Selenium is a chemical element, its chemical symbol is Se, and it is located in the VI A group of the fourth period in the periodic table of chemical elements. It is a non-metal. It can be used as photosensitive material, electrolytic manganese industry catalyst, essential nutrient elements for animals and beneficial nutrient elements for plants, etc. Selenium exists in nature in two ways: inorganic selenium and plant active selenium. Inorganic selenium generally refers to sodium selenite and sodium selenate, which are obtained from the by-products of metal mineral deposits; the latter is a combination of selenium through biotransformation and amino acids, generally in the form of selenomethionine.
The main raw material (90%) for industrial extraction of selenium is the anode slime produced by the electrolytic refining of copper, and the rest comes from the calcine produced by the refining of lead, cobalt, and nickel, and the residue from the production of sulfuric acid. Since selenium in copper electrolysis anode slime is in the form of selenium compound symbiosis with precious metals, the selenium content is about 5% to 25% (mass fraction). Therefore, the process is generally to recover the precious metals gold and silver first, and then recover selenium. A method of recovering selenium from anode slime to produce gold and silver alloys.
There are three main types of anode slime treatment processes at home and abroad: One is the full wet process. