Malcolm Gent

Recycling of plastic waste by density separation: prospects for optimization.

A review of existing industrial processing and results of alternative processing investigations for separating solid mixtures and specifically recycling plastic waste by density separation is presented. Media density separation is shown to be fundamental for separation and/or pre-concentration in the recycling of plastics. The current use of static media processes limits the capacity and size of material that can be treated commercially. Investigations have shown that the hydroscopic properties of plastics can be reduced to improve such separations. This indicates that an alternative processing method is required to increase the commercial recovery of recyclable plastics. Cylindroconical and cylindrical cyclone-type media separators, such as those used for processing coal, are reviewed and suggested as a potential substitute. Both have superior production capacities and are able to process a larger range in particle sizes treated. A summary of results of investigations with cyclone media devices for recycling plastics is presented.

Cylinder cyclone (LARCODEMS) density media separation of plastic wastes

Cylindrical cyclone media separators using a suspended calcite separation media simulating industrial scale operations are demonstrated to effectively separate a wide variety of forms and a greater range of particle sizes of plastics by density than presently recycled. Purities of plastic products and recoveries obtained from mixed plastic wastes are comparable to those reported for established separations. Products of approximately 100% purity with recoveries of >99% were obtained for high density fractions and >98% purities and recoveries for the low density fractions. Cyclonic centrifugal forces and/or the fine particle size of the separation media appear to minimize hydroscopic and particle shape effects. A mathematical model is proposed for defining plastic waste feed rates and treatable particle size ranges for the LARCODEMS media separator. Waste plastic separations yielded Ecart probable (Ep) values 0.024 for a water only separation media. The Ep for 1.1gcm(-3) separation medias was <0.032 with minimal to no variation in values for 1-8mm particle sizes. Variation in the quality of separations is shown to be minimal with <72microm, <45microm and <2microm media particle sizes. Media density offset created varied according to particle size.

Offshore Occurrences of Heavy-Mineral Placers, Northwest Galicia, Spain

ABSTRACT Results of offshore water-jet sediment sampling demonstrate the potential for interstadial placer deposits of industrial minerals in the shore-face to inner-shelf of Cape Ortegal, NW Spain. Placer deposition is interpreted to have occurred during glacial interstadials since the Last Glacial Maximum, and deposits sampled at 24 to 42 m. BSL were formed during the Younger Dryas, and subsequently preserved as a result of very rapid rising sea-levels. The sediments are almost entirely terrestrially derived with a particularly high heavy mineral content (Sp. Gr. >2.9), of more than 75% in all samples. Reworked garnet from earlier-sedimentary deposits constitutes an important fraction of the placer deposits identified but is generally absent in other sediments. Indications of the presence of +5 m-thick paleo-placer deposits with sections include: Placer garnet + spinel grades increase with depth in those sediments at 24 to 42 m BSL to the ocean-floor. The d50 of sediments with background grades decrease with depth while those of placer deposits do not display any significant trend. Garnets in non-mineralized sediments are almost entirely angular, whereas in placer enriched sediments they vary in form from well-rounded to angular. Some grains in the latter display surface morphologies typical of reworked sediment while none of the former do. Sediments deposited during glacial interstadials at depths of up to 130 m BSL may represent important, undeveloped exploration targets for offshore placer deposits of industrial minerals. Industrial mineral exploration should extend the depths of investigations to those corresponding to major interstadial periods.

