Difference between revisions of "Lunar Aluminum Production"

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Our satellite lacks of bauxite, therefore, anorthite will be used instead.<ref>http://www.permanent.com/l-minera.htm#aluminum</ref> [[Anorthite]] (CaAl<sub>2</sub>Si<sub>2</sub>O<sub>8</sub>) could be separed from [[Anorthosite]] with mechanical and chemical methods to produce [[Alumina]] (aluminium oxide, Al<sub>2</sub>O<sub>3</sub>). <ref> http://en.wikipedia.org/wiki/Anorthosite</ref>
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Since Luna lacks any known deposits of bauxite, the ore most commonly used on earth for aluminum production, [[anorthite]] (CaAl<sub>2</sub>Si<sub>2</sub>O<sub>8</sub>) is most commonly proposed as a lunar substitute.<ref>http://www.permanent.com/l-minera.htm#aluminum</ref> [[Anorthite]] could be separated from the lunar highland material [[Anorthosite]] with mechanical methods. It could then be reduced through various chemical and electrochemical methods to produce [[aluminum]].
  
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There are several proposed methods to obtain aluminium (even those that doesn't require electrolysis). However, almost all include an 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]].
 
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Aluminium is a strong reducing agent, therefore it cannot undergo a normal [[Reduction]] by carbon. <ref>http://en.wikipedia.org/wiki/Anorthite</ref>
 
  
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== Proposed Anorthite Production Process ==
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== Anorthite Production ==
  
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Anorthosite is a mix of [[Plagioclase]]s, [[Olivine]]s, and [[Pyroxene]]s. To separate the anorthite, anorthosite a must be grind. Then, magnets could be put in contact with the powder to separate everything from the non-magnetic anorthite.
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The [[Anorthosite]] which makes up the Lunar highlands is a mix of [[Plagioclase]]s, [[Olivine]]s, and [[Pyroxene]]s. To separate the [[anorthite]], [[anorthosite]] must be ground. Then, magnetic separation could leave the non-magnetic anorthite.
  
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The magnetic materials (even [[Ilmenite]], iron oxide, silica and magnesia) could be stored for production of [[Titanium]] and other metals.
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The magnetic materials ([[Ilmenite]] and iron oxide) could be stored for production of [[titanium]], [[iron]], and [[oxygen]].
  
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== Proposed Alumina Production Process ==
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== Anorthite Refinement ==
  
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On Earth aluminium is subjected to the Hall-Heroult process where bauxite undergoes the Bayer process to become alumina.
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===Direct Reduction===
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Main Article: [[FFC Cambridge Process#Aluminum/Silicon/Calcium Production from Anorthite|FFC Cambridge Process]]
  
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On the Moon [[Alumina]] could be produced from Anorthite by boiling the impurities (between 1500 ºC - 2000 ºC ). The resulting material would be calcium aluminate (CaAlO<sub>4</sub>). That can be leached in sulfuric acid. The following reaction would be:
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[[Anorthite]] could be directly reduced to its component metals using the [[FFC Cambridge Process]]. The [[Anorthite]] is pressed/sintered into a cathode, which is placed in a bath of molten calcium chloride and electrolyzed. The oxygen is stripped out, leaving behind [[Aluminum]], [[Calcium]], and [[Silicon]].
  
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CaAl<sub>2</sub>O<sub>4</sub> + 4H<sub>2</sub>SO<sub>4</sub> ==> CaSO<sub>4</sub> + Al<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub> + 4H<sub>2</sub>O
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This process has the advantage of inherent simplicity, as well as having only one component to recycle, the calcium chloride, which does not react chemically with the inputs, making recovery much simpler. In addition, this process runs at lower temperatures (900º-1100º C) than many other electrolysis procedures, and inert(non-consumable) anodes have been successfully demonstrated with it<ref>http://www.lpi.usra.edu/meetings/roundtable2006/pdf/tripuraneni.pdf</ref>. On the downside, energy must be expended to split all the components of the [[Anorthite]], not just the [[aluminum]]. Splitting the silicon and calcium adds a significant amount of extra energy to the process, as both of them are strong reducers. However, if the silicon and calcium byproducts were needed for other purposes (calcium is a good [[Electrical Conductors|electrical conductor]], and silicon could be used for solar panels or [[In-Situ Propellant Production|rocket fuel]]), this extra energy cost may not be an issue.
  
