Geochemical framework for CO2 mineralization in coastal aquifers: Lessons from the Coda Terminal project, Iceland

[Geoengineering News]

https://www.sciencedirect.com/science/article/pii/S1750583625002634

Authors: Iwona Galeczka, Martin Voigt, Daniel Andres Duque Carrillo, Kjartan Marteinsson, Thomas Ratouis, Sandra Ósk Snæbjörnsdóttr, Fríða Jónsdóttir, Paula Fernandez-Acosta, Gunnar Hrafn Gunnarsson, Bergur Sigfússon, Jóhann Gunnarsson Robin et al.

07 January 2026

https://doi.org/10.1016/j.ijggc.2025.104565

Highlights

The Coda Terminal project in Iceland aims to store 3 MtCO2/yr in basaltic subsurface.

•The geochemical exploration work shows high potential for CO2 mineralization.

•The groundwater salinity stratification is more complex than previously thought.

•Both freshwater and seawater are suitable for CO2 injection.

•Legislation on groundwater protection is still being developed for big scale CO2 mineralization projects.

Abstract

Freshwater scarcity can limit the scalability of subsurface CO2 mineralization projects which rely on dissolving CO2 in water before injection into basaltic reservoirs. While ongoing Carbfix projects primarily use freshwater or process water such as geothermal condensate to dissolve CO2, in the Coda Terminal project, in Straumsvík, SW Iceland, it is proposed to use seawater due to its availability. The storage reservoir contains a mix of freshwater, brackish, and saline groundwater, with measured conductivities ranging from ∼100 to ∼40,000 μS/cm. Water chemistry of the brackish and saline water indicates extensive water-rock interaction with depletion of Na, K, B, and Mg, and strong enrichment in Ca - essential for calcite precipitation, the dominant carbonate mineral in low-temperature basalt alteration.

Dissolution experiments conducted on Straumsvík basalt show similar trace element mobility in both freshwater and seawater, with only Al, Fe, and Mn exceeding WHO drinking water limits, suggesting low risk of groundwater contamination. Reaction path modelling indicates that mineralization efficiency can reach 100% for both water types, and that mixing of CO2-charged injection water with reservoir water does not significantly affect water chemical evolution or secondary mineral formation.

These results support the feasibility of using seawater for CO2 storage in basaltic settings and high potential for CO2 mineralization in Straumsvík. However, complex groundwater stratification and regulatory framework highlight the need for integrated hydrogeological, geochemical, and regulatory planning to ensure safe and effective implementation of large-scale CO2 mineral storage at coastal sites.

Source: ScienceDirect