following section. The field can be approximated by the superposition of a dipole field on the uniform background field. Industrial magnetic separation is performed most often on ferromagnetic materials such as iron ores or magnetite used in coal cleaning but kaolin clay is cleaned of paramagnetic impurities commercially and other HGMS applications await only economic improvement. To indicate that very small particles can be trapped. Fig. 4 shows the recovery of hematite with a size range from 5 to 10 p,m. Hematite is actually antiferromagnetic with a small susceptibility. The curve represents a model done in part by Clarkson (4). Notice that we have to go to very high fields in order to magnetize this material, but it can be collected. Recently, matrices have been developed which collect diamagnetic mineral components such as those labeled in Fig. 5 and magnetite shown collected on a screen matrix in Fig. 6. MAGNET SYSTEMS There are a number of possible candidates for magnet systems for lunar surface use. The three important categories are superconducting magnets operated at cryogenic temperatures, electromagnets with iron return paths and low voltage coils to be compatible with solar cell power supplies, and permanent magnets. The features and advantages of each would have to be considered in light of a specific application. The collection of 100 p.m iron-nickel particles from soil requires a very different approach than separating diamagnetic aluminum ores from crushed rock. Superconducting magnets generally are considered to be perhaps the only suitable means for high magnetic field applications. Because of economics and the reluctance of some industries to install sophisticated technological equipment to do dirty jobs, there has been limited terrestrial application of superconducting magnets. For lunar
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