Reductive Roasting Process for the Recovery of Iron Oxides from Bauxite Residue through Rotary Kiln Furnace and Magnetic Separation

Bauxite residue (BR), the main by-product formed during the Bayer process for alumina production, is a secondary raw material source, containing usually iron (Fe), titanium (Ti), aluminium (Al) and in some cases rare earth elements (REEs) including Sc. This work addresses the high temperature carbothermic conversion of hematite and goethite in the BR to magnetic iron phases. The reductive process developed in a laboratory scale static tube furnace, was scaled up using a rotary kiln furnace. Experiments were carried out by mixing BR with a carbon source (C/BR=0.225) and an additive (Na2CO3/BR=0.25), at 1000 °C in the presence of N2. The results show that hematite is almost fully (> 99 wt.%) converted to magnetic iron phases after 1 hour. Subsequently, this work was focused on the magnetic separation process through a wet high-intensity magnetic separator. Two current intensities (0.01 and 0.5 A) were employed to collect three fractions (Magnetic I, Magnetic II and Non Magnetic), 70 % of the total Fe content was concentrated in the first magnetic fraction, producing a secondary iron concentrate while the non-magnetic fraction is enriched in Ti and REEs.