Gontran Richard

Corona-assisted plate-type electrostatic separation process for granular plastic wastes

Plate-type electrostatic separators are commonly employed for the selective sorting of conductive and non-conductive granular materials. Unfortunately, the purity of the conductive products is often compromised by the fact that the trajectories of the non-conductive granules cannot be controlled. The aim of the present work is to validate a relative simple solution to this problem: subjecting the granules to a corona discharge during their sliding down the plate electrode. This discharge does not affect the conductive granules but charges the non-conductive ones, so that the electric force would tend to pin them to the surface of the grounded electrode. In this way, the friction forces between the granules and the plate increase and the inertia forces decrease. Design of experiments methodology is employed to identify the optimum high-voltage, relative position of the electrodes, and configuration of the collector. The conclusions of this study served at the optimum design of an industrial corona-assisted plate-type electrostatic separator for the recycling of metals and plastics from granular electric cable wastes.

Experimental and Numerical Study of the Electrostatic Separation of Two Types of Copper Wires From Electric Cable Wastes

Electrostatic separators are not commonly used for the selective sorting of different sorts of metals contained in a granular mixture. However, the separation might be possible if their characteristics (density, conductivity, size, etc.) are different enough. The aim of this paper is to evaluate the feasibility of sorting tinned and bare copper strands (length: 2–5 mm; diameter: 0.8–1.6 mm) contained in granular electric cable wastes using a roll-type electrostatic separator with three different high-voltage electrode configurations: plate; S-shaped; and reverse S-shaped. Experimental design methodology is used to investigate the effects of three factors: 1) high voltage applied to the electrode; 2) system, inclination of the high-voltage electrode; and 3) interelectrode distance. The recovery and purity of the bare copper product are evaluated for each experiment. The best results of the electrostatic separation experiments are obtained with the reversed S-shaped electrode configuration (recovery of 55.4% of the bare copper wire in a product having a copper content of 85.1%). Numerical modeling and experimental visualization of particle trajectories facilitate the interpretation of the electrostatic separation experimental results.

Factors that affect tribocharging of PE granules after exposure to a dielectric barrier discharge (DBD)

Triboelectric charging is used in many applications including electricity nanogeneration, safety or electrostatic separation of insulating materials. Insulating granules charge must be the highest in electrostatic separators so that the electric field forces allow their separation. Dielectric Barrier Discharge (DBD), used for ozone production, depollution or surface treatment, is able to change the triboelectric properties of insulating materials. The aim of this study is to improve the triboelectric charging of Polyethylene (PE) particles by exposing them to an atmospheric Dielectric Barrier Discharge. Signal shape, exposure duration, voltage amplitude and frequency, which rule the DBD, are studied. After exposing the particles to DBD, they are charged in a vibratory device during 5 min. Then, particles are put in a Faraday pail connected to an electrostatic voltmeter to measure the acquired charge. Results show that the square waveform has the best effect and that the duration of the DBD treatment should not exceed 10 s, for the amplitude of the applied voltage of 21 kV.

Optimal Operation of a Plate-Type Corona-Electrostatic Separator for the Recovery of Metals and Plastics from Granular Wastes

Plate-type electrostatic separators are commonly employed for the selective sorting of conductive and nonconductive granular materials. Unfortunately, the purity of the conductive products is often compromised by the fact that the trajectories of the nonconductive granules cannot be controlled. The aim of the present work is to validate a relative simple solution to this problem: subjecting the granules to a corona discharge during their sliding down the plate electrode. This discharge does not affect the conductive granules but charges the nonconductive ones, so that the electric force would tend to pin them to the surface of the grounded electrode. In this way, the friction forces between the granules and the plate increase and the inertia forces decrease. Design of experiments methodology is employed to identify the optimum high-voltage, relative position of the electrodes, and configuration of the collector. The conclusions of this study served at the optimum design of an industrial corona-assisted plate-type electrostatic separator for the recycling of metals and plastics from granular electric cable wastes.

Distinct recovery of copper and aluminum from waste electric wires using a roll-type electrostatic separator

Electrostatic separators are commonly employed for the sorting of insulating and conducting fractions of granular mixtures. However, separation of the various metals that compose the conductive fraction still represents a major challenge for the recycling industry. The aim of this paper is to identify the conditions in which a roll-type electrostatic separator could be used for distinctly recover the copper and aluminum from waste electric wires. A numerical model of particle trajectories was employed to predefine these conditions and guide the experimental study. The electrostatic separation experiments were carried out using a reverse-S-type-plate high-voltage electrode. The visualization of particle trajectories using a high-speed camera paved the way to an original design. Thus, a metallic trap was attached to the high-voltage electrode, to facilitate the collection of the aluminum flake-like particles from a mixture that also contains copper strands. With a plastic trap replacing the metallic one, to avoid electric field modification, 68.6% of the copper was recovered with a purity attaining 99%.

Premises for industrial application of a two-rotating-disks-type tribo-aero-electrostatic separator for micronized WEEE

Waste electric and electronic equipment (WEEE) recycling technologies often include electrostatic separation of mm-size granular plastics mixtures as a major operation. The aim of this work was to pave the way to industrial application of a new two-rotating-disks-type tribo-aero-electrostatic separator for finely-grinded matter (i.e. granule diameter < 1 mm). The experiments were carried out on binary granular mixtures composed of various proportions of Polypropylene (PP) and Polycarbonate (PC) of size 125 to 1000 microns. The charges and masses of the separated products were continuously and simultaneously recorded using a custom-designed “on-line” measurement system. The purity of the products was evaluated “off-line”, using a colorimetric system. It was thus possible to quantify the performances of the separator under various conditions that simulated industrial operation situations.