0 10 20 30 40 50 60 70 3 5 7 9 11 Eu (I II ) s u rf ac e c o n ce n tr at io n (n m o l E u /m ² α -Al 2 O 3 ) pH data 0.1M data 0.01M model 0.1M model 0.01M 0.0E+00 1.0E-08 2.0E-08 3.0E-08 4.0E-08 5.0E-08 6.0E-08 7.0E-08 8.0E-08 0 20 40 60 80 Eu( III ) sur face c once ntr at ion (m ol /m ²) R (mg/g) data pH = 3.9 data pH = 6.2 ± 0.2 data pH = 7.4 ± 0.2 model pH = 3.9 model pH = 6.2 ± 0.2 model pH = 7.4 ± 0.2 0 1 2 3 4 5 4 5 6 7 8 9 10 7
F
2/
7F
1 0 100 200 300 400 500 4 5 6 7 8 9 10 L u m in e s c e n c e d e c a y t im e ( µ s ) pH τ2↑ τ1↓Plain symbols: 0.1 M NaClO4 Empty symbols: 0.01 M NaClO4
0.0E+00 1.0E-08 2.0E-08 3.0E-08 4.0E-08 5.0E-08 6.0E-08 7.0E-08 8.0E-08 0 2 4 6 8 10 Eu (I II ) s u rfa ce c o n ce n tr ai to n (m o l/ m ²) [α-Al2O3] (g/L) data pH ≈ 6.2 0 100 200 300 400 500 0 10 20 30 40 50 Lu mi n e sc e n ce d e ca y tim e ( µ s) R (mg/g) τ2 pH≈4.3 τ1 pH≈4.3 τ2 pH≈6.3 τ1 pH≈6.3 τ2 pH≈7.4 τ1 pH≈7.4 Range of τ2 values in Eu(III)/PAHA system
0 1 2 3 4 0 10 20 30 40 50 7 F 2 / 7 F 1 R (mg/g) / [PAHA] (mg/L) pH = 7.4 ± 0.2 pH = 7.6 ± 0.2 pH = 6.3 ± 0.1 pH = 6.0 ± 0.2 pH = 4.3 ± 0.1 pH = 4.0 ± 0.1
Ternary system Binary system
0 10 20 30 40 50 60 70 3 4 5 6 7 8 9 10 S u rf a c e c o n c e n tr a ti o n (n m o l E u /m ² α -Al 2 O 3 ) pH 0 0.5 1 1.5 2 2.5 3 3.5 575 585 595 605 615 625 N o rm a li ze d l u m in e s c e n c e Wavelength (nm) Eu/PAHA (pH = 4.1) Eu (pH = 4.3) 5D 07F0 5D 07F1 5D 07F2
N. Janot
1,2*
, M.F. Benedetti
1
,
P.E. Reiller
2
njanot@slac.stanford.edu
1 : Université Paris Diderot, Sorbonne Paris Cité, IPGP, UMR CNRS 7154, F-75205 Paris, Cedex 13, France.
2 : CEA/DEN/DANS/DPC/SEARS/Laboratoire de développement analytique nucléaire, isotopique et élémentaire, Bâtiment 391 PC 33, F-91191 Gif-sur-Yvette Cedex, France
* Current address: Stanford Synchrotron Radiation Lightsource, 2575 Sand Hill Rd, Menlo Park, CA 94025, USA.
Interactions between Natural Organic Matter (NOM) and minerals modify mobility and bioavailability of trace elements. A better description of these ternary metal/NOM/mineral surface systems is needed to improve the understanding of radionuclides transfer from a repository site to the geosphere. This study is focused on Europium(III) speciation in presence of aluminum oxide α-Al2O3 and Purified Aldrich Humic Acid (PAHA) as a surrogate of NOM. In case of lanthanides, one way to obtain both macroscopic and spectroscopic information on metal sorption onto mineral surfaces is through Time-Resolved Laser-induced Luminescence Spectroscopy (TRLS), which allows to have a direct insight on speciation of ions in solution at relevant environmental metal concentration. Macroscopic and spectroscopic experiments have been carried out to see the influence of solution parameters (pH, ionic strength, humic concentration) on the evolution of the different binary Eu(III)/α-Al2O3 and Eu(III)/PAHA and ternary Eu(III)/PAHA/α-Al2O3 systems.
