Characterisation of BOG manganese ore associated with BIF in iron ore group, north orissa for its optimum utilization

Abstract

Keonjhar and Sundargarh districts, north Orissa occurring along with other low to medium-grade Mn-ore. It is powdery, fine grained, black to blackish-brown in colour, very soft, readily soils the fingers. Its hardness on the mineralogical scale is 1–3, specific gravity between 2.8–3.9 g/c3 having 40.76 m2/g specific surface area and lose 20% weight at 1000°C. Mineralogically, this ore constitutes two phases, viz.: manganese (δ-MnO2, manganite, romanechite with minor pyrolusite) and iron (goethite/limonite and hematite) with minor kaolinite and free quartz. Mixed limonite-clay and δ-MnO2-limonite are commonly observed. Under microscope the ore appears oolitic/pisolitic to globular in shape having small detritus of quartz, pyrolusite/romanechite and hematite at the core. Globules of cryptocrystalline δ-MnO2 are often seen encrusted by mixed limonite-clay phase. The ore contains around 23% Mn and 28% Fe with ~7% of combined alumina and silica. It is considered as waste because of its low-grade nature and abovementioned physical characteristics. The ore did not respond to any sorts of physical beneficiation techniques though silica content is reduced through simple size classification. The sample along with appropriate charge mix was then processed through pyrometallurgical route in a plasma furnace, for recovery of valuable. High manganese steel having 25% Mn was produced within 10 minutes.