Attenuation of pollution risks in sulfidic lead‑zinc tailings through accelerating weathering of sulfides by indigenous Acidithiobacillus consortia

The long-lasting pollution risks from sulfidic and metalliferous tailings are caused by the unpredictable weathering of unstable sulfidic minerals and associated release of potentially toxic soluble metals. The present study aims to investigate whether indigenous Acidithiobacillus consortia containing ferrous iron (Fe) and sulfide (S) oxidizing bacteria could be harnessed to accelerate the weathering of sulfidic minerals (e.g., pyrite, galena) in lead (Pb)‑zinc (Zn) tailings for rapidly attenuating the risks of toxic metal contamination. After a 72-day incubation of the tailings bioaugmented with indigenous Fe oxidizing bacteria (FeOB), sulfur oxidizing bacteria (SOB) and their combination (FeSOB), it was found that sulfidic minerals were significantly weathered to form secondary mineral cements and develop cementation structure. The combined indigenous FeSOB groups exhibited greater functional advantages over the individual groups. According to the synchrotron-based X-ray fluorescence microscopy coupled with X-ray absorption near edge fine structure spectroscopy (XFM-XANES) analysis, the mineral cements were largely composed of secondary Fe oxyhydroxides and jarosite which captured metals (such as Zn) released from the weathered minerals. Furthermore, the in situ formation of cementation structure passivated and encapsulated remnant sulfide particles, presenting a physical barrier against further weathering and toxic metal release. The study has revealed the critical role of indigenous FeSOB in sulfidic mineral weathering and toxic metal immobilization in Pb-Zn tailings, providing important basis for developing in situ field-based technologies towards pollution control of sulfidic and metalliferous tailings.