Release Behaviors of Arsenic in Fine Particles Generated from a Typical High-Arsenic Coal at a High Temperature

To make an accurate assessment on transformation behaviors of arsenic in coal at a high temperature, a typical high-arsenic coal collected from southwest China has been chosen in the study and a series of high-temperature experiments in different atmospheres have been conducted with the help of a lab-scale drop-tube furnace. Fine particulate matter were collected by a low-pressure impactor, for obtaining their mass size distributions and further quantifying for arsenic distributions and speciation in fine particles of different sizes. The results indicated that the bleeding ratios of arsenic in air combustion, CO2 gasification, and N2 pyrolysis were 85, 65, and 45%, respectively, at 1300 °C. The ratio was found to remain relatively constant when the temperature increased from 1200 to 1400 °C. Organically associated arsenic would be more inclined to vaporize in N2 pyrolysis, while both organic and inorganic associated arsenic would vaporize in CO2 gasification and air combustion. Pyrite-associated arsenic would vaporize together with sulfur in pyrite inclusions. The decomposition of pyrite followed the principle of an unreacted core model and was mostly controlled by the surface sulfur vapor pressure. Mass size distributions of fine particulate matter generated from coal gasification presented a bimodal distribution, and two major peaks appeared at 0.4 and 5 μm. Particles in the size range of 5 μm were presented as a round shape with pores and cracks on the surface, while particles in the size range of 0.4 μm were confirmed to be soot. Arsenic was obviously enriched in fine particles with a size of around 0.1–0.2 μm in both combustion and gasification. The major speciation of arsenic identified in fine particles generated from coal combustion was As2O5 and Ca3(AsO4)2, while that in fine particles generated from coal gasification was As2O5, As, AsO, and Ca3(AsO4)2.