Metal release in shallow aquifers impacted by deep CO2 fluxes

The impact of CO2 leakage from underground storage formations on shallow water resources is a concerning aspect in CO2 capture and storage (CCS) risk assessment. In Campo de Calatrava region (Spain), natural CO2 fluxes from the Earth’s mantle interact with shallow aquifers, resulting in significant changes in their physical and chemical properties. The resultant water is slightly acidic (pH 5.9-6.4), oxidizing, and enriched in iron (up to 6.1×10-4 mol·L-1) and other metals usually found at trace concentrations. Thermodynamic calculations reveal that aqueous Fe(III) carbonate complexes play an important role in the persistence of this high concentration of iron and trace metals in solution.