|01.05.2010 - 31.10.2011
|NAPASAN - Forschungsverbund
|Bundesministerium für Wirtschaft und Technologie (BMWi)
|Dr. Ulrich Harm
Since some years, iron nanoparticles (so called nanoscale zero-valent iron, nZVI) have been used to treat ground water and rock environment for the decomposition of chlorinated hydrocarbons, heavy metals, radionuclides and other contaminants. This technology started to be used tentatively in U.S.A. several years ago.
The method is based on injection of Fe(0) nanoparticles to ground water through drill holes. Due to nanodimensional character and suitable surface stabilization, the injected nanoparticles can migrate through the rock environment, where they induce reduction reactions with pollutants dissolved in the ground water.
It was experimentally confirmed that by this way, it is possible to eliminate or significantly reduce the content of many toxic substances as for example chlorinated hydrocarbons.
As a consequence of reduction and co-precipitation processes, which occur after application of nano iron, it is also possible to transform a wide variety of heavy metals (for example, Pb, Ni, Cr, Cu, Zn, U, Se) and also highly toxic arsenic into an insoluble form, which remains tightly bounded in the rock environment. Thus, these pollutants can not migrate any more, which leads to a significant reduction of their ecological impacts.
This work is a part of the NAPASAN project, which is dedicated to the development of ferrous nanoparticles for the treatment of contaminants. The particles are modified in such a way that transport in the groundwater zone can take place and contact with contaminants can be achieved to ensure degradation.
The tendency of iron nanoparticles to aggregate after getting in contact with the soil and groundwater is the problem to be solved.
Our primal aim within this project is to develop appropriate coatings, starting with synthesized nanoparticles and proceed with milled nanoparticles.
Synthesized Iron Nanoparticles
A method for the formation of iron nanoparticles covered by surface active agents was developed. The nanoparticles can be coated during their formation process. The function of this coating is to diminish aggregation / precipitation of the dispersed nanoparticles and also to increase their stability. Iron nanoparticles were synthesized by reduction of FeCl2 with NaBH4 in ethanol-water solution in the presence of stabilizing molecule.
Milled Iron Nanoparticles
Ethylene glycol (EG) was found suitable to dissolve nZVI produced by milling process (produced at project partner UVR-FIA) and Methoxyethoxy-ethoxyacetic acid (MEEA) was used to stabilize the nZVI.
The EG-MEEA-nZVI-suspensions are stable over several weeks but oncethe particles get in to contact with oxygen or salts (e.g. drinking water or ground water) precipitation starts immediately. Sodium dodecyl sulfate (SDS) was found to give EG-MEEA-nZVI additional stability against precipitation caused by oxygen and salts. Aggregation of EG-MEEA-nZVI in presence of SDS is inhibited and dispersions in drinking water are stable for several hours.
Summary and Outlook
Aggregation of iron nanoparticles can be strongly reduced by adding stabilizing molecules during the formation process. However, the lifetime of the coated iron nanoparticles is still limited, especially in the presence of air/oxygen or salts (e.g. calcium or magnesium salts in the ground water).
NAPASAN research association
Further information in respect of the whole NAPASAN research association is available via internet at the following link :