Assessment of silver modification's impact on the internal structure stability, phase and textural properties of fly ash-derived X and A zeolites

Abstract

Zeolites X and A able to bind elemental mercury were synthesized via a hybrid method. The procedure involved melting fly ash with sodium hydroxide, followed by simultaneous activation and crystallization of zeolites during the hydrothermal synthesis stage. The influence of silver modification on the phase composition and textural properties of zeolites X and A was systematically investigated. The applied method resulted in the formation of highly crystalline zeolite X coexisting with residual quartz and mullite, as well as mono-mineral zeolite A. Compared to unmodified zeolites and those modified with lower doses of the activating agent, a higher dose of silver nitrate slightly reduced the degree of crystallinity of the synthesized zeolites. Zeolites X and A exhibited significant differences in their specific surface areas. Although zeolites X displayed surface area values approximately six times higher than those of zeolites A, both types demonstrated comparable efficiency in elemental mercury sorption. Results from mercury removal experiments suggest that silver ions, after occupying narrower micropores, facilitate the formation of mesoporous layers when no additional micropore surfaces are available. Consequently, mercury removal occurs within mesopores via amalgamation with silver deposited on their surfaces.