This study presents a new electrostatic separation device for recovering high-purity metals and plastics from waste electrical and electronic equipment. The device is constituted by a rotating plate conveyor, an air suction system, and a vibrating hopper. It utilizes electro-adhesion force to selectively attract metal particles onto the conveyor surface, while precisely calibrated suction air effectively collects plastic particles into a dedicated box. A key feature is the employment of a low-level AC high voltage, significantly enhancing operational efficiency and safety compared to conventional electrostatic methods. Experimental results demonstrate high performance, achieving recovery and purity rates of up to 100 % depending on applied voltage and airflow settings.

ABSTRACT The electrical curtain board (ECB) is constituted of parallel linear electrodes deposited on a dielectric layer plate and supplied by a poly-phase electrical voltage. This paper reports a study of the movement of Polyvinyl Chloride (PVC) µm-size particles on such an ECB. The experimental setup comprised three ECB plates of different inter-electrodes spacing, and a homemade electric supply. Obtained results show that it is possible to move the quasi-totality of the particles on the ECB if adequate values are given to the voltage, the frequency and the inter-electrodes spacing.

ABSTRACT This paper reports an experimental and numerical analysis of a tribo-electrostatic separation process based on a fluidised bed tribo-charging system and two rotating disks connected to two high-voltage DC supplies of opposite polarities. The experiments were performed using a granular mixture composed of µm-size white Polyvinylchloride particles (WPVC) and grey Polyvinylchloride particles that contain a small percentage of carbon (GPVC). A numerical analysis supported the experimental results. It was deduced that the separation outcome is efficient and depends on the high-voltage level, the rotating speed of the electrodes and the fluidisation rate.

A new configuration of tribo-electrostatic separator equipped with an insulating belt conveyor is described and analyzed in this paper. The insulating belt is continually charged by corona discharge produced by a thin wire electrode (diameter: 0.3 mm), placed at a distance of 40 mm above it. The accumulated charge on the belt leads to the enhancement of the electric field at the surface of the conveyor. Two material types of the conveyor belt, namely Polyvinyl Chloride (PVC) and Polyester (PET), were used and compared. A comparison with the same configuration without charging the belt has shown that the performance of the new separator is much better, in terms of recovery and purity rates.

The electrical curtain conveyor (ECC) is generally used for moving high-resistivity micronized particles. A new separation technique of μm- and cm-sized metal/plastic particles was developed after analysing a newly observed attraction force applied on metal particles. A three-phase vibrating ECC was described in this paper, where the plastic particles move because of the vibration, and the metal granules remain attached to the surface of the ECC. Thus, the results revealed the feasibility of separation of μm- and cm-sized metal or plastic particles with high purity values and the existence of an attraction force depending mainly on the amplitude of the applied voltage.

A traveling wave conveyor (TWC) is generally employed for moving high-resistivity micronized particles. In this study, a planar TWC was used to analyze the attraction force applied on metal pieces. A three-phase conveyor comprising parallel electrodes that obtained power from high-voltage amplifiers (2 kV, 20 mA) controlled by digital function generators was used for analyzing the attraction force on 15 x 15 mm(2) square metal pieces made of copper, bronze, and steel. The TWC was fixed on a mechanical device that allowed its manual inclination from 0 degrees (horizontal; initial condition) to 180 degrees. The intensity of the force was then estimated by measuring the drop angle at which the metal piece detached from the surface of the conveyor. The obtained results revealed the existence of an attraction force that depends on the frequency, amplitude, and waveform of the applied voltage. This force is maximum at high voltages and frequencies and for a square waveform.

Triboelectrostatic separation of millimeter-size granular mixtures is nowadays widely used in the recycling industry. However, the separation of micronized particles of an average granulometric size of 100 mu m is still inefficient. This paper is aimed to carry out an experimental investigation of a triboelectrostatic separation process based on a fluidized bed tribocharging system produced between a pair of rotating aluminum disks supplied by two high-voltage DC supplies of opposite polarities. The granular mixture used in this work is composed of micronized white pure virgin PolyVinyl Chloride particles (WPVC) and gray PolyVinyl Chloride particles that contain a small percentage of carbon (GPVC) of average size 100 mu m. Moreover, a homemade method was developed to estimate the purity of the separated products. It was deduced that the separation outcome, in terms of recovery and purity, is efficient and depends on several factors: the high-voltage level, the rotating speed of the disks, the fluidization rate, the total mass of the fluidized bed and the composition ratio of the granular mixture. (C) 2019 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.

Although the dielectric barrier discharge (DBD) has been widely considered and studied for ozone generation, only a few studies have examined the influence of the alternating voltage waveform on the ozone rate production. This paper analyses the influence of the voltage shape on the ozone concentration and the energy efficiency of a DBD cylindrical ozone generator. Three voltage signals were studied using a high-voltage amplifier: sinusoidal, triangular and rectangular signals with voltage values up to 8 kV and frequencies up to 1.1 kHz. The obtained results showed that the efficiency of the ozone generator depends strongly on the type of the voltage waveform. The maximum values of the energy efficiency and the ozone concentration were obtained with the triangular voltage signal. This wave shape configuration has been successfully used for discolouration of water contaminated by textile dye.