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Aluminium sulfate in hexadecahydrate form (Al<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub>) is then separated from calcium sulphate (CaSO<sub>4</sub> + Al<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub>) by filtering and from water by evaporation (and then recovered).
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=== Alumina Production ===
  
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Finally Alumina is obtained by roasting the aluminium sulfate releasing S<sub>2</sub>.<ref>http://www.moonminer.com/Lunar_Aluminum.html</ref>
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Many processes used on earth or proposed for Lunar use require [[alumina]] ([[Aluminum|Al]]<sub>2</sub>[[Oxygen|O]]<sub>3</sub>) as an input. On Earth, alumina is produced from bauxite through the Bayer process. As this process is not feasible using Anorthite, another method must be utilized.
  
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== Future Hall-Heroult Adaptation ==
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====Vacuum Distillation====
  
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Alumina is dissolved in molten cryolite ([[Sodium]] hexafluoroaluminate, Na<sub>3</sub> AlF<sub>6 </sub>) around 1400 ºC. This mix is electrolyzed to separate two byproducts: aluminium and CO<sub>2</sub>.
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[[Alumina]] could be produced from Anorthite by boiling out the impurities between 1500 ºC - 2000 ºC under vacuum conditions. The resulting material would be calcium aluminate ([[Ca]][[Al]][[O]]<sub>4</sub>). Raising the temperature further could cause [[alumina]] to volatilize as well. <ref>http://www.moonminer.com/Lunar_Aluminum.html</ref>
  
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Pure alumina can be electrolyzed, but, it melts around the impractical 2000 ºC without the addition of cryolite. It is not known how refractory containers are going to be made on the Moon, neither if the Hall-Heroult process can be adapted with or without the importation of fluorine for the cryolite.<ref>http://en.wikipedia.org/wiki/Hall-H%C3%A9roult_process</ref>
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====Sulfuric Acid Leaching====
  
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== Subchloride Process ==
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Another method is to produce calcium aluminate as outlined previously, which is then leached in sulfuric acid, resulting in the following reaction:
  
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Chlorine and carbon would be imported from Earth. The alumina is then carbochlorinated (carbonated and chlorinated) to yeild AlCl<sub>3</sub> which is electrolyzed. Electrolysis of AlCl<sub>3</sub> does not consume the precious lunar carbon electrodes as does conventional Hall-Heroult electrolysis of alumina.  The carbochlorination byproduct CO<sub>2</sub> must be [[recycled]]. <ref>http://www.moonminer.com/Lunar_Aluminum.html</ref>
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[[Ca]][[Al]]<sub>2</sub>[[O]]<sub>4</sub> + [[Sulfuric Acid |4H<sub>2</sub>SO<sub>4</sub>]] ==> [[Ca]][[S]][[O]]<sub>4</sub> + [[Al]]<sub>2</sub>([[S]][[O]]<sub>4</sub>)<sub>3</sub> + 4[[water |H<sub>2</sub>O]]
  
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== Proposed Carbothermal Reduction ==
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Aluminium sulfate in hexadecahydrate form ([[Al]]<sub>2</sub>([[S]][[O]]<sub>4</sub>)<sub>3</sub>) is then separated from calcium sulphate ([[Ca]][[S]][[O]]<sub>4</sub> + [[Al]]<sub>2</sub>([[S]][[O]]<sub>4</sub>)<sub>3</sub>) by filtering and from water by evaporation (and then recovered).
  
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Carbon would be imported from Earth. Then the alumina would be mixed with silica and carbon and melted near 2000 ºC. An aluminium-silicon alloy will form. This could be separated by cooling the Al-Si mixture to 700 ºC-1000 ºC. and the silicon will solidify and settle out of the melt. CO<sub>2</sub> must be recovered and carbon recycled. <ref>http://www.moonminer.com/Lunar_Aluminum.html</ref>
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Finally Alumina is obtained by roasting the aluminum sulfate releasing [[S]]<sub>2</sub>.<ref>http://www.moonminer.com/Lunar_Aluminum.html</ref>
  
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== Other Electrolysis Methods ==
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====Hydrochloric Acid Leaching====
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Another option is to react [[Anorthite]] with hydrochloric acid, which results in following reaction:
  
