Removal of arsenic and antimony from complex lead bullion via vacuum distillation, The

Abstract

Vacuum distillation is based on the selective evaporation of volatile impurities from liquid melts and has been extensively studied. It is known to provide better operation conditions and a better control of product composition. In order to understand the thermodynamics of vacuum distillation, it is essential to know the activity coefficient of the impurity in the melt. In this research, three thermodynamic models were used to calculate the activity coefficient. The models are the molecular interaction volume model (MIVM), the Wilson equation, and the non-random two liquids (NRTL) model. The research focused on the determination of binary parameters for the Pb-As and the Pb-Sb binary systems and the prediction of vapor-liquid (VLE) necessary to understand the removal of arsenic and antimony from their binary lead alloys under reduced pressure. Vacuum distillation experiments were conducted on Pb-As and Pb-Sb alloys by varying distillation pressure, temperature, time, and the alloy composition. It was discovered that the removal of arsenic increased with a decrease in distillation pressure, and an increase in distillation time and temperature. The removal was a strong function of temperature; at 5 Pa, 650 °C and 45 min, 79.2wt. % removal extent was achieved, and arsenic content decreased from 2.46 wt. % to 0.53 wt. %. It was discovered that antimony removal also increased with a decrease in distillation pressure, and an increase in distillation time, and temperature. At 5 Pa, 700°C, and 90 minutes, 38.6 % antimony was removed and its content was decreased from 3.5 wt.% to 2.2 wt. %. It is noted however, that antimony removal required higher temperatures processing time for its removal compared to arsenic. The research main’s contribution to vacuum distillation is the VLE prediction for the removal of arsenic.