Abstract: Based on the purpose of fine coal slurry separation and rational utilization, in order to enhance the flotation recovery and separation effect of medium ash coal slurry, and achieve the separation of three products of fine coal slurry: low ash clean coal, medium ash coal slurry, and high ash mud gangue, this paper selects two samples of flotation clean coal and medium ash coal slurry, and investigates the flotation effect under different sorting parameters through flotation experiments. The differences in flotation behavior between flotation clean coal and medium ash coal slurry are studied, and the interaction between strong/weak hydrophobic substrates and bubbles during liquid film thinning process is measured using atomic force microscopy. Research has shown that the contact angle of flotation clean coal is 109.25 °, which is 28.62 ° higher than that of medium ash coal slurry; Flotation clean coal contains a large number of cationic groups such as alkyl and amino groups, while medium ash coal slurry contains a large number of oxygen-containing functional groups such as carboxyl and hydroxyl groups. Increasing the amount of diesel and secondary octanol, as well as increasing the flotation stirring speed, can help improve the recovery efficiency of flotation clean coal and medium ash coal slurry; Increasing the inflation volume can improve the recovery efficiency of flotation clean coal, but the recovery efficiency of medium ash coal slurry is reduced. The flotation rate of flotation clean coal is significantly higher than that of medium ash coal slurry, and under the same flotation conditions, flotation clean coal preferentially floats out. For the enhanced recovery of medium ash coal slurry, the order of influence of sorting parameters is stirring speed>slurry concentration>aeration amount>foaming agent>collector. When strengthening the separation and recovery of coarse ash coal slurry, the separation conditions of "high dosage of reagents, strong stirring speed, low gas charge, high slurry concentration, and extended flotation time" should be adopted; For the separation of flotation clean coal and medium ash coal slurry, the separation conditions of "low reagent dosage, low stirring speed, high gas charge, low slurry concentration, and reduced flotation time" should be adopted. The theoretical values of the critical liquid film thickness between strong/weak hydrophobic substrates and bubbles are 39nm and 16nm, respectively. Under the attractive separation pressure, bubbles break through the liquid film and adhere to the substrate. When the thickness of the liquid film thins to the hydrophobic range, the total separation pressure begins to shift towards attraction, and the thinning of the film drives a sharp increase in pressure, causing the liquid film to rupture under the action of hydrophobic forces.