When selenium is extracted from copper electrolyte slurries, soda-alkaline selenium-containing solutions are usually obtained. In addition to the main component, selenium, they contain impurities: tellurium, various heavy metals, silver, iron, arsenic, mercury, etc. The main impurity is tellurium, which is isolated from the solution as hydrated dioxide by neutralization to pH = 5--6. At the same time, it is very important to remove other impurities, the ingress of which into selenium reduces its quality.