Bioleaching for metals removal from mine tailings flotation fractions

This study investigated two bioleaching strategies for removing heavy metals from three mine tailings fractions generated by flotation processes. On the one hand, bioleaching with microbial consortia of acidophilic mesophiles and moderate thermophiles efficiently extracted Co, Cu, Zn, and As, while the leaching of Pb was facilitated through the use of organic acids produced by a heterotrophic bacterium and a fungus. Approximately 100% Co, 68% Zn, 63% As, and 31% Cu were bioleached with acidophilic mesophiles from the barite tailings (BT) sample after 14 days, whereas for the barite concentrate (BC) sample the results showed about 100% Co, 70% Zn and As, and 45% Cu removal at the same period. The sulfide concentrate (SC) sample underwent bioleaching with both consortia, acidophilic mesophiles and moderate thermophiles over 28 days. Approximately, 67% of Co, 28% of Zn, 56% of As, 28% of Cu, and 6% of Mn were extracted from the sample using mesophiles, whereas the leaching efficiency with the moderate thermophiles was about 72% of Co, 50% of Zn, 28% of As, 36% of Cu, and 5% of Mn in 20 L bioreactors. On the other hand, bioleaching of Pb was explored using the bacterium Gluconobacter oxydans and the fungus Penicillium simplicissimum for the production of gluconic acid and citric acid, respectively. Additionally, besides glucose-based media, glycerol and crystal sugar were tested as alternative and cheaper carbon sources. The metabolic activity of P. simplicissimum allowed a maximum Pb leaching of 39-43% from the BT sample in 28 days in glycerol-based medium, while for the BC sample, the maximum Pb extraction was around 60% in glucose-based medium. A lower extraction of Pb was achieved with G. oxydans for both samples. The maximum extraction of 34% and 39% of Pb was reached within 7 days when glucose was used as the carbon source. Further optimization should address both the enhancement of metals removal and - especially for the organic acid bioleaching - the reduction of costs related to media formulation and fungal biomass production on a larger scale.