New insights for improving low-rank coal flotation performance via emulsified waste fried oil collector

A novel emulsified waste fried oil collector (EWFOC) of the oil-in-water (O/W) type was prepared via transesterification and ultrasonic emulsification, and to be used as an alternative collector to improve the flotation performance of low-rank coal while reducing the collector dosage. The preparation process of EWFOC was optimized, and its performance was compared to that of a common collector (diesel) and waste fried oil collector (WFOC) in the flotation of long-flame coal collected from two top coal-producing province (autonomous region) in China. The micrograph, particle size distribution and dispersion of EWFOC were observed under optical microscope. In addition, the functional groups and wettability were also analyzed. The optimized emulsification conditions for EWFOC were determined as HLB = 14.0, emulsifier dosage of 1 %, oil–water ratio of 3:7, ultrasonic time of 5 min, and a NaCl concentration of 0.02 mol/L. Compared to diesel, WFOC improved the recovery of clean coal and reduced the ash content of clean coal. EWFOC, on the other hand, demonstrated better flotation performance, resulting in up to a 70 % reduction in WFOC dosage. This significant improvement is attributed to the cavitation mechanism of phacoemulsification, which renders EWFOC stable in water with homogenous dispersion and enhances its attachment to coal particles. EWFOC showed better performance compared to diesel and WFOC in terms of improved contact angle as well as adherence to oxygen-containing functional groups (especially O=C–O and C–O) on the surface of long-flame coal, thus enhancing the hydrophobicity of the said coal.