Reaction kinetics of direct reduction of mineral iron carbonate with hydrogen: Determination of the kinetic triplet

Direct reduction of mineral iron carbonate with hydrogen is a CO2-lean technology for the production of elemental iron from iron carbonate ore. In this study, the reaction me-chanism and reaction kinetics were investigated by thermogravimetric analysis and in a fixed-bed tubular reactor. The degree of metallization increases with increasing tem-perature from 773 to 1023 K. At 1023 K, the degree of metallization is 93 wt%, with the remaining iron species being wustite. The reduction proceeds via two reaction pathways: calcination of iron carbonate to wustite with consecutive reduction of wustite to ele-mental iron and direct reduction of iron carbonate to elemental iron. The reaction steps occur simultaneously. During the first hour of reaction, which corresponds to the heat-up phase, calcination of iron carbonate to wustite adopts the dominant reaction path. Then wustite reduction and direct iron carbonate reduction with hydrogen to elemental iron, become dominant, facilitated by the increasing porosity of the ore due to the release of CO2. Towards the end of the reduction process the remaining wustite is reduced to ele-mental iron. The kinetic triplet - solid phase reaction kinetic model, activation energy and frequency factor - was determined for each reaction step. The reaction kinetics can be described by a combination of an Avrami-Erofeyev model (A3 model for iron carbonate calcination to wustite), and reaction-order models (F2 model for the reduction of iron carbonate to elemental iron and F3 model for the reduction of wustite to elemental iron).(c) 2022 The Authors. Published by Elsevier Ltd on behalf of Institution of Chemical Engineers. This is an open access article under the CC BY license (http://creative-commons.org/licenses/by/4.0/).