Adsorption of Hg0 from Coal Combustion Flue Gases by Novel Iodine-Modified Bentonite/Chitosan Sorbents

Adsorption experiments of vapor-phase elemental mercury (Hg⁰) were carried out by using modified bentonite/chitosan in a laboratory-scale fixed-bed reactor. VM3000 online mercury analyzer was applied to detect the inlet and outlet mercury concentrations. The characterizations of the sorbents were analyzed using the method of nitrogen (N₂) adsorption-desorption, Thermal gravimetric analysis (TGA) and X-ray diffraction (XRD). It is observed that porosity and specific surface area decreases after modifying. The TGA analysis demonstrates these sorbents will operate stably at flue-gas temperatures below 140°C, which can meet the temperature requirement of mercury removal after the electrostatic precipitator. The XRD analysis indicates that the iodine and chitosan is found in the inlayer of bentonite, and the chemical reactions of iodine and sulfuric acid with the amide of chitosan occurr. Fixed-bed adsorber tests show that iodine-modified bentonite-chitosan sorbents exhibit better mercury capture than that of iodine-modified chitosan. For the iodine-modified chitosan-supported bentonite sorbents, mercury removal capacity could be significantly promoted when an appropriate content of H₂SO₄ was added. The mercury capacities of modified chitosan sorbents increase with increasing temperature. The increase in mercury removal efficiency with an increase in temperature is a typical of a chemisorption mechanism.