Comparative analysis of flotation agents for enhanced separation of acrylonitrile butadiene styrene and polystyrene mixtures

Effective separation of plastic mixtures with similar physicochemical properties requires the utilization of appropriate flotation agents. In this study, both virgin and post-consumer acrylonitrile–butadiene–styrene (ABS) and polystyrene (PS) plastics were chosen as research objects to investigate the effects of flotation agents in ABS–PS flotation. Optimal conditions and wetting behaviors of wetting agents for efficient separation were identified. Tannic acid (TA) demonstrated superior selectivity than lignosulfonate (LS), attributed to its selective wettability on ABS, referring to greater surface-free energy and stronger repulsive interfacial interaction. Additionally, Polyoxyethylene (5) Lauryl Ether (laureth-5) was identified as a potential frother as well as methyl isobutyl carbinol (MIBC); however, its application was limited at high concentrations due to rapid surface tension reduction. These findings suggest that the selection of a suitable frother for ABS–PS flotation should not only consider the ability to produce fine bubbles and stabilize the froth but also the ability to reduce the surface tension of the liquid medium. Overall, high recovery and purity, exceeding 90%, were achieved for both virgin and post-consumer ABS–PS at TA concentration of 5 mg/L, MIBC concentration of 5 mg/L, and conditioning time of 15 min.