Abstract
Metallurgical grade alumina is produced worldwide through the well-known Bayer process, which unavoidably generates bauxite residue (BR, also known as red mud) in almost equal amounts to alumina. This study aims the valorization of BR through a smelting-reduction process to obtain calcium aluminate slags that can be a proper feed for alumina recovery via the Pedersen process. It investigates the thermodynamics and characteristics of the slags and pig iron produced from mixtures of BR, a bauxite beneficiation byproduct, and lime. In this context, the evolution of the different phases in the slags is studied with advanced analytical techniques and thermodynamic calculations. According to the results, a CaO/Al2O3 mass ratio within 1.3 to 1.4 in the slags can yield more Al2O3-containing leachable phases, such as CaO·Al2O3 and 12CaO·7Al2O3. The cooling dictates the amount and the characteristics of these phases, and the slower cooling rate yields improved slag characteristics. The distribution of the elements between the slag and metal phases shows that iron is separated, and the majority of the P, Cr, Ni, and V are distributed in the produced pig iron, while S, Ti, and Si are mostly concentrated in the slags.
Highlights
ALUMINA is the feedstock to produce aluminum and is mainly extracted from Bauxite ore.[1]
Aluminum is found in hydroxides as gibbsite AlO(OH)3, diaspore a-AlO(OH), and boehmite b-AlO(OH), in complex alumino-sodium-silicate phases as Na1.15Al1.15Si0.85O4 and cancrinite (Na6Ca2(AlSiO4)6(CO3)2 (H2O)2), and as katoite (Ca3Al2(SiO4)(OH)8) in the bauxite residue (BR)
BR contains a significant amount of Fe2O3, 43.59 wt pct, while the alumina content is 22.78 wt pct, indicating levels of alumina losses that occur in the Bayer process
Summary
ALUMINA is the feedstock to produce aluminum and is mainly extracted from Bauxite ore.[1]. BR holds all the insoluble/less-soluble compounds of bauxite ore in the Bayer leaching solution, containing Fe, Si, and Ti as the main elements, and Manuscripe submitted September 2, 2020; accepted January 14, 2021.
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