| Having studied other pages of Lunar Resources, it becomes clear that I have concentrated on getting aluminum from regolith. The Damascus Project is all about steel production and steel will probably be the most used metal on the Moon and in outer space, but aluminum is very important for wires and cables since copper is lacking on the Moon, and it will be a major metal for constructing SPS and power relay satellites.. The Typically Favored Al subchloride process Anorthositic highland regolith is 75% to 90+% plagioclase (CaAl2Si2O8 and a little Na2Al2Si2O8) with some pyroxenes and olivines. Magnetic separation will clean the iron bearing minerals including titanium bearing ilmenite out of this leaving fairly pure anorthite-CaAlSi2O8. Intense solar heat at 1500 C. to 2000 C. could boil the remaining iron oxide, silica and magnesia out of the anorthite as well as sodium and potassium, leaving calcium aluminate-CaAlO4. This could be leached in sulfuric acid. CaAl2O4 + 4H2SO4 ==> CaSO4 + Al2(SO4)3 + 4H2O Calcium will form CaSO4, calcium sulphate (plaster of Paris), and water. Al2(SO4)3 will be dissolved in water that will be drained out of the leaching tank, dried to recover water, and roasted to Al2O3. Al2O3 is not attacked readily by sulfuric acid. The CaSO4 (anhydrite, gypsum) can be filtered out with a glass cloth filter, dried, and the water recycled and used to reconstitute H2SO4. During the roasting of Al2(SO4)3 to Al2O3 sulfur dioxide and sulfur trioxide will form and these will react with water to reform sulfuric acid, basically. The Na, K, FeO, SiO2 and MgO roasted out of the anorthostic material with solar heat will be condensed in a ceramic retort since these have many valuable uses of their own. The Al2O3 is then carbochlorinated to yeild AlCl3 which is electrolyzed. Electrolysis of AlCl3 does not consume the precious lunar carbon electrodes as does conventional Hall-Heroult electrolysis of Al2O3. The carbochlorination step yeilds CO2 that must be shifted to methane that can be decomposed to carbon and hydrogen on red hot refractories like solar heated black cast basalt perhaps. Solar carbothermal? If solar carbothermal reduction of alumina is tried, we must mix the alumina with silica and carbon (1). A very high temperature ceramic retort and window will be necessary. An aluminum-silicon alloy will form. This could be separated by cooling the Al-Si mixture to 700-1000 C. and the silicon will solidify and settle out of the melt. See: Acid Leaching etc. This would not require chlorine which is so rare on the Moon to be virtually nonexistent. Carbon would be required so CO and CO2 formed by the carbothermal reduction must be shifted to methane and pyrolized to recover carbon. Electricity would not be needed for the carbothermal reduction. It is said that this will use less energy than electrolysis and since the energy comes directly from solar radiation without the inefficiencies of conversion to electricity and power conditioning I suspect that this may be better than the AlCl3-electrolysis process on the Moon. Destructive Distillation? Combined with Fluxed Electrolysis? Preparing Al2O3 for solar carbothermal redux still requires H2SO4 leaching and this will involve complexities preferrably avoided. Harvesting sulfur oxides will corrode mining equipment, esp. if it reacts with H2O to form H2SO4 in the volatiles miner. Though leaching tanks can be made of steel lined with cast basalt (resists up to 96% sulfuric acid), and piping and pumps can be made of high silicon alloy iron (3.5 % carbon, 15% silicon) the danger of leaks and loss of precious water exists. It may be possible to subject anorthite to intense solar heat to decompose the mineral particles and boil off iron oxide, silica and magnesium oxide leaving calcium aluminate (2). This CaAl2O4 could be subjected to electrolysis in a flux of LiF and CaF2 (EMEC process), but then lithium and fluorine are required and these must be upported to the Moon at great cost and recycled. However, large amount of aluminum are not required on the Moon. Building materals will consist of iron, steel, titanium, cast basalt, ceramics, glass, glass-glass composites and concrete. Aluminum will be used mainly for wiring. 