Molten-salt method for the synthesis of zeolitic materials I. Zeolite formation in alkaline molten-salt system

The molten-salt method has been applied for the zeolitization of fly ash an d other mineral wastes. Fly ash was converted into zeolitic materials by a simple thermal treatment at molten states of some salt mixtures without any addition of water. Various combinations of salt mixtures were employed for the zeolitization of fly ash, using NaOH, KOH, or NH4F as mineralizer, and NaNO3, KNO3, or NH4NO3 as stabilizer. The resultant zeolitic materials wer e composed of sodalite and cancrinite as major crystalline phases. This mol ten-salt method was also confirmed for the facile zeolitization of kaolinit e, montmorillonite, and natural zeolite waste. The main zeolite species syn thesized by the molten-salt method were dependent on the types of salt mixt ure and raw material used. The molten-salt method developed in this study c ould open a new and alternative approach for the mass treatment of these mi neral wastes at low cost, as well as for the improvement of the purity and alkalinity of zeolitic materials. (C) 2000 Elsevier Science B.V. All rights reserved.