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It seems that oxygen may be extractable from oxides in lunar regolith using "some variant of the" molten oxide electrolysis.

Assuming that solar energy is used in a lunar setting, what would require more power for a modest demonstration-scale implementation; keeping the material molten or performing the electrolysis separating the oxygen from the metal and silicon oxides?

I ask because the heat for melting could come from solar concentrators but for the electrolysis you need to convert the incident solar power to electricity first.

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    $\begingroup$ Which process are you thinking of? Molten salt or melting the rock?? $\endgroup$
    – user2702772
    Commented Aug 24, 2020 at 6:42
  • $\begingroup$ @user2702772 The comment I link to says only "...it's likely some variant of the molten oxide electrolysis that Boston Metals is commercializing here on Earth" so I'll adjust the wording to leave that open. Thanks! $\endgroup$
    – uhoh
    Commented Aug 24, 2020 at 8:06

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It depends on what rock you use, but possibly the waste heat from electrolysis is enough to keep it hot.

Take aluminum oxide as an example (Springer):

About half of the energy spent in aluminium electrolysis is lost as heat. A preliminary study concerning the possibilities of recovering part of that heat was carried out, primarily focusing on electrical power production. The three main heat sources (cathode sides, anode yokes, and gas) were combined in different ways, using different types of power cycles. The potential for electric power production is significant (up to 9 percent of the total consumption).

Other rocks should be similar. To keep it molten at the optimal temperature and not boiling, you need quite a bit of negative power (cooling).

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  • $\begingroup$ I never thought of this but it certainly makes sense, thanks! Any idea how many kW hours necessary to liberate a kilogram of oxygen? (maybe I should ask that separately). $\endgroup$
    – uhoh
    Commented Jul 12, 2020 at 4:22
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    $\begingroup$ @uhoh This area is pretty well researched by aluminum production. I think this article is a good start: res.mdpi.com/d_attachment/sustainability/… $\endgroup$
    – user3528438
    Commented Jul 12, 2020 at 4:35
  • $\begingroup$ There is no fixed number how many kW hours are necessary to liberate a kilogram of oxygen. Aluminum oxide requires more energy than iron, that is why thermide works. $\endgroup$
    – Uwe
    Commented Jul 12, 2020 at 9:37
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    $\begingroup$ Cooling is a concern on Earth because the operators want to maintain a high throughput for their aluminum smelting hardware. If cooling is difficult (like it would be on the moon), you could always just reduce the current (or operate in pulses at a lower duty cycle) until thermal balance is reached. And of course electrical heating is quite simple to implement if not enough heat is being produced (as may be the case with iron, copper, etc). $\endgroup$
    – Christopher James Huff
    Commented Jul 12, 2020 at 16:21

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