Carbothermic Reduction of Bauxite Residue for Iron Recovery and Subsequent Aluminium Recovery from Slag Leaching.

Industrially and historically, alternative processes were developed to recover alumina from low-grade ores of non-bauxitic origin as well as for economic reasons. The Pedersen process from Norway was adapted towards high ferruginous and high silica containing bauxitic ores. This paper considers the adaptation of the Pedersen pyro-hydrometallurgical route of reductive smelting with lime and coke to recover iron and aluminium from bauxite residue (BR), which is the by-product of the Bayer process where aluminium is typically lost in complex desilication product matrices. Greek BR was firstly smelted in an Electric Arc Furnace (EAF) to recover pig iron (>95 %). The fluxing strategy entailed feeding lime to favour lower operating temperatures (1500–1550 °C) and slag viscosities, and to produce a slag containing calcium aluminate phases (12CaO·7Al2O3, 3CaO·Al2O3 and CaO.Al2O3). The calcium aluminates were identified as thermodynamically favourable in descending order to form NaAlO₂ when leached in Na₂CO₃ solution (ΔGrxn298K= -782, -188 and -68 kJ/mol, respectively). Leaching temperature, Na2CO3 concentrations, residence time and different particle sizes were varied to investigate the leachability of slags for aluminium recovery; up to 43 % aluminium was recovered with 95 % of silicon content remaining in leached residue. SEM studies also aided understanding of interstitial leaching mechanism