Sintering Behavior and Mineralization Mechanism of Red Mud for Pyrometallurgical Iron Extraction

To address the resource waste caused by the ineffective recycling of large quantities of red mud, this study proposes an innovative technical route consisting of red mud sintering followed by smelting in a small blast furnace or solid-waste smelting furnace for pyrometallurgical iron extraction. Under optimized process conditions—binary basicity of 4.97, a raw material composition of 78.27% wet-based red mud, 15.67% quicklime, and 6.05% fuel, with a solid fuel consumption of 121 kg/t—the produced sinter meets the feeding requirements of blast furnace smelting. The results indicate that the liquid phase generated during red mud sintering mainly consists of composite oxides in the CaO–Al2O3–SiO2 system; calcium aluminosilicate (Ca2Al2SiO7) was detected and inferred to be a potential bonding phase in the sinter matrix. Thermodynamic analysis shows that the Gibbs free energy of Ca2Al2SiO7 is lower than that of calcium ferrite, indicating that its formation is thermodynamically more favorable. The formation amount of this phase is closely related to the Ca/Al ratio, while temperature has a limited influence. In addition, Na2O can react with CaO·2 Al2O3 to form a low-melting-point phase, which significantly reduces the sintering temperature and enhances the fluidity of the liquid phase. These findings provide a new theoretical basis for the sintering of high-alumina ores and offer technical support for the efficient utilization of red mud as well as energy conservation and emission reduction.