- 學位論文
表面修飾之奈米零價鐵在飽和多孔介質中的傳輸模擬及管柱試驗
Model Simulation and Soil Column Tests of the Transport of Surface-Modified NZVI in Saturated Porous Media
摘要
近年來，在土壤與地下水汙染場址中發現含氯有機物被洩漏至地下水層中。此類物質容易形成比水重之非水相液體 (Dense Non-Aqueous Phase Liquids，DNAPLs)且因其低水溶性及高比重的特性，較難於複雜且未知的地下水層中被移除。因此，要清除被DNAPLs所汙染之場址就需要採用針對此一特性的處理技術。奈米級零價鐵(nano-scale zero valence uron，NZVI)被嘗試使用於處理土壤與地下水汙染，因為奈米顆粒具有高比表面積及高反應性，同時零價鐵亦是良好的還原劑，可以以還原脫氯法來還原含氯有機物質。再者，直接注入法搭配奈米級零價鐵，較固定式的透水性反應牆能更有彈性地針對汙染區域做處理。注入之水相奈米鐵懸浮液隨著地下水流流動，可與DNAPLs之殘餘相及DNAPLs汙染池釋出之汙染物進行反應，清除水體中的有害物質。 學者研究指出直接注入法搭配奈米級零價鐵的處理效果與奈米級零價鐵的懸浮性及移動性極為相關。奈米級零價鐵具有高比表面積因而導致顆粒間的吸引力及接觸機會增加，容易互相吸引團聚成較大顆粒而降低其反應性及移動性。奈米鐵懸浮液的不穩定性主要因為奈米顆粒表面間的作用力以吸引力為主，因而有學者開始使用修飾劑來修飾奈米顆粒的表面性質以降低吸引力，增加排斥力。常見之修飾劑有陽離子型、陰離子型及非離子型界面活性劑以及聚合物。本研究採用前人之研究結果係使用PAA(poly acrylic acid)、CDE(cocamide diethanolamine)及SDS(sodium dodecyl sulfate)三種修飾劑來修飾奈米鐵。奈米鐵的表面修飾可以提供顆粒間的排斥力，例如靜電力(steric repulsion force)、空間阻隔力(steric repulsion force)及震盪結構力(oscillatory force)。排斥力產生能量屏障(energy barrier)，阻擋顆粒間的團聚，進而達到穩定懸浮之效果。 本研究也透過模式模擬及管柱實驗來探討奈米鐵在不同修飾情況下的表現，並考慮顆粒間排斥力的影響。Wei和Wu (2010)建立了一套軌跡模式，預測奈米顆粒在多孔介質中的傳輸行為。本研究運用此模式並加入顆粒間的排斥力於作用力方程式(Newton’s second law)中，使用Chen(2012)的部分實驗參數及文獻值做校正，來預測修飾後之奈米鐵的傳輸行為。模式模擬結果與Chen(2012)的管柱實驗收集效率做比較，顯示加入空間阻隔力之模擬結果與PAA修飾之奈米鐵懸浮液的收集效率是接近一致的。另外，有無加入震盪結構力之模擬結果與CDE及SDS修飾之奈米鐵懸浮液的收集效率比較後，可看出加入震盪結構力的模擬結果更貼近實驗值。因此，在模式中修正顆粒間排斥力，能有效預測修飾後之奈米鐵在飽和多孔介質中的傳輸行為。
並列摘要
Dense Non-Aqueous Phase Liquids (DNAPLs) in the groundwater aquifers cannot be easily removed due to their low solubility and high specific gravity. Cleaning up DNAPLs contaminated sites is challenging. It has been attempted to use nano-scale zero valence iron (NZVI) to treat DNAPLs by direct injection. NZVI is able to reduce chlorinated hydrocarbons through reductive dechlorination. However, due to the high surface area, frequent contact between nanoparticles and high attraction force between particles they could easily aggregate together, form lumps and become unstable in suspension. Surface modifiers may increase electrostatic force, steric repulsion force, or oscillatory force, all of which are able to enhance the stability and mobility of nano-scale particles in aqueous solution. The main purpose of this research is to conduct column tests with surface modified NZVI and perform model simulation with modified Wei and Wu’s model by taking oscillatory force into account. Three different types of surface modifiers, poly acrylic acid (PAA), cocamide diethanolamine (CDE) and sodium dodecyl sulfate (SDS) were used. The results indicate that the simulation of the breakthrough of PAA-modified NZVIs with the consideration of steric repulsion force is consistent with the experimental results. The simulation results of the collection efficiencies of CDE-modified NZVI and SDS-modified NZVI with the consideration of oscillatory force are consistent with the final experimental results. The result has shown that the modified model are able to describe the transportation of NZVI with various surface modification and become an useful tool for predicting the behavior of the nanoparticles moving through saturated soil columns and the collection efficiency of a filter bed.
參考文獻
延伸閱讀
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