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Selective collection is a common practice in many countries. However, even in some of those countries there are recyclable materials, like packaging glass, erroneously deposited in the Mixed Municipal Solid Waste (MMSW). In the present paper, a solution is proposed to recover glass from the inert reject of Mechanical and Biological Treatment (MBT) plants treating MMSW aiming at its recycling. The inert reject of MBT (MBTr) plants is characterized by its small particle size and high heterogeneity. The study was made with three real samples of diverse characteristics superimposed mainly by the different upstream MBT. One of the samples (VN) had a high content in organics (approximately 50%) and a particle size smaller than 16 mm. The other two were coarser and exhibited similar particle size distribution but one (RE) was rich in glass (almost 70%) while the other (SD) contained about 40% in glass. A flowsheet was developed integrating drying, to eliminate moisture related with organic matter contamination; magnetic separation, to separate remaining small ferrous particles; vacuum suction, to eliminate light materials; screening, to eliminate the finer fraction that has a insignificant content in glass, and to classify the >6mm fraction in 6-16 mm and >16 mm fractions to be processed separately; separation by particle shape, in the RecGlass equipment specifically designed to eliminate stones; and optical sorting, to eliminate opaque materials. A pilot plant was built and the tests were conducted with the three samples separately. With all samples, it was possible to attain approximately 99% content in glass in the glass products, but the recovery of glass was related with the feed particle size. The finer the feed was, the lower the percentage of glass recovered in the glass product. The results show that each one of the separation processes was needed for product enrichment. The organic matter recovered in the glass product was high, ranging from 0.76% to 1.13%, showing that drying was not sufficient in the tests but that it is a key process for the success of the operation.

Solid waste are today new ores needing innovative separation techniques or adaptations of the current ones used, for instance in mineral processing, for the recovery of materials. “RecGlass” is a device developed to separate materials with similar density but exhibiting different particle shape. It is inspired in the “vanner” and in the “Bartles cross belt” processes but it is applied in dry conditions to separate materials with specific weight slightly above 2 g/cm 3 and particles in the range size 4 to 12 mm. In the work presented, it was applied to the processing of the heavy reject of Mechanical Biological Treatment of mixed Municipal Solid Waste aiming at the recovery of glass, the main constituent of this product, which is landfilled today, and to eliminate the stones, generally the second main inert constituent. The glass particles are predominantly flat while stones are sub-spherical. The core of the equipment is an inclined belt moving upwards. The particles are continuous and steadily fed by a vibrating feeder placed above the belt. Depending on the operational variables such as belt speed and slope and feed position, and also on the belt surface material, the flat particles move upwards and the round ones roll down. In the present paper the equipment is described and the physical principles of the concentration process are explained. Using samples of two different plants it was shown that it is possible to achieve a significant upgrading in glass. With a sample from one plant the glass content was increased from 88% to 92% while with a completely different sample, from another plant, the glass content in the process feed was 59%, attaining 71% in the glass concentrate. The recovery of the glass in the glass concentrate reached more than 80% by removing about 80% of the stones.

Mechanical Biological Treatment inert reject (MBTr) is mostly composed by recyclable glass. Yet, it is usually sent to landfills because, due to the small particle size and high level of particle surface organic contamination, the processes commonly used in glass recycling, like optical sorting, are inefficient in the separation of glass from contaminants. This paper presents the results of a study undertook to characterize MBTr, aiming at the subsequent separation of recyclable glass from contaminants. A representative sample of the reject from a MBT plant was collected. The particle size analysis was carried out and the composition of the different size fractions was determined. It was found that the MBTr sample was composed by almost 80% of recyclable glass. The product is quite fine. About 80% in weight of the product has a particle size lower than 10 mm. However, the size fraction below 2 mm is insignificant since it represents less than 3% in weight and contains less than 1% of the recyclable glass in MBTr. Using methods of image analysis, the shape of each individual particle, separated by material class and by size fraction, was evaluated. It was observed that the average shape of the particles of “stone”, the main contaminant, is significantly different from the shape of other materials, including recyclable glass. Gravity concentration methods may take advantage of the shape of the particles and are thus potentially adequate to recover recyclable glass from MBT.

