Suppose mare regolith is heated to 2400 K, then left to cool slowly in a tank. Samples of powder regolith from the mare are about half glasses and half crystals of composition as shown below. Would some pure minerals separate into their own layer? Might one hope to find layers of pure metal oxides before the mix started to crystallize at 1700 K according to Bowen's reaction series

mineral oxide composition of lunar soils

If they wouldn't separate as they cooled, what would they do? Is the low gravity an issue?

I've been working on very rough ideas for solar furnaces on the Moon, to model a virtual colony, and I'm trying to work out its general format and applications. Suggestions for reading at an introductory level are also welcome.

2400 K is above the melting point of all the constituent minerals, and all the metal oxides except MgO and CaO, while being below the temperature at which some of the oxygen would separate (at about 2700 K). It's my best guess at the appropriate temperature to try this. Bowen's reaction series begins at about 1700 K, so until the mix cools to that temperature, it shouldn't crystallize (other than tiny crystals of MgO and CaO floating around).

  • $\begingroup$ Are these materials mixed heterogeneously or are they bonded into other compounds? Looking at the column for ilmenite, you can see it is mostly made up of TiO2 and FeO, which makes sense, but aren't those two bonded to form FeTiO3? If so, then you are talking about more than just separating them, but actually decomposing them -- and that means a lot more chemistry than just a furnace. But, I have little knowledge of metallurgy so maybe I'm wrong! $\endgroup$ Nov 21, 2015 at 12:29
  • $\begingroup$ For example, this paper mentions that "Fe2O3 is a reaction product when ilmenite is subjected to molten sodium hydroxide". $\endgroup$ Nov 21, 2015 at 12:34
  • $\begingroup$ @BrianLynch - i wondered about that but didn't find any information - so thanks for the link. I've gone on the presumption that some compounds are simply mixed, that would seem to make sense. Purifying any of them would be a useful first step. SiO2 for glass, or even better quartz, Al2O3 to sapphire would be awesome, it and CaO is the basis of cement, MgO is an excellent refractory material. In the Apollo 15 soil most of the FeO would have to be free, or at least not bonded with the the TiO2. $\endgroup$
    – kim holder
    Nov 21, 2015 at 14:48
  • $\begingroup$ I seem to remember there was a problem with creating sapphire even though it looked promising at first -- maybe some kind of doping element that would be necessary yet not easily available. See if you can find any papers by Prof. Alex Ellery, he has a keen interest in lunar ISRU and did some preliminary work on the type of processing you're describing. $\endgroup$ Nov 21, 2015 at 15:40
  • $\begingroup$ The question has now been edited in the hopes it is more answerable (i.e., less confused). $\endgroup$
    – kim holder
    Nov 21, 2015 at 16:10

1 Answer 1


The concentration of metals with the regolith will be critical a factor to the amount of effort, energy required and regolith required.

The other important factors will be what other metals will be in the regolith and how this may influence the formation and degree of alloyed metals.

Also what metal do you want to concentrate by melting regolith?

Getting the metal you want from its particular layer with a melt will be a problem. One of the problems will be the thickness, or thinness of the layer, and its proximity to layers of other metals or alloys and the need to get the metals from layers without contamination.

  • $\begingroup$ Its the metal oxides being considered, not the pure metals - oxides of silicon, iron, calcium, aluminum, magnesium, and titanium, in descending order of average abundance. Other constituents are minor. I'm not trying to get at the metals in this. With 99% of the soil those 6 things, if they can be separated, the layers wouldn't be thin. $\endgroup$
    – kim holder
    Nov 21, 2015 at 2:24

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