Experimental Modelling of a New Tribo-electrostatic Separation Process for Mixed Granular Polymers Mohamed Fodil Boukhoulda Mohamed Miloudi, Karim Medles, Mohamed Rezoug, Amar Tilmatine, SM IEEE Electrostatics and High Voltage Research Unit IRECOM, University Djillali Liabès Sidi Bel Abbès 22000, Algeria kmedles@univ-sba.dz Lucian Dascalescu Fellow IEEE Electrostatics of Dispersed Media Research Unit, Institut P’, CNRS-University of Poitiers-ENSMA, IUT, Angoulême 16021, France lucian.dascalescu@univ-poitiers.fr Abstract -- Recycling of plastics from industrial wastes requires appropriate sorting technologies, such as the free-fall electrostatic separation of tribocharged granular materials. This paper introduces a novel electrostatic separation process characterized by the fact that the granules to be separated are charged in a fluidized bed affected by an electric field generated by two rotating roll electrodes. The experimental design methodology was employed for the modelling and optimization of the separation of a mixture composed of Acrylonitrile Butadiene Styrene (ABS) and High Impact Polystyrene (HIPS), originating from shredded obsolete computer cases. After processing the experimental data using the MODDE 5.0 software, the masses of ABS, HIPS and middling collected after separation were expressed as quadratic functions of three of the control variables of the process: (1) duration; (2) speed of the fluidization air; (3) high voltage applied to the electrode system. The obtained results demonstrate the effectiveness of this method for the separation of plastics from granular wastes. Index Terms — high voltage, electrostatic separator, tribo- electrity, waste electric and electronic equipment I. INTRODUCTION Electrostatic separation technologies have been widely employed for the recycling of industrial wastes and the purification of mineral products [1-7]. The electric field forces are extremely effective in the selective sorting of corona and/or induction charged granular mixtures of conducting and insulating materials from waste electric and electronic equipment (WEEE) [8-10]. Tribocharging the granular plastics contained in the WEEEs prior to exposing them to the action of the electric field forces in a free-fall electrostatic separator is a solution that has already been validated by the recycling industry [ 11, 12]. During recent years, several attempts have been made to improve the efficiency of the existing technologies, which make use of vibrating or cyclone-like tribocharging devices [13-17]. In several previous paper, the authors examined the possibility of tribocharging the granular WEEEs in a fluidized bed [18-20]. In such devices, the granules get charged by colliding against each other and with the walls of the fluidized bed; then they fall freely in the electric field generated between two vertical plate electrodes energized from two high-voltage supplies of opposite polarities. Fig. 1, Schematic representation of the new tribo-aero-electrostatic separation process. The problem is that the charge acquired by the granules in these devices is not homogeneous. Some carry enough charge to be separated in an intense electric field, while others exit the tribocharging device with a less satisfactory charge level. The charge level can certainly be improved by increasing the duration of the tribocharging process, but this would diminish the hourly output of the installation. For a given particle residence time in the tribocharging device, the acquired charge can significantly vary with the ambient humidity, and with the surface state of the granules. A recently patented installation avoids these drawbacks, by the simultaneous usage of the triboelectric effect, the Coulomb force and the electric image force [21-25]. Thus, the triboelectric effect provides the homogeneity of the electric charge acquired by the granules in a fluidized bed generated by a vertical air flow. The granules move in the electric field generated between two conveyor-belt-type high-voltage electrodes. Under the action of the Coulomb force, the granules are driven to the surface of these electrodes, to which they stay pinned by the electric image force. Then the electrodes convey them to the product collectors. The aim of the present paper is to investigate the efficiency of a new design, in which the conveyor-belt electrodes are replaced by two metallic rolls (Fig. 1). The modified process is modeled using the experimental design methodology [26]. Cylindrical electrodes Air blower ABS granules Air chamber HIPS granules Fluidized bed A B