Can Toxic Mining Waste Help Remove CO2 from the Atmosphere?

Many mined materials, including nickel, platinum, diamonds, and asbestos, are found in so-called ultramafic rock: rocks that are high in magnesium, an alkaline metal. After mining companies extract the targeted materials, they bulldoze the magnesium-rich leftovers into enormous tailings piles, where that material reacts with atmospheric carbon dioxide to form magnesium carbonate, a solid. This “new” rock can permanently sequester that carbon — whether in the earth or, potentially, in uses like concrete.

This process, commonly referred to as “carbon mineralization,” occurs in nature, but it happens over a much longer time scale — hundreds or thousands of years. But as the planet warms and scientists call not only for cutting the use of fossil fuels but also removing carbon dioxide from the atmosphere, more and more companies are investigating how to speed up carbon mineralization, either by breaking up alkaline rocks with heat or chemicals to create more surface area or by moving air through large piles of tailings.

The business case for carbon mineralization, as this process is known, rests on the sale of carbon removal credits and the sale of tailings byproducts, like silica and nickel, for use in construction and electrification. “That’s what’s going to make these projects happen, if there’s enough funding [from either of these revenue streams,]” says Abby Lunstrum, research associate at the Clean Energy Conversions Laboratory at the University of Pennsylvania, where researchers are investigating carbon removal using asbestos tailings and other sources.

A 2022 report by the Lawrence Livermore National Laboratory estimated that existing asbestos tailings in Canada and the United States could remove up to 750 million tons of CO2 in total — while also removing an environmental health hazard.

“It’s potentially a win-win situation on so many different levels,” says Lunstrum.

Asbestos is the name for a group of minerals whose fibrous structures make them extremely strong, lightweight — and deadly. When asbestos fibers enter human bodies — by being inhaled — they cause cancers in the lungs, ovaries, and gastrointestinal tract, as well as other diseases, which develop decades after exposure. The U.N. has said there’s no safe threshold of exposure, and for former miners, the risk is particularly acute; one 2019 study of asbestos miners in Italy found rates of asbestos-related diseases up to 360 times higher than the general population. A 2013 registry of former Baie Verte miners found that of 1,003 registrants, 109 had asbestos-related diseases.

Living near tailings also poses a r­­isk. Studies of communities close to asbestos mines in the town of Thetford Mines, in Quebec, found that nearby towns were “severely contaminated” by asbestos dust from tailings piles, and that asbestos fibers had contaminated nearby water bodies, likely impairing aquatic life and reducing biodiversity.

A 2006 study commissioned by the province of Newfoundland found the mine site in Baie Verte was “heavily laden” with airborne asbestos. While a 2011 report found “acceptable quantities” of asbestos in samples taken intermittently outside the Baie Verte town hall, residents say the full impact of airborne asbestos remains unknown. Calls to expand the miner’s registry to include residents were unsuccessful.

Carbon mineralization has helped regulate the Earth for millions of years, and there’s more than enough alkaline material on the planet to stabilize our changing climate. But most alkaline rocks are not exposed to the atmosphere — a potential missed opportunity, since the International Panel on Climate Change has estimated that keeping global warming to 2 degrees Celsius will require sucking up to 20 billion tons of carbon dioxide from the atmosphere every year by 2100.

On their own, asbestos tailings, which consist of mounds of gravelly rock, already absorb large amounts of CO2; a 2022 study conducted at the King City asbestos mine, in San Benito County, California, found the tailings pile was absorbing up to 179 tons of CO2 a year. But processing can accelerate absorption, vastly increasing the carbon removal potential.

The first pilot project using tailings of any kind is underway at an operating nickel mine in Western Australia. The project is run by the startup Arca, which was spun out of research conducted at the University of British Columbia. To increase the rate of reaction with CO2, Arca uses “rovers” — remote-controlled robots that look like go-carts perched on corkscrews — to churn the tailings, bringing unmineralized rock to the surface. According to the company’s analysis of tailings’ mineralogy at sites around the world, roughly 50 tons of ultramafic tailings will absorb a ton of CO2, and with this churning approach, tailings capture CO2 10 to 25 times faster.

