Processing of ochre from Daitari Iron ore mines, Singbhum Craton, Eastern India for optimum utilisation

Abstract

Ochre, a naturally occurring powdery material, has been commonly appeared associated with different iron ore morphotypes in many iron ore deposits of the Singhbhum Craton, eastern India. It appears in yellow, red, gray and black colours. The present paper has described the characteristics of ochre occurring in the Daitari Iron Ore Mines in Odisha, India, and has discussed its processing for sustainable iron making and optimum utilization. Usually, ochre shows poor iron value, fine size and therefore being considered as a waste. However, in the present set-up, the ochre sample has shown ~60% Fe, 4% combined Al₂O₃ + SiO₂ and ~10% LOI, contributed by hematite, goethite and limonite phases. Though compositionally it appears to be a good candidate for iron making, it has remained unsuitable as blast furnace feed due to its fine particle size and high LOI content. Attempts have been made to convert this powdery ochre to a lumpy form by adopting the pelletization technique. The sample below 150 μm size has been mixed thoroughly with three different charge mixes (bentonite, limestone and coke fines) and pellets have been prepared in a laboratory-scale disc pelletizer., Three sets of samples have been prepared with variable bentonite contents (0.5, 0.75 and 1%) keeping fixed limestone and coke amount. The green pellets from the pelletizer have been exposed to drop test and Green Compressive Strength (GCS), followed by thermal indurations at 1100, 1200 and 1300 °C. The porosity (%) and Cold Crushing Strength (CCS) (kg/pellet) of the indurated pellets have shown variations at three different temperatures. Pellets prepared with 1% bentonite content and indurated at 1300 °C have given 22% porosity and 255 kg/pellet CCS. XRD, optical and electron microscopy studies have revealed that recrystallization of hematite during induration has enhanced pellet strength and properties, while fayalite and calcium ferrite formation has provided stability through slag bonding. Pellets indurated at 1300 °C have shown Fe enrichment from ~60% to ~67% with ~3.2% combined Al₂O₃ + SiO₂, making them suitable as blast furnace feed. If this technique is adopted, an appreciable quantity of ochrous waste accumulated at mine sites can be converted to wealth