Grinding-induced particle liberation and size–density redistribution governing Falcon separation of coal gasification fine slag

Coal gasification fine slag (CGFS) contains substantial residual carbon, but its efficient separation from mineral matter is hindered by fine particle size and complex carbon–mineral intergrowth. This study investigates how ball milling modifies particle liberation and size–density characteristics and consequently governs enhanced gravity separation using a Falcon concentrator. Grinding time was systematically varied, and separation performance was evaluated using product yield, combustible recovery, separation efficiency index (SEI), particle-size distribution, density fractionation, and microstructural characterization. An optimum grinding time of 10 min achieved a combustible recovery of 99.51%, concentrate yield of 96.76%, and SEI of 94.40%, while increasing tailings ash content from 76.29% to 93.90%. Grinding disrupted carbon–mineral composite particles and redistributed the feed toward particle populations more favorable for centrifugal separation. The proportion of intermediate-sized particles (0.074–0.25 mm) increased from 27.02% to 30.38%, while the low-density fraction (<1.7 g/cm3) increased from 6.56% to 9.23%. Microstructural observations supported enhanced carbon–mineral liberation. These coupled changes increased the effective density contrast and promoted centrifugal stratification, demonstrating that grinding-enhanced Falcon separation is governed by the synergistic effects of particle liberation and size–density redistribution.