Effect of ambient humidity on the tribo-electrostatic separation of granular plastic wastes

The separation of plastic mixtures from waste electrical and electronic equipment is an increasingly active domain of research. Several electrostatic separation processes and devices have been developed to recover plastic waste. All these processes are based on the use of the triboelectric effect to charge the plastic granules to separate them in an intense electric field. The objective of this study is to investigate the effect of ambient humidity on the efficiency of the triboelectric charging and electrostatic separation process, especially in an industrial environment where granular plastic waste may contain residual moisture due to previous processing by flotation or inappropriate storage. The experiments were carried out using a rotating-multi-cylinder tribocharger and a roll-type electrostatic separator. The samples were composed in equal proportions of either: (1) acrylonitrile butadiene styrene (ABS) and polystyrene (PS) or (2) polypropylene (PP) and polyethylene (PE), the average particle diameter of which was between 2 and 6 mm. The efficiency of the tribo-electrostatic separation was evaluated by measuring the purity and recovery of the products. The results confirm that separating (ABS + PS) and (PP + PE) mixtures is feasible. The best separation results were obtained when the materials were stored and processed at an ambient relative humidity of around 50%.