10 gauge Al wire can carry 25 amps. At 14.2 gr/m we need 14.2 kg/1000m and only14.2 metric tons per 1000 km! We could do plenty of wiring with that. 0000 cable 165 amps 290 gr/m 290 kg/km 290 tons/1000 km AWG 1000 cable 380 amps 672 gr/m 672 kg/km 672 tons/1000 km Enormous quantities of aluminum are not needed since it will be used mainly for wiring and cables rather than structural purposes. Thus, the masses of flux upported to the Moon will be limited and not represent an excessive cost. At least in the early years of lunar industrialization, before large scale industry and construction of SPS and power relay satellites. A system that can produce 150 tons of Al per year, 360 tons of calcium and 1000 tons of oxygen from 2500 tons of anorthite using tens of tons of LiF/CaF2 flux has been designed by EMEC consultants. (3) A smaller scale system could be used in early years of lunar industrialization until lunar sources of fluorine were tapped. Possible sources of flourine would be trapped sub-selene volcanic gas, polar ice if of cometary origin, thermal decomposistion of phosphate minerals, acid leaching of phosphate minerals (KREEP bearing regolith). Calcium could be produced on the Moon for flux and sodium or potassium might substitute for some of the lithium. Whether or not lithium exists on the Moon in deposits of any kind is unknown; however, one Apollo 12 sample consisting of 70% anorthite was enriched in potassium, rubidium, barium, zirconium, yttrium, lithium and ytterbium. Did it come from the "mother load" somewhere, ejected by a meteroite impact??? (4) Fluxed electrolysis will require the use of inert electrodes. Patents for Ni-Fe-Al oxide ceramic anodes exist (5). These elements can be obtained on the Moon. SPS and Relay Satellites What happens when we want to go beyond wiring for Moon bases as string out power cables from solar plants all over the Moon and build power satellites in GEO. We will need tens of thousands of tons of aluminum for lunar power grids and millions of tons of aluminum for large numbers of power satellites up to 20 km in diameter. We will not be able to upport the thousands of tons of lithium flouride needed for fluxed electrolysis if we must produce millions of tons of aluminum. The aluminum subchloride process becomes more attractive and so does the solar carbothermic redux process since these can operate primarily with lunar available materials, although some chlorine must be upported for the AlCl3 process preferabley in salt form, IE plastic bags of CuCl3 and ZnCl2, instead of supercold liquid chlorine in heavy insulated tanks. The salts can be electrolyzed to get Cl gas and copper and zinc metals of great value on the Moon for alloying aluminum and magnesium respectively. Titanium resists chloride corrosion but not flouride corrosion. 1) Jean P. Murray Engineering Division, Colorado School of Mines SOLAR PRODUCTION OF ALUMINUM BY DIRECT REDUCTION OF ORE TO AL-SI ALLOY <http://www.kenes.com/Ises.Abstracts/Htm/0450.htm> 2) Rudolf Keller and David B. Stofesky of EMEC Consultants " Selective Evaporation of Lunar Oxide Components" reported in SPACE MANUFACTURING 10 PATHWAYS TO THE HIGH FRONTIER Proceedings of the Twelfth SSI-Princeton Conference May 4-7, 1995; pg. 130. 3) Processing Lunar Soils for Oxygen and Other Materials Christian W. Knudsen and Michael A. Gibson <http://www.belmont.k12.ca.us/ralston/programs/itech/SpaceSettlement/spaceresvol3/plsoom1.htm> 4) David M. Harland. Exploring the Moon. page 49. Praxis Publishing: 1999. 5) Ni-Fe-Al oxide ceramic inert anode http://www.freepatentsonline.com/7033469.html |
| Lunar Aluminum Notes |
| D.A.Dietzler, 2007 |
