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

Abstract

To mitigate the detrimental effects of sulfur and enhance the enrichment efficiency of valuable elements in desulfurized diasporic bauxite, the effects of CaO dosage, caustic alkali concentration, reaction temperature and time on the digestion behavior of alumina, sulfur and gallium were illustrated, and the digestion thermodynamics and mechanism were also revealed. During high-temperature Bayer process, alumina and gallium were digested synergistically, while pyrite is digested to S²⁻ and SO₄²⁻. Appropriate CaO dosage promotes the digestion of alumina and gallium, and facilitates the precipitation of sulfur as calcium sulfoaluminate hydrate, effectively removing sulfur from the solution. Excess CaO leads the formation of hydrogarnet, wherein Ga³⁺ incorporates into the crystal lattice by substituting for Al³⁺, reducing the digestion efficiency of gallium. Under the right conditions (CaO dosage = 3%, T = 260°C, t = 60 min, caustic alkali concentration = 260 g·L⁻¹), the corresponding alumina and gallium digestion efficiencies reach 90.82% and 77.58%, respectively, with a significantly reduced sulfur concentration of 1.32g·L⁻¹ in the solution. This work provides theoretical guidance for the efficient co-extraction of alumina and gallium from high-sulfur bauxite via the Bayer process.

Keywords

desulfurization concentrate / bayer process / alumina / gallium / high-temperature digestion

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Central South University