Influence of Diesel Emulsification Methods on the Flotation Behavior of a High−Ash Lignite from Inner Mongolia

The flotation performance of low−rank coal is severely hindered by its high ash content and abundance of oxygen−containing functional groups, which limit the efficacy of diesel as a collector, leading to inefficient resource recovery and potential environmental issues. This study investigates the regulatory effects of three diesel emulsification strategies—chemical emulsification, physical emulsification, and combined chemical–physical emulsification—on diesel dispersion characteristics and flotation behavior, using a high−ash lignite from Inner Mongolia as the test material. Emulsions were prepared and characterized through droplet size distribution, contact angle measurements, Zeta potential analysis, and flotation performance evaluation. The results show that emulsification significantly enhances flotation efficiency. The combined emulsification system (Tween−80+SDS+ultrasonic treatment) results in the smallest median droplet size (D₅₀ reduced from 48.2 μm to 1.5 μm) and exhibits superior kinetic stability. With an optimized diesel dosage of 1.8 kg/t, the maximum combustible recovery is 72.40%, a minimum clean coal ash content is 13.50%, and the highest flotation perfection index is 39.09%. Surface characterization reveals that the combined emulsification markedly increases coal particle hydrophobicity (contact angle increases from 48.6° to 82.3°) and reduces surface electronegativity (Zeta potential shifts from −32.1 mV to −15.4 mV), thereby improving bubble–particle attachment and mineralization efficiency. These findings demonstrate that the synergistic emulsification approach enhances diesel dispersion, adsorption, and interfacial behavior on coal surfaces. This offers a promising approach for developing high−efficiency collectors and advancing flotation technology for low−rank coal slurry.