Those steps (along with follow-up reactions to restore the acid or other chemicals to a usable state) obviously add up in terms of cost and energy use. Tallying up the energy to do all this using common techniques, the researchers found that you need to use a little more than double the energy of traditional production from limestone.
The interesting thing is that, according to thermodynamics, the chemical conversion of basalt minerals to calcium oxide only requires around half as much as the conversion from limestone. The problem is that our techniques to facilitate that chemical conversion are quite inefficient, so we don’t get anywhere near what is theoretically possible.
Better options?
The researchers note that there are at least some known lab techniques that could greatly improve our efficiency if they can be applied at scale, but even if we’re stuck with doubled energy usage, producing Portland cement from basalt would significantly reduce CO2 emissions. That’s because the direct liberation of CO2 from limestone is eliminated and because the whole process can run on electricity.
Assuming you use electricity from a fossil-fuel-dominated grid, they estimate that emissions would be cut by almost 30 percent. Using clean electricity would eliminate most of the remaining emissions.
