Evaluation of ground calcite/water heavy media cyclone suspensions for production of residual plastic concentrates

Abstract

Viable recycled residual plastic (RP) product(s) must be of sufficient quality to be reusable as a plastic or source of hydrocarbons or fuel. The varied composition and large volumes of such wastes usually requires a low cost, high through-put recycling method(s) to eliminate contaminants. Cyclone separation of plastics by density is proposed as a potential method of achieving separations of specific types of plastics. Three ground calcite separation medias of different grain size distributions were tested in a cylindrical cyclone to evaluate density separations at 1.09, 1.18 and 1.27 g/cm³. The differences in separation recoveries obtained with these medias by density offsets produced due to displacement of separation media solid particles within the cyclone caused by centrifugal settling is evaluated. The separation density at which 50% of the material of that density is recovered was found to increase from 0.010 to 0.026 g/cm³ as the separation media density increased from 1.09 to 1.27 g/cm³. All separation medias were found to have significantly low Ep₉₅values of 0.012-0.033 g/cm³. It is also demonstrated that the presence of an excess content of <10 µm calcite media particles (>75%) resulted in reduced separation efficiencies. It is shown that the optimum separations were achieved when the media density offset was 0.03-0.04 g/cm³. It is shown that effective heavy media cyclone separations of RP denser than 1.0 g/cm³ can produce three sets of mixed plastics containing: PS and ABS/SAN at densities of >1.0-1.09 g/cm³; PC, PMMA at a density of 1.09-1.18 g/cm³; and PVC and PET at a density of >1.27 g/cm³.

Keywords: Cylindrical cyclone; Density separation; Ground calcite; Heavy media; Waste plastics separation.