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Institut für Wasser- und Umweltsystemmodellierung - IWS



"Transport of zero-valent iron colloids in aquifers "

Reactive zero-valent iron is currently being used for remediation of contaminated groundwater. Permeable reactive barriers are the current state-of-the-art method for using zero-valent iron. Instead of an excavated trench filled with granular zero-valent iron, a relatively new and promising method is the injection of a nano- to micro-scale zero-valent iron colloid suspension in the subsurface using injection wells. The goal is to deposit the iron in the aquifer and hence form a reactive permeable zone which is no longer bound to limited depths and plume treatment, but can also be used directly at the source. A good understanding of the transport behavior of zero-valent iron colloids is necessary to design a field application. So far, there are no measuring techniques available to continuously and non-destructively determine the iron colloid concentration in the soil directly. Hence, the spreading and distribution of the iron in the subsurface during injection could not be proven.
In the presented work, column experiments were conducted to better understand transport phenomena of iron colloids in porous media and to find constitutive relations of the parameters controlling the transport in the subsurface. Based on the columns, large scale experiments with a radial flow field and, hence, a hyperbolically decreasing velocity profile, were conducted. Within these large container experiments a radial symmetrical spreading with a radius of close to two meters was possible.
Parallel to the transport experiments measuring devices with a very high resolution based upon magnetic susceptibility have been developed to non-destructively determine the concentration of nano-scale iron during and after the injection in a column as well as the large (field-) scale container experiment. The new method was used to quantitatively monitor movement of iron colloids throughout the injection.
To predict the results of the large scale experiment and later a field application, a method is being developed to upscale the results from column experiments. Additionally, within the ongoing EU research project AQUAREHAB the measuring technique is being further developed to make it suitable for field usage.