- Extreme rock weathering is a carbon removal technology that is attracting investment from the likes of Microsoft
- The technology, based on mineral-rich rocks like basalt, has the ability to both sequester carbon into the oceans and return nutrients to tired soil
- ERW startups are looking to raise money through carbon credits, at a current rate of around $300 per tonne
- Although the efficacy of ERW is not in doubt, the technology needs methodologies to verify CO2 removal
October 31 – Of all the ideas and technologies touted for carbon removal, enhanced rock weathering (ERW) seems to garner some of the greatest enthusiasm. Scalable, with a variety of catalytic units available, it also has the ability to both sequester carbon in the oceans and return nutrients to tired soils.
However, there are questions as to whether the science is still robust enough to support some of the claims being made about it.
The technology is relatively simple. First, mineral-rich rock such as basalt is broken up to form a fine dust that is spread over fields and pastures, reacting with CO2 and water in the atmosphere to form carbonates. They lock in CO2 and, over time, are released from the fields, passing through rivers and streams before finally ending up at the bottom of the ocean.
According to Professor David Burling, director of the Leverhulme Center for Climate Change Mitigation at the University of Sheffield, the idea of sequestering carbon and then releasing it into the deep ocean was first mooted in the journal Nature in 1990. Viewed as “quite leftist idea,” Birling says, was largely forgotten until 2016, when scientist Olaf Schuyling began investigating the carbon-trapping power of a silicate called olivine.
Interest in science was revived and the Leverhulme Center was established that year, which soon began a series of international ERW trials with an emphasis on basalt. The center was also the first to demonstrate the dual benefits of ERW and its ability to improve soil health and yields as well as sequester carbon.
The research, Beerling says, saw the market spiral. “I’ve never seen my work stimulate so much commercial interest,” he says.
Called the mother rock, basalt is a volcanic mineral and one of the most abundant on the planet. That makes it obvious for scaling, Burling says, especially since it’s so rich in both the elements needed to capture carbon—calcium and magnesium silicates—and in nutrients like phosphorus and potassium for crops.
Olivine, a common underground mineral mined around the world, also has its champions, and Eion Carbon is one of several companies looking to harness its insulating powers. It has been approved in the U.S. as a soil improver since 1940, despite the fact, Burling says, that it can contain both chromium and nickel and is mined along with asbestos, neither of which would be welcome in the food chain.
However, Eion claims extensive research has been carried out on the raw materials that come from the same quarry in Norway, a country that supplies almost half of all olivine used for industrial purposes. They have shown that levels of asbestos are lower than those normally found in background air.
In the Netherlands, the company greenSand is promoting olivine for use in urban settings such as bike lanes, parking lots and general landscaping, while Vesta is spreading olivine on US beaches, where it can absorb carbon before being washed away by the tide, at the same time, the charity says organization, helps neutralize acidity in the sea.
A third possible additive is unused concrete. This is currently limited to pulverizing primary waste into a fine powder, with the processes required to sort concrete from other contaminants in demolition waste still being developed.
Silicate Carbon works with farmers in Ireland to distribute the crushed concrete, CEO Maurice Bryson explains in a written response to The Ethical Corporation. Additional trials are planned in the United States and Europe.
“Our material is completely safe for application on agricultural land and meets European regulations for liming materials,” he says. Adding lime to soil changes its pH and increases its effectiveness. Returned concrete accounts for between 1-4% of the 30 billion tonnes of concrete produced globally each year, he adds, providing an abundance of aggregates.
“ERW has huge potential,” says Bryson. “Once you apply the material to the fields, it goes to work—no energy required.” And while it may lack the rich mineral mix of basalt, he adds, concrete weathers 20 times faster, speeding up the sequestration process.
However, basalt remains the clear market leader. Edinburgh-based UNDO was one of the first companies to use basalt commercially, its rapid growth limited by a recent deal with Microsoft to spread 25,000 tonnes on UK farmland, permanently removing 5,000 tonnes of CO2 over the next 20 years. The basalt used by UNDO is a waste product produced by mining industries.
