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In this work, the kinetics of Pb evaporating from Pb-Sn alloy has been investigated. The experiments were performed in the temperature range 1200 K–1400 K and the pressure of 10 Pa. The results indicated that the evaporation of Pb follow first order kinetics. The overall mass transfer coefficients of lead evaporation from Pb-Sn alloy are 2.68 × 10−6 m s−1, 5.01 × 10−6 m s−1 and 1.92 × 10−5 m s−1 at 1200 K, 1300 K and 1400 K, respectively. Additionally, the apparent activation energy of lead evaporation from molten Pb-Sn alloy was calculated. It revealed that the mass transfer of lead in the vapor phase is not rate limiting in the vacuum distillation. The Pb evaporation from Pb-Sn alloy was mix-controlled by vaporization and liquid mass transfer. The mass transfer in the liquid phase is a major rate-limiting step under the present experimental conditions.

Vapor-liquid equilibria (VLE) and purification of tin from crude Sn containing Bi and Sb has been studied in vacuum distillation. The Sb-Sn and Bi-Sb-Sn systems were investigated in the temperature range from 1000 to 1500 K and at pressure of 5 Pa. Consequently, the content of Sn for the Bi-Sb-Sn system in the liquid phase reached more than 0.99 mol fraction as the temperature higher than 1500 K. It is shown that Bi and Sb can be satisfactorily removed from crude Sn. The VLE data of Sb-Sn and Bi-Sb-Sn alloys were calculated by using Wilson equation and compared with experimental values under vacuum condition. The capability of the equation to predicting the activities of components in whole composition range was also tested. It provides an efficient way to guide the process of vacuum distillation. The experiment results revealed that vacuum distillation is a promising method for the separation and purification of crude metals.

The vapor-liquid equilibria (VLE) for Sn Bi binary alloy at 5 Pa were carried out at distillation temperatures in the range of 1150 K–1550 K under vacuum condition. The experimental results indicate that Bi can be satisfactorily removed from crude Sn, the content of tin in liquid phase reaching more than 99.99 wt% at a temperature higher than 1300 K. The thermodynamic consistency of the experimental data was checked by Van Ness method. The Wilson equation is used to predicate VLE data. The results show good agreement with the experimental data, indicating that VLE phase diagram is feasible and practical for the process of vacuum distillation of alloys.