1 / 17

Lanthanide and actinide speciation in molten fluorides Structural approach by high temperature NMR

Lanthanide and actinide speciation in molten fluorides Structural approach by high temperature NMR. Catherine Bessada , Anne Laure Rollet, Aydar Rakhmatullin. CNRS-CRMHT 1D Av de la Recherche Scientifique 45071 Orléans cedex 2 France bessada@cnrs-orleans.fr.

farren
Download Presentation

Lanthanide and actinide speciation in molten fluorides Structural approach by high temperature NMR

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Lanthanide and actinide speciation in molten fluoridesStructural approach by high temperature NMR Catherine Bessada, Anne Laure Rollet, Aydar Rakhmatullin CNRS-CRMHT 1D Av de la Recherche Scientifique45071 Orléans cedex 2 France bessada@cnrs-orleans.fr

  2. Pyrochemical treatment of spent nuclear fuel • (% hydrometallurgical separation processes) • dissolution in a molten salt (chlorides or fluorides) separation Nuclear applications Molten Salts • Physical and chemical properties: • non aqueous solvent • high thermal and electrical conductivity • wide range of thermochemical and electrochemical stability • mutual miscibility, moderate viscosity… LiCl-KCl LiF-NaF-KF … • Molten salts reactor / Thorium cycle/ « Generation IV » • Salt = coolant and fuel • Lower radiotoxicity • On site fuel regeneration… Physical and chemical properties of the bath?  Comprehension of the species solvation / distribution, coordination, oxidation

  3. Lanthanide fluorides La, Ce, Pr, Nd, Sm, Eu - Gd, Tb, Dy,Ho, Er, Tm, Yb, Lu + Y Cristallographic structure of solid LnF3 compounds at room temperature LaF3 1400 1200 1000 800 600 0 20 40 60 80 100 LaF3 LiF YF3 1400 1200 LiYF4 1000 800 600 0 20 40 60 80 100 LiF YF3

  4. NdF3 CeF3 19F MAS SmF3 LaF3 YF3 500 0 -500 -1000 -1500 -2000 (ppm) NMR in solid Lanthanide fluorides (RT) La, Ce, Pr, Nd, Sm, Eu - Gd, Tb, Dy,Ho, Er, Tm, Yb, Lu+ Y LaIII, YIII and LuIII have no unpaired ē : diamagneticThe others have 1-7 unpaired ē : paramagnetic Paramagnetic properties of the trivalent lanthanide cations Ln(III) electronic configuration 4fn (n= 0 – 14) Strong effects on the NMR spectrum of the observed nuclei  important shift and broadening

  5. In binaries melts : Medium range order generated by bridging fluorine between octahedra (compositions rich in LnX3) Molten Trifluorides Informations on the structure of molten rare earth halides XRD, Neutrons, Raman, MD… In pure trihalide melts : Octahedral coordination (LnX6)3- G.Papatheodorou & al.. HT raman spectroscopy • X (LnF3) 0.25 the predominant species are LnF63- octahedra • X (LnF3) >0.25 distorded LnF63- octahedra bound by common fluorine (edges sharing) The structure of all the LnX3 melts are similar and independent of the structure of solids.

  6. High temperature NMR up to 1400°C Boron Nitride crucible Radio-frequency coil sample Thermal shield NMR probe ~ ~ ~ ~ Cryomagnet Argon ZnSe window He / Ne dm CO2 laser (120W) Laser beam N.M.R. ( ppm) single, narrow peak fully averaged local environment dexp = S Xidi

  7. 19F 19F NMR in MF-YF3 YF3 LiF Free F 850°C 1150°C Bridging F RT RT -140 -160 -180 -200 -220 -240 -260 20 -20 -60 -100 -140 (ppm) (ppm) Non Bridging F K3YF6 LiYF4 990°C a, 910°C 1150°C d,RT RT 20 0 -20 -40 -60 -80 -100 -120 -140 -80 -20 -40 -60 -100 -120 -140 (ppm) (ppm)

  8. YF3/LiF YF3 100/0 80/20 70/30 50/50 40/60 30/70 20/80 -20 YF3 molten 10/90 0/100 YF3 solid RT LiF -60 LiYF4 molten -20 -60 -100 -140 -180 -220 LiYF4 solid RT -100 d 19F, ppm ppm -140 -180 LiF solid RT LiF molten -220 0 20 40 60 80 100 mol. %, YF3 19F 19F HT NMR in LiF-YF3 melts (800-1100°C) 1400 ( 800 to1300°C) Tm YF3 = 1150°C 1200 1000 800 600 0 20 40 60 80 100 LiF YF3

