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Comment by mumblemumble | Hacker News Reader

So, back of the envelope, I'm no chemist, I haven't tried doing something like this on my own since high school, etc. But, if the reaction is something along the lines of

  3CO2 + 4Ga => 3C + 2Ga2O3

and CO2 has a molecular weight of about 44, and Ga's is about 70, then I believe that would imply that eliminating 1 tonne of CO2 would require about 2 tonnes of gallium.

How much spare gallium is there in the world? Is it anywhere near enough to put a dent in the ~1,000 tonnes per second that humans are emitting?

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While I agree with you, upon quick search it seems Ga2O3 is an intermediate in the purification of gallium[0]

So, process can be created wherein

  3CO2 + 4Ga => 3C + 2Ga2O3 => 4Ga + ... => 3CO2 + 4Ga ....

basically, the Gallium oxide is reconverted to Gallium to be used in CO2 capture.

[0] https://en.wikipedia.org/wiki/Gallium(III)_oxide

I believe that converting Ga2O3 back into gallium metal should not necessarily release any CO2, just the O2 that I suppose was originally in the atmosphere anyway.

You should be able to do it with heat, electrolysis hydrogen + heat to reduce it, or electrolysis itself. Theoretically you can do these all with electricity.

It makes way more sense than when I see carbonates brought up as a way to sequester things at least, since the thing being cycled has no carbon in it at least.

Though, if we have enough clean electricity generation capacity to convert that gallium oxide back to gallium without releasing more CO2 than we had sunk in the first place, then one wonders why we're rube goldberging it rather than eliminating the carbon-intensive processes altogether.

In other words, this doesn't sound to me like a solution to our clean energy problems, so much as a cool thing we might be able to do on a mass scale after our clean energy problems have already been solved.

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