PHYSICAL SEPARATION OF LUNAR SOIL Much has been written on physical separation of lunar soil (e.g., 3, 4, 5), and answers are still needed to many questions but the properties of the major components of lunar soils are sufficiently different that at least partial separation seems very likely. Other papers in this series cover certain separation procedures in detail. Physical separations of granular materials are now being made commercially, with large throughputs, on the basis of seemingly trivial differences in the nature and behavior of the several constituents under a wide range of special conditions. The materials involved include seeds, grains, and other foods, small manufactured objects, and of course, minerals. A striking example of how effective small differences between mineral grains can be is provided by a novelty item put out by a chemical company. The item consists of a glass bottle containing subspherical grains of essentially pure, precipitated A12O3 that are all identical except for a small range in grain size. The various grain sizes were separated, each size range was dyed a different color, and then recombined. It is almost impossible to mix the contents to a uniform color, without streaks representing partial size separation by flowage. The lunar soils contain minerals varying in size, shape, density, surface electrostatic properties, magnetic properties, electrical conductivity, etc., and any one of these differences may be exploited for separations. Color differences may even be used for separation. For example, if mixed grains of glasses that are similar except in color were all given an electrostatic charge and then were heated by visible light during passage through an intense beam of sunlight from a solar mirror, even different intensities of coloration of the same color glass would probably be heated differently; thus, they would lose different amounts of their static charge, as the electrical conductivity of glass is extremely sensitive to temperature. The differences in charge could then be used to effect a separation. In view of the wide range of both the wavelengths in sunlight and the absorption bands in various glasses, filters might be necessary to make a separation based on color. Good reasons exist for delving into the separation of lunar soil in some detail. Others have discussed the concentration (or perhaps better “purification”) of bulk constituents such as plagioclase, and the concentration of lesser constituents such as ilmenite, and such separations might well be made early in the development of a lunar minerals industry. Obvious lunar metallic iron concentrates could be separated relatively easily during any bulk handling of the lunar soil and would be very useful. Separation of other constituents in the lunar soil will probably merit consideration in the future, particularly if the soil is handled for other reasons anyway. Included here are the high-chromium spinels, and even several zirconium phases. High-potassium glass and silica, in particular, seem far more important than their relatively low concentrations in the lunar soil would seem to indicate, and they do not seem to have been considered in the literature on lunar resources. High-Potassium Glass One of the two late-stage residual melts in practically all mare basalts is a high- silica, high-potassium melt (now a glass), which formed as a result of silicate liquid immiscibility (6). Because the original basalts contain only ~ 0.3% K2O maximum, and many have only 0.05%, and this late melt contains 6%-8% K2O, not much of it
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