The scope of this work is to develop and optimize a reductive roasting process followed by wet magnetic separation for iron recovery from bauxite residue (BR). The aim of the roasting process is the transformation of the nonmagnetic iron phases found in BR (namely hematite and goethite), to magnetic ones such as magnetite, wüstite, and metallic iron. The magnetic iron phases in the roasting residue can be fractionated in a second stage through wet magnetic separation, forming a valuable iron concentrate and leaving a nonmagnetic residue containing rare earth elements among other constituents. The BR-roasting process has been modeled using a thermochemical software (FactSage 6.4) to define process temperature, Carbon/Bauxite Residue mass ratio (C/BR), retention time, and process atmosphere. Roasting process experiments with different ratios of C/BR (0.112 and 0.225) and temperatures (800 and 1100°C), 4-h retention time, and, in the presence of N 2 atmosphere, have proven almost the total conversion of hematite to iron magnetic phases ([ 99 wt%). Subsequently, the magnetic separation process has been examined by means of a wet high-intensity magnetic separator, and the analyses have shown a marginal Fe enrichment in magnetic fraction in relation to the sinter.

In this study, microwave-assisted heating is presented as a suitable method to transform the hematite and goethite contained in bauxite residue into magnetite, wüstite, and metallic iron, with a short processing time. The final target was the production of a sinter with strong magnetic properties, allowing the magnetic separation of Fe from the residue. The influence of microwave energy on the sample, the effect of irradiation time, and the carbon/bauxite residue mass ratio (C/BR) were the parameters that have been analyzed to optimize the process. Their optimized combination allowed transforming 79% of the iron present in the sinter into metallic iron. However, hercynite was also formed, and the presence of this mineralogical phase could be considered a possible drawback for its magnetic properties.

In this study an integrated process is presented as a suitable method to transform Fe3+ oxides present in bauxite residue into magnetic oxides and metallic iron through a microwave roasting reduction, avoiding the formation of hercynite (FeAl2O4). In the first step, all the alumina phases were transformed into sodium aluminates by adding sodium carbonate as a flux to BR and then leached out through alkali-leaching to recover alumina. Subsequently, the leaching residue was mixed with carbon and roasted by using a microwave furnace at the optimum conditions. The iron oxide present in the sinter was converted into metallic iron (98%). In addition, hercynite was not detected. The produced cinder was subjected to a wet high intensity magnetic separation process to separate iron from the other elements.

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