化學機械研磨廢水混凝沈澱效能之評估

Abstract

半導體製造業為我國最重要產業之一，由於精密度要求的提升，製程所須求之用水量及其排放之廢水量也是與日俱增，其中研磨廢水的處理問題在未來也會逐漸浮上檯面。目前絕大部分的半導體廠皆以化學混凝沉澱方式來去除研磨廢水中的懸浮固體，廢水中顆粒特殊，具有粒徑微小、粒徑分佈範圍狹窄及擁有極強的界達電位特性，因此造成混凝沉澱操作的效能不彰普遍有大量加藥的現象。 本研究以實廠廢水進行實驗，分為金屬膜研磨廢液及氧化膜研磨廢液兩種，觀察不同混凝劑（氯化鐵、氯化亞鐵、硫酸亞鐵、多元氯化鋁及幾丁聚醣）及搭配藥劑（活性白土、聚丙烯醯胺等）對濁度去除之表現。結果顯示，欲有效處理研磨廢水，以先達到顆粒吸附及電性中和的去穩定步驟後，再輔以增重、架橋或沈澱掃除的方式加速沈澱，若掌握此原則，大部分的混凝劑即可達到90%左右的去除率，且可節省不少藥劑使用量。 如果在進行混凝步驟前先對研磨廢水顆粒進行酸洗步驟，以去除顆粒之穩定性，可增加混凝時之最適pH值範圍，使pH控制操作方便，除此之外，也可在相同藥劑使用量下，將濁度去除率提升至98.5%以上。

Semicondoctor Manufacturing is one of the most important industries in Taiwan. With respect to promoting precision, the amount of consuming water and discharging wastewater are steadily on the increase. And the problem of Chemical Mechanical Polishing (CMP) wastewater treatment is going to appear soon. At present the majority of semicondutor factories remove the suspended solids from CMP wastewater by coagulation and sedimentation. Particles in CMP wastewater are tiny, with narrow size distribution, and have remarkable Zeta potential. Due to these special properties of theses particles, and so the coagulation performs bad that increase a lot of coagulant dosage. In this study, we evaluated the turbidity removal efficiency of metal CMP spent slurry and oxide CMP spent slurry by using various coagulant including ferric chloride, ferrous chloride, ferrous sulfate, PAC, and chitosan, with the aid of activated clay, polyacrylamide, et al. Results indicate that if we depend on the principle which destabilize these particles first and then accelerate the sedimental velocity by weighting, bridging, or sweeping, we can get about 90% efficiency with most types of coagulants, and economize much coagulant dosage. If we acid wash to destabilize the particles before the coagulation, we can make convenience of pH control due to the broader optimum pH range. And we will promote the efficiency to 98.5% by the same dosage.