Abstract: In order to improve the flotation efficiency of low−rank coal, the flotation performance of biodiesel as a collector was investigated. Soybean oil−based biodiesel, rapeseed oil−based biodiesel, and conventional diesel were selected as collectors. Flotation experiments were conducted to compare their flotation effects. The mechanism by which biodiesel enhances the flotation of low−rank coal was analyzed using methods such as infrared spectroscopy, contact angle measurement, Zeta potential analysis, and molecular dynamics simulation. The results indicate that, under the same dosage of 5 kg/t, the flotation effects of biodiesel collectors are superior to those of conventional diesel. The combustible recovery rate of soybean oil−based biodiesel reaches 62.47%, which is 11.52 percentage points higher than that of conventional diesel. Gas chromatography−mass spectrometry analysis shows that polar molecules, such as methyl linoleate and methyl oleate in biodiesel, interact with low−rank coal through hydrophobic long chains. The ester groups form hydrogen bonds with hydroxyl groups on the surface of low−rank coal, leading to a directional molecular arrangement. Surface characteristic analysis reveals that the contact angle of coal samples treated with soybean oil−based biodiesel collector reaches 91°. The absolute value of Zeta potential decreases from −31.29 mV to −26.96 mV, which improves the surface hydrophobicity and electronegativity of low−rank coal. Molecular dynamics simulation demonstrates that the diffusion coefficient of water molecules on the surface of low−rank coal increases from 4.09×10⁻⁹m²/s for untreated coal to 5.05×10⁻⁹m²/s for coal treated with soybean oil−based biodiesel. This indicates that the coverage of the collector weakens the adsorption restriction of water molecules. Furthermore, frontier molecular orbital energy gap (ΔE) analysis shows that the ΔE of coal samples treated with soybean oil−based biodiesel is 0.25 eV, which is significantly higher than 0.16 eV for conventional diesel. This further reduces the restriction on water molecules and significantly enhances flotation efficiency. This study provides a theoretical basis and technical reference for the development of green and efficient collectors for low−rank coal flotation.