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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.

In this work, interaction energies between pairs of atoms for the Ag–Pb, Cu–Pb and Sn–Pb systems have been calculated using ab initio methods. These energies are then used as the interaction energy parameters in the Wilson equation. Phase diagram of vapor–liquid equilibria (VLE) for the Pb-based alloy systems in vacuum distillation are obtained based on the calculated parameters. The results indicate that this approach can lead to accurate VLE predictions for alloy systems in vacuum distillation based only on properties of pure components and the structure of the clusters. The comparisons show the computational results are in good agreement with the experimental data.

In this work, vapor–liquid equilibria (VLE) of the Ag–Cu–Pb system were experimentally investigated in vacuum distillation. The experimental results show that the content of Pb in liquid phase is 0.005 (mole fraction) under the experimental condition of 1173 K, 90 min and 10 Pa. The amount of Pb in volatiles increased to 0.9911 (mole fraction). It indicates that Pb can be satisfactorily removed from Ag–Cu alloy. With the Wilson equation, the partial Gibbs free energies of Pb in liquid Ag–Cu–Pb alloys were calculated, and the predicted values agree well with the experimental data, which shown that the interaction parameters are reliable. Using binary data only, the VLE for the Ag–Pb and Ag–Cu–Pb systems under vacuum condition were obtained. The calculation results demonstrate that this approach can lead to accurate VLE data predictions for the binary and ternary systems based on the Wilson equation.

Vacuum distillation experiments were conducted for tin-antimony alloy (Sn–Sb alloy) under the system pressure of 5 Pa. The content of Sb (mole fraction) in crude Sn, viz., xSb was reduced from 0.5000 to 0.0619 in a single stage distillation process under the condition of residual pressure of 5–10 Pa, distillation temperature of 1373 K and distillation time of 60 min. The activity coefficients of components of Sn–Sb alloy were calculated by using the molecular interaction volume model (MIVM), and the calculated average relative deviation and the average standard deviation were ±0.00039 and ± 0.173%, respectively for both Sn and Sb. The vapor–liquid equilibrium (VLE) phase diagrams, including the temperature-composition (T-x) and pressure-composition (p-x) diagrams of Sn–Sb alloy in vacuum distillation were calculated based on VLE theory and the MIVM. A reasonable agreement between the calculated results and the experimental data indicates that VLE phase diagrams obtained by this method are reliable. The VLE phase diagrams of alloys will provide an effective and convenient way for the designing of the process parameters of industrial production of vacuum metallurgy, and for the prediction of the needed product component dependence of temperature and pressure during the process of vacuum distillation.

In this study, vacuum distillation experiments of high-lead crude copper were performed under the vapor pressure 5 Pa. The content of lead in crude copper was reduced from 15% to less than 0.01% in a single stage distillation process with residual vapor pressures of below 10 Pa, distillation temperatures of 1423 K and distillation times of 60 min. The vapor–liquid equilibrium (VLE) phase diagrams of Cu–Pb binary alloy in vacuum distillation were calculated using the Wilson equation. Thermodynamic experimental data taken from literature were used for calculating Wilson equation temperature dependent interaction parameters. The calculations give a satisfactory accuracy with the experimental data for separation of Cu–Pb alloy in vacuum distillation. The results indicate that VLE phase diagrams under vacuum obtained by this method are reliable for predicting the process of vacuum distillation for Cu–Pb alloy. The VLE phase diagrams of alloys will have significant benefits for the industrial production of vacuum metallurgy especially for the process of multistage distillation in the vacuum furnace.

Based on the molecular interaction volume model (MIVM), the pair-potential energy parameters Bji and Bij of the related binary Sn–Pb, Pb–Sb and Sn–Sb alloy systems were calculated using the infinite dilution activity coefficients γi ∞ and γj∞. The activities of components of the Sn–Pb–Sb ternary alloy system were predicted using Bji and Bij. Finally, the vapor–liquid phase equilibrium of the Sn–Pb–Sb alloy system was predicted using only the properties of pure components and the activity coefficients, which indicates that Sn can be separated from Pb and Sb by vacuum distillation thoroughly. A significant advantage of the model lies in its ability to predict the thermodynamic properties of multi-component liquid alloys using only two parameters. Moreover, the MIVM is reliable due to it has certain physical meaning from the viewpoint of statistical thermodynamics.

A modified model with temperature-dependent parameters is proposed based on the Hoch–Arpshofen model. The enthalpies of formation of multicomponent liquid alloy systems were calculated using the modified model. Results for the Pb-Sn-Zn, Cd-Ga-Sn, Bi-Cd-Ga-Zn, Bi-Cd-Ga-In-Zn, Cd-Ga-In-Sn-Zn and Bi-Cd-Ga-In-Sn-Zn systems are in excellent agreement with experimental data and highly accurate than obtained via the original Hoch–Arpshofen model, which indicate that the method is reliable.