Microwave-Enhanced Pyrolysis of Waste Printed Circuit Board

The concentration of gold in waste printed circuit board （WPCB） used in this study can be up to 20 ppmw, whereas it is only 0.5 ppmw in the gold ore. Moreover, it also contains other precious metals such as silver, platinum, and palladium. Therefore, as one of the most important branches of the waste electrical and electronic equipment （WEEE） stream, if WPCBs can be recycled properly, the city will be an abundant vein of various metals. Besides, urban mining not only achieves materials recycling but also diminishes environmental impact from ore mining. The aim of this study is to provide a simple, high efficiency, and low environment impact technique to recover the metals in WPCBs. By microwave-enhanced pyrolysis （MEP）, the inner layers of WPCBs separated, and thus metal recovery efficiency was enhanced. The maximum weight loss in thermogravimetric analysis （TGA） occurred at 350 °C, which was also achieved by MEP at 300W. Afterwards, the pyrolyzed WPCB was treated by a three-step hydrometallurgical process to recover metals separately. The first two steps are sulfuric acid leaching to dissolve copper and tin. The final stage is the leaching of gold, palladium, and silver by using thiourea and ferric ion.