Simultaneous recovery of valuable metal ions and tailings toxicity reduction using a mixed culture bioleaching process

Lead–zinc sulfide mine tailings without appropriate disposal would cause resource waste and heavy metal pollution in the environment. This study aims to design a novel mixed culture A with higher leaching performance to improve the leaching efficiency of tailings, because mixed culture B consisting of ferrous oxidizer Leptospirillum ferriphilum (L. ferriphilum) and sulfur oxidizer Acidithiobacillus thiooxidans still has a long leaching period. The results showed that mixed culture A containing ferrous/sulfur oxidizers Acidithiobacillus ferrooxidans and Sulfobacillus thermosulfidooxidans shortened the bioleaching cycle by 30% to achieve the same zinc yield (94.0%) as mixed culture B. Thus, ferrous/sulfur oxidizers offer a competitive advantage over ferrous oxidizer and sulfur oxidizer, respectively, during bacterial combination to leach tailings. The better performance of mixed culture A was verified by its higher content of extracellular polymeric substances and living cells density (30.2 × 10⁷ cells mL⁻¹). Furthermore, data from microbial community succession also revealed that two bacteria could together produce acid in the mixed culture A system to substantially facilitate zinc leaching, while only L. ferriphilum played a role in mixed culture B system. Interestingly, results from toxicity evaluation of bioleached residues indicated that mixed culture A dramatically reduced the potential ecological risk index of tailings from 161.80 to 7.50, transforming tailings from hazardous waste into non-hazardous one. In brief, this study proposes a novel perspective for bacterial combinations to improve tailings bioleaching and reveals that bioleaching can reduce the eco-environmental risk of tailings.