Immobilization of cesium in fly ash-silica fume based geopolymers with different Si/Al molar ratios

Quanzhi Tian, Shingo Nakama, Keiko Sasaki

Research output: Contribution to journalArticle

3 Citations (Scopus)

Abstract

Geopolymers are considered as promising matrixes for waste solidification. However, the effects of the Si/Al molar ratio of geopolymer on the immobilization efficiencies for metal ions have not been fully studied and understood. In the present study, geopolymers with different Si/Al ratios were synthesized from coal fly ash and silica fume. Adsorption tests were conducted to evaluate their immobilization efficiencies for Cs+. The results indicated that geopolymer with low Si/Al ratio could have a better immobilization performance for Cs+ than that with high Si/Al ratio. High Si/Al ratio could contribute to a more compact structure of geopolymer. Each sorption process fitted better with the pseudo-second-order model, and all of them were governed by film diffusion. However, the diffusion mode was gradually closed to particle diffusion with the increase in the Si/Al ratio. Both Langmuir and Freundlich models could well fit the sorption data, and the free energy of each sorption process decreased with the increase in the Si/Al ratio according to D-R equation. The distribution of AlO4 tetrahedron in the geopolymer structure plays a significant role in the immobilization of Cs+. Low Si/Al ratio could result in that more AlO4 tetrahedrons distribute in the small rings (<eight-member), which has stronger locking effects on Cs+. However, high Si/Al ratio leads to the distribution of AlO4 tetrahedrons mainly in larger rings (≥eight-member), and this could contribute to the high leaching amount of Cs+. In addition, high-temperature treatment could contribute to the formation of nepheline or pollucite in geopolymer matrix. These minerals locked Cs+ in their structures, and the leaching amount of Cs+ was reduced correspondingly from high levels (26.36%, 27.26%, and 66.92%) to very low levels (0.67%, 0.53%, and 0.95%).

Original languageEnglish
Pages (from-to)1127-1137
Number of pages11
JournalScience of the Total Environment
Volume687
DOIs
Publication statusPublished - Oct 15 2019

Fingerprint

Coal Ash
Geopolymers
Cesium
Silica fume
cesium
Fly ash
fly ash
immobilization
silica
sorption
Sorption
leaching
matrix
nepheline
Leaching
solidification
coal
adsorption
Coal
fume

All Science Journal Classification (ASJC) codes

  • Environmental Engineering
  • Environmental Chemistry
  • Waste Management and Disposal
  • Pollution

Cite this

Immobilization of cesium in fly ash-silica fume based geopolymers with different Si/Al molar ratios. / Tian, Quanzhi; Nakama, Shingo; Sasaki, Keiko.

In: Science of the Total Environment, Vol. 687, 15.10.2019, p. 1127-1137.

Research output: Contribution to journalArticle

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