Dissolution behaviour of Li, Ga and Sc in roasted high-sulphur bauxite during the Bayer process

High-sulphur bauxite is an important resource for alumina production and critical elements such as lithium, gallium and scandium. Roasting is a technique for processing high-sulphur bauxite. However, it alters the leaching behaviour of these critical elements, affecting their recoveries. In this study, the leaching behaviours of Li, Ga and Sc in unroasted and roasted high-sulphur bauxite were investigated. The results indicate more than 96% of sulphur in bauxite was removed after roasting process at 900°C for 120 minutes. For the Bayer process, the optimum leaching conditions were found at 270°C for 120 minutes with 9% of CaO mass addition in a 230 g L^–1 of Na₂O concentration Bayer liquor. The extraction efficiencies of the elements in unroasted and roasted bauxite were tested as 85.29% and 93.14% for Al₂O₃, 50.05% and 74.08% for Li, 87.93% and 93.73% for Ga, and 28.89% and 45.17% for Sc, where the leaching ratios were elevated after roasting. The calculated leaching activation energies were 52.03 kJ mol^–1 (Al₂O₃), 32.33 kJ mol^–1 (Li), 60.21 kJ mol^–1 (Ga) and 19.12 kJ mol^–1 (Sc), suggesting that the digestion process was controlled by internal diffusion, which is attributed to the increase of free surface area of host minerals after roasting. These findings enhance the understanding of leaching behaviour in roasted high-sulphur bauxite and provide new strategies for recovering valuable elements.