The Equilibrium of the System “Gas–Liquid” for Alloy Sn-Sb in Vacuum Distillation

Abstract

In the processing of lead bullion necessary to separate the metal from impurities – copper, tin, antimony, arsenic, silver, bismuth, and with the possible use of environmentally friendly, technologically effi cient and cost-eff ective high performance vacuum distillation. To analyze the behavior of multicomponent alloy processing, pre-selection of temperature and pressure of the system, evaluate the eff ectiveness of component separation in a vacuum distillation using phase diagrams temperature–composition “of T–h,” pressure–composition “R–x”. The aim of this work was to calculate the equilibrium “gas–liquid” VLE (vapor liquid equilibrium), including the dependence of phase composition on temperature (T-x) and pressure (P-x) for Sn-Sb alloy during vacuum distillation on the basis of the three-dimensional model of molecular interaction MIVM (мolecular interaction volume model), as well as determination of thermodynamic parameters of the process. In the temperature range 823-1073 to the calculated saturated vapor pressure (Pa) Sn (3.32.10–9–8.12.10–5) and Sb (3.954–273.66). High values of the ratio р*Sb / р*Sn = (1190–3.37).106 and separation factor logβSb = 6.25–9.44 create a theoretical background for the selective separation of these metals by vacuum distillation, when the antimony is enriched in the gas phase (βSb > 1), and tin – liquid. The mole fraction of tin in the gas phase уSn = (1–5000).10–9 increases with increasing temperature 823-1073 K and the molar fraction of the metal in the alloy хSn = 0.1–0.9. Using the MIVM model calculated activity coeffi cients of antimony γSb = 0.439–0.992 and tin γSn = 0.433–0.992 for Sn-Sb alloy with diff erent composition in the investigated temperature range. For phase diagrams VLE can be used by the lever rule (rule lines) to help predict quantities of substances, residues and sublimates at a predetermined temperature. For the phase boundary “liquid–gas” Sn-Sb alloy the values of the excess Gibbs energy, enthalpy and entropy: 􀈂 􀜩􀯠 􀮾 = 0.744–2.096 kJ/mol; – = 0.763–2.166 kJ/mol; = 0.0181–0.0891 J/mol.K. VLE phase diagrams alloys provide the necessary information for the design of technological parameters in industrial production, vacuum metallurgy, as well as to predict temperature and pressure process for obtaining Sn – and Sbcontaining products of a given composition