Thermodynamics And Kinetics Of Vacuum Distillation Of Zinc-Based Alloys

With the extensive application of zinc and zinc alloys,the purity of zinc is required to be higher and higher.Therefore,the study of zinc refining process is of great significance to the crude zinc refining and the recycling of zinc secondary resources.Vacuum distillation has the advantages of no pollution,low energy consumption,high efficiency and high recovery rate,which is widely used in the separation and purification of alloys and the refining of crude metals.Zinc vapor pressure is high,vacuum metallurgy is an effective method for separation and purification of zinc,impurity elements will be enriched in the liquid phase and vapor phase to varying degrees.In this paper,based on the theory of VLE(vapor-liquid equilibrium)and the theory of metal volatilization,the vacuum distillation separation process of zinc-based alloys was systematically studied.The activity of metal components in Cd-Zn,Bi-Zn,Bi-Sn,Sn-Zn and Bi-Sn-Zn alloys was predicted by Wilson equation and the modified T-K-Wilson equation.According to VLE theory,the VLE phase diagram of zinc-based alloy with full concentration range was plotted.VLE data of Cd-Zn,Bi-Zn and Bi-Sn-Zn alloys were obtained by vacuum distillation.In the process of studying the evaporation rule of zinc alloy,the introduction of activity coefficient improves the accuracy of Langmuir equation in predicting the evaporation rate of zinc alloy.Kinetic experiments were carried out on pure Zn,Cd-Zn,Bi-Zn and Bi-Sn-Zn alloys.The evaporation coefficient of zinc was determined by the ratio of experimental and predicted values,the evaporation rate constant and evaporation activation energy of zinc were calculated.The results show that the Wilson equation and the modified T-K-Wilson equation are suitable for the calculation of the component activity of zinc-based alloy.The error between the experimental value and the calculated value of the VLE data are within a reasonable error range,indicating that the VLE phase diagram drawn has high reliability.For Cd-Zn,Bi-Zn and Bi-Sn-Zn alloys,the evaporation coefficients of Zn are 0.044?0.057,0.129?0.162,0.200?0.332,respectively.And the evaporation activation energies are 107.72 k J/mol,30.70 k J/mol and 20.70 k J/mol,respectively.In the case of the same zinc content,the interaction between components leads to the change of the activity coefficient of zinc in the metal melt,and then affects the vapor pressure and evaporation rate of zinc in different systems.The research work can be used to guide the experiment and production of vacuum distillation of zinc alloys,and has reference significance to perfect the basic data of physical chemistry of vacuum distillation metallurgy.