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Microsoft is betting big on a creative new method for reducing its carbon footprint: limestone rock powder.
The tech giant recently announced a multiyear deal to purchase 315,000 metric tons of carbon dioxide removal from a startup called Heirloom Carbon, which claims to use the natural properties of limestone to siphon the gas from the atmosphere. The Wall Street Journal, which first reported the news, estimated the contract to be worth upward of $200 million, making it one of the biggest purchases of carbon-removal credits to date.
The blockbuster investment comes as companies continue to see potential in the nascent industry around carbon removal and capture, despite the tech behind it remaining fairly experimental. A BloombergNEF report last year found that while the direct air capture tech hasn’t made much of a dent in overall carbon emissions, its capacity could increase sixfold by 2030 as companies and investors pour billions into developing it.
Rocks on a roll: The Microsoft deal is just the latest vote of confidence for Heirloom, which also recently won up to $600 million in funding from the Department of Energy (DOE) to build a new facility in Louisiana. The company will work with Microsoft at that plant as well as another site it’s planning in the United States in an attempt to help the software behemoth reach its goal of being carbon negative by 2030.
Heirloom’s tech works by heating crushed-up limestone powder in a kiln to separate its components—calcium oxide and carbon dioxide. The latter is stored in “deep geological reservoirs, or in long-lasting materials like concrete,” according to the company. The remaining calcium oxide is then treated to absorb carbon dioxide again, and the process is repeated. Heirloom claims its methods can reduce the time it takes for limestone’s natural carbon-absorbing properties to take effect “from years to just three days.”
A mixed record: A number of pricey and inefficient carbon capture projects have given the technology a bad rap over the years. But DOE principal deputy assistant secretary for the Office of Fossil Energy and Carbon Management Jennifer Wilcox, whose research has contributed to the technology behind Heirloom, told Tech Brew last year that direct air capture has its place among a wider toolbox of climate solutions, especially when directed at “hard-to-decarbonize” industries.
Heirloom CEO Shashank Samala claimed in a statement that deals like the one it inked with Microsoft will help the company scale up its operations significantly.
“Bankable agreements of this magnitude enable Heirloom to raise project finance for our rapid scale-up, fueling exponential growth like what we’ve seen in the renewable energy industry,” Samala said.