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 and 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 were composed of sodalite and cancrinite as major crystalline phases. This molten-salt method was also confirmed for the facile zeolitization of kaolinite, montmorillonite, and natural zeolite waste. The main zeolite species synthesized by the molten-salt method were dependent on the types of salt mixture and raw material used. The molten-salt method developed in this study could open a new and alternative approach for the mass treatment of these mineral 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.