Abstract: The upper limit of particle size for conventional flotation is only around 150 μm. Raising the upper limit of flotation particle size can not only reduce grinding energy consumption but also achieve pre-enrichment of ore through pre-selection and tailings rejection under coarse particle conditions. However,coarse particles are mainly poorly-liberated composites, and the adhesion kinetics behavior and regulation mechanism of bubbles on such surfaces are still unclear,resulting in low recovery rates of coarse particle flotation and loss of valuable minerals. To address this issue,this paper studied the liquid film rupture and spreading behavior of three bubble sizes (550,750,and 950 μm) on four hydrophilic surfaces with discrete hydrophobic sites (hydrophobic site diameter 100 μm,and hydrophobic site spacings of 40,100,200,and 400 μm,respectively) through high-speed dynamic observation and MATLAB image processing. It was found that the formation time of the three-phase contact line (TPC) of the bubble was positively correlated with the hydrophobic site spacing,and the average spreading speed and spreading diameter of the TPC were negatively correlated with the hydrophobic site spacing,indicating that an increase in hydrophobic site spacing is not conducive to bubble adhesion and subsequent spreading. As the bubble size increases,the hindrance effect of the hydrophobic site distribution dispersion on the TPC spreading decreases,suggesting that increasing the bubble size on the surface to a certain extent promotes the TPC spreading. The research results are expected to provide certain theoretical support for the intensification of coarse particle flotation processes. 

Key words: heterogeneous surface,bubble size,liquid film,three phase contact