designing wasteforms for technetium anion sorption with precursors for ceramic phases
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DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for DisposalDIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal
Designing Wasteforms for TechnetiumAnion sorption with precursors for ceramic phases
Jonathan PhillipsCentre for Advanced Structural CeramicsDepartment of Materials, Imperial College LondonPrince Consort Road, London, SW7 2AZ
SupervisorDr Luc Vandeperre
DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal
Overview
DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal
•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.
Background
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
•Ca cations: coordination 7 (with additional water/anion in interlayer)
•Edge sharing of octahedra forming large sheets
Hydroxide GroupCalcium
Portlandite - Ca(OH)2
DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal
+
+ +
+
+
+
M(II)
+
Isomorphous Substitution
Al,Fe(III) M(III)
Mg,Ca
Layered Double Hydroxides
DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal
+
+ +
+
+
+-
-
-
-
-
-
H2O
Anions
+
+ +
+
+
+
M2+(1-x) M3+
x (OH)2 (Az+)x/z.nH2O
Charge Balance
DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal
Materials and Methods
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.
NaOH + NaNO3
pH >12.5Stirrer bar
Ca(1-x) (Al(1-y)Fey )x(OH)2 (NO3)x
1M TotalCa(NO3)2.4H2O Al(NO3)3.9H2OFe3+(NO3)3.9H2O
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
Topotactic Exchange Dissolution Reprecipitation
Preference for to be intercalated therefore exchange with
LDH dissolves, increasing the solution pH and then reprecipitates with new anion
Anion Exchange Mechanism
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
J.D. Phillips, L.J. Vandeperre, J. Nucl. Mater.(2010),doi:10.1016/j.jnucmat.2010.11.101
•Formation of two distinct interlayer spacings in the short term.
•Prolonged exposure to high [CO3] solutions deleterious.
DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal
Results : Anion Exchange
NO3:CO3
Cl:CO3
CO3 effect
DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal
Position [°2Theta]10 20 30 40 50
Counts
0
100
400
900
0
100
400
900
0
100
400
900
939ATT2
P3HTFUR
P3H2O
Untreated LDH Powder
Calcined LDH Powder
Rehydrated -Calcined LDH Powder
BB
xB B
OO
XRD- Memory effect
B = BrownmilleriteO = Calcium OxideX = Calcium Carbonate
Calcine Capture
DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal
Wang Y. et al Jour. Coll and Int. Sci. 301 (2006) 19-26
•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
Anion Capture with LDHs
DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal
DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal
•Temperatures associated with the Tc system:•Tc2O7 = MP 119.5°C BP 311°C
•TcO2 = sub ~900°C
•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
Thermal Conversion
Ca2(Fe,Al)2O5
*ICSD, Vanpeteghem et al, 2008
CaFe,AlO
DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal
5 10 15 20 25 30 352-Theta(°)
Inte
nsity
(a.u
)
400°C
BB
x
B B
OO
B = BrownmilleriteO = Calcium OxideX = Calcium Carbonate
Thermal Conversion
•A sample of LDH-NO3 was calcined to 400°C for 1 hour•Browmillerite and Calcium Oxide have formed.
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
23
B: Brownmillerite Ca2AlFeO5
P: Calcium Hydroxide Ca(OH)2
C: Calcium Oxide CaO
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
25
B: Brownmillerite Ca2AlFeO5
P: Calcium Hydroxide Ca(OH)2
C: Calcium Oxide CaO
DIAMOND Decommissioning, Immobilisation and Management of Nuclear Waste for Disposal
Thermal Product – Cl
26
B: Brownmillerite Ca2AlFeO5
P: Calcium Hydroxide Ca(OH)2
C: Calcium Oxide CaO
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
This project is funded by the UK Engineering and Physical Sciences Research Council through the DIAMOND
consortium
Thank you for your attention
Acknowledgements
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