Synthesis of zeolite from coal fly ash by microwave hydrothermal treatment with pulverization process

Coal fly ash was hydrothermally treated with a NaOH aqueous solution at 373 K using microwave heating with zirconia beads. We investigated the effect of the pulverization of coal fly ash on the generation rate and crystalline phase of synthesized zeolite. As a result, it was found that the pulverization process increased the generation rate of phillipsite in the early stage of the hydrothermal treatment because it enhances the dissolution of aluminate and silicate ions from coal fly ash and the generation rate of the aluminosilicate-gel precursor. On the other hand, prepulverization before the hydrothermal treatment and long-term pulverization during the hydrothermal treatment promote the formation of hydroxysodalite rather than phillipsite. In addition, we examined the effect of the addition of an aluminum source on the yield of synthesized phillipsite. This examination revealed that the excess addition of aluminate ions promotes the generation of hydroxysodalite and that timely and proper addition improves the yield of synthesized phillipsite. From these results, it was concluded that pulverization in the early stage of the hydrothermal treatment is effective for the generation of phillipsite from coal fly ash. Moreover, the timely and proper addition of an aluminum source improves the yield of synthesized phillipsite.