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Paulina Svoboda

This document summarizes a molecular dynamics simulation study of uranyl hydroxide species in aqueous solution. The simulation found that UO2(OH)4^2- best matched experimental EXAFS data, with bond lengths of 1.87(1) Angstroms for the first shell and 2.29(3) Angstroms for the second shell. UO2(OH)5^3- was also simulated but dissociated into UO2(OH)4^2- over time. The exchange of axial and equatorial ligands on UO2(OH)4^2- matched experimental activation energy. Hydrogen bonding of the axial ligand was also analyzed and found to correlate with ur

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Car Parinello Molecular Dynamic Simulations of UO2(OH)4 2- in Explicit Liquid Water Paulina Svoboda Chimie ParisTech promo 2010 Projet de fin d¨└tudes, 21 f└vrier-31 aout, CEA,LSRM 27/08/2010 1CPMD U(VI) in alcaline media
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 /O└q 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 ?, CN = 2, r2 = 2, 21(1) ?, CN=5,3(5)) ? Speciation ? A reaction ? H-bond Schreckenbach et al., 1998
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 (?) CN1 R2 (?) 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
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 (?) CN1 R2 (?) 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)
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- 27/08/2010 CPMD U(VI) in alcaline media 5
UO2(OH)5 3- 27/08/2010 CPMD U(VI) in alcaline media 6
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)
The axial H-Bonds across isoelectronic actinides 27/08/2010 CPMD U(VI) in alcaline media 8 PaO2 + , UO2 2+ : Riccardo Spezia, CNRS, LAMBE UMR 8587 CNRS, Universit└ 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 nbdeHli└sparLH Charge sur Oaxial (e-) Correlation entre la charge sur Oaxial et nombre de H li└s par LH PaO2+ UO22+ NpO23+ UO2(OH)42-
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
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 ? 27/08/2010 CPMD U(VI) in alcaline media 10

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presentation27aout

  • 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¨└tudes, 21 f└vrier-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 /O└q 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 ?, CN = 2, r2 = 2, 21(1) ?, 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 (?) CN1 R2 (?) 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 (?) CN1 R2 (?) 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- 27/08/2010 CPMD U(VI) in alcaline media 5
  • 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 27/08/2010 CPMD U(VI) in alcaline media 8 PaO2 + , UO2 2+ : Riccardo Spezia, CNRS, LAMBE UMR 8587 CNRS, Universit└ 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 nbdeHli└sparLH Charge sur Oaxial (e-) Correlation entre la charge sur Oaxial et nombre de H li└s 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 ? 27/08/2010 CPMD U(VI) in alcaline media 10