Upgrading Diasporic Bauxite Ores for Iron and Alumina Enrichment Based on Reductive Roasting

Abstract

A technical route has been proposed to upgrade diasporic bauxite ores for iron and alumina enrichment based on reductive roasting, followed by magnetic separation and alkaline leaching. The thermodynamic analysis revealed that by reductive roasting of the bauxite ore at 980–1100°C, hematite in the ore is transformed to magnetite and kaolinite is converted into γ-Al₂O₃ and SiO_{2 (amorphous)}. Meanwhile, the diaspore changes to α-Al₂O₃, which favors the recovery of alumina via the Bayer process. The experimental results showed that, after reductive roasting and magnetic separation, iron and alumina in the bauxite ores could be effectively separated into magnetic and non-magnetic fractions, respectively. The iron was enriched in the magnetic fraction as iron concentrate with iron content of 60.15 wt.% and iron recovery of 42.89% after reductive roasting of the bauxite ore at 1000°C for 20 min in 10 vol.% CO/(CO + CO₂) atmosphere, followed by magnetic separation at magnetic field intensity of 0.1 T. After desilication of the non-magnetic fraction, which was obtained from the magnetic separation in 160 g/L sodium hydroxide solution with a liquid to solid ratio of 8 mL/g at 125°C for 45 min, alumina was enriched in a bauxite concentrate with Al₂O₃ content of 53.30 wt.% and the mass ratio of alumina to silica (A/S) of 9.38, meeting the requirement of alumina production by the Bayer process.