Kinetics of Attachment and Detachment of Colloidal Particulate in Magnetic Field.

The attachment and detachment of various colloidal particles (hematite, akageneite, chromium hydroxide and magnetite) in contact with beads of different kinds (steel C 1018 or 316 LSS, and glass) was studied using the packed column technique under the influence of magnetic field. The kinetics of deposition was interpreted with models for convective diffusion proposed by Levich, Pfeffer and Happel in terms of excluded area and collision efficiency. The application of high intensity magnetic fields reduced the excluded area to zero and increased significantly the collision efficiency. In the interpretation of the results the total interaction energy was calculated by taking into consideration the electrostatic, dispersion, and magnetic contributions. Long-range magnetic forces caused the formation of a secondary minimum. Accumulation of particles took place in this minimum and multilayers of colloidal particles were observed when this minimum was sufficiently deep. The rate of accumulation was sensitive to the particle size and magnetic characteristics. Larger particles of higher magnetic moment adhered much faster. The rate of accumulation of magnetite particles was further influenced by the already deposited particles on the collectors. Almost 100% removal was obtained for hematite and chromium (hydrous) oxide particles from steel surfaces on elimination of the magnetic field. Only a fraction of particles were retained in the primary minimum. The removal of magnetite particles was much less efficient due to its stronger magnetic moment.