Thermal decomposition and pre-reduction of goethitic iron ore fines and their effects on phase transformation and material properties

Abstract During high-temperature in-flight flash reduction of iron ores, goethitic particles undergo rapid structural changes. This study examines the influence of goethite on pre-reduction performance in a drop-tube furnace, focusing on the hematite to magnetite reduction step. Three iron ores (OreA, OreB, and OreC) with distinct mineralogical and physical characteristics were reduced in N 2 and atmospheres containing 95 % CO 2 with 5 % CO or H 2 at temperatures between 1658 and 1760 K. Compared to ores containing hematite as the sole iron-bearing phase, goethite-containing ores exhibit enhanced cracking and fragmentation during thermal decomposition, leading to changes in particle size and density. A comparison of OreB (lower goethite) and OreC (higher goethite) shows that the importance of particle residence time increases with goethite content. Higher pre-reduction was achieved at 80 ms for OreB and at 430 ms for OreC during thermal decomposition. Despite the use of reducing gases, reduction beyond magnetite was not observed due to large particle sizes (> 100 µm) and residence-time limitations of the drop-tube furnace. Further reduction (Fe 3 O 4 → FeO) was assessed using thermogravimetric analysis. Across both experimental set-ups, thermal decomposition has a higher impact on the total reduction than the gas reduction. EBSD analysis identified two reaction mechanisms, internal pore diffusion and surface product layer diffusion. Balanced mineralogical properties (as in OreB) were found to be critical for effective early stage in-flight flash reduction.