DETERMINATION OF THE CAPTURE RADII OF MAGNETITE BEARING HYDROXIDE FLOCS IN MAGNETIC FILTRATION

Magnetic filtration may be applied in water technology for the separat ion of flocs which are formed in a flocculation tank together with mag netite as an additive. The capture radius is an important mathematical quantity to calculate the performance of such filters in advance. Thu s, the capture radii of magnetite bearing copper hydroxide flocs were measured with a direct visual evaluation of the hoc trajectories in th e neighborhood of a single magnetized wire. For this purpose, an exper imental setup was assembled, which allowed the observation and the mea surement of the trajectories. With the image processing system used, i t was possible to observe flocs larger than 30 mu m and the how veloci ty was limited to a maximum value of 20 mm/s. Capture radii were calcu lated by the established single-wire theory under the assumption of po tential and creeping flow conditions. It has been proved that further information on the solids content of the flocs, which strongly influen ces the flee susceptibility, was necessary to obtain an agreement betw een the experimental data and the theoretical predictions. By introduc ing a hoc size dependent solids content into the single-wire theory, m easured by means of sedimentation analysis, an accurate description of the observed capture radii was possible.