Study On Liquid-solid Mixing Characteristics And Modification Performance Of Strong Turbulence Hydraulic Counter Conditioning Equipment

Flotation is the main method to separate useful minerals in fine particles from gangue minerals through differences in hydrophobicity.The conditioning pretreatment is an essential step before flotation,which aims to promote the uniform mixing of mineral particles in the slurry and to modify the hydrophobic surface of the mineral particles in advance through the action of chemicals.At present,most of the traditional conditioning equipment are mechanical stirring tanks with impellers,which have uneven flow field distribution,excessive local concentration of energy,and defects such as wear,rust,and possible contamination of raw materials during use of the impeller.The strong turbulent hydraulic counter-rotating conditioning equipment（hereinafter referred to as counter-rotating conditioning equipment）designed by the author’s team uses a pair of high-intensity jet impacts generated by hydrodynamics to perform uniform mixing and interaction of mineral particles and agents,and strengthen the hydrophobicity of the target mineral.In this paper,the flow field characteristics,liquid-solid mixing characteristics and modification properties of quartz minerals in the equipment are compared with traditional mechanical stirring tanks by computational fluid dynamics（CFD）numerical simulation,particle image velocimetry（PIV）measurement,and modification experimental research.In the research process,the relationship between liquid-solid mixing characteristics,slurry modification performance and important hydrodynamic parameters were also explored.Based on the PIV measurement and numerical simulation of two-phase flow field,the flow field inside the equipment was studied,and the mechanism of its mixing effect on the two phases was explored.Firstly,the numerical calculation model of the two-phase flow field is established.The Eulerian multiphase flow model,the RNG k-εturbulence model and the Syamal-O’Brien drag model are used to obtain the simulation results of the particle axial velocity consistent with the PIV measurement.,The trends of the two are the same,it is verified that the maximum value of the relative error of the numerical simulation,the average relative error is 11.01%.Next,the liquid-solid two-phase numerical simulation is carried out by using CFD method.The particle traces show that the upper and lower regions inside the equipment produce swirling flows in opposite directions and are opposed to the center in the axial direction.,Two mixing methods of shearing and convection are formed inside the equipment.The particle velocity and volume fraction of the flow field in the equipment are evenly distributed.The relationship between the particle distribution uniformity index COV（the smaller the COV,the higher the uniformity）and the fluid mechanics parameters（turbulent kinetic energy,turbulent dissipation rate,and fluid strain rate）are studied,the results show that as the circulation rates changes from 1.8m³/h increased to 3.6m³/h,the COV of particles with an average particle size of 45μm,74μm and 125μm decreased by 39.83%,26.58%and 33.14%,respectively.The average values of turbulent kinetic energy,turbulent dissipation rate and fluid strain rate were 0.001 m²/s²,0.01m²/s³ and 7s^-1 increased to 0.004 m²/s²,0.57 m²/s³ and18s^-1.The greater turbulence intensity,turbulence dissipation rate and fluid strain rate can effectively promote the internal liquid-solid two phases are uniformly mixed.Using the CFD method,under the same input effective power conditions,the liquid-solid two-phase mixing effect in the equipment was compared and analyzed with the traditional 6RT（six straight-blade disk turbine）mechanical stirring tank.The results show that the mixing effect of the equipment is much better than the mechanical stirring tank.Compared with the single radial（shear mixing）flow in the traditional mechanical stirring tank,the fluid swirling（shear mixing）and axial opposite（convection mixing）coexisting flow mode in the equipment brings about more uniform particle velocity distribution.The particle velocity under the impeller is only 0.1～0.2m/s,resulting in the maximum volume accumulation of particles up to21%.The modification performance of the equipment was studied by measuring the change of the contact angle of quartz minerals before and after mixing.The results show that the modification effect of this equipment on quartz is significant.Under low circulation rate（1.8m³/h）,the contact angle of the three particle sizes before and after mixing increases by 50°.As the circulation rates increases,the modification effect first increases and then decreases.The uniformly distributed fluid strain rate(the volume average is 8～15 s^-1),that is the shear stress,is conducive to the adsorption of the collector droplets on the particle surface,but when the fluid strain rate(the volume average is 75 s^-1)is too large,it will cause the collector droplets desorb on the surface of the particles,which affects the modification effect.The conditioning test of the mechanical stirring tank under the same effective input power（129w,153w and 165w）shows that the modification performance of the equipment on quartz minerals is better than that of the mechanical stirring tank.This is because the mechanical stirring tank has serious particle accumulation in the low shear zone(strain rate 0-10 s^-1)below the impeller,making it difficult for a large number of particles to achieve drug adsorption on the surface,and the strain rate of the impeller area(75 s^-1)is too high.Largely cause a part of the particle surface agent to desorb.