Mineralogical Study of Low and Lean Grade Iron Ore Fines during Slow and Rapid Reduction Roasting

The present study focuses on the mineralogical aspects and roasting of iron ore (Fe: 55.4%) fines in both fixed bed and fluidized bed roaster. Goethite is the dominant mineral phase in this low-grade iron ore containing hematite, silica and alumina. Such ore was roasted at a constant temperature of 900°C, with non-coking coal of 20% at residence time ranging from 15 to 60 minutes at intervals 15-minute in the fixed bed and 2 to 8 minutes at intervals 2-minute in the fluidized bed reactor. Non-coking coal was utilized as a reductant in the reduction reaction. A high-grade iron ore concentrate was subsequently extracted using Low Intensity Magnetic Separation (LIMS) from the roasted ore. Phase changes in both cases were different due to the difference in the mechanism of reduction. In the fixed-bed reduction roasting phase, transformation occurs as Goethite — Hematite — Magnetite — Wustite, whereas in a fluidized bed, it has followed Goethite — Hematite — Magnetite — Maghemite route. The maghemite phase formed during the fast reduction process due to reoxidation of the reduced magnetite. The wustite phases are reported in the non-magnetic fractions during LIMS, lowering the yield. On the other hand, the maghemite phase is reported to the magnetic portions. It has a simple cubic structure like magnetite, which increases the yield in the fast reduction roasting process. The results show that 65.85-grade iron ore can be obtained after 30 minutes of residence time with a recovery of 51.5% from the fixed bed and 62.17-grade iron ore can be obtained after 4 minutes of residence time with a recovery of 53.2 % from the fluidized bed.