Mechanochemical synthesis of ZnS-based sepiolite composites for accommodation of gaseous mercury from coal-fired flue gas

Based on the high volatility and low water solubility, Hg0 poses a difficulty and is the focus of mercury control. In this work, SEP@ZnS was firstly and successfully prepared through one-step mechanochemistry for Hg0 removal. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analysis revealed the existence of characteristic peak phases of Sepiolite (SEP), ZnS, Mg-O,-OH, and Zn-S bonds on SEP@ZnS, confirming the synthesis of SEP@ZnS. High-resolution transmission electron microscope (HRTEM) and Scanning electron microscope (SEM) displayed that the surface of SEP was rough with multi-medium pore distribution and the characteristic ZnS fringes, which could facilitate the physicochemical adsorption of elemental mercury. The mercury removal of SEP@ZnS with outstanding efficiency (97 %) and high capacity (2400 mu g & sdot;g-1) was obtained, and SEP@ZnS had high temperature and gas hourly space velocity (GHSV) resistance because of the adsorption reaction belonging to chemisorption and the presence of S 2 2- on SEP@ZnS. Thus, the captured mercury was predominantly presented as alpha-HgS and beta- HgS. O2, CO2, NO, and SO2 had both inhibitory and promotion effects for mercury removal. The results of thermal decomposition system (TPD-AFS) demonstrated the inhibition of flue gas was because the formation of alpha-HgS was inhibited during the reaction. Finally, the leaching toxicity test displayed the low leaching content (0.169 mu g & sdot;L-1) from spent-SEP@ZnS, which significantly dropped the mercury secondary environmental risks due to the existence of beta- HgS. It can be observed that SEP@ZnS was prepared by the mechanochemical strategy for mercury removal, which favored the environmental safety.