• Efficient iron recovery from high-iron red mud achieved via multi-physical field coupling (microwave, gas-solid flow, temperature) using biomass as a reducing agent.
• Optimal conditions yielded an iron concentrate with 78.4% yield, 59.23% iron grade, and 86.65% recovery rate.
• XRD, XPS, TEM, and SEM-EDS confirmed complete conversion of hematite to magnetite during roasting, with biomass-derived reductant driving magnetization.
• Formation of cracks and pores on particle surfaces enhances mineral phase transformation and subsequent magnetic separation efficiency.