China Nonferrous Metallurgy

Iron minerals in red mud mainly exist in the form of hematite, limonite and goethite, and the iron recovery rate of direct magnetic separation is low, and it is difficult to obtain high-quality iron concentrate. The suspension magnetization roasting process has significant advantages in the extraction of iron ore resources. On the one hand, suspension roasting can ensure the reaction efficiency of fine-grained red mud；on the other hand, the flash magnetization roasting time is short, the magnetization effect is good, and the energy consumption is low. In this paper, the red mud (Fe₂O₃ 62.15 wt%) from an enterprise was used as raw material, and it was treated by flash magnetization roasting-low intensity magnetic separation process. The effects of process parameters on the iron separation effect were investigated, and the reconstruction behavior of the phase in red mud and the reaction mechanism of magnetization roasting were discussed by characterization analysis. Under the conditions of fluidization speed of 0.3m/s, temperature of 800℃, roasting time of 2.0min, CO concentration of 15%, grinding fineness of -0.032mm content of 72% and magnetic separation field strength of 0.25T, the yield of iron concentrate was 67.69%（TFe 56.21%）, the recovery rate was 87.45%, the tailings yield was 22.51%（TFe 24.26%）, which could be used to prepare cement. The results of characterization analysis show that the weak magnetic hematite (limonite) in the red mud is directional reduced into strong magnetic magnetite during the flash magnetization roasting process, and some diaspore, gibbsite and diaspore are dehydrated into Al₂O₃, while the gangue minerals such as quartz and rutile do not change. The main mechanism of magnetization roasting is that CO reacts with Fe³⁺ on the surface of hematite (limonite) to form Fe²⁺, and Fe²⁺ reacts with Fe³⁺ to form magnetite Fe₃O₄; the outer layer of Fe²⁺ and electrons diffuse to the inner layer of Fe₂O₃ through lattice vacancies; after lattice reconstruction, it is transformed into magnetite Fe₃O₄. The inner layer of O₂ diffuses to the outer layer and reacts with CO to form CO₂, which is continuously removed.