Meet a startup that plans to use mining waste to capture carbon dioxide

Travertine Technologies has backing from Stripe’s carbon-removal fund for a novel system to store CO2 in discarded rocks and help clean up the mining industry.

several excavators sit idle at a large lithium mine site
A lithium mine in Zimbabwe (Tafadzwa Ufumeli/Getty Images)
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A new startup in Boulder, Colorado says it has developed a way to use discarded rocks to remove carbon dioxide from the atmosphere.

Travertine Technologies is among the latest entrants in the fast-growing field of carbon dioxide removal.” Hundreds of early-stage ventures and research initiatives are attempting everything from building enormous air filters and planting kelp forests to improving soil health and, in Travertine’s case, accelerating geological processes — all in an effort to draw down planet-warming CO2.

What makes Travertine unique is that it’s also focused on cleaning up the mining sector. When mining companies dig for metals and minerals, they leave behind enormous piles and ponds of residual rocks, chemicals and contaminated water. Deposits of mine tailings” are only expected to grow in the coming years as the demand for metals soars, driven by the increasing need for electric-vehicle batteries and other clean energy technologies.

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Travertine aims to curb that waste in two ways: by recycling chemicals used during mineral extraction and by transforming leftover rock into CO2 sponges.

We really want to facilitate mining those critical elements that are needed for electrification, and to make [mining] more environmentally friendly,” Laura Lammers, founder and CEO of Travertine, told Canary Media.

Earlier this year, Lammers spun Travertine out of her lab at the University of California, Berkeley and opened a facility in Boulder using $3 million in seed funding. Now the startup is working to scale its relatively tiny laboratory model to a pilot-sized project at a mine site by the end of 2023.

several people with safety gear on work in a scientific laboratory
Researchers test a lab-scale model of Travertine's carbon-removing technology. (Travertine)

Frontier, a new fund owned by online-payment company Stripe, recently agreed to pay in advance for every ton of CO2 the Travertine pilot project will eventually remove. The fund’s members also include Google’s parent Alphabet, Facebook’s parent Meta, the consulting firm McKinsey and the e-commerce platform Shopify. Together, participants have committed to spend nearly $1 billion to pay for carbon removal. The idea is to help fledgling, expensive technologies achieve commercial operation — while also allowing corporations to claim credit for offsetting their own emissions. 

In late June, Travertine was one of six carbon-removal companies to receive a combined $2.4 million in Frontier’s first purchase round. Two of the other startups — Lithos Carbon and Calcite-Origen — are also working with minerals, though neither is focused on mine waste. AspiraDAC and RepAir are both building systems that capture carbon directly from the air, while Living Carbon is attempting to sequester CO2 using algae.

We are always looking for more pathways [for carbon removal] because doing this at scale is so challenging,” said Scott Litzelman, the program lead for Stripe’s Frontier fund. And it’s important to show that there is private-sector demand for these services.”

Climate scientists say that while the world must prioritize rapidly reducing greenhouse gas emissions and replacing fossil fuels with clean energy, those actions alone likely won’t be enough to limit global warming to 1.5 degrees Celsius. Eventually, countries may need to draw down billions of tons of CO2 from the atmosphere every year to avoid dangerous warming levels, according to the United Nations’ Intergovernmental Panel on Climate Change. So far, however, companies and researchers have intentionally removed fewer than 10,000 tons of CO2.

If you think of where we are on carbon dioxide removal now compared to where we need to be by midcentury, that gap is just massive,” Litzelman said.

Speeding up Earth’s slow-moving process

Travertine’s approach stands apart in that it plays to both sides of the climate-fighting coin: decarbonization and carbon removal.

The basic premise of the company’s technology is to combine mine waste with air in an electrochemical reactor powered by renewable electricity. A series of chemical reactions then take place. Sulfate in the mine waste is upcycled to produce sulfuric acid. The chemical is commonly used to leach critical elements like lithium from claystone deposits, and it can be used to further extract battery metals like nickel and cobalt from certain types of mine tailings.

A small metal device with several cords and tubes attached to it
An electrolyzer drives the electrochemical reactions that turn mine waste into sulfuric acid and carbonate minerals. (Travertine)

Lammers, who until recently was a professor at UC Berkeley, said she was inspired to focus on the mining sector after learning about companies’ plans to expand lithium production. In Nevada, for example, developers of the proposed Thacker Pass lithium mine plan to truck sulfur into the high desert and burn it there to produce up to 5,800 tons of sulfuric acid per day. Much of that will ultimately end up as sulfate waste, threatening to contaminate water and the fragile ecosystem.

