Effect of reaction temperature on hydrothermal syntheses of potassium type zeolites from coal fly ash

Syntheses of potassium type zeolites were carried out from coal fly ash in the temperature region from 393 K to 453 K, in order to produce the zeolites containing exchangeable K+ with short reaction time. The formation behavior of zeolites and the possibility to advance the reaction time were investigated in this study.From 393 K to 453 K, the obtained zeolite species change from potassium–chabazite (K-CHA) into potassium aluminum silicate hydrate (K-H) via co-crystallization, with an increase in reaction temperature. The K-CHA and K-H are generated simultaneously in an early reaction stage at 433 K, and then the formation of K-H becomes predominant gradually with increasing reaction time in a later reaction stage. The cation exchange capacity (CEC) of zeolite obtained depends on the ratio of K-CHA formation in the potassium type zeolite. The mixture of K-CHA and K-H with high CEC of 175 meq/100 g can be synthesized as a potassium type zeolite under the reaction condition of 433 K, 3 h, 3.0 mol/dm3 KOH.