On a hayfield in Seeley’s Bay, Ontario, a tractor pulling a spreader left a trailing cloud of crushed wollastonite rock, showcasing a strategy to capture carbon dioxide from the air and permanently store it in the mineral’s ashy particles.
The spreading was coordinated by nearby mining company Canadian Wollastonite and United Kingdom-based carbon credit startup UNDO Carbon, both aspiring to remove and store carbon on farmland through a process called enhanced rock weathering (ERW). They are partnering to mine and spread the rock on farmers’ fields for free, their costs covered by selling carbon credits.
Their plan is attracting interest from companies looking to offset emissions. In one recent deal signed with Microsoft, UNDO is selling credits to remove 15,000 tonnes of carbon dioxide by spreading crushed rock on farms in the UK and Canada, including by spreading 25,000 tonnes of wollastonite in Ontario.
Compared to other on-farm carbon credit schemes that store carbon in organic matter, ERW removes carbon through inorganic, rather than organic, chemistry — a difference that makes the removal more permanent and offers farmers a better deal.
What is Enhanced Rock Weathering?
Earlier in the day, Canadian Wollastonite President Bob Vasily brought a small crowd to see towering grey mounds of crushed wollastonite. He said wollastonite — a “little-known but extremely useful” mineral made up of calcium, silicon, and oxygen — can be important for both farmers and combating climate change. When crushed, it is perfect for mimicking a natural process that removes carbon from the air as it binds to eroding rock particles.
The process begins when rain combines with carbon dioxide in the atmosphere to create carbonic acid. When the rain reaches the ground, the carbon from the acid binds to rock surfaces as a bicarbonate molecule. That carbon remains bound as the rock slowly breaks down into sand and erodes away, eventually getting washed into rivers and, perhaps, settling on the ocean floor.
The carbon attached to the eroded rock is removed from the atmosphere for thousands of years. But the natural process happens much too slowly to combat the rapid warming of the planet. ERW speeds up that process by crushing rocks by the tonne and spreading the dust on vast expanses to bring carbon from the air to underground — accomplishing in years a transformation that naturally occurs on geologic time scales.
“It’s an incredibly low-cost way of taking carbon dioxide out of the air and storing it in the ground forever,” Vasily told the group.
According to MIT’s Climate Portal, scientists generally agree that the idea of ERW is scientifically sound, but “the challenge is making this a practical solution to climate change.”
UNDO Carbon is still collecting data to inform its models, but says that in a best-case scenario, one tonne of carbon is removed for every 1.6 tonnes of wollastonite. Farmers in the program apply an average of two to four tonnes of wollastonite per acre each year, said Canadian Wollastonite Project Manager Harris Ivens.
The net removal ends up being a bit lower because of emissions associated with the trucking and spreading, and from mining and crushing operations that can be energy- and resource-intensive. But Vasily said the company is trying to address and reduce some of those environmental damages: during a tour of the grounds, he pointed out wetland habitats being nurtured on the site and spoke of plans to establish a solar farm to power the mine’s operations.
UNDO tries to account for its own emissions, reporting that every 100 tonnes of carbon dioxide removed from spreading of wollastonite results in less than 10 tonnes of the greenhouse gas being “emitted in the process of getting it from mine to farm.”
Though different rock types can be used for ERW, those that contain silicon — like wollastonite — create a more stable bond that provides a more permanent removal. Vasily added that, because wollastonite can remove carbon fairly quickly, it is a “good demonstration mineral” to show the potential of ERW, which is still a new approach to removing carbon.
“Because wollastonite acts so quickly it can give us time to get the confidence of governments,” he said, adding that he hopes Ottawa will eventually create programs to help farmers use ERW.
If that happens, he said, “we all win.”
How does ERW fit into farming?
A plan to remove carbon by spreading rock dust on farmers’ fields wouldn’t work without buy-in from farmers. But ERW can help replace other amendments that farmers use. They have long spread crushed limestone to provide calcium and keep soil acidity within a certain range — crop and hay fields are most productive when the soil pH is around 6.0 to 7.5 — and crushed wollastonite can replace lime for that purpose.
But while farmers have to pay for the lime, Canadian Wollastonite supplies and spreads its rock dust for free, as long as the farmer pays for trucking and UNDO can sell credits for the stored carbon.
