This is nonsense. Start with limestone. Cool, there's lots of that. Cook it - using energy - which you'd otherwise have to do other stuff. That drives off CO2.

This is nonsense. Start with limestone. Cool, there's lots of that. Cook it - using energy - which you'd otherwise have to do other stuff. That drives off CO2. Put it somewhere. You get something nastier that would indeed absorb CO2 from the air. The sketchy parts are the "put it somewhere" and the energy going into the process. Thermodynamics is a harsher mistress than lifecycle analysis. Not a chance this is a net decrease in atmospheric CO2.