Zeolites were synthesized trom the mixture of the fly ash with a relatively low silica content and the rice husk ash by a hydrothermal treatment method. The fraction of phillipsite in the formed zeolite was increased with the fraction of rice husk ash whereas the fraction of by-product hydroxysodalite was decreased. Phillipsite can be selectively synthesized from the mixture, using new or recycled NaOH aqueous solutions. It is found that the product powder prepared from the mixture of the fly ash and the rice husk ash has almost the same ammonium ion adsorption capacity as the product from the mixture of the fly ash and pure silica powder. Phillipsite can be synthesized from the mixture of the fly ash and the rice husk ash for shorter treatment time than that from the mixture of the fly ash and pure silica powder, being independent of NaOH concentration.
