Preparation of nanoscale iron suspension for in-situ applications
Date Issued
2006
Date
2006
Author(s)
Yang, Shih-Wei
DOI
zh-TW
Abstract
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.
Subjects
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
Cocoamide DEA
nanoscale iron suspension
trichloroethylene
transport
porous medium
Type
thesis