Recovery Of Packaging Glass From The Mechanical Biological Treatment Reject

Abstract:

The management of Mechanical Biological Treatment reject (MBTr) is today a significant problem in several countries due to the large quantity of material sent to landfill. This product is composed mainly by glass, especially packaging glass. In Portugal, for instance, there are 5 MBT plants in operation and 7 to be commissioned in the next year. It is estimated that about 75000ton/year of glass from MBT-r will be landfilled. When MBT is correctly operated the non organic residue is composed mostly by mineral type materials such as stones and anthropogenic inert materials, like glass and ceramics, with particle size under 20 mm. The recycling of glass obliges its separation from the other materials. Optical sorting, currently used in the sorting of the packaging glass disposed by citizens in glass containers and bottle banks, has not been an option to be applied directly in MBTr for the process efficiency decreases drastically with particle size and it is very sensitive to feed composition and organic contamination. The present paper describes the experimental work carried in the search for economic and technological solutions for the recovery of the glass contained in the MBTr that could significantly contribute to the “closed loop recycling”. A thorough experimental work was carried out by testing different processes applied before optical sorting. Separation methods commonly used in mineral processing, like screening, were used. The apparent difference in the shape of glass particles (flaky particles) and other material particles (mostly sub-spherical particles), mainly in the upper size range, were exploited applying gravity concentration. Pre-processing by washing and drying was tested too. The optical sorting efficiency was evaluated and its limitations were related with particle size, feed composition and organic contamination.

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