<p>Vapor–liquid equilibria and impurity separation behavior in Pb-Zn, Pb-Bi and Pb-Ag binary systems were investigated using CALPHAD-based activity calculations combined with Gibbs-energy minimization equilibrium simulations performed in HSC Chemistry software. Separation coefficients of Zn, Bi, and Ag were evaluated as a function of temperature and composition to quantify the relative volatility of impurity elements with respect to lead. The results reveal three distinct thermodynamic regimes. The Pb-Zn system exhibits strong positive deviations from ideality and extremely high separation coefficients (<i>β</i>_Zn ≫ 1), indicating a very high selective volatility of Zn relative to Pb. The Pb-Bi system shows near-ideal solution characteristics with separation coefficients approaching, but remaining below unity (<i>β</i>_Bi≈ 0.56-0.93), indicating limited separation efficiency. In contrast, the Pb-Ag system is characterized by very low separation coefficients (<i>β</i>_Ag ≪ 1), reflecting the thermodynamic stability of Ag in the condensed phase and its negligible tendency to evaporate relative to Pb. Equilibrium composition diagrams demonstrate the combined influence of temperature and total pressure on phase redistribution. Both increasing temperature and decreasing pressure promote vapor-phase enrichment of impurities; however, these conditions simultaneously enhance lead volatilization, thereby reducing separation selectivity under single-stage equilibrium conditions. The theoretical predictions are consistent with experimental data reported in the literature, where efficient impurity removal was achieved through two-stage high-low temperature vacuum distillation of crude lead. The present study provides a quantitative thermodynamic framework for evaluating the feasibility and limitations of vacuum refining of lead alloys.</p>