  9. 19F HT NMR in KF-YF3 YF3/KF 100/0 90/10 80/20 K3YF6 70/30 -20 60/40 YF3 molten 50/50 -40 40/60 YF3 solid RT -60 30/70 d 19F, ppm -80 20/80 K3YF6 solid RT 10/90 -100 0/100 -120 -40 -60 -80 -100 -120 -140 KF solid RT -140 (ppm) KF molten -160 0 20 40 60 80 100 mol. %, YF3 ( 900 to1200°C) 1200 1000 Tm KF = 858°C 800 Tm YF3 = 1150°C 600 40 60 80 20 KF YF3 19F 400

  10. 1000°C 50 LaF3 CeF3 0 -50 YF3 KF LuF3 -50 -100 d 19F, ppm LiF -100 -150 -150 SmF3 NaF -200 -200 0 20 40 60 80 100 0 20 40 60 80 100 mol. % YF3 mol% LnF3 • direct NMR observation of the structural evolution around F anions in LnF3-MF melts 19F NMR free  non bridging  bridging fluorines 19F 19F HT NMR in MF-LnF3 d 19F, ppm 89Y & 139La

  11. 89Y MAS NMR YF3 LiYF4 NaYF4 d-K3YF6 40 0 -40 -80 -120 89Y HT NMR (ppm) LiF-YF3 30%YF3 YF63- YF85- YF96- Liquid 50%YF3 Solid 70%YF3 0 -40 -80 -120 (ppm) 0 -20 -40 -60 -80 -100 (ppm) 89Y 89Y NMR in solid and molten YF3-MF mixtures n(89Y) à 9.4 Teslas : 19.6 MHz Spin ½; nat. abundance 100%

  12. solid LaF3 1000 900 1400 746°C 800 1200 RT17.6T 625°C 700 d= -133ppm nq=1100kHz 1000 600 T (°C) T (°C) 800 540°C 500 400 600 300 400 200 KLaF4 K3LaF6 200 100 0 3000 2000 1000 0 -1000 -2000 -3000 0 0 20 40 60 80 100 0 10 20 30 40 50 60 70 (ppm) %LaF3 mol%LaF3 mol%LaF3 50 50 30 30 40 25 25 22 30 20 15 20 15 10 10 10 5 300 200 100 0 -100 -200 -300 -400 0 300 200 100 -100 -200 -300 (ppm) 1600 1400 1200 1000 810°C T (°C) 730°C 800 630°C 600 400 200 0 0 10 20 30 40 50 60 70 80 90 100 %LaF3 300 200 100 0 -100 -200 -300 139La 1000-1200°C HT 139La NMR in MF-LaF3 melts (M=Li, Na, K) mol%LaF3 LiF-LaF3 NaF-LaF3 KF-LaF3

  13. LaF3-LiF LaF3-NaF LaF3-KF 139La 139La chemical shifts evolution in MF-LnF3melts 80 60 40 20 139La chemical shift, ppm 0 -20 -40 -60 -80 0 10 20 30 40 50 Mol% LaF3 • Evolution of the local structure around the lanthanum cation: • different in the melt and in the solid, • depend on the composition for NaF and KF-LaF3 systems, but not for LiF-LaF3, • evolution of the average coordination of the La.

  14. %ThF4 = 0 to 100% Tm+10°C 1050 850 LiF-4ThF4 650 LiF-2ThF4 3LiF-ThF4 7LiF-6ThF4 450 0 20 40 60 100 80 ThF4 ThF4 LiF 100 90 80 70 19F d 66.7 50 40 30 20 LiF 12 5 0 19F chemical shift evolution in LiF-ThF4 melts 120 80 40 0 -40 -80 -120 -160 -200 (ppm) 150 100 50 0 -50 -100 -150 -200 -250 0 20 40 60 80 100 19F 600-1200°C LiF-ThF4

  15. 100 19F Chemical shift, ppm 50 NaF 0 LiF KF -50 -100 -150 -200 -250 0 20 40 60 80 100 mol. %, ThF4 19F Comparison of 19F chemical shifts evolution in MF-ThF4 (M= Li, Na, K)

  16. Conclusion • The evolution of 19F NMR signal in melts over a large composition range in MF-LnF3 (M= Li, Na, K) Ln = La, Ce, Sm, Lu, Y systems confirm the existence of complexes in melts : Free Non bridging  bridging fluorines (depending on the LnF3 content) The same evolution is also observed for MF-ThF4 systems • 139La, 89Y NMR in the solid and the melt provides another direct detection of the chemical species. ? LnF63- coordination in melts ? From 89Y NMR data, the coordination should be 7 or 8 • For the other Lanthanides , EXAFS experiments would give also structural information about the local bounding.

  17. Acknowledgements RMN CRMHT, Orléans Yannick Auger Philippe Melin Vassilis DracopoulosGeorges Papatheodorou K3YF6 GDR PARIS

More Related