Physical and chemical separation of Ti, rare earth elements, Fe, and Al from red mud by carbothermal reduction, magnetic separation, and leaching

In this study, a combination of physical and chemical separation processes was used to recover the metallic components of red mud. At first, the impact of carbothermal reduction on magnetic separation of iron was studied. Low magnetic properties of iron minerals resulted in insignificant separation of iron from other components in the non-carbothermally reduced sample. Various carbothermal reduction parameters were optimized to maximize iron separation from other components. The optimum conditions were found T = 1350 °C, t = 120 min, coal/red mud ratio of 3, reaction time of 120 min, and the soda ash/red mud ratio of 0.2. Under the optimum condition, the iron recovery of the magnetic product was observed 91% with 81% Fe content, while the non-magnetic product has contained 90% of Ti and Al and 80% of rare earth elements (REEs). Following the physical separation of iron, the chemical separation of remaining red mud components was investigated using leaching with sulfuric, hydrochloric, and nitric acids. The leaching experiments were performed on two samples, treated red mud with carbothermal reduction and an untreated sample. The untreated sample had a higher dissolution efficiency for Ti and REEs than the carbothermally reduced sample. Different dissolution behavior of the red mud components was explained by samples’ mineralogy. In the end, considering the obtained results, various scenarios for the recovery of red mud components were evaluated from technical and environmental aspects.