Removal of barium impurities from selenium by vacuum distillation

Abstract

We have studied the behavior of barium impurities in the form of BaF₂ and BaO during vacuum distillation of selenium. The effective Ba partition coefficient is shown to depend on the impurity concentration and evaporation rate. At initial barium contents in the range 3 × 10⁻³ to 2 × 10⁻⁵ wt %, the effective Ba partition coefficient is 600 and 1.5 at distillation rates of 4.7 × 10⁻⁶ and 1.5 × 10⁻³ cm³/(cm² s), respectively. The chemical form of barium has no significant effect on its partition coefficient. Using a Rayleigh distillation equation, we have determined the equilibrium partition coefficient and the thickness of the diffusion boundary layer in the system.