High intensity and high gradient magnetic separation in mineral processing

Abstract: Natural minerals often lack well defined magnetic susceptibilities. Instead they must be thought of as occurring in a susceptibility range where the bulk susceptibility is affected by present impurities. Inclusions or foreign atoms in solid solution may alter a materials magnetic properties to a large extent. Mixed particles of dia andlor paramagnetic materials display a linear relationship while ferromagnetic inclusions involve a demagnetisation factor. The susceptibility distribution of value minerals in relation to gangue in the ore is the most important factor governing magnetic separation performance. Until recently, high gradient and high intensity separators of matrix type were exclusively used in wet processing. Now, new dry separators are extending the particle range for dry, fine particle separation. The capture characteristics of the matrix has been shown to change with the magnetic field strength. The separation cut is more precise at high fields, at low fields the capture probability graph cants. By superimposing the capture function on the susceptibility distribution of an ore, it is shown that materials containing value minerals at either high or low susceptibility is ideal for HGMS separation. Complex ores carrying value and gangue minerals distributed over a wide susceptibility range are unfavourable. The former situation is common in industrial mineral processing and in the upgrading of flotation concentrates. The latter susceptibility distribution is very common in complex sulphide ore feeds.