Moon Miner
  

The Moon, sitting in a gravity well only 1/21 as deep as Earth's, could supply millions of tons of oxygen, raw regolith, basalt, ceramics, glass, silicon, iron, calcium, aluminum, magnesium, titanium, sodium, sulfur, potassium, manganese, chromium,volatiles and more annually for construction in outer space.

 

 Tapping Lunar Resources



Lunar soil, regolith, or Moon dust is mostly oxygen and silicon along with iron, calcium, aluminum, magnesium, titanium and traces of chromium, manganese, sodium, potassium, phosporus,sulphur and miniscule amounts of many other elements. It also contains traces of hydrogen, helium, methane, CO, CO2 and nitrogen implanted by the solar wind that can be extracted by mining millions of tons of regolith and heating it to about 700 C. Numerous processes for extracting and separating these elements have been described.  Ideally, it should be possible to heat regolith until it decomposes and separate the elements with something similar to a mass spectrometer.  Dr. Peter Schubert has designed a device pictured above that heats and decomposes regolith into oxygen and other elements like iron, aluminum and silicon.  A slag of calcium and magnesium oxides forms too.  These are all separated in what he calls an "All Isotope Separator" (not pictured here) that resembles a mass spectrometer or calutron for enriching uranium.  This device holds a lot of promise.  If it fails to meet up to expectations economically, Moon miners will have to use a different process.  Proposals involving the use of HF acid, fluorine gas and/or many other chemical reagents not available on the Moon have been made.  Below is an attempt to deliniate an alternative process for extracting resources from lunar regolith that relies on heat and electricity moreso than chemicals.

Producing Lunar Materials with Heat and Electricity

Numerous processes for extracting oxygen and metals from lunar regolith have been proposed. Most of them use chemical reagents like HF, fluorine, chlorine and other substances not common on the Moon. A process that doesn't require water and/or lots of corrosive and imported chemicals is desired. Solar wind implanted volatiles like hydrogen, helium, carbon and nitrogen can be extracted by roasting huge quantities of regolith at 700 C. Mare regolith can be excavated, pressed into forms and sintered with heat from solar or electrical furnaces, or melted and cast to make numerous basalt items. Highland regolith can be sintered or cast to make glassy products with a melting point of about 1500 C. Meteoric iron fines can be magnetically extracted from large amounts of regolith just about anywhere on the Moon. After some grinding, screening and a second magnetic separation, 99% pure iron-nickel particles can be obtained [1]. This can be refined further with carbon monoxide to extract nickel. Another possibility is the use of a device similar to a mass spectrometer to separate iron, nickel, cobalt, gallium, germanium and platinum group metals from this meteoric material. It will also be possible to melt and cast the iron fines in sand molds and it should be possible to run these particles in 3D printers after sizing them to make pure iron items for low stress applications. It will also be possible to melt and cast the iron into rods, pack them in carbon powder, and get them red hot for a few days in solar or electrical furnaces to convert the iron into strong steel. So far, so good. Mining the Moon for these materials doesn't require any water, acids, halogens or other substances rare or practically non-existent on the Moon.

Heating regolith to 700 C. will release hydrogen and helium. Carbon will react with oxygen in the regolith to form CO and CO2 gases. Hydrogen will react with carbon to form methane and it will react with oxides to form water. At the University of Wisconsin in Madison, scientists have designed a machine that can dig up and heat regolith from a square kilometer of lunar surface to a depth of three meters in a years' time. They predict harvesting of substantial quantities of volatiles [2].

                                                           Materials Harvested per Year in Tonnes

Element/Compound Mass
water 109
nitrogen 16.5
CO2 56
hydrogen 201
helium 4 102
methane (CH4) 53
CO 63
helium 3 33 kg.

Polar ices may also serve as a source of water and thus hydrogen and oxygen. The ice might also contain ammonia (NH3), methane (CH4), carbon monoxide and carbon dioxide.

Sulfur, potassium and sodium can be roasted out of large quantities of regolith by heating the Moon dust up to 1200 C. and possibly higher [3]. At 1200 C. in the vacuum FeO will volatilize. At 1500 C. and hotter SiO2 and MgO will boil out. If anorthite is heated to 2000 C. in the vacuum SiO2 will boil out and calcium aluminate, CaAl2O4 will remain [4]. Calcium aluminate can be used to make hydraulic cement. Plain sand mixed with molten sulfur also makes a kind of cement. Regolith should work as well as terrestrial sand.

What about oxygen? Regolith will give up oxygen simply by heating it to 2000 C. and hotter. Ilmenite obtained by electrostatic refining of high-Ti mare regolith can be reduced with hot hydrogen gas. The resultant water can be electrolyzed to gain oxygen and recycle hydrogen. Magma electrolysis at 1600 C. can release oxygen and produce ferrosilicon and a spinel rich ceramic. This last process requires platinum anodes and equipment that can handle high temperatures. An actively cooled magma cell and oxide ceramic electrodes instead of platinum might be used. More research is called for.

At this point, Moon miners will have hydrogen, helium, carbon monoxide, carbon dioxide, methane and nitrogen, basalt, a glassy ceramic, iron, nickel, sodium, sulfur, potassium, oxides of iron, silicon and magnesium as well as cement and oxygen. Silicon dioxide is glass, a useful material. Add some Na, K and CaAl2O4 and we can make a lower melting point glass that is more workable. Given a way to separate SiO2 and MgO from roasted regolith, perhaps electrostatic separation, we can take MgO and reduce it with ferrosilicon at 1200 C. under low pressure to obtain magnesium. It should also be possible to reduce FeO with hot hydrogen to get iron and oxygen. What can we do with basalt, ceramics, glass, cement, iron and magnesium on the Moon? Since these can be obtained with purely electrical and thermal processes without imported chemicals it seems these will be comparatively inexpensive.

Steel could be made on the Moon if iron is available. Carbon from mining for solar wind implanted volatiles and/or polar ice mining can be combined with iron by the simple "crucible" or "blister steel" process. Since steel is 0.05% to 1.5% carbon, a little carbon can make a lot of steel. When pure iron won't do, we could make some steel.

What about titanium? We can get titanium without water but we need imported chlorine to make CaCl2 electrolyte for FFC process cells. We will need carbon for electrodes and a system to recycle the carbon as it burns up...unless we can use imported non-consumable electrodes made of tin oxide or calcium ruthenate. If the CaCl2 electrolyte breaks down we will need to recover and reuse the chlorine. The chlorine would be shipped to the Moon in salt form and this will cost thousands of dollars per pound; therefore titanium might be rather expensive.

Aluminum can be obtained on the Moon. It might be possible to reduce CaAl2O4 with hot potassium and sodium. If this is true, then aluminum could be produced without water and without imported chemicals and the price of aluminum should be reasonable.

Highland regolith consists mostly of anorthite (CaAl2Si2O8). There is no bauxite on the Moon because this is a sedimentary rock and there has never been any water on the Moon. Anorthite could be concentrated using electrostatic separation processes. I've read about aluminum production using a complex process that involves leaching anorthite with H2SO4, carbochlorinating the aluminum sulfate and electrolysis in a flux of lithium and sodium chloride. Sulfuric acid and carbon could be obtained on the Moon and recycled. Chlorine and lithium would be imported and also recycled. This process is complicated and puts precious water at risk. It is also possible to electrolyze CaAl2O4 in an electrolyte of LiF and CaF with electrodes made of some exotic metals that was developed by EMEC Consultants [5]. Imports would be required but water would not, so I prefer the EMEC process to the acid leach-carbochlorination-electrolysis process. Even so, it would be preferrable to use a process that doesn't require any imports of chemical reagents. Something resembling a mass spectrometer or simply heating anorthite to drive off the silicon to get calcium aluminate (CaAl2O4) and reducing this with lunar sodium and potassium seems more desirable.

It seems then that we can get all the major lunar materials with purely thermal and electrical processes, but we need some imports for titanium and perhaps for aluminum. The chemistry of these processes is not to complicated, but the solar and electrical furnaces, electrolysis cells, retorts and other pieces of equipment are going to be a challenge for chemical engineers to figure out how to construct on the Moon with lunar materials. One mechanical engineer that I know designed a silicon carbide furnace that could reach 2000 C. and concluded that there would be a lot of thermal management problems. Heat radiating from the furnace could actually melt nearby regolith! We will need to look at more "bone headed" solutions like building a furnace from a massive pile of bricks that has so much "thermal inertia" that it never gets red hot and instead of using conduction to heat the whole furnace as well as the material in the furnace we could just hit "ore" with an electron beam in the free vacuum or use radio waves (induction heating). Ceramic furnaces and magma electrolysis cells could have cooling passages drilled in them and CO2 could be used as coolant. The waste heat could be disposed of with metal space radiators coated by vapor deposition with a very thin layer of dark basalt to increase emissivity. Regolith is such a good insulator that waste heat cannot be rejected into the ground.

Since basalt will be so easily obtained it seems that there should be a focus on using basalt whenever possible. See: Unique Lunar Products

1) Dr. William Agosto. "Lunar Beneficiation." http://www.nss.org/settlement/nasa/spaceresvol3/lunarben1b.htm.

2) Matthew E. Gajda et al. "A Lunar Volatiles Miner." nasa-academy.org/soffen/travelgrant/gadja.pdf

3) Handbook of Lunar Materials, NASA Reference Publication 1057, 1980, pg. 115, http://www.nss.org/settlement/moon/library/1980-HandbookOfLunarMaterials.pdf

4) Rudolf Keller and D.B.Stofesky. "Selective Evaporation of Lunar Oxide Components." Space Manufacturing 10, pp. 130-135, Abstract: http://ssi.org/ssi-conference-abstracts/space-manufacturing-10/                                                                                                         

5) Christian W. Knudsen and Michael A. Gibson, Processing Lunar Soils for Oxygen and Other Materials, http://www.nss.org/settlement/nasa/spaceresvol3/plsoom1.htm


(left) Magma electrolysis cell. (below) Electrostatic separator               


MgO from roasting of mare regolith at 1500 C+ followed by electrostatic separation from SiO2 could be mixed with FeSi from magma electrolysis and calcium aluminate (CaAl2O4) from roasting of anorthite at 2000 C.+.  This mixture could be heated to 1550 C. under free vacuum conditions to reduce MgO and produce magnesium vapor that is condensed to form crystals that are melted and cast.





The processes flowcharted above do not require huge quantities of sulfuric and/or hydrofluoric acids that would in the case of HF require costly imports and for either acid the formation of lots of water that would require complex systems to recycle and reform the acids. Corrosion is avoided, but high temperatures must be dealt with perhaps by using active cooling systems and lots of electrical power is needed. Fortunately, plenty of solar energy is available on the Moon and in high orbit. Mining is easy. Vacuum is free and shielded space radiators can emitt waste heat into the cold of outer space efficiently. Methods to recover and use waste heat are desirable. Reduction of ilmenite and iron oxide with hydrogen will form water but that is easily decomposed to oxygen and recycled hydrogen. Oxygen, ferrosilicon, iron, steel, magnesium, aluminum, calcium, titanium, glass, basalt, cement and slag blocks for construction can all be produced without large amounts of acid and water. Silicon is notably absent, but the best way to get silicon and dopants for solar panels is to use Dr. Peter Schubert's patented Lunar Dust Roaster and All Isotope Separator. This device requires no chemical reagents but it does require some exotic materials to construct like thorium oxide and platinum-rhodium bushings. Most of the device could be made with lunar materials and eventually Pt-Rh from meteoric iron fines harvesting will be available on the Moon. These metals have other uses like bushings for drawing basalt and glass fibers and possibly for magma electrolysis anodes although there may be "Moon-makeable" ceramic materials that become conductors at high temperatures that can resist the corrosion and heat of molten silicates. Thorium could eventually be derived from massive quantities of KREEP and this metal would have nuclear power applications as well as high temperature applications. KREEP could also supply uranium, potassium, phosphorus and REEs. For more information about Dr. Schubert's Lunar Dust Roaster and All Isotope Separator and solar panel production see:  http://nsschapters.org/hub/pdf/MoonRockstoSaveEarth.pdf   

What kind of equipment will we need to produce materials on the Moon?

1) Obviously we will need excavators and solar panels to recharge the batteries in these digging machines.

2) We will need teleoperated robots to service, repair and maintain the machines.

3) Furnaces and iron molds will be required to melt and cast basalt. Special molds and RF or induction heaters will be used to sinter basalt.

4) Magma electrolysis cells will yield oxygen that is piped thru space radiators and cryo-chillers to buried insulated LOX tanks. Slag can pour out into sand molds dug in the ground by excavators. FeSi will pour into briquetting molds. Devices for powdering FeSi and devices for mixing it with LOX to make a slurry rocket monopropellant will also be used.

5) Mare regolith will be roasted at 700 C. in furnaces to drive out solar wind implanted gases and these will be cooled, condensed and separated by fractional liquefaction and stored in buried insulated tanks. Piping, pumps, compressors, space radiators, refrigeration equipment, storage tanks, etc. are called for to do this.

6) This regolith will then be heated to higher temperatures in retorts similar to Magnetherm retorts to drive out Na, K and S. The removable condensor buckets will be swapped out and the condensed material will be melted out. Then the regolith will be heated more to drive out FeO.

7) FeO will be scraped out of the buckets and shoveled by robots into a fluidized bed for reduction with hydrogen. The water that then forms will be sent to electrolysis cells and the H2 recycled and the oxygen stored. This means more piping, cryo-chillers, insulated tanks, etc.

8) The iron powder will then be melted and cast and used as is or converted to steel in carburization boxes.

9) The removable condensor buckets will be swapped again and the regolith will be heated up to 1500 C.+ to drive out SiO2 and MgO which will then be scraped out, crushed in ball mills to a powder, and separated in electrostatic separators. Remaining material will be melted and cast in sand molds to make blocks.

7) Highland regolith will be excavated and heated to drive out volatiles then run through magnetic and electrostatic separators to concentrate anorthite. The anorthite will be placed in retorts with active cooling systems and heated to 2000 C. to drive off SiO2 and yield CaAl2O4 which will be used for cement and flux in magnesium production.

8) CaAl2O4 will melt at 1500 C. and pour out of the reactors to briquetting molds. These will then be placed in electrolysis cells with CaF2/LiF flux to get calcium and aluminum.

9) MgO will be shoveled into Magnetherm type retorts with briquettes of FeSi and CaA2O4 and heated to 1200 C. to 1500 C. to get magnesium and slag blocks. The magnesium crystals that form in the removable condensor buckets will be melted out and cast.

10) Ilmenite rich mare regolith will be excavated and subjected to magnetic and electrostatic separation to concentrate ilmenite. This mineral will be subjected to hot hydrogen gas and reduced in a fluidized bed to get water that is electrolyzed to recycle H2 and gain O2 thus more piping, space radiators, cryo-chillers are needed. The fused partices of TiO2 and iron that result will be separated somehow. They might simply be ground fine and magnets used to remove the iron. Or, they could be roasted in the vacuum to boil off the iron. They might be treated with hot CO gas that reacts with iron to form carbonyl vapors for chemical vapor deposition of various items and/or simply decomposed with heat to get iron. Finally, separating fused iron and TiO2 might be as simple as melting the iron and letting the TiO2 float on top and skimming it off. The TiO2 would be shoveled into FFC electrolysis cells and the result will be titanium.

It becomes rather obvious that digging up mare soil and casting or sintering it to make basalt products is one of the simplest jobs we can do on the Moon and this can be done at an early stage. Oxygen will be desired also. At first oxygen production and storage equipment will be landed on the Moon. For oxygen and other gases we will need piping, cryo-chillers, etc. If we can get steel production going (perhaps with meteoric iron fines) we can make these on the Moon with robot and human crews using 3D printers and conventional casting techniques and machine tools. Fluidized beds could be welded up from steel plates and pipes could be extruded or rolled.

Thus, we are looking at furnaces, rolling miles, extruders and welders to make fluidized beds and other pieces of regolith refinery equipment. Magma electrolysis cells and furnaces might be built with slag blocks, iron or steel jackets and refractory linings. Cooling pasages could be drilled through the slag blocks and piping, space radiators and pumps could be made of lunar steel. FFC electrolysis cells could also be made this way and since this process works at lower temps cooling might not be necessary.

Magnetherm type retorts could be made of slag blocks and iron jackets. The condensors will also require cooling gas, piping, pumps and space radiators.

Electrostatic and magnetic separators could be made of lunar steel and iron along with calcium and aluminum wires with woven basalt or glass fiber insulation. Some parts for these like input hoppers, support frames and collection bins could be made of cast or sintered basalt.

Lots of cargo will be required to do this job.  It will be necessary to figure out how to make all this on the Moon from an initial stock of devices or a "lunar industrial seed" that might have a mass of several hundred or several thousand tons.  Energy requirements and times for each step of the process must be calculated; a job for chemical engineers.  The economics of all processes must be determined by doing research on the ground in vacuum chambers that simulate the lunar environment, at lunar analog research bases and at a Lunar Industrial Research Park on the Moon where hard facts are determined.   

Naturally, many solar panels will be needed to power this equipment. The 3D printers, casting foundries and machine shops where we replicate this regolith refinery equipment will not be limited to the expansion of the refinery. They will also use lunar materials to crank out all the other items needed for life in space including bathroom and kitchen fixtures, plumbing systems, everyday items like dishes and bottles, robot parts, vehicle parts and complete vehices, excavator parts and complete excavators, spacecraft and more 3D printers and machine tools.

At some point in time, growth of the lunar mining, refining and manufacturing complex will become exponential. The first base will produce enough stuff to build a second base, then a third and fourth base, then eight bases, sixteen bases, etc. We will need dirt roads and eventually railways to connect the bases. When we grow large enough to produce millions of tons of materials on the Moon every year we will build large mass drivers with lunar calcium and aluminum coils to launch materials into space for solar power satellite construction, large space stations, space observatories and telescopes, telecommunication platforms that replace myriad communication satellites, micro-gravity factories, space ships, etc.


A DETAIL

Sulfur on the Moon is present mostly in troilite, FeS, a non-magnetic mineral of meteoric origin.  If we roast regolith at 900 to 1200 C. the sulfur will be released possibly as H2S and SO2.  We could react the H2S gas with oxygen to form water and sulfur dioxide that could be combined to make sulfuric acid for making sulfate cement ingredients and fertilizer.  Of importance, is the fact that H2S is very toxic and oxygen produced by magma electrolysis will be contaminated unless we roast out the sulfur first.  For rockets, H2S contamination of LOX doesn't matter.  For breathing oxygen the removal of H2S is vital.  Zinc oxide can remove H2S but zinc is very rare on the Moon, so it would be wise to pretreat the regolith by roasting out sulfur before extracting oxygen for life support.  Converting H2S and SO2 to solid elemental sulfur for sulfur cement is a problem.  Perhaps pyrolysiss of H2S and SO2 will work.