An experimental study of basalt–seawater–CO2 interaction at 130 °C.

Over millions of years, the interaction of marine basalt with percolating seawater in low-temperature ocean floor hydrothermal systems leads to the formation of calcite and aragonite. The presence of these minerals in marine basalts provides evidence for substantial CO 2 fixation in these rocks. Here, we report on laboratory experiments to study this process under enhanced CO 2 partial pressures (p CO 2) at 130 °C. Mid-ocean-ridge-basalt (MORB) glass was reacted with North Atlantic Seawater charged with CO 2 in batch experiments lasting up to 7 months. For experiments initiated with seawater charged with ~2.5 bar p CO 2 , calcite and aragonite are the first carbonate minerals to form, later followed by only aragonite (±siderite and ankerite). For experiments initiated with seawater charged with ~16 bar p CO 2 , magnesite was the only carbonate mineral observed to form. In total, approximately 20% of the initial CO 2 in the reactors was mineralized within five months. This carbonation rate is similar to corresponding rates observed in freshwater-basalt-CO 2 interaction experiments and during field experiments of the carbonation of basalts in response to CO 2 -charged freshwater injections in SW-Iceland. Our experiments thus suggest that CO 2 -charged seawater injected into submarine basalts will lead to rapid CO 2 mineralization. Notably, at p CO 2 of tens of bars, magnesite will form, limiting the formation of Mg-rich clays, which might otherwise compete for the Mg cation and pore-space in the submarine basaltic crust. This suggests that the injection of CO 2 -charged seawater into subsurface basalts can be an efficient and effective approach to the long-term safe mineral storage of anthropogenic carbon. [ABSTRACT FROM AUTHOR]