Crystallization of K-L and K-W zeolites from fly-ash

The experimental conditions for the synthesis of K-L and K-W zeolites by hydrothermal alkaline treatment of coal-fired power plants fly-ash (FA) have been established. Thanks to their high stability in acid environments, these zeolites--in their sodic form--can be utilized to remove the ammonium ion NH4 _ from municipal and industrial wastewaters. The addition of SiO2 to FA or to the alkaline solution increases the Si:Al ratio of the slurry. This boosts the selectivity of the synthesis, ensures larger amounts of K-L and K-W zeolites, and prevents the formation of phases such as kaliophilite that are unsuitable for absorption. The zeolites thus synthesized exhibit high thermal stability up to 600°C. Industrial use of such zeolites could generate additional income for power producers and reduce the expenditure incurred in storing FA or wasting it to landfill.