 degrees C. It aims to examine the rate controlling processes of Fe2O3 reduction by H-2 in the widest and lowest possible temperature range. This is to be related with efforts to decrease the emission of CO2 in the atmosphere thus decreasing its green house effect. Reduction of hematite to magnetite with H-2 is characterized by an apparent activation energy 'E-a' of 76 U/mol. E-a of the reduction of magnetite to iron is 88 and 39 kJ/mol for temperatures lower and higher than 420 degrees C, respectively. Mathematical modeling of experimental data suggests that the reaction rate is controlled by two- and three-dimensional growth of nuclei and by phase boundary reaction at temperatures lower and higher than 420 degrees C, respectively. Morphological study confirms the formation of compact iron layer generated during the reduction of Fe2O3 by H-2 at temperatures higher than 420 degrees C. It also shows the absence of such layer in case of using CO. It seems that the annealing of magnetite's defects around 420 degrees C is responsible for the decrease of E-a. The rate of reduction of iron oxide with hydrogen is systematically higher than that obtained by CO. (C) 2005 Elsevier B.V. All rights reserved.