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.

Stringent leaching conditions including high pressure, temperature, and chemical consumption limit the extraction of valuable metals from circulating fluidized bed-derived high-alumina fly ash (CFB-HAFA) via the acid leaching method. In the present study, a complex utilization of CFB-HAFA, including the extraction of valuable metals (Al, Li, and Ga) and preparation of mesoporous material, is realized via a moderate acid–alkali-based alternate method. The results show that 82, 78, and 69% of Al, Li, and Ga, respectively, in CFB-HAFA are extracted by two treatments of acid leaching under moderate conditions of 15 wt % HCl concentration and 90 °C leaching temperature. The leaching behaviors of metals follow a shrinking core model, and the leaching process is first controlled by the surface chemical reaction at the initial stage and H⁺ diffusion thereafter. Numerous slit-shaped mesopores form in the residue during acid leaching. The final residue with a specific surface area of 273 m²/g can be used as an efficient adsorbent for removing methylene blue from dye wastewater. The maximum adsorption capacity is approximately 140.0 mg/g at room temperature. The Langmuir adsorption isotherm and pseudo second-order model can well describe the adsorption process and kinetics, implying that the adsorption is a monolayer and chemical adsorption.