Study on Volatilization Kinetics of Bismuth

The market consumption of bismuth has been increasing annually owing to its green characteristics. Currently, vacuum distillation is the primary method used to recover bismuth from secondary resources. However, the kinetic data for bismuth associated with this process are scarce, and the migration pattern is unknown. In this study, the volatilization rate of bismuth was determined using a vacuum thermogravimetric furnace, and the maximum volatilization rate of bismuth was obtained under different temperature conditions. Furthermore, the maximum volatilization rate of bismuth was fitted to obtain the equation of maximum volatilization rate of bismuth versus temperature (variance = 0.9371). The critical pressures of bismuth at 973 K, 1023 K, 1073 K, 1123 K, and 1173 K were 0.50, 1.00, 4.20, 7.69, and 18.85 Pa. The theoretical maximum volatilization rate of bismuth was calculated using the Langmuir equation, and the cohesion coefficient of bismuth was corrected. The molecular mass transfer coefficients through the melt surface, gas boundary layer, and total mass transfer coefficients during the vacuum distillation of bismuth at different temperatures and conditions were calculated. The activation energy of bismuth during vacuum distillation and the activation energy required to pass through the melt surface and the liquid-phase boundary layer were calculated, and it is known that the step limiting the volatilization of bismuth is to pass through the gas-phase boundary layer at less than 100 Pa, and the step limiting the volatilization of bismuth is to pass through the gas-phase boundary layer and the melt surface at the 100-1000 Pa condition. The kinetic data of bismuth were enriched, the migration law of bismuth was obtained, and bismuth purification experiments were conducted based on the results of this study.