Research On The Behavior And Mechanism Of Bubble-Particle Aggregate Collision Detachment

Foam flotation is one of the most effective methods to achieve mineral separation and obtain high-quality mineral composition.In the process of foam flotation,the impact between bubbles particles and walls,and between different bubbles particles will inevitably cause the attached mineral particles to fall off from the bubble surface,which will adversely affect the flotation efficiency and particle recovery.Due to the complexity of the flotation environment,it is difficult to directly observe the collision and detachment processes between bubbles and particles.Currently,there is limited experimental research in this field,and the experimental phenomena and intrinsic mechanisms of bubble particle collision and detachment still need to be further studied and verified.Therefore,this article conducts a systematic experimental study on the rise,collision,and detachment processes of bubbles and particles,in order to explore the general mechanism of bubble particle detachment caused by collision.Firstly,a visualization experimental setup for bubble particle ascent and collision was introduced,including a dual camera based 3D visualization imaging method and 3D bubble particle reconstruction theory.Taking the floating bubbles generated by different inner diameter pinholes as an example,the error of three-dimensional reconstruction of bubbles is within 4.5%,which meets the requirements of experimental accuracy and achieves accurate description of the structure and motion characteristics of bubble particle position,shape,posture,etc.Secondly,using a high-speed camera observation system and visual image processing methods,the buoyancy and collision processes of bubbles and particles are observed and recorded,and the motion behavior of bubbles and particles is analyzed.During the upward process,the bubble particle motion exhibits a high degree of randomness.As the bubble diameter and particle size increase,the final velocity vT of the bubble particle floating decreases,and the main axis tilt angle γ reduce.Due to the randomness of the rising process,the angle at which bubbles particles collide with the wall each time y Different,it is normally distributed within a certain range.Among the small collision angle mode(γ≤16℃),the relative motion of particles relative to bubbles is mainly radial velocity,following a complete"compression expansion" cycle of the bubbles.When the bubbles rebound and expand to the maximum radial distance rmax,they fall off,which is called "rebound detachment";In the large collision angle mode(γ≥32℃),the relative velocity of particles is mainly tangential,sliding along the surface of the bubble to the maximum radial distance rmax and falling off,without following the bubble rebound,which is called "slip detachment".Once again,based on the static bubble particle model and the principle of force balance in the bubble inertial frame,a dynamic radial force model of particles is proposed to describe the collision and detachment process of bubbles particles.The dynamic analysis of the collision and detachment process of bubbles particles is carried out.In the two different particle detachment modes of "slip detachment" and "rebound detachment",capillary force is always the main adhesion force that adsorbs particles on the surface of the bubble.With the change in the relative size of capillary force and other components,the radial combined force continuously switches between the roles of "adsorption force" and "push off force",thereby driving particles to move inward or outward.The critical condition for particles to detach from the bubble surface during the dynamic process of bubble particle collision and detachment from the wall is when the contact angle reaches its upper limit(forward contact angle θR)The capillary force reaches the critical value(theoretical maximum capillary force FC,max).This requires that the radial force exert a sufficiently high "detachment work" during the process of particles moving away from the center of the bubble,allowing the particles to have sufficient kinetic energy to move to the critical position where detachment occurs.At this point,the three-phase contact line between the bubbles and particles contracts,and the capillary force exceeds the theoretical maximum capillary force and irreversibly decreases until the three-phase contact line ruptures,and the particles lose the capillary force adsorption on the bubble surface and detach from it.Finally,based on dimensional analysis and experimental data,the fitting analysis of particle detachment probability and influencing factors when bubble particle collides with the wall was carried out,and the fitting formula of particle collision detachment probability was obtained.When the particle size is larger,the bubble diameter is smaller,and the contact angle between bubbles and particles is smaller,the probability of particle detachment is higher.