Valorization of waste fried oil into microemulsion collector for sustainable flotation separation of coal gasification fine slag

Coal gasification fine slag (CGFS) is a typical bulk solid waste from coal‑chemical industry. The porous residual carbon in CGFS contains abundant surface oxygen‑containing hydrophilic groups, which gives rise to poor inherent floatability and hinders carbon‑ash separation for subsequent resource utilization. Diesel, the widely‑used collector for CGFS flotation, requires extremely high dosage to obtain acceptable separation indices, which raises processing cost and aggravates consumption of fossil‑derived reagents. Aiming at these bottlenecks, this work valorizes waste fried oil (WFO), a common kitchen waste, into a high-efficiency microemulsion collector for sustainable CGFS flotation. The flotation performances of diesel, raw WFO, and the as-prepared WFO microemulsion were systematically compared across a wide dosage range, and the underlying enhancement mechanism was clarified via laser particle size analysis, FTIR, and XPS characterization. Results show that microemulsification reduces the median droplet diameter (D50) of WFO from 120.00 μm to 3.23 μm, greatly improving its aqueous dispersion uniformity and collision probability with residual carbon particles. At a dosage of only 25 kg/t, the WFO-based microemulsion collector achieves concentrate yield (~62%) and combustible recovery (~77%) equivalent to diesel at 75–90 kg/t, cutting reagent consumption by over 50%. The superior performance stems from the synergistic effect of nanoscale dispersion enhancement and stronger hydrogen-bonding masking of hydrophilic oxygen-containing sites on residual carbon. This study provides a cost-effective waste-to-resource strategy, realizing simultaneous high-value reuse of waste oil and efficient resource recovery of coal chemical solid waste.