Speciation of actinides and lanthanides in ionic liquids by XAS
IPHC, IPNL, MSM labI. Billard, C. Gaillard, A. Ouadi, S. Georg, V. MazanO. Klimchuk, E. Jobin, S. Mekki , S. StumpfO. Klimchuk, E. Jobin, S. Mekki , S. StumpfG. Wipff, A. Chaumont, R. Schurhammer
INE (FZK), M. Denecke, K. Dardenne, P. PanakROBL (FZR)C. Hennig
French-German seminar, Strasbourg, 22-23 February 2012
with the financial help of EURATOM, ACTINET, GnR PARIS, ANR
Studies led in the frame of nuclear fuel reprocessingIL use in replacement of organic solvents (kerosene) or for electrodeposition
→→→→ IL are easy to handle, non flammable, non toxic, non volatile
Work purpose
Which IL? Hydrophobic and stable in presence of water
N
N
C H3
NS S C F3
OO
F 3C
Need for fundamental data on solute-solvent and solute-solute interactions in IL
C4mimTf2N, (TfO-, PF6-, BF4
-)
NOO
F 3C
C H3
French�German collaboration, what for?
� EXAFS experimentsOn ROBL (ESRF, for uranium), on INE-BL (americium) and XAS-BL (europium) (ANKA, Karlsruhe)
Gives an average speciation of f-elements in IL samples (nature, number and distance of close neighbours)
� TRLFS experiments
To get speciation of f-elements in IL samples, by combination of spectroscopic techniques
� TRLFS experimentsAt INE, on Cm3+ in IL
Gives number and nature of fluorescent species in solution (Eu, Cm)
� combined with “French” data, obtained by UV-vis spectroscopy, TRLFS (Eu) and theoretical (MD) calculations
Dried IL solutions (< 1 H2O / An-Ln)
Solvatation of U(VI) in IL
In water: [UO2(H2O)5]2+
In IL?� Various U(VI) salts in C4mimTf2N
0
10
20
30
40
50
350 370 390 410 430 450 470 490
ε(m
ol-1
.cm
-1)
λ (nm)
UO2(NO3)2
UO2(ClO4)2
UO2(Tf)2
UO2(Tf2N)2
UO2(NO3)2.6H2OUO2(ClO4)2.6H2OUO2(CF3SO3)2
UO2(Tf2N)2
UO2(Tf2N)2
UO2(CF3SO3)2
UO2(ClO4)2.6H2O
UO2(NO3)2.6H2O
Salt is dissolved but may not be dissociated (≠ water)
U L3 edge @ ROBL (ESRF)
3.5 6 8.5 11 13.5 16
k3.c
hi(
k)
k (Å-1) 0 1 2 3 4
FT m
ag.
R + Δ (Å)
∼5 O @ 2.43 Å + 2.7 S @ 3.62 Å [UO2(Tf2N)5-6]
∼ 4.5 O @ 2.42 Å
∼ 4.4 O @ 2.42 Å
∼ 5 O @ 2.49 Å + 2 N @ 2.92 Å [UO2(NO3)2] + (1 or 2) Tf2N
Gaillard et al., Inorg Chem, 2007, 46, 4815.
“Simple” complexation reactions in IL
- In IL, possibility to get rid of counter-ions:
UO2(Tf2N)2 + nC4mimNO3 → [UO2(NO3)n]2-n + nC4mimTf2N
0 < R = [NO3-]/[UO2
2+] < 5
UO2(Tf2N)2 + C4mimNO3 in C4mimTf2N
U-Oeq @ 2.48 ÅU-N @ 2.92 Å
U L3 edge @ ROBL (ESRF)
3 5 7 9 11 13 15
k3.c
hi(
k)
k (Å-1)0 1 2 3 4 5
FT m
ag.
R+Δ (Å)
R = 0
R = 1
R = 2R = 3
Total complexation, up to the formation of [UO2(NO3)3]-
Same structural parameters as in organic solvents
Georg et al., J. Phys.Chem B, 2010,114,4276.Gaillard et al. Inor Chem, 2010, 49, 6484
UO2(NO3)2: 2 bidentate NO3Mixture of 1:1, 1:2 and 1:3 cpx2 UO2(NO3)2 → UO2(NO3)+ + UO2(NO3)3
-
UO2(NO3)+ : 1 bidentate NO3-
UO2(NO3)3-: 3 bidentate NO3
R = 600
“Simple” complexation reactions in IL (2)
- an IL can be solvent AND reactant
UO2(Tf2N)2 IN C4mimNO3 and, even better, UO2(NO3)2 IN C4mimNO3
-3
-1
1
3
5
3 5 7 9 11 13 15
k3.c
hi(
k)
2
4
6
8
10
FT m
ag
[UO2(NO3)3]-
UO2(NO3)2
[UO2(NO3)]+
UO2(NO3)2 in BMINO3
Gaillard et al., Dalton Trans., submitted
Same structural parameters as in solid state
∼ 4 NO3- complexed to U(VI),
2 bidentate and 2 mono-dentate
→ Formation of UO2(NO3)4]2-
-5
-3
k (Å-1)0
0 1 2 3 4 5R + Δ (Å)
U L3 edge @ ROBL (ESRF)
Competition between strong ligands (with the help of MD)
UO2(TfO)2 + 4 C4mimCl in C4mimTf2N
→ Chlorides are strong ligands
U(VI) + 2 strong ligands: chlorides + nitrates
UO2(NO3)2 + 4 C4mimCl in C4mimTf2N
UO2(NO3)2 + 2 C4mimCl in C4mimTf2N0
10
20
370 420 470 520
ε(m
ol-1
. cm
-1)
λ (nm)
0
10
20
370 420 470 520
ε(m
ol-1
. cm
-1)
λ (nm)
0
10
20
370 420 470 520
ε(m
ol-1
. cm
-1)
λ (nm)
-6
-1
4
9
14
3 8 13
k3.c
hi(
k)
k (Å-1) 0 1 2 3 4
FT m
ag.
