Application of modified <i>n</i> -dodecane oily bubbles for enhancing flotation of Shendong Jurassic coal maceral and its mechanism

The utilization of Jurassic bituminous coal as a chemical feedstock is constrained by its high inertinite content, and the separation of vitrinite from inertinite is the basis for its fractional utilization. In this study, enhanced flotation tests were conducted on macerals from two typical Shendong coal samples, using n-dodecane-based oily bubbles modified with methylnaphthalene (MN), octylphenol polyoxyethylene ether (OP-4), and oleic acid (OL). The characteristics of the coal samples and modified n-dodecane were analyzed using Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), Zeta potential, surface tension, and viscosity measurements. The interactions between modified oily bubbles and coal macerals were investigated via induction time tests and the extended Derjaguin-Landau-Verwey-Overbeek (EDLVO) theory. The results indicated that the surface of vitrinite-rich coal is more hydrophobic than that of inertinite-rich coal. Meanwhile, when MN was used as the modifier, selective enrichment of vitrinite was achieved. It was found that the excellent flotation separation effect arises from the ability of MN-modified n-dodecane oily bubbles to selectively increase the mineralization energy barrier between the oily bubbles and inertinite-rich coal, while widening the flotation difference between vitrinite-rich and inertinite-rich coal. This study provides experimental evidence and theoretical support for the separation of vitrinite from inertinite.