Development of a novel self-emulsifying collector for low-rank coal flotation: dispersion characteristics and interfacial interaction mechanisms

Froth flotation based carbon recovery from low-rank coal (LRC), particularly from fine coal slimes, is generally more challenging than that from higher-rank coals, such as bituminous and anthracite coals, owing primarily to the lower surface hydrophobicity, abundant oxygen-containing functional groups, and the relatively high collector dosages required to achieve satisfactory recovery. In this study, a novel self-emulsifying flotation collector (EFC) comprising kerosene, Span 80, AEO-9, and n-butanol was developed using a low-energy stirring process. The self-emulsification behavior of the EFC was evaluated through droplet-size analysis, while its flotation performance was investigated through batch flotation tests. Changes in surface chemistry and collector–coal interactions were further investigated using SEM–EDS, XPS, and FTIR analyses. The EFC spontaneously dispersed in water to form fine droplets with median diameters (d50) of 2.33–3.60 μm, indicating enhanced dispersion of the kerosene phase. Among the EFC formulations investigated, the 40 wt% EFC achieved a maximum combustible recovery of 69.45% at a collector dosage of 20 kg/t, which was comparable to 72.16% obtained with conventional kerosene under the same conditions. Among the EFC formulations investigated, the 40 wt% EFC formulation reduced hydrocarbon oil consumption by approximately 68% relative to pure kerosene. XPS and FTIR analyses revealed substantial changes in the surface chemical composition of LRC following EFC treatment, including an increase in the relative abundance of non-polar carbon species and a reduction in the contribution of oxygen-containing surface functionalities, particularly for the 30 wt% EFC formulation. These changes are consistent with enhanced modification of the coal surface and improved interaction between the dispersed collector phase and coal particles. Overall, the self-emulsifying collector provides a low-energy and hydrocarbon-efficient approach for improving the flotation of LRC, demonstrating its potential for more efficient beneficiation of fine low-rank coal.