Process introduction and process parameters: 

Selenium is mainly produced as a by-product in the process of extracting gold and silver from copper electrolytic anode mud, and the rest is extracted from lead anode mud.

Selenium has a fusion point of 221 ° C and a boiling point of 684.9 ° C. The relationship between the vapor pressure and temperature is shown in Table below.

Vapor pressure of selenium at different temperatures

The above table shows that the refining of crude selenium vacuum can be carried out at a lower temperature.

Impurities with low vapor pressure (such as high-boiling substances: copper, lead, gold, silver, etc.) in the process of crude selenium distillation remain in the slag during distillation, while arsenic and antimony may form selenide with higher vapor pressure than selenium. Arsenic is easily sublimed at high temperatures, making it difficult for arsenic and antimony to separate from selenium vapor during distillation. Therefore, in order to obtain high-purity selenium, it is necessary to control the content of antimony in the raw material not to be too much.

Using 98% crude selenium as raw material, 99.99% purity selenium can be obtained by vacuum distillation technology. The distillation temperature is controlled at 350-400 ° C. The condensation temperature is controlled at 250-300 ° C, and the vacuum is 30 Pa or less.