Lunar Aluminum Production
Luna lacks bauxite, therefore, anorthite will be used for Aluminium production instead.[1] Anorthite (CaAl2Si2O8) could be separated from Anorthosite with mechanical and chemical methods to produce Alumina (aluminium oxide, Al2O3). There are several proposed methods to obtain aluminium (even ones that do not require electrolysis). However, almost all require the importation of catalysts and/or reactants. It is true that reactants can be recycled but they limit the total output to the total amount of reactant present and to the speed that the process can recycle them. Another process would be Ion-sputtering to obtain other material and as a residue Aluminium. Aluminium is a strong reducing agent, therefore it requires special conditions to reduce it with carbon.
Contents
Proposed Anorthite Production Process
Anorthosite is a mix of Plagioclases, Olivines, and Pyroxenes. To separate the anorthite, anorthosite must be ground. Then, magnetic separation could leave the non-magnetic anorthite. Other means would separate silicon, calcium and magnesium.
The magnetic materials (Ilmenite and iron oxide) could be stored for production of Titanium, iron and oxygen.
At this point, the Anorthite could processed directly into it's component metals using the FFC Cambridge Process, or could be further processed into Alumina.
Proposed Alumina Production Process
On Earth aluminium is subjected to the Hall-Heroult process where bauxite undergoes the Bayer process to become alumina.
On the Moon Alumina could be produced from Anorthite by boiling out the impurities (between 1500 ºC - 2000 ºC ). The resulting material would be calcium aluminate (CaAlO4). That can be leached in sulfuric acid. The following reaction would be:
CaAl2O4 + 4H2SO4 ==> CaSO4 + Al2(SO4)3 + 4H2O
Aluminium sulfate in hexadecahydrate form (Al2(SO4)3) is then separated from calcium sulphate (CaSO4 + Al2(SO4)3) by filtering and from water by evaporation (and then recovered).
Finally Alumina is obtained by roasting the aluminium sulfate releasing S2.[2]
Future Hall-Heroult Adaptation
Alumina is dissolved in molten cryolite (Sodium hexafluoroaluminate, Na3 AlF6 ) around 1400 ºC. This mix is electrolyzed to separate two byproducts: aluminium and CO2. The carbon comes from the consumption of carbon electrodes.
Pure alumina can be electrolyzed, but, it melts around the impractical 2000 C without the addition of cryolite. It is not known how refractory containers are going to be made on the Moon, nor whether the Hall-Heroult process can be adapted with or without the importation of fluorine for the cryolite.[3]
Subchloride Process
Chlorine and carbon would be imported from Earth. The alumina is then carbochlorinated (carbonated and chlorinated) to yeild AlCl3 which is electrolyzed. Electrolysis of AlCl3 does not consume the precious lunar carbon electrodes as does conventional Hall-Heroult electrolysis of alumina. The carbochlorination byproduct CO2 must be recycled. [4]
Proposed Carbothermal Reduction
Carbon would be imported from Earth. Then the alumina would be mixed with silica and carbon and melted near 2000 C. An aluminium-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. CO2 must be recovered and carbon recycled. [5]
Alternate Carbothermal Process
Al203 and carbon can be processed at high temperatures and low pressure into Al4C3.[6] [7] This breaks down into Aluminium and Carbon between 1900 and 2000 centigrade. Carbon monoxide given off in processing[8] can be recycled into carbon.
Other Electrolysis Methods
There are two process that do not require imported chemicals from Earth.
The first one is just boil the anothite and to obtain gases at different temperatures, first silica glass then calcium aluminate. With more temperature we obtain alumina and calcium oxide the temperature is reduced and the gases condensed and the liquid is electrolyzed to obtain aluminium, calcium and oxygen (all of them pure). This would require temperatures over 2560 ºC and a tremendous input of energy. The bath would be heated in the center and contained by the cooled crust on the outside. [9]
The second just electrolyzing anorthite at about 1600 C. The other byproduct would be calcium oxide. [10]
See Also
References
- ↑ http://www.permanent.com/l-minera.htm#aluminum
- ↑ http://www.moonminer.com/Lunar_Aluminum.html
- ↑ http://en.wikipedia.org/wiki/Hall-H%C3%A9roult_process
- ↑ http://www.moonminer.com/Lunar_Aluminum.html
- ↑ http://www.moonminer.com/Lunar_Aluminum.html
- ↑ Aluminum section Production and refinement
- ↑ Lunar Aluminum at Moondust index
- ↑ Aluminium carbide at Wikipedia
- ↑ http://www.moonminer.com/Lunar_Aluminum.html
- ↑ http://www.moonminer.com/Lunar_Aluminum.html
