Study On The Preparation Of High Purity Zinc By Vacuum Distillatio

High purity metal with high chemical purity and low impurity content is widely used in the field of high technology,and has a good development prospect in the field of electronic information,aerospace,precision instrument and other high technology.Among them,high purity zinc with 5N-6N purity is widely used in the preparation of compound semiconductors,alloys,reducing agents and electronics industry.At present,the main production methods of high purity zinc include vacuum distillation,electrolytic refining and zone melting,and vacuum distillation is the main production method of high purity zinc because of its advantages of high purity products and low energy consumption.However,there are some problems in the preparation of high purity zinc by vacuum distillation,such as dominant condensing zone,unclear condensation temperature,unstable product purity,low pressure requirement and mi ssing volatile kinetic parameters.This paper carried out a vacuum volatilization thermodynamic study.Based on the impurity elements in the industry standard of high purity zinc,the thermodynamic parameters of metal zinc and impurity elements were calculated and analyzed.According to the calculation results,the migration rules of metal zinc and impurity elements in the vacuum distillation process were judged.The feasibility of vacuum separation of impurity elements such as lead and cadmium was determined.According to the calculation results of gas-liquid equilibrium phase diagram,the lower limit of system temperature for obtaining high purity zinc theoretically was 700 K and 750 K under the conditions of system pressure of 5 Pa and 10 Pa.The mass-time relationship of vacuum zinc distillation at different temperature(673-823K)and pressure(5-400Pa)was studied by vacuum differential weight method.The mathematical model of the relationship between evaporation rate and system pressure and system temperature of zinc was obtained by data processing.At the same time,using the data obtained from the differential weight experiment,the rate control step of the vacuum volatilization process of metal zinc is defined as the process of metal zinc vapor passing through the gas phase boundary layer.According to the results of thermodynamics and kinetics,the experiment of preparing high purity zinc by vacuum distillation and fractional condensation was carried out under the system pressure of 5Pa,and the dominant condensation zone and mass distribution of metal zinc condensate at 748 K,773K,798 K and 823 K were determined.According to the detection results of impurity elements of condensate,Under the experimental conditions of 823K-7h(condensation height 45-70mm),6N high pure zinc was obtained,and the yield was 61.2%.On the basis of traditional vacuum distillation to prepare high purity zinc,the migration behavior of elements in the process of vacuum distillation was calculated,the volatilization kinetic parameters of metal zinc were improved,and the distribution law of main metal and impurity elements was clarified.On the basis of thermodynamics,kinetics and experimental research,the pressure requirement of high purity zinc production system is reduced,and the production cost is saved,which provides theoretical support and practical reference for the preparation of 6N high purity zinc by vacuum distillation...