Zeolitization of mineral wastes by molten-salt method: NaOH-KNO₃ system

Salt-thermal method exhibits several features such as high production yield, large-scale conversion, low elemental loss, and environmentally benign nature. This study has investigated the optimization of the NaOH-KNO₃ system for the zeolitization of fly ash and elucidated the characteristics of the resulting zeolitic materials. The following are the optimal reaction conditions for zeolitization of fly ash in NaOH-KNO₃ system: a temperature of 250 °C, 0.3-0.5 weight ratio of NaOH/KNO₃ and 0.7-1.4 weight ratio of KNO₃/fly ash. The NaOH-KNO₃ system is also confirmed for facile zeolitization of anthracite briquette, kaolinite, and pumice. The NaOH-KNO₃ system is likely to result in KNO ₃ occlusion or/and trapping. Because KNO₃ supplies two plant nutrients, the zeolitic materials synthesized by the NaOH-KNO₃ system could be used in agriculture as soil conditioners and fertilizer additives. It is clearly shown in this study that KNO₃ could be employed in place of NaNO₃ in the salt-thermal method with a potential use of the product as soil conditioner and fertilizer.