Investigation of oily bubble–enhanced flotation characteristics of coarse low-rank coal: Experimental insight, extended DLVO theory, and Stefan–Reynolds model analysis

This study quantitatively demonstrated the flotation enhancement of coarse low-rank coal using innovative oily bubble technology, combining experimental characterization with advanced theoretical modeling. Systematic X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy revealed that the coal surface contains 53.43 % oxygen-containing functional groups and 38.14 % hydroxyl groups, which traditionally hinder flotation efficiency. The novel application of oily bubbles, generated through hydrodynamic cavitation, remarkably improved coarse particle (1.00–0.75 mm) recovery, achieving up to 78.94 % yield compared to 73.28 % with conventional flotation. The extended DLVO theory revealed a fundamental mechanistic shift: while air bubbles exhibited repulsive energy barriers (critical thickness = 21.02 nm), oily bubbles created attractive interactions with a negative total energy barrier owing to their minimal polar component (46.88 % vs. 0.82 %, respectively). Complementary Stefan–Reynolds modeling showed that oily bubbles accelerated wetting film drainage by 3.6 times, with hydrophobic force constants markedly surpassing those of air bubble systems. These findings provide new insights into interfacial science and address a persistent industry challenge—the inefficient recovery of coarse low-rank coal particles. Future studies will focus on scaling up the oily bubble generation system for industrial deployment.