UBC Reports | Vol.
51 | No. 1 | Jan.
Turning Gold into Green with Old Mine Tailings
Waste rock may help slow global warming, says geochemist
By Michelle Cook
Long considered an eyesore and an environmental problem,
mine tailings -- the waste rock produced in the mining process
-- may actually be helping to slow global warming by absorbing
the greenhouse gases thought to cause climate change.
Greg Dipple, an associate professor of earth and ocean sciences,
has been studying the waste rocks’ ability to soak up
carbon dioxide (CO2) and hold, or sequester, it for long periods.
His findings could impact mining operations worldwide.
Dipple first saw the phenomenon during a joint project in
southern Quebec with Laval University. Working at decommissioned
mines in Cassiar, northern B.C., and Clinton Creek, Yukon,
for the past two summers, Dipple and his research team documented
how the tailings -- the crushed rock left over after the profitable
ore has been extracted -- suck CO2 from the atmosphere.
“It was pretty exciting to see this. This is something
that occurs naturally on geologic timescales,” Dipple
says. “We found that it happens quite quickly in mine
tailings. We didn’t expect that.”
The effect is very similar to chemical weathering he explains,
and occurs in tailings rich in magnesium silicate -- such
as those derived from nickel, diamond, chrysolite, platinum
group elements and some types of gold mines.
In a natural process called mineral carbonation, CO2 carried
in rainwater reacts with silicate minerals on the surface
of the tailings. The reaction binds CO2 in a solid form to
the rock where it can remain in a benign state for thousands
Human activity releases about eight billion tons of CO2
annually. With 500 million tons of waste rock in southern
Quebec alone, Dipple thinks their potential as a CO2 sink
“With tweaking, the tailings could soak up all the
greenhouse gases that mining operations produce. I think it’s
possible that we could turn large mining projects into a greenhouse
gas neutral industry,” he says.
It’s also possible that mines could soak up more than
they produce, earning them carbon credits -- the system being
developed under the Kyoto Protocol, an international agreement
aimed at reducing greenhouse gas emissions. The credits could
be used to pay for mine reclamation. CO2 credit futures currently
trade for about CD$1.23 / tonne at the Chicago Climate Exchange,
and are predicted to increase in value to CD$10/tonne or more
as the Kyoto Protocol is implemented.
Not surprisingly, mining companies have taken notice of
“They didn’t believe it at first, but now they’re
starting to call,” he says.
But Dipple cautions that his findings don’t offer
a simple “throw it in a hole” solution to reducing
carbon dioxide emissions. The next step is to figure out how
to speed up the absorption process. Although Dipple and his
team were surprised at how fast the process was occurring
naturally in some mine sites, at others it was hardly noticeable.
The challenge will be to model and accelerate the natural
reaction between the mine tailings and CO2 at a cost that
will be viable for mine owners.
“It’s unpredictable because it all comes down
to money,” Dipple says. “How much money will they
spend? Studies show it’s possible to get an 80 per cent
reaction in 28 minutes but only by spending lots of money.”
Nonetheless, he is optimistic that industrial CO2 sequestration
could be in use in mines in the near future.
“I think we’ll have substantial field tests
running within five years,” Dipple predicts.
He and his research team from UBC’s Mineral Deposit
Research Unit will continue their field work at an active
mine in Australia in February 2005.