I just found out about this Yale study that shows that "adding volcanic rock dust to cropland could help the world reach a key carbon removal goal." 

How does it work? Rain absorbs carbon dioxide from the air. When it falls on the rock dust, the carbon in the rain reacts with the silicates in the rocks. (I would like to better understand this process. If someone can explain it in a comment, I'd appreciate that.)

It sounds as if this is a fairly new thing. I don't know if there is any organization doing this on a broad scale. But it sounds like something for the EA community to keep its collective eye on.