1156 4 SEPTEMBER 2020 • VOL 369 ISSUE 6508 sciencemag.org SCIENCEPHOTO: DE BEERS GROUPI
n July 2019, Gregory Dipple, a geolo-
gist at the University of British Colum-
bia, Vancouver, hopped on a 119-seat
charter flight in Yellowknife, Canada,
and flew 280 kilometers northeast to
the Gahcho Kué diamond mine, just
south of the Arctic Circle. Gahcho
Kué, which means “place of the big
rabbits” in the Dënësu ̧łinë language
of the region’s native Dené or Chipewyan
people, is an expansive open pit mine
ringed by sky-blue lakes. There, the mining
company De Beers unearths some 4 mil-
lion carats’ worth of diamonds annually.
But Dipple and two students weren’t there
for gems. Rather, they were looking to use
the mine’s crushed rock waste as a vault to
lock up carbon dioxide (CO 2 ) for eternity.
At Gahcho Kué, Dipple’s team bubbled
a mix of CO 2 and nitrogen gas simulatingdiesel exhaust through a grayish green
slurry of crushed mine waste in water.
Over 2 days, the slurry acquired a slight
rusty hue—evidence that its iron was oxi-
dizing while its magnesium and calcium
were sucking up CO 2 and turning it into
to carbon-based minerals. The CO 2 -hungry
waste from the diamond mine is an exotic
deep-earth rock, shot up to the surface
in the volcanic eruptions that bring up
diamonds. But a wide array of rock and
mudlike wastes from mining, cement and
aluminum production, coal burning, and
other large-scale industrial processes share
a similar affinity for the greenhouse gas.
Known as alkaline solid wastes, these ma-
terials have a high pH, which causes them
to react with CO 2 , a mild acid. And unlikeother schemes for drawing excess CO 2 from
the atmosphere, these reactive rocks can
both capture the gas and store it, locked
away permanently in a solid mineral.
“The potential is real,” Dipple says. “It
will make an important contribution to
lowering CO 2 .”
If he and others can make the scheme
practical, it could address two environ-
mental problems at once. Today, mines
and industry generate some 2 billion tons
of alkaline solid wastes every year, and
more than 90 billion tons are stored be-
hind fragile dams and heaped in waste
piles, a threat to people and ecosystems
(Science, 21 August, p. 894). In 2010, for ex-
ample, a dam failure in Hungary released a
2-meter-high wall of red mud—an alkaline
waste from aluminum production—that
killed 10 people and buried villages. AndIndustrial waste can combat climate change
by turning carbon dioxide into stone
THE CARBON VAULT
By Robert F. Service
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