WEEE AND ELV | INNOVATION


WEEE and the problem of complex black plastics


Recovering all polymer fractions from black waste streams is not easy, but electrostatic separation provides a solution, says Hamos


Recovery of clean plastic fractions from electrical and electronic waste is much more laborious than recycling of the metals, says Selinda Sliz, Marketing Director at Hamos Recycling- und Separations- technik in Penzberg, Germany. This article is derived from a recent report she wrote. Hamos builds complete recycling lines incorpo-


rating electrostatic separation technologies, which make it possible to separate even black plastics into clean separate fractions according to the types of materials involved. The granulate material purities achievable with electrostatic separation are very high and sometimes stretch beyond 99.5%, meaning it can be used again to produce high- grade compounds for new technical products. It is not only the type of plastic that plays a large


role in plastics recycling, but also the colour. WEEE material involves a particularly high proportion of black plastics, which can amount to between 60 and 75%; in toner cartridges, it sometimes amounts to more than 90%. For sorting post-consumer packaging waste, opto-electronic sorting equipment has been widely adopted. Near-infrared recognition (NIR) technol- ogy can automatically recognise different polymers in complete packages, and also in flakes and other granulated recyclate materials. But historically, NIR sorting has only been able to recognise light coloured plastics with a high level of accuracy, so it has not been economic for separating different WEEE plastics (although some NIR technology companies have been developing sorting units for dark plastics). A large proportion of recyclable ABS and PS has ended up as non-recyclable waste. Electrostatic separation technology can be used


with great success for separation of such mixed plastics from electronics scrap, says Hamos. Completion of the separation process results in receipt of ABS or PS fractions with a purity of in some instances more than 99%. Electrostatic separation takes place irrespective of the colour. Completely black coloured material mixtures can therefore also be easily separated. But there is a catch. Complex mixtures found in


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Above: Toner cartridges waiting for recycling. Hamos says electrostatic separation is ideal for these products. After running through the recycling line, the resulting granulates of ABS and PS are so clean that they can be used again in production of new toner cassettes


electronics scrap cannot be simply processed as such. There has to be a form of pre-concentration applied prior to the electrostatic process, so that undesired plastics, such as those containing for example flame retardants, can be separated. A combination of dry and wet processing technologies is recommended for the required plastics precon- centration from these complex material mixtures. Dry separation processes can separate all


undesired foreign materials such as for example film, dust, and fibres from pre-shredded WEEE plastics materials with particle sizes less than 50mm. After sieving and the removal of any remaining metal parts, comes wet separation using a series of float-or-sink basins containing liquids of different densities. In the first stage, with a liquid density of approximately 1.08 g/cm³, product groups like PS, ABS, PP and others float, but others, including flame retarded plastics, sink. A subsequent stage sepa- rates out polyolefins from styrenics and other denser polymers. It is easy to separate ABS and PS from each other with the electrostatic separation technology. ABS takes on a positive charge, while PS takes on a negative charge.


July/August 2020 | PLASTICS RECYCLING WORLD 41


IMAGE: HAMOS


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