Selective extraction of scandium from bauxite residue (red mud) utilizing iron sulfate roasting followed by water leaching

Scandium (Sc) is the most commercially valuable rare earth element due to its unique superior properties and extensive application. Bauxite residue (red mud) is regarded as one of the industrial wastes but has the potential to recover Sc. In this study, a two-step process via sulfation roasting with iron sulfate and water leaching was developed to selectively recover Sc from red mud. The results showed that the leaching efficiency of Sc depended on various factors including roasting temperature, the dosage of iron sulfate, and roasting atmosphere. The leaching efficiency of Sc reached 78.8 % with 5.1 % of Fe and 13.0 % of Al dissolved in the Sc-rich solution at the optimum conditions of the SO₃-controlled roasting at 700 °C for 15 min with red mud and iron sulfate mass ratio of 1:1, followed by water leaching at room temperature for 180 min. It is demonstrated that the Sc-rich solution could be recycled for leaching clinkers to accumulate Sc concentrations to meet the requirements of solvent extraction. This study also provides new insights about the reaction mechanisms and phase transformations of the roasting and water leaching process. The findings provided a valorization route of red mud by recovery of Sc resource due to the relatively simple process, high selectivity, and low-cost reagents.