Recycling of a fine, heavy fluff automobile shredder residue by density and differential fragmentation

A compilation of the physical properties of materials which might typically occur in automobile shredder residue and an analysis of their suitability for the separation of materials in fine (<15mm) heavy fluff ASR (fhf-ASR) is presented. Differences in density and resistance to crushing of fhf-ASR materials were identified as potentially the most suitable low cost, technologically simple means for the separating this waste into its three principal components - metals, minerals (glass/stones) and organics (plastics). Results presented of laboratory scale tests demonstrate that fhf-ASR can in large part be separated into three principal components. Tests were conducted with 0.63-2.0mm and 2-10mm fractions. Recovery of plastics by density separations were conducted with water only jigs for the 2-10mm fraction and shaker tables for the 0.63-2mm fraction. Comparisons are presented of the separations of glass and stones from metals obtained by linear screening and vibratory screening of roller mill and impact mill crushing products of the high density 2-10mm fraction. Equipment used for these tests are of a laboratory or demonstrative scale. It is reasonable to anticipate that industrial scale processing would produce significantly better results. The 2-15mm fraction was found to constitute 91.6% of the fhf-ASR sampled. The metals content of the 2-10mm portion of this fraction was upgraded from 2.5% to 31% and 76.9% with recoveries varying inversely with grade from 91.9% to 40.1%. From 63.6% to 17.1% with a recovery of 93.5% of the organic materials. A residual product of fine sand of crushed glass/stones of 99.4% purity recovered 71.3% of these.

Mathematical and fuzzy logic models in prediction of geological and geomechanical properties of rock mass by excavation data on underground works

Abstract In underground works, the continual consciousness of geological and geomechanical properties of rock mass during drilling, is of major importance to optimize the works and the equipment used. In this paper, the mathematical relationship obtained from tunnel excavations, considering percussion drilling for blasting by a drilling machine and by a tunnel boring machine (TBM) are exposed. These mathematical relationships are useful in the percussion drilling case, to adjust the drilling parameter recorder (DPR) tools, and in the case of TBM to predict the rock mass geomechanical index (RMR). Taking into account the complexity of these mathematical models obtained, as a consequence of the affected variables and their relations, a fuzzy logic model based on parameters accessible to the drilling machine has been used in tricone bit drilling.

DMS cyclone separation processes for optimization of plastic wastes recycling and their implications

It is demonstrated that substantial reductions in plastics presently disposed of in landfills can be achieved by cyclone density media separation (DMS). In comparison with the size fraction of plastics presently processed by industrial density separations (generally 6.4 to 9.5 mm), cyclone DMS methods are demonstrated to effectively process a substantially greater range of particle sizes (from 0.5 up to 120 mm). The purities of plastic products and recoveries obtained with a single stage separation using a cylindrical cyclone are shown to attain virtually 100% purity and recoveries >99% for high-density fractions and >98% purity and recoveries were obtained for low-density products. Four alternative schemas of multi-stage separations are presented and analyzed as proposed methods to obtain total low- and high-density plastics fraction recoveries while maintaining near 100% purities. The results of preliminary tests of two of these show that the potential for processing product purities and recoveries >99.98% of both density fractions are indicated. A preliminary economic comparison of capital costs of DMS systems suggests cyclone DMS methods to be comparable with other DMS processes even if the high volume capacity for recycling operations of these is not optimized.

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.

LIDAR technique application to the analysis of environmental pollution

Landfill sites are the simplest and most common ways to eliminate urban solid waste, although large amounts of pollutants are introduced into the environment, such us dust, gas, soluble and insoluble substances. Both the digital model of the landfill surface and the three-dimensional meshing of the domain, where the dispersion phenomena is analyzed, are essential when modelling pollutant behaviour using Computational Fluid Dynamics (CFD3D). The commonly used Digital Surface Models are generated by combining a set of geometric primitives. These are obtained through a process of scanning, in which a set of points, which geometrically defines the landfill site, are identified by the derived cartography. In this study, we propose a procedure to digitally model a real surface from a data point cloud obtained through LIDAR (Light Detection and Ranging) technology, which identifies, in real-time, the main geometry that defines its surface. Thus, these landfill digital models are exported into the Ansys CFX 10.0 software for numerical modelling, in order to analyze the behaviour of dust and odours generated by the landfill site. The importance of LIDAR data technology in the study of environmental pollution produced by landfill sites is supported by the correlation between the obtained results through modelling and those obtained through field measurement programmes.