Comparison of microwave and conventional carbothermal reduction of red mud for recovery of iron values

Abstract This study investigates the recovery of iron values from Indian red mud through different routes. The conventional beneficiation was found futile to recover iron values from the red mud due to complex structure. The carbothermal reduction is carried out in both muffle and microwave furnace using statistical design. The XRD quantitative phase analysis of the magnetic concentrate indicates distinct phase transformation of hematite to ferrite as a function of temperature and in the sequence Fe2O3 → Fe3O4 → FeO → Fe. In microwave furnace, concentrate with ∼47% grade and 88% recovery at a yield of 72% is attained at optimal conditions of 1000 °C, 10 min with 11% C whereas in muffle furnace, optimal conditions of 1000 °C, 50 min reduction time with 16.5% C yields a concentrate ∼49% iron, 87% iron recovery with a yield of 56%. On comparison of carbothermal reduction in muffle and microwave routes, the microwave route provides a significant improvement in iron grade and recovery at comparatively lower levels of time and reductant dosage. Along with enhanced iron grade-recovery, significant ferrite balls of 1 ± 0.5 mm (∼92% iron content with 94% purity) are observed in the microwave route and were handpicked from the product. Nevertheless, the ferrite phase is forming in both the routes, but in microwave route, ferrite balls of appreciable size and purity accounting ∼8–10% of total iron values in the feed are also observed. In addition, the microwave assisted carbothermal reduction offers a faster reduction rate, cleaner processing and relatively economical in terms of energy and reductant consumption. The product obtained is rich in magnetite, wustite and ferrite phase which can be further used in alternate iron making units.