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Designing Wasteforms for Technetium Anion sorption with precursors for ceramic phases

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Designing Wasteforms for Technetium Anion sorption with precursors for ceramic phases

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    1. Designing Wasteforms for Technetium Anion sorption with precursors for ceramic phases Jonathan Phillips Centre for Advanced Structural Ceramics Department of Materials, Imperial College London Prince Consort Road, London, SW7 2AZ

    2. Overview

    3. 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

    4. 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-.

    5. 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.

    9. Materials and Methods LDH powders were produced by a co-precipitation method: Solution A: Ca(NO3)2.4H2O , Al(NO3)3.9H2O and Fe3+(NO3)3.9H2O were combined in the desired stoichiometric ratio in distilled water to make a 1M (total) solution. Solution B: NaOH + NaNO3 were dissolved in distilled water to make a pH 12.5 solution containing a five fold excess of the desired interlayer anion. Solution A was added drop wise to Solution B whilst being stirred vigorously and allowed to react for 1 hour. The solids were separated by vacuum enhanced filtration, rinsed then dried at 80°C in air before being ground for further use.LDH powders were produced by a co-precipitation method: Solution A: Ca(NO3)2.4H2O , Al(NO3)3.9H2O and Fe3+(NO3)3.9H2O were combined in the desired stoichiometric ratio in distilled water to make a 1M (total) solution. Solution B: NaOH + NaNO3 were dissolved in distilled water to make a pH 12.5 solution containing a five fold excess of the desired interlayer anion. Solution A was added drop wise to Solution B whilst being stirred vigorously and allowed to react for 1 hour. The solids were separated by vacuum enhanced filtration, rinsed then dried at 80°C in air before being ground for further use.

    11. Characterisation of product

    13. Link: effect can be enhanced by thermally driving off anions to next slide.Link: effect can be enhanced by thermally driving off anions to next slide.

    14. 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

    15. Results : Anion Exchange Cl:NO3

    16. Results : Anion Exchange

    18. 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

    20. 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

    22. Results : Thermal Analysis NO3

    23. Thermal Product - NO3 23

    24. Results : Thermal Analysis Cl

    25. Thermal Product – Cl 25

    26. Thermal Product – Cl 26

    27. 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.

    28. This project is funded by the UK Engineering and Physical Sciences Research Council through the DIAMOND consortium Thank you for your attention

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