Ivens said the program can also accommodate farmers using variable-rate technology that increases amendment efficiency by adjusting spreading rates to match changing soil conditions across fields.
Jim Dennet, a crop and livestock farmer in the area, has had the partnership spread wollastonite on his fields for the past couple years. He told The Mix he signed on because he was looking to get some calcium in the soil, and it seemed like a good opportunity that would save him some money.
Dennet’s farm itself doesn’t benefit from the carbon removal. But UNDO and Canadian Wollastonite say the mineral does provide other nutrients to soils. Dennet said he hasn’t tested the soil to know for sure, but was pleasantly surprised to notice that his alfalfa crop “greened up more than [he’s] ever seen.”
His overall yields were good, as well, and though he didn’t do a direct comparison to past years, one field that usually gets fewer amendments than the others produced a lot more than usual, he said. Dennet is waiting to see if the technique will improve future soybean crops, as well.
Organic versus inorganic soil carbon
Soils store carbon either inorganically, by binding to minerals, or organically. Many existing soil carbon credit programs focus on the second option, in which carbon is stored organically in decomposing plant and animal matter. But organic carbon storage can be complicated.
For one thing, organic soil carbon can reach a saturation point that eventually stops it from being able to offset emissions.
But with ERW — which stores carbon inorganically — the limit is set by the amount of wollastonite put on the field, and that can be repeated every year. Though ERW does become less effective at higher pH levels, UNDO maintains that ERW can be continued indefinitely without becoming saturated, so long as the soil is given time for its pH to fall to lower levels after rising too high.
Furthermore, soil organic carbon is not permanently stored. Changes in weather or farm management can release that carbon back into the air. Carbon stored by using no-till practices, for instance, could be released if a farmer ploughed up a field to address a weed control issue. To address this gap, farmers may sign multi-year contracts to guarantee the carbon will stay in the soil, and they might be held financially accountable if the carbon storage goes awry, Michigan Farm News says.
In comparison, carbon stored with ERW is nearly permanent once the wollastonite is spread on the field. Farmers do need to sign a contract with UNDO to take part in their program. A copy of the contract shared with The Mix includes obligations for coordinating the spreading of crushed rock and ensuring UNDO’s access to the fields for soil testing and measurements.
The contract also specifies that farmers cannot make any claim to the carbon removed through ERW — meaning that the carbon removed by the wollastonite cannot be counted towards a farm’s own sustainability or net-zero claims. And UNDO cannot make any claim to any organically stored carbon.
Dennet said he hasn’t taken part in past carbon credit schemes and isn’t sure of their details, but so far, UNDO’s contract has not caused him any problems. He has no complaints about participating in the program, and said both UNDO and Canadian Wollastonite have been easy to deal with.
What can Enhanced Rock Weathering achieve?
Research on ERW generally supports claims that it can deliver net carbon removals, though its effectiveness can vary across soil types, climates, and application methods. One analysis by carbon research non-profit (carbon)plan found that some studies reporting ERW carbon removal in a lab-based setting did not hold up under field trials, though successful on-farm removals were reported in other studies.
(carbon)plan cautions that while ERW “might seem easier than other carbon removal approaches logistically, quantifying its impact on the atmosphere is far from straightforward.”
However, one study 2020 from the University of Guelph — which is not affiliated with UNDO Carbon — measured carbon removal from wollastonite sourced from the Seeley’s Bay mine and spread on farmland in Ontario. The study found that the applications did increase the amount of inorganic carbon found in the soil, indicating that carbon was being removed from the atmosphere. The study also supported claims that wollastonite can add nutrients to the soil, balance pH, and improve crop health.
On a global scale, UNDO Carbon says ERW “can remove four billion tonnes of carbon dioxide on an annual basis.” This could be enough to meet 40 per cent of the target to remove 10 billion tonnes of carbon each year until 2050, which some groups say is needed to avoid the worst impacts of climate change.
UNDO CEO and founder Jim Mann said Canada in particular has “immense potential” to remove carbon with ERW because of its geology and large amount of farmland. Other research has identified China, India, and the United States as three countries with the highest potential.
“I think this is going to be the most powerful tool we have for climate change,” said Mann.
This article was originally published by The Energy Mix on Sept. 30, 2024. It is republished here with permission.
