Kinetics study of Pb evaporation from pure Pb and Pb–Ag alloy in vacuum evaporation process

Traditional method for treatment of Pb–Ag alloy has disadvantages of a long metal production cycle, long process, and high energy consumption. Vacuum distillation has obvious advantages, such as a short flow, short production cycle, high direct yields of metal, and low cost. Kinetics is the key factor that determines production efficiency. Therefore, evaporation kinetics of Pb evaporation from pure Pb and Pb–Ag alloy has been investigated. The evaporation rate of pure Pb was experimentally determined as 0.044, 0.13 and 0.32 g cm−2·min−1at 1173 K, 1273 K and 1373 K, respectively. Pb evaporation from Pb–Ag alloy followed first order kinetics and the rate controlling step were mainly mass transfer in liquid which indicated that increasing the stirring of the melt during the production process can improve the removal efficiency of lead. In addition, some kinetic parameters were obtained such as the apparent activation energy of Pb evaporation from Pb–Ag alloy was 148.8 kJ mol−1, the mass transfer coefficient was 6.48 × 10−8, 1.90 × 10−7and 6.00 × 10−7 m s−1at 1173 K, 1273 K and 1373 K, respectively. The research enriches the Pb evaporation kinetic database and can provide theoretical guidance for the vacuum distillation of noble lead alloys. In addition, the research designs a set of alloy configuration and vacuum evaporation device with simple assembly and convenient operation which can be used for the research on vacuum evaporation kinetics of other non-ferrous metal alloy systems.