McClean Lake's JEB tailings management facility
A lot can happen in ten thousand years. This is longer than the lifespan of any human civilization to date, and longer than all but the sturdiest human-built structures can remain standing. Yet predicting what will happen over this time frame — and building to withstand anything from earthquakes and floods to beaver infestations — is a challenge uranium mining operators must overcome.
The millennia-long time frame is one mandated by Canada’s nuclear regulators, explains Jim Hendry, a professor of hydrogeochemistry and Cameco Research Chair at the University of Saskatchewan. The regulators place the same restrictions on uranium mine tailings as those placed on nuclear waste, says Hendry.
“What we have to do is take what we know about the tailings and ask, ‘What could happen in 10,000 years? What could change?’ And some of these changes could be arsenic, selenium or molybdenum leaching into a solution.” Coming up with progressively more accurate answers to this question is what Hendry and his team have been working on for almost 20 years.
The main danger in the tailings is not radiation, but a mix of arsenic, selenium and molybdenum. All three are highly toxic and can pose a significant danger if they happen to leach into the groundwater. Radiation is a lesser concern; the tailings contain a small amount of radium-226. But Hendry points out that radium is fairly short-lived, the element’s half-life being roughly 1,600 years — the term “short-lived” having a very different meaning for geologists.
To construct a reliable model for what arsenic, for example, might do over a few thousand years, Hendry first had to find out where it was now. This was not as straightforward a question as one might first think because in the overall mass of earth and clay, the dangerous minerals comprised a very small percentage and could be attached to any number of otherwise harmless particles, in any number of ways.
“It’s only because of synchrotron radiation, the high-energy beam lines, that we’ve been able to answer this,” says Hendry, looking back on the last decade’s worth of efforts. “Now we know fairly well where these materials sit, what solids they’re on, what they’re associated with, what the binding angles are, and so on.”
Most recently, Hendry has been using the information to run experiments, attempting to further refine and validate the models for what factors might influence the tailings ponds in the very distant future.
Despite the extremely long outlook, there are some short-term implications for the uranium industry’s work. Hendry’s team has been working in partnership with Cameco and, more recently, AREVA Canada. Today, Cameco is looking at modifying their extraction process based on Hendry’s results.
Hendry explains: “Now that we understand the geochemical controls on present-day tailings, the question is, can we go back into the mill process and modify that process to improve on the minerals going into the tailings? So, if there is a potential that one of the minerals may form and not be very stable at certain pH levels, we’ll say ‘we’re not going to precipitate that mineral. We’re going to consider precipitating this other mineral by changing the mill process, and the new mineral may have a lower solubility and, thus, fewer chances of contaminating the groundwater.’”
Hendry’s work is not limited to the uranium industry — most mining operations create tailings ponds and must ensure the long-term safety and stability of those. Radium is the only aspect that is unique to the uranium industry, he says; most of his lab’s work can be applied elsewhere in the mining world. Illustrating this is a second set of projects Hendry has been working on, looking at the long-term movement of salts from tailings generated by the potash industry.