Estimation of hybrid jig separation efficiency using a modified concentration criterion based on apparent densities of plastic particles with attached bubbles

The hybrid jig, which combines the principles of jig separation and flotation, was recently developed to separate mixed-plastics with similar specific gravities (SG) effectively. In this type of jig, air bubbles are introduced during water pulsation to modify the apparent SG (SG apparent ) of plastics by the attachment of air bubbles to the particles so that the hybrid jig can separate materials having identical SGs if their surface wettabilities are different. Because the change in SG apparent —determined by the volume of attached bubbles on the particle surface—is critical for efficient separation in hybrid jigs, a method to estimate this parameter should be developed. In this study, a laser-assisted measurement apparatus was developed to quantify the attached-bubble volume on plastics during water pulsation. Hybrid jig separation was also conducted using three mixtures containing plastics of almost identical SGs: (i) polyvinyl chloride (PVC)/polyethylene terephthalate (PET), (ii) polypropylene with glass fiber (PPGF)/high-impact polystyrene (HIPS), and (iii) cross-linked polyethylene (XLPE)/polyethylene (PE). Finally, to estimate the separation efficiency of hybrid jig, a new index called the apparent concentration criterion (CC apparent ) is proposed. The results showed that SG apparent and CC apparent calculated using the proposed methods could be used to estimate the hybrid jig separation efficiency.