Abstract The aim of this research was to separate a mixture of six post-consumer plastics (PS, PMMA, PVC-D, PVC-M, PET-D and PET-S) by combination of sink-float separation and froth flotation.. In sink-float method two mediums of separation were used: sodium chloride water solution and ammonium nitrate water solution. Sink-float method allowed complete separation of the less dense plastic (PS) from intermediate density plastics (PMMA and PVC-D) and from high density plastics (PET-S, PET-D and PVC-M); also allowed good separation of intermediate density plastics (PMMA and PVC-D) from high density plastics (PVC-M, PET-D and PET-S) with an efficiency close to 100%. Separation of PVC-M from PET-D and PET-S by sink-float method led to fair results allowing a separation efficiency of about 60%. Since PMMA and PVC-D have similar density, their separation was achieved by froth flotation, using sodium lignosulfonate as selective wetting agent of PVC-D, with a separation efficiency of 85%.

Abstract Plastics are naturally hydrophobic, so the selective flotation of plastic mixtures is impossible without changing their surface properties. The objective of this research is flotation separation of PET from PS, PMMA and PVC combined with sodium hydroxide pretreatment. NaOH pretreatment had a strong effect on PET’s floatability, medium effect on PMMA and PVC and limited effect on PS. The reduction of PET floatability is ascribed to a sharp decline of contact angle. The optimal pretreatment conditions were: 10% NaOH concentration, 70 °C (PET/PMMA and PET/PVC) to 80 °C (PET/PS) and plastic treatment times in the alkaline solution of 20 min (PET/PMMA and PET/PVC) to 30 min (PET/PS). Flotation separations were achieved efficiently and the best results were obtained for the PET/PS mixture, with a floated PS grade of 98% and a sunk PET grade of 100%. PET and PS was separated effectively, implying that sodium hydroxide treatment possesses superior applicability.

Abstract Froth flotation is the most common process in mineral processing. For the separation of plastic mixtures by flotation, the use of appropriate wetting agents is mandatory. The floatability of six post-consumer plastics was studied at different concentrations of the wetting agents, saponin and sodium lignosulfonate. Also, the influence of size and shape of the particles were analyzed. Contact angle and floatability of the six plastics decreased with increasing wetting agents concentration. The order of floatability is similar to the order of the contact angles values. However, the influence of the wetting agents in the plastics floatability is more pronounced than in the contact angle. Floatability decreased with the increase of particle density, particle size and spherical shape. For fine particles floatability is fundamentally conditioned by the contact angle, while for coarse particles floatability is fundamentally conditioned by the particles weight.