印刷電路板業含銀廢液電解之研究;Electrolysis of Silver-Containing Waste Liquid in the Printed Circuit Board Industry

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Title:	印刷電路板業含銀廢液電解之研究;Electrolysis of Silver-Containing Waste Liquid in the Printed Circuit Board Industry
Authors:	徐梓源;Hsu,Tzu-Yuan
Contributors:	環境工程研究所在職專班
Keywords:	印刷電路板;含銀廢液;電解還原;printed circuit board;silver-containing waste liquid;electrolytic reduction
Date:	2015-07-17
Issue Date:	2015-09-23 15:29:38 (UTC+8)
Publisher:	國立中央大學
Abstract:	印刷電路板PCB (Printed Circuit Board)製程一般可區分為乾式製程(dry process)及濕式製程(wet process)，傳統印刷電路板濕式製程(wet process)廢液處理方式是將廢水分類收集後，再分別導入調整槽、快混槽、中和槽、慢混槽調勻後，再經過沉澱池沈降及中和槽調整，最後排放至承受水體，以符合相關法令範疇。印刷電路板製程廢液大部份是含銅廢液，其在高濃度部份因牽涉廢棄物清理法及考量公司生產運作成本，所以大部份都是委外清運及回收，低濃度貴金屬廢液則直接排入廢水廠處理，本研究之主要目的在於如何將低濃度廢液中之貴金屬取出，以增加廢棄物回收效益、降低廢水廠運作成本、及降低廢液中之銀離子含量，以符合放流水管制標準。本研究將製程所產生的含銀廢液導入電解設備內進行電解，以石墨為陽極(十)、不鏽鋼為陰極(—)，通入電流後，廢液中銀離子被還原成金屬銀，並沈積於陰極不鏽鋼桶上。研究結果顯示，將電解時間設定為2小時，電流設定為2安培(A)為最佳的電解操作條件(此操作條件電解去除效率可達97%)，含銀廢液先經過電解設備電解後，再導入化學混凝系統處理，利用串聯方式進行含銀廢水處理，處理後之含銀廢水再使用原子吸收光譜儀AA (Atomic Absorption Spectrophotometer)來分析處理後之廢液中銀離子含量，並計算其去除效率。利用串聯方式來處理含銀廢水，處理過程所產生之污泥量比直接將含銀廢液進行化學混凝所產生之污泥量少約4倍，其主要是因為含銀廢水已先經過電解處理，所以在化學混凝階段所需之藥水添加量相對較少，因去除效率高達98.32%，所以處理後之放流水質可以符合放流水管制標準(最大限值為0.5毫克/公升)、飲用水水源水質標準及飲用水水質標準(最大限值為0.05毫克/公升)，並可將廢液中之貴金屬析出增加廢棄物回收效益(以實廠每月生產線排放含銀廢液3,000L計算，所電析出之銀約為2.488公斤，可增加電解回收效益約57,224元)。 ;Generally speaking, a Printed Circuit Board (PCB) can be manufactured by a dry process or a wet process. When the wet process is used, the waste liquid is typically treated by first separating and collecting the waste liquid produced; then Passing the waste liquid sequentially through a conditioning tank, a fast mixing tank, a neutralization tank, and a slow mixing tank in order to produce a well-blended liquid mixture; Passing the liquid mixture through a sedimentation tank and a second neutralization tank is for precipitation and further conditioning. Then discharging the treated liquid mixture to a receiving body of water, with a view of complying with applicable laws and regulations. The waste liquid of a PCB manufacturing process is basically a copper-containing waste liquid. The collection, disposal, and recycling of the high-concentration portion are generally outsourced to a contractor not only to meet the requirements of the Waste Disposal Act, but also in consideration of the operational costs involved. The portion with a low concentration of noble metals, on the other hand, is directly released to a wastewater treatment plant for treatment. Thus, the main objective of this study is to retrieve the noble metals in such a low-concentration waste liquid so as to increase the benefit of waste recycling, reduce the operational costs of wastewater treatment plants, and lower the silver ion content of such a waste liquid to that allowed by the effluent standards. In this study, the silver-containing waste liquid of a PCB manufacturing process is introduced into an electrolysis apparatus in order to be electrolyzed. When electricity is applied to the graphite anode (+) and the stainless steel cathode (-), the silver ions in the waste liquid are reduced to metal silver and deposit on a stainless steel tank (serving as the cathode). According to the experiment results, the optimal electrolysis conditions (under which the removal rate reached 97%) include a 2-hour duration and a 2-A current. The electrolyzed silver-containing waste liquid is then passed to a chemical coagulation system to complete the serial treatment. The treated waste liquid is analyzed with an Atomic Absorption (AA) Spectrophotometer to determine the silver ion content and the removal rate. The sludge generated by treating a silver-containing waste liquid in the foregoing serial manner is about one fourth of that generated by directly subjecting the waste liquid to chemical coagulation. This is mainly due to the fact that a silver-containing waste liquid to be electrolyzed requires relatively a small amount of additives during chemical coagulation. Moreover, with a removal rate as high as 98.32%, the effluent of the serial treatment meets both the effluent standards (the upper limit being 0.5 mg/L) and the water quality standards of drinking water sources and of drinking water (the upper limit being 0.05 mg/L). Now that noble metals can be extracted from waste liquids and the benefit of waste recycling will also be enhanced (e.g., approximately 2.488 kg of silver can be extracted by electrolysis from a 3,000-L monthly discharge of silver-containing waste liquids, yielding a monetary return of about NT$57,224.).
Appears in Collections:	[Executive Master of Environmental Engineering] Electronic Thesis & Dissertation

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