Kinetic Analysis and Pollutant Evolution During Thermal Degradation of Printed Circuit Boards Considering the Effect of Metals

Abstract

A kinetic study has been carried out by thermogravimetry in order to compare the thermal behavior of printed circuit boards of mobile phones before and after the removal of the metallic fraction. Experiments were performed in nitrogen atmosphere (pyrolysis runs) as well as in an oxidative atmosphere (10% and 20% oxygen in nitrogen). Several dynamic and dynamic + isothermal runs have been carried out at different heating rates (5, 10 and 20 K min−1), from room temperature to more than 900 K. Moreover, TG–MS experiments were performed (in inert and oxidizing atmosphere) in order to better understand the thermal decomposition of these wastes. Different reaction models are proposed, one for pyrolysis and one for combustion of the two kinds of wastes studied, which proved to simulate appropriately the experimental results at all the heating rates simultaneously. Regarding the analysis of pollutants evolved, pyrolysis and combustion runs have been carried out at 600 ºC and 850 ºC in a horizontal laboratory furnace in order to analyze a wide range of gases, hydrogen halides, carbon oxides, light hydrocarbons, polycyclic aromatic hydrocarbons (PAHs), chlorinated phenols (ClPhs), chlorinated benzenes (ClBzs) and brominated phenols (BrPhs), among others. Furthermore, polybromo- and polychloro-dibenzo-p-dioxins and furans (PBDD/Fs and PCDD/Fs) and dioxin-like polychlorobiphenyls (PCBs) are being analyzed.