Context
Interfaces Against Pollution 2012 – Interfacial Processes
Influence of solution parameters on
Europium(III), α-Al
2
O
3
and humic acid interactions
1. Janot et al., Environ. Sci. Technol. 2011, 45, 3224. 2. Janot et al., Geoch. Cosm. Acta Submitted.
3. Janot et al., Environ. Sci. Technol. 2010, 44, 6782. 4. Kinniburgh et al., Colloids Surf. A 1999, 151, 147.
5. Hiemstra and VanRiemsdijk, J. Colloid Interface Sci. 1996, 179,
488
6. Janot et al., Water Research 2012, 46, 731.
7. Milne et al., Environ. Sci. Technol. 2003, 37, 958.
Description of experiments
• Contact time: 3 days• Ultracentrifugation: 2h, 60000 rpm • PAHA concentration: DOC, UV
• [Eu(III)] = 10-6 mol/L
• [α-Al2O3] = 1 g/L
• [PAHA] = 28 mgHA/L
• I = 0.01 or 0.1M NaClO4
Modeling Europium(III) speciation in ternary systems
Methodology
• Eu(III) complexation (asymmetry ratio 7F
2/7F1)
• Symmetry of Eu(III) environment (7F 0)
• Quenching groups in the first coordination sphere (Luminescence lifetime)
Time-Resolved Laser Induced Luminescence Spectroscopy
Influence of pH and ionic strength on Eu(III) speciation in the ternary system
(1,2)
1-pK modeling:
≡AlOH-1/2 + Eu3+ ≡AlOHEu+5/2 logK = 13.5
Repartition of Eu(III) charge in the Stern layer: Δz0 = 1.93
Δz1 = 1.07
Good correlation with this study and literature data in a wide range of parameters
0 1 2 3 0 10 20 30 40 7 F 2 / 7 F 1 [PAHA] (mg/L) 0% complexation 100% complexation 0 20 40 60 80 100 0 10 20 30 40 % Eu (I II ) co m p le xe d t o P A HA [PAHA] (mg/L) data
NICA-Donnan modeling with generic parameters NICA-Donnan modeling with adjusted parameters
Evolution of Eu(III) environment symmetry
• In the ternary system, at pH < 7 : similar to Eu(III)/PAHA
• At high pH, shift of maxima and change of peaks shapes. Eu(III) on the surface but bound to HA
Evolution of luminescence lifetimes
• τ1 presence: Eu(III) always bound to PAHA
• Higher τ2 in the ternary system: more constrained environment, but of the same symmetry than in
binary Eu(III)/PAHA system (comparable spectra) • τ2 decreases when pH increases: Eu(III) more
exposed to quenching groups; progressive change in structure of Eu(III)/PAHA complexes onto the
surface
Evolution of Eu(III) retention onto the surface
In the binary system:
• Sorption-edge observed at pH 7 (expected) • Low dependence to ionic strength
Evolution of PAHA retention in the surface
• Sorption decreases with increasing pH
• Sorption decreases with ionic strength (electrostatic repulsion)
•Presence of Eu(III) increases the humic sorption in the whole pH range (from 88 to 38%) • Less effect of Eu(III) addition at lower ionic strength 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 3 4 5 6 7 8 9 10 S u rf a c e c o n c e n tr a ti o n (m g P AH A/m ² α -Al 2 O 3 ) pH 0 10 20 30 40 50 60 70 80 0 20 40 60 80 Su rf ac e co n cen tr at io n (n mo l E u /m² α -Al 2 O 3 ) R(mg/g) pH = 3.9 pH = 6.2 ± 0.2 pH = 7.4 ± 0.2 0.0 0.5 1.0 1.5 2.0 2.5 3.0 0 10 20 30 40 50 60 70 80 Surf ac e conc en tr at ion (m g PAH A/m ² Al2 O3 ) R (mg/g) pH = 3.9 pH = 6.2 ± 0.2 pH = 7.4 ± 0.2 pH = 4.2 ± 0.2 pH = 6.1 ± 0.1 pH = 7.2 ± 0.2 Tern ar y B in ar y 0% 20% 40% 60% 80% 100% 3 5 7 9 11 Eu (I II ) r e p ar ti ti o n pH solution HAsol HAads surface ACKNOWLEDGEMENTS
This work was financed through the MRISQ (DEN/DISN/AvC) project of CEA.
