Development and Optimization of a Thermo-Chemical Process for Recycling Waste Electrical and Electronic Equipment

In this thesis, a process and a corresponding bench-scale plant for a thermo-chemical treatment of different fractions from WEEE were developed and optimized, with the aim to accumulate and/or extract metals from different feedstocks to enable downstream recycling as well as to dehalogenate pyrolysis products. From tests with shredder residues, best results regarding metal accumulation and dehalogenation were achieved at a pyrolysis temperature of 650 °C and a residence time of 30 min. Most metals were part of the pyrolysis solid products, but, for instance, Cd, In, and Mo were strongly mobilized to pyrolysis vapor. In addition, levels of polyhalogenated dibenzo-p-dioxins and -furans (PXDD/F) in the solid products were minimized, going even below threshold values of corresponding legal requirements. PXDD/F decomposition in liquid products was achieved using blends of polypropylene and a metal compound resulting in a complete decomposition of polyhalogenated dioxins. For a following dehalogenation, a novel filter-material was developed, which was able to absorb more than 90 wt.-% of Br2 and HBr in preliminary tests. In order to investigate efficiencies of selective mobilizations of metals, different pyrolysis approaches with Liquid Crystal Displays (LCD) as feedstock were conducted and allocations of metals analyzed. Tests clearly revealed that co-pyrolysis with polyvinylchloride could be used to completely mobilize As while pyrolysis of PVC with LCD in vapor-phase mode enabled a selective extraction of In. In contrast, from pyrolysis of Ta capacitors at 550 °C in combination with sieving at 500 µm, a targeted enrichment of nearly 90 wt.-% Ta in pyrolysis solid products <500 µm was achieved. In an ecological and an economical assessment, the performance of a prospective, continuous pyrolysis process for shredder residues was compared to a treatment following the status quo. The process could result in strong ecological exonerative effects and a high economic performance.