以使用過的綠茶茶葉與咖啡渣
萃取銅、鎘及鉛離子

資源回收沖泡過的綠茶茶葉與咖啡渣作為吸附重金屬的材料對於廢水中之重金屬具有良好的吸附能力；因茶葉與咖啡渣結構中帶有大量的羥基、胺基之官能基與纖維成分會與金屬離子形成螯合或離子吸附作用，且經過不同pH處理後的綠茶茶葉與咖啡渣更容易與重金屬離子形成螯合或離子吸附作用；所以本實驗是將綠茶茶葉與咖啡渣烘乾磨碎後找出適用的緩衝溶液並探討在不同緩衝溶液的環境中不同pH值對吸附能力的影響；於實驗結果得知銅、鎘及鉛離子吸附之最佳pH條件分別為: pH=5.3、pH=6.7及pH=4.8以原子吸收光譜偵測其量，綠茶茶葉對銅、鎘及鉛離子去除率分別為76%、87%及90%；咖啡對銅、鎘及鉛離子去除率分別為82%、90%及85%。在不會產生沉澱的狀況下以最佳pH值對銅、鎘及鉛三種有毒金屬進行2.5 小時恆溫振盪吸附實驗，結果顯示在前1小時的吸附效果非常快速；綠茶茶葉與咖啡渣萃取銅、鎘及鉛離子的最佳時間分別為90分鐘與60分鐘；鎘的最佳時間分別為60分鐘與45分鐘；鉛為45分鐘與90分鐘吸附趨近平衡。以真實樣品維萃取後再以1M硝酸酸洗的結果進一步證明綠茶茶葉與咖啡的吸附型態主要不是藉著靜電吸引，乃是藉由離子產生鉗合或吸附作用。由實驗結果之濃度取對數求得動力學關係式為ln〔A〕＝-kt＋ln〔A〕0，斜率k；得知實驗之反應速率為一級反應；本實驗只需以簡單的前處理過程資源回收使用過的綠茶茶葉與咖啡渣，應用在移除水中的重金屬是既有效又符合經濟效應。

關鍵字

萃取；重金屬

並列摘要

Resource reutilization is and will be an excellent way to fight resource insufficiency in the ever expanding human population. Spent green tea leaves and coffee ground can be used as good sorbents for removing heavy metal ions in aqueous solutions due to the high carboxyl amine group content and fiber composition. The pH for optimum extraction with both green tea leaves and coffee ground was determined to be 5.3, 6.7, and 4.8 for copper, cadmium, and lead, respectively. The removal efficiencies for copper, cadmium, and lead by green tea leaves are 76%, 87%, and 90%, respectively, while those by coffee ground are 82%, 90%, and 85%, respectively under optimum pH condition. Under room temperature and for 2.5 hours of continuous shaking at the optimum pH condition, sequential analysis of the extract shows that the adsorbing is very fast in the first hour and follows first order kinetics. However, the removal rate is quite slow. For green tea, the time it took to reach equilibrium was 90, 60, and 45 minutes for copper, cadmium, and lead, respectively. For coffee ground, the time was 60, 45, and 90 minutes, respectively. Back extraction of metal ions from both matrices performed by washing the extractants with 1 M nitric acid shows that less than 10% of the ions were leached out, indicating that the principal mechanism involved is by chelation of the heavy metal ions by the abundant carboxyl amine groups and fiber content in both matrices. This result indicates that spent green tea leaves and coffee ground can be economic and effective materials to remove some heavy metals from contaminated aqueous solutions.