Researchers look back to explore future of mine tailings

University of Saskatchewan researchers in partnership with AREVA Resources Canada have recently completed a major study on the long-term health of the company's uranium mill tailings at McClean Lake.

The goal of the research was to use the Canadian Light Source synchrotron to investigate the life cycles of elements contained in uranium ore milling waste, or tailings. Synchrotron technology allowed scientists to observe elements such as lead, arsenic and molybdenum at concentrations so small they cannot be observed using conventional techniques.

"We want to know how the materials that contain these elements of concern are changing over time, and if they reach a point where they form an insoluble product in which case everything would stay put," said Andrew Grosvenor, associate professor in the Department of Chemistry and the U of S lead on the project.

Uranium ore milling waste at McClean Lake is stored in a repurposed open pit mine where layers of tailings represent the evolution of uranium mill tailings over time. Drilling down into these layers gave the U of S-AREVA team an opportunity to directly observe tailings at different stages in their lifetimes.

By shining the synchrotron's bright light on 25 differently aged tailing samples, the team could see even slight fluctuations in molybdenum-containing materials over time. While a thermodynamic model predicted that the formation of solid molybdenum materials would eventually stop the element from dissolving into water, this was the first study to test and confirm this model.

The result will be invaluable to the long-term care of the McClean Lake site, and researchers are prepared to move on to other elements of concern.

"Once you understand the geochemical reactions that are occurring then you can start to predict what will be occurring over the next 50, 100 or 1,000 years in the environment," said Grosvenor.

"Our partnership with the U of S and Canadian Light Source to better understand our tailings at McClean Lake helps us provide assurance that the environment is protected over the very long term," said Dale Huffman, AREVA Resources' vice-president of safety, health, environment and quality in a June 4 media release.

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