Study On The Kinetics Of Vacuum Distillation Separation Of Lead-based Alloy

Recovery of alloy waste cleanly and efficiently from the production and consumption of non-ferrous metals is of great significance.Vacuum separation and purification of crude metals and alloys has advantages of short process,no pollution and high metal recovery rate.Existing basic research on vacuum separation of alloys mainly focuses on thermodynamics,and there are few kinetic studies.This work takes lead-based binary and ternary alloys as the object,and carries out vacuum distillation separation kinetics of lead-based alloys,mainly including:activity calculation,gas-liquid phase equilibrium model calculation,alloy vacuum distillation separation kinetic experiment and modeling,application research of new alloy vacuum separation kinetic model,as follows:1.Molecular interaction volume model（MIVM）,modified molecular interaction volume model（M-MIVM）and Wilson equation were used to calculate activity and activity coefficient lead-based of Pb-X（Ag,Au,of Cu,Pd,Sn,Sb）binary alloys and activities of Pb-Cu-Ag,Pb-Sn-Ag ternary alloys.By comparing the calculated and experimental values,the alculation deviation of each model was calculated.The results show that the calculation accuracy of M-MIVM is higher than that of MIVM and Wilson equation.In binary alloys,mean standard deviation is±0.0059 and mean relative deviation is±8.85%;and in ternary alloys,mean standard deviation is±0.0194,mean relative deviation is±8.60%.2.On the basis of the research on the activity of alloys,theoretical calculation research of alloy vacuum distillation separation was carried out.Separation coefficient of Pb-X（Ag,Au,Cu,Pd,Sn,Sb）binary alloys was calculated based on M-MIVM.The calculation results showed that separation coefficient of Pb-Ag,Pb-Au,Pb-Cu,Pb-Pd,Pb-Sn alloys were much greater than 1,the alloys can be separated by vacuum distillation,and Pb mainly enters the gas phase during the separation process;separation coefficient of Pb-Sb alloy is much less than 1,and Pb mainly stays in the liquid phase during separation process;vapor-liquid phase equilibrium（VLE）model is used to calculate the VLE diagrams of above alloys,which can be used to determine optimal temperature and system pressure required for the experiment;the relationship between theoretical maximum volatilization rate and composition is calculated,which can be used to analyze the degree of difficulty of alloys separation.3.Study on the evaporation kinetics of lead during the vacuum separation of Pb-X（Ag,Sn）binary and Pb-Sn-Ag ternary alloys was carried out.Evaporation amount of lead in different time periods was measured by weight loss method,and the change law of lead evaporation rate with time was obtained;the evaporation reaction order of lead was measured as n=1,indicating that evaporation of lead from the above alloys belongs to the first-order reaction kinetics;total mass transfer coefficient of lead was measured,and the results show that in the same alloy systems,the higher the temperature,the greater the mass transfer coefficient,and lead is evaporated more easily;at the same temperature,total mass transfer coefficient of lead in Pb-Sn（62wt.%）-Ag（2wt.%）alloy is greater than that in Pb-63Sn alloy,indicating that the presence of a small amount of silver in Pb-Sn alloy melt is beneficial to the evaporation of lead;at the same time,reliable experimental data were provided for the test of dynamic model of alloy vacuum separation.4.Combined with the alloy vacuum separation kinetic theory,M-MIVM and HKL equations,vacuum separation kinetic model of binary and ternary alloys is established.Modeling study shows that the model modeling process is flexible,and the model can be used to simulate computational the effects of temperature,system pressure,distillation time,evaporation area,initial composition and other factors on the separation of alloys by vacuum distillation.（1）Experimental data of the evaporation ratio and evaporation rate of lead in Pb-X（Ag,Sn）binary and Pb-Sn-Ag ternary alloys measured in this study were used to verify the accuracy of the model,and evaporation coefficients of lead was determined in different alloys and at different temperatures;（2）The rate constant of lead evaporation reaction on the surface of alloy melt and the mass transfer coefficient in the liquid phase were deterimened,and compared the mass transfer coefficients of each step,the rate limit steps of lead evaporation were analyzed,the rate control step at low temperature is mainly liquid phase mass transfer,which is converted into evaporation of lead on the surface of the alloy melt as the temperature increases;（3）Distillation temperature,system pressure,distillation time,volatilization area and other factors on the vacuum separation of Pb-X（Ag,Sn）binary and Pb-Sn-Ag ternary alloys were investigated using this model.It shows that at low temperature,the system pressure has a great influence on the evaporaion rate,and with the increase of temperature,the influence of the pressure gradually decreases;the distillation temperature and system pressure determine the limit of the vacuum separation of the alloy,that is,when the volatilization rate of lead reaches the"limit value"”,continuing to increase the holding time cannot improve the lead removal rate;increasing the volatilization area can shorten the distillation time,but cannot improve the lead removal rate.（4）In other Pb-based alloys（Pb-Cu,Pb-Cu-Ag,Pb-Pd,Pb-Sb）,calculated values of the model are in good agreement with the experimental values,indicating that the model is reliable;It is easy to form stable intermetallic compounds（such as Pb-Pd）,polyatomic gas molecules exist in the gas phase（such as Sb will volatilize in the form of Sb,Sb₂,and Sb₄）,and there is an"azeotrope"point in the distillation process（such as Pb-Sb alloy）,because liquid phase mass transfer process is not considered in the modeling process,and the model cannot describe the interactions between atoms in the gas phase,resulting in a poor model calculation effect.5.Application of the new model in vacuum separation of tin-based Sn-X（Sb,Zn）,zinc-based Zn-X（Bi,Cd）binary alloys and Sn-Bi-Zn ternary alloys was carried out.The results show that:（1）Calculated values of the model are in good agreement with the existing literature values,and the new alloy vacuum volatilization kinetic model is reliable and universal;（2）For a small amount of experimental research,combined with the new alloy vacuum separation kinetic model,optimal time,temperature,pressure and other parameters of alloy vacuum separation can be obtained,and the time spent on experimental exploration can be reduced.