Low rank coal is typically difficult to float using traditional flotation processes. In this study, a novel flotation process, oily bubble flotation, was proposed and evaluated using samples of low rank coal. X-ray photoelectron spectrometer (XPS) and scanning electron microscope (SEM) were used to characterize the surface chemical and morphology properties of coal samples. Induction time tests were used to compare the mineralization degree between air or oily bubble and low rank coal particle surfaces. It was found that flotation selectivity in the oily bubble flotation process was considerably higher than that in the traditional flotation process. With the increase of collector dosage, the combustible matter recovery in the oily bubble flotation process increased from 62.92% to 82.65% while the ash content of the concentrate slightly increased from 7.43% to 821%. Moreover, the ash content of concentrate obtained from the oily bubble flotation process was slightly lower than that in the air bubble flotation process. Therefore, a comparison of the performances of air and oily bubble flotation indicated that the oily bubble flotation process was feasible for upgrading low rank coal. (C)2017 Elsevier B.V. All rights reserved.