Abstract. One of the possible ways to recover components from the Hg–Se alloy formed during the processing of copper-electrolyte sludge is vacuum distillation. Object of research: Hg–Se alloys of composition, mol %: 0.01–99.99 Hg; 99.99–0.01 Se, the formation of which is possible during the processing of copper-electrolyte sludge in the production of commercial selenium concentrate. The purpose of the work: calculation of the “gas – liquid” VLE (vapor liquid equilibrium) equilibrium states, including the dependence of the phase composition on temperature (T – x) and pressure (P – x) for the Hg–Se alloy during vacuum distillation. Methods and approaches used. The activity coefficients of the Hg–Se alloy components were calculated using a simplified version of the simple molecular interaction volume model (SMIVM). Phase diagrams of temperature (T – x) and pressure (P – x) are used to pre-select the system temperature and pressure, and to evaluate the efficiency of component separation during vacuum distillation. Novelty: calculation of activity coefficients using a simplified version of the SMIVM model. Main results. In the temperature range of 823‒1073 K, saturated vapor pressures were calculated for Hg (pHg * = 1.418·106‒1.046·107 Pa) and Se (pSe * = 1.42·104‒3,66·105 Pa). High values of the ratio pHg */pSe * = 100.2‒28.6 and the separation coefficient lgβHg = 2.73‒1.01 create theoretical prerequisites for the selective separation of these metals by vacuum distillation, when mercury is enriched in the gas phase (βHg > 1), and selenium – in the liquid phase. The molar fraction of selenium in the gas phase xSe = 0.553–1.43·10‒12 decreases with a decrease in the temperature of 1073‒823 K and the molar fraction of the element in the alloy xSe = 0.99–0.01. For the “liquid – gas” interface of the Hg–Se alloy, the values of changes in the excess Gibbs energy, enthalpy, and entropy are determined ‒ΔGm E = 0.8–3.0 kJ/mol; ‒ΔHm E = 1.86–5.39 KJ/mol; ‒ΔSm E = 0.99–2.94 J/mol.K. Practical significance: reducing the number of time-consuming and expensive installation experiments during the processing of Hg–Se compositions to optimize the temperature and pressure values of the vacuum treatment process distillation in order to obtain Se-containing products of a given composition.
In this work, gas-liquid equilibrium states are calculated, including phase composition dependences on temperature (T-x) and pressure (P-x) for the Hg-Al alloy during vacuum distillation. The objects of research comprised Hg-Al alloys having the following composition, mole %: 20–80 Hg; 80–20 Al, whose formation may occur during the processing of copper anode slime upon producing commercial selenium concentrate. A simplified molecular interaction volume model was used to calculate the activity coefficients of the components in the Hg-Al alloy. Phase diagrams of temperature (T-x) and pressure (P-x) are used for the preliminary selection of temperature and pressure in the system, as well as for the evaluation of the separation efficiency of components. The novelty of the research stems from calculating activity coefficients using the selected simplified model. Saturated vapour pressures for Hg (p*Hg) and Al (p*Al) were calculated in the temperature range of 823–1073 K. The high values of the p*Hg / p*Al ≥ 3 . 1010 ratio and separation coefficient llogβHg ≥ 10 provide theoretical premises for selective extraction of these metals by vacuum distillation, where mercury is concentrated in the gas phase (βHg > 1) and aluminium in the liquid phase. The values of excess Gibb’s energy, enthalpy and entropy changes for the liquid-gas interface of Hg-Al alloy were determined: ΔGE/m = 1–3 кJ/mol; = 1-3 kJ/mol; +-ΔGE/m = 0,03–0,17 kJ/mol. The practical significance of the research lies in minimising the number of initial experiments during the processing of Hg-Al compositions for optimising the temperature and pressure in the vacuum distillation process.
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