Thermochemical treatment of non-metallic residues from waste printed circuit board: Pyrolysis vs. combustion

Abstract

The non-metallic fraction of waste printed circuit board (NMF-WPCB) mainly consists of plastics with high content of Br, glass fibers and metals (e.g., Cu). This work studied the pyrolysis and combustion of NMF-WPCB pretreated by alkalis, acids and alkali-salts. Copper (Cu, 2.5%), calcium (Ca, 28.7%), and aluminum (Al, 6.9%) were the main metal constituents. Meanwhile, the silicon (Si, 28.3%) and the bromine (Br, 26.4%) were the predominant non-metallic constituents. The heavy metal such as Cu was significantly reduced by 92.4% with the acid (e.g., HCl) pretreatment. The organic Br in the plastics can be converted to HBr via the pyrolysis process. The alkali pretreatment was benefit for the Br fixation in the char. In particular, the Br fixation efficiency can reach up to 53.6% by the NaOH pretreatment combined with the pyrolysis process, since the formed HBr reacted with NaOH to generate NaBr. Compared with the pyrolysis process, most of Br in the solid phase can be transferred to the liquid and gas phase in the combustion process. The gaseous organic-Br can cause serious environmental pollution. Furthermore, the ecological risk assessment analysis showed that the HCl leaching combined with the NaOH pretreatment has a high potential to be used for the pyrolysis disposal of NMF-WPCB environmentally friendly.