Screening
Sieves are available for screening particles ranging from 5 to 30 micrometers at 5-micrometer intervals. It is unlikely, however, that such fine sieving can be accomplished without suspension of the fines in a gas or fluid medium. Even under those conditions, fines sieving is a laborious process. The fluid most likely to be available on the Moon is oxygen, and, since cryogenic temperatures can be relatively easily maintained there, it might be instructive to attempt lunar soil sieving in liquid oxygen. This may be a practical technique because it is unlikely that significant oxidation of lunar soil components will occur at liquid oxygen temperatures (below -18~P C). In addition, the only combustible component is FeNi metal, which is less than 1 percent of the soil by weight and which is predominantly encapsulated in glassy agglutinates.
Gas Elutriation and Classification
Gaseous classifiers, cyclones, and fluidized-bed separators operate by stratifying particles in a rapidly moving gas stream according to size and density. They are available on the market for sizing fine particles from 0.5 to 35 micrometers. These devices can deliver the narrowest size ranges (at best, at the small end, a spread of about 0.2 pm) on a commercial scale (kilograms to tons per hour). On the Moon, gas classification might be done in oxygen. The possibility and consequences of oxidizing reduced lunar soil phases under these conditions will have to be considered and experimentally determined. However, it appears unlikely that, by commercial standards, significant oxidation of soil components will occur in dry gaseous oxygen at sufficiently low temperatures (e.g., -20°C) over the short period required for gaseous classification (minutes).
References
Agosto, William N. 1981. Beneficiation and Powder' Metallurgical Processing of Lunar Soil Metal In Space Manufacturing 4, Proc. 5th Princeton/AIM Conf" ed. Jerry Grey and Lawrence A. Hamdan, 365-370. New York: AIM.
Agosto, William N. 1984, Electrostatic Separation and Sizing of Ilmenite in Lunar Soil Simulants and Samples. Abstract in Lunar & Planetary Sci. XV: 1-2. Houston: Lunar & Planetary Inst.
Agosto, William N. 1985. Electrostatic Concentration of Lunar Soil Minerals. In Lunar Bases and Space Activities of the 21st Century, ed. W. W. Mendell, 453-464. Houston: Lunar & Planetary Inst.
Castle, Peter. 1983. A New Electrostatic Separator and Sizer for Small Particles. IEEE Trans. on Industrial Appl., vol. 1A-19, no. 3, pp.318-323.
Gibson, E. K., Jr., et al. 1987. Hydrogen Distributions in Lunar Materials. Abstract in Lunar & Planetary Sci. XVIII:326-327. Houston: Lunar & Planetary Inst.
Goldstein, J. I.; H. J. Axon; and C. F. Yen. 1972. Metallic Particles in Apollo 14 Lunar Soil. Proc. 3rd Lunar Sci. Cont. Suppl. 3, Geochim. Cosmochim. Acta, 1037- 1064. M.I.T. Press.
Goldstein, J. I., and H. J. Axon. 1973. Composition, Structure, and Thermal History ot Metallic Particles From 3 Apollo 16 Soils, 65701, 68501, and 63501. Proc. 4th Lunar Sci. Cont. Suppl. 4, Geochim. Cosmochim. Acta, 751-775.
McKay, David S., and Richard J. Williams. 1979. A Geologic Assessment of Potential Lunar Ores. In Space Resources and Space Settlements, ed. John Billingham, William Gilbreath, and Brian O'Leary, 243-255. NASA SP-428.
Wittenberg, L. J.; J. F. Santarius; and G. L. Kulcinski. 1986. Lunar Source of 3He for Commercial Fusion Power. Fusion Technology 10:167-178.