https://www.vice.com/en_us/article/akgxvk/iceland-has-built-a-carbon-negative-power-station-using-volcanic-rock

At a terminal located about 20 minutes outside of Reykjavik, scientists have found a new way to eliminate carbon using volcanic rock. 

Carbon dioxide is dissolved in water and injected into the ground where it reacts with natural rock formations, such as basalt. The carbonated water is typically denser than the surrounding water so it sinks once it’s injected. The reaction releases elements such as magnesium, calcium, and iron, which combine with the dissolved carbon dioxide and fills the empty spaces of the volcanic rock. It can remain stable for thousands of years in that state.