High Temperature Transformation of Iron Minerals in Bauxite

Mössbauer hyperfine and X-ray diffraction studies have been carried on original bauxite sample and thermally treated (between 200 and 1200°C) samples. Mössbauer spectrum of original bauxite shows the dominance of hematite (α-Fe₂O₃) along with Al-substituted hematite and goethite (α-FeOOH) of fine particle size. Mössbauer parameters for thermally treated samples indicate transformation of almost all of iron oxy-hydroxides into hematite up to 350°C. Around 800°C the formation of a new iron phase, assigned as iron substituted mullite (3Al₂O₃ 2SiO₃), occurs and its intensity increases with the rise in temperature and reaches a saturation around 1200°C. Furthermore, our studies confirm that HCl leaching is quite effective for the iron oxide removal.