Have you looked at Project Vesta? It's a proposal to create olivine beaches around the tropics to boost sequestration due to rock weathering. I think it's somewhat disputed because rock weathering in a surf happens at a different rate than normal, but their analysis is that if "only" 2 percent of tropical beaches were covered in olivine the weathering would counteract current emissions. I can't tell how serious this proposal is and am curious to hear from anyone who knows more about this process.
I’ve seen this thrown around as well, and would love to hear more. I’m interested in helping the project since it’s about the only one that has stood up to any scrutiny that I’ve seen
https://projectvesta.org/