Distribution Characteristics of Valuable Elements, Al, Li, and Ga, and Rare Earth Elements in Feed Coal, Fly Ash, and Bottom Ash from a 300 MW Circulating Fluidized Bed Boiler

Feed coal, fly ash (FA), and bottom ash (BA) were collected from a 300 MW circulating fluidized bed boiler. A mechanical screen classifier was used to separate and obtain particles with different sizes. The distribution of valuable elements, including aluminum (Al), lithium (Li), and gallium (Ga), and rare earth elements (REE) in the samples was investigated. Results indicate that the contents of SiO2 and Al2O3 in sized ash particles decreased as the particle size decreased; meanwhile, the contents of CaO, SO3, and Fe2O3 apparently increased. The sulfur-fixing product anhydrite tended to be distributed in the fine ash particles. The valuable elements were more enriched in FA than in BA. The Li, Ga, and REE were evenly distributed in FA particles with different sizes. Separating ash particles with a superhigh concentration of these rare elements was difficult using the mechanical screen, but a part of the anhydrite or CaO in circulating fluidized bed ash could be removed easily. The Li and REE in the feed coal were highly associated with quartz, kaolinite, and other fractions containing SiO2 and Al2O3. No definitive relationship between the Ga concentration and Al2O3 content in the feed coal and ash samples was observed.