Integrated density concentration and surface treatment for selective separation of plastics from a mixture

Froth flotation and elutriation were found to be effective in separating individual plastics from a plastic mixture by exploiting differential hydrophobicity and settling characteristics, respectively. The present work investigates selective separation of six different plastics, using a combination of advanced density concentration and froth flotation. Elutriation principle in a teeter bed separator was successfully employed to achieve density-based concentration of plastics. Contact angle measurements of the plastics exhibited high contact angles of more than 80°, signifying a strong hydrophobicity. Surface active reagents, such as tannic acid and KMnO4, were used to change floatability of plastics to enhance selectivity in separation. The crossflow separation technique of gravity concentration using elutriation principle was integrated with froth flotation to develop a simple process flowsheet. The novel flowsheet developed was shown to recover plastics with high efficiency and selectivity. Most purity levels were above 87% in the single run at each stage of the process. High-density polyethylene and polyvinyl chloride were recovered at 100% and 86.7% recovery, respectively, in two stages of gravity concentration. The rest were recovered by flotation with recovery levels of 91.3% for polymethyl methacrylate, 87.3% for polycarbonate, 70.2% for polystyrene and 94.2% for acrylonitrile butadiene styrene.