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There are two process that doesn't require importation on Earth.
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: [[Ca]][[Al]]<sub>2</sub>[[Si]]<sub>2</sub>[[O]]<sub>8</sub> + 8 [[H]][[Cl]] + 2 [[H]]<sub>2</sub>[[O]]==> [[Ca]][[Cl]]<sub>2</sub> + 2 [[Al]][[Cl]]<sub>3</sub>.6 [[H]]<sub>2</sub>[[O]] + 2 [[Si]][[O]]<sub>2</sub>
  
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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, very efficient super-refractories and a tremendous input of energy. <ref>http://www.moonminer.com/Lunar_Aluminum.html</ref>
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The calcium chloride and hydrated aluminum chloride dissolve in the solution and are removed. They are then precipitated out of solution, dried, and heated under partial vacuum until the calcium chloride evaporates out of the mix. Temperatures of this range will cause the hydrated aluminum chloride to become [[alumina]], releasing water and hydrogen chloride in the process:
  
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The second is not going that far with just electrolyzing anorthite at about 1600 ºC. The other byproduct would be calcium oxide.<ref>http://www.moonminer.com/Lunar_Aluminum.html</ref>
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: 2 AlCl<sub>3</sub>.6 H<sub>2</sub>O ==> Al<sub>2</sub>O<sub>3</sub> + 6 HCl + 3 H<sub>2</sub>O
  
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The water and hydrogen chloride are separated from the calcium chloride and fed back into the system. The calcium chloride is then electrolyzed into metallic calcium and chlorine. A portion of the recovered water is then [[Water Splitting|split]] into hydrogen and oxygen. The hydrogen component is reacted with the evolved chlorine to produce hydrogen chloride, which is then fed back into the main system.
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=== Direct Calcium Aluminate / Alumina Reduction ===
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Calcium Aluminate (see above for production) could be simply melted and electrolyzed directly, producing aluminum and calcium oxide.<ref>http://www.moonminer.com/Lunar_Aluminum.html</ref> This has two advantages. First, it requires no imported reagents, and second, only the aluminum is split, reducing the amount of energy needed. The disadvantage is that temperatures of approximately 1600 ºC are required, making electrode material of prime concern. Carbon electrodes could be utilized at those temperatures, but the anode would continually wear away as oxygen was produced around it, creating carbon monoxide. The carbon would need to be [[Lunar Carbon Production|recovered]] and new anodes made from it. This effectively means that a rare reagent is needed, negating the process's first stated advantage. Finding an anode material that would produce oxygen without wearing away at those temperatures could be quite difficult.
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Alumina could also be directly melted and electrolyzed in the same fashion. However, this would require temperatures of approximately 2000 ºC, bringing with it again the issue of electrode material.
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=== Hall-Heroult Process ===
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In the Hall-Heroult process, alumina is dissolved in molten cryolite ([[Sodium]] hexafluoroaluminate, Na<sub>3</sub> AlF<sub>6 </sub>) around 1400 ºC. This mix is electrolyzed to separate two byproducts: [[aluminium]] and [[Carbon Dioxide|CO<sub>2</sub>]]. The carbon comes from the consumption of the carbon anode.
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This procedure is used extensively on earth for aluminum production, and as such has the advantage of being a very mature technology. The biggest issue is the consumption of the anode, which would require the produced carbon dioxide to be captured, [[Lunar Carbon Production|converted back into carbon]], and recast into new anodes; an energy intensive process. It is not known if an inert(non-consumable) anode material can be found that would work under these conditions.<ref>http://en.wikipedia.org/wiki/Hall-H%C3%A9roult_process</ref>
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=== Subchloride Process ===
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In the subchloride process [[alumina]] is reacted with [[carbon]] and [[chlorine]] to yield [[Al]][[Cl]]<sub>3</sub> and [[Carbon dioxide |CO<sub>2</sub>]]. The [[Al]][[Cl]]<sub>3</sub> is electrolyzed to produce [[aluminum]] while recovering the [[chlorine]]. This has the advantage that conventional [[carbon]] electrodes can be used continuously, as the produced [[chlorine]] does not react with them. However, the [[Carbon dioxide |CO<sub>2</sub>]] byproduct must be [[Lunar Carbon Production|recycled]], adding extra complexity and energy requirements to the system. This makes it similar to the Hall-Heroult process in difficulty, except for two advantages. First, the recycled carbon can be directly used in powdered form, it does not need to be recast into electrodes. Second, due to the low melting point of [[Al]][[Cl]]<sub>3</sub> (120 ºC), the process does not require significant energy to melt, and is more easily handled.  <ref>http://www.moonminer.com/Lunar_Aluminum.html </ref>
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=== Carbothermal Reduction ===
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Carbon reduction of Alumina is impossible under normal smelting conditions, due to [[aluminum]]s high reduction potential. However,  Alumina could be mixed with silica and carbon and melted near 2000 ºC, which would form an aluminium-silicon alloy, as well as CO<sub>2</sub>. This could be separated by cooling the Al-Si mixture to 700 - 1000 ºC and allowing the silicon to solidify and settle out of the melt.<ref>http://www.moonminer.com/Lunar_Aluminum.html </ref>
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An alternate process involves alumina and carbon processed at high temperatures and low pressure into Al<sub>4</sub>C<sub>3</sub> and carbon monoxide.<ref> [http://en.wikipedia.org/wiki/Aluminium ''Aluminum'' section ''Production and refinement''] </ref>
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<ref> [http://www.moonminer.com/Lunar_Aluminum.html ''Lunar Aluminum'' at ''Moondust index''] </ref>  This breaks down into Aluminum and Carbon between 1900 and 2000 ºC.<ref> [http://en.wikipedia.org/wiki/Aluminum_carbide ''Aluminium carbide'' at ''Wikipedia''] </ref>.
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In either case, CO<sub>2</sub>/CO would have to be recovered and and the [[Lunar Carbon Production|carbon recycled]].
  
