EXTRACTION OF IRON COMPOUNDS FROM CALCINED BAUXITE RESIDUE: AN INVESTIGATION ON MAGNETIC SEPARATION

Robert, Y., Simard, G., Leclerc, A., Perrachon, L., Fortin, S., Fortin, L.

The valorization of bauxite residue generated by the Bayer process is a key issue for the alumina industry, from both economic and environmental aspects. Iron oxides, mainly goethite and hematite, are a major constituent of bauxite residue that have a potential economic value. Many attempts have been reported in the literature of reducing these species to magnetic iron oxides, such as magnetite, followed by its recovery using magnetic separation. Limited commercial success has however been reported to date. This paper describes the initial steps of a detailed study undertaken on the various parameters of a magnetic separation process to extract the iron compounds from calcined bauxite residue. Experiments have shown that a basic magnetic separation alone cannot recover the magnetite contained in bauxite residue calcined under reductive conditions. Macroscopic and microscopic observations indicate that particles are aggregated together, and each aggregate contains several mineral phases. Various pre-treatment strategies were studied to enhance magnetite liberation and allow the parametric study to take place. A home-made experimental magnetic separator has been fabricated for that purpose and the influence of key parameters, such as water flow velocity, magnetic field intensity and solids concentration, was quantified. After four cycles, the collected material’s iron content is enriched from an initial 30 wt % up to 60 wt %.