Desulfurization of high‑sulfur bauxite through roasting with various additives: phase transformation and micromorphological evolution

The high‑sulfur content of bauxite presents a significant challenge in alumina production. This study explored oxidative roasting as a desulfurization strategy, examining the effects of roasting temperature, duration, and various additives on sulfur removal. The results indicated that under conditions of 600 °C for 120 min without additives, the sulfur mass fraction in the roasted bauxite decreased from 16.63 % to 0.27 %, achieving a sulfur removal rate of 98.75 %. The addition of O₂ enhanced desulfurization efficiency. At 500 °C for 120 min with an O₂ flow rate of 1.2 g/min, sulfur content decreased to 0.66 %, corresponding to a 96.83 % removal rate, which was 26.53 % higher compared with that achieved without O₂ assistance. However, when NaNO₃ and Na₂O₂ were introduced, the formation of Na₂SO₃, NaFeS₂, and Na₂SO₄ significantly suppressed sulfur release. Furthermore, upon using various modern analytical techniques, the study investigated mineralogical characteristics, phase transformations, chemical composition, and microstructural evolution of bauxite before and after roasting. Results indicated that pyrite, the primary sulfur-bearing phase, decomposed to Fe₂O₃ and SO₂. Notably, both additive-free and O₂-assisted roasting increased surface roughness, porosity, and crack formation of the bauxite, which enhanced its digestion performance.