Carbon Mineralization

Carbon Dioxide Mineralization and Associated Critical Mineral Resources

In 2019, the U.S. Geological Survey (USGS) released a carbon dioxide mineralization feasibility report (Blondes and others, 2019). This report was an important first step toward our current work of conducting a national assessment of CO₂ storage resources accessible via mineralization. The focus of the work is on mafic (e.g., basalt) and ultramafic (e.g., peridotite and serpentinite) rock formations that have high concentrations of magnesium, calcium, and iron - these types of rocks are abundant throughout the U.S. In addition, many of these mafic and ultramafic rock units hold large quantities of critical minerals like nickel and cobalt, which could potentially be recovered when CO₂ is injected into the subsurface and may constitute a new target for critical mineral resource exploration in the United States. The initial steps of the assessment involve refining maps of surface and subsurface CO₂ mineralization targets and compiling geochemical and mineralogic data. All of these data contribute to an equation for estimating CO₂ mineralization potential that considers the volume, mineralogy, geochemistry, surface area of reaction, and extent of natural carbonation (which would reduce mineralization potential) of the rocks. The overall aims are to provide an accurate assessment of available lithologic feedstock for CO₂ mineralization across the conterminous United States, and to address the significant geologic variability seen in naturally occurring rocks.

Unlike CO₂ storage in subsurface reservoirs, where CO₂ is stored under high pressure as dissolved and supercritical fluid phases, CO₂ mineralization stores carbon in solid-phase carbonate minerals that have the potential to remain stable over geologic timeframes (millions of years). In addition to the assessment work, the USGS is also performing fundamental research on the conditions and mechanisms for CO₂ mineralization and associated critical mineral release in collaboration with researchers at the Pacific Northwest National Laboratory (Steup and others, 2024). The research is relevant to CO₂ mineralization applications both in situ, where CO₂ injected into the subsurface will mineralize while interacting with mafic and ultramafic host rocks that are potentially rich in critical minerals, and ex situ, where mined geologic materials can be introduced to settings (surface or marine) conducive to enhanced rock weathering to facilitate the removal of CO₂ directly from the atmosphere.