An experimental study of the mineral carbonation potential of the Jizan Group basalts

The ability of Jizan basalts, a potential subsurface mineral carbon storage formation located in southwest Saudi Arabia, to carbonate water-dissolved CO2 has been examined through a set of closed system batch fluid-rock experiments performed at 60 °C. Two Jizan basalt samples were collected from a CO2 injection pilot test well at depths of 375 and 665 m below surface. The basalt samples are dominated by intermediate plagioclase (An∼60) and a Ca-Mg pyroxene with minor chlorite and zeolite. The cleaned basalts were placed into individual sealed reactors along with either aqueous sodium carbonate or sodium bicarbonate solutions, and the experiments were conducted over a period of up to 250 days. The reactive fluid compositions in all experiments suggest that the dissolution of plagioclase dominates the basalt dissolution; calculations suggest that the fluids rapidly approach pyroxene equilibrium. The reactive fluids rapidly become saturated with respect to calcite. SEM imaging and EDS analysis confirm calcite growth on the basalt grains. In contrast, Al-bearing secondary minerals were not identified despite apparently being retained by the solid phases during the experiments. Notably, the dissolution rates of the Jizan basalts slowed considerably over time during the static batch experiments. This observation suggests that the relatively rapid dissolution of basalt by acidic CO2-rich fluids in a dynamic flow system creating a dissolution zone and precipitation zone, is essential for efficient in situ mineralization of CO2 in basalts.