 
== See Also ==
 
== See Also ==
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*[[List of Proposed Metal Production Methods]]
 
*[[List of Proposed Metal Production Methods]]
  
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== References ==  
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== References ==
 
<references/>
 
<references/>
 
   
 
   
 
[[Category:Industrial Production]]
 
[[Category:Industrial Production]]

Latest revision as of 10:38, 10 April 2019

Since Luna lacks any known deposits of bauxite, the ore most commonly used on earth for aluminum production, anorthite (CaAl2Si2O8) is most commonly proposed as a lunar substitute.[1] Anorthite could be separated from the lunar highland material Anorthosite with mechanical methods. It could then be reduced through various chemical and electrochemical methods to produce aluminum.


Anorthite Production

The Anorthosite which makes up the Lunar highlands 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.

The magnetic materials (Ilmenite and iron oxide) could be stored for production of titanium, iron, and oxygen.

Anorthite Refinement

Direct Reduction

Main Article: FFC Cambridge Process

Anorthite could be directly reduced to its component metals using the FFC Cambridge Process. The Anorthite is pressed/sintered into a cathode, which is placed in a bath of molten calcium chloride and electrolyzed. The oxygen is stripped out, leaving behind Aluminum, Calcium, and Silicon.

This process has the advantage of inherent simplicity, as well as having only one component to recycle, the calcium chloride, which does not react chemically with the inputs, making recovery much simpler. In addition, this process runs at lower temperatures (900º-1100º C) than many other electrolysis procedures, and inert(non-consumable) anodes have been successfully demonstrated with it[2]. On the downside, energy must be expended to split all the components of the Anorthite, not just the aluminum. Splitting the silicon and calcium adds a significant amount of extra energy to the process, as both of them are strong reducers. However, if the silicon and calcium byproducts were needed for other purposes (calcium is a good electrical conductor, and silicon could be used for solar panels or rocket fuel), this extra energy cost may not be an issue.

Alumina Production

Many processes used on earth or proposed for Lunar use require alumina (Al2O3) as an input. On Earth, alumina is produced from bauxite through the Bayer process. As this process is not feasible using Anorthite, another method must be utilized.

