| Molten Silicate Electrolysis by David A. Dietzler Overview Molten silicate electrolysis requires no chemical reagents upported from Earth, can use unbeneficiated lunar soil, and can produce oxygen, iron, iron-silicon alloy, silicon and ceramic blocks composed of magnesium-aluminum spinel and silicates. It has been thoroughly researched (1). Suggested Prodedure STEP 1) Step one is always volatile harvesting by roasting regolith to get vital H, He, Ne, C, N, S, Fl and Cl. STEP 2) Ultrafine grinding of moondust to break up agglutinates and magnetic/electrostatic separation of ilmenite (FeTiO3). This is done to prevent loosing titanium into the melt. STEP 3) The CARBOTEK process using a fluidized bed to reduce ilmenite with hydrogen gas. FeTiO3 + H2 + heat = Fe + TiO2 + H2O H2O electrolysis= H2 and Oxygen The hydrogen is recycled. The oxygen is stored to be used for many purposes. Fe and TiO2 is separated magnetically after ultrafine grinding to break up fused Fe and TiO2 particles. If grinding is insufficient, carbonyl extraction or acid leaching might be required (2). Iron has many uses and TiO2 makes a good refractory. TiO2 can be reduced further by electrolysis in molten calcium chloride using the new FFC process to get titanium metal and oxygen. STEP 4) Molten silicate electrolysis of regolith after ilmenite removal at 1300 C to 1600 C. Iron requires the least free energy to deoxidize and calcium the most. Thus, iron and silicon are produced along with oxygen and a calcium enriched silicate residue containing MgAl2O4 spinel remains. This residue can make hard high temp ceramic blocks (3). If voltage is too high, magnesium will be reduced (by silicon in the melt???) and volatilize, thereby ruining the spinel(4). |
 |
 |
| * Dr. Larry Haskin of Washington University in St. Louis, Mo. has done much work on molten silicate electrolysis. Of interest to the reader who wants to know more: "Oxygen Production by Silicate Melt Electrolysis" by R.O. Colson and L.A. Haskin. Resources of near-Earth Space. pg. 109. |
| A 70 ton "magma electrolysis' unit with a thru put of 5000 tons regolith per year and a 3 MWe power source could produce 1000 tons of oxygen (5). Hundreds of tons of iron and silicon would be produced and perhaps 2000 tons of ceramic blocks. |
| Make it on the Moon Really large scale regolith refining on a level needed to industrialize the Moon in preparation for space colonization, SPS construction and construction of He3 mining machine fleets on the Moon would demand that molten silicate electrolysis furnaces be constructed on the Moon of indigenouse materials. Ceramic blocks, steel from iron fines and titanium would be used to build large "magma" electrolysis furnaces. Electrode materials presents a problem. Upported platinium could be used for anodes but it will form a Pt-Si alloy at the cathode (6). Irridium is the most inert metal and might be superior, but costly. Ferrosilicon, available from upported electrolysis units, could be used as it will be in thermal balance with the melt or a consumable electrode(s) of some kind could be used (7). This author suggests lunar calcia as it becomes a conductor at high temperates (8). This would require preheating of the electrodes. Whether or not the CaO will be attacked by the corrosive melt and dissolve rapidly remains to be studied. |
 |
 |
| 1)Oxygen From the Lunar Soil by Molten Silicate Electrolysis Russell O. Colson and Larry A. Haskin* 1990 <http://www.belmont.k12.ca.us/ralston/programs/itech/SpaceSettlement/spaceresvol3/oflsmse1.htm> 2) "Toward a Spartan Scenario for use of Lunar Materials" Lunar Bases and Space Activities of the 21st Century pg. 440 Larry A. Haskin <http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?bibcode=1985lbsa.conf..435H> 3) Oxygen From the Lunar Soil by Molten Silicate Electrolysis Russell O. Colson and Larry A. Haskin* 1990 <http://www.belmont.k12.ca.us/ralston/programs/itech/SpaceSettlement/spaceresvol3/oflsmse1.htm> 4) http://epsc.wustl.edu/admin/research/psmrg/nvm3_00/a_m00h02.pdf We know the power required (~13 MWh per tonne O2), the overvoltage required (~0.2V), the practical upper limit to cell voltage (lest Mg2+ be reduced and volatilized), effects of surface tension and how to relieve them (clinging of O2 bubbles at the anode, balling of metal at the cathode), compositional effects of magma composition, suitable container composition and stability, suitable electrode composition and stability, etc. 5) Development of the Moon. Michael B. Duke et al. section 4.3.5.1 pg. 40 http://www.lpi.usra.edu/lunar_resources/developmentofmoon.pdf 6,7) Oxygen From the Lunar Soil by Molten Silicate Electrolysis Russell O. Colson and Larry A. Haskin* 1990 <http://www.belmont.k12.ca.us/ralston/programs/itech/SpaceSettlement/spaceresvol3/oflsmse1.htm> 8) Lime and Magnesia 1924, E. Benn at 1466 C. CaO resistance 91 ohms per cubic centimeter |
| Molten ceramic from magma electrolysis could be poured into sand molds made in compacted lunar regolith. These will be easy to extract. Differentiation of components in molten ceramic might not be a problem in low lunar G. Molten substances sublimate in vacuum. A first cooling "skin" or layer atop the molten blocks might prevent excessive evaporation and loss of material. |
| More Information on heat probe: Steve Howe's Moon Base Technology <http://internet.cybermesa.com/~mrpbar/moon.html> Rowley, John C. and Neudecker, Joeseph W. "In Situ Rock Melting Applied to Lunar Base Construction." Lunar Bases and Space Activities in the 21st Century. ed. W.W.Mendell. pg 465 <http://ads.harvard.edu/books/lbsa/toc.html> |
| Si 21% regolith, hence 1000 tons, Fe 14% thus 700 tons, 2000+ tons remains as MgAl2O4 spinel and calcium silicates, only half the O2 is extracted, but that's enough. 13 MWhrs/ton O2 and 1t Si, 0.7t Fe, some mixed as FeSi, and 2+t of ceramic |
| Pt anodes, FeSi cathode? |