Unveiling the interfacial mechanisms of kerosene-based emulsified collectors for efficient carbon recovery from coal gasification fine slag

The effective recovery of organic matter from coal gasification fine slag (CGFS) remains a significant environmental challenge, as its efficient decarbonization is hindered by a highly developed porous structure and a strongly hydrophilic, oxygen-rich surface. The separation of carbon from ash is therefore a crucial prerequisite for the subsequent valorization of CGFS. However, age-old collector regimes exhibit clear limitations in such systems, necessitating the development of advanced reagent strategies such as emulsified collectors. To overcome the low separation efficiency arising from inadequate surface hydrophobicity and the complex modes of carbon occurrence, this study comprehensively investigates the enhancement of CGFS carbon recovery using an optimized kerosene-based emulsified collector with a 25:10:65 formulation ratio. A comprehensive approach combining macroscopic flotation performance evaluation with detailed microscopic characterization – including particle size analysis, SEM–EDS, XPS, FTIR, and mercury intrusion porosimetry (MIP) – was employed to elucidate the underlying synergistic interfacial mechanisms. The results demonstrate that the optimized emulsified collector significantly outperforms conventional kerosene, achieving a maximum combustible recovery of 50.61% and a carbon content of 90.67% at comparatively lower reagent levels. Droplet size analysis in conjunction with MIP reveals a critical pore-sealing mechanism, whereby the ultra-fine emulsion droplets (d50 = 2.08 μm) are slightly larger than the most probable pore size of CGFS (2.07 μm). Rather than being drawn into the pore network via capillary forces, these stable micro-droplets preferentially bridge and seal surface pore openings, thereby preventing internal reagent loss. This unique mechanism not only enhances reagent utilization but also improves dispersion characteristics, resulting in a substantially increased effective specific surface area. Furthermore, XPS and FTIR analyses confirm that this highly selective interaction promotes the enrichment of hydrophobic C–C functionalities while facilitating the rejection of inorganic mineral phases. Overall, this work provides a robust mechanistic understanding and presents an efficient, reagent-saving strategy for the advanced beneficiation and high-value utilization of coal gasification solid waste.