Treatment of neutral gold mine drainage by sequential in situ hydrotalcite precipitation, and microbial sulfate and cyanide removal

This study proposed and validated a method integrating in situ hydrotalcite precipitation (Virtual Curtain™ (VC) technology) with bioprocess for treating a cyanide (CN)-augmented (ca. 5 mg-CN L−1) sulfate-laden neutral mine drainage, from a waste rock dump (WD2) of an Australian gold mine. Efficacies of various carbon (C) sources (ethanol, lactate, and two natural substrates; Eucalyptus wood sawdust (EW) and Typha biomass (TB)) for promoting microbial reduction in both: CN-augmented WD2 water and VC-treated CN-augmented WD2 water were assessed in a 60-days microcosms study at 30 °C. The microcosms were monitored over time for pH, redox potential, dissolved hydrogen sulfide, chloride, nitrite, nitrate, sulfate, phosphate, biogas production, dissolved organic carbon, total dissolved nitrogen, and dissolved CN. The VC treatment removed a range of metals (Mg, Ni and Zn) and metalloid Se from the CN-augmented WD2 water to below detection. Other elements substantially reduced in concentration included Ba, F, Si and U. However, the VC treatment did not remove substantial nitrate, sulfate or CN. Microcosm trials revealed that the indigenous microbial community in WD2 could effectively denitrify and reduce sulfate, with TB was the most efficient C source for promoting sulfate and CN removal; whereas, EW facilitated only marginally higher sulfate reduction compared with controls. The highest sulfate reduction rate (76 g-SO42− m−3 d−1) was achieved with VC-treated water amended with TB, indicating that VC pre-treatment was beneficial. Further, all treatments amended with external C, facilitated 100% removal of dissolved CN after 60 days, whereas only partial (65%) CN removal was recorded in the control. Overall, the proposed integrated method appears a viable option for treating neutral gold mine drainage. [Display omitted] •Hydrotalcite formation and bioreduction were combined to treat neutral mine drainage•The drainage contained cyanide (CN), nitrate, sulfate and various metals•Eucalyptus sawdust and Typha biomass were assessed as natural carbon (C) sources•The two C sources promoted complete nitrate and CN removal in microcosms in 60 days•Typha biomass was the most efficient natural C source for microbial sulfate removal