Distribution model of highly volatile impurity in distillate of rare earth metal

Abstract Distribution model of highly volatile impurity in distillate was established based on the mass-transfer rate equation in liquid boundary layer, the calculated methods of model parameters were determined, and a verification experiment of vacuum distillation purification of terbium (Tb) metal had been carried out. The research results indicated that, the mass-transfer processes of highly volatile impurities of Mn and Cr are controlled by the mass transfer in liquid boundary layer, impurities concentrations in gas phase are equal to that in liquid phase, and impurities concentrations in distillate present exponentially decreasing tendency as the distillation proceeds; the calculated results of Cr impurity are slightly larger than experimental results, whereas that of Mn impurity are much larger than experimental results in the former stage of the distillation experiment, which the average standard deviations of Cr and Mn impurities are ± 0.104 and ± 0.333 respectively, so Cr impurity has a better agreement than Mn impurity; the calculated removal rate of Cr impurity is 75.03%, which is slightly lower than experimental removal rate of 79.85%, while the calculated removal rate of Mn impurity is 75.11%, which is much lower than experimental removal rate of 94.55%.