Optimization of microwave carbothermal reduction for processing of banded hematite jasper ore

Abstract

This study investigates the microwave carbothermal reduction of low grade banded hematite jasper iron ore ∼37% Fe. Due to complex association of the iron phase and impurities, the conventional beneficiation was found futile. The susceptibility of iron phases to microwave exposure assists in the liberation of iron values from impurities. The thermodynamic calculations revealed the selective reduction of iron ore phases in the Fe-O-C-Si-Al system. The preliminary experiments revealed that during a few minutes of microwave exposure, a temperature of ∼400 °C and ∼1100 °C was achieved for feed and charcoal mixture respectively. Besides iron enrichment in the concentrate, the ferrite balls were also observed in statistical design experiments. It was found that a small fraction of microwave irradiated BHJ ore-charcoal mixture was rapidly melted to produce ferrite balls. The presence of a sufficient amount of bonded silica content in the BHJ ore leads to an easy formation of the fayalite phase. The iron grade falls at prolonged exposure due to the interaction of iron phases with the quartzite as revealed by the XRD analysis. The optimal condition 720 W power, 9% charcoal and 8 min based on statistical design yielded a magnetic concentrate having ∼61.6%Fe, ∼73.4% recovery at a yield of 44% and has a potential to be used for pellet making industry. Similarly, the experimental condition 900 W power, 12% charcoal and 8 min yielded a magnetic concentrate with ∼49.1%Fe, ∼89.3% recovery at a yield of 59.7% along with ferrite balls with a saturation magnetization of ∼153 emu/g.