This research was prompted by a natural process called mineral carbonation, whereby surface rocks interact with carbon dioxide in the atmosphere and lock it away in solid form. This happens more quickly in ultramafic rocks such as the kimberlite from which diamonds are extracted, but still too slowly to offset man-made carbon emissions.
De Beers is now looking at ways to accelerate this natural process to safely store the carbon dioxide released as a byproduct from mining operations in tailings dams containing previously mined waste rock. Kimberlite tailings turn into a solid compound when mixed with carbon dioxide, effectively trapping the gas in rock.
Mervine says academics have been looking at the potential of mineral carbonation for years, but De Beers has now given the green light to scientists to start exploring this process in depth. With her team’s desktop research completed, assessments will be carried out at two De Beers sites – the Venetia mine near Musina in Limpopo and the Gahcho Kué open-pit mine in Canada’s Northwest Territories – to gauge the potential of their kimberlite tailings for carbon storage.
Tests will also begin in Botswana next year, Mervine says, explaining that it’s vital to assess different sites because “kimberlite varies in composition and there are subtle differences in minerology”. The process will entail laboratory experiments, conducted in association with Anglo American’s Technical team, the University of British Columbia in Canada and other research partners.
“We are targeting early 2019 to have a small small-scale pilot on a mine site in Venetia and/or Gahcho Kué,” she says. “We hope to find a solution to suit both environments.” The De Beers-funded research comes amid revised emissions targets set in the Paris Climate Agreement, and the moral and social imperative for mines to increasingly “green” their operations. It also comes when several countries (including South Africa and Canada) are implementing carbon pricing to charge companies a tax for each ton of greenhouse gas emitted.
The De Beers researchers are looking at three possible technologies: spreading the waste tailings more thinly to increase carbon extraction from the atmosphere; injecting carbon dioxide into the rock; or adding microbes to the tailings to accelerate the mineral carbonation process.
Mervine says it’s possible that the carbon storage technology could be extended to other types of mining.
“Mineral carbonation occurs in other ultramafic rocks and the potential for carbon storage there is enormous.” She says past research on carbonating ultramafic rocks has focused on storing the carbon dioxide off site, which is expensive. “Now, the research is shifting to seeing what technologies work to do this in situ in a tailings pile or rock outcrop. This method will work out much cheaper – as low as $10 (R135) to $20 per ton of carbon dioxide stored.” When carbon pricing is factored in, such technology makes good economic sense for mining operations. Mervine says carbon dioxide can be locked away in kimberlite for “thousands to millions of years”. It makes sense to invest in a greener product. “It’s really exciting. It’s important to reduce our social and environmental footprint, but I think it will also position De Beers as a leader in reducing carbon emissions.”