In situ synchrotron X-ray diffraction studies of the high-temperature hydrogen reduction of New Zealand titanomagnetite ironsand

Abstract

To characterise the hydrogen fluidised bed reduction of New Zealand titanomagnetite ironsand, this study reports the hydrogen reduction behaviour in situ via synchrotron X-ray diffraction at 938 °C. Titanomagnetite is directly compared with a synthetic magnetite. The crystalline phase evolution and changes in lattice parameter confirm that Ti significantly alters the reduction pathway at high temperature, following a 5-stage reduction process. Stabilisation of Fe_(3−x)Ti_xO₄ (inverse spinel) by Ti results in two distinct reduction pathways that favour reduction of low Ti content crystallites. First, reduction of inverse spinel via wüstite results in the exsolution of an amorphous Ti rich oxide phase. This reaction halts as FeO is metallised, causing a plateau in the net lattice parameter of Fe_(3−x)Ti_xO₄. A transition to the accumulation of Ti during direct reduction of the remaining inverse spinel is followed by conversion to ilmenite and pseudobrookite phases. Lower Ti content inverse spinel reduces first throughout the entire reduction process, emphasising the significant stabilising effect of Ti content.