Influence of oxidation regulation on flotation desulfurization of fine coking coal

Desulfurizing high-sulfur coking coal, a strategically valuable resource, optimizes its utilization and reduces environmental sulfur emissions. This study investigated moderate oxidation to enhance flotation desulfurization of a fine coking coal (1.66% sulfur) from Guizhou, China. Without oxidant, single flotation of -0.2 mm feed yielded clean coal (89.91% yield, 1.32% sulfur and 11.89% ash), while adding 500 g/t oxidizing agent with 9-minute conditioning improved desulfurization performance (90.64% yield, 1.10% sulfur, 11.21% ash). Adopting a single roughing-single cleaning circuit further reduced the sulfur content of the final clean coal (84.73% yield, 1.04% sulfur, 11.37% ash). Flotation tests of pure minerals, combined with coating angle, induction time, microcalorimetry, AFM and Raman revealed oxidation significantly modifies pyrite. The contact angle decreased (75.6° to 31.3°), coating angle decreased (103.70° to 57.85°), induction time increased (5 ms to 50 ms), and wetting heat increased (1.85 J/g to 3.66 J/g). This is attributed to hydrophilic compound formation (e.g., Fe2(SO4)3, CaSO4, Fe(OH)3) on pyrite. Deposited hydrophilic species enhance pyrite hydrophilicity, leading to reduced floatability. The oxidation of the slurry significantly governs the amount of hydrophilic species formed on pyrite. Moderate oxidation effectively regulates their formation, enhancing pyrite depression. This provides a scientific basis for deep desulfurization technologies.