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DFG Research Unit 580: Electron transfer processes in anoxic aquifers PowerPoint PPT Presentation


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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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Dfg research unit 580 electron transfer processes in anoxic aquifers

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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