Jig separation of crushed plastics: the effects of particle geometry on separation efficiency

Secondary resources (i.e., wastes) contain a wide variety of materials (e.g., plastics, metals, and wood) of various sizes and shapes that complicate separation especially when using gravity-based separation techniques. In this study, the effects of particle geometry (i.e., size and shape) on jig separation of crushed plastics were investigated. Plastic boards with 2-mm and 3-mm thicknesses of acrylonitrile butadiene styrene (ABS, specific gravity (SG) = 1.03) and polystyrene (PS, SG = 1.06) were crushed to obtain a size fraction of + 2.0-8.0 mm. The shape distribution in each size fraction (+ 2.0-2.8, + 2.8-4.0, + 4.0-5.6, and + 5.6-8.0 mm) showed the strong effects of crushing on particle shape; that is, particles are more disk-like at coarser size fraction but becomes more sphere-like at finer size fraction. Settling velocity of sphere-like PS increased with increasing particle size while those of disk-like ABS had similar values regardless of the size, which were consistent with the results of jig separation of single-type plastics. The results of jig separation of mixed-type plastics showed that separation efficiency was higher for the mixture of light, disk-like particles (ABS) and heavy, sphere-like particles (PS).