Underground CO₂ storage: Researchers measure carbon mineralization on an unprecedented scale

As we look to the sky and ponder one of the biggest questions of our time – how to combat the carbon emissions that are driving climate change – a potential answer may lie beneath our feet, deep beneath the Earth’s surface.

Scientists at Pacific Northwest National Laboratory (PNNL) have developed a process that transforms carbon dioxide (CO₂) in solid rock. It mimics natural processes on Earth, but at a much faster rate, from thousands of years to months. But storing CO₂ In solid minerals, a process called carbon mineralization, on a scale large enough to have an impact, requires more than just discovery.

“We need ways to measure, verify and communicate that CO₂ “The carbon we put into the soil is mineralized and won’t escape,” said Todd Schaef, PNNL’s chief chemist who pioneered carbon mineralization in basalts.

Madeline Bartels, an intern in Schaef’s team, contributed to this result. Her research, published in the journal Analytical Chemistrycounts mineral carbon molecules on a scale no one has measured before: less than 100 parts per million.

“We can see how much carbon we’re locking up in the rock,” Bartels said. “Imagine putting a playing card on a football field. It would be like one part per million, but in reality we’re measuring the amount of carbon minerals in a tiny powdered rock sample.”

Before, it was like they were watching the playing cards on the field from the top row of the stands. Now, they are right on the field with a close-up view.

The United States emits more than 6,300 million tons of carbon dioxide per year. Using PNNL’s carbon storage technology at the Wallula Basalt Pilot Demonstration Site in 2013, researchers injected 977 tons of liquid CO₂ underground, I revisited it after 22 months and found that it had transformed into a solid mineral.

How do we know CO₂ turned into rock?

Although carbon mineralization can trap CO₂ in large quantities, there has not yet been a commercial-scale project in the United States. A special permit to inject CO₂ Access to the basement is required but has not yet been achieved as industrial requirements are still being developed and tested.

“The Department of Energy, communities, stakeholders, industry and national laboratories are working together to ensure we have the best tools for sustainable, safe and secure CO storage.₂ “via mineralization in basalts and other reactive rocks,” said Quin Miller, co-author of the paper and Bartels’ mentor.

If adopted as a standard, thermogravimetric analysis mass spectrometry (TGA-MS) could one day be used by private companies to measure and verify the amount of CO₂ is locked up.

“It’s really cool that the research I worked on as an undergraduate could potentially make a meaningful contribution to the field as it’s emerging,” said Bartels, who participated in two SULI internships with the Department of Energy and the Office of Science Workforce Development for Teachers and Scientists while earning his bachelor’s degree at Yale.

TGA-MS was performed on drill cuttings samples recovered from the Wallula well as a test.

“We grind rock samples to a very fine, powdery form and put a small amount, about the size of a sunflower seed, into a machine that heats and tracks the weight of the sample,” Bartels said.

At high temperatures, various reactions occur. Water molecules and CO₂ The molecules are released from the sample and enter a small tube, connected to a mass spectrometer.

“It can be difficult to determine the amount and source of carbon,” Miller said. “We can do a lot of things, like shine X-rays on rocks and try to look at carbonates that way, but TGA-MS allows us to look at much smaller amounts than we could detect with our X-rays.”

This technique allowed the researchers to quantify the carbon minerals as they entered the mass spectrometer through the tube. They detected the minerals at a minuscule 48 parts per million, the first known study to get TGA-MS quantification down to double digits. Using the measurements, the PNNL team created a calibration curve to relate the weight of the carbon minerals to their TGA-MS signal, allowing them to quantify the amount of carbon minerals in the sample.

Mentoring the next generation of carbon mineralization experts

As the research field grows, Schaef and Miller are committed to bringing the discovery of PNNL carbon mineralization to commercial scale and to inspiring students and early-career researchers to join the quest for carbon management solutions.

“Madeline’s involvement with SULI gave her the opportunity to learn in the field, publish a paper as first author, and be featured on a cover. It was a tremendous, impactful job,” Miller said. “The more people we have on this team, the more perspectives, ideas, and methods we bring to how to do things to move this research forward.”

Bartels joined PNNL this summer as a SULI intern and plans to continue his research in carbon mineralization and geochemistry as a graduate student.

“As a national laboratory, we want to attract the next generation and that’s what we’re doing here,” Schaef said. “I’ve been in this field for over 32 years and I’d like to train more people like Madeline to find solutions to the challenges society faces.”