重金屬污泥之酸萃取暨離子交換

HEAVY METAL SLUDGE TREATMENT BY ACID LEACHING AND ION EXCHANGE

李逸先(I-Hsien Lee)

指導教授 ： 陳嘉明

大同大學/工程學院/化學工程學系所/博士(2007年)

摘要

一般含重金屬之工業廢水多採化學沉澱法處理，此法雖能有效地去除廢水中之重金屬，但重金屬污泥也隨之而生。目前，台灣因科技產業蓬勃發展，大量重金屬之污泥已從全台各地之工業區及科學園區快速累積。因重金屬具毒性之故，含重金屬的污泥亦被歸類為有害事業廢棄物，不能隨意棄置。如果能將污泥中的重金屬移除，使處理過後的污泥通過毒性溶出試驗，則可將之視為一般事業廢棄物，而降低其最終處置成本，而污泥中的重金屬甚至可分離回收，製成有價值的副產品。本計畫研究對象為印刷電路板製程廢水處理所產生的污泥，擬以酸劑萃取配合離子交換法，移除並分離污泥內主要之重金屬銅、鋅、鎘、鉻、鎳、與鐵等。首先以實驗設計法尋找影響本系統之主要因子，並確定此系統對於重金屬之酸瀝取與離子交換回收有明顯的效益。再者，分別探討污泥內酸瀝取重金屬之動力學模式、重金屬與離子交換樹脂之平衡批次實驗及動力學模式、離子交換之管柱試驗。以期最終能設計一結合瀝取反應器與離子交換管柱之複合式系統，有效地分離與回收污泥內之重金屬。同時建立重金屬之萃取與離子交換數學模式，以作為污泥處理程序設計之用。

關鍵字

波傳遞理論 ； 動力學 ； 離子交換 ； 重金屬污泥 ； 實驗設計 ； 管柱動態 ； 酸萃取

並列摘要

A huge quantity of sludge containing heavy metals was and is being generated from wastewater treatment processes in order to treat the industrial wastewaters in Taiwan. Heavy metal sludge is classified as hazardous solid waste and cannot be disposed off because of its toxicity. This study aims at developing a combined acid extraction and ion-exchange process by using ion exchange resin to facilitate remove heavy metals such as copper, zinc, cadmium, chromium, nickel and iron from the sludge generated by a PCB manufacturing plant in Taiwan. Factorial experimental design methodology was first used to study the feasibility of using the combined acid extraction and ion exchange process. The statistical analysis shows that leaching acid and reaction temperature plays an important role in the sludge extraction or metal recovery. The individual extraction kinetic results showed that the metal extraction rates increased with the acid concentration, temperature, but decreased with increasing particle size. Nitric acid was found to be more effective than citric acid to extract the heavy metals from the sludge. The ion-exchange equilibrium data were analyzed by the Langmuir isotherm, Freundlich isotherm, and thermodynamic equilibrium constant approaches. The Langmuir isotherm fits the ion-exchange equilibrium data better than the Freundlich approach. But for ions with different valences such as heavy metal and hydrogen ions the ion-exchange equilibrium was better described by the mass action law using thermodynamic equilibrium constant. The reversible reaction model was capable to predict the effects of resin to solution ratio, initial heavy metal concentration, and temperature on the ion-exchange kinetic curves. The ion-exchange column results showed that the total cation concentration in the mobile-phase played a key role on the breakthrough curves; a higher feed concentration resulted in an earlier breakthrough. The self-sharpening wave model assuming local ion-exchange equilibrium could provide a simple and quick estimation for the breakthrough volume, but the predicted breakthrough curves did not match the experimental data very well. On the contrary, the constant-pattern wave model using a constant driving force model for finite ion-exchange rate provided a better fit to the experimental data. The obtained liquid-phase mass transfer coefficient was correlated to the flow velocity and other operating parameters; the breakthrough curves under varying operating conditions could thus be predicted by the constant-pattern wave model using the correlation. Experiments carried out in a re-circulation system including a leaching reactor and an ion-exchange column supported the concept of enhanced heavy metal leaching from the sludge and heavy metal recovery by the ion exchange resin. A mathematical model for batch heavy metal extraction in the presence of ion-exchange resin was established for the purpose of process design for sludge treatment.

並列關鍵字

heavy metal sludge ； experimental design ； column dynamics ； acid extraction ； wave propagation theory ； ion-exchange ； kinetics

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