Our process upcycles that back into sulfuric acid to further the extraction process,” Lammers said, so we can mitigate waste in that way.”

Also inside the reactor, minerals in the mine waste react and form a bond with CO2 from the air. This creates carbonate minerals, such as limestone or magnesium carbonate. The resulting material can be used to make cement — in turn helping clean up another carbon-intensive process. Or it can serve as inert filler in mine waste landfills to keep toxic metals from leaching out. 

Either way, the CO2 stays locked in the rocks for potentially millions of years. In nature, the process of carbon mineralization” happens when volcanic and metamorphic rock are exposed to air, though at dramatically slower timescales. 

We’re trying to accelerate the processes that the Earth uses to sequester CO2,” Lammers said.

Travertine can’t yet disclose the site for its pilot project, but the startup is in early conversations with mine operators in the U.S. and other countries, she said. The facility will be designed to produce and recycle 2.2 tons of sulfuric acid and remove 1 ton of CO2 per day, according to its application to Stripe’s Frontier fund. Ultimately, Travertine aims to remove hundreds of millions of tons of CO2 every year as part of the broader global effort to curb carbon in the atmosphere.

Using rocks to sequester CO2

At least a dozen other initiatives worldwide are striving to use rocks in various ways to limit global warming. These efforts are often described as carbon mineralization, enhanced mineralization” or enhanced weathering.” They all broadly involve supercharging the natural processes by which minerals absorb CO2 from the atmosphere.

In Iceland, Carbfix takes the CO2 captured by Climeworks’ giant air-sucking fans and injects it below ground, where it reacts with and stays sequestered to basaltic rock. Lithos Carbon proposes to crush basalt rock into dust and then sprinkle it over croplands. Minerals in the rocks soak up carbon while also adding nutrients to the soil that, ideally, boost crop growth. Vesta is taking its approach to the sea. For its first field pilots, the company — backed by Stripe and climatetech accelerator Third Derivative — is planning to pulverize and spread the mineral olivine across the coastal waters of Southampton, New York and Puerto Plata, Dominican Republic. (Third Derivative and Canary Media are both subsidiaries of think tank RMI.)

Other researchers are exploring carbon mineralization for mine waste in particular, though in different ways than Travertine. 

Mine waste is particularly appealing because there’s already so much of it in the world, and it often contains favorable minerals such as calcium and magnesium, said Rachael James, a geochemistry professor at the University of Southampton in England, who is also studying the CO2-absorbing potential of mine tailings. 

Whereas other mineral-focused approaches require digging for fresh rocks and crushing them up — creating carbon emissions in the process — mine waste can more easily be repurposed using existing infrastructure. Plus, the waste itself poses an enormous hazard to communities and ecosystems, particularly when the dams and ponds that hold it all in place burst or leak.

That started us thinking about if, in a circular economy, those waste products could be used for enhanced rock weathering,” James said. A, it sort of helps solve the issue of what to do with these mine tailings, and B, it redeploys those mine tailings to remove carbon dioxide from the atmosphere.”

James is heading a research project to determine whether the rock waste stockpiled at mine sites can be safely and effectively dusted over fields to sequester CO2. She’s also leading real-world experiments at the University of Illinois Urbana-Champaign to study how crushed volcanic rock affects corn and soybean crops. Other affiliated experiments include spreading basalt particles on a sugarcane field in Australia and sprinkling rock dust on palm oil plantations in Malaysian Borneo. 

The scientists are looking to monitor and measure not only how minerals absorb CO2 but also what happens across the ecosystem, including when rainwater washes those minerals into streams and, ultimately, the ocean. A key concern is that the minerals could increase concentrations of heavy metals in water supplies, threatening people’s health and potentially hampering crop productivity, James said.

Scott Chang, a professor in soil science at the University of Alberta in Canada, said he’s skeptical that crushing and applying rocks to sequester carbon will pan out as a climate change solution, given that significant amounts of material would need to be spread over massive tracts of land to make a dent in atmospheric CO2. Last year, he co-authored a paper that argued the current assessments of enhanced weathering are too optimistic, as environmental and human health risks have been overlooked.”

However, he said, Travertine could potentially sidestep some of those risks, owing to its closed-loop approach. Rather than spread material across farms or beaches, the byproducts from Travertine’s electrochemical reactor will either go back into mining operations or be stored on mine sites.

There is that potential benefit, in that they have more control over the fate of some of these contaminants,” Chang said. If done properly, it could potentially be quite an environmentally friendly operation.”

Maria Gallucci is a clean energy reporter at Canary Media, where she covers hard-to-decarbonize sectors and efforts to make the energy transition more affordable and equitable.