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Futurism's news item NASA Pumps Funding into Startup That Says It Can Harvest Oxygen From Lunar Regolith says:

NASA just awarded substantial funding to Pioneer Astronautics, a company that claims it can gather up lunar regolith and turn it into usable oxygen.

Question: How is it proposed to extract oxygen from lunar regolith? Is there molecular oxygen as O2 trapped in the regolith, or will they somehow break down oxygen-containing minerals or oxides, or are they targeting hydroxides?

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    $\begingroup$ It seems there are no hydroxides in lunar regolith. See lunar geology. There is only oxygen as a part of oxides like SiO2, Al2O3, CaO and FeO. $\endgroup$
    – Uwe
    Jul 11, 2020 at 11:27
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    $\begingroup$ It's actually pretty simple...but yes, energy-intensive. Haven't found details of what Pioneer Astronautics is doing, but it's likely some variant of the molten oxide electrolysis that Boston Metals is commercializing here on Earth: bostonmetal.com/moe-technology/#moe-process $\endgroup$
    – Christopher James Huff
    Jul 11, 2020 at 17:09
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    $\begingroup$ A solar furnace would avoid conversion losses, but regulating temperature is more difficult and the furnace obviously can't be as well insulated. An electrically heated furnace can be extremely well insulated, and the mechanics of getting material in and out of the furnace much simpler. I suspect the simplicity will put the electric furnace ahead. $\endgroup$
    – Christopher James Huff
    Jul 12, 2020 at 3:18
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    $\begingroup$ @ChristopherJamesHuff: If you have an answer, please write it as a proper answer. Then you can earn reputation for it! $\endgroup$
    – DrSheldon
    Jul 12, 2020 at 4:36
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    $\begingroup$ Aluminium smelting on the Moon, with oxygen as byproduct and powered by a nuclear reactor, is a plot element in Andy Weir's "Artemis". $\endgroup$
    – matz
    Jul 13, 2020 at 11:04

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Pioneer Astronautics is likely doing some variant of the molten oxide electrolysis that Boston Metal is commercializing here on Earth: https://www.bostonmetal.com/moe-technology/#moe-process

This involves melting rock (potentially just random basalt) and electrolyzing it. Graphite may be used as a cathode, but the anode must be resistant to oxidation, or the anode will be consumed by reaction with the O2 and CO2 will be released instead. Earlier work used precious metals like iridium for anodes, some recent work (related to Boston Metal's process) uses chromium alloys (https://www.chemistryworld.com/news/greener-cleaner-steel-/6155.article), and I've also seen mention of ceramic electrodes that become conductive at the temperatures involved.

And of course, while oxygen is collected at the anode, the cathode collects the metallic (or semimetallic) components of the oxides...iron, silicon, copper, etc. This is the desired end product for Boston Metal, and might eventually be the primary end product on the moon as well, with the oxygen being a waste product produced in greater quantities than needed.

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Melting rock is expensive. A better process is to melt a salt, dump the rock in and apply an electric current. Such a process is described here: https://www.sciencedirect.com/science/article/pii/S0032063319301758?via%3Dihub

Similar outputs to melting the rock, but you're looking at temperatures of 800-900 degrees, not thousands. Slight problem is the bucket and electrodes - the oxygen ions will oxidise almost anything. Best bets are gold coats (will go soft at temperatures, weak metal anyway), platinum (expensive!) Or accept that you're going to burn your way through your containing bucket.

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