Application of ultrasonically produced nano zerovalent iron for the degradation of chloroethenes

Andreas Tiehm 1Aharon Gedanken 2

1. Water Technology Center (TZW), Karlsruher Str. 84, Karlsruhe 76139, Germany
2. Bar-Ilan University, Ramat-Gan 52900, Israel

Abstract

Halogenated pollutants, such as chlorinated ethenes, are the most often found contaminants in subsurface environments. In recent years, it has been demonstrated that zerovalent iron (ZVI) can be used to dehalogenate chloroethenes and chloroethanes due to hydrodechlorination. For example, perchloroethene (PCE) is essentially reduced completely to ethane with ZVI:

C2Cl4 + 5 Fe + 6 H+ → C2H6 + 5 Fe 2+ + 4 Cl-

In-situ zerovalent iron permeable barriers have been implemented for the treatment of chlorinated solvents contaminated groundwater. However, the construction of permeable barriers is very expensive due to high investment costs. The direct application of nanosized materials in the subsurface represents a more cost-efficient alternative. Nanoscale iron particles would provide enormous flexibility for in situ applications. However, pure iron nanoparticles have no protective shell on the surface and hence they are not stable in contact with air. On the contrary, they are pyrophoric and burn spontaneously upon exposure to air.

Therefore, a new sonochemical method was developed to prepare air stable iron nanoparticles in the presence of commercial edible oils. The sonochemistry leads to the formation of iron nanoparticles surrounded by a polymer. Air stability was demonstrated for several months. Our study focussed on the dechlorination activity of the novel nanoparticles.

The air-stable nanoparticles were added to polluted groundwater samples containing approx. 1 mg/l PCE. As a result, the new material proved to be efficient for PCE dechlorination. More than 50 % of the initial PCE was completely dechlorinated to ethene and ethane. As compared to conventional ZVI, that is used for Permeable Reactive Barriers, the reactivity of the nanomaterial is approx. 10 times higher. The experiments demontrate the high potential of the material for environmental remediation.

Keywords: chloroethenes, nanoparticles, dehalogenation, groundwater, remediation

Acknowledgement: This cooperation was stimulated by COST D32 "Chemistry in High-Energy Microenvironments". The authors gratefully acknowledge financial support
 

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Presentation: Poster at COST action D32 Mid term evaluation meeting, by Andreas Tiehm
See On-line Journal of COST action D32 Mid term evaluation meeting

Submitted: 2006-03-24 13:36
Revised:   2009-06-07 00:44