電路板產業是三大零件製造業之一，為用水需求極高的產業，製造過程會排出大量重金屬廢水，如未經適當處理，可能會間接造成人體危害。 有研究發現於pH>9.25時，利用低亞硫酸鈉可將含氨與銅離子之水中將銅還原為零價銅顆粒，去除率可達99%，作者認為氨存在是必要的，能與銅螯合為銅氨形式，最後還原為零價銅顆粒。本研究利用MINEQL+ 化學平衡軟體模擬含氨與銅離子之化學物種，發現銅在低pH下以離子形式存在，不會與氨螯合，在pH6- pH10少部分與NH3螯合，大部分以氫氧化銅形式存在，顯示銅與氨螯合效果不佳。因此，本研究先探討氨存在的必要性，並欲利用原本廢水中含有EDTA的特性，代替以低亞硫酸鈉做化學還原法去除銅所需要的氨。 實驗結果顯示，高pH時氨會變為氣態，逸散回空氣中，無法有效與銅螯合，造成去除率下降，長時間反應雖有高去除率，但以氫氧化銅形式被去除，如以曝氮氣方式，能有效防止氫氧化銅產生。在低pH下無氨水螯合時，低亞硫酸鈉也能將銅離子還原為銅顆粒，顯示還原過程氨水並非必要存在。以低亞硫酸鈉還原EDTA-Cu廢水，在pH3- pH11皆能有效將銅離子還原為銅顆粒，去除率達80%以上。EDTA系統長時間攪拌後以顆粒形式存在，與氨系統中氫氧化銅形式不同。 Printed Circuit Board is one of the three major electronic parts manufacturing industries. The manufacturing of PCB consumes a lot of water and produces enormous heavy metal-containing wastewater. Without appropriate treatment wastewater will cause great damage to human health. The literature shows that Cu ion could be reduced to Cu atom by sodium dithionite and removed from water with removal rate of 99% at pH>9.25. According to these authors, NH3 played a key role in the reduction process by chelating with Cu ion to form [(Cu(NH3)4)]2+ . In this research, we use MINEQL+ (chemical equilibrium software) to simulate the chelation between Cu ion and NH3. The simulation indicates that Cu ion doesn’t chelate NH3 at low pH value and most of Cu ions are in the form of Cu(OH)2 at pH6-10. Fraction of [(Cu(NH3)4)]2+ species is very tiny at pH>9.25, therefore, the significance of NH3 in Cu reduction needs to be verified. Meanwhile, if chelation of copper is important in copper reduction, EDTA which is ubiquitous in PCB wastewater might play the same role as NH3, and the effect of EDTA on copper reduction is also investigated. Experimental results show that at high pH value NH3 molecules vaporize into gas phase, Cu ion doesn’t chelate NH3 and cause lower removal rate. After a long time, the removal rate recovered due to formation and precipitation of Cu(OH)2. Nitrogen purging can effectively prevent formation of Cu(OH)2. At low pH value without ammonium ligand, Cu ion could be reduced to Cu atom by sodium dithionite, which indicated NH3 is not essential in reduction. The reduction of Cu ion to metallic Cu in EDTA-Cu water by sodium dithionite could happen efficiently at pH3-11 at reaction time of 30 min.
