Solidification of wastewater sledge from Nuclear Power Station

1
Solidification of wastewater sledge from Nuclear
Power Station

• 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
Wastewater sledge resource

• Sedimentation tanks gather radioactive, generally
  inorganic sledge accompanying wastewater
  treatment and contains mixture of different
  materials.
• The inorganic sledge is highly watered from 30
  60 wt..
• In certain cases sledge contains also small
  quantities up to 5 of Spent Ion Exchangers
  and may content some textile or rubber fibers and
  rests.
• Wastewater sledge is considered as radioactive
  material and must be treated according to the
  regulation.

3
Geopolymer matrix

• The studied geopolymer matrix was prepared from
  the waste clay materials (Eximos A.S., Sklopísek
  Strelec East Bohemia Region) lowering the price
  of binder as much as it could be.
• Advantage of used clay is content of 48 52 of
  fine sand grains (smaller than 100 ?m), which
  finally help to reach higher compressive strength
  resistence (over 10 MPa).
• Geopolymer matrix is activated by alkali aqueous
  solution and than water content in solidificated
  sledge could be recalculated according to its
  necessary quantity.

4
The sledge with 30 wt. of water

• The samples were prepared by mixing the
  geopolymer matrix with watered sledge reducing
  the water content in first step of preparation.
• In that case the inorganic sledge with small
  amount of spent ion exchangers ( up to 2 3
  volume ) was not retaining the water content.
• During the mixing of the pretreated matrix with
  inorganic matter sledge could be on the beginning
  observed the act of added water the prepared
  mixture slightly lose its viscosity.
• After homogenization all content of fluid mass (
  during aprox. 10 minutes) could be easily filled
  into the mould.
• The content of dry sledge reaches 35 wt. of the
  final mass weight.

5
The sledge with 60 wt. of water

• The highly watered sledge was of the same origin
  (inorganic mixture of sediments with low
  quantities of spent ion exchangers).
• In that case was necessary to prepare the
  geopolymer matrix doped with ash gathered in coal
  burning power plant in textile filters because
  water excess in sledge could misbalance the
  geopolymer reaction.
• Obtained mixture was a viscous matter and
  difficult to mould but with slight vibration the
  samples were satisfactory prepared.
• By the ash additive and use of very watered
  sledge the final content is much lower than in
  above mentioned series of sample. The maximum
  content is about 15 wt..

6
The qualities of solidificated sledges

• According to the previous works using geopolymer
  structure to immobilize toxic metals and
  radioactive tracers we could suppose that all
  dangerous elements are to be captured in
  geopolymer network.
• In both cases solidificated matters were
  insoluble in water and if submerged any cracks or
  fissures could be observed.
• Detected compression pressure resistance in both
  cases overpass the limit of the appropriate norms
  results show the resistance higher than 10 MPa.
  
• According to the economic point of view must be
  mentioned the volume of toxic waste which in
  first case is 3 times bigger and in highly
  watered sledge is more than 6 times bigger.

7
Solidification versus final volume of the
dangerous waste

• Because of escalating volume 3, respectively 6
  times the experiments were leaded by the idea to
  use only very cheap and easily obtained raw
  materials.
• This was a reason to choose waste clay material
  (yearly more than 20,000 tons and in case of
  highly watered sledge the use of daily
  increasing, immeasurable quantities of ashes.
• The only problem could be seen in large areas of
  storage but the advantages of geopolymer binder
  are to be taken into consideration
• long term stability,
• high resistance to the rising temperature up to
  1000 C,
• geopolymer does not burns and not release smoke.

8
Conclusion

• Geopolymer matrix could fix different impurities
  which contains water sledge and encapsulate them
  into the siloxo-sial network.
• Geopolymer matrix could immobilize radioactive
  metals in the formatted polymer like network.
• Geopolymer matrix is an economic way how to
  solidify partially dewatered radioactive sledge
  (30 wt. of water) incidents as sediment in
  wastewater tanks of nuclear power plants.