Magnetic hetero-flocculation of paramagnetic colloidal particles

The feasibility of a high-gradient magnetic separation process, utilizing magnetite as the energizable element in lieu of stainless steel wool, is evaluated by means of an equilibrium, two-particle, magnetic hetero-flocculation model. The model calculates the net force, defined as the sum of the magnetic, electrostatic, and van der Waals forces, exerted on a paramagnetic nanoparticle that is in the proximity of a fixed magnetite particle. Since the nanoparticle-magnetite system is assumed to be in direct contact with the moving fluid, the influence of the hydrodynamic force on the magnetic attractive force between the two particles is also explored. This model clearly reveals the ranges and conditions over which each of these various forces contributes to the net force relative to Brownian (thermal) motion. The model also reveals the feasibility of using magnetite particles instead of stainless steel as the energizable element for high-gradient magnetic separation. Important variables investigated include the size and surface charge of the particles, the magnetic field, the flow velocity, the electrolyte concentration, and the magnetic susceptibility of the nanoparticle. (C) 2000 Academic Press.