Mechanism Study On Heterogeneous Nucleation And Growth Process Of Interfacial Micro-nano Bubbles

Micro-nano bubbles are widely used in many fields,especially in mineral flotation.It has been proved that adding micro-nano bubbles can effectively improve flotation efficiency.In recent years,although many researchers have investigated the change of particle properties and improvement of beneficiation efficiency,most of them added two-phase micro-nano bubbles in the flotation process to make them adhere to the surface of mineral particles and realize the auxiliary of mineral flotation.However,insufficient attention has been made to the evolution process of supersaturated dissolved gas molecules on the mineral surface and the variation law of heterogeneous bubble nucleation.Taking this into account,heterogeneous bubbles are generated on the surface of glass slides,quartz and hematite by means of a sudden drop of environmental pressure in this paper.The bubble growth process is observed by a self-made setup using a high-speed camera,the experimental data are fitted by the modified diffusion model of dissolved air and molecular kinetics theory.The main research contents and conclusions are as follows:1)Using the self-built bubble growth observation system,the bubbles nucleation and grow in different phases on the solid surface in response to the sudden drop of pressure has been investigated.The results show that the growth process of visible interface micro-nano bubbles has experienced three stages: the floating stage with constant radius growth,the transition stage with the change of contact angle and radius,and the expansion stage with constant contact angle growth.2)Taking high purity quartz as the research carrier,the effects of different conditions on the nucleation,growth and evolution of heterogeneous bubbles were preliminarily explored.It is found that the increase of depressurization amplitude is beneficial to the nucleation and growth of bubbles.At the same time,there is no bubble nucleation on the surface of the hydrophilic quartz glass slide.The surface area of nucleated bubbles gradually increases with the hydrophobicity increase,which is ranked as follows: 120° > 104° > 68° > 32° = 19°.The roughness test shows that interfacial bubbles are easier to nucleate and grow on the rough surface of high-purity quartz.With the increase of the roughness of the quartz slide,the interfacial bubble surface area becomes larger.In addition,the increase of dissolved gas content in the solution and reduction of the surface tension can promote the nucleation and growth of micro-nano bubbles.3)Representative oxidized ore(hematite)and gangue ore(quartz)were selected to further study the effects of surface properties and solution environment on bubble nucleation and growth on the mineral surface.Firstly,it is found that the mineral interfacial bubbles nucleate and grow faster with the increase of the depressurization amplitude,which is consistent with the observation experiments using a glass slide.At the same time,there is no bubble nucleation on the smooth quartz surface,while the bubbles on the smooth surface of hematite grow slowly.Many interfacial bubbles are generated with the increase of mineral surface roughness.In addition,the hematite surface is more conducive to bubble nucleation and growth at pH 4,while the quartz surface has no bubbles at pH 10,and the bubble growth rate is faster at pH 6.In addition,it is also found that a low concentration of collector can promote the growth of bubbles at the hematite surface,while the high concentration of collector can inhibit it.The presence of collector can promote the nucleation and growth of bubbles on the quartz surface.As for the case of depressant,the bubble nucleation occurred on the hematite surface but depressed with the increase of depressant starch.When the concentration of depressant starch reaches 40 mg/L,there is no bubble nucleation on the hematite surface.On the other hand,there are no bubbles generated on the quartz surface in the presence of different concentrations of starch,which may be caused by insufficient depressurization range and the influence of starch.4)Based on the modified diffusion model of dissolved air and molecular kinetics theory,the bubble radius and contact angle under different depressurization conditions are predicted.The modified diffusion model of dissolved air can perfectly fit the variation of bubble radius and contact angle of interfacial bububles in different stages.However,the ρ value is large in the transition stage,which may be caused by the reciprocal interaction between R and θ in the transition stage.On the other hand,the transition stage can not be perfectly fitted by the molecular kinetics theory model because the modified Young’s equilibrium contact angle is variate,but the bubble growth and evolution characteristics can be well predicted in the floating stage and expansion stage using the molecular kinetics theory model.