Mixed plastics waste separation by combination of sink-float method and selective flotation technique

Abstract

The aim of this research is to separate a mixed post-consumer plastics waste based on type of plastics by using gravity method and then follow by selective flotation. Analogous to gravity method, six mixed plastics wastes with 0.3 - 0.5 centimetre in size, composed of high density polyethylene (HDPE), polypropylene (PP), poly(vinyl chloride) (PVC), polystyrene (PS), polyethylene terephthalate (PET) and acrylonitrile-butadiene-styrene copolymers (ABS) were stirred thoroughly in a medium solution and then left for four minutes to ensure complete separation. Plastics whose density less than that of medium solution was floated to the solution surface, while the one whose density was greater than that of medium solution was sunk to the bottom of the solution. The experimental results showed that more than 99% of PP (with commercial grade) could be separated from a mixture of pp and HDPE when using 50% by volume of ethyl alcohol acted as light medium solution. Mixture of PS and ABS could be separated completely from a mix of PS, ABS, PET and PVC by using 20% by weight calcium chloride aqueous solution. Consequently, selective flotation was then employed to separate these mixtures by which gravity method could not achieve. In this section, effect of wetting agent, frother, pH, conditioning time and electrolyte were studied. The results showed that PET could be separated from mixture of PET/PVC with 98.05 % of recovered PET when using 500 ppm Calcium lignosulfonate (CaLS) as wetting agent, 0.1% CaCI2 as electrolyte, 0.02 ml MIBC as a frother, at pH 11 and conditioning time 3 minutes. It was found that 99.01% of PS was separated from the mixture of PS/ABS as by using different condition.