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Fast formation of supergene Mn oxides/ hydroxides in the oxic transition zone of a shallow aquifer in interaction with quaternary sediments

Franziska Schäffner1, Dirk Merten1, Giovanni De Giudici2, Sven Linzen3, Georg Büchel1
1 Friedrich Schiller University, Institute of Geosciences, Applied Geology, Jena, Germany
2 University of Cagliari, Department of Chemical and Geological Sciences, Cagliari, Italy
3 Institute of Photonic Technology, Department of Quantum Detection, Jena, Germany

P 6.14 in Groundwater, soil and surface water interactions

The formation of near-surface supergene Mn-oxides/ hydroxides in an area influenced by former U mining activities (Ronneburg, Germany) could be classified as a natural attenuation process for certain heavy metals, e.g. Cd, Ni, Co and Zn. As a consequence of geologically fast formation the supergene mineralization provide a cost efficient contribution for remediation of residual contaminated substrates, e.g. glacial sediments. The secondary minerals occur as colored layers close to the shallow aquifer in glacial sediments in a former U leaching heap area (heap Gessen) and could be identified as birnessite and todorokite as Mn minerals and goethite as the Fe mineral. Eh/pH stability fields reveal that the formation of goethite is favorable under the given physicochemical conditions (acidic and oxic) whereas Mn exists at the border of soluble Mn2+ and the stable MnO2. Different morphologies of mineralization (Liesegang bands, compact layer - both with acicular or layer like structures) are dependent on different water flow regimes according to different stages during remediation. The Mn-oxides in Ronneburg can be discussed under the aspect of supergene mineralization deposits as they occur relatively close to the surface, are not strata bound and include processes of circulating meteoric water with concomitant oxidation and chemical weathering. Furthermore, they occur within a relatively small timeframe of 3-9 years and therefore developed independently and long time after the sedimentary adjoining Quaternary deposits. For examination of the hypotheses for the formation of the supergene mineralization a special designed lysimeter approach was developed. The predominant phases observed in the field: Mg phase (evaporative salts), Fe phase (goethite), Mn phase (Mn-oxides/ hydroxides) and Al phase could be simulated in the lysimeter experiment due to capillary rise of contaminated groundwater. Additionally, a microbe mineral interaction for the Mn phase is hereby likely since Mn-oxides occur in the lysimeter next to organic material and microbes and as physicochemical conditions do not reveal the formation of solid Mn phases. Further, a SQUID (Superconducting Quantum Interference Device) gradiometer technique was applied for the first time to monitor the formation of the magnetic mineral phases.   

last modified 2013-11-01