CO₂ mineralization is a natural process that has stabilized Earth’s climate for billions of years by converting volcanic CO₂ into solid carbonates like calcite, the main component of chalk and limestone, storing carbon securely for millions of years. The speed of CO₂ mineralization depends on the interactions between carbonic acid (dissolved CO₂) and silicate minerals with high contents of metals like calcium, magnesium, and iron, which are particularly abundant in basaltic (volcanic) and ultramafic (from Earth's mantle) rocks.

The aim of C•ASH is to investigate the potential of Eocene basaltic volcanic ash in the Danish subsurface for efficient, inexpensive, local, and nature-inspired CO₂ storage by carbonate mineralization. Denmark’s potential to pioneer CO₂ mineralization is bolstered by several important factors:

• The fine-grained volcanic ash has vast surface areas (>80 m²/gram) for geochemical reactions.
• Compared to volcanic and ultramafic rocks, sedimentary ash deposits enable porous water transport.
• At 200–400 m depths across the Jutland peninsula, the volcanic ash deposits align with biogenic CO₂ capture from existing biogas and biomass plants.
• Denmark’s ambitious CCUS (Carbon Capture, Utilization, and Storage) plans and evolving regulations further support geological carbon storage, including mineralization.