Numerical Simulation And Optimization Of Extracting Vanadium In The Stirred Tank By Hydrometallurgy Method

Mechanical stirred tank was a leaching equipment,which was widely used in hydrometallurgical process.In the industrial production process,there were still many problems of the large-sized stirred tank,such as uneven speed,concentration distribution,solid phase deposition at the bottom of the tank,which leads to poor mixing effect of solid-liquid,low leaching ratio,and all of these factors affected negatively the production.Due to the closure of the stirred tank,it was difficult to know the mechanism of liquid flow and solid phase distribution by means of experience and limited testing methods.Therefore,numerical simulation of the solid-liquid two phase flow in the stirred tank can provide certain guidance for optimizing the design of the stirred tank and parameters for leaching process.In this study,it is focus on the numerical simulation of the novel leaching process for extracting vanadium from the vanadium-bearing titanomagnetite using the fluid dynamics software,Fluent.The solid-liquid two phase mathematical model was established in order to discuss the effect of stirring speed,blade height,double-layer pitch,perforated baffle,particle diameter,particle density,fluid viscosity and solid volume fraction on the flow field distribution.The major achievements are listed as follows.(1)The liquid flow velocity increases with the increase of stirred speed,which is favorable to the solid-liquid mixing in the stirred tank.However,when the liquid flow velocity is higher than a certain speed,the distribution of the flow field in the stirred tank is almost constant,the increase of the rotation speed has no practical effect on the whole velocity distribution,the dead zone of the lower part of the blade still exists,and the power of the mixer would increase with the increase of stirring speed.Therefore,the stirring speed should be appropriately chosen if not only the effect of solid-liquid mixing is met but also costs are reduced.The maximum value of the suspending solid particles in the bottom is the criterion for suspension and used in this study and the critical suspension speed Njs=425r/min was estimated.(2)With the decrease of the height of the blade,the dead zone below the blade becomes smaller and smaller,and solid particles in the bottom are easier to disperse in the solution.However,if the blades are mounted too low,the impact and abrasion of the solid particles at the bottom will adversely affect the blades.Considering the influences of the different bottom height on the velocity field and the concentration distribution of the solid phase,the bottom height L=0.4D1,for the solid-liquid mixing effect is optimal.(3)When the interlayer spacing,S,is greater than 0.5D,there would be four independent cyclic zones between the two blades.The interaction between the two blades is very weak and there is obvious subregion phenomenon.When S = 0.5D,the concentration distribution of solid phase in the stirred tank is the most uniform during the range of 0.3D?0.9D.Considering the influence of S of the double-layer on the velocity vector and the concentration distribution of the solid phase,the interlayer spacing S = 0.5D has the optimal effect on the solid-liquid mixing.(4)The installation of perforated baffles in the stirred tank conducted the formation of complex flow fields and the elimination of vortices,the axial velocity of the system is improved obviously,the tangential motion in the flow field is restrained.Therefore,the effect of solid-liquid mixing is improved.(5)The decrease of particle diameter and density is beneficial to the increase of liquid phase velocity and the uniformity of solid phase distribution,but the smaller the particle diameter,the more cost manpower and material resources.Taking into account of the abovementioned factors,the particle diameter of 75 ?m is of optimal effect for the mixing of solid-liquid in the stirred tank.(6)The decrease of fluid viscosity and solid volume fraction is beneficial to the increase of liquid phase velocity and the uniformity of solid phase distribution,but the decrease of viscosity was not conducive to the uniformity of solid phase distribution.So the fluid viscosity of 0.005Pa·s is most appreciate for the mixing of the solid-liquid mixture.(7)The critical suspension speed corresponding to different particle diameters,densities,fluid viscosities,and solid volume fractions is obtained by simulation calculation,The data are regressed and analyzed to obtain the relationship between Njs and the parameters,such as particle diameter dp,solid-liquid difference(?s-?l),liquid flow velocity ?,and solid phase volume fraction as,the relational formula is listed as follows.(?)The relational formula is close to the empirical formula of Zwietering(?),which is reliable and accurate,and can reasonablypredict the critical suspension speed under different working conditions.