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
(>1300°C). 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.