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1 2015

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Analiza możliwości oczyszczania gazów wylotowych z Hg0 i CO2 na zeolitach syntetycznych otrzymanych z popiołów lotnych

Wdowin M., Baran P., Panek R., Zarębska K., Franus W.

Rocznik Ochrona Środowiska

2015

Tom 17, cz. 2

1306--1319

The paper presents the usage possibility of Na-X zeolite as a sorbent of elemental (Hg0) form of mercury or carbon dioxide (CO2). The research material was zeolite obtained in the hydrothermal reaction of fly ash and an aqueous solution of sodium hydroxide. To improve the adsorption capacity of the zeolite with respect to vapour of mercury (Hg0), the zeolite was silver activated by ion exchange method. As a result a form of Ag-X zeolite was obtained. To determine the influence of a modification on sorption capacity of obtained zeolites (Na-X, Ag-X) were subjected to mineralogical and textural characteristics. Then for both zeolites the Hg0 and CO2 sorption studies were performed. Mineralogical analysis of SEM-EDS showed that the sodium ions have been substituted in its entirety with silver ions. After activation of the specific surface area and the share of mesoropores have decreased. However, the share of micropores increased which is associated with substitutions of Na+ ions by ions with a larger ionic radius i.e. silver. Mercury vapour sorption experiment showed almost immediate breakthrough across zeolite Na-X at a flow rate of gas stream at 80 ml/min. Activation of silver greatly improved sorption capacity of tested zeolite and breakthrough of 5% wt. Hg0 occurred after the time of 13017 min. The time for breakthrough of Hg0 for Ag-X is five times longer than for the commercially available activated carbon modified with bromine (AC/Br). Carbon dioxide adsorption studies have shown little effect for sorption capacity for zeolite with silver, where the result for the zeolite Na-X and Ag-X were similar at average level of 25 cm3g-1 for p/p0 = 0.01 (lower values for Ag-X). From obtained results the constants of Dubinin-Raduszkiewicz and Langmuir isotherms were calculated. The monolayer capacity calculated from the equation of Langmuir have shown the lack of differentiation for both examined samples, indicating that the modification of the starting zeolite with silver ions did not improve the sorption capacity with respect to carbon dioxide. Besides in the considered pressure range sorption capacity of zeolites terms to carbon dioxide decreased slightly. The results indicate that the silver modification improves the adsorption of mercury vapour, but has no effect on the sorption of carbon dioxide.