Potential of single and designed mixed cultures to enhance the bioleaching of chalcopyrite by oxidation-reduction potential control

Biomining is the extraction of target metals from ores or wastes such as the dissolution of chalcopyrite for copper recovery. A key outstanding topic of study is to improve the rate and total copper released from chalcopyrite that can become 'passivated' by surface layers, which hinders oxidative attack on the metal sulfide bond. One strategy to increase chalcopyrite bioleaching is to control of the oxidation-reduction potential in the desired range by using 'weak' iron oxidizers. In this study, 15 acidophilic species were evaluated for their ability to catalyze chalcopyrite dissolution that resulted in the addition of Acidithiobacillus ferrianus, Sulfobacillus thermotolerans, and Metallosphaera sedula to the known 'weak' iron oxidizing species. Based upon these data, four microbial consortia were designed including mesophiles (25 degrees and 37 degrees C), moderate thermophiles (49 degrees C), and thermophiles (70 degrees C) that increased copper recoveries by up to 32% compared to abiotic controls. The best performing consortium was the moderate thermophiles Sulfobacillus thermotolerans, Sulfobacillus acidophilus, and Ferroplasma acidiphilum that maintained the oxidation-reduction potential in the desired range. However, the consortia also showed evidence of synergistic interactions between 'weak' iron oxidizers that increased the efficiency of ferrous iron oxidation that resulted in oxidation-reduction potentials above the desired range and lower copper release. Therefore, while designing microbial consortia is a promising strategy to improve the performance of chalcopyrite bio-leaching, care must be taken to ensure synergistic effects do not result in high oxidation-reduction potentials.