The physics of open-gradient dry magnetic separation

This paper reviews the current understanding of the principles of operation of open-gradient dry magnetic separators. The physics of separation in low and high-intensity devices is described. The fundamental laws of magnetostatic fields are presented and the concept of magnetic potential energy is used to develop the expression for the force on a particle in a magnetic field. The forces which compete with the magnetic forces in dry magnetic separators are described. These are applied to the analysis of the acceleration of particles on roll-type separators and the definition of the point of departure from the roll. The drag forces which affect the motion of particles through air are defined for low and high velocity particles. The interparticle forces between magnetic and non-magnetic particles which determine how pure the products of the separation will be are also discussed. This review highlights the fact that, while the physics of dry magnetic separation is reasonably well understood, few attempts have been made to exploit this knowledge to develop comprehensive mathematical models of industrial separators. This is due to the lack of fundamentally derived mathematical descriptions of the magnetic fields generated in these separators. Studies of these fields which combine direct measurements with fundamental techniques such as the Laplace solution are now required. When the magnetic fields within dry magnetic separators are better understood there will be few impediments to the development of reliable mathematical models of these devices