Immobilization of lead in tailings by Bacillus subtilis through microbially induced phosphate precipitation (MIPP)

The accumulation of heavy metal tailings has raised serious environmental concerns, especially in China. Therefore, remediation and utilization of heavy metal tailings have become urgent and vital. In this paper, an emerging technology MIPP (microbially induced phosphate precipitation) was applied and the commercial Bacillus subtilis were employed to mitigate the Pb contamination risks in tailings. Through aqueous Pb-removal experiments and tailings remediation experiments, the process and mechanism of MIPP treatment for heavy metal tailings were systematically explored. In addition, the optimal Pb-removal conditions were discussed. The results shows that the commercial Bacillus subtilis can be served as a preferable MIPP-stabilization commercial strain with lower application cost, better heavy metal tolerance, and excellent Pb stabilization compared to traditional strains isolated from contaminated sites. The mobile Pb was almost converted into Pb9(PO4)6 through MIPP treatment contributing to the Pb immobilization. According to SPLP (the synthetic precipitation leaching procedure), the leaching concentration of Pb from tailings dropped from 0.86 mg/L before treatment to less than 0.02 mg/L after MIPP remediation, which is far below China's groundwater environmental requirements (0.1 mg/L). This technology has the advantages of on-site construction and environmental friendliness. The treated tailings are expected to be safely used as construction sand for road base and mine backfilling.