This Youtube video describes a beach in Hawaii that has a lot of olivine sand:
I mention that because Schuiling and de Boer propose building many such beaches. The one in the video above is not man-made. But one could imagine depositing large amounts of grinded olivine to the beaches of the World.
The interesting idea there is with waves pounding the sand all the time, it gets grinded into smaller peaces at zero cost. That in turn speeds up the weathering process (which is disposing of CO2).
I think this is an interesting idea. Here is a shorter article by the same authors explaining it in brief.
Lenz Blog 