Synergistic Removal of Sulfur, Ash, and Fluorine from Coal via an H₂O₂-Microwave-Enhanced Flotation Process

To enable the coordinated removal of sulfur, ash, and fluorine from coal, we employed an H₂O₂-microwave-enhanced flotation process. The effects of the solvent (type and concentration) and microwave conditions (temperature, power, and irradiation time) were evaluated sequentially using Xinjiang AL coal. Under the optimal conditions (H₂O₂ concentration of 0.15 mol/L, microwave temperature of 80 °C, power of 800 W, and time of 10 min), the desulfurization rate reached 61.83%. The deashing and defluorination rates reached 74.82% and 53.95%, respectively. Compared with flotation alone, these efficiencies increased by 54.69%, 28.87%, and 43.87%, respectively. FTIR combined with XPS-(S 2p) spectra indicated that sulfur in multiple forms decreased in the AL cleaned coal. Relative to the raw coal, pyritic sulfur, sulfate sulfur, and organic sulfur decreased by 55.24%, 59.78%, and 32.75%, respectively. XPS-(F 1s) spectra showed that the relative content of inorganic fluorides (e.g., fluorite and fluorapatite) occurring in the ash decreased from 47.73% to 37.03%. XRD and SEM-EDS further confirmed an overall decrease in sulfur-and fluorine-bearing minerals accompanying ash reduction. The relative contents of S and F decreased by 51.79% and 46.67%, respectively. The relative contents of the major mineral elements in the ash (Fe, Mg, Ca, Si, and Al) decreased by 27-88%. The interaction between H₂O₂ and microwave irradiation promotes the liberation of part of the ash and its associated minerals. Minerals such as pyrite, fluorite, and fluorapatite are removed together with ash during flotation. This enables the synergistic removal of sulfur, fluorine, and ash.