Determination of the capture radii of magnetite bearing hydroxide flocs in magnetic filtration

Magnetic filtration may be applied in water technology for the separation of flocs which are formed in a flocculation tank together with magnetite as an additive. The capture radius is an important mathematical quantity to calculate the performance of such filters in advance. Thus, the capture radii of magnetite bearing copper hydroxide flocs were measured with a direct visual evaluation of the floc trajectories in the neighborhood of a single magnetized wire. For this purpose, an experimental setup was assembled, which allowed the observation and the measurement of the trajectories. With the image processing system used, it was possible to observe flocs larger than 30 /spl mu/m and the flow velocity was limited to a maximum value of 20 mm/s. Capture radii were calculated by the established single-wire theory under the assumption of potential and creeping flow conditions. It has been proved that further information on the solids content of the flocs, which strongly influences the floc susceptibility, was necessary to obtain an agreement between the experimental data and the theoretical predictions. By introducing a flee size dependent solids content into the single-wire theory, measured by means of sedimentation analysis, an accurate description of the observed capture radii was possible.