It'll depend on the specific project in question (there are quite a few methods under investigation), but for enhanced weathering (the type under discussion), I

It'll depend on the specific project in question (there are quite a few methods under investigation), but for enhanced weathering (the type under discussion), I found some articles in a quick search that suggest the energy cost of grinding and transporting the rocks is significantly smaller than the carbon removed by the programme, e.g. https://www.researchgate.net/publication/322664372_Potential_and_costs_of_carbon_dioxide_removal_by_enhanced_weathering_of_rocks https://www.researchgate.net/publication/322664372_Potential...