微波增進裂解廢棄印刷電路板

Abstract

根據ICP-OES的分析，本實驗使用之廢棄印刷電路板中，金的濃度可達20ppmw以上；相較於金礦中，濃度只要達0.5ppmw即有開採價值，高出百倍有餘。此外，亦含有銀、鉑、鈀等貴金屬，銅的含量更是佔總重的一半以上。因此，若能有效的回收這些金屬資源，將城市當成一座礦場，除了可以減少開採礦石時對環境造成的衝擊，亦可以達到物質循環再利用的目的。本研究利用微波是由內而外加熱的特性，裂解廢棄之印刷電路板，使電路板層與層之間產生分離，進而提升金屬回收的效率；除此之外，亦可以減少傳統機械破碎法中粉塵散逸以及質量損失的問題。根據熱重分析的結果，印刷電路板的最大失重峰發生在350℃左右，可視為裂解反應主要發生的溫度；而三百瓦的微波功率可達到這個效果。經裂解之後的印刷電路板，經過三階段的冶金程序溶出金屬：前兩階段利用硫酸，輔以過氧化氫，溶解銅、錫等賤金屬，以減少後續對貴金屬所造成的屏蔽效應；之後，利用硫脲將金、銀等貴金屬溶出，達到金屬分別回收的目的。本研究旨在提供一個快速、設備成本低廉、低環境衝擊，且能夠有效的回收金屬資源的廢棄印刷電路板處理技術。

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.