Dissolution of silicate materials at high pH for ex situ CO2 mineralisation: Basaltic glass

A clearer understanding about the effect of high pH solutions on silicate material dissolution in nature and engineered systems would increase the credibility of predictive models for global element cycling, safety assessment of radioactive waste disposal sites and point source, industrial capture of CO 2 . The coupling of basalt dissolution with carbonate mineral formation is a safe, long term, carbon disposal option. We investigated divalent cation release from basaltic glass in aqueous solutions at pH 12. In such alkaline conditions, basalt dissolution is favoured and carbonate minerals are stable. Dissolution rates from < 63 µm crushed Stapafell basaltic glass were measured in batch reactors for 70 days, at T = 22 and 50 °C. Element release during the first days was consistent with reported dissolution rates for basaltic glass powders in mixed flow reactors but change in solution concentration in our batch experiments slowed considerably after 2 to 3 weeks. Although solution concentrations essentially reached steady state, geochemical speciation calculations indicated undersaturation relative to basaltic glass. We interpret these observations as evidence of passivating secondary phases (brucite, minor calcite and Al and Fe hydroxides) that formed on the particle surfaces. This is interesting with respect to natural systems, suggesting weathering rate decreases as secondary minerals form. Our results also suggest that efficient use of basaltic glass for CO 2 disposal by ex situ mineralisation or enhanced weathering would require continuous creation of fresh surfaces to promote divalent cation release.