8. Avoid rejection of large amounts of process heat at low temperatures. No heat is lost with permanent magnets and small amounts with superconductors. 9. Structural materials must offer reasonable service lives. With proper care, magnets live forever. Matrices could be made on the Moon and as noted above, corrosion is minimal in the lunar environment. Refrigeration systems for superconducting magnets are reliable. 10. Reliability is excellent. 11. Remote, unmanned operation is straightforward. 12. There are no unusual potential hazards to personnel. 13. Separators can be built with no moving parts for reliability and minimum need for repairs. 14. Corrosion of Earth-derived parts and use of lunar materials for construction (see No. 9). Use lunar iron for magnets and perhaps aluminum for coils. Superconductors have to come from Earth. Cryogenic fluids can be lunar-derived. EFFECT OF LUNAR ENVIRONMENT Elements of the lunar environment which will affect almost any process and which are very different from those on Earth include atmosphere, gravity and temperature (11). Magnetic separation is most often carried out in fluid streams at or near room temperature although successful separations have been made with an experimental HGMS apparatus at temperatures as high as 287 °C under pressures of 5-10 atm (nitrogen). Working fluids have included water (most commonly), air or nitrogen, alcohol, oil and coal-derived liquid. Gravity generally is in the same direction as the flow but, in some cases, opposite or perpendicular to it. Environmental conditions on the lunar surface present no serious problems for magnetic separation and in some ways are ideal. 1. Atmosphere (vacuum) (a) There is a small effect on the magnetic trapping force on particulates (d). (b) The competing fluid drag force is eliminated. (c) There is no oxidation of metal or freshly broken surfaces which might change magnetic properties. (d) The magnetic susceptibility is that of the material alone, not relative to a background fluid medium. (e) There is no atmospheric or fluid corrosion of matrices used in HGMS. (f) Surface charges will have to be controlled. This is proposed for electrostatic separations and can be done here as well. 2. Gravity (reduced) (a) In the normal configuration of down flow, the gravitational force competes with the magnetic trapping force. Here, that competition is reduced. (b) Dry separations generally requires relatively slow flows. Lunar gravity should be sufficient. 3. Temperature (heat loss) (a) Permanent magnets generate no heat and might act as a heat sink for the small amount generated in the mechanical separation process. (b) Superconducting magnets generate heat only in the leads during charging and in the refrigerator, a much reduced effect at lunar temperatures. (c) Electromagnets could be equipped with heat sink coils connected to radiators.
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