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