PNNL

The Science                                

Finding ways to limit the effects of carbon dioxide (CO₂) is essential for human life. Researchers are studying carbon mineralization, where CO₂ and minerals react underground to form stable carbon-containing solids. New work studied diopside, a mineral that includes calcium and magnesium, to understand how it interacts with CO₂ during mineralization. Through a combination of experimental and computational work, the team found that diopside reacts with CO₂ to form mixed carbonates containing calcium and magnesium. The rate limiting step for carbonate formation is the diopside dissolving, with exposed calcium ions highly susceptible to dissolution when in contact with water.

The Impact

Combatting increasing CO₂ emissions requires permanent storage options. Of potential strategies for storing CO₂, carbon mineralization in basalt-containing sites is among the most promising. Diopside is present in many potential carbon mineralization sites, so understanding its fundamental carbonation behavior is essential to developing practical large-scale carbon storage. The fundamental knowledge obtained in this work will help researchers better understand the overall carbon storage potential of diopside-containing areas and develop approaches to most effectively trap CO₂ underground.

Summary

Mitigating CO₂ emissions is of critical importance. One approach is sequestering CO₂ underground in basaltic formations, where the minerals and CO₂ can react to form stable carbonates. However, the composition of these basaltic formations is complex. Researchers studied how diopside, commonly found in basaltic formations, interacts with CO₂ under mineralization-relevant conditions. In situ experiments at elevated temperatures and CO₂ pressures showed that diopside forms numerous magnesium and calcium-based carbonates with different metal ratios. More in-depth ex situ characterization found that temperature does not alter the mechanism of carbonate formation. The team calculated the activation energy of the diopside carbonate formation, which corresponds to the energy of diopside dissolution. This indicates that the rate limiting step of carbonate formation is diopside dissolution. Simulations of the process showed that calcium ions exposed to water were the most susceptible to dissolution, beginning the process of carbonate formation. Overall, this work provides fundamental insights on how an important component of basaltic formations converts CO₂ to carbonate. These findings could help enable effective mineralization projects that consider the complexities of multiple geological species.

PNNL Contact

Kevin Rosso, Pacific Northwest National Laboratory, kevin.rosso@pnnl.gov

Funding

This material is based on work supported by the Department of Energy (DOE), Office of Science (SC), Basic Energy Sciences program (BES), Chemical Sciences, Geosciences, and Biosciences Division through its Geosciences program at Pacific Northwest National Laboratory (PNNL). BA and LH were supported by the DOE, SC, Office of Workforce Development for Teachers and Scientists under the Visiting Faculty Program. JEH and HTS were supported by Darin Damiani at DOE Headquarters and the DOE Office of Fossil Energy at PNNL through the National Energy Technology Laboratory, Morgantown, West Virginia. HTS also acknowledges support from the Carbon Utilization and Storage Partnership. SZ and MJAQ were supported by the DOE SC BES through an Early Career Award.