Abstract: The separation precision of coal−slime flotation is fundamentally governed by the molecular characteristics of collectors. Alkanes, as the principal constituents of nonpolar oily collectors, exert a decisive influence on interfacial wettability and selective separation through variations in their carbon chain length. To elucidate the underlying mechanism by which the carbon chain length of alkane collectors affects the flotation behavior of coal slime and to enhance both separation efficiency and clean−coal quality, a series of normal alkanes ranging from C₆ to C₁₆, along with their binary mixtures, were systematically investigated. Batch flotation experiments, contact−angle measurements, and kinetic analyses were conducted to evaluate the effects of chain−length variation on surface wettability, flotation rate, and the selective separation between coal particles and kaolinite. The findings demonstrate that the carbon chain length of alkanes has a pronounced regulatory effect on flotation performance. Increasing chain length enhances molecular hydrophobicity, promoting the formation of a coherent hydrophobic film on coal surfaces and strengthening bubble–particle adhesion. Among single−collector systems, C₁₄ achieves the best overall performance, with a clean−coal yield of 69.10%, an ash content of 10.20%, a flotation perfection coefficient of 49.01%, and favorable kinetic behavior. In contrast, a binary collector composed of C₁₂ and C₁₄ at a 7︰3 mass ratio exhibits a clear synergistic enhancement, raising the clean−coal yield/ flotation perfection coefficient to 70.01%/50.14%, reducing ash content to 10.01%, and enabling concurrent improvement in kinetic efficiency and selectivity. Short−chain alkanes (e.g., C₆) displayed pronounced nonselective adsorption on hydrophilic minerals such as kaolinite, leading to higher clean−coal ash, whereas medium− to long−chain alkanes show reduced gangue affinity and thus superior selectivity. By correlating carbon chain length with coal floatability, flotation kinetics, and mineral selectivity, this work elucidates an intrinsic linkage among “carbon chain length–wettability–flotation kinetics–mineral selectivity.” The results further support a collector design strategy based on the principle of carbon−chain complementarity, providing both theoretical foundations and practical pathways for optimizing reagent performance in fine−coal flotation..