Study On The Settling Velocity And Purification Law Of Aluminum Chloride Hexahydrate Crystals

The process of making alumina from fly ash can alleviate the shortage of aluminum resources in China in a large extent.The process mainly includes acid method,alkaline method and acid-base method,among them,the acid method has been widely studied for its advantages such as not using of co-solvent,low material flow and slag formation,and acid renewable cycle.Evaporation crystallization is the core step in the acid process,crystal purity directly affects the grade of alumina products.Therefore,it is particularly important to effectively control the content of impurities in the crystal.The elutriation leg has the advantages of simple equipment,large operation flexibility and large processing capacity.So it is proposed to increase the elutriation process after the last-effect evaporation,thereby effectively improving production efficiency and product quality.The elutriation leg is a liquid-solid two-phase countercurrent contact process,and establishing the relationship between the crystal particle settling velocity and various influencing factors is the key to optimize the purification effect.Set up an elutriation process experimental bench to establish a liquid-solid elutriation process simulation experiment.The effects of liquid density,viscosity,particle size,and volume fraction on the settling velocity of the particles were investigated,and the resistance of the liquid to the particles was used to modify it,and fit a calculation model for settling velocity.Use numerical simulation to analyze the flow field of the setting process to make the analysis of the setting process more comprehensive.Static experiments were designed according to the simulated experimental conditions of the elutriation process and the corresponding particle settling velocity,The impurities are sodium,calcium,magnesium and potassium,the change law of impurity ions with elutriation time was obtained,and the relationship between the purification law and crystal precipitation was studied.The main conclusions are as follows:1?The simulation experiment of settling process using glass spheres with a similar crystal density and equivalent diameter to the single variable study found that the particle settling velocity decreases with increasing solution viscosity,density,and particle volume fraction,and increases with increasing particle size.Inverted buckets greatly increase the settling velocity,while countercurrents hinder particle sedimentation.Keeping other parameters consistent,it was found from the settling velocity of the inlets of different washing solutions that the growth rate of the middle and upper inlet and the sensitivity of the settling velocity to the inlet position increase with the increase of the solution density and decrease with the increase of the solution viscosity.2?The relationship between the influencing factors and the settling velocity is fitted,and the resistance of the liquid to the particles is used to correct the expression of the settling velocity of the system and make the error within 10%.3?Through numerical simulation of the settling process,it is found that the particle distribution range increases with increasing solution density.When the solution viscosity and particle size are large,the particles are likely to accumulate at the bottom of the elutriation leg.The particles have a tendency to gather and distribute along the wall surface,and the less they are distributed toward the center.The degree of disorder of the flow field increases with the increase of the particle volume fraction.4?The better elutriation time of this elutriation process is 60s.After calculation,the removal rate of each impurity ion is:Na⁺>Ca²⁺>Mg²⁺>K⁺,and the highest removal rate can reach more than 80%.The removal rate of impurity ions increases with the decrease of crystal volume fraction and solution viscosity,which is consistent with the trend of the settling velocity calculation model,and provides a reference for the design calculation and optimization of the elutriation process.