New technology of microwave fluidization roasting for enhancing iron recovery from red mud: Mineral phase transformation mechanism

Red mud, a by-product of alumina production from bauxite, is a strong alkaline industrial solid waste. The high alkalinity, complex composition, and fine particle size of red mud pose significant challenges in terms of recycling and utilisation. This study proposes a novel approach for efficient recovery of iron in red mud using microwave fluidization roasting technology. The present study systematically investigates the iron mineral recovery process in high-iron content red mud, elucidating the underlying mechanisms of mineral phase transformation from four distinct perspectives: phase transformation, alterations in crystal surface characteristics, lattice transformation, and microstructure evolution. The experimental results demonstrated that, under the optimised conditions of microwave roasting at a temperature of 600 °C for 20 min, the addition of coal powder at a rate of 10 %, the injection of carbon dioxide at a rate of 100 ml/min, and a grinding fineness of −0.0 74 mm accounting for 90 %, and magnetic field strength of 2000 Gs, an iron concentrate with a yield of 74.4 %, iron grade of 59.43 %, and iron recovery rate of 87.61 % was obtained. In addition, analysis via XRD, XPS, TEM, and SEM-EDS detection revealed that hematite in high-iron content red mud during the roasting process was efficiently converted into magnetite, resulting in the formation of a substantial number of cracks and pores on the surface of the roasted product particles. This transformation of the particles from a dense block structure to a porous and loose block structure is conducive to the efficient conversion of iron minerals.