New Vibrating-Table-Type Tribo-Electrostatic Separator for Selective Sorting of Granular Plastic Wastes

Triboelectrostatic separation has already been proven its effectiveness as a solution for processing mixtures of plastics originating from waste electric and electronic equipment (WEEE). However, its adaptation to industrial conditions is not straightforward because of the diversity of particle shapes and sizes. This justifies the orientation of this work towards the functional validation of a new vibrating-table-type electrostatic separator (VTE) for granular plastics. In this separator, the granular mixtures are tribocharged in a rotating-cylinder-type device, then fed onto the Plexiglas plate of a vibrating table and subjected to an electric field created between two plate electrodes connected to DC high-voltage supplies of opposite polarities, ± 16 kV, distanced at 8 cm to 40 cm. Under the action of the electric field forces, the particles are deflected towards these electrodes and then recovered in a collector composed of 13 compartments. The experiments presented in the present work demonstrate the effectiveness of this device to separate two distinct mixtures of granules (sizes 2 mm to 6 mm) composed in equal proportions of: 1) polypropylene (PP) and high impact polystyrene (HIPS); 2) acrylonitrile butadiene styrene (ABS) and polyvinyl chloride (PVC). The efficiency of the separation quality was evaluated by measuring the purities and the recoveries of the separated products. The performances of the tribo-electrostatic separation process (60% to 85% of each plastic was recovered at purities higher than 85%) could be further improved by increasing the residence time of the granules in the rotating cylinder of the triboelectric charging device and by appropriate adjustment of the control variables of the VTE: vibration amplitude of the table, level of applied high-voltage, relative position of the electrodes.