Rotating magnetic field separation of minerals

The behaviour of particles in a rotating magnetic field can be used as a basis for a new mineral separation method, where particles are separated on the basis of their relative ability Ito rotate in a rotating magnetic field. Both particle attraction and particle rotation separations may be combined in a single separation process, to offer previously impossible magnetic mineral separations, such as the separation of high-Mg ilmenites (picro-ilmenites) from other ilmenites of the same magnetic susceptibility, or to produce separations which are more precise than those currently available, such as the low-entrapment separation of magnetite or monoclinic pyrrhotite. Whereas mineral separation by particle attraction involves the use of material properties such as the number of unpaired electron spins and their relative orientations, separation by particle rotation adds the properties of magnetic anisotropy and such dynamic magnetisation processes as domain wall velocity in ordered magnetic compounds. The use of a continuously rotating magnetic field also generates eddy currents in particles, in proportion to particle electrical conductivity, which allow conductive particles to be rotated by eddy current effects, and extends the same separation process into the practical separation of small particles of non-magnetic metallic compounds. Particle rotational characteristics may be estimated using similar equipment to that used for practical rotating field mineral separations, so that these characteristics may be readily applied to practical separations. These estimations are presented in the form of a \rotation index\" which relates the actual particle rotation strength to the maximum possible rotation strength indicated by particle magnetisation. Although the measurement of particle rotational characteristics by these methods is only approximate it is accurate enough to demonstrate the presence of and estimate the magnitude of such dynamic magnetisation processes as domain wall velocities in small particles of natural ordered magnetic compounds. Particle rotation by magnetisation is also shown as being able to cause particle rotations for which the particle rotation axis is at right angles to the field rotation axis and which are of sufficient strength to play a part in a rotating magnetic field mineral separation process."