Introduction to Lunar Resources Pages

These pages about metal and gas extraction from lunar regolith are based partly on research with Apollo samples and regolith simulants and partly on my own speculations.  There are no definite processes for extracting metals and gases from regolith to be found.  This will await more research on Earth and research on the Moon. 

Many challenges exist.  I have depicted some nice, neat text book style drawings.  In reality things won’t be so nice and neat.  Thermal stresses on brick retorts must be analyzed and the retorts must be built so that they don’t crack.  Silicon and metals condensing in retorts will not form nice powders like sand or flour that can easily be drained out.  Coatings will form inside retorts and lumps and crystals will accumulate that have to be melted out of the retorts and cast in molds.  Eventually there will be build-ups of material in the retorts that make them unusable unless robots can grind out the deposits or the deposits can be melted out.  Otherwise, the best thing to do would be do knock down the retort, recycle the bricks and build a new one.  Things wear out. 

Another challenge involves separation of minerals in regolith.  For instance, ilmenite (FeTiO3) must be separated from regolith before reduction with hot hydrogen.  Electrostatic separation seems to be the way to do this, but so far there hasn’t been a lot of success in this area.  Even so, I am confident that ways to separate ilmenite, agglutinates that compose 50% of the regolith particles, anorthite, pyroxenes and olivines will be found.

From "Electrostatic Separation of Mixed Granular Solids" by Oliver C. Ralston (Elsevier Publishing Co. 1961) we read that "electrostatic separation [is] the most versatile method for treating mixtures of dry solids while floatation is the most versatile method of treating mixtures of wet solids."

Also from Ralston's book we find that there are many kinds of electrostatic separation processes and that, "what cannot be effected by one process, may be easy work for another type." Ralston lists these processes:

1) charging by conduction
2) charging by induction
3) charging by dielectric hysteresis
4) contact potential
5) charging by spray, corona or electric leakage
6) charging by thermionic emission
7) photoelectric charging
8) pyroelectric polarization, piezoelectric polarization
9) the dielectric medium sep. process

Photoelectric charging in interesting.  This might be done with powerful IR or UV lamps or with lasers. Once the mineral grains are separated from each other it will be possible to process them electrically, thermally and with chemicals to extract metals and oxygen. But what are the electrostatic charge properties of lunar mineral grains in a vacuum? Will sharp jagged real regolith particles exhibit different charging properties than simulants? This must be known if mineral grains are to be separated by electrostatics on the Moon.

Molten silicate electrolysis does not require separation of mineral grains.  Raw regolith is fed into the furnace and deoxidized with electricity.  Experiments have been done with costly platinum electrodes.  It might be possible to find electrode materials other than platinum that can be produced on the Moon. On my page electrodes I list 21 hi temperature materials that might be produced on the Moon.  Of the 21 hi temp "Moon-makable" electrodes I listed, which ones conduct at high temps and at what temp do they conduct? Can they stand up to hot oxygen? Will they corrode in the molten silicate and/or dissolve? If they do corrode/dissolve, how long do they last? Will they crack? Long term experiments with molten silicate electrolysis must be done.
The output from molten silicate electrolysis will be oxygen, ceramics and ferrosilicon unless serial electrolysis is possible to get iron and silicon separately. What temps, voltages and currents are needed for serial electrolysis to get iron first and then silicon? Can silicon be purified by vacuum evaporation? Or must silicon be reacted with chlorine gas to form gaseous SiCl4 that is then decomposed thermally?

I have also drawn simple diagrams of distillation retorts in which various substances are separated, but what should the dimensions be for various distillation systems? Will various gases cool by radiation or must there be cooling coils in the retorts? Will low lunar gravity affect the diffusion rates of gaseous carbonyls and vapors of metal oxides?

Aluminum extraction presents challenges. Can we find insoluble electrodes for electrolyzing aluminum oxide at 2000 C. or calcium aluminate at 1600 C. ? Our choices would be limited to the 21 listed, otherwise we have to ship up electrodes or do lower temp. electrolysis of aluminum chloride meaning we have to ship up chlorine and make carbon electrodes unless one of the ceramic electrodes works in AlCl3.

Temperature extremes on the Moon present challenges too. Iron will become extremely brittle in the lunar night, but all materials including GLAX, cast basalt, concrete, titanium and other metals will become brittle in the lunar night. Here are some points:

· All materials will be effected by the cold of lunar night and heat of day.

· Mining machines will have to be designed to withstand the heat of day. Foil sheilds might be a part of their protection. In any case, orbital satellites withstand the heat of the Sun for years.

· More sensitive manufacturing devices will either work in inflatable chambers or be kept under foil "garages." At night IR lamps could keep machines warm.

· At Mt. Malapert the Sun will only set 5 times a year for about 5 days at a time, so the main problem there will be shielding.

· Energy for systems to keep machines out-vac under foil sheds warm will either come from a superconducting power grid or energy storage systems or both.

· Habitat will be buried under several feet of regolith for thermal protection and so will inflatable chambers with concrete floors for mounting machines.

· A metalworking plant out on the lunar surface might be expensive because it would only be working during lunar day span. It would become too brittle at night. Lunar day lasts 354 hours, plenty of time to do the metalworking and then move to the next stage of manufacturing when the Sun rises again. At a base on Mt. Malapert, sunlight will be available 340 days per Earth year. Newton Base will be located near shadowed polar crater deposits of water ice or hydrogen that could be combined with oxygen to make water. Oxygen will be produced by numerous processes including molten silicate electrolysis, ilmenite reduction (requires an ilmenite mining outpost in Aitken Basin), and aluminum production.

These pages about lunar resources seem to bring up more questions than answers.  Much research remains to be done.