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DFG Research Unit 580: Electron transfer processes in anoxic aquifers

Source. Absorber. Detector. Output. 57 Co. 57 Fe*. 57 Fe*. 57 Fe. 57 Fe. velocity. (mm/s). Cl-NB. Cl-AN. - velocity. 57 Fe(II). 57 Fe(III). 56 Fe(III). 56 Fe(II). 56 hematite. % Absorption. 0. 6. 12. 6. 0. -12. -6. 0. 6. 12. + velocity. KAP. ZWI. RIC. PLA. MEC.

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DFG Research Unit 580: Electron transfer processes in anoxic aquifers

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  1. Source Absorber Detector Output 57Co 57Fe* 57Fe* 57Fe 57Fe velocity (mm/s) Cl-NB Cl-AN - velocity 57Fe(II) 57Fe(III) 56Fe(III) 56Fe(II) 56hematite % Absorption 0 6 12 6 0 -12 -6 0 6 12 + velocity KAP ZWI RIC PLA MEC KNO PEI HAD 4.2 K recycling humic substances, colloids e-shuttle metabolites Iron oxide containing aquifer material, sulfate,CO2 mineral reactivity electrontransfer DOM e-donors terminal e-acceptors CH4 pathway control Z DFG Research Unit 580: Electron transfer processes in anoxic aquifers SP Z: Mössbauer spectroscopy and speciation modelling Stefan Haderlein and Stefan Peiffer University of Tübingen , University of Bayreuth • Objectives: • Elucidation of reactive iron species and phases in geochemically heterogeneous anoxic aquifer systems: • Design and apply Mössbauer experimental setups for in situ process identification • Identify iron species & phases, reactive intermediates and dynamic surface processes in Fe-S-DOM systems • Quantify key geochemical processes by chemical speciation modelling Context of SP Z within the Research Unit Experimental approach Mössbauer spectroscopy: .... Principle .... discerns most iron phases at in situ conditions • SP Z interfaces ... • iron, sulfur and OM reactivity and speciation • bulk- and surface properties of reactive minerals • macroscopic , spectroscopic & modelling approaches .... can be surface sensitive by using 57Fe and 56Fe isotopes aqueous 57Fe(II) 56Fe- hematite 57Fe(II)aq sorbs, transfers electrons to hematite, and becomes 57Fe(III)-hematite natural hematite Preliminary work and perspectives Work schedule of SP Z Example: Fe(III) phases formed on 56hematite by heterogeneous oxidation of aqueous 57Fe(II) t = 0 min • Speciation of Fe in the presence of natural organic matter and effect(s) of OM on iron mineral geochemistry ( SP HAD, SP KAP, SP ZWI, SP MEC). • Mineralogy and dynamics of iron phases formed in Fe-S systems ( SP PEI, SP PLA, SP HAD). • Mineralogy and speciation of iron phases formed in Fe-S-DOM systems( SP PEI, SP PLA, SP KNO, SP HAD, SP ZWI). • Quantitative description of geochemical processes by chemical speciation modelling ( SP PEI, SP HAD, SP ZWI, SP KAP). t = 15 min t = 360 min Hematite(weakly ferromagnetic) Hematite(antiferromagnetic) Goethite Data: Larese-Casanova et al., Univ. Tübingen; 2009 in prep. for ES&T

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