The effect of low solid/liquid ratio on hydrothermal synthesis of zeolites from fly ash

Tomasz T. Wałek, Fumio Saito, Qiwu Zhang

Research output: Contribution to journalArticlepeer-review

64 Citations (Scopus)


Hydrothermal synthesis of zeolites from class F fly ash was carried out at solid/liquid (S/L) ratio of 4 g/dm3 to investigate the initial dissolution stage of the process. The low S/L ratio caused a significant increase in fly ash dissolution (up to 85 wt%) during first 4 h of reaction. It was shown that for S/L ratios typically used (50-150 g/dm3) fly ash dissolution is largely limited. In these conditions zeolite crystals are formed on the surface of partially dissolved fly ash particles. This precludes further dissolution and results in formation of a low-crystallinity zeolite-like material. At low S/L ratio, a degree of crystallization of 80 wt% was observed, and NaP1, analcime and/or hydroxy-sodalite phases were obtained depending on the applied NaOH concentration and temperature. Single phase NaP1 zeolite was obtained in 2 M NaOH solution at temperature maintained at 104 °C during the stage of dissolution and reduced to 80 °C in the stage of crystallization. Application of low S/L ratio allows a clearer description of the relationships between the synthesis conditions and the products obtained.

Original languageEnglish
Pages (from-to)3194-3199
Number of pages6
Issue number15-16
Publication statusPublished - 2008 Nov


  • Dissolution
  • Fly ash
  • Solid/liquid ratio
  • Synthesis
  • Zeolite

ASJC Scopus subject areas

  • Chemical Engineering(all)
  • Fuel Technology
  • Energy Engineering and Power Technology
  • Organic Chemistry


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