designing wasteforms for technetium anion sorption with precursors for ceramic phases

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


•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


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

-.


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.


•Ca cations: coordination 7 (with additional water/anion in interlayer)

•Edge sharing of octahedra forming large sheets

Hydroxide GroupCalcium

Portlandite - Ca(OH)2


+

+ +

+

+

+

M(II)

+

Isomorphous Substitution

Al,Fe(III) M(III)

Mg,Ca

Layered Double Hydroxides


+

+ +

+

+

+-

-

-

-

-

-

H2O

Anions

+

+ +

+

+

+

M2+(1-x) M3+

x (OH)2 (Az+)x/z.nH2O

Charge Balance


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


X-Ray Diffraction Pattern and SEM


Characterisation of product


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


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


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.


Results : Anion Exchange

NO3:CO3

Cl:CO3

CO3 effect


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


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


•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


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.


Results : Thermal Analysis NO3


Thermal Product - NO3

23

B: Brownmillerite Ca2AlFeO5

P: Calcium Hydroxide Ca(OH)2

C: Calcium Oxide CaO


Results : Thermal Analysis Cl


Thermal Product – Cl

25





Thermal Product – Cl

26





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.


This project is funded by the UK Engineering and Physical Sciences Research Council through the DIAMOND

consortium

Thank you for your attention

Acknowledgements

designing wasteforms for technetium anion sorption with precursors for ceramic phases

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