Floatability, selectivity and flotation separation of plastics by using a surfactant

In this paper, the floatability of seven plastics (POM, PVC, PET, PMMA, PC, PS and ABS) in the presence of alkyl ethoxylated nonionic surfactant (15-S-7) was investigated. It was found that the floatability of all the plastics decreases with the addition of the surfactant; but they are different in floatability and follow the order POM<PVC<PMMA<PET<PC<ABS<PS. From the separation test results of several plastic mixtures, it was shown that Gamma flotation method not only can be used to separate plastics mixture with different density, such as separation of POM and PVC from PC, POM and PVC from PS and ABS, PET and PMMA from PS and ABS, but also can be used to separate plastics mixture with similar density, such as separation of PMMA from PC. Products with grade higher than 99% and recovery higher than 97% can be obtained for the separation of some plastic mixtures. Finally, surface chemical factors, such as wettability of plastics and surface tension of flotation medium, and gravity factors, such as particle density and shape, were studied. It was found that the depressing effect of surfactant 15-S-7 on the plastics is mainly due to the reduced liquid surface tension, and flotation selectivity for the plastics with identical particle size is dominated by contact angle, particle density and shape.