Calorific value recycling of low-value metal leaching residues in waste printed circuit boards assisted by debromination

Abstract

Metals in waste printed circuit boards (WPCBs) are usually recovered by hydrometallurgical processes. The reuse of leached residues, i.e. non-metallic components, has become a new challenge. In this study, the calorific value properties of leached residues with various particle sizes were studied to explore their potential utilization value. In order to realize the clean recovery of calorific value, bromine in resin was debrominated by pyrolysis. The morphology and phase of the leaching residue were analyzed by scanning electron microscope (SEM) and X-ray diffraction (XRD), the results show that the residue is mainly composed of irregular resin particles. Subsequently, thermogravimetric analyzer was adopted to determine the pyrolysis characteristics, the resin particles were debrominated and pyrolyzed in a tubular furnace, the composition and functional groups of the pyrolysis products were analyzed by gas chromatography mass spectrometer (GC-MS) and fourier transform infrared spectroscopy (FT-IR). The results show that the optimal pyrolysis temperature of the residue is 300–400 °C. Both calcium carbonate and calcium hydroxide can achieve effective debromination. Pyrolytic oil, as the main pyrolysis product, is mainly composed of phenols. Finally, the calorific value of pyrolysis products was measured by calorimeter, and the calorific value of pyrolysis oil and pyrolysis residue reached 31.72 MJ/kg and 8.54 MJ/kg. Therefore, leached residues have the potential as a secondary fuel. The ultimate goal is realize the clean and harmless treatment, a comprehensive utilization method of the leach residue of metal components in WPCBs was proposed.