以超聲波增強浸出法回收廢棄印刷電路板中之貴金屬研究

Abstract

印刷電路板其成分複雜，當中包含金、銀、鈀等貴金屬，其他金屬如銅、鈣、錫等亦佔大多數。傳統的處理流程中常造成環境污染，危害人體健康。因此，如何有效和環保地回收當中的金屬成了最關注的問題。 本研究目的是利用微波裂解結合超聲波輔助濕式冶金法以較低的能耗去提高整體的回收效率。內容主要分為四個部分，第一部分為利用微波裂解對印刷電路板做前處理，以提高後續浸出程序之效率。第二部分以硫酸-過氧化氫系統酸浸除銅，以利後續貴金屬之溶出，並以電解法回收銅。第三部分使用硫代硫酸銨-氧氣系統輔以超聲波浸出貴金屬，再與傳統以硫代硫酸銨-硫酸銅-氨水系統作比較。第四部分是以過氧化氫使貴金屬離子沉澱分離，並與銅粉置換所得之結果作出比較。 研究結果表明，微波功率在333W裂解40分鐘能有效使印刷電路板裂解並分層，使酸浸時反應面積增加。在硫酸溶銅實驗中，以 1 M 硫酸加20ml過氧化氫，在固液比1:10下反應6小時，酸溶二次，銅有溶出率高達98%以上，電解後之總回收率為97.28%純度為99%。在硫代硫酸銨輔超聲波浸出實驗中，以0.2M硫代硫酸銨在超聲波功率300W；固液比1:40下反應1小時，金的溶出率為97.16%，銀則為100%。比傳統硫代硫酸銨-硫酸銅系統的最佳溶出率高出5%以上。最後使用過氧化氫作沉澱劑使金銀離子以固體方式沉澱回收，在pH=7時，金的回收率為94.58%，銀則為99.9%。整個實驗金回收率為91.89%，其純度8.26%，銀更逹99.73%，其純度67.71%，得到之沉澱物需再進行精鍊才可進一步使用。反觀銅粉置換法只能回收40.37%金和78.57%銀。 以超聲波輔助濕式冶金法回收貴金屬具良好的效果，在低污染以及高效益的回收流程中，減少傳統回收上的問題。

A printed circuit board is made up of many different elements, including gold, silver, copper and other metals, but its traditional treatment and recovery process often causes environmental pollution. Thus, effective and environmentally-friendly metal recycling has become the most concerned issue. The aim of this research is to combine microwave pyrolysis and ultrasound augmented leaching to increase the overall recovery efficiency with low energy consumption. This study consists of four parts. The first part considers microwave-enhanced pyrolysis as a pretreatment to enhance metal recovery efficiency. The second part proposes removing copper in a mixture of sulfuric acid and hydrogen peroxide. The third part presents the leaching of precious metals by thiosulphate-oxygen system with ultrasound and the comparison with its conventional process. The last part reveals the precipitation of precious metals by using H2O2 and compares it to the outcome of copper powder substitution. The results showed that printed circuit board can be stratified at 333W for 40 minutes in microwave pyrolysis. Over 98% of copper was removed during the leaching process by using 1M sulfuric acid with 20mL hydrogen peroxide, at a solid-liquid ratio of 1:10 for 6 hours, with two times of acid dissolutions. The total copper recovery rate after electrolysis was 97.28% and the purity was 99%. The leaching rate of 97.16% for gold, and 100% for silver, was achieved by using 0.2M thiosulphate with an ultrasound power of 300W, at a solid-liquid ratio of 1:40 for 1 hour. Compared with the conventional process, ultrasound-assisted leaching gave a 5% higher recovery efficiency. Finally, the leachate of gold and silver was precipitated by H2O2 oxidation process. The recovery rates of gold and silver were 94.58% and 99% at pH 7, respectively. The overall experimental recovery rate of gold was 91.89%, and of silver was 99.73%; their purity were 8.26% and 67.71%, respectively. The use of ultrasonic-assisted metallurgy to recover precious metals is effective. With low-pollution and high-efficiency recycling process, it decreases the problems derived from traditional recycling methods.