The existing industrial tribo-electrostatic separators have proved their efficiency for sorting mixtures of millimeter-sized granular plastics. The objective of this paper is to validate a new tribo-aero-electrostatic separator designed for processing granular mixtures of insulating materials (average size: 10-100 μm). The device consists of two vertical plate electrodes of dimensions 20 cm × 30 cm, connected to two DC high voltage supplies of opposite polarities. Both electrodes perform “back-and-forth” motions inside a fluidized bed containing the micronized materials to be separated. Fluidization is achieved by injection of air using a variable speed air blower. The experimental study is carried out with samples of white PVC and gray PVC having an average size of 50 μm, and enables the analysis of the effects of several factors on the separation efficiency: the linear speed of the electrodes, the electric field, the mass of processed materials and the fluidization air flow rate. The new separation process is characterized by high product recovery rates. The purity of the separated products, estimated by visual examination, exceeds 90% in all experiments.

Tribo-electrostatic separation of mm-size granular insulating materials is a process widely used in plastics recycling industry. However, the separation of micronized plastics is still inefficient because the adhesion and aerodynamic forces of such particles are most often stronger than the electrostatic forces. The aim of this paper is an experimental investigation of a new separation process for micronized mixed plastics based on a fluidized bed tribocharging system and ADC high voltage cylinder rotating electrode is placed at 3 cm above the fluidized bed. The micronized insulating materials to be separated (white and grey PVC particles of average size 20 μm) are tribocharged using a fluidization air provided at variable-speed blower. The charged particles are pinned to the rotating electrode of opposite polarity. This process allows the sorting of one product while the other materials are left in the fluidized bed. The separation outcome, in terms of recovery and purity, depends on several factors and has been found to be optimal for a voltage of 35 kV and a rotation speed of 60 rpm. This new process has also been tested for ternary samples and the obtained results demonstrate its effectiveness for screening a targeted product, according to the voltage polarity, leaving the other products in the bed.

The recycling of plastic materials is considered nowadays as a major strategic issue, since several million tons of plastic are the subject of recovery and recycling. The consumption of plastics in African countries is continuously growing up and the need of low-cost recycling methods is becoming more pressing. The purpose of this paper is an experimental investigation for recycling of plastic waste from PET water bottles using the free-fall electrostatic separation device. Water bottles are manufactured with two kinds of plastic, PET (Polyethylene terephthalate) and HDPE (High-density polyethylene), are first crushed into 2-3 mm size particles. Triboelectric charging of the granules was performed using a fluidized air device build-up with a plastic located between PET and HDPE in the triboelectric series. Due to the plate-shape of the particles, the free-fall tribo-electrostatic separator is efficient in terms of recovery and purity of the separated products.

Several tribocharging devices are commonly used for charging insulating particles in order to separate granular plastic mixtures using a vertical triboelectric separator. However, there is no comparative analysis of these devices when tribocharging is achieved using identical samples of insulating particles. The objective of this paper is to carry out an experimental study that compares several tribocharging devices built up in the laboratory: a rotating cylinder, a tribo-cyclone, a static tribocharger, a propeller-type unit, and a fluidized bed. The study was performed using two granular samples of polyvinyl chloride (PVC) and high-density polyethylene (HDPE), for two different particle sizes: 1 and 2 mm. Experimental results showed that, when tribocharging pure samples of either PVC or HDPE, tribo-cyclone is the most efficient. However, when mixed samples are processed, the fluidized bed device gives the best results in terms of electric charge and separation efficiency.

A cyclone can be employed as tribocharging device for free-fall electrostatic separation of granular plastic mixtures. The objective of this work is to validate the possibility of modifying the "standard" operation of such a device, so that the turbine of the cyclone to participate in the charging process of the granules. Thus the granular product is introduced through a funnel into the turbine and then blown into the cyclone. When processed independently in the cyclone tribocharger, the charge acquired by the granules is significantly higher than in a fluidized bed device. On the contrary. when mixtures of granules are introduced into the tribocharger, the electrostatic separation efficiency is lower than with the latter device. However, the efficiency of the triboelectrostatic separation increases when covering the inner wall of the cyclone with a material that is located in the triboelectric series in-between the plastics to be sorted.

The selective sorting of mixed granular plastics can be achieved by tribocharging them in a vibrated parallelepiped chamber of variable height prior to introducing them in a free fall electrostatic separator. Although such vibrating tribochargers are currently used in industry, no experimental investigation of these devices has been carried out, yet. The objective of this work is to characterize this class of tribochargers by estimating both the electric charge imparted to the granules and the electrostatic separation efficiency. The granular product (a mixture of high-density poly-ethylene - HDPE - and poly-vinyl-chloride - PVC) is introduced through a funnel into the vibrating chamber, where the particles get triboelectrically charged by undergoing collisions between themselves and with the walls of the device. The obtained results showed that the efficiencies of both the charging and the separation depend on the geometry and the operating conditions of the tribocharger (height, length. inclination angle, motor speed). Charge per mass ratios beyond 3 nC/g have been easily attained and the efficiency of the separation was excellent: more than 90% of the HDPE and PVC in the feed are recovered at the outlet of the installation.