Understanding the tailings ponds breach at Mount Polley near Likely, B.C., which has emptied mine waste into waterways
On Monday, an Imperial Metals tailings pond in B.C. breached its embankment, spilling contaminated water and waste material into the surrounding waterways and spurring a state of emergency in the area. It’s raised the ire of First Nations groups, who say the company ignored a report that the growth of the pond was unsustainable.
It’s angered environmental groups, furious at the suggestion that water with arsenic and mercury was released into the lakes. But what exactly are tailings ponds? Does the industry have an alternative? We talked to Scott Dunbar, the head of the University of British Columbia’s school of mining engineering, to explain the issues at play and the institutional attitudes that need to change so this doesn’t happen again.
Q: So what is a tailings pond, and how does it work?
When you take the rock out of the ground, you grind it up to particles about the size of sand and silt, then you run it through what they call a concentration plant and it separates the minerals of interest from the waste. The waste becomes tailings, and it gets mixed up with water, and it’s pumped out into this pond. The purpose of this pond, with an embankment around it, is to retain the tailings and allow them to drain as much as possible. It’s basically sand-sized particles, but there’s an awful lot of it that’s produced relative to the minerals that generate all that cash. This waste that has to be dealt with. It’s mostly silicates. If the filtering is done well, which it usually is, there would be very few metallics.
The tailings pond is eventually drained and the tailings are disposed in a big stack of dry sand. The biggest problem with all this is water–I suspect that’s the problem here. You get rid of the water, it’s a lot easier to manage. And then the pond is eventually reclaimed; there’s some plant life that grows on top of it and other things done to it, too.
Q: Is there another way to handle the waste?
No, short of processing in situ–in other words, don’t move the rock in the first place, just process the rock right there. And that can’t be done for these copper and gold mines that are in operation, the minerals are just too tightly bound up in the rock mass, so you have to extract, crush and grind the rock. If you could do that—and this is really futuristic—with a swarm of small machines and not move the material on the ground, you could eliminate it. But otherwise, it’s a fact of life.
I wouldn’t say there’s a strong move in that direction. In situ mining and processing is done in some cases, uranium is one example, but not in others. I would have to say all of Canadian mining uses tailing ponds.
Q: What’s in the run-off?
In this particular case, I think the contamination is very dilute. The president said you could almost drink the water. Frankly, I’m more concerned about the tailings themselves. There are 15-million cubic metres spread all over the countryside. That’s going to be a bigger problem. The water’s gone, and it was diluted considerably already, and I don’t think that’s going to be a problem. They’re going to have to go over all the area and look at individual parts and places and say, ‘Do we keep it here, or do we have to move it.’ That’s going to be a long and tedious exercise.
It’s a case-by-case basis, every square kilometre will have to be looked at. It’ll depend on the site, and how close it is to the river. It doesn’t do fish habitat much good, because it covers up the river bottoms and all that. Maybe the system can tolerate that, but how much, I don’t know.
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