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Designing Wasteforms for Technetium
Anion sorption with precursors for ceramic phases
Jonathan Phillips
Centre for Advanced Structural Ceramics
Department of Materials, Imperial College London Supervisor
Prince Consort Road, London, SW7 2AZ Dr Luc Vandeperre
DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal
Overview
DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal
Background
•Common form: 99Tc with a half life of 2.13x105 years.
•Tc is a low energy beta emitter.
•It is produced with sufficient yield (6.1%) to be a concern for the
environment.
•Technetium compounds generally do not bind well with soils and are
highly mobile in the environment.
DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal
Background
• In the UK, Tc was formerly discharged to the sea by BNFL however it
is now separated using a process involving
tetraphenylphosphonium bromide (TPPB).
• The TPPB enables Tc to be disposed of by cement encapsulation.
• In alkaline environments TPPB is known to degrade releasing the
pertechnetate anion TcO4-.
DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal
Aim
The aim is to capture the pertechnetate anion from
solution using layered double hydroxide materials with
a suitable composition to be thermally converted to
stable ceramic phases.
DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal
Portlandite - Ca(OH)2
•Ca cations: coordination 7 (with
additional water/anion in
interlayer)
•Edge sharing of octahedra
forming large sheets
Hydroxide
Group
Calcium
DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal
Layered Double Hydroxides
Mg,Ca M(II)
Isomorphous
+ Substitution
+ +
Al,Fe(III) M(III)
+
+ +
+
DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal
Charge Balance
+ - Anions
+ +
+
+
+ +
+ - +
-
+ -
- +
-
+
M2+(1-x) M3+x (OH)2 (Az+)x/z.nH2O
H2O
DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal
Materials and Methods
1M Total
Ca(NO3)2.4H2O
Al(NO3)3.9H2O
Fe3+(NO3)3.9H2O
NaOH + NaNO3 Ca(1-x) (Al(1-y)Fey )x(OH)2 (NO3)x
Stirrer bar
pH >12.5
Phillips, J. and L.J. Vandeperre, Production of Layered Double Hydroxides for Anion Capture and Storage, in Materials Research
Needs to Advance Nuclear Energy, Mater. Res. Soc. Symp. Proc., Vol. 1215, G. Baldinozzi, et al., Editors. 2010, MRS: Warrendale,
PA. p. V11-04.
DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal
X-Ray Diffraction Pattern and SEM
DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal
Characterisation of product
DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal
DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal
Anion Exchange Mechanism
Topotactic Exchange Dissolution Reprecipitation
Preference for
to be intercalated LDH dissolves, increasing the
therefore exchange solution pH and then
with reprecipitates with new anion
DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal
Anion Exchange Method
• 1g of LDH powder (NO3 intercalated) was added to a solution containing the
desired interlayer anions
• The composition of the anionic solution were varied in the following molar ratios
(balanced for charge differences of the anions)
• 0.1 : 0.9 0.5 : 0.5 0.9 : 0.1
• The exchange was allowed to occur for a period of 1hr and for 14 days.
• The solids were separated by vacuum enhanced filtration before being dried in an
oven.
14
DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal
Results : Anion Exchange Cl:NO3
•Formation of two distinct interlayer spacings in the short term.
•Prolonged exposure to high [CO3] solutions deleterious.
J.D. Phillips, L.J. Vandeperre, J. Nucl. Mater.(2010),doi:10.1016/j.jnucmat.2010.11.101
DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal
Results : Anion Exchange
NO3:CO3
CO3
effect
Cl:CO3
DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal
XRD- Memory effect
900 939ATT2
Untreated LDH Powder
400
100
B O
0
900 P3HTFUR
x O B Calcined LDH Powder
400 B B
100
0
P3H2O
900 Rehydrated -Calcined LDH Powder
400
100
0
10 20 30 40 50
B = Brownmillerite Position [°2Theta]
O = Calcium Oxide
X = Calcium Carbonate
Calcine Capture
DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal
Anion Capture with LDHs
•Competition with other anions.
•Capture of pertechnetate or other anions with calcined LDH,
taking advantage of the memory effect
•Adsorption efficiency for surrogates of TcO4- - ICP OES
Wang Y. et al Jour. Coll and Int. Sci. 301 (2006) 19-26
DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal
DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal
Thermal Conversion
•Temperatures associated with the Tc system:
•Tc2O7 = MP 119.5°C BP 311°C
•TcO2 = sub ~900°C Ca
Fe,Al
O
•Conversion at as low a temperature as
possible desirable.
•The aim is to convert these LDH phases to
Brownmillerite Ca2(Fe,Al) 2O5 which are
compositions commonly found in cements
Ca2(Fe,Al)2O5
*ICSD, Vanpeteghem et al, 2008
DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal
Thermal Conversion
•A sample of LDH-NO3 was calcined to 400°C for 1 hour
•Browmillerite and Calcium Oxide have formed.
400°C
x
O B O
Intensity(a.u)
B
B B
5 10 15 20 25 30 35
2-Theta(°)
B = Brownmillerite
O = Calcium Oxide
X = Calcium Carbonate
DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal
Results : Thermal Analysis NO3
DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal
Thermal Product - NO3
B: Brownmillerite Ca2AlFeO5
P: Calcium Hydroxide Ca(OH)2
C: Calcium Oxide CaO
23
DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal
Results : Thermal Analysis Cl
DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal
Thermal Product – Cl
B: Brownmillerite Ca2AlFeO5
P: Calcium Hydroxide Ca(OH)2
C: Calcium Oxide CaO
25
DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal
Thermal Product – Cl
B: Brownmillerite Ca2AlFeO5
P: Calcium Hydroxide Ca(OH)2
C: Calcium Oxide CaO
26
DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal
Conclusions
• Layered double hydroxides with a composition suitable for thermal
conversion to ceramic phases have been produced.
• The absorption capacity of these materials for the perhenate anion is
significantly reduced due contamination with CO3 from equilibrium with
the atmosphere.
• Capture of Cl- is favourable even in the presence of CO3, these materials
may be applicable to the remediation of 36Cl- from the processing of
graphitic wastes.
• Thermal conversion product dependent on interlayer anion.
DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal
Acknowledgements
This project is funded by the UK Engineering and Physical
Sciences Research Council through the DIAMOND
consortium
Thank you for your attention
DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal
