Abstract
Eighty per cent of the world's steelmaking is through the blast furnace route and hence the role of iron ore as a raw material and its quality become very critical to achieve steel with the best quality from hot metal. The world's iron ore resource base has been estimated at 180 000 million tonnes (MT), while the reserves are 79 000 MT. India ranks the sixth among producers of iron ore, with a 6200 MT reserve base. The majority of Indian iron ore deposits occur in the eastern, central and southern parts of India in the regions of Jharkhand, Orissa, Karnataka, Chhattisgarh and Goa. Among these provinces, the iron ores of Eastern India are of high quality and present in large quantities. Indian iron ore resources consist of both hematitic (10 052 MT) and magnetite (3408 MT) varieties. Major ore types are hard, flaky/friable, lateritic and blue dust or powdery ores. The ratio of lumps and fines in the deposits is 50 : 50, but the high grade lumpy variety is rare and constitutes <10% of the total reserves. India's iron ore production has just doubled in the last 5 years, achieving a total of 154 MT in 2005–06 compared with 86 MT in 2001–02. The Indian iron ores in general and Eastern Indian iron ores in particular consist of various impurities in the forms of Al, P and Si, and this poses major beneficiation problems especially in fines processing. The presence of these elements along with sulphur adversely affects the quality of iron ores and has a great bearing on performance of blast furnaces. Reduction of the alumina content in iron ore by 1% improves blast furnace performance by 3%, reduces reduction degradation index (RDI) by 6 points, lowers the coke rate by 14 kg per tonne of hot metal and increases sinter productivity by 10–15%. The presence of phosphorus and sulphur increases surface cracking during steel processing. High alkali contents lead to a lowering of the mechanical strength of coke and sinter, imbalances in the furnace operation and a reduction in furnace productivity. The Indian iron ore industry is going to face major challenges in the near future, as the production trend of iron ore worldwide is swinging up every year owing to the iron ore boom in recent years. It calls for mineral conservation and prevention of mineral losses in terms of wastes/slimes. This needs to be achieved through detailed exploration work, mine planning techniques, scientific exploitation and mineral beneficiation processes. For optimum utilisation of mineral resources, total beneficiation of iron ores, mineral rejects and wastes need to be augmented. In addition, alternative processes for ironmaking, such as COREX, ROMELT and HISMELT, need to be introduced by the major producers. This paper addresses the importance of quality raw materials in achieving benchmark iron- and steelmaking while maintaining the cost effectiveness. Emphasis has been given on the value addition of the subgrade and marginal-grade ores for mineral conservation and prevention of losses.
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