Magnetic separation utilizing a magnetic susceptibility gradient

A method of magnetic separation utilizing a colloidal suspension of small submicron magnetic particles is described. In a magnetic field gradient, the magnetic susceptibility of a colloidal magnetic fluid is not constant, but changes spatially with the magnetic gradient, since the concentration distribution of the colloidal magnetic particles is determined by the magnetic force and the thermal diffusion. This susceptibility distribution makes possible a method of particle separation in which particles are positioned at equilibrium due to the magnetic susceptibilities of both the material and the fluid. The method presented here makes possible a separation of particles according to their magnetic susceptibilities only, independent of their densities, sizes, and shapes. A colloidal fluid of magnetic submicron particles can be used to change the magnetic susceptibility of a slurry analogously to the method of using a paramagnetic salt solution in magnetic separation systems.