High-Iron Bauxite Residue (Red Mud) Valorisation Using Hydrochemical Conversion of Goethite to Magnetite

Abstract

Bauxite residue (BR), also known as red mud, is a by-product of the production of alumina via the Bayer process. Because of the high sodium oxide and other impurities content, this material is not used to obtain iron or other iron-containing products. In this paper, the hydro-chemical conversion of goethite (FeOOH) to magnetite (Fe3O4) in high-iron BR from the Friguia alumina refinery (Guinea) by Fe2+ ions in highly concentrated alkaline media was studied. The simultaneous extraction of Al and Na made it possible to obtain a product containing more than 96% Fe3O4. The results show that the magnetization of Al-goethite and Al-hemetite accelerates the dissolution of the Al from the iron mineral solid matrix and from the desilication product (DSP). After ferrous sulfate (FeSO4·7H2O) was added directly at the FeO:Fe2O3 molar ratio of 1:1 at 120 °C for 150 min in the solution with the 360 g L-1 Na2O concentration, the alumina extraction ratio reached 96.27% for the coarse bauxite residue size fraction (Sands) and 87.06% for fine BR obtained from red mud. The grade of iron (total iron in the form of iron element) in the residue can be increased to 69.55% for Sands and 58.31% for BR. The solid residues obtained after leaching were studied by XRD, XRF, TG-DTA, VSM, Mössbauer spectroscopy and SEM to evaluate the conversion and leaching mechanisms and the recovery ratio of Al from different minerals. The iron-rich residues can be used in the steel industry or as a pigment.