Reaction behaviors of iron and hematite in sodium aluminate solution at elevated temperature

Abstract

The simultaneous transformation and dissociation of minerals containing iron in reductive Bayer digestion of bauxite are important to separate iron minerals from red mud and thus reduce the waste solid disposal in alumina production. In order to better understand the reaction mechanism of iron and hematite in sodium aluminate solution, the phase composition, valence variation and micro-morphology of transformation products were studied by XRD, XPS, FT-IR and SEM respectively. The results show that the intermediate alumogoethite, α-Fe(1−x)AlxOOH, preferentially forms by the reaction of HFeO2−and AlO2− and then converts to magnetite in Fe-Na2O-Al2O3-H2O system at digestion temperature of 533K. Meanwhile, the transformation of hematite to magnetite in Fe-Fe2O3-Na2O-Al2O3-H2O system sequentially involves HFeO2− generation by dissolution of iron powder, HFeO2− diffusion to hematite particles, and magnetite formation on hematite particles by reaction of HFeO2− and hematite or dissolved FeO2−. Fe addition can prevent hematite particle from becoming much smaller by surface magnetization in reductive Bayer digestion compared with current industrial Bayer digestion. This work is conducive to develop a novel technology for efficiently processing high-iron diasporic bauxite.