Mercury removal by the S2Cl2 modified biomass coke with mechanochemical versus impregnation method

Abstract

Mercury is a global pollutant. In this work, wood sawdust-based biomass coke and S2Cl2 were selected as the raw material and modifier, respectively. Two modification methods were adopted to prepare the mechanochemical S2Cl2-modified biomass coke (BC-S2Cl2-MC) and S2Cl2 impregnated-modified biomass coke (BC-S2Cl2-IM). The flue gas fixed mercury-removal experiment rig was used to evaluated the mercury removal performance of the adsorbents. The Brunauer-Emmett-Teller (BET), scanning electron microscope (SEM), Fourier transform infrared spectrometer (FTIR), and X-ray photoelectron spectroscopy (XPS) were adopted to characterize the surface physical and chemical properties of some typical samples. Hg temperature-programmed desorption (Hg-TPD) was used to analyze the main mercury forms in the used adsorbents. The results show both mechanochemistry and impregnation methods can significantly improve Hg0 removal performance with the addition of S2Cl2. Increasing S2Cl2 addition amount increases the Hg0 removal efficiency of BC-S2Cl2-MC overall. Considering the economy and mercury removal performance, 800 μL is the optimum addition amount for the 3 g raw biomass coke with the Hg0 removal rate of 91.94%. The change of ball milling parameters within a certain range has little effect on the mercury removal performance of BC-S2Cl2-MC. The best ball milling parameters in this work are a ball-to-material ratio of 10:1 and big balls (diameter = 20 mm), which corresponds to the Hg0 removal rate of 97.12%. Chemical adsorption plays a great part in the Hg0 removal of BC-S2Cl2-MC and BC-8S2Cl2-IM. The surface functional groups such as O–H, C = O, C = S and thiophen/element sulfur and sulfoxide are the main Hg0 adsorption active sites. HgS (black) is the main mercury form in the used BC-S2Cl2-MC and used BC-S2Cl2-IM. The mechanochemical method has more prospects for industrial application than the impregnation method.