WHITEHORSE—Research conducted at Yukon College in partnership with Alexco Environmental Group has confirmed that bacteria native to Yukon can efficiently remove heavy metals from mine impacted water in cold climates.
Ph. D. candidate Guillaume Nielsen is the lead author of a paper published recently by Mine Water and the Environment, the journal of the International Mine Water Association (IMWA), detailing the results of a series of experiments conducted at the Yukon Research Centre lab in 2015.
Alexco Environmental Group is contracted to remediate the historic Keno Hill Silver Mine District. Presently, contaminants of potential concern in water flowing out of the mine site are removed at water treatment plants through an active process of mixing lime with the water which renders the dissolved contaminants solid, enabling them to settle and be removed.
This process requires human, industrial and financial resources to maintain over the long term, such as shipping the lime to the mine site from outside Yukon, powering the plant and daily supervision.
Alexco Environmental Group has investigated the use of a passive in situ treatment processes—specifically how to successfully apply in-mine microbiological treatment processes in a cold northern climate. They have been operating a full-scale pilot system at the Silver King Mine in the Keno district.
The goal of Nielsen’s experiments was to confirm several aspects of this passive process, namely evaluating the use of organic materials and how microbes could create a sustained process that could require less resources than active water treatment processes.
Nielsen collected sediment containing bacteria from Crystal Creek, located within the mining district, and added it to water taken from the treatment plant intake.
The key to Nielsen’s experiment was zeroing in on the most efficient carbon food source to sustain the bacteria so it would actively remove the contaminants, in a similar fashion as lime in the active process. Nielsen used molasses and methanol as food sources, both separately and mixed together.
After 90 days the food source was depleted and cadmium and zinc levels in the water had reduced by 95 and 89 per cent respectively. Further experiments showed that a mix of molasses and methanol resulted in 95 percent of the zinc and up to 99 per cent cadmium was removed.
Alexco reports these are similar to results being obtained in ongoing work being done as a full scale pilot test in the historic Silver King mine.
“These initial results are very promising and prove the theory that, with the right food source, bacteria native to Yukon are activated sufficiently to significantly reduce contaminants in mine impacted water,” said Nielsen.
Previously, experiments conducted in warmer climates achieved similar results at temperatures of 23 to 26 degrees Celsius. The experiments at Yukon College were conducted at five degrees Celsius, the year-round temperature of underground water flowing through the historic mine site.
The published paper forms one chapter of Nielsen’s Ph. D. thesis which he will defend this month at the Institut National de la Recherche Scientifique (INRS) in Quebec. Since concluding his research at Yukon College, Nielsen now works as a Mine Water Management Specialist at the Whitehorse office of CH2M.
“This research presented a unique opportunity to host a Ph. D. candidate in Yukon—to perform detailed chemistry and microbiology at small scale showing, in more detail, the full scale processes that are happening inside the mine where it is harder to determine specific mechanisms. We believe that this ongoing work strengthens industry knowledge and capacity around passive treatment systems for mine waste water in cold climates,” said James Harrington, Senior VP of Alexco Environmental Group.
“We look forward to the publication of further results from Nielsen’s work and are pleased to work with Yukon College to further develop passive water treatment expertise.”
Nielsen’s research was supervised by Dr. Amelie Janin, the NSERC Industrial Research Chair in Mine Life Cycle at Yukon College, who co-authored the paper along with Lucie Coudert, Jean Francois Blais and Guy Mercier of INRS.
Nielsen’s Ph. D. research also received support from Mitacs, a national non-for-profit research organization, and Cold Climate Innovation at Yukon College.