Use of Additives as Internal Heat Sources in Hematite Ore Pellets- A Review

Magnetite ore pellets oxidize to hematite during their induration in a mild oxidizing atmosphere of strand which produces internal heat in the pellet and enhances diffusion bonding. Hematite ore pellet does not have such oxidation. Therefore, hematite pellets require a much higher induration temperature (>1300degree celsius). To reduce the induration temperature requirement (maximum temperature of the strand) of hematite pellets, investigators have added several additives, namely, coke fines, coal fines, charcoal, anthracite, Jhama coal, blast furnace flue dust, etc. as carbon sources. Carbon in these materials oxidizes in the mild oxidizing atmosphere of the strand and provides in-situ exothermic heat which helps in the bonding of pellets. Investigators have also added lower iron oxides containing materials for this purpose, namely, magnetite ore, mill scale, and sludge which oxidize and provide diffusion bonding and exothermic heat. However, each of the above materials has a different character of reaction based on its chemistry, particle size and shapes, surface morphology, distribution, and concentration. Therefore, they affect differently on the pellet properties. Several studies reported so far on the effects of each material, their optimum requirement, advantages, and disadvantages are discussed along with their comparative analysis. This will help identify the appropriate additive and their amount of requirement in hematite pellets.