Long-term environmental stability of bromide coupled mechanical modified fly ash after mercury adsorption

Abstract

Bromide coupled mechanical modified (BMM) fly ash showed good mercury adsorption performance. However, we have no information about the environmental stability after mercury adsorption. In this paper, environmental stability was investigated by desorption method in different temperature and improved continuous extraction experiments. Long-term environmental stability experiments showed that mercury desorption rates of BMM fly ash and activated carbon (AC) were both less than 5 % after placing them in the natural environment for one year. The stability of BMM fly ash after mercury adsorption was similar to that of AC. BMM method not only increased the specific surface area, but also improved the stable binding of bromide modifier on the surface, thereby improving the adsorption performance and stability. After adsorption, mercury in BMM fly ash existed in the form of HgBr2, HgS and HgO. Moreover, the improved continuous extraction experiments showed that the residue fraction of mercury in BMM fly ash was highest reaching 28 %, which was higher than that of AC (21 %). DFT calculation also showed that the presence of bromine reduced the adsorption energy of the mercury adsorption process, which proved that the presence of bromine improved the adsorption efficiency and stability of the adsorbent. These results indicate that BMM fly ash has the same environmental stability as AC, thus it has great potential application value for mercury removal from flue gas in coal-fired power plants.