Integrated Aluminum, Iron, and Silicon Extraction using SiC Alumina Reduction

On Earth, a complex and expensive electrolytic reduction process is used to extract aluminum, which would be a poor choice on the moon for two reasons. The first is that it involves large amounts of fluorine electrolytes and consumes a carbon cathode in the chemical process, and the second is that its power source is electrical and not thermal. As unlimited solar heating is available with the use of inexpensive solar reflectors on the moon, the energy intensity of a process contributes little to the overall cost. On Earth, most of the usual price of US$1,500 per tonne is made up of electrical energy costs.

One promising process simultaneously extracts aluminum, silicon, and iron, without involving the costs inherent in halide electrolysis. The first step of the process involves reducing silica with carbon to produce silicon carbide:

SiO₂ + 3 C = SiC + 2 CO

Silicon carbide is also a handy abrasive, although titanium carbide is stronger for the imported carbon mass, and alumina is another good abrasive, but it can be found on the moon.

The silicon carbide is then used to reduce alumina, yielding metallic silicon and aluminum:

Al₂O₃ + 3 SiC = 2 Al + 3 Si + 3 CO

The carbon monoxide can then be used to reduce iron oxides:

Fe₂O₃ + 3 CO = 2 Fe + 3 CO₂

Carbon dioxide can be recycled for further use by producing methane via the sabatier process, pyrolizing the methane, and electrolyzing the water:

CO₂ + 4 H₂ = CH₄ + 2 H₂O
CH₄ = C + 2 H₂
2 H₂O = 2 H₂ + O₂