TECHNIQUES FOR SELECTIVE MAGNETIC SEPARATION OF FINE PARTICLES

Magnetic separation as a particle-particle or particle-fluid separation technique has been extended to be effective for particulates with the smallest known magnetic susceptibility. Most commonly found materials are diamagnetic but the effectiveness of high magnetic field gradient separators for even these very weakly magnetic materials makes it difficult to separate more magnetic species of particles from them. The selectivity of such separations has been improved by matrix design and by several separation techniques. Regular arrays of matrix wires can be arranged according to the calculated field profile to exclude regions of capture for magnetic particulates of positive or negative susceptibility. The magnetic field orientation with respect to the array provides control over the competition between magnetic capture forces and those of fluid flow. The size of particle depletion regions in model arrays depends on particle size and susceptibility and suggests a method of measurement of these even for submicron particulates.