Inhibition of Spent Ion Exchangers in Geopolymer Matrix

1
Inhibition of Spent Ion Exchangers in Geopolymer
Matrix

• Institute of Rock Structure and Mechanics,
  Academy of Sciences of the Czech republic
• Dept. Of Chemistry of Geopolymers
• Laboratory of raw material treatment
• Hanzlicek T.,
  Steinerova M., Perná I., Straka P.
• Report on Project
  No. FI IM/128
• 
  reported 10/2005

2
Definition of problems

• Spent ion exchangers are gathered in area of
  nuclear power station in storage tanks with
  limited capacity.
• Spent ion exchangers are stored under the water
  level.
• Spent ion exchangers change their volume when
  dried and expand volume when watered.
• Storage of spent ion exchanger after their
  solidification and inhibition should be
  economically reasonable which means that one
  important condition is to fix maximum quantity of
  spent ion exchanger to any solidification matter.
  

3
Previous proves and tests

• The most important is to recognize the behavior
  of geopolymer matrix and its possibility to bind
  different type of metals in their soluble forms,
  which was studied and after it published in
  Journal of American Ceramic Society, titled
  Immobilization of Toxic Metals in Solidified
  Systems of Siloxo-Sial Networks 2005,
• The main aim of the above mentioned paper was to
  identify that the metals are chemically bound to
  the geopolymer network and even when the samples
  were fine crushed the metals were not detected in
  leaching water.

4
Following control tests

• The geopolymer matrix acquired by alkali aqueous
  reaction with activated clay was tested when
  usual sodium or potassium in soluble form was
  substituted by cesium carbonate.
• Was found that solidificated matter could be
  reached and as well as in case of sodium or
  potassium, the cesium is able to form insoluble
  geopolymer matrix.
• That means that cesium is chemically bind to the
  siloxo-sial network and equilibrate the
  electro-negativity of such a formed network by
  oxygen bridges.
• Next study employed radioactive tracers 152 Eu,
  134 Cs, 60 Co and 59 Fe in soluble form applied
  directly to the formatted geopolymer precursor.,
• Leaching tests prove that 99,9 of radioactive
  tracers are incorporated into the geopolymer
  network in case of water leaching and in case of
  sulphuric acid leaching the inhibition of
  radioactive tracers is about 40 .

5
Complementary proves

• Solidification of geopolymer matrix was proved
  also by use of D2O instead of water, when alkali
  aqueous solution was alternated by alkali
  solution of D2O.
• Sample of a solidificated matter is insoluble in
  water with very hard surface and as in cases with
  water any separated liquid or partially
  decomposition of a solid was observed.
• Means that eventual problem with presence of
  deuterium will not bother the solidification of
  geopolymer matrix.

6
The assays with spent ion exchangers

• Spent ion exchangers with 50 of water were
  applied directly to the geopolymer mixture in
  quantities starting at 10 wt. and ended by 50
  wt..
• In all cases the solidification is successful but
  immediately when submerged in water the samples
  are disintegrated into the small particles of
  matrix with visible ball shaped ion exchangers.
  Only in case of 10 wt of applied ion exchanger
  the sample resists to submerge.
• Problem is a homogenous distribution of
  relatively light watered spherical shaped ion
  exchangers in geopolymer mixture and when dried
  the shrinkage of the ion exchanger balls.
• In all experiments we have to mentioned the open
  porosity of geopolymer matrix and than
  possibility of liquid to penetrate the
  solidificated body.

7
Picture of the sample cross cut
8
Observation

• The sample with 20 wt. of spent ion exchangers
  present the above mentioned problems with no
  homogenous distribution of originally spherical
  shaped ion exchangers and visible pores around
  the shrinked balls.
• Also the compression resistance is lower ( 3,75
  MPa) than allows acquired norm.
• The open porosity of matrix and possibility of
  ion exchanger volume extension are the reasons of
  the sample disintegration.

9
Propounded solution

• The main problem of shrinkage and extensions of a
  spherical shaped exchangers could be resolved by
  their friction.
• The volume change is unalterable even of the
  non-formatted particles of the ion exchangers,
  the small no defined shape could be less
  dangerous than originally spherical shape.
• Also the homogenization of no defined particles
  in geopolymer matrix could be reached more
  effectively.
• The prepared series containing 14,8 wt. than
  17,2 wt. and 22,7 wt. of dry spent ion
  exchanger in dry geopolymer matrix resist the
  water submersion no crack or fissures were
  observed.
• Next series of samples were prepared with foamed
  geopolymer matrix with idea to allow the
  extension of spent ion exchangers into the free
  space in foamed matrix. In that case there is no
  disintegration of submerged samples but its
  necessary mentioned the growth of volume of the
  final material in order of percent.

10
Conclusion

• Next study should be orientated to the inhibition
  and encapsulation of radioactive tracers added to
  the smashed ion exchangers and according to the
  previous tests and assays we suppose the binding
  of radioactive metals into the geopolymer
  network. If there is a proof of inhibition than
  regardless to the compressive strength the
  geopolymer matrix could be used.
• Because the geopolymer matrix is prepared from
  waste industrially extracted clays and its
  activation and mixing is lowering considerably
  the price comparing it with cement we could
  recommend this method of solidification even up
  now the amount of radioactive waste in total will
  be 5 times bigger than amount of dry ion
  exchangers itself.