A. A. Korolev, K. L. Timofeev, G. I. Maltsev.
ABSTRACT
During the bismuth removal from lead, Pb–Bi product is formed, which requires complex processing, with the production of commercial mono-element materials. One possible method of its processing is vacuum distillation, which is considered one of the most efficient and environmentally friendly method for the separation and purification, processing and refining of various metals. Phase diagrams are used for the preliminary select on of the temperature and pressure of the system and to evaluate the efficiency of component separation during vacuum distillation. The aim of the work is to calculate the equilibrium states of “gas–liquid” VLE (vapor liquid equilibrium), including the dependence of the phase composition on temperature (T–x) at a given pressure for binary Pb–Bi alloys in vacuum distillation based on models MIVM (molecular interaction volume model) and simplified – SMIVM (simple molecular interaction volume model), which includes a smaller number of changing parameters of the system, in particular, at fixed values of coordination Zi numbers and molecular volume of Vmi components of alloys. As a result, the adequacy of the SMIVM model in the used calculation method is confirmed. In the VLE phase diagrams, the steam and liquid phase curves are close enough to each other because the difference between the boiling temperatures of Bi (1837 K) and Pb (2022 K) is only 185 K. Based on the T–x and P–x diagrams, even with a small initial lead content (1–10 mol % Pb) in the Pb-Bi alloy in Bi-condensate passes 36–51% lead at a given pressure of 13.3–1330 Pa and a temperature of 1093–1418 K or at a fixed temperature of 1073–1473 K and a pressure of 8–2600 Pa. Qualitatively separate the Pb–Bi alloy by conventional distillation or fractionation in one stage is not possible, since Pb and Bi evaporate almost simultaneously into the gas phase when the alloy is heated in vacuum. For effective separation of Pb–Bi alloy a similar process of rectification should be used, carried out in vacuum apparatus with a vertical nozzle, consisting of a large number evaporative containers and a temperature gradient in height. The liquid phase of the alloy feeding to the upper plate with the minimum specified temperature as you move down and increase in temperature will be enriched sublimation hard component of the alloy, and moving her towards the gas phase easily sublimation metal that condenseries in the composition of the sublimate in the upper segment of the nozzle.
KEYWORDS
lead, bismuth, equilibrium phase diagram, vacuum distillation, conventional and simplified molecular volumetric models of interaction
DOI:10.31857/S0235010620030056