Sustainable integration of red mud in iron ore sinter manufacturing via composite agglomeration process (CAP): Multiscale consolidation mechanisms and pilot-scale industrial validation
Lingyun Yi, Xiaoshuai Shen, Haowen Hao, Liangping Xu, Hongzhuang Dong, Jun Luo, Guanghui Li, Tao Jiang
Abstract
The global alumina industry faces mounting pressure to address red mud (RM) recycling - a critical environmental challenge posed by this highly alkaline bauxite residue. This study demonstrates an innovative application of the composite agglomeration process (CAP) to sustainably incorporate RM into iron ore sinter production. Unlike direct powder addition methods that compromise sinter quality by degrading liquid phase bonding capacity, the CAP approach enables effective RM utilization while maintaining blast furnace raw material specifications. Through systematic micro-sintering experiments, this study elucidates the fundamental consolidation mechanisms of red mud (RM) briquettes and their interfacial bonding with powdery feed materials during the sintering process. The CAP unit forms a layered structure (from core to periphery): (1) RM briquette core, (2) intermediate transition zone, and (3) outer high-basicity matrix. Multiscale characterization reveals that the mechanical integrity of CAP unit stems from the hematite grains recrystallization in the briquette core, SFCA (silico-ferrite of calcium and aluminum) phase cementation in the matrix, and the interlocking of hematite grains with SFCA phase in the transition region. Pilot-scale trials confirm the industrial viability of this approach, demonstrating successful incorporation of up to 10% RM while maintaining sinter quality parameters (yield: 77.21%, TI: 65.03%, RI: 88.87%, RDI +3.15 : 74.70%). The CAP technique transforms this problematic waste into valuable ironmaking feedstock, achieving both environmental and metallurgical benefits through controlled phase formation and microstructure optimization.