Contact Us

Case Study

Homestake's Nickel Plate Mine

A view of Tank 1 in the anaerobic circuit.

At the end of mine life, Homestake's Nickel Plate Mine had a tailings pond containing water with over 1.4 g/L of thiocyanate (a sulphur derivative of cyanide), which needed to be treated before the water could be discharged. Homestake initially looked at chemical treatment processes, but they proved unreliable and inadequate. Biological degradation was investigated as an alternative. Microbial Technologies was part of a team that developed the treatment process eventually adopted. In this process, thiocyanate is biologically oxidized to ammonia, then to nitrate in an aerobic circuit. Next, nitrate is converted to nitrogen gas by denitrifiying bacteria in an anaerobic circuit.

Microbial Technologies provided bacterial cultures and characterized microbial populations in the aerobic and anaerobic circuits for both the pilot-scale and full-scale treatment plants. Our work demonstrated that thiocyanate biodegradation is very robust, being unaffected by sudden influxes of thiocyanate, ammonia, or nitrite. We also demonstrated that metal-cyanide complexes are biodegraded in the aerobic circuit. Finally, we identified key operational and process control parameters for the treatment plant.

The treatment plant has operated continuously since October 1996, treating flows of 750 - 1,100 L/min . Considering that winter temperatures average minus 20ºC at the mine site, this system demonstrates that biological treatment can operate effectively in a northern setting. We are proud of our contribution to this unique solution to a difficult environmental problem.