beneficiation or extraction, and as new data on lunar mineralogy are acquired. Conceivably, new opportunities could arise with new knowledge, for example if concentrations of rare elements were discovered, such as in a carbonate or chloride deposit [Gillett, 1990]. Nonetheless, terrestrial experience suggests that a major part of optimizing the extraction of even common elements will consist of finding areas where they are exceptionally concentrated already. Tentative suggestions for exploration for sources of some bulk lunar commodities are presented below. Oxygen In many ways this is the easiest commodity, as oxygen is the most common element in the Moon's crust (as it is in the Earth's), being an essential constituent of silicates. Nonetheless, as would be expected, oxygen is not equally easy to extract from all lunar materials. Pyrolysis of undifferentiatedregolith [e.g., Agosto, 1983; Steurer & Nerad, 1983] has the virtue of being simple and of requiring little beneficiation; any silicate or oxide will work, at least to some degree. However, it has the disadvantage of being inefficient and extremely energy intensive. Moreover, at the extreme temperatures needed to pyrolyze silicates, many other volatile species besides oxygen are driven off and must be separated. Last, handling such high-temperature material, especially in the quantities needed for high-volume extraction, is likely to be difficult. Oxygen is also an automatic by-product of electrolysis of molten silicates or oxides, and thus would be a very attractive by-product of such a process [e.g., Haskin & Lindstrom, 1979; Steurer, 1982; du Fresne & Schroeder, 1983], As is pyrolysis, however, magma electrolysis is energy intensive and requires the routine handing of extremely hot material in large volumes. Ilmenite reduction is another possibility. Ilmenite, a double oxide of Fe and Ti (FeTiO3), is a common accessory mineral in mare basalts, especially in the "high-Ti" basalts, which can contain more than 10% TiO [e.g., Taylor, 1982, p. 286-287]. Furthermore, its physical properties are different enough from common silicates that beneficiation may be possible even under anhydrous conditions [Agosto, 1985], although achieving high ilmenite concentrations is evidently difficult [e.g., Vaniman & Heiken, 1990; Oder & Taylor, 1990], because many ilmenites are bound up in polycrystalline aggregates. At moderately elevated temperatures ilmenite reacts with H2 to yield water and a mixture of Fe and TiO2 - both potentially useful by-products, as noted below. The water can then electrolyzed to yield O2 and recover the H2 [e.g., Gibson & Knudsen, 1985; Gibson et al., 1990]. Alternatively, C may be the reductant of choice [Cutler & Krag, 1985]. The disadvantages of such processes include the initial need to import C or H2, and the ongoing need to recycle them with hivh efficiencv.
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