The integrated blast furnace and oxygen steelmaking (BF-OSM) route is still a dominant process for worldwide steel production, currently producing more than 60 % of the world's total output of crude steel. The counter-current principle on which the blast furnace operates makes it reliant heavily on the quality of its burden to maintain a sufficient level of gas permeability in its upper shaft and of liquid and gas permeability in its lower part. Iron ore sinter, constituting a major proportion of blast furnace burden in most countries, particularly in the Asia-Pacific region, is therefore expected to have a significant impact on blast furnace performance.The chemical composition of iron ore fines, together with the thermal conditions that sinter blends are subjected to, plays an important role in forming the primary melt during the sintering process and consequently determines the sinter structure and quality. Considerable emphasis has therefore been placed on the chemical composition and consistency of iron ore fines, particularly in terms of alumina content. However, due to the limited reserves and increasing depletion of high-grade iron ore resources, the alumina content of iron ores is expected to increase gradually. While the increase in such constituents is relatively slow over a long period, it has still caused problems for blast furnace operators.This paper attempts to clarify the role of different types of alumina present in iron ore fines and their effects on melt formation, sinter structure and sinter quality, as well as the sintering process itself. Mechanisms responsible for the deterioration of the low temperature reduction degradation characteristics (RDI) of sinter due to the increasing alumina content are also reviewed. In addition, potential measures to counter the adverse impacts of alumina on sintering performance of hematite iron ore fines are also discussed.KEY WORDS: High alumina iron ores; kaolinite; gibbsite; melt formation; sinter structure; sintering performance, sinter quality.ISIJ International, Vol. 47 (2007), No. 3, pp. 349-358 Review 349 © 2007 ISIJ alumino-silicates like kaolinite (Al 2 O 3 · 2SiO 2 · 2H 2 O), while the A type ores contain gibbsite (Al(OH) 3 ). 9) Extensive work has been conducted on the effects of alumina on sinter structure, quality and productivity. 1,2,[4][5][6][9][10][11][12][13][14] While the results are not conclusive and sometimes contradict each other, it is generally believed that too much alumina impairs the sinter quality, particularly the low temperature reduction degradation characteristics. However, much of the previous work showing the strong adverse effects of alumina on sinter quality and the sintering process has been focused mainly on Indian ores, 1,[4][5][6]9) which often belong to A type iron ores. Only limited work has been conducted on the majority of iron ores that contain alumina in the form of kaolinite. 2,10,12) From high temperature X-ray diffraction studies on Fe 2 O 3 -SiO 2 -CaO-Al 2 O 3 ores, it has been found that kaolinite ty...