Company founder Jim Mann says UNDO is now starting trials in Australia, Canada and East Africa, where he believes ERW can also play an important role in supporting climate justice because the work can be done locally. “You’re not using Western technology like you would with other high-tech solutions,” he says.
This is also where basalt’s role as a soil improver pays off, he adds, increasing yields in areas where artificial fertilizers are scarce and expensive.
Seattle-based basalt Lithos Carbon views basalt as a fertilizer substitute first, and its carbon sequestration potential second. Crushed basalt is currently spread over 130,000 acres in nine US states and, as with UNDO, is provided free to farmers.
Lithos is one of the businesses receiving investment from Frontier, the collaboration of leading businesses including Alphabet, Shopify and Meta that acts as an Advance Market Commitment (AMC) to accelerate the development of carbon removal technologies. Last year, Lithos also became one of Frontier’s largest providers of carbon dioxide removal (CDR) credits created through ERW.
This improves collaboration, explains company co-founder Mary Yap, who works closely with farmers to monitor what’s happening to the soil. Details of basalt’s impact on different soils and the amount to apply are added to a database that Lithos uses to demonstrate its effectiveness, says Yap, who has seen yields improve by up to 47% in some cases.
She believes nature-based solutions like ERW are ready to scale, but they need to be proven to work if farmers want to use them, and their capture powers stamped so individuals and companies can buy credits for remove carbon with confidence. “We want to create a carbon removal product that really has no doubt,” she says.
Beerling agrees that measurement, reporting and verification (MRV) is critical. Currently, the standard method is to measure how much basalt has been mixed into the soil and then regularly measure soil samples to see how much has dissolved. The gray area is “leakage” and the amount of carbonate lost during the journey to the sea.
The key standard in the market is Puro.earth’s improved rock weathering methodology, which launches in 2022 for use in the voluntary carbon market and enables the issuance of what Puro calls CO2 Removal Certificates (CORCs). Two US-based organizations, Verra and CarbonPlan, are also working on their own verification frameworks.
Lithos offers “cradle-to-grave” measurement, Yap says. “We don’t ship anything until we measure it.” Under certain conditions, she says, such as particularly acidic water environments, bicarbonate can be re-released as a gas. To counter this, Lithos is working with the US Geological Survey, which uses 2 million data points across the United States’ river network to monitor water chemistry.
Yap says this allows Lithos to remove the carbon element from each leak, so when it comes to offering remediation credits, they’re accurate and transparent.
Lithos also licenses its technology, helping agricultural companies as well as NGOs by testing samples of their basalt “to make sure it’s free of heavy metals and safe,” says Yap. They also make sure that the crushed basalt has the right particle size so that the kinetics and chemistry of the rock dust are optimized for carbon sequestration.
“By adding it safely to just a small percentage of the world’s arable land, you can start to remove the gigatons (CO2) we need,” she adds.
Most ERW startups are looking to raise money by selling CDR credits, with the going rate around $300 per ton. While the efficacy of ERW is not in doubt, some of the claims being made are very ambitious, Beerling says, with companies talking about their ability to deliver megatons of CO2 removal without specifying how they will achieve it.
In many cases, he suggests, marketing may have trumped science, which risks muddying the waters when it comes to selling CDR credits. “Things need to be reported in a verified way … (we) need to see the methodologies they used to verify the C02 removal.
“What we want to avoid is some of these spurious claims … without hard evidence that are still out there in the peer-reviewed literature.”
There is also a need for a clearer international standard for ERW that unifies non-standard protocols developed by individual companies, Beerling says. He also wants to see more government support and is part of a delegation heading to Brussels to convince the EU that ERW deserves a place alongside direct air capture and biochar in the upcoming Carbon Removal Certification Framework (CRCF) of the block.
But despite the pressure, Beerling remains confident that ERW is the removal technology that will reach gigatons the fastest. “We’re not inventing new technology,” he says, “it can be deployed immediately.”
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