Enhancing spectroscopic systems for characterisation and sorting of metals and plastics in the context of a circular economy

Promovendus/a: Simon Van den Eynde

Promotor(en): Prof. dr. Jef Peeters, Prof. dr. Isiah Zaplana Agut

Recycling is an essential circularity strategy to make our society’s way of living more sustainable. However, recycling metals and plastics, especially from cars and electronic products, which include ever more complex materials, is a highly challenging task. Due to this high material complexity, extensive sorting of these types of waste is necessary to achieve similar properties for recycled materials as for virgin materials. Therefore, to achieve higher quality recycled metals and plastics and to increase material circularity, this PhD investigates how spectroscopic techniques can be used in novel sorting applications and characterisation procedures.

Spectroscopy is the study of radiation emitted by matter. Infrared, X-rays, and lasers can be used to tell us something about a material’s composition. While already thoroughly studied fundamentally, the implementation of these techniques for sorting and characterising mixed waste streams in the field of recycling has faced several challenges. This PhD aims to accelerate the use of these techniques in this field by contributing to several solutions.

Firstly, this PhD focuses on metals, and aluminium in particular, since the current sorting and recycling approach for aluminium is found to be unsustainable. The need to improve current aluminium sorting practices is demonstrated by forecasting the global flows of aluminium on an alloy level. Then, the presented research investigates the use of spectroscopy to enable the separation of different aluminium alloys. Sorting aluminium scrap on an alloy level improves its recyclability. Several methods are developed to make this goal possible.

Afterwards, the focus of the PhD shifts to plastic sorting and recycling. While advanced spectroscopic sorting systems are commonly adopted for plastic waste streams, little detailed information is currently available on the overall composition of these fractions. An automated system has therefore been developed to spectroscopically characterise fractions of plastic waste. With the novel system, the composition of the investigated fractions and the performance of the used sorting processes can be assessed.

Finally, a strategy based on intelligent product clustering prior to shredding and an effective combination of density-based and spectroscopic sorting processes was developed to produce higher quality recycled plastics.