Conversion of carbon dioxide into solid minerals underground for more stable storage

A new scientific review article in Nature Reviews Chemistry discusses how carbon dioxide (CO₂) converts from a gas to a solid in ultrathin water films on subsurface rock surfaces. Known as carbonates, these solid minerals are both stable and widespread.

“As global temperatures rise, so does the urgency of finding ways to store carbon,” said Kevin Rosso, lab fellow and co-author at the Pacific Northwest National Laboratory (PNNL). “By taking a critical look at our current understanding of carbon mineralization processes, we can identify the key gaps for work over the next decade.”

The underground mineralization presents a way to contain CO₂ imprisoned, unable to escape back into the air. But researchers must first know how it happens before they can predict and control for carbonate formation in realistic systems.

“Reducing human emissions requires a fundamental understanding of how to store carbon,” said PNNL chemist Quin Miller, co-lead author of the scientific review featured on the journal’s cover. “There is an urgent need to integrate simulation, theory and experimentation to study mineral carbonation problems.”

Under the ground and in the water

Instead of emitting CO₂ in the air, one way is to pump it into the ground. set CO₂ The deep underground theoretically binds the carbon. However, gas leaks remain a problem. But if the CO₂ Gas can be pumped into rocks rich in metals like magnesium and iron, the CO₂ can be converted into stable and common carbonate minerals. PNNL’s basalt pilot project in Wallula is a field site dedicated to the study of CO₂ Storage in carbonates.

Although these subsurface environments are generally dominated by water, the conversion of gaseous carbon dioxide to solid carbonate can also occur when CO is injected₂ displaces this water and produces extremely thin residual water films when it comes into contact with stones. But these highly confined systems behave differently than CO₂ in contact with a pool of water.

In thin films, the ratio of water and CO₂ controls the reaction. Small amounts of metal are leached from the rock and react both in the film and on the rock surface. This leads to the creation of new carbonate materials.

Previous work led by Miller, summarized in the review, showed that magnesium behaves similarly to calcium in thin water films. The nature of the water film plays a central role in the system’s response.

Understanding how and when these carbonates form requires a combination of laboratory experiments and theoretical modeling studies. Laboratory work allows researchers to tune the ratio of water to CO₂ and watch carbonates form in real time. Teams can see which specific chemicals are present at different points in time and provide important information about reaction pathways.

However, laboratory-based work has its limits. Researchers cannot observe individual molecules or see how they interact. Chemistry models can fill this gap by accurately predicting how molecules move and giving experiments a conceptual backbone. They also allow researchers to study mineralization in conditions that are difficult to access experimentally.

“There are important synergies between models and laboratory or field studies,” said MJ Qomi, a professor at the University of California, Irvine and co-lead author of the article. “Experimental data grounds models in reality, while models provide deeper insight into experiments.” Qomi has been working with the PNNL team for three years and plans to study carbonate mineralization in adsorbed water films.

From basic research to solutions

The team outlined key questions that need to be answered to make this form of carbon storage viable. Researchers need to develop knowledge of how minerals react under different conditions, particularly conditions that mimic real deposits, including in ultrathin water films. This should all be done through an integrated combination of modeling and laboratory experiments.

The mineralization has the potential to safely store carbon underground. Knowing how CO₂ Reacting with various minerals can help what is pumped below the surface stay there. The fundamental science derived from mineralization work can lead to practical CO₂ storage systems. The basalt pilot project represents an important study site, bridging the gap between small-scale basic research and large-scale research applications.

“This work combines a focus on fundamental geochemical insights with the goal of solving critical problems,” said Miller. “Without prioritizing decarbonization technologies, the world will continue to warm at a rate that humanity cannot afford.”

Miller, Rosso, and Todd Schaef were the PNNL authors of this study. This work was performed in collaboration with MJ Qomi and Siavash Zare from the University of California, Irvine and John Kaszuba from the University of Wyoming.