Surfactant-assisted spent fried oil for gasification slag flotation: An innovative approach for simultaneous waste oil utilization and slag separation

Waste fried oil (WFO) and coal gasification fine slag (CGFS) are both environmentally hazardous wastes, and the flotation separation of resources from CGFS is over-reliant on non-renewable petrochemicals as collectors, it is significant to utilize WFO to prepare renewable collectors for CGFS separation. In this study, six surfactants were selected to be compounded with WFO to prepare renewable collectors, and the flotation effect of the compounded collectors on CGFS and the surfactant-enhanced mechanism for WFO flotation effect were examined through flotation experiments, flotation kinetics experiments, laser particle size analysis, FTIR analysis, XPS analysis, and induction time tests. The results show that WFO alone needs to be used in a large dosage (>30 kg/t) in order to show better flotation performance than diesel, while the flotation performance is greatly improved after compounding with surfactants, among which the best effect is achieved with Span80, and the dosage cut-off point of the compounded collector for flotation better than diesel is reduced to 12.5 kg/t. The surfactant can make the dispersed droplet size of WFO in water decrease from D 50 = 120 μm to 5.63 μm. Meanwhile, the surfactant-assisted WFO can be adsorbed on the residual carbon surface of CGFS through hydrophobic and hydrogen-bonding forces, which can mask the hydrophilic region of the carbon surface and enhance its hydrophobicity. Surfactant-assisted WFO can further shorten the adhesion induction time between CGFS particles and air bubbles, thus facilitating the recovery of more residual carbon in a shorter period of time. The findings can provide theoretical basis and technical support for the resourceful disposal of WFO and CGFS synergistically.