Investigation of the sorption of mercury vapour from exhaust gas by an Ag-X zeolite

Abstract

AbstractThe removal of gaseous mercury from flue gases from coal-fired power plants is currently an environmental challenge under investigation. Therefore, the main aim of this paper was to evaluate the suitability of faujasite group zeolites (Na-X) to adsorb mercury compounds. Previous, initial tests showed negligible Hg0 uptake by Na-X zeolite, but silver impregnation improved adsorption markedly. Therefore, the testing of mercury adsorption from flue gases into Ag+- impregnated Na-X synthetic zeolite (Ag-X zeolite) derived from coal fly ash was carried out. This material was characterized by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy, X-ray fluorescence and nitrogen adsorption/desorption before being evaluated for mercury removal from exhaust gas. After preliminary mercury adsorption tests (fixed bed) under a nitrogen atmosphere, the adsorbent was examined with a simulated flue gas composition under various conditions, i.e. weight of zeolite, temperature of experiment and zeolite in powder and granulated forms. The removal of mercury was shown to depend on the sorbent texture (powder or granulate), exhaust gas flow rate and contact time, as well as the temperature of the experiment. The Ag-X zeolite tested reduced the level of mercury in the flue gas and, depending on the experimental conditions, long-time mercury breakthrough ranges from 15 to 40% were obtained. The best results for mercury capture were obtained for granulated material.