The Immobilisation of Magnesium Hydroxide Sludge in Composite Cement Systems

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• 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.

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Immobilisation of Magnesium Hydroxide Sludgein
Composite Cement Systems

• Background
• Arise from re-processing Magnox fuel rods and
  storing Magnox swarf in ponds at Sellafield since
  early 1980s.
• 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.

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Immobilisation of Magnesium Hydroxide Sludgein
Composite Cement Systems
S. Moore, Wet ILW Historic Wastes at
Sellafield, Proceedings of a Seminar on the
Retrieval, Processing, Packaging and Storage of
Wet ILW/Sludge Originating from UK Nuclear
Installations, British Nuclear Group, June 2007.
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Immobilisation of Magnesium Hydroxide Sludgein
Composite Cement Systems

• Project Aims
• Experimental study of waste/cement interactions.
• Study the fate of the Mg in the sludge.
• Compositional.
• Microstructural.
• Physical.
• Chemical.
• Prepare simulant waste.
• Design cement immobilisation formulations.
• Encapsulation experiments.

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Immobilisation of Magnesium Hydroxide Sludgein
Composite Cement Systems

• Experimental - I
• Simulant material.
• 30 wt solids
• Cement formulations.
• 91 BFS1OPC2.
• 41 BFSOPC.
• 54 PFA3OPC.
• Sludge free and sludge cement samples.
• Prepared using distilled water and 0.01M NaOH.

11 sludgecement solids
15 wt waste solids
1BFS Blastfurnace slag, 2OPC Ordinary
Portland cement, 3PFA Pulverised fuel ash.
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Immobilisation of Magnesium Hydroxide Sludgein
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).

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Immobilisation of Magnesium Hydroxide Sludgein
Composite Cement Systems

• Results Discussion
• Simulant powder.
• 80.81 wt Mg(OH)2, 8.48 wt MgCO3.
• Negligible carbonation on mixing.
• Majority particle size 0.35 microns.

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Immobilisation of Magnesium Hydroxide Sludgein
Composite Cement Systems

• Results Cement Encapsulation
• Composition.

XRD trace of cemented sludge made with 91
BFSOPC and distilled water
Legend HT - Hydrotalcite (Mg6Al2(CO3)(OH)16.4H2O)
MH - Mg(OH)2 Ge - Gehlenite (2CaO.Al2O3.SiO2) A -
Alite (3CaO.SiO2) B - Belite (2CaO.SiO2)
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Immobilisation of Magnesium Hydroxide Sludgein
Composite Cement Systems

• Results Cement Encapsulation
• Composition.

TGA DTG trace of cemented sludge made with 91
BFSOPC and distilled water
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Immobilisation of Magnesium Hydroxide Sludgein
Composite Cement Systems

• Results Cement Encapsulation
• Composition - Summary.

Mix Mix Solution Main Phase Main Phase Other Minor Phases Other Minor Phases Other Minor Phases Other Minor Phases Other Minor Phases Other Minor Phases Other Minor Phases Other Minor Phases
C-S-H Mg(OH)2 MgCO3 Hydrotalcite Gehlenite Portlandite Calcite Ettringite Quartz Mullite
91 BFSOPC1 Water ? ? ?
91 BFSOPC Water ? ? ? ? ?
NaOH ? ? ? ? ?
41 BFSOPC1 Water ? ? ? ? ?
41 BFSOPC Water ? ? ? ? ? ? ?
NaOH ? ? ? ? ? ? ?
54 PFAOPC1 Water ? ? ? ? ? ?
54 PFAOPC Water ? ? ? ? ? ? ? ? ?
NaOH ? ? ? ? ? ? ? ? ?
Notes a) 1 Sludge free samples. b) All mixes
hydrated for 7, 28 and 90 days. c) Alite and
belite omitted. d) C-S-H - Calcium silicate
hydrate, HT - Hydrotalcite (Mg6Al2(CO3)(OH)16.4H
2O), Ge - Gehlenite (2CaO.Al2O3.SiO2),
Portlandite (Ca(OH)2), Calcite, (CaCO3),
Ettringite (3CaO. 3CaSO4.32H2O), Quartz (SiO2),
Mullite (Al6Si2O13)
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Immobilisation of Magnesium Hydroxide Sludgein
Composite Cement Systems

• Results Cement Encapsulation
• Microstructure.

SEM BEI micrograph and EDS maps of cemented
sludge made with 91 BFSOPC and distilled water,
and hydrated for 90 days
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Immobilisation of Magnesium Hydroxide Sludgein
Composite Cement Systems

• Results Cement Encapsulation
• Microstructure.

SEM BEI micrograph and EDS maps of cemented
sludge made with 41 BFSOPC and distilled water,
and hydrated for 90 days
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Immobilisation of Magnesium Hydroxide Sludgein
Composite Cement Systems

• Results Cement Encapsulation
• Microstructure.

SEM BEI micrograph and EDS maps of cemented
sludge made with 54 PFAOPC and distilled water,
and hydrated for 90 days
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Immobilisation of Magnesium Hydroxide Sludgein
Composite Cement Systems

• Results Cement Encapsulation
• Physical and chemical properties.

- made with distilled water
- made with NaOH solution
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Immobilisation of Magnesium Hydroxide Sludgein
Composite Cement Systems

• Results Cement Encapsulation
• Physical and chemical properties.

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Immobilisation of Magnesium Hydroxide Sludgein
Composite Cement Systems

• Results Cement Encapsulation
• Physical and chemical properties.

For samples hydrated for 90 days
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Immobilisation of Magnesium Hydroxide Sludgein
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.

1 N C Collier, X Li, Y Bai, N B Milestone, Cem.
Concr. Res., In press.
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Immobilisation of Magnesium Hydroxide Sludgein
Composite Cement Systems

• Further questions
• Which active ions are adsorbed onto Mg(OH)2?
• What happens to the active material during
  cementation?

• Acknowledgements
• Ed Butcher, Steve Palethorpe and Hugh Godfrey
  from Nexia Solutions for useful discussions.

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Immobilisation of Magnesium Hydroxide Sludgein
Composite Cement Systems

• Thanks for your attention.
• Any questions?