奈米級零價鐵懸浮液之製備及於土壤飽和層中傳輸模擬之研究

Abstract

以直接注入零價鐵之方式來處理受含氯有機物污染之地下水，已有廣泛之研究及應用。然因鐵顆粒於地下環境中之低傳輸性而侷限了此法之成效及提高處理之成本，因此若能以表面改質之方法提高奈米鐵顆粒於多孔性介質中的傳輸性，必能彰顯此整治方法之優勢。 本研究加入不同之穩定分散劑以批次式製備奈米級懸浮液，並探討其穩定分散之能力。其中以聚丙烯酸 (PAA) 為分散劑以及最終PAA及總鐵之濃度均為5000ppm時有最好之懸浮性。所得之奈米鐵懸浮液可於28天後仍持續90%以上之懸浮效果。鐵顆粒之平均粒徑約為87 nm。SEM-EDS 觀察顯示奈米鐵顆粒似包裹於含氧量較高之穩定分散劑中 ，基本之粒徑約為200 nm左右。以奈米鐵懸浮液注入10 cm、20 cm及30 cm之土柱實驗中，其濃度之穿透率分別為75.6 %、61 %及41 %，經計算得知奈米鐵顆粒隨距離被滯留之衰減係數κ為0.01cm-1。 最後以顆粒之表面性質分析及土柱穿透試驗之結果撰寫奈米鐵顆粒於土壤中傳輸之模式。模式之內容為以楔型管模擬土壤顆粒之孔洞，在楔型管內對粒子進行跡軌分析以探討其於土壤表面之吸附情況，使得顆粒穿透土柱之情況在電腦之計算中重現。比較鐵顆粒穿透10cm土壤時穿透率之模擬值與實驗值可發現，模式有高估之現象。假設此誤差為被過濾粒子之粒徑於楔型管內改變而導致，調整粒徑為1000 nm 、堵塞係數α為5及考慮布朗運動造成之影響時，模擬之結果與實驗結果則較為吻合。

Direct injection zero valent iron method has been widely used for treating chlorinated hydrocarbon contaminated groundwater aquifers. However, the efficiency decreases and the cost rises due to the poor spreading ability of iron particles in the subsurface environment. Therefore, if we can enhance the spreading ability of iron in porous media by adding surface modifier we may increase the applicability of iron particles. We used different stabilizing to produce nanoscale iron suspension by means of batch experiments. Also we evaluated the performance of the stabilizing dispersants. It was found that PAA can get the most stable suspension when the final concentration of PAA and total iron were both 5000 ppm. About 90% of the nano-particles remained in suspension for 28 days. The average particle sizes was 87 nm determined by ZetaSizer. Particle sizes were all found to be around 200 nm and the particles seemed to be wrapped in high oxide-containing stabilizing dispersants under the examination with SEM-EDS. Percolation rates of nanoscale iron particles through the soil was tested using column experiments. The percolation results for soil columns with depth of 10 cm, 20 cm and 30 cm were 75.6%, 61%, and 41%, respectively; and the decay coefficient (κ) of the suspended nanoscale iron particles per unit distance was 0.01 cm-1 A transport model of NZVI in saturated soil layer was constructed. The pore structure in soil layer was characterized by the constructed tube model. The absorbing situation of particle of soil surface was determined by trajectory analysis in the constricted tube. The modeling analyses and experimental results indicate that the prediction has over estimated the breakthrough concentration . Simulation value relatively conforms the experimental value when adjusting the diameter of the particles and considering Brownian forces.