應用於現地注入之奈米鐵 懸浮液製備研究

Preparation of nanoscale iron suspension for in-situ applications

楊士衛(Shih-Wei Yang)

指導教授 ： 吳先琪

國立臺灣大學/工學院/環境工程學研究所/碩士(2006年)

https://doi.org/10.6342/NTU.2006.02435

摘要

三氯乙烯及四氯乙烯等含氯有機物釋放到地下水中，會形成比水重非水溶性液體相（DNAPL），過去常用抽取處理法（pump and treat）進行整治，依據經驗，以此法進行整治需耗費較長時間及大量成本，故開發高效率及低成本的整治技術，已是目前研究方向。
值得注意的是，USEPA指出透水性反應牆已是一個標準成熟的整治技術，其中填充材料以零價鐵金屬為主，而零價鐵顆粒脫氯機制，在理論及學理上已經明瞭。若能結合奈米技術，將金屬顆粒奈米化，則可提高其反應性及在多孔介質中之穿透性，再以鑿井方式將奈米鐵顆粒注入地下含水層中，以形成反應鐵牆方式阻擋污染源之擴散。
濃度高之奈米金屬懸浮液中，粒子與粒子間的距離很小，彼此容易吸引團聚在一起，而失去奈米顆粒在地下水中傳輸的優勢。為了抑制此效應，本研究使用不同的穩定分散劑，以批次方式探討鐵顆粒在懸浮液中的穩定分散效果。再以實驗所得較佳條件，以硫酸亞鐵及硼氫化鈉為原料(0.0225M FeSO4 及 0.125M NaBH4)及添加穩定分散劑CDE於硼氫化鈉溶液槽中(最終濃度為5000 mg/L)，以連續迴流方式製備奈米鐵懸浮液。所得之奈米鐵懸浮液在4天內，均維持100 % 之懸浮效果。以ZetaSizer測得懸浮顆粒之大小介於 300 nm 至 600 nm 之間。以電子顯微鏡觀察奈米鐵顆粒似包裹於界面活性劑中，基本顆粒大小約小於100 nm。
實驗最後進行奈米鐵懸浮液貫穿土壤管柱試驗及進行污染物脫氯反應測試。以奈米鐵懸浮液貫穿10 cm土柱、20 cm土柱及40 cm土柱實驗結果，其貫穿率分別為33%、19.3% 及8.2%，經計算得知奈米鐵顆粒隨距離被留滯之衰減係數κ為0.0963 cm-1。以含污染物（TCE）之溶液注入含奈米鐵之土柱進行脫氯實驗，結果顯示去除率經回收率校正後為 54.4%。
未來還需加強奈米鐵顆粒在土柱中的貫穿能力，建議後續實驗可適度降低硼氫化鈉使用量。

關鍵字

DNAPL ； 椰子油乙二醇醯胺 ； :奈米鐵懸浮液 ； 三氯乙烯 ； 傳輸 ； 多孔介質

並列摘要

Chlorinated hydrocarbons such as trichloroethene, tetrachloroethylene, etc. can leach into groundwater and form dense non-aqueous phase liquid（DNAPL）. The commonly used method of Pump and Treat is known to be time-consuming and costly; therefore, the objective of this research is to develop a more efficient and cost-effective groundwater remediation method.

It is important to note that USEPA has already claimed that permeable reactive barrier is a mature and standard technology. With zero-valent iron as its principal filling and the chemical mechanism of chlorinated hydrocarbon removal fully understood, an integration with the nano-technology may enhance its performances. Metal particles can be nanonized to be more active and become easier to spread through porous media. When nanoscale zero-valent iron is injected into the underground aquifer through the injection well, an “iron wall” is formed to prevent the contaminants from further migrating.

In highly-concentrated metallic nanoparticle suspension, with the distance between particles very small, particle aggregations tend to happen, which in turn will slow down their distribution in groundwater. To solve this problem, this research first used different stabilizing dispersants to see how iron particles were dispersed in the suspension. Next, optimal results from the batch experiment were applied to make a nanoscale iron suspension by means of continuous circulation, with sodium borohydride and ferrous sulfate as raw materials, and CDE, a stabilizing dispersant, added into sodium borohydride solution (final concentration 5000mg/L). This suspension was maintained 100% of nanoparticle suspension stability for four days. The particle sizes measured to range from 300 nm to 600 nm, with the use of the Zetasizer. With a scanning electronic microscopy, particle sizes were all found to be less than 100nm and the particles seemed to be wrapped in surfactant.

The last stage of the experiment with the nanoscale iron suspension was to test its percolation rates through soil columns and TCE dechlorination rates. The percolation results for soil columns that were 10cm, 20cm and 40 cm long were 33%, 19.3%, and 8.2%, respectively; and the decay coefficient (k) of the suspended nanoscale iron particles per unit distance was 0.0963 cm-1. By injecting the solution laden with TCE into soil columns containing nanoscale iron, the dechlorination rate is 54.4%.

To heighten the percolating ability of nanoscale iron particles through soil columns, less doses of sodium borohydride solution is suggested for future experiments.

並列關鍵字

DNAPL ； Cocoamide DEA ； nanoscale iron suspension ； trichloroethylene ； transport ； porous medium

參考文獻

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