On-Line Detection of Heavy Metals and Brominated Flame Retardants in Technical Polymers with Laser-Induced Breakdown Spectrometry

摘要

During the recycling process of end-of-life waste electric and electronic equipment (EOL-WEEE), downgrading of valuable technical polymers has to be avoided by separating the collected material in fractions of high purity. Most EOL-WEEE pieces are doped with several additives to improve their mechanical, electrical and chemical properties. Common additives are flame retardants, antioxidants, light stabilisers, fillers, dyes and pigments. Their concentration varies typically from traces to several percent [1]. Waste pieces containing brominated flame retardants (BFR) and additives with heavy metals have to be automatically identified and removed from the waste stream to be recycled. This is due to the significant environmental problems during the waste management phase caused by these substances. To establish an economically feasible recycling process which meets these requirements, high speed automatic sorting systems performing the identification of both the polymer and the detection of the critical additives at a rate of several parts per second are required. In the scope of the European project Sure-Plast (BRPR-CT98-0783) a prototype automatic identification and sorting line has been set-up and evaluated for material specific sorting of EOL-WEEE pieces. The detection unit of this automatic sorting line is a multi-sensor system for the rapid identification of the polymer matrix and the detection of the contained additives. It comprises three spectroscopic modules based on LIBS (= laser induced breakdown spectroscopy), NIR (= near infrared spectroscopy) and MIR (= mid-infrared spectroscopy). This paper focuses on the LIBS analyser developed by Fraunhofer ILT and its application for the detection of heavy metals. In addition, results regarding the detection of brominated flame retardants in the waste pieces applying a co-operative analysis by the LIBS analyser and the MIR sensor are described.