FFC Cambridge Process
The FFC Cambridge Process reduces oxides to their metal components by electrolysis in a bath of molten calcium chloride. The process has potential to directly produce oxygen and metal from virtually any oxide. The process works by placing the oxide to be refined into a bath of molten calcium chloride and creating a voltage differential between the oxide component (which forms the cathode) and an anode which is also placed in the bath. Oxygen is stripped off the cathode, where it forms calcium oxide, which is soluble in the calcium chloride bath. This oxide is split at the anode, producing oxygen. The cathode meanwhile is gradually reduced to a porous metallic sponge.
The process is currently being developed by Metalysis for terrestrial metal production, specifically for the production of titanium; the developers hope it will eventually replace the Kroll Process.
Application To Lunar Colonization
In a lunar environment, this process could enable much simpler resource extraction. Experiments have already been done using pellets of sintered lunar regolith stimulant, as well as a non-consumable anode, producing metalized pellets and oxygen.
Aluminum/Silicon/Calcium Production from Anorthite
Anorthite (CaAl2Si2O8), which makes up much of the Lunar Highlands, could be separated from the regolith by grinding, followed by electrostatic/magnetic beneficiation, and then pressed/sintered into an appropriate cathode. As the oxygen is stripped off, metallic aluminum, silicon, and calcium are produced. The calcium is soluble in the calcium chloride bath, and would need to be continuously distilled out to keep the calcium concentration from becoming too high (which can reduce current efficiencies). Since silicon is not very soluble in aluminum at bath temperatures (900-1100 C), the aluminum and silicon should separate, the silicon remaining solid, the aluminum melting. This molten aluminum is denser than calcium chloride, and should drip out and collect at the bottom, where it can be siphoned off. Once the anorthite cathode is completely reduced, a very porous sponge of silicon remains.
Iron/Titanium Production from Ilmenite
Ilmenite (FeTiO3), is found in abundance on the lunar Maria and is easily separated through magnetic means. This substance could be processed in the same fashion as Anorthite, resulting in a 54% Iron, 46% Titanium sponge. Separating this alloy into iron and titanium could be done by either distillation or carbonyl extraction.
Another option is to first subject the Ilmenite to Hydrogen Reduction, producing Iron and titanium dioxide. The iron could then be separated by carbonyl extraction, distillation, grinding followed by use of a magnet, or by melting and then allowing the products to separate out. The remaining titanium dioxide could then be run through the FFC Cambridge process, producing a titanium sponge.
Lunar Chromite could also be reduced in the same fashion, producing Ferrochrome, which could be used to add Chromium content to Iron alloys. Many of the above listed reductions would also contain amounts of Magnesium and Sodium (Lunar Ilmenite in particular is known to be highly enriched with Magnesium), which could be distilled out fairly easily due to their low boiling points.
The only substance used which is not readily available on the Lunar surface is chlorine. Chlorine is available on the lunar surface in the form of Apatite (Ca10(PO4)6(OH, F, Cl, Br)2), but only in trace quantities. If a viable procedure for concentrating apatite out of the lunar regolith is not found, then a high degree of chlorine recycling would be necessary for the FFC Cambridge process to be useful in a lunar environment.
Chlorine losses from the system would come in the form of calcium chloride trapped in the pores of the metallic sponge produced in the reduction process, as well as any amount lost from the distillation of calcium metal out of the bath during anorthite processing. The latter losses could be reduced to acceptable levels through careful design of the distillation equipment.
In terrestrial applications, the salt trapped in the pores of the sponge is removed by grinding the sponge and washing the resulting powder with water, as calcium chloride is highly water soluble. The same procedure could be followed in a lunar environment, followed by reverse osmosis and distillation to recover the dissolved salt.
A simpler method is to melt the sponge, which would be required for many processes anyway. Since calcium chloride is not soluble in (and less dense than) most metals, it should separate into a distinct top layer, where it can be easily drained off, while the metallic elements are drained from the bottom.
Another method involves heating the sponge under partial vacuum until the calcium chloride evaporates out. This is useful in circumstances where the sponge itself is the desired product. Proper design of the process should allow for sufficient salt removal.