Triboelectrification of Granular Plastic Wastes in Vibrated Zigzag-Shaped Square Pipes in View of Electrostatic Separation

This paper presents an original device for the electrification of granular mixtures in vibrated zigzag-shaped pipes. Spatial movement of the granules introduced in the pipes is controlled by varying the oscillation amplitude and the frequency of a slider-crank mechanism. In the first set of experiments, two sorts of granular plastics (ABS and HIPS) were separately processed through the vibratory tribocharging device. Both ABS and HIPS charged negatively in contact with the aluminum pipes. The absolute value of charge/mass ratio increased with the amplitude and frequency of the vibratory movements to attain a maximum of 26 nC/g for the HIPS particles. In the second set of experiments, 100-g samples of 50% ABS + 50% HIPS were tribocharged, than introduced in a freefall electrostatic separator. A composite experimental design was performed for modeling the process. The output variable was the extraction of ABS while the speed and length of the crank were with the applied voltage the three control variables under investigation. ABS extractions higher than 85% were obtained for optimally chosen values of the control variables.