R + Δ (Å)
U L3 edge @ ROBL (ESRF)
-6
-1
4
9
14
3 8 13
k3.c
hi(
k)
k (Å-1) 0 1 2 3 4
FT m
ag.
R + Δ (Å)
-6
-1
4
9
14
3 8 13
k3.c
hi(
k)
k (Å-1) 0 1 2 3 4
FT m
ag.
R + Δ (Å)
∼ 4 Cl @ 2.69 Å ⇒ 100 % of [UO2Cl4]2�
∼ 4 Cl @ 2.70 Å ⇒ [UO2Cl4]2' + some [UO2Cl3(NO3)]
2�
∼ 1 Cl @ 2.67 Å + 2 bid. NO3-⇒ [UO2Cl(NO3)2]
�
Ion competition can lead to the formation of mixed complexes
May IL anions interfere in complexation reactions?
Dissolution of Eu(TfO)3 in various IL (≠ anions, same cation) and addition of 6xCl-
Eu/Cl complexation?
0
2
4
6
8
10
12
0 1 2 3 4
FT m
ag.
R + Δ (Å)
C4mim-TfO
0
1
2
3
4
5
6
7
8
9
0 1 2 3 4
FT m
ag.
R + Δ (Å)
C4mim-BF4
0
2
4
6
8
10
12
14
0 1 2 3 4
FT m
ag.
R + Δ (Å)
C4mim-Tf2NEu-ClEu-O
[EuCl3-4]
R + Δ (Å)
[EuCl2-3]
R + Δ (Å)
0
2
4
6
8
10
12
0 1 2 3 4
FT m
ag.
R + Δ (Å)
C4mim-PF6
No Cl complexation but fluorides!
Eu-L3 edge @ XAS-BL (ANKA)
R + Δ (Å)
[EuCl63-]: total complexation
Gaillard et al., Inorg Chem, 2005, 44, 8355
The species formed are the result of competition between all components of the solution, including the solvent→ Formation of mixed complexes
⇔ PF6- (and possibly BF4
-) decomposition into F-
Comparison Ln(III) and An(III)
Eu(III) + N3- in C4mim-Tf2N
• Eu(OTf)3 or Eu(ClO4)3; C = 10-2 M;
• [N3-] = 10-5 M to 5x10-1 M
• Cm(ClO4)3; C = 1.2x10-7 M;
• [N3-] = 2x10-8 M to 10-5 M
Cm(III) + N3- in C4mim-Tf2N
→ Complexation is fast (instantaneous) but not total
→ Complexation is slow (≈ 7 days)
1500
2000
2500
3000
Inte
nsi
ty
time elapsed
30000
40000
50000
60000
70000
Inte
nsi
ty
[N3-] ↑
Eu and Cm solvate similarly in IL→ concentration effect?
TRLFS, INE (FZK)
0
500
1000
1500
575 585 595 605 615
Inte
nsi
ty
λ (nm)TRLFS, IPHC
0
10000
20000
30000
570 590 610 630
Inte
nsi
ty
λ(nm)
Am(III) + N3- in C4mim-Tf2N
Comparison Ln(III) and An(III)
Eu(III) + N3- in C4mim-Tf2N Cm(III) + N3
- in C4mim-Tf2N
11 O @ 2.42 Å + ~ 4 Cl/S @ 3.60 Å
• Am(ClO4)3; C = 10-3 M; [N3-] = 10-2 M;
• Eu(OTf)3 or Eu(ClO4)3; C = 10-2 M;
• [N3-] = 10-5 M to 5x10-1 M
• Cm(ClO4)3; C = 1.2x10-7 M;
• [N3-] = 2x10-8 M to 10-5 M
→ Complexation is fast (instantaneous) but not total
→ Complexation is slow (≈ 7 days)
5Am(ClO4)3 in C4mimTf2N
→ Complexation is slow and non-total after 7 days
Am-L3 edge @ INE-BL (ANKA)
11 O @ 2.42 Å + ~ 4 Cl/S @ 3.60 Å
→ Am solvatation in IL
9 O @ 2.42 Å; no 2nd shell
→ destruction of Am solvatation sphere
11 O @ 2.40 Å + MS from [Am(N3)x]3-x
→ azide complexation to Am
� In both cases: formation of mixed complexes postulated� ≠ complexation kinetics can not be explained by concentration effects
⇒ ≠ reactivity of An(III) and Ln(III) in IL
0
1
2
3
4
0 1 2 3 4 5
FT m
ag.
R +Δ (Å)
Am(ClO4)3 in C4mimTf2N
Am(ClO4)3 + N3 ; fresh
Am(ClO4)3 + N3 ; 1 week
S. Stumpf et al., Inorg. Chem., 2008, 47, 4618
Conclusion
- The final coordination sphere of An/Ln depends on competition phenomena, in which the IL ions and Ln/An counter-anions take part
- IL can be solvent + reactant: formation of unusual species in liquid state like [(UO2(NO3)4]2-
- Impurities may have a drastic effect (cf. example of fluorides, but also water – not shown here)
- Strength of Ln/An ligands in IL:Tf2N- < TfO- < ClO4
- < Cl- ≈< NO3- < F-
- Evidence of Ln/An(III) different kinetics of complexation- Evidence of Ln/An(III) different kinetics of complexation
Danke schön to all persons that have contributed more or less to this work: on ROBL, at INE, at ANKA.