Low-temperature Roasting Desulfurization of High-sulfur Bauxite and Study on Desulfurization Kinetic

Roasting is an effective and rapid method for achieving the desulfurization of high-sulfur bauxite to meet the requirements of digestion in the Bayer process. Most current research focuses on the roasting desulfurization of high-sulfur bauxite in the high-temperature region of 600–800 ℃. In this work, the thermodynamic and kinetic characteristics of desulfurization reactions were studied during the roasting process at low temperatures of < 600 ℃. The effects of roasting temperature, roasting time, and particle grinding size on the desulfurization reaction kinetics and phase transformation were explored, and the results show that the pyrite and diaspore in high-sulfur bauxite start to oxidize and dehydrate at about 432 ℃ and 470 ℃, respectively. Comprehensively considering the roasting energy consumption and desulfurization effect, suitable conditions for roasting are a temperature of 500–550 ℃, a roasting time of about 10 min, and a particle size of 0.150–0.830 mm. Under these conditions, the desulfurization ratio of sulfur in the form of S²⁻ in roasted ore is more than 90%, the mass fraction of S²⁻ is less than 0.1%, and the total sulfur (including SO₄²⁻ and S²⁻) desulfurization ratio is more than 70%. Kinetic analysis shows that this oxidative desulfurization reaction is a second-order reaction. When the particle size is 0.150–0.830 mm and the temperature is 450–525 ℃, the apparent activation energy is 63.546–64.746 kJ·mol⁻¹ and the interfacial chemical reaction is as the rate-controlling step of the desulfurization process.