Bioleaching of Valuable Elements from Red Mud: A Study on the Potential of Non-Enriched Biomass

Red mud (RM) is the main residue produced by alkaline extraction of alumina (Al2O3) from bauxite, and it contains valuable metals such as iron (Fe), aluminium (Al), titanium (Ti), magnesium (Mg), manganese (Mn), rare earth elements, etc. This research aimed to investigate biologically induced leaching some elements raw RM without preliminary biomass enrichment inoculum, simultaneously reducing polluting potential extracting for their subsequent recovery within a circular economy-based approach. In addition missing an approach challenging since high alkalinity pH, well absence any sulphides, constrain use most common biohydrometallurgical techniques. Muds two European locations were tested (RM-I RM-II, respectively). Bioleaching tests performed at different temperatures (T = 22 °C 28 °C; also 15 RM-II) solid-to-liquid ratios (S/L 2%, 5%). A sudden drop in pH constant neutral/acidic values was observed almost all tests, results attributed biological activity abiotic did not show decrease. The best terms achieved with particular Al, Mg Mn (17%, 42% 47%, At 2% S/L, highest temperature allowed better metal release, while 5% Ti °C. As expected, less available leach values, mostly present hematite both RMs. Finally, first microbiological characterisation autochthonous selected during bioleaching treatment provided.