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

Abstract 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 NH 4 + from municipal and industrial wastewaters. The addition of SiO 2 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.