Migration behavior and distribution of impurities in purifying crude tellurium by vacuum distillation

Abstract

Vacuum distillation technology demonstrates significant advantages in the field of crude tellurium purification. However, the unclear dynamic migration mechanisms of impurities during the distillation process remain a primary bottleneck restricting the improvement of purification efficiency. This study established impurity distribution models and conducted distillation experiments to investigate the effects of distillation temperature and holding time on the migration behavior and distribution patterns of impurities at different condensation positions. The results show that the mass transfer controlling steps for highly volatile impurities (Se, Na) are liquid-phase boundary layer mass transfer processes, while those for medium/low volatile impurities (Mg, Bi, Fe, Cu) involve mixed or evaporation-dominated mass transfer processes. The theoretical impurity distribution curves exhibit consistent trends with experimental results. Distillation temperature exerts a significant impact on tellurium purity enhancement and induces impurity condensation deviation. Prolonged holding time enhances the separation of highly volatile impurities but impedes that of medium/low volatile species. Under optimal conditions (823 K, 4 h), 4 N tellurium was successfully prepared via two-stage vacuum distillation, achieving total contents of 4.168 ppmw (98.85 % removal) for highly volatile impurities, 12.605 ppmw (38.03 % removal) for medium volatile impurities, and 6.876 ppmw (98.75 % removal) for low volatile impurities.