Characterization vis-á-vis utilization of blast furnace flue dust in the roast reduction of banded iron ore

The present study explores the process of simultaneous roast-reduction and magnetic separation of blast furnace flue dust (BFD) and a low grade banded iron ore without using any extra reductant. The optical microscopic studies on the BFD sample revealed the presence of hematite, magnetite, silicates and unburnt carbon while the elemental mapping using Electron Probe Micro Analysis (EPMA) indicated the close association of silicates with Ca, K and Na bearing phases. The studies using the Scanning Electron Microscopy coupled with an Energy Dispersive X-ray Spectroscope (SEM-EDS) confirmed the presence of carbon both as an individual entity and in association with other phases as carbonates. The iron ore used was banded in nature and mostly consisted of hematite and quartz. Under statistically optimized conditions such as temperature: 850 °C, time: 90 min and BFD to ore ratio: 0.4, the process of reduction roasting followed by low intensity magnetic separation (LIMS) could yield an iron ore concentrate of ∼63% Fe at an iron recovery of ∼68% from the BFD with 32% Fe and banded iron ore with 47.2% Fe. Similar results were also obtained using the same BFD to ore ratio for a roasting temperature of 950 °C and a time period of 30 min. The products roasted at a high temperature of 1050 °C or at a temperature of 950 °C with a higher residence time of 120 min showed poor iron recovery and high grade in the LIMS magnetic fraction, which was attributed to the formation of feebly magnetic phases like wustite and fayalite.