Method for preparing 3N selenium from selenium slag

The invention discloses a method for preparing 3N selenium from selenium slag. The invention provides a method for preparing 3N selenium by purifying selenium slag, which comprises the following steps: crushing and grinding the selenium slag to 200-400 meshes, adding sulfuric acid for pickling to remove copper, and carrying out solid-liquid separation to obtain copper liquid copper-removed slag; adding the copper removal slag into a sodium sulfite solution, carrying out pressure leaching, and carrying out solid-liquid separation to obtain leaching slag and a leaching solution; and after being repeatedly washed with water, the red selenium is converted into ash selenium under high-temperature baking of an infrared lamp, and the ash selenium can reach the standard of 3N selenium. The technology of pressure leaching, low-temperature selenium precipitation and high-temperature transformation is adopted, the technological process is short, the selenium recovery rate is high, the grade of obtained refined selenium