| FLUX David A. Dietzler, 2007 The electrically heated direct reduction furnace would use ferrosilite ( Fe2Si2O6 or FeSiO3 for short) and possibly fayalite (Fe2SiO4) as ores. These contain a lot of silicon dioxide that would ruin the iron. The only way to prevent that would be to use lots of CaO flux. Flux may be a problem. Could the ceramics produced by molten silicate electrolysis that will consist of spinel- MgAl2O3 and CaO could be sources of flux? Could they be used as is? Must we leach out the CaO with H2SO4 to get CaSO4 that is calcined to CaO? Several possibilites: Acid Leaching of Anorthosite Highland regolith containing high concentrations of anorthosite would be mined. Some Apollo samples contained up to 95% CaAl2Si2O8. This would be purified magnetically to remove iron bearing minerals and with solar heat to boil off magnesium bearing minerals. The pure anorthosite would be melted, cooled, ground fine and leached in sulfuric acid made from sulfur and hydrogen volatiles mined from the mare. An aluminum sulfate bearing solution would be filtered out leaving silca and calcium sulfate behind. These would be dried, separated electrostatically and the CaSO4 roasted to CaO. Vapors of sulfur oxide released would be used to recycle acid stocks. The leaching vats might consist of high silicon alloy iron or would be lined with cast basalt as cast basalt resists up to 96% sulfuric acid. The success of this would depend on mining large qtys. of sulfur and hydrogen present only in traces in the mare. Leakage would be disastrous. Complex apparatus is needed. Production would probably be limited. Fluxed Electrolysis The EMEC process uses a flux of LiF and CaF2 and aluminum metal to reduce silicon from anorthosite (1). The lithium and fluorine must be upported from Earth and the flux must be recycled. The process operates at about 1000 C. After aluminum reduction calcium aluminate remains and this is subjected to electrolysis to obtain oxygen, aluminum and calcium. The calcium can be reoxidized to CaO. Besides the need for flux from Earth, corrosion of containers and electrodes could be a problem with this process, but it may be the best process available. Destructive Distillation of Anorthosite It has been suggested that intense solar energy be used to thermally decompose anorthosite. Calcium aluminate and possibly CaO would be the products of this. This would be the simplest, most direct, most brutal way to do the job. It would require no chemicals from Earth and no electricity. The appartus could be built on the Moon from ceramic blocks, cast and sintered basalt blocks, etc. This demands investigation. It might be highly productive (?). see: http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?bibcode=1985lbsa.conf..435H "Solar furnaces are capable of producing very high temperatures...but no systematic study has been made on condensates or residues from the destructive distillation of simulated lunar silicates. The most refractory material formed probably would be calcium aluminate, or,.perhaps, calcium oxide.' ( L. Haskin. Toward a Spartan Scenario for Use of Lunar Materials.) From Mark Prado's PERMANENT (see: http://www.permanent.com/i-distil.htm) we find that experiments were done by 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). Samples were heated in vacuum from 1200 C. to 2000 C. At 1200 C. iron oxide boiled out. At 1500 C. silica and MgO volatilized. Calcium aluminate remained. Could CaO be obtained at higher temperatures? After obtaining the article we find that experiments were done with anorthite, silica and MLS-1. The experimenters encoutered many difficulties but did prove that FeO, SiO2 and MgO could be boiled out of the materials in vacuum. Cement can be made by frying regolith with solar radiation at about 2000-2200 K. Oxides of iron boil out at 1200 C., silica and magnesium boil in the vacuum at about 1500 C. A mix of about 40% CaO, 50% Al2O3 and 10% SiO2 remains (2). This will not be a mixture of oxides but a mixture of calcium aluminate (CaAl2O4) and aluminosilicate. I The cement mix could then be subjected to intense solar heat to break it down further. As for differential evaporation the CRC handbook indicates that CaO will boil at lower temperatures than Al2O3 under low pressure conditions. Can we take the ceramic blocks or highland soils and fry them with solar heat and collect fairly pure calcium oxide for flux? The advantage of doing this rather than H2SO3 leaching is that we don't have to worry about water, leakage or recycling huge quantities of H2SO4. So more research must be done. |
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| A temps of 2000 C. FeO, SiO2 and MgO will boil out. Apollo missions found highland regolith that was 75% to 95% anorthosite. Iron bearing minerals could be extracted magnetically and ilmenite, present in small amounts compared to the mare regolith could be extracted with electrostatic separators. Electrostatic sep could even get the breccias, agglutinates, olivine and pyroxenes apart from the anorthite. Silica and smaller qtys. of magnesia will boil out and this could be used as starting material for aluminosilicate glass. Regolith is a good thermal insulator. As some melts it will flow between the spaces between the sharp particles and conduct heat into it and melt it. The concept is simple. Calcium aluminate could be used for flux in iron and steel furnaces. Robots will be lowered into the furnace thru a hatch (not pictured) to dig up the oxide powders and hardened CaAl2O4 and CaO at the bottom of the furnace. Smelting 100 tons of iron with hot CO gas from ferrosilite will require 100 tons of CaO! Will it be practical to produce huge amounts of flux to keep up with iron/steel production in the future, decades after the first Moon base when large projects like smelting 100 tons of iron per day are possible??? Could it be more efficient to roast ferrosilite, condense iron oxide, and use that for ore instead of the SiO2 rich mineral itself? Producing large qtys of iron oxide or large qtys. of flux, or both? What will be the most efficient strategy? |
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| On the Moon, there is very little carbon for hi temp crucibles, besides molten alumina, calcium aluminate, calcia mixtures could be reduced by the carbon and erode the crucible. Ceramic blocks from molten silicate electrolysis will be largely spinel, an oxide with a high m.p. Additionally, regolith is a good thermal insulator, so much of the unmelted regolith iitself in the crucible serves as insulation. |
| 1) 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 2) T.D. Lin "Concrete for Lunar Base Construction" Lunar Bases and Space Activities of the 21st Century ed. W.W.Mendell Lunar and Planetary Institute, Houston pg. 381 <http://ads.harvard.edu/books/lbsa/toc.html> |
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