(263b) One-Dimensional and Two-Dimensional Particle Separation. Experiments and Theoretical Models

Separation and purification of nano- and microparticles becomes essential for technical applications in manifold industrial fields such as biotechnology, drug development, coating and pigment to name only a few. Despite numerous papers since the pioneering work of Kynch, the separation process of concentrated dispersions driven by gravity or a centrifugal field, are not well understood, especially if particles interact with each other. In the centrifugal case additinal difficulties emerge from the Coriolis coupling between the radial and the azimuthal velocity and the geometry of the "containers". Batch centrifuges operate with a constant cross section (one-dimensional sedimentation [1D]) whereas for disk or cylinder centrifuges the cross sectional area changes with the distance from the axis of rotation (two-dimensional sedimentation [2D]). In this paper we shall focus on 1D and 2D sedimentation. Experimentally the separation process of dispersions of monodisperse silica, polydisperse quartz and limestone (different pH and flocculation) at different volume concentrations was investigated by analytical centrifugation (LUMiSizer). Space and time resolved extinction profiles (STEP-Technology) during the centrifugation were measured using cells with constant [1D]and increasing cross sections [2D]. In general, the separation velocity in the 2D cells are very similar compared to 1D, but the alteration of the concentration is much more pronounced using the 2D cells. The differences diminishes as the filling height in both cells were reduced. Theoretically the separation was computed based on the kinematic Kynch model advanced by Buerger. It will be shown that the predictions of the physical model match the experiments very well and that from results of the batch centrifugation [1D] the behaviour in a rotating axisymetric cylinder [2D] may be well predicted. This allows to use anylytical batch centrifugation to optimise the separation and purification processes of nano- and microparticles by industrial cylinder centrifuges.