利用過硫酸鹽氧化法處理電鍍製程產生之氰化物廢水

Abstract

由於添加氰化物有助於增加電鍍金屬表面的光澤與美觀，因此被廣泛應用於電鍍製程，若未經妥善處理直接排放至環境，將會對生態及人類健康造成極大的危害。鹼性氯化法是一般常見的處理方法，但其可能會產生有毒的中間產物、過量消耗試劑、對金屬錯合氰化物去除效率低等缺點。本研究利用電鍍廢水中普遍存在的銅離子活化過二硫酸鹽，以降解水中氰化物，並透過調整不同水質參數，包含過二硫酸鹽(peroxydisulfate, PDS)、氰化物、銅離子濃度、陰離子、重金屬，探討其對過二硫酸鹽及氰化物降解效率的影響。此外，藉由副產物分析、自由基捕捉劑以及電子順磁共振實驗，確立相關的反應途徑及反應機制，最後，採集實廠電鍍廢水添加特定濃度的過二硫酸鹽，觀察氰化物降解效率並評估此方法的應用可行性。不同水質參數下的實驗結果顯示，當總氰化物濃度為4 mM、過二硫酸鹽濃度為10 mM、銅離子濃度為1 mM時，具有較好的氰化物降解效率，於反應20分鐘後，氰化物濃度降至0.03 mM (相當於0.83 mg/L CN-)；添加多重陰離子的組別對於氰化物降解沒有顯著影響，而添加電鍍廢水常見的其他重金屬對氰化物降解效率的影響發現以下趨勢：Cu2+ > Zn2+ > Fe2+ > Ni2+。在分析副產物的實驗結果，發現於PDS/CN-/Cu2+的系統中，隨著氰化物的降解，氰酸鹽(OCN-)濃度有逐漸上升的趨勢；自由基捕捉劑以及電子順磁共振實驗結果顯示，於此活化系統中，明顯偵測到氫氧自由基與硫酸根自由基的存在，代表銅離子能成功活化PDS產生自由基促進氰化物降解。最後，於處理實際電鍍廢水的部分，添加40 mM PDS可於反應20分鐘內完全降解廢水中的氰化物。

Cyanide is widely used in electroplating process to ensure the smooth metal plating on the finished product surfaces. Alkaline chlorination process is commonly used to remove cyanide from electroplating wastewater. However, several drawbacks exist, including the formation of toxic intermediates, high consumption of chemical reagents, and low removal efficiency of metal-cyanide complexes. In this study, persulfate advanced oxidation process was explored for cyanide removal from electroplating wastewater. Peroxydisulfate (PDS) was activated by copper ion that is commonly present in electroplating wastewater to generate free radicals for cyanide removal. The influences of PDS concentration, cyanide concentration, copper ion concentration, common anions and heavy metals present in electroplating wastewater on cyanide removal and PDS consumption were investigated using batch experiments. The mechanism of cyanide oxidation was studied via the analysis of by-products, radical scavenging experiments, and electron paramagnetic resonance (EPR). Finally, real electroplating wastewater was collected from a local electroplating factory to the applicability of this process. It was found that 99% removal of cyanide (4 mM) was achieved in the presence of 10 mM PDS and 1 mM Cu2+ within 20 min in the PDS activation process. The presence of anions had no significant effects on cyanide removal. The ability of heavy metals on the activation of PDS for cyanide removal showed the following trend: Cu2+ > Zn2+ > Fe2+ > Ni2+. For by-product analysis, cyanate was detected and its concentration gradually increased with cyanide concentration decreased as a function of time. The results of radical scavenging experiment and EPR showed that hydroxyl radical and sulfate radical were responsible for cyanide removal, indicating that copper ions can successfully activate PDS to generate free radicals to promote cyanide removal. For real electroplating wastewater, the addition of 40 mM PDS could completely remove cyanide in 20 min.