Investigation for the Long-Term Reactivity of elemental iron Materials (DFG - No 626/2-1)

Hydrochemie6

The phenomenon of contaminant removal from aqueous solutions in the presence of elemental iron materials (metallic iron, zerovalent iron or Fe0) is an ongoing research area (iron wall technology). Contaminant removal in Fe0–H2O systems involves a series of mechanisms such as: adsorption, co-precipitation, surface precipitation, and reduction. It has been generally accepted, that abiotic contaminant reduction through electrons from the bulk metal (Fe0) is the major contaminant removal pathway. However, it is currently acknowledged that the real decontamination mechanisms have not yet been completely elucidated. Next to the mechanism of contaminant removal, the longevity of iron walls is the other major problem making iron wall technology an experimental technology. The longevity is defined as the length of time that a wall continues to treat groundwater to design levels. The long-term behaviour of an iron reactive wall has two distinct aspects: (i) the long-term efficiency of Fe0 for contaminant removal (long-term reactivity), (ii) the build-up of mineral precipitates possibly yielding to permeability decrease (long-term permeability). The build-up of microbial biomass affects both aspects (reactivity and permeability). There is currently a disagreement about what factors control iron walls longevity.

This project aims at investigating the long-term reactivity of iron materials in long-term undisturbed batch experiments and in column studies. Beside column studies, undisturbed batch experiments (stirred at 0 rpm) are selected because they allow the formation of an universal oxide-layer at the Fe0 surface. The reactivity of Fe0 materials will be access upon their ability to avoid/retard uranium release in the aqueous phase. The uranium source is a well-characterized ore bearing rock. In clear, uranium release will be characterized in preliminary experiments and the results will be used to optimised Fe0 characterization tests. Parallel experiments will be conducted with different Fe0 materials (“rock + Fe0” systems) and the Fe0 free system as reference. The impact of selected significant variables (alkalinity, Cl-, EH, PO43-) on the reactivity of Fe0 materials will be investigated.
Beside a better characterization of the long-term reactivity, a purposeful procedure for site specific material selection is expected.