Effects of step-change of synthesis temperature on synthesis of zeolite 4A from coal fly ash

Pure form, single phase and high crystalline zeolite 4A samples were synthesized by applying step-change of synthesis temperature during hydrothermal treatment of coal fly ash prepared solution. The results indicate that step-change of synthesis temperature during hydrothermal treatment plays an important role in reducing the overall synthesis time while maintaining a high degree of crystallinity for the samples. In order to obtain similar quality of zeolite 4A sample, a reduction by half of the total synthesis time could be achieved by applying step-change of synthesis temperature compared to using constant temperature throughout the synthesis process. Generally, the crystallinity of the synthesized zeolite 4A samples was in the range of 75–87%. The yielding (quantity) of pure zeolite 4A samples obtained in all the experiments was about 15–18%. In addition, crystals of smaller particle size existing in a narrower particle size distribution were synthesized.