Phytoremediation to improve pit lake water quality Wen, Marc Eric An-Ping; Pelletier, Clem; Norlund, K.; Wolff, W. R. Gareth; Berthelot, Debbie S.
The flooding of open pits is a key feature of closure plans for many metal mines. Once filled, pit lakes typically discharge to the environment. Pit lake water requiring treatment prior to discharge can represent a significant cost of long-term closure care and maintenance. We present phytoremediation technology that has been successfully used in many industries as a relatively low-cost technique to attenuate contaminants in water. Phytoremediation describes the use of plants to mitigate environmental contamination. In the context of mine pit lakes, phytoremediation is the biologically mediated removal of contaminants using photosynthesizing organisms to improve water quality. The relatively low-cost option of phytoremediation can make it an attractive alternative to conventional lime neutralisation for metal contamination resulting from metal leaching and acid rock drainage. Phytoremediation has also been investigated for treatment of other contaminants in mine water. Metal mine pit lakes present an opportunity to use phytoremediation to treat waters affected by metal leaching and acid rock drainage. Within a pit lake, the greatest opportunity for phytoremediation of water is in the limnetic zone, which usually occupies a much greater area and volume than the littoral zone. However, other important variables may influence the potential success of phytoremediation. Phytoremediation has been used successfully for more than a decade to treat metal-contaminated pit lake waters at the closed Island Copper Mine. We discuss how the phytoremediation program at the Island Copper Mine has been designed to treat pit lake waters to meet permit requirements and significantly reduce metal loads in the lake. Through this case study we also explore the relationships between the physical and biogeochemical characteristics of the water column and show how an understanding of this relationship is critical to planning, designing and identifying the potential success and risks of phytoremediation treatment of mine pit lakes.
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