This article addresses the separation of polyethylene terephthalate (PET) from ternary blends with polyvinyl chloride (PVC) and polystyrene (PS) by froth flotation. The experimental work was carried out with representative samples from post-consumer waste packages collected at drop-off-points. Previous to froth flotation, PET selective wetting was achieved by alkaline treatment followed by surfactant adsorption. For this purpose, an aqueous solution of NaOH and an industrial detergent commonly used for waste plastic washing were tested as alkaline treatment, and calcium lignosulphonate and Hostaphat were tested as surfactants. An enriched product with 98.9% grade in PET and only 0.6% in PVC was recovered in the nonfloated product. The PET recovery in this product was 97% while 96% of PVC and 91% of PS were recovered in the floated product. An analytical method was developed for the quantification of the waste plastic composition. The method was based on the selective dissolution of the plastics in the mixture., Fundação para a Ciência e a Tecnologia (FCT) - POCTI/ECM/60335/2004

The objective of the experimental work described in this paper is the study of the separation of PS (polystyrene) from PET (polyethylene terephthalate) and PVC (polyvinyl chloride) from drop-off points using a fluidized bed separator. This is a low-cost process commonly used in the hydro-classification of mineral ores. Firstly, experimental tests were carried out with artificial granulated samples with different grain sizes, types and sources of plastic ("separability tests"). The particle settling velocities were determined under different operating conditions. Then, based on the results, the laboratory tests continued with real mixtures of waste plastics ("separation tests") and the efficiency of the process was evaluated. From a PET-rich mixture, a concentrate of PS with a 75% grade in PS was produced while the underflow was quite clear from PS (grade less than 0.5% in PS).

With the purpose of reducing the waste generated by end-of-life vehicles (ELVs) by enhancing the recovery and recycling of nonferrous metals, an experimental study was conducted with the finest size fraction of nonferrous stream produced at an ELV shredder plant. The aim of this work was to characterize the nonferrous stream and to evaluate the efficiency of a gravity concentration process in separating light and heavy nonferrous metal particles that could be easily integrated in a ELV shredder plant (in this case study the separation explicitly addressed copper and aluminum separation). The characterization of a sample of the 0-10mm particle size fraction showed a mixture of nonferrous metals with a certain degree of impurity due to the present of contaminants such as plastics. The majority of the particles exhibited a wire shape, preventing an efficient separation of materials without prior fragmentation. The gravity concentration process selected for this study was the wet shaking table and three operating parameters of the equipment were manipulated. A full factorial design in combination with a central composite design was employed to model metals recovery. Two second order polynomial equations were successfully fitted to describe the process and predict the recovery of copper and aluminum in Cu concentrate under the conditions of the present study. The optimum conditions were determined to be 11.1° of inclination, 2.8L/min of feed water flow and 4.9L/min of wash water flow. All three final products of the wet shaking table had a content higher than 90% in relation to one of the metals, wherein a Cu concentrate product was obtained with a Cu content of 96%, and 78% of Cu recovery and 2% of Al recovery.

The objective of the research was to apply froth flotation to separate post-consumer PET (Polyethylene Terephthalate) from other packaging plastics with similar density, in a continuously operated pilot plant. A representative sample composed of 85% PET, 2.5% PVC (Polyvinyl Chloride) and 11.9% PS (Polystyrene) was subjected to a combination of alkaline treatment and surfactant adsorption followed by froth flotation. A mineral processing pilot plant, owned by a Portuguese mining company, was adapted for this purpose. The experimentation showed that it is possible to produce an almost pure concentrate of PET, containing 83% of the PET in feed, in a single bank of mechanical flotation cells. The concentrate grade attained was 97.2% PET, 1.1% PVC and 1.1% PS. By simulation it was shown that the Portuguese recycling industry specifications can be attained if one cleaning and one scavenger stages are added to the circuit.