Tribocharging techniques for the electrostatic separation of granular plastics from waste electric and electronic equipment

ABSTRACT

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.

KEYWORDS:

• Electrostatic separator
• fluidized-bed
• plastics
• triboelectric effect
• Weee

Acknowledgment

Several former or present PhD and MS students (Marius Blajan, Radu Beleca, Laur Calin, Lucian Caliap, Ciprian Dragan, Mohamed Miloudi, Gabriela Buda, Ovidiu Fati, György Tamas, Vasile Barna, Vasile Ilies, Silviu Cornestean, Sofiane El Moussoueas) contributed to the design and engineering of the various tribocharging devices described in this article; they also carried out most of the experiments. Thanks are due also to Dr Eng. Adrian Mihalcioiu, for the development of the virtual instrumentation, and to Ass. Eng. Marc Gauthier, for the technical assistance.