Spotlight: Carbon mineralization companies making better use of mining waste

Carbon dioxide is both an asset and a liability: a molecule essential to life on Earth that has accumulated in our atmosphere to dangerous excess. Carbon removal companies are working to capture that excess and transform it into healthier soils, cleaner industrial inputs, and other valuable products. They are experts at converting a planetary liability into an economic and environmental benefit.

It turns out, the same logic applies to mine waste. Active mines and industry in the United States produce more than 1.5 billion tonsopens in a new tab of solid waste every year — creating piles you can see from space. Over time, this waste piles up and can eventually require taxpayer dollars for management and remediation. In addition to the environmental liability, those piles often contain valuable critical minerals that sit unused. In fact, the U.S. could supply almost the entirety of U.S. critical mineral needsopens in a new tab by recovering the minerals already present in American mining and industrial waste.

There’s an emerging opportunity to pair carbon removal technologies and industrial waste management to solve several problems at once. The technological process is called carbon mineralization, and it can help break down mine waste to reveal the valuable minerals hidden within them. In the process, mineralization also removes atmospheric carbon and can neutralize hazardous toxins.

This blog takes a closer look at three wastes or byproducts that can be mineralized and transformed to alleviate environmental burdens, generate economic value, and remove carbon dioxide in the process.

Sulfur waste

Sulfuric acid is the most used chemical on earth. It’s used to treat municipal water, create batteries, make up fertilizers, and flavor popular sodas. It would be easier to name something that doesn’t rely on sulfuric acid somewhere in a given supply chain.

Despite the economy-wide demand for sulfur, there are massive amounts of sulfate waste — also called phosphogypsum — that pile up in stacks of white powder at a rate of hundreds of millions of tons per year. These stacks are an environmental liability, with radioactive elements that can leach into waterways if not carefully managed.

A new technology can produce sulfuric acid by recycling this waste. Travertineopens in a new tab uses direct air capture and mineralization together in its regenerative process to electrochemically recycle sulfuric acid and remove carbon — and they’ve just opened a demonstration facility to show this process works at scale. There are two inputs into Travertine’s Ontario NY demonstration facility: carbon dioxide from the atmosphere and phosphogypsum which is the sulfate waste from American phosphoric acid production. The facility produces sulfuric acid for use across industries and calcium carbonate for use in cement production.

That means Travertine is producing one of the most used chemicals on earth without creating environmentally toxic waste while removing carbon from the atmosphere. The company can reduce sulfur consumption and sulfate waste by 45 to 100 percent.

Those numbers are especially compelling right now: the price of sulfur has been soaring due to demand for critical mineral production, and the closure of the Strait of Hormuz has further strained our import supply. Integrating carbon removal technologies into the critical minerals supply chain like this offers a practical path forward — transforming waste into a valuable product reducing environmental impacts.

Asbestos

Asbestos is one of the most recognizable toxic materials. From 1920 to the 1980s, asbestos was used widely in construction and manufacturing because of the mineral’s naturally occurring heat tolerance, strength, and insulating properties. Now, of course, we know how harmful asbestos is to human health: when inhaled, microscopic asbestos fibers become trapped in the body, causing cancer.

Asbestos mines — now closed and tightly regulated — still contain hundreds of millions of tons of toxic asbestos waste. That’s where carbon removal mineralization could play a role, converting asbestos mine tailings into stable carbonate materials, destroying the dangerous fibers and sequestering carbon.

Arcaopens in a new tab, a mineralization company that processes industrial waste to remove carbon, is exploring the possibility of applying their technology to asbestos mine tailings.

It’s a massive opportunity: The Lawrence Livermore National Laboratory recently estimated that existing asbestos tailings in the U.S. and Canada could remove up to 750 million tons of carbon dioxide while also removing an environmental health hazard.

Steel slag

The U.S. is the world's third largest producer of steel — and steel production unavoidably generates slag. Slag is the left over material from the metallurgical process, and contains a wide variety of minerals. Some slag is used in construction materials and asphalt, but because most of it has no economic use, hundreds of millions of tons of slag sit in piles near steel facilities, unused and unmonetized.

Carbon mineralization of slag is the first new industry-wide revenue opportunity for steel producers in decades. Instead of treating slag as a waste disposal issue, companies like Karbonetiq use the material’s naturally-reactive minerals to absorb carbon dioxide from the air. The process amplifies and accelerates carbonation through material processing such as crushing and screening to create new reactive surfaces, and aeration of the slag. All activities take place within established industrial sites and do not require significant energy inputs or new infrastructure.

Karbonetiqopens in a new tab is operating projects globally, including here in the U.S. Karbonetiq provides project development, technology, and quantification services, and has partnered with Harsco Environmental to operate projects. This is the waste-to-value logic in action: converting steel slag to a valuable economic asset for the steel industry, while increasing valuable mineral extraction, including nickel and chrome, and delivering carbon benefits.

Feedstocks of the future

There’s still much to be tested and assessed: discovering minerals that are highly reactive to carbon dioxide and result in net removal of carbon dioxide from the atmosphere is a priority. Across the country, there are mineral deposits that could store billions of tons of carbon dioxide annually, but aren’t currently mined or are difficult to access. 

Anvilopens in a new tab, a carbon removal mineralization company, uses a combination of traditional mining techniques, low-energy reactors, and processes to react feedstocks with air at ambient temperature, pressure, and carbon dioxide concentration. Their technology can operate in locations with the most efficient carbon dioxide reactivity, and achieve a net removal efficiency of 85 to 98 percent.

A little-known EPA program incubating mining technology

A bipartisan program started in 2023 was developed to mitigate public health risks, bolster American-made critical mineral technology, and improve the long-term outlook for the mining industry.

The Environmental Monitoring and Remediation Technology Assessment Initiative (EMRTAI)opens in a new tab works on legacy mine sites and connects them with American technologies that can help unlock new minerals and remediate harm.

We think the EMRTAI program should be extended and expanded to enable the evaluation of more innovative technologies, including carbon mineralization. Doing so would allow us to validate carbon removal technologies in real-world conditions and it could make a world of difference for the companies pioneering mineralization. They need trusted, federally-backed performance data to prove their technologies work — like feedstock analysis and assessment. Innovation like this can help American mining companies stay competitive, keeps cutting-edge technology at home, and creates the valuable products that underpin our supply chain.  

To learn more about the program and our proposal, read our policy memo.