Kinetics of magnetic flocculation. I. Flocculation of colloidal particles

Abstract

The magnetic dipole-dipole interaction between magnetized colloidal particles can lead to particle aggregation (flocculation) when it is strong enough to outweigh the stabilizing forces of electro-chemical origin. An understanding of the timescale at which the magnetic flocculation process is developing is of essential importance for its practical use as a separation technique. Incorporation of the magnetic dipole-dipole interaction between the particles into the well established Fuchs theory of flocculation kinetics is difficult, due to the fact that this magnetic interaction is not spherically symmetric. In this paper a numerical approach is presented, in which the basic equation for flocculation is solved allowing for a cylindrically symmetric interaction, such as due to the presence of induced magnetic moments in paramagnetic particles. Experimental observations on the flocculation kinetics of fine-particle (about 0.2 mu m diameter) electrostatically stabilized Mn2O3 colloids corroborate the predictions of the model calculations.