Laser-induced Breakdown Spectroscopy and Multivariate Data Analysis Applied to in-line Sorting of Brominated Plastics from Waste Electric and Electronic Equipment

Abstract

The presence of Persistent Organic Pollutants (POP) in consumer products such as electrical and electronic equipment represents a major obstacle for the recycling of the materials they contain at their end-of-life. Current technologies applied to recover plastics from waste electric and electronic equipment (WEEE) struggle to meet the requirements from recyclers regarding restrictions on some of these POPs, mainly brominated flame retardant (BFR) content. In this study, laser-induced breakdown spectroscopy (LIBS) technique combined with partial least squares regression (PLSR) was investigated for the real-time classification of WEEE plastics based on their total bromine (Br) content, in order to foster their reintroduction into the market as secondary raw materials. With this aim, a classification method was trained and tested in a sorting prototype using mixed plastic samples from TV set and computer monitor housings containing an average of 1.34% of Br. Regardless of polymer colour and type, up to 56% of the tested material could be segregated into a single fraction with a final Br concentration of 1,280 mg/kg. The achieved values met the requirements established in the CENELEC EN 50625 series of standards for the depollution of BFRs (< 2,000 mg/kg of Br) and the concentration of polybrominated diphenyl ethers (PBDEs) was estimated to be 213 mg/kg. These findings demonstrate the potential of the LIBS technique together with multivariate data analysis to ensure WEEE plastic sorting and depollution compliance with current regulations, reducing disposal rates and ultimately contributing to its circularity.