以減壓蒸餾技術處理含銅廢水與再利用於活性碳改質創新技術研發

Abstract

濕式冶金法能夠有效回收電子廢棄物中的金，但最終此方法會產生含銅廢水，一般含銅廢水會以化學沉澱法處置，然而，廢水中金屬離子濃度高，所需強鹼添加量大，使得處理成本隨之提升，且會產生大量汙泥造成二次污染，所以化學沉澱法並非最合適之廢水處理方法；另外此廢水成分包含高濃度的銅離子，具回收之潛力。本研究目的在於處理與再利用含銅廢水，可分為三個部分：第一個部分為使用減壓蒸餾技術去除並回收含銅廢水中金屬，並且定量及定性分析回收結晶固體。第二個部分再利用含銅廢水作為合成硫化銅原料，並藉由真空含浸將硫化銅(CuS)含浸一般商用活性碳(AC)，合成硫化銅活性碳(CuSAC)作為吸附材料；最後測試CuSAC在純氮氣及模擬煙氣對汞之吸附能力及不同條件下對其之影響。 測試結果顯示，經減壓蒸餾處理完之廢水可以發現低濃度金屬離子存在，主要是由於突沸現象所造成。不同的操作條件下，溫度與真空度影響蒸餾速率、能耗與突沸程度。在操作條件為溫度60oC與真空度-72 cm Hg，金屬離子去除效率高達99.99%以上。蒸餾出金屬結晶固體經定性及定量分析後，判別主要由鹼式硝酸銅與硝酸鈉組成，並能以水分離結晶固體中硝酸鈉，得到純度92%之鹼式硝酸銅固體。另外，由成本效益評估推算，若以減壓蒸餾取代傳統化學沉澱處理，處理一公升的含銅廢水能夠省下22.49新台幣，因此確認本技術具經濟之可行性。 再利用含銅廢水合成之10、25、50% CuSAC。物化特性分析結果顯示，硫化銅活性碳比表面積與孔體積明顯下降，是由於硫化銅堵塞活性碳的孔洞。SEM圖中可觀察到，在真空含浸下，硫化銅顆粒會先分佈於活性碳孔洞內，在孔洞近飽和後才會在活性碳表面上出現。XRD分析結果證實硫化銅成功由含銅廢水合成，並結晶於活性碳表面上。XPS結果顯示對汞具高親和力之活性位置如S2-、多硫化物與氧官能基被建立在活性碳表面。 在純氮氣條件中，比較三種CuSAC與原始活性碳，結果顯示以50% CuSAC對汞之吸附效果為最佳，並明顯優於原始活性碳。在175°C下，50% CuSAC對汞吸附效果大為下降，因為原先吸附汞而形成之硫化汞，在此溫度下會被分解。相對於氮氣條件，在模擬煙氣條件下汞吸附效果略為減少，主要是由於水氣會與汞競爭吸附。最後，由TPD結果得知CuSAC吸附汞的主要機制為硫化銅在表面與汞鍵結形成硫化汞。

A hydro-metallurgical process can efficiently recycle gold from electronic waste (e-waste), but the process may produce copper (Cu)-containing wastewater. In general, the wastewater is treated by the chemical precipitation, causing sludge disposal as well as an expensive cost for chemical used. Therefore, chemical precipitation is not an adequate method for treating Cu-containing wastewater. The aim of this study was to treat and recycle Cu-containing wastewater. Firstly, vacuum distillation technique was utilized in treatment of Cu-containing wastewater. The qualitative and quantitative analyses were conducted to evaluate the recycling potential of the crystalline solid derived from vacuum distillation process. Secondly, Cu-containing wastewater was reused in synthesizing copper sulfides (CuS), deposited into the pore of activated carbon (AC) to prepare CuSAC by vacuum impregnation. The physical and chemical characterization of CuSAC was subsequently investigated. Finally, the effects of different parameters on the Hg adsorption performance of CuSAC was examined. The distillate derived from vacuum distillation process was observed with low concentration of metals due to the bumping effect. Different temperature and vacuum degree in vacuum distillation process affected distillation time, energy consumption, and bumping effect. The metals removal efficiency of vacuum distillation process was over 99.99% at 60°C and -72 cm Hg. The crystalline solid derived from vacuum distillation process mainly composed of Cu2NO3(OH)3 and NaNO3, which could be easily separated by water. The Cu2NO3(OH)3 purity of insoluble crystalline solids was 92%, supporting the Cu species of the insoluble crystalline solid was Cu2NO3(OH)3. Through the cost-benefit evaluation of vacuum distillation, to replace the traditional treatment by vacuum distillation would save 22.49 NT$ per liter of wastewater, confirming that vacuum distillation was economic feasible. Among all tested adsorbent, 50% CuSAC exhibited the greatest Hg adsorption performance, which was much larger than raw AC under N2 environment at 75°C. The Hg removal efficiency of 50% CuSAC significantly decreased at 175°C due to the decomposition of HgS. Comparing to N2 environment, simulated flue gas (SFG) slightly inhibited Hg capture of CuSAC because of adsorption competitive between Hg0 and H2O. In addition, TPD results showed that the principle Hg adsorption mechanism of CuSAC was the reaction between sulfur active sites and Hg0 to form HgS on the adsorbent.