Particle-Particle Agglomeration Of Fine Minerals In The Flow Field Of Vortex Separator

Flotation is the main method for the separation of fine minerals by collision and adhesion between bubbles and target mineral particles in dynamic fluid environment.As the size of fine minerals decreases continuously,it is difficult for particles and bubbles to collide and adhere in the flotation process.The high-intensity turbulent environment can effectively improve the collision probability between bubbles and particles,which is widely used in the flotation separation process of fine minerals.However,the strong turbulence in the flow field also strengthens the collision between particles,resulting in the occurrence of mineral particles clumping and floating up carried by bubbles,which affects the flotation performance.In this thesis,from the perspective of fluid mechanics,based on the turbulent flow field in the micro-particle vortex separator developed by the research group in the early stage,aiming at the agglomeration problems of different hydrophobic particles,CFD numerical simulation,PIV measurement and sedimentation experiment are adopted.Firstly,key turbulence parameters affecting the agglomeration of particles are identified.Further,The influence of key hydrodynamic parameters on the agglomeration and fragmentation of different types of particles was revealed.Finally,the flow field parameters were used to predict the agglomeration behavior of flotation devices with different physical structures,and the experimental verification was carried out.This study has important guiding significance for improving concentrate grade.The specific research results are as follows:A numerical model suitable for the study of liquid-solid flow field in vortex separator was established.The internal flow field of vortex separator was simulated by Mixture model and LES large eddy simulation turbulence model.PIV measurement was used to verify the numerical model.The error is less than 9.8%,which proves the reliability of the numerical simulation method.Based on this model,the turbulence characteristics inside the vortex separation flow field were verified.The main characteristics are as follows:the vortex is generated behind the vortex generator,and the turbulence intensity is relatively high,which gradually decreases with the direction of flow.The influence of key hydrodynamic parameters such as turbulent kinetic energy,turbulent dissipation rate,vorticity and shear rate on particle agglomeration was revealed.The higher turbulent kinetic energy and vorticity make the fine particles have the necessary kinetic energy for collision and the conditions for micro-local rotation and stay,which promote the occurrence of agglomeration.The fluid shear caused by the turbulent dissipation rate and shear rate will cause the agglomeration to break.（1）For hydrophobic and hydrophilic particles,the ratio of vorticity to shear rate at the same flow rate is the closest to the trend of particle agglomeration.The agglomeration effect of hydrophobic and hydrophilic particles in vortex separator decreases with the decrease of the ratio of vorticity to shear rate.When the flow rate is0.3 m³/h,the ratio of vorticity to shear rate of rectangular vortex separator varies from0.53 to 0.73 from 25 degrees to 55 degrees,and the relative turbidity varies from 104NTU to 21 NTU.（2）For hydrophobic and hydrophobic particles,agglomeration can occur under minimum vorticity and slight breakage can occur under higher shear rate.The change of shear rate is closest to the law of particle agglomeration,and the agglomeration effect decreases with the increase of shear rate.（3）For the hydrophilic-hydrophilic particles,there is a critical value of agglomeration within the study range.When the shear rate is less than 836.99s^-1,the vorticity is the dominant factor affecting the clustering of hydrophilic particles,and the clustering increases with the increase of the vorticity.When the shear rate is greater than this value,the influence of the vorticity will be weakened,and the shear rate is the dominant factor affecting the clustering of hydrophilic particles,and the degree of breakage increases with the increase of the shear rate.Based on the effect of vorticity and shear rate on particle agglomeration,the particle agglomeration behavior in vortex separators with different structures was studied and verified.（1）From the perspective of agglomeration between hydrophobic and hydrophilic particles,the agglomeration effect of triangular vortex separator is the strongest under the same flow rate,which may affect the grade of flotation concentrate.The rectangular vortex separator has the weakest clustering behavior and has little influence on the grade of flotation concentrate.（2）From the perspective of hydrophobic and hydrophobic particles agglomeration,the agglomeration behavior of triangular vortex separator is the strongest,which has a positive effect on the recovery rate of target minerals.（3）From the perspective of hydrophilic and hydrophilic particles clustering,the clustering behavior of triangle vortex separator is weakest at low flow rate.Finally,the prediction was verified by the clustering behavior experiment,which has a good agreement and proves that the influence law of the key hydrodynamic parameters on the agglomeration behavior of particles is reliable.It should be noted that the above factors should be considered comprehensively for the impact on flotation performance.This thesis has 57 figures,6 tables and 96 references.