In-FurnaceControl of Arsenic Vapor Emissions UsingKaolinite during Low-Rank Coal Combustion: Influence of Gaseous SodiumCompounds

Using additives in the in-furnace control of arsenic emissions is promising for reducing the impact on the downstream selective catalytic reduction (SCR) system and blocking the spread of arsenic pollutants into the environment. The study quantifies the arsenic adsorption capacity of kaolinite at high temperature and clarifies its fixation pathway with and without the existence of sodium vapor, which is easily adsorbed by kaolinite. Thermodynamic equilibrium calculations, Al-coordination and acid sites of products, as well as the adsorption energy based on density functional theory were performed. During separated arsenic adsorption, nearly 40% of trivalent arsenic [As(III)] is oxidized to pentavalent arsenic [As(V)] and bonded to kaolinite, forming an As-O-Al structure. In this respect, the arsenic adsorption capacity of kaolinite is 200 ug g-1, with 24% of arsenic shown to be well-crystallized Al-bound. During the co-adsorption process, 82% of As(III) is oxidized to As(V) and connected to the Al surface...