Removal of elemental mercury from coal combustion flue gas by bentonite-chitosan and their modifier

Adsorption experiments of vapor-phase elemental mercury were carried out using modified bentonite-chitosan in a laboratory-scale fixed-bed reactor. VM3000 online mercury analyzer was applied to detect the inlet and outlet mercury (Hg0) concentrations. The characterizations of the sorbents were analyzed using the methods such as nitrogen (N2) adsorption/desorption, scanning electron microscopy (SEM), and Fourier transform infra-red spectroscopy (FT-IR). It was observed that the porosity and specific surface area decreased after modification. The FT-IR spectra demonstrated that the iodine was found in the inner layer of bentonite and the chemical reactions of iodine and sulfuric acid with the amide of chitosan occurred. The tests in the fixed-bed reactor showed that the bentonite-supported chitosan exhibited lower mercury capture than raw bentonite, which indicated that the mechanism of gas phase mercury removal was different from that of ionic state mercury in liquid. In general, the iodine-modified sorbents demonstrated higher mercury capture efficiency than raw sorbents and the iodine-modified bentonite showed the best one. Mercury removal efficiency of bentonite supported by chitosan sorbents could be promoted from 85 to 100% when added appropriate amount of H2SO4, while that of iodine- and sulfuric acid-modified bentonite exhibited opposite tendency because of their absolutely different physicochemical properties.