A comparative study of two methods for the synthesis of fly ash-based sodium and potassium type zeolites

Fly ash (FA) from the Rugeley Power Station, West Midlands (England) was used in a study on synthesis at laboratory scale of zeolitic materials under various conditions by two different routes. Zeolitic materials were synthesized from FA by hydrothermal treatment in NaOH (Na-phillipsite, hydroxysodalite, hydroxycancrinite, tobermorite, analcime and herschelite) and KOH (hydroxysodalite, zeolite Barrer-KF, K-chabazite and zeolite Linde Type F) solutions. By fusion with NaOH followed by hydrothermal reaction, FA was converted into faujasite and hydroxysodalite. No zeolitic materials were obtained by this method using KOH as alkali activator. The process of synthesis was optimised by applying a wide range of experimental conditions with a wide range of reaction temperature, time, alkali hydroxide concentration and solid/solution ratio. The efficiency FA-based zeolites (FAZs) for heavy metal and ammonium uptake from synthetic solutions at laboratory scale have been investigated by the authors, revealing that these FAZs may reach appropriate cation exchange capacities for their application in industrial wastewater treatment.