The contact electrification, also designated as the triboelectric effect, is commonly used in association with the electric field forces for the electrostatic separation of positively and negatively tribocharged granular plastic mixtures that have otherwise similar size, density, magnetic properties, and electric conductivities. However, the wide-scale industrial application of triboelectrostatic separation to the recycling of plastics from waste electric and electronic equipments is hampered by the relatively poor efficiency of this technique, due to nonhomogeneous charging and sensibility to changes in the environmental conditions. This article reviews several of the technical solutions developed by the authors during the last 10 years, in their attempt to improve the overall performances of the triboelectrostatic separators. Initially applied to mineral separation, the vibrated zigzag aluminum and PP tubes have been successfully tested in plastics recycling industry. Different types of metallic and plastic tubes of circular or square cross-section have been used for the construction of fluidized beds in view of the tribocharging of granular plastics mixtures. Several laboratory and pilot-plant experiments have confirmed the high efficiency of a recently patented installation, the tribo-aero-electrostatic separator, which combines in one unit a fluidized bed tribocharger and an electrostatic separator. The article concludes with several considerations on future developments in the field of triboelectrostatic separation.

New fractionation technologies are presently under investigation in order to enhance the wheat bran nutrient value. The explicit aim of this paper is to evaluate the possibility of using electric field forces for the separation of the fine particles generated from each wheat bran tissue during the milling process. Corona-charging and surface-potential-decay experiments were performed on samples of finely ground wheat bran and aleurone tissues (maximum size of 0.3 mm). Ground bran, which has a higher moisture content, more rapidly loses the charge imparted by corona discharge. For both kinds of samples, finer particles charged better than larger particles, and lyophilized samples were found to better preserve their charge than those not subjected to a freeze-drying process. An experiment carried out using a belt-type corona electrostatic separator validated the possibility of sorting these tissues based on the differences in their charge decay characteristics. Tribocharging experiments performed on the same tissues have also led to encouraging results: The charge/mass ratio of ground bran tissues was twice that of aleurone. These differences in the physical properties of the two types of tissues provide the technical basis for the development of electrostatic-separation technologies as part of more efficient bran-cracking strategies.

Electrostatic separation is able to process mixtures of plastics from waste electrical and electronic equipment. The efficiency of the electrostatic separation depends on the electric charge acquired by the particles in the appropriate tribocharging devices. The aim of the present work is to validate the possibility of using a roll-type electrostatic separator to sort mixtures of particles which are difficult to process by other means. In this type of separator, the plastic particles are charged by triboelectric effect. Two types of charging devices have been used: fluidized bed and rotating-multicylinder. Two series of experiments were performed with samples composed in equal proportions of: (1) acrylonitrile butadiene styrene (ABS) and polystyrene (PS); (2) polypropylene (PP) and polyethylene (PE). A third series of experiments were carried out with a mixture of three plastics: polypropylene (PP), polyethylene (PE) and acrylonitrile butadiene styrene (ABS), and the last series of experiment were carried out with a mixture four plastics of (PE / PP / ABS / PS), with an average particle diameter ranginig between 3 mm and 6 mm. The efficiency of the electrostatic separation was evaluated by measuring the charge, the purity and the recovery of the granules collected at the outlet of the electrostatic separation. The results confirm that the separation of ABS / PS and PP / PE mixtures is feasible and the best separation results were obtained using the fluidized bed tribocharger.