Binary Eu(III)/α-Al
2O
3system
Binary Eu(III)/PAHA system
Ternary Eu(III)/α-Al
2O
3/PAHA system
Figures legend:
ternary Eu/α-Al2O3/PAHA system
binary Eu/PAHA system binary Eu/α-Al2O3 system
binary PAHA/α-Al2O3 system
Spectroscopic results
Macroscopic results
Influence of humic concentration on Eu(III) speciation
(2)
Plain symbols: 0.1 M NaClO4 Empty symbols: 0.01 M NaClO4
Use of spectroscopic data (peak ratio) at pH 4 as a titration curve of
Eu(III)-PAHA complexation
Adjustement of generic Eu(III)/HA binding parameters of the NICA-Donnan model(7) to fit our system:
logK̃ n S1-Eu 1.05 0.50 S2-Eu 3.43(7) 0.36(7) Dissolved PAHA α-Al2O3 Eu(III) Sorbed PAHA Macroscopic results CD-MUSIC model (5) Eu3+ + AlOH½- ↔ AlOHEu5/2+
Potentiometric titrations: Description of surface reactivity (CD-MUSIC model (5))
Adapted parameters for Eu binding
(NICA-Donnan model(4))
Proton-binding parameters from spectro-photometric titrations of supernatant from
retention experiments(3,6)
(NICA-Donnan model(4))
Conclusions
Acquisition of data set in a various range of solution conditions
Importance of humic concentration, ionic strength on contaminant mobility, not only pH
Good description on Eu(III) repartition in a ternary system
Need to take into account the modifications of PAHA reactivity with fractionation due to adsorption
Humic concentration dependence
• Good prediction at high concentration
• Use of average parameters for humic protonation
Need improvement at low ratio (high fractionation rate)
Parameters from adsorption experiments at pH 7(6) (explains the poor
description at low pH)
pH and ionic strength dependence
• Good prediction of the model
• Variations due to initial concentration variation between batches • Need more data at lower ionic strength
• Modified PAHA parameters from adsorption experiments at 0.1 M at pH 7(6)
Eu(III) speciation in the ternary system depending on pH
• Humic complexation in the whole range • Surface complexation at high pH
Agreement with spectroscopic results
In the ternary system:
• Eu(III) behavior shows high
dependence to PAHA retention onto the mineral
• At high pH, increase due to direct sorption of Eu(III) onto the mineral
REFERENCES
Evolution of luminescence lifetimes
• τ1 presence: Eu(III) always bound to PAHA
• Increase of τ2 with humic concentration, due to progressive complexation of Eu(III)
• In the ternary system, higher τ2: more constrained environment of Eu(III) when it is bound to adsorbed PAHA moieties
Evolution of Eu(III) environment symmetry
• At same PAHA concentration, no difference of
asymmetry ratios between binary and ternary systems • Presence of mineral surface has almost no influence on Eu(III) environment symmetry below pH 8
• Unlikely presence of europium-bridged humic-surface complexes
Evolution of Eu(III) retention onto the surface
Below pH edge:
• Presence of HA increases Eu(III) adsorption
Around the pH edge:
• Eu(III) retention increases at low HA concentration • After saturation of the surface, competition with non-sorbed HA fractions
Evolution of PAHA retention onto the surface
• No influence of Eu(III) presence at medium and high pH
• At low pH and high HA concentration, presence of HA increases HA retention
• No saturation of surface seen at low pH
Methodology
0 10 20 30 40 50 60 70 80 3 5 7 9 11 Eu (I II ) s u rf ac e c o n ce n tr at io n (n mo l E u /m² α -Al 2 O3 ) pH data 0.1M data 0.01M model 0.1M model 0.01M• Influence of ionic strength on humic molecules conformation, and on
