Purification of crude selenium by vacuum distillation and analysis

Abstract

In this study, metallurgical grade crude selenium (99.4%), comprehensively recovered from copper electrolysis anode slime, was purified to 99.992% through triple consecutive vacuum distillation (TCVD) on a laboratory scale. The actual evaporation rate and accommodation coefficient α of crude selenium were found to be 0.0231 g cm−2 min and 0.3236, respectively, at 523 K and approximately 4 Pa by a vacuum thermogravimetric furnace. Internal heat vacuum distillation equipment was employed in the purification experiments with a dynamic vacuum level of approximately 4 Pa. Detailed analysis of the initial and purified selenium was performed using inductively coupled plasma mass spectrometry (ICP-MS) to identify the 15 most common impurity elements. The analysis confirmed the reduction in the total impurity content from 2997.38 ppmw to <79.08 ppmw. The microscopic impurity elemental distribution was analyzed using an electron probe microanalyzer (EPMA), and it shows that the impurities were relatively concentrated and gathered in crude selenium. The results enrich the database of selenium evaporation kinetics and lay a foundation for the industrial purification of selenium.