DFG Research Unit 580 Electron transfer processes in

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: Ø Design and apply Mössbauer experimental setups for in situ process identification Ø Identify iron species & phases, reactive intermediates and dynamic surface processes in Fe-S-DOM systems Ø Quantify key geochemical processes by chemical speciation modelling Experimental approach Context of SP Z within the Research Unit Source Mössbauer spectroscopy: . . Principle recycling KAP e-donors DOM humic substances, colloids e-shuttle ZWI RIC 57 Fe* 57 Fe MEC electron transfer Z mineral HAD reactivity CH 4 pathway control terminal e-acceptors metabolites PEI 57 Fe* Detector Output % Absorption PLA Absorber 57 Co 0 6 12 6 0 -12 -6 + velocity Iron oxide containing aquifer material, sulfate, CO 2 0 velocity (mm/s) . . discerns most iron phases at in situ conditions SP Z interfaces. . . . can be surface sensitive by using 57 Fe and 56 Fe isotopes • iron, sulfur and OM reactivity and speciation Preliminary work and perspectives • bulk- and surface properties of reactive minerals • macroscopic , spectroscopic & modelling approaches 56 Fe- aqueous 57 Fe(II) Work schedule of SP Z hematite 57 Fe(II) natural hematite sorbs, transfers electrons to hematite, and becomes 57 Fe(III)-hematite aq Cl-NB Cl-AN Fe(III) phases formed on 56 hematite by heterogeneous oxidation of aqueous 57 Fe(II) 56 Fe(III) 12 - velocity KNO Example: 6 57 Fe(III) 56 Fe(II) 56 hematite t = 0 min Ø 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). t = 15 min t = 360 min Ø Mineralogy and dynamics of iron phases formed in Fe-S systems ( SP PEI, SP PLA, SP HAD). Hematite (weakly ferromagnetic) Hematite (antiferromagnetic) Ø Mineralogy and speciation of iron phases formed in Fe-S-DOM systems ( SP PEI, SP PLA, SP KNO, SP HAD, SP ZWI). Goethite 4. 2 K Data: Larese-Casanova et al. , Univ. Tübingen; 2009 in prep. for ES&T Ø Quantitative description of geochemical processes by chemical speciation modelling ( SP PEI, SP HAD, SP ZWI, SP KAP).