Geochemistry at the nanoscale: chemistry of fluid-mineral interfaces, phytoremediation, nanotoxicology - Roland HELLMANN, Géraldine SARRET & ...
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Geochemistry at the nanoscale:
chemistry of fluid-mineral interfaces,
phytoremediation,
nanotoxicology
Roland HELLMANN, Géraldine SARRET & Laurent CHARLET
Environmental geochemistry group, Geochemistry ‘4D’
Institute for Earth Sciences. Grenoble
ISTerre
ISTerre
Institute for Earth Sciences
University of Grenoble, CNRS UMR 5275
Observatory for Earth, Planetary and Space Sciences
(OSUG)
Who we are and what we do:
ISTerre is dedicated to the study of the Earth using
Physics, Chemistry, and Geology
Geochemistry Mineralogy
Seismic cycles & deformation Geo-risks
Waves and structures Fault mechanics
Geophysics of volcanoes Tectonics
Geodynamo of Earth’s core
ISTerre Grenoble: 260 people total, with 95 researchers, 40 scientific staff
Environmental geochemistry group-
key nanoscience research areas:
• Biogeochemistry of metal contaminants (soils, plants)
• Nanoparticles and health issues
• Chemical reactivity of minerals, glasses, nanoparticles
• Geological sequestration mechanisms (radwaste, CO2)
Chemistry of fluid-mineral interfaces at the nanoscale, applied to chemical weathering roland.hellmann@obs.ujf-grenoble.fr Why is chemical weathering important? • controls element cycling on Earth’s crust • major abiotic sink for CO2 atm- climate control • environmental issues (As contamination) • geological burial of radwaste, sequestration of CO2
Chemical weathering:
investigations at which scale?
101- 104 m
watershed scale
outcrop scale
10-2- 101 m
laboratory scale:
10-5- 10-2 m rate laws
µm scale:
CEKA, Penn State
10-7- 10-5 m etch pits
mineral Å-nm scale:
10-9- 10-7 m interface chemistry,
structure of
interfaces
altered zone
Understanding the mechanism
of chemical weathering: evolution of fluid-
fluid-solid interface
the interface is where all exchange of
matter and energy occurs
between fluid and solid
(via: dissolution, precipitation, oxidation/reduction, adsorption, absorption, ion exchange, catalysis)
energy, matter
fluid solid
structural, chemical evolution of interface (near-surface region)
molecular-level reactions = analytical methods at (sub-) nm resolution
mechanism at this scale
influences behavior at macroscopic scale,
both in laboratory and in field
prevailing concept for chemical weathering
leached layer is an amorphous relict structure:
(structurally contiguous with unaltered mineral)
thickness depends on mineral & fluid (pH, etc.)
Chemical weathering investigated using surface sensitive methods:
evolution of structure + chemistry of fluid-
fluid-mineral interface
classical methods: (70’s to present)
ion, X-ray, or electron beam incident to surface
(SIMS, XPS, Auger, RNRA, RBS, etc.)
altered layer
interface
µm-mm
SIMS ARXPS
mineral
fluid altered zone mineral
conc.
profile obtained
by surface
incident beam
depthChemical weathering investigated using surface sensitive methods:
evolution of structure + chemistry of fluid-
fluid-mineral interface
classical method: (70’s to present) new method: prep in cross section
ion or electron beam incident to surface FIB (or ultramicrotome) + TEM
altered layer
altered layer
interface
µm-mm
mineral mineral
SIMS ARXPS
µm-mm beam size (poor lateral resolution) nm TEM probe
chemical profiles obtained indirectly- : meas. chemical profiles direct
a) deconvolution of chemical profiles
b) ion beam-solid interactions
c) thin layers (sample preparation in cross section (TEM foil):
(from Wirth, 2004)
a. ultramicrotomy (difficult)
b. focused ion beam (FIB)
+ fast, choice of study area
- costly, creation of artefacts
(ultrathin section 15µm x 5 µm x 50-100 nm)
outer interface
inner interfaceNew methods new results . . .
laboratory weathering (silicates):
labradorite feldspar
wollastonite
garnet
natural weathering:
K-feldspar in soil/surface of granite
lizardite/lichen in serpentinitel’interface fluide-solide à une échelle nanométrique
chain silicate: wollastonite
BF image
physical separation ?
EFTEM profilestectosilicate: labradorite feldspar
400 nm-thick alt. layer,
pH 1, 25 °C
EDX line scans +
SIMS H profile
HRTEM EFTEM Ca EFTEM Sitectosilicate:
l’interface labradorite feldspar
fluide-solide à une échelle nanométrique
differences in ELNES fine structure
sp2-modif.sansBkgd (Al)
40 unaltered
35 } interface
Al K edge altered
30
CCD counts x 1000
25
20
15
10
5
0
1550 1600 1650 1700 1750 1800
Energy Loss (eV)
EELS: information on atomic environments, e.g. coordination, oxidation state1.00
-16
DH = 10
0.90
0.80
0.70
-15
DH = 10
0.60
[M ] [A.U.]
z=1
0.50 z=2
z+
z=3
0.40
-14
DH = 10
0.30
0.20
0.10
0.00
0 250 500 750 1000
Depth [nm]
DH (H+ diffusion coefficient), DH / Dcation = 10-3
cation valence (z)
a = 10-2 Å s-1Chemical weathering in the field:
can we identify sharp chemical and structural
interfaces on minerals altered in field?
Pte. Andey, Hte. Savoie
case 1
EMSI Stanford
zone critique
EMSI-Stanford
glacial erratic granitic boulder,
10Be age ~ 14 ka,
multi-mineral
2 environments of alterationK-feldspar
massive overlayer
surface altered layer
crystalline K-feldsparK-feldspar
Chemical maps: EFTEM
Si map
amorphous layer
K profile
K-feldspar
amorphous layer
Al map
HRTEM
K-feldsparcoupled interfacial dissolution-
dissolution-reprecipitation mechanism
(a unifying mechanism for chemical weathering)
1. advance of reaction front into mineral is a chemical hydrolysis reaction, not
interdiffusion (all bonds are broken, no relict structure present)
2. intrinsic dissolution process (i.e. at interface of unaltered mineral) is
stoichiometric at all pH conditions (no pH-dependent preferential release).
3. precipitation of Si-rich (acid pH) amorphous hydrated phase, permeable
4. ion exchange can occur, but only at surface (see e.g. Fenter et al., 2000)Large scale or global implications for surface altered layers
created by dissolution-reprecipitation
std. carbonation reaction:
MeSiO 3 CO 2 2H 2 O MeCO 3 H 4SiO 4
carbonation reaction, metals co-precipitate in silica layer:
MeSiO 3 (1 )CO 2 xH 2 O (1 )MeCO 3 SiO 2 MeO xH 2 O
net effect: less CO2 sequestered per mole of mineral reactant !
implications for CO2 uptake during weathering, CCSTransmission Electron Microscopy + SIMS
METSA Platform CNRS + CEA
R. Wirth GFZ Potsdam, Germany
J.--M. Penisson
J. CEA Grenoble, France
J.--P. Barnes. B. Florin
J. LETI CEA Grenoble, France
T. Epicier INSA Lyon, France
R. Hervig Arizona State Univ., USA
Belledonne Massif, GrenobleYou can also read
