1. Car Parinello Molecular Dynamic
Simulations of UO2(OH)4
2-
in Explicit Liquid Water
Paulina Svoboda
Chimie ParisTech promo 2010
Projet de fin d’études, 21 février-31 aout, CEA,LSRM
27/08/2010 1CPMD U(VI) in alcaline media

2. 27/08/2010 2CPMD U(VI) in alcaline media
Context
• U in nuclear industry (mining, fuel, reprocessing, + wastes of all these processes)
-> control of the speciation and reactivity: the alkaline media
-> Molecular Dynamics
• Experimental data :
- 9 conformers and their energies (Schreckenbach 1998) (computational)
- *β3 et *β4 (no *β5 data) (Chemical Thermodynamic of Uranium 1992, 2003)
- Oax /Oéq exchange ΔH‡= 9,8±0,4 kcal/mol, kex
298K=45±15s-1 (Clark 1999)
- EXAFS ((TMA)OH 3,5 M media, r1 = 1,81 Ǻ, CN = 2, r2 = 2, 21(1) Ǻ, CN=5,3(5))
 Speciation
 A reaction
 H-bond
Schreckenbach et al., 1998

3. Speciation : experimental data
• Thermodynamics :
• Equilibrium
ΔH‡ = 9,8 kcal/mol (Clark)
• EXAFS
27/08/2010 CPMD U(VI) in alcaline media 3
[(TMA)OH] = 3,5 M Chem. Thermodyn.
Of U. (1992) (1)
Update 2003 (2)
0,35
Equilibrium,
predominance of 3
1563
Predominance of 4
)]()([
)]()([
32
2
42
aqOHUO
aqOHUO


3, 4 or 5 equatorial OH ligands ?
media R1 (Ǻ) CN1 R2 (Ǻ) CN2
(TMA)OH 3,5 M 1,81(1) 2 2,21(1) 5,3(5)
1. Chemical Thermodynamics of Uranium, 1992
2., 3. Clark, Conradson, Donohoe, Chemical
Speciation of Uranium Ion under Highly
Alkaline Conditions, 1998

4. Radial Distribution Functions (RDF)
27/08/2010 CPMD U(VI) in alcaline media 4
speciation Simulation conditions
UO2(OH)4
2- CPMD/BLYP ,90 Ry, 8,7 ps, ts 4
a.u., emass 400, NVE, T~330K,
118 H2O
UO2(OH)5
3- CPMD/BLYP ,70 Ry, 1,3 ps, ts 2
a.u., emass 120, NVE, T~330K,
118 H2O
Best correspondance with
EXAFS : UO2(OH)4
2-
UO2(OH)3
- should be
simulated too
media R1 (Ǻ) CN1 R2 (Ǻ) CN2
UO2(OH)4
2- 1,87(1) 2 2,29(3) 4,0(3)
UO2(OH)5
3- 1,85(2) 2 2,37(3) 5,0(3)
(TMA)OH 3,5 M 1,81(1) 2 2,21(1) 5,3(5)

5. R1, CN1 R2,CN2
UO2(OH)5
- first 1,2 ps 1,84(2) ; 2 2,36(3); 5(3)
UO2(OH)4
2- last 1 ps 1,85(2); 2 2,27(3); 4(3)
UO2(OH)5
3-
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6. UO2(OH)5
3-
27/08/2010 CPMD U(VI) in alcaline media 6

7. The Oax and Oeq position exchange
27/08/2010 CPMD U(VI) in alcaline media 7
UO2
2+ : inert (Oax half live; 40 000h)
UO2(OH)4
2- :
Experimental: ΔH‡ = 9,8 kcal/mol (Clark, 1998)
Computational: ΔH‡ = 12,5 kcal/mol
(Schreckenbach, Shamov 2009)

8. The axial H-Bonds
across isoelectronic actinides
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PaO2
+ , UO2
2+ : Riccardo Spezia, CNRS, LAMBE UMR 8587 CNRS, Université d'Evry, France
NpO2
3+ : Peter Pogany, PhD, LAMBE (Evry-CEA)/ LSRM (CEA)
UO2(OH)4
2- : This study
1.8
1.85
1.9
1.95
2
2.05
2.1
2.15
-0.8 -0.6 -0.4 -0.2 0
longueurdelaLHOax··H(A)
Charge sur Oaxial (e-)
Correlation entre la charge sur Oaxial et
longueur de la LH Oaxial··H
PaO2+
UO22+
NpO23+
UO2(OH)42-
0
0.5
1
1.5
2
2.5
3
-0.8 -0.6 -0.4 -0.2 0
nbdeHliésparLH
Charge sur Oaxial (e-)
Correlation entre la charge sur Oaxial et
nombre de H liés par LH
PaO2+
UO22+
NpO23+
UO2(OH)42-

9. conclusion
• UO2(OH)4
2- Major specie in high alkaline media
• dissociation of UO2(OH)5
3- into UO2(OH)4
2- ->
UO2(OH)4
2- limiting complex:
• UO2(OH)4
2- axial H-bond: between PaO2
+ and UO2
2+
• Lability of axial O in UO2(OH)4
2- correlated with the
charge on Oaxial
27/08/2010 9CPMD U(VI) in alcaline media

10. Special Thanks:
Lambe :Marie-Pierre Gaigeot, Riccardo Spezia
CEA : Pierre Vitorge, Peter Pogany, Alexandre Quemet
ENS : Rodolphe Vuilleumier, Daniel Borgis
Chimie ParisTech : Carlo Adamo
Thank you for your attention
Any questions ?
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