Reaction mechanism of alumina, sulfur and gallium in desulfurization concentrate from diasporic bauxite during high-temperature digestion

• Optimal CaO dosage (3%) enhances alumina and gallium digestion while effectively removing sulfur as calcium sulfoaluminate hydrate, reducing sulfur concentration to 1.32 g/L. • Excess CaO leads to hydrogarnet formation, where Ga3+ substitutes Al3+ in the lattice, decreasing gallium digestion efficiency. • Under optimum conditions (260 °C, 60 min, 260 g/L caustic alkali), alumina and gallium digestion efficiencies reach 90.82% and 77.58%, respectively. • The study provides theoretical guidance for efficient co-extraction of alumina and gallium from high-sulfur bauxite via the Bayer process.