Hematite and Anatase Conversion to Magnetic Phases During Reductive Re-digestion of Gibbsitic Bauxite Residue

Abstract

Bauxite residue (BR) is a by-product of the Bayer process for alumina production. The physical and chemical characteristics of BR from gibbsitic bauxite such as the fine particle size distribution and mineralogical phases (hematite, sodalite, goethite, anatase, gibbsite and quartz) prevent its wide use and limit the recovery of elements by conventional physical operations. As an example, the magnetic recovery of hematite from gibbsitic RB is unfeasible. An alternative to enable a magnetic concentration operation would be to obtain higher magnetic susceptibility phases, whose magnetic properties could overcome the processing limitation determined by the fine size of the RB particles. In this work, a Brazilian BR from gibbsitic bauxite processing with an iron and titanium concentration of 47.03% Fe2O3 and 5.45% TiO2 was re-digested in presence of iron(II) sulphate 7-hydrate (FeSO4•7H2O), at high temperature (230ºC) and high caustic concentration (370 g/l Na2CO3). Magnetite, ulvite (titanium-magnetite) and cancrinite minerals were obtained. The results demonstrated that this route may be promising for magnetic iron recovery, especially if side reactions were minimized. For future studies, one should evaluate the threshold for the conversion when the severity of conditions was diminished, as well as, the assessment of magnetic properties and the evaluation of potential recovery of the magnetic product.KeywordsBauxite residueIronTitaniumMagnetiteRecovery