An evaluation of hydrocyclones and the LARCODEMS cylindrical cyclone for the separation of waste plastics of proximate densities.

Results of an evaluation of hydrocyclones and the LARCODEMS version of Density Medium Separation (DMS) cyclones for the separation of plastics are presented. This study presents the results of tests of the precision of density separations and the effect of flakiness of particles on the quality of density separations obtained in these devices. The cylindrical DMS cyclone (LARCODEMS) tested produced significantly more precise density separations of both flaky particles of varying size and of equidimensional particles of similar size than did a hydrocyclone of similar diameter. Particles with densities approximating that of the real separation density fed into the cyclone along with the separation medium are susceptible to misclassification into both the dense "sinks" and light "floats" products. In such instances, it appears that the only pure dense product that can be obtained is with the LARCODEMS and this only when particles to be processed are fed into its vortex. It is shown that the cylindrical DMS cyclones such as the LARCODEMS are indicated to be the most suitable for precise density separations of waste plastic particles. This device is also the most versatile cyclone density separation process as it is suitable for conducting density separations by either feeding material to be processed either dry or moist directly into its vortex or submerged along with the separation medium.

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

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.

A Parametric Model of the LARCODEMS Heavy Media Separator by Means of Multivariate Adaptive Regression Splines.

Modeling of a cylindrical heavy media separator has been conducted in order to predict its optimum operating parameters. As far as it is known by the authors, this is the first application in the literature. The aim of the present research is to predict the separation efficiency based on the adjustment of the device's dimensions and media flow rates. A variety of heavy media separators exist that are extensively used to separate particles by density. There is a growing importance in their application in the recycling sector. The cylindrical variety is reported to be the most suited for processing a large range of particle sizes, but optimizing its operating parameters remains to be documented. The multivariate adaptive regression splines methodology has been applied in order to predict the separation efficiencies using, as inputs, the device dimension and media flow rate variables. The results obtained show that it is possible to predict the device separation efficiency according to laboratory experiments performed and, therefore, forecast results obtainable with different operating conditions.