XPrize in Carbon Removal Goes to Enhanced Rock Weathering

The XPrize Foundation today announced the winners of its four-year, US $100 million XPrize competition in carbon removal. The contest is one of dozens hosted by the foundation in its 20-year effort to encourage technological development. Contestants in the carbon removal XPrize had to demonstrate ways to pull carbon dioxide from the atmosphere or oceans and sequester it sustainably.

Mati Carbon, a Houston-based startup developing a sequestration technique called enhanced rock weathering, won the grand prize of $50 million. The company spreads crushed basalt on small farms in India and Africa. The silica-rich volcanic rock improves the quality of the soil for the crops but also helps remove carbon dioxide from the air. It does this by reacting with dissolved CO₂ in the soil's water, turning it into bicarbonate ions and preventing it from returning to the atmosphere (see the sidebar, How Does Enhanced Rock Weathering Remove CO²?" for more detail).

More than a dozen organizations globally are developing enhanced rock weathering approaches at an industrial scale, but Mati's tech-heavy verification and software platform caught the XPrize judges' attention. On the one hand, they're moving rocks around in trucks-that's not very techy. But when we looked under the hood...what we saw was a very impressive data-collection exercise," says Michael Leitch, XPrize's technical lead for the competition.

Mati Carbon's Data-Driven Carbon Removal

Mati monitors each farm's soil both before and after the basalt treatment to verify how much carbon is being stored. This verification process involves bringing an inductively coupled plasma mass spectrometer to farms to analyze soil composition and help determine how well the basalt is working. The company also tracks other measures of soil chemistry, performs geotagging to determine the precise location of all measurements, and uses software to track the carbon footprint of transporting and sourcing the basalt.

How Does Enhanced Rock Weathering Remove CO2?

Enhanced rock weathering is a way to accelerate one of the Earth's natural processes for removing carbon dioxide from the atmosphere. It works like this: Carbon dioxide in the air dissolves into rainwater, forming carbonic acid. As rocks are worn away (or weathered) by this slightly acidic water, silicate minerals in the rock dissolve. This releases calcium, magnesium, and other positively charged ions called cations. These cations react with carbonic acid in the water, forming bicarbonate ions. In this bicarbonate form, the carbon can't return to the atmosphere. Eventually the bicarbonate ions wash into the oceans, where the carbon is locked away for thousands of years. Researchers can accelerate this natural rock weathering process by adding finely crushed basalt, olivine, or other silicate rocks to cropland.

All of this must be repeated for thousands of small farms. The quantity and the density of sampling we're doing today is intense-really it's ridiculous," says Shantanu Agarwal, the CEO and founder of Mati Carbon. For each field, we're collecting hundreds of data points."

The company organizes the data with a proprietary enterprise resource-planning software platform it calls matiC. The company also uses machine learning and analytics software driven by AI to weed out manual errors, keep track of field conditions, and model carbon removal. The goal is to develop a prediction tool that will allow the company to reduce the amount of physical sampling it must do, says Agarwal.

Mati Carbon began by spreading basalt on rice paddies in India and has now expanded to Zambia and Tanzania. Mati Carbon

Solid monitoring and verification is crucial for carbon-removal companies because their revenue is largely based on selling carbon credits. The only way to build up a viable carbon-credit market is for companies to prove they're actually removing the amount of carbon they say they are.

Mati will use the $50 million to expand to more small-farm owners globally. The farmers pay nothing to have the basalt spread on their crops; all of Mati's revenue comes from carbon credits, Agarwal says.

In addition to the prize money for Mati Carbon, XPrize awarded three runners-up. Paris-based NetZero received $15 million for extracting carbon from agricultural waste and converting it to biochar, a type of charcoal, using pyrolysis. Houston-based Vaulted Deep won $8 million for geologically sequestering carbon-filled organic waste. And London-based Undo Carbon received $5 million for its enhanced rock-weathering approach. XPrize awarded additional prize money earlier in the competition for milestones and student teams. The Musk Foundation funded the competition.

XPrize Runners-Up Don't Include Direct Air Capture

Conspicuously absent from the list of winners were companies developing direct air capture (DAC) and ocean carbon removal systems. The contest rules stipulated that to win, contestants must remove and store at least 1,000 tonnes of carbon over the course of a year. None of the DAC or ocean carbon removal contestants met that threshold, XPrize's Leitch says.

For example, the ocean carbon startup Captura operates a pilot plant in the Port of Los Angeles that's been stripping 100 tonnes of CO₂ out of the Pacific Ocean each year. But the company's new 1,000-tonne facility in Hawaii didn't begin operating until February this year when the contest was concluding. That one's a good example of a team that has really pushed the envelope on the tech development," says Leitch. It's just an unfortunate reality that for those more tech-heavy solutions, there are more barriers to short-term deployment," he says.

In the field of air capture, there are DAC facilities that can remove well over 1,000 tonnes of carbon from the atmosphere in a year. For example, Climeworks last year switched on a 36,000-tonne DAC facility in Iceland. And Carbon Engineering is building a 500,000-tonne DAC plant in Texas through a partnership with 1PointFive. But neither company participated in the competition.

The DAC team that entered the contest and came the closest to the 1,000-tonne threshold was Project Hajar, which is sequestering air-captured CO₂ in peridotite rocks in the UAE. Project Hajar won a $1 million milestone award from the competition in 2022 and another $1 million honorary XFactor award today. XPrize also awarded a $1 million honorary XFactor prize to ocean carbon startup Planetary Technologies.

As these technologies inch toward arbitrary competition thresholds, the only way to make a dent in the more than 1,000 gigatonnes of excess CO₂ lingering in Earth's atmosphere is scale up, and fast. Says Leitch: A thousand tonnes is a very significant undertaking from a project-deployment perspective, but...from a climate perspective, it really doesn't move the needle."