Reduction Roasting Kinetics of Red Mud Composite Micropellets Using Biochar as an Alternative Reductant

Abstract

Red mud, a by-product of alumina extraction from bauxite, poses significant environmental challenges due to its high alkalinity. However, its composition offers the potential to be reused in various applications. As India targets 300 Mt of crude steel production by 2030, red mud, rich in iron content, presents itself as a viable secondary resource for iron extraction. Its iron is primarily in goethite (FeOOH) and hematite (Fe2O3), making it suitable for recovery through appropriate processing methods. Reduction roasting combined with Low-Intensity Magnetic Separation (LIMS) has emerged as an effective and environmentally friendly method for extracting iron from red mud. Further, reducing coal usage attracted many researchers to use biomass-based reductants as an alternative, promoting defossilization. This study used red mud containing 35.03% Fe mixed with three reductants, including non-coking coal, biomass, and biochar, to obtain composite micropellets and further roasted at 600–900 ℃ and 15–60 min’ residence times. The results showed that biochar demonstrated superior performance, producing 62.2% Fe content and 90.56% recovery at 900 ℃ after 30 min. Moreover, the reduction kinetics was governed by the interfacial chemical reaction model, and the apparent activation energy ($${E}_{a}$$) was 21.84 kJ/mol for the biochar-containing micropellet sample, which is the lowest among all the three samples.