Fundamental investigations of differences in bonding mechanisms in iron ore sinter formed from magnetite concentrates and hematite ores

Abstract

Whilst increasing amounts of imported hematite ores are being added with the magnetite concentrates that dominate sinter blends in the People's Republic of China, little is known about the fundamental behaviour of magnetite concentrates during sintering compared to hematite ores. Compacted tablets of fluxed magnetite, magnetite–hematite and hematite concentrates and ores were fired under simulated sintering conditions in the laboratory to establish the fundamental differences in sintering behaviour, mineralogy and bonding mechanisms between magnetite concentrates and hematite ores. Sinter made from magnetite concentrates (<10% hematite) relies on the formation of a network of fused magnetite–magnetite grains (diffusional bonding) and high temperatures (1350–1370 °C) to obtain satisfactory sinter tumble strength. Magnetite–hematite concentrate mixtures, with <45% hematite, behave during sintering like magnetite concentrates. The large phase field for Magnetite+Liquid under typical sintering compositions and temperatures was found to prevent all but minor formation of Ca-ferrites via hematite from low-basicity (<2.0) sinter blends dominated by magnetite concentrates. In contrast, hematite ores with high (>2.0) effective basicity are able to form a high tumble strength sinter matrix composed of a network of abundant calcium ferrites (e.g. SFCA, SFCA I) below 1300 °C.