Stepwise Treatment and Valuable Metal Recovery from an Acidic Pyrite Mine Drainage

The direct discharge of acid mine drainage (AMD) severely degrades surrounding ecosystems. This study aims to develop an integrated microbial treatment technology for AMD and achieve the recovery of valuable metal resources.

A microbially based integrated "aerobic-anaerobic" reactor system was constructed to treat AMD from the Yunfu pyrite mine in Guangdong. By combining physicochemical analysis, mineralogical characterization, and 16S rRNA gene V4 region sequencing, we systematically investigated the treatment performance and the response mechanisms of the microbial community.

The effluent pH increased from 2.23 to 8.17, with 100% removal of Fe³⁺, Al³⁺, Zn²⁺, and Cu²⁺, and 97% and 88% removal of Mn²⁺ and SO₄²⁻, respectively. Aerobic iron oxidation and primary alkali neutralization led to the formation of schwertmannite, while further alkali neutralization produced jarosite and hydrated iron oxides. The subsequent pretreatment and anaerobic stages effectively precipitated ionic species, including Zn²⁺, Cu²⁺ and Mn²⁺. The aerobic reactor was dominated by acidophilic iron-oxidizing bacteria (e.g., Acidiphilium and Ferroplasma), which mediated ferrous iron oxidation and mineral formation was critical for iron removal. The anaerobic reactor enriched sulfate-reducing bacteria (e.g., Desulfosporosinus and Clostridium), driving sulfate reduction and metal sulfide precipitation. Notably, the anaerobic microbial community structure was significantly influenced by pH.

The system leveraged the metabolic activity of iron-oxidizing bacteria in the aerobic reactor and sulfate-reducing bacteria in the anaerobic unit to achieve stepwise AMD treatment and valuable metal recovery. These findings demonstrate a promising technical solution, in which the metabolic potential of iron- and sulfur-cycling microbes is deployed for AMD treatment.