Study On Particle-bubble Collision And Attachment Characteristics Under Different Flow Patterns In Froth Flotation

Particle-bubble collision and attachment are the basis of flotation.At present,the theoretical models of particle-bubble collisions are mostly semi-analytical models in laminar flow environments.These models simplify the calculation of complex physical processes in the calculation process,and ignore the effects of interception,gravity,inertia and other effects to varying degrees,resulting in low model accuracy and a small scope of application.On the other hand,most particle-bubble collisions and adhesions occur in areas of high turbulence.At present,there is little research on the influence of turbulence in particle-bubble collisions in the academic field.This has become the research and application of particle-bubble collisions and adhesion.Important bottleneck.Studying the influence of turbulence on particle-bubble collision and adhesion process is helpful to understand the bubble mineralization process,and then to explore the bubble mineralization area and the effect of turbulence on the flotation recovery rate,which is the development and improvement of flotation equipment Provide guidance.Aiming at the defects in the existing semi-analytical particle-bubble collision model,the paper uses the CFD numerical simulation method to systematically study the particle-bubble collision process and perfect the particle-bubble collision theory.By comparing the collision theory model with the CFD model,the particle-bubble collision dynamics is analyzed,and the particle-bubble collision law is summarized.The results show that:First,gravity is the main cause of collisions between particles and bubbles,but the effect of gravity decreases with the increase of the particle-bubble relative velocity.Specifically,the collision efficiency increases with the increase of particle diameter increases with the increase of particle density and decrease with the increase of bubble diameter.Second,the surface properties of the bubbles have an important influence on the particle-bubble collision efficiency.Normally,the collision efficiency of non-sliding bubbles is greater than that of sliding bubbles,but when the particle diameter is less than 31 ?m,the collision efficiency of non-sliding bubbles is less than that of sliding bubbles.Based on the CFD collision efficiency model in a laminar flow environment,and according to the impact of different turbulent environments on particle-bubble collisions,a CFD model of particle-bubble collision efficiency in a turbulent environment is established.Taking the bubble size as the boundary,in a large-scale vortex environment,an increase in the relative velocity will increase the collision efficiency.By comparing the conclusions of the Schulze model and the CFD model,the paper proved for the first time that Schulze used the sum of inertia and gravity when calculating the collision efficiency,which caused repeated calculations.This is also the reason why the Schulze model overestimates the collision efficiency of coarse particles in a laminar fluid environment.In the environment of small-scale eddy currents,the paper analyzes the influence of small-scale eddy currents through the trajectory fluctuations of turbulent kinetic energy on particle motion.When the Stokes number of the particles is less than 1,the increase of turbulent kinetic energy can improve the collision efficiency.When the Stokes number of the particle is greater than 1,the turbulent kinetic energy has little effect on the collision efficiency.Under the condition that the Stokes number is less than 1,the paper fits the extra collision efficiency equation caused by turbulence as ECt=0.286(?).The thesis also used empirical methods to study the influence of flow regime on particle-bubble collision and adhesion.Improve the Milli-Timer test system,use high-speed cameras to observe the particle-bubble collision and adhesion processes in different flow states.The following results are obtained:First,when the liquid velocity around the bubbles increases,more and more particles It slips from the bubble surface area before reaching the 90° position of the vertical axis,and the probability of particle adhesion is reduced.Second,the necessary condition for particle adhesion is:the contact time must be greater than the induction time.For particles with smaller mass,the contact time is mainly determined by the sliding time.For particles with larger mass,after the particles collide with the bubbles,the rebound phenomenon causes the particles to separate from the bubbles before the sliding phenomenon on the bubble surface occurs,so the contact time of the coarse particles is only the bounce time.Because the bounce time is much shorter than the sliding time,coarse-grained minerals are often difficult to recover.