Iron As pointed out by many people, native Fe exists in the lunar regolith and is a potentially attractive resource. (The native Fe is not all meteoritic, as is sometimes asserted; about a third is indigenous to the lunar rocks, and another third results from solar-wind reduction of lunar FeO [Morris, 1980].) Although the concentration is low [—0.5%; Morris, 1980], beneficiation may be relatively easy, even under anhydrous conditions, because of the large contrast in physical properties between metallic Fe and silicates. Moreover, enhanced concentrations of native Fe may occur locally. However, much of this Fe occurs as extremely small grains (—4-33 nm) bound up in agglutinate glass, and as noted earlier separating the glass will be difficult. Alternatively, Fe may be a byproduct of ilmenite reduction for oxygen; the residue after reaction with H2 is an intimate mixture of metallic Fe and TiO2. Separating this mixture economically is challenging, but Lewis & Lewis [1987] suggest that extraction of Fe as the carbonyl may be useful. (Note that, although ilmenite is an ore of Ti on the Earth, it is not an ore of Fe!) Direct electrolysis of silicates or oxides is yet another alternative source. It is less attractive on the one hand because separating the cations that plate out at the cathode is a problem, as all silicates contain at least one cation (Si) in addition to Fe [e.g., Colson & Haskin, 1990; McCullough & Mariz, 1990], Depending on the cell conditions, various ferrosilicon alloys containing a few tenths of a percent of other metals (Ti, Cr) result. On the other hand, electrolysis itself is conceptually simple, although it remains to be seen whether conceptual simplicity will translate into operational simplicity. Moreover, ferrosilicon itself may be a useful reductant for other processes, such as reduction of Mg from olivine [Kuck, 1979], Aluminum The abundant aluminum mineral in the lunar crust is anorthite (CaAl2Si2Og), one of the feldspar minerals. It is the dominant constituent of the rock anorthosite, which makes up most of the lunar highlands. Thus, not only is Al abundant in the crust, but an aluminum-rich mineral is dominant over most of the lunar surface. Nonetheless, extracting aluminum from anorthite is difficult, especially under anhydrous conditions: not only is extraction energy-intensive, due to the high energy of the Al-O bond, but anorthite is a complex, highly polymerized silicate in which other cations are present to further hinder separation, regardless of whether wet-chemical [e.g., Waldron, 1983a], electrolytic, pyrolitic, or more exotic chemical techniques [e.g., Steurer, 1982, p. 88; Waldron, 1983b] techniques are used. Because of these difficulties, extraction of lunar Al will probably not be carried out at first. Titanium Ti will undoubtedly be extracted from ilmenite; the question is when. The titania residuum resulting after the extraction of oxygen and iron is an obvious feedstock.
RkJQdWJsaXNoZXIy MTU5NjU0Mg==