Impact of H₂-enrichment and ore mineralogy on the reduction of varying iron ores in suspension smelting ironmaking

Abstract

Due to the high temperatures present in the HIsarna® process (∼1773 K), the two reaction mechanisms thermal decomposition and gas reduction occur simultaneously during the pre-reduction of the injected iron ore fines. The objective of this study is to investigate the impact of H₂-enrichment in HIsarna reducing gas atmospheres on the pre-reduction of iron ores. Therefore, several iron ores, named OreA, OreB and OreC, with increasing amounts of goethite, were reduced by gas mixtures of H₂-CO-CO₂-Ar in a thermogravimetric analyser (TGA). A first approach studied the gas reduction as isolated process in isothermal conditions, whereas the second, non-isothermal approach, investigated thermal decomposition and gas reduction occurring simultaneously. In isothermal conditions the increase of H₂ in the atmosphere leads to an increase in conversion to wustite, and also to an increase in reaction speed. At 7.5 % H₂ in the atmosphere, the reaction saturates after 502–794 s, at 22.5 % H₂ after 375–583 s and at 37.5 % H₂ after 206–297 s, depending on the temperature. The reaction is controlled by the diffusion of the reducing gas through the developing product layer and the calculated activation energy is 77.60, 69.12 and 79.91 kJ/mol for H₂-contents of 7.5 %, 22.5 % and 37.5 %, respectively. In non-isothermal conditions, the influence of ore mineralogy is more significant compared to the H₂ increase in the atmosphere. An increase in total conversion is observed with an increase in goethite content in the ores.