Another thing is where will all that energy required to break down CO2 come from. It's so bizarre that you hear so little about that, almost like nobody can do simple accounting on Joules:
The pilot project for was ran in Iceland and was successful enough to lead to both constructing a full-scale plant and scaling the process out to multiple different locations in Europe. The current main open problem is substituting seawater for fresh water for the process (Using a lot of fresh water is not exactly a problem in Iceland, but presents challenges for scaling the process out).
[1] If it costs more, or even not significantly (an order of magnitude at least) less than the cost of oil for equivalent emissions, than the economic proposition is dire. Solutions so far have those economic difficulties afaik, and we're still at a stage where we have easily available capture resources (i.e. we haven't depleted or saturated a number of them) -- we're talking about a planetary scale solution here
The current results are promising, but there are still challenges to overcome. Notably, the system they run in Iceland absolutely guzzled fresh water, and while this is not a problem in Iceland, it would prevent the scaling up of this project to a true planetary-scale solution. Work is ongoing for figuring out if saltwater would clog up the wells too badly, and how this can be mitigated.
Also, as the carbfix project took in CO2 and H2S as highly concentrated gases, as the direct problem was to get rid of the emissions of a geothermal plant. To scale up to carbon capture from the atmosphere, they'd have to either set up their system to use less concentrated input gases, or figure out a cost-effective method of separating and concentrating CO2 from the atmosphere.
Not saying this is necessarily a silver bullet for all our emissions, just saying that the original concern of the poster I replied to about where the energy to split CO2 it going to come from is not actually as big of a deal as it seems.
How would you like to create CaO without providing energy if the reverse reaction is exothermic?
Or am I missing the fact that there's a lot of unbound CaO in rocks?
Also, production of cement is one of the major sources of CO2 emissions.
Although most of it is not directly as oxides but some form of silicates. (This forces the use of lots of water in the process -- you can go from CaO -> CaCO3 without much water, but to dissolve silicates you need the CO2 dissolved in water.)
(More recent stats)
https://yearbook.enerdata.net/total-energy/world-energy-prod...
https://yearbook.enerdata.net/total-energy/world-consumption...