Vacuum Distillation

Alumina could be produced from Anorthite by boiling out the impurities between 1500 ºC - 2000 ºC under vacuum conditions. The resulting material would be calcium aluminate (CaAlO4). Raising the temperature further could cause alumina to volatilize as well. [3]

Sulfuric Acid Leaching

Another method is to produce calcium aluminate as outlined previously, which is then leached in sulfuric acid, resulting in the following reaction:

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 aluminum sulfate releasing S2.[4]

Hydrochloric Acid Leaching

Another option is to react Anorthite with hydrochloric acid, which results in following reaction:

CaAl2Si2O8 + 8 HCl + 2 H2O==> CaCl2 + 2 AlCl3.6 H2O + 2 SiO2

The calcium chloride and hydrated aluminum chloride dissolve in the solution and are removed. They are then precipitated out of solution, dried, and heated under partial vacuum until the calcium chloride evaporates out of the mix. Temperatures of this range will cause the hydrated aluminum chloride to become alumina, releasing water and hydrogen chloride in the process:

2 AlCl3.6 H2O ==> Al2O3 + 6 HCl + 3 H2O

The water and hydrogen chloride are separated from the calcium chloride and fed back into the system. The calcium chloride is then electrolyzed into metallic calcium and chlorine. A portion of the recovered water is then split into hydrogen and oxygen. The hydrogen component is reacted with the evolved chlorine to produce hydrogen chloride, which is then fed back into the main system.

Direct Calcium Aluminate / Alumina Reduction

Calcium Aluminate (see above for production) could be simply melted and electrolyzed directly, producing aluminum and calcium oxide.[5] This has two advantages. First, it requires no imported reagents, and second, only the aluminum is split, reducing the amount of energy needed. The disadvantage is that temperatures of approximately 1600 ºC are required, making electrode material of prime concern. Carbon electrodes could be utilized at those temperatures, but the anode would continually wear away as oxygen was produced around it, creating carbon monoxide. The carbon would need to be recovered and new anodes made from it. This effectively means that a rare reagent is needed, negating the process's first stated advantage. Finding an anode material that would produce oxygen without wearing away at those temperatures could be quite difficult.

Alumina could also be directly melted and electrolyzed in the same fashion. However, this would require temperatures of approximately 2000 ºC, bringing with it again the issue of electrode material.

Hall-Heroult Process

In the Hall-Heroult process, 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 the carbon anode.

This procedure is used extensively on earth for aluminum production, and as such has the advantage of being a very mature technology. The biggest issue is the consumption of the anode, which would require the produced carbon dioxide to be captured, converted back into carbon, and recast into new anodes; an energy intensive process. It is not known if an inert(non-consumable) anode material can be found that would work under these conditions.[6]

Subchloride Process

In the subchloride process alumina is reacted with carbon and chlorine to yield AlCl3 and CO2. The AlCl3 is electrolyzed to produce aluminum while recovering the chlorine. This has the advantage that conventional carbon electrodes can be used continuously, as the produced chlorine does not react with them. However, the CO2 byproduct must be recycled, adding extra complexity and energy requirements to the system. This makes it similar to the Hall-Heroult process in difficulty, except for two advantages. First, the recycled carbon can be directly used in powdered form, it does not need to be recast into electrodes. Second, due to the low melting point of AlCl3 (120 ºC), the process does not require significant energy to melt, and is more easily handled. [7]

Carbothermal Reduction

Carbon reduction of Alumina is impossible under normal smelting conditions, due to aluminums high reduction potential. However, Alumina could be mixed with silica and carbon and melted near 2000 ºC, which would form an aluminium-silicon alloy, as well as CO2. This could be separated by cooling the Al-Si mixture to 700 - 1000 ºC and allowing the silicon to solidify and settle out of the melt.[8]

An alternate process involves alumina and carbon processed at high temperatures and low pressure into Al4C3 and carbon monoxide.[9] [10] This breaks down into Aluminum and Carbon between 1900 and 2000 ºC.[11].

In either case, CO2/CO would have to be recovered and and the carbon recycled.

See Also

References

  1. ↑ http://www.permanent.com/l-minera.htm#aluminum
  2. ↑ http://www.lpi.usra.edu/meetings/roundtable2006/pdf/tripuraneni.pdf
  3. ↑ http://www.moonminer.com/Lunar_Aluminum.html
  4. ↑ http://www.moonminer.com/Lunar_Aluminum.html
  5. ↑ http://www.moonminer.com/Lunar_Aluminum.html
  6. ↑ http://en.wikipedia.org/wiki/Hall-H%C3%A9roult_process
  7. ↑ http://www.moonminer.com/Lunar_Aluminum.html
  8. ↑ http://www.moonminer.com/Lunar_Aluminum.html
  9. ↑ Aluminum section Production and refinement
  10. ↑ Lunar Aluminum at Moondust index
  11. ↑ Aluminium carbide at Wikipedia
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