NH4Br-Modified Biomass Char for Mercury Removal in a Simulated Oxy-fuel Atmosphere: Mechanism Analysis by X-ray Photoelectron Spectroscopy

Mercury from recycled oxy-fuel gas needs to be removed because it can damage the aluminum devices in the system. In this work, low-cost NH4Br-modified rice husk char (RHCBr) was prepared as the biosorbent for mercury removal in an oxy-fuel atmosphere. RHCBr was characterized by scanning electron microscopy, Brunauer-Emmett-Teller, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy (XPS) technologies to study the physical and chemical properties of the prepared sorbents. Effects of O-2, HCl, SO2, and HCl/SO2 synthesis on mercury removal in a simulated oxy-fuel atmosphere were investigated in a fixed-bed reactor. XPS technology was applied to explore the mercury adsorption species and deduce the potential mercury heterogeneous oxidation mechanism in an oxy-fuel atmosphere. It was found that enriched CO2 in an oxy-fuel atmosphere could facilitate the mercury removal process. Generally, O-2 and HCl could promote the mercury removal efficiency in an oxy-fuel atmosphere, while SO2 could inhibit it. However, a low concentration of SO2 could promote it with the presence of HCI and O-2. The mercury adsorption species on RHCBr were mainly HgSO4, HgCl2, and HgBr2 in the presence of acid gas components (HCl and SO2). HCl could actively facilitate the generation of C-CI groups, which were also active sites for mercury removal, while SO2 could generate active site cover NH4HSO4, causing the deactivation of active sites. When HCl/SO2 synthesis was added, active site cover HSO4- would be removed by HCl, facilitating the mercury removal process. Meantime, HgCl2 species could be further converted to the strong-bonded species HgSO4 in the presence of O-2 and SO2, which was also beneficial for mercury removal.