Roll-type versus Free-fall Electrostatic Separation of Tribocharged Plastic Particles

摘要

Tribocharged mixed granular materials are commonly separated in the electrostatic field generated between two vertical plate electrodes. However, the existing technologies are not appropriate for sorting coarse granules (size > 2 mm) for which the effect of gravity is stronger than the Coulomb forces. The aim of the experiments reported in this paper was to show that particle sorting is more efficient when done in a roll-type electrostatic separator. The granular materials to be separated, a mixture of 50% low-density polyethylene (LDPE) and 50% highdensity polyethylene (HDPE) were charged by particle-to-particle and particle-to-wall collisions taking place inside the rotating tube of a custom-designed tribocharging device. The study was performed with charging tubes made of four different materials: steel, aluminium, polyvinyl chloride and polyethylene. Under optimal operating conditions, more than 97% of the LDPE (purity: 97,83%) and 92% of the HDPE (purity: 92,45%) were recovered in the collector of the roll-type electrostatic separator, as compared to only about 60% and 75%, respectively, in the case of a standard free-fall separator.