Het verbeteren van spectroscopische systemen voor de karakterisatie en het sorteren van metalen en plastics in de context van een circulaire economie

Recycling is one of the circularity strategies that must make our society's way of living more sustainable. However, recycling metals and plastics, especially from cars and electronic products, is not an easy task. Achieving similar properties for recycled materials as for materials that are used for the first time requires extensive sorting of the collected waste. This PhD investigates how spectroscopic techniques can be used in novel sorting applications and characterisation procedures to achieve higher quality recycled metals and plastics. Aluminium recycling is currently characterised by significant quality losses, as aluminium post-consumer scrap is typically not yet sorted on an alloy-level. Therefore, many different aluminium alloys are melted together during recycling and the resulting secondary aluminium alloys have high concentrations of several alloying elements. Because of its particular mechanical properties, this type of recycled aluminium can only be used in a limited number of applications. Therefore, it is more correct to say that aluminium is mostly downcycled. Firstly, this dissertation clarifies why this downcycling approach is not sustainable. As the demand for highly alloyed aluminium is dwindling due to the electrification of the automotive sector and the collection of post-consumer scrap increases, a surplus of highly alloy scrap is forecasted to emerge in the coming years if no improved scrap sorting approaches are implemented. In this PhD, a novel method is developed for performing a material flow analysis at alloy level, which allowed to forecast that this scrap surplus will grow to a size of 5.4 million tonnes by the end of the decade if no measures are taken. Secondly, this dissertation investigates the application of Laser-Induced Breakdown Spectroscopy (LIBS) as a solution to reduce the quality losses during recycling. LIBS-based sorting experiments with post-consumer aluminium scrap pieces are conducted in realistic industrial conditions. Several novel methods are developed to classify the irradiated scrap pieces into different alloy groups and to estimate the concentrations of the present alloying elements based on LIBS spectra. These methods are tested on a pilot LIBS-based sorting system to sort a mix of post-consumer aluminium scrap into three commercially interesting output fractions. To improve plastic sorting and recycling performances, an automated system has been developed to spectroscopically characterise fractions of plastic waste. With this novel system, the composition of the investigated fractions and the performance of the used sorting processes can be assessed with great detail. The used spectroscopic characterisation techniques, Fourier-Transform Infrared (FTIR) and X-Ray Fluorescence (XRF) allow to both identify the present polymer type and estimate the concentrations of elements of concern, such as brominated flame retardants. With this system, several fractions of plastic waste are investigated that were separated with density-based sorting processes with the purpose to landfill, incinerate and recycle these respective fractions. By investigating material from all of these outputs with the automated system, generating over 10 000 measurements, it could be assessed whether the density-based sorting processes performed well and which adaptations to the processes could be useful. Finally, a strategy based on intelligent product clustering prior to shredding, and the application of effective sorting processes, including spectroscopic ones, was developed to produce high quality recycled plastics. In addition to the novel sorting approach, emerging recycling techniques such as solvent-based recycling and chemical recycling are considered to achieve the goal of introducing the recycled plastics in a series of selected plastic products. By contributing to these different research projects, this PhD has accelerated the development and adoption of spectroscopic characterisation and sorting methods in the field of recycling, with the overarching goal to increase the circularity and sustainability of metals and plastics.