Producing high purity metallic iron from bauxite residue through hydrogen reduction followed by flux smelting

Abstract

The effective management and utilization of bauxite residue poses a significant challenge for the alumina industry, especially given the escalating demand for aluminum. This investigation focuses on utilization of bauxite residue to produce high-purity iron and the creation of leachable calcium aluminate slag through processes involving hydrogen reduction and smelting. Bauxite residue was pelletized and then underwent reduction at 1000 °C in the presence of hydrogen. The resulting reduced bauxite residue was subsequently milled and blended with varying percentages of CaO, followed by smelting at 1500 °C to recover iron and a leachable calcium aluminate slag. Analytical techniques such as X-ray diffraction, Electron Probe Microanalysis, scanning electron microscopy, and X-ray fluorescence were employed to assess the phases, microstructure, and chemical compositions. The hydrogen reduction process successfully transformed iron oxide in the bauxite residue into metallic iron. The increasing amounts of CaO in smelting led to the dominance of the calcium aluminate (CaO·Al₂O₃) phase in the slag products, with the phase composition remaining relatively stable after reaching a 40% CaO content. Key phases identified in the smelted slag included CaO·Al₂O₃, Ca₂Al₂SiO₇, and CaTiO₃. Notably, the iron produced during smelting exhibited a purity exceeding 99.5%, comparable to electrolytic iron. Experimental analysis revealed a positive correlation between the purity of iron and the concentration of CaO in the slag melt. Only a minimal amount of iron, primarily in the form of FeO, was observed in the slag, a phenomenon corroborated by Factsage analysis.