Arca is also developing a technology that heats tailings to over 1,000 degrees F using microwaves, breaking apart the mineral structure of the rock and liberating its magnesium; that magnesium could then be taken to a storage site where the churning ensures it mineralizes. This process not only accelerates carbon dioxide removal by making the tailings more reactive — it could also, if applied to asbestos tailings, potentially destroy the carcinogenic fibers, though the company said it still needs to test this. Arca is currently exploring a partnership with BAIE Minerals and is conducting tests on samples from the site in Baie Verte to determine whether the tailings are the right type for their technology.

BAIE Minerals cofounder Mike Sullivan says the company’s primary aim is to extract critical minerals such as magnesium and silica from the tailings for use in cement, fertilizer, and other industrial purposes. That will involve wetting the tailings so that they don’t become airborne and then leaching minerals from the tailings using an acid solution. Eventually, the company will also begin using tailings for carbon removal, potentially using the microwave method.

In Val-des-Sources, Quebec, Montreal-based Exterra Carbon Solutions opened a pilot facility to process asbestos tailings from the region’s mines in March 2024. The company treats tailings with a strong acid to disintegrate the asbestos fibers and extract silica, nickel, and other desired metals. What’s left is high-purity magnesium oxide, which absorbs 1.1 tons of CO2 per ton of material and forms magnesium carbonate. According to CEO and cofounder Olivier Dufresne, the process allows absorption of CO2 “within a few hours.”

Dufresne said the pilot facility can currently process around 200 pounds of tailings an hour, producing about 300 tons of magnesium oxide per year. The company says it aims to build a full-scale facility in 2027.

Ian Power, an assistant professor in environmental geosciences at Trent University, in Ontario, says that processing asbestos tailings with chemicals or in microwave reactors has the advantage of destroying fibers, but it’s expensive. Whether such projects can be economically viable depends on the price of carbon credits. “If you have a price of $200 a ton, then that opens up the doors to do certain things,” he says. “If it’s lower, then maybe that doesn’t make sense.” Power says pilot-level projects still have a way to go before reaching commercial application.

Still, critics are concerned that using asbestos tailings for carbon removal could exacerbate human health risks if the material is pulverized to increase its surface area, as has been explored for other types of reactive rock. “The last thing we want is to grind up these tailings and distribute killer asbestos fibers into the air,” says Daniel Green, with the group Société pour Vaincre la Pollution. “It is dangerous to the workers. It is dangerous to the communities where these plants will be built.”

Paul Demers, director of the Occupational Cancer Research Center in Toronto, says that disturbing tailings could send them into the air and increase health risks, particularly for workers — but leaving the tailings as they are isn’t a safe option either. “I think there is enough evidence of people living near sites having an increased risk of cancer that I would worry about it,” he says. “There’s really no easy answers to this.”

Amanda Humby, chief administrative officer of the town of Baie Verte, says that the town’s priority is residents’ safety. Any tailings project that goes forward will need oversight from both the town and the province, she says. But she’s “cautiously optimistic” that the BAIE Minerals project could deliver a solution for the community.

Natural Resources Canada considers carbon mineralization a sector with long-term growth and export potential. Agency spokesperson Maria Ladouceur said in an email that the specific safety measures and regulations for carbon mineralization of tailings will depend on the type of mine waste being used.

Mick Breen isn’t convinced.

Breen grew up in Baie Verte. While he left after high school, he still has a place in town and comes back regularly to visit his mother (his father, who worked in the mine, died in 2023). Breen is frustrated by the province’s lack of reclamation on the site. “If you go down there now, all that’s missing is the big heavy-haul trucks. It looks the same as it was when it was in operation.” He is skeptical that BAIE Minerals has the technology it needs to use the asbestos safely.

To help reassure residents that the mine site can be safely remediated, BAIE Minerals plans to establish a demonstration project at the community college campus in Baie Verte this year. But if there are health effects from using asbestos for carbon removal, says Demers, it could take about 30 years for those impacts to manifest.