Experimental investigation of a new tribo-electrostatic separation process for mixed fine granular plastics

Tribo-electrostatic separation of mm-size particles is a well-known process, widely used in the recycling industry. However, when processing fine particles having an average diameter of 0.1 mm or less, this technique is still inefficient. The aim of this paper is the experimental investigation of a patent-pending tribo-electrostatic separation process based on a fluidized bed tribocharging system where the fine granules to be sorted are exposed to the electric field generated between a pair of rotating metallic disks connected to two high-voltage supplies of opposite polarities. The lower parts of the disk electrodes are immersed in the fluidized bed. The experiments were carried out on a granular mixture composed of fine white and grey PVC particles of average size 20 μm. The particles to be separated are positively and negatively tribo-charged using the fluidization air provided by variable-speed blower, and then they are pinned to the disk electrodes of opposite polarities. The separation outcome, in terms of recovery and purity, is highly efficient and depends on several factors: the high voltage level, the rotating speed of the disks, the inter-electrodes gap, the thickness of fluidized bed and the fluidization rate.