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
Context of SP Z within the Research Unit Experimental approach
Work schedule of SP Z
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).
Preliminary work and perspectives
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
DOM
e-d
on
ors
term
ina
l e-a
cce
pto
rs
Iron oxide containing aquifer material, sulfate,CO2
electrontransfer
e-shuttle
humic substances, colloids
pathway control
recycling
metabolites
mineral
reactivity
KNO
MEC
RIC
ZWI
KAP
HAD
CH4
Z
PEIPLA
SP Z interfaces ...
• iron, sulfur and OM reactivity and speciation
• bulk- and surface properties of reactive minerals
• macroscopic , spectroscopic & modelling approaches
Mössbauer spectroscopy: .... Principle
12
8
4
0
-10 -5 0 5 10Velocity (mm/s)
1086420
43210
8642086420
hematite
magnetite
goethite
lepidocrocite
ferrihydrite
.... discerns most iron phases at in situ conditions
.... can be surface sensitive by using 57Fe and 56Fe isotopes
57Fe(II)aq sorbs, transfers electrons to hematite,
and becomes 57Fe(III)-hematite
aqueous57Fe(II)
56Fe-hematite
natural hematite
Absorption (%)
-10 -5 0 5 10
Velocity (mm/s)
56hematite pseudocubes
153 uM 57
Fe(I I ) reacted
79 uM 57
Fe(I I ) sorbed
~900 uM 57
Fe(I I ) reacted
2769 uM 57
Fe(I I ) reacted
-10 -5 0 5 10
Velocity (mm/s)
56hematite pseudocubes
153 uM 57
Fe(I I ) reacted
79 uM 57
Fe(I I ) sorbed
~900 uM 57
Fe(I I ) reacted
2769 uM 57
Fe(I I ) reacted
4.2 K
Example: Fe(III) phases formed on 56hematite by heterogeneous oxidation of aqueous 57Fe(II)
Data: Larese-Casanova et al., Univ. Tübingen; 2009 in prep. for ES&T
56hematite
57Fe(II)
Cl-NB Cl-AN
57Fe(III)
56Fe(III) 56Fe(II)
Hematite(antiferromagnetic)
Hematite(weakly ferromagnetic)
Goethite
S
S
FeIII
FeIIFe
bulkmineral
Probered
[CHCl3]
DOMDOSC
Probe ox
[CCl4]
0 06 612 0 12-6 6-12
% A
bso
rpti
on
57CoDetecto
rAbsorber Output
57Fe*
57Fe
57Fe*
57Fe
Source
velocity
- velocity
(mm/s)+
velocity
t = 0 min
t = 360 min
t = 15 min
