Harmless treatment of cyanide tailings by functional bacteria: Degradation of cyanide and the secondary pollutant ammonia nitrogen

The eco-friendly treatment of cyanide tailings (CT) using microorganisms is a cost-effective and promising technology. However, this process often generates the secondary pollutants, such as ammonia nitrogen (NH₄⁺–N), which can adversely impacts the surrounding environment. The accumulation of NH₄⁺–N is also toxic to cyanide-degrading microorganisms, presenting a significant challenge in achieving simultaneous cyanide degradation and NH₄⁺–N mitigation. In this study, a group of functional bacteria CG305-1 with the ability to degrade cyanide and perform nitrification and denitrification was successfully enriched for the first time and used to treat CT by in situ microbial drenching technology. Results demonstrated that the total cyanide (CN_T) concentration in the leaching solution decreased from 49.96 ± 1.51 mg/L to 0.19 ± 1.11 mg/L. NH₄⁺–N was degraded to 0.25 ± 0.18 mg/L, and nitrate nitrogen (NO₃^––N) was reduced to 0.41 ± 0.20 mg/L. Furthermore, CN_T in the CT leachate was reduced to 0.94 ± 0.11 mg/L, meeting the storage standard for CT leachate (CN_T < 5 mg/L). The potential synergistic microbial degradation mechanisms were elucidated through scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and metagenomic sequencing. This study provides significant insights into green and sustainable methods for the harmless treatment of CT.