Abstract
Problem Statement (Relevance): This article examines the possibility of creating an environmentally friendly, efficient and cost-effective high-performance integrated circuit for the processing of lead-containing industrial products and wastes (in particular, silver-zinc dross) resulting in the commercial production of single-element products. Among the practicable techniques for the recovery of silver-zinc dross, we distiguish vacuum distillation, which is considered one of the most effective and environmentally friendly methods for the separation, purification, processing and refining of various metals. To analyze the behavior of the multicomponent alloy during processing and in order to pre-select the system temperature and pressure and evaluate the separation efficiency in a vacuum distillation process, the following phase diagrams are applied: temperature–composition "T–x" and pressure–composition "P–x". Objectives: To estimate the VLE (vapor liquid equilibrium), including the dependence of the phase composition on temperature (T-x) and pressure (P-x) for the Pb-Zn alloy during vacuum distillation based on the MIVM (мolecular interaction volume model) model; to determine the thermodynamic parameters of the process. Methods Applied: The мolecular interaction volume model (or, MIVM) was applied to calculate the activity coefficients of the Pb-Zn alloy components. Originality: The VLE diagrams were built with the help of the MIVM model. Findings: Saturated vapour pressures were calculated for Pb (1.26.10–3–1.026.102) and Zn (1.552.103–1.756.106) within the temperature range of 873 to 1573 K. High values of the ratio p*Zn / p*Pb = (123.2–1.72) .104 and the separation factor βZn = 4.1–6.2 provide a theoretical basis for the selective separation of these metals by vacuum distillation, when zinc is enriched in the gas phase (βZn > 1) and lead – in the liquid phase. The mole fraction of lead in the gas phase уPb = (1–633) .10–6 increases with an increase of the temperature 873–1573 K and the mole fraction of the metal in the alloy xPb = 0.1–0.9. Using the MIVM model, the activity coefficients of zinc γZn= 0.682–0.997 and lead γPb= 0.73–0.998 were calculated for various compositions of the Pb-Zn alloy within the target temperature range. For VLE phase diagrams, the lever rule (or, the rule of lines) can be applied to help predict the quantities of the substance, residues and sublimates at the set temperature. The values of the excess Gibbs energy, enthalpy and entropy were found for the liquid–gas phase boundary in the Pb-Zn alloy: = 0.16–0.56 kJ/mol; = 0.087–0.292 kJ/mol; = 0.09–0.18 kJ/mol.К. Practical Relevance: The VLE phase diagrams of the alloys supply the information necessary for calculating the vacuum metallurgy process parameters, as well as for predicting the process temperature and pressure values required to obtain specific compositions of the Pb- and Zn-containing products.
Keywords
VLE phase diagram, vacuum distillation, мolecular interaction volume model.
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