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The Immobilisation of Magnesium Hydroxide Sludge in Composite Cement Systems N C Collier, N B Milestone Immobilisation

Immobilisation of Magnesium Hydroxide Sludge in Composite Cement Systems. BackgroundArise from re-processing Magnox fuel rods and storing Magnox swarf in ponds at Sellafield since early 1980's.Many ponds containing many sludges.Aqueous suspensions of Mg(OH)2 .NaOH added to maintain high pH and k

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The Immobilisation of Magnesium Hydroxide Sludge in Composite Cement Systems N C Collier, N B Milestone Immobilisation

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    1. The Immobilisation of Magnesium Hydroxide Sludge in Composite Cement Systems N C Collier, N B Milestone Immobilisation Science Laboratory, Department of Engineering Materials, The University of Sheffield, Mappin Street, Sheffield S1 3JD, UK.

    2. Immobilisation of Magnesium Hydroxide Sludge in Composite Cement Systems Background Arise from re-processing Magnox fuel rods and storing Magnox swarf in ponds at Sellafield since early 1980’s. Many ponds containing many sludges. Aqueous suspensions of Mg(OH)2 . NaOH added to maintain high pH and keep solubility of waste ions low. Atmospheric carbonation. Organic contamination. Different sludges have different compositions.

    3. Immobilisation of Magnesium Hydroxide Sludge in Composite Cement Systems

    4. Immobilisation of Magnesium Hydroxide Sludge in Composite Cement Systems

    5. Experimental - I Simulant material. 30 wt% solids Cement formulations. 9:1 BFS1:OPC2. 4:1 BFS:OPC. 5:4 PFA3:OPC. Sludge free and sludge cement samples. Prepared using distilled water and 0.01M NaOH. Immobilisation of Magnesium Hydroxide Sludge in Composite Cement Systems

    6. Immobilisation of Magnesium Hydroxide Sludge in Composite Cement Systems Experimental - II Analysis. Compositional - XRD, TGA. Microstructural - SEM/EDS. Physical - Porosity (water absorption), compressive strength. Chemical - Quantity of slag reaction (TET preferential dissolution).

    7. Results & Discussion Simulant powder. 80.81 wt% Mg(OH)2, 8.48 wt% MgCO3. Negligible carbonation on mixing. Majority particle size ~ 0.35 microns. Immobilisation of Magnesium Hydroxide Sludge in Composite Cement Systems

    8. Immobilisation of Magnesium Hydroxide Sludge in Composite Cement Systems Results – Cement Encapsulation Composition.

    9. Results – Cement Encapsulation Composition. Immobilisation of Magnesium Hydroxide Sludge in Composite Cement Systems

    10. Immobilisation of Magnesium Hydroxide Sludge in Composite Cement Systems Results – Cement Encapsulation Composition - Summary.

    11. Immobilisation of Magnesium Hydroxide Sludge in Composite Cement Systems Results – Cement Encapsulation Microstructure.

    12. Immobilisation of Magnesium Hydroxide Sludge in Composite Cement Systems Results – Cement Encapsulation Microstructure.

    13. Immobilisation of Magnesium Hydroxide Sludge in Composite Cement Systems Results – Cement Encapsulation Microstructure.

    14. Immobilisation of Magnesium Hydroxide Sludge in Composite Cement Systems Results – Cement Encapsulation Physical and chemical properties.

    15. Immobilisation of Magnesium Hydroxide Sludge in Composite Cement Systems Results – Cement Encapsulation Physical and chemical properties.

    16. Immobilisation of Magnesium Hydroxide Sludge in Composite Cement Systems Results – Cement Encapsulation Physical and chemical properties.

    17. Immobilisation of Magnesium Hydroxide Sludge in Composite Cement Systems Conclusions Successful cementation using conventional encapsulation grouts. Majority of sludge is not reacting with the cement and remains as Mg(OH)2. Small amount of magnesium reacting with the cement to form a hydrotalcite-type phase. Majority of sludge is encapsulated rather than immobilised by the cement. Sludge has little influence on the cement hydration products formed. A small increase in sludge pH increases the porosity, reduces the compressive strength and increases the amount of slag reaction. Suggests the stoichiometry of the C-S-H caused by the alkali activation of the BFS and PFA is different to that formed without activation [1]. Washing the sludge before encapsulation will produce a more durable wasteform.

    18. Immobilisation of Magnesium Hydroxide Sludge in Composite Cement Systems Further questions Which active ions are adsorbed onto Mg(OH)2? What happens to the active material during cementation?

    19. Immobilisation of Magnesium Hydroxide Sludge in Composite Cement Systems Thanks for your attention. Any questions?

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