| A Simpler Way to Get Al? by Dave Dietzler 2008 What if it is possible to subject anorthite to solar heat, boil off and condense the SiO2 for pure silica glass, and get calcium aluminate that is then subjected to even higher temps to break it down into Al2O3 and CaO? Presumably the the Al2O3 will boil off in the vacuum at a lower temp than the CaO because it melts at 2000 C. while CaO melts at 2560 C. and liquids boil in the vacuum. Could the Al2O3 then be condensed and placed in a sealed furnace and melted at 2000 C. with solar heat and electrolyzed with super high temp. oxidation resistant electrodes.? Conductors become resistive at high temp. but semiconductors like many ceramics become conductors at high temp. What if we didn't have to go that far, but just electrolyzed CaAl2O4 at about 1600 C.? This would be the simplest most direct way of getting Al and it would not involve any sulfuric acid, chlorine, flourine, lithium or carbon all of which are in short supply on the Moon. However, this would involve very high temperatures and this presents problems. Perhaps ceramic electrolysis cells and electrodes with active cooling would work. Also, lots of energy will be required. http://www.inspi.ufl.edu/data/htmp1_updated.jpg http://www.inspi.ufl.edu/data/htmp2.jpg At these URLs, are the melting points of a large number of ceramics. Some of them are sure to fit the bill of high temperature oxidation resistance (oxides are already oxidized and won't react with oxygen) and conductivity at high temp. as well as being insoluble in molten Al2O3. Potential “Moon makeable” electrode materials are: Carbides) Ni3C mp 2300 K, CaC2 2500 K, SiC 2950 K, TiC 3400 K Oxides) Al2NiO4 2200 K, Cr2MgO4 2200 K, Al2O3 2300 K, NiAl2O4 2350 K, Ca3TiO5 2350 K, MgAl2O4 2350 K, CaCr2O4 2400 C, Cr2O3 2500 K, CaO 2800 K, MgO 3100 K Sulfides) CaS 2250 K, TiS 2300 K, Phosphide) Ti2P3 2400 K Silicide) Ti5Si3 2350 K Silicates) Mg2SiO4 2350 K, Ca2SiO4 2400 K, NItride) AlN 2650 K. |
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| Electrolysis of molten CaAl2O4 obtained by roasting anorthite at 1500-2000 C. in a solar furnace that drives off Na, K, SiO2, FeO and MgO. Since this furnace will run at 1500 C.+ it must be sealed so that aluminum does not boil away. While this would require more energy that the Hall-Heroult process or even the aluminum sub-chloride process, energy is one of the few things we have an abundance of on the Moon. Sulfur, chlorine and carbon for acid leaching and carbochlorination are sparse. Sulfur and chlorine could come from volcanic gass mining and carbon from volatiles mining. Still, we have to go thru millions of tons of volcanic glass and regolith to get them. Lithium flouride for the EMEC process is even more rare on the Moon and would have to be upported. Simply roasting anorthositic highland regolith in a solar furnace and using hi temp electrodes that won't dissolve in the melt would require no chemicals, so this should be studied. Furnace would be made of ceramic blocks from magma electro, or cast basalt, with a steel outer jacket and a fused silica lining, Forced or active cooling may be applied to electrodes and lining. Typical lunar engineering. But won't oxygen bubble out too? So what, it will add pressure to the furnace to keep the molten aluminum from boiling. But won't the oxygen oxidize the top layers of aluminum to Al2O3? I don't care. If we can get some Al2O3 we can use it for emery paper and emery wheels. So we win either way. And we get more oxygen for Moon bases. What about the calcium oxide, CaO, slag? The liquid aluminum will float on it and we will drain off the aluminum.. Calcium oxide can be used to make soda-lime glass for drinking glasses and canning jars. All we need is some sodium oxide. Soda-lime glass has a lower m.p. than pure silica, so it is easier to work with. If we produce millions of tons of Al for SPS we will have more CaO than we know what to do with. We could use it for cement. CaO, also known as lime, has many uses, including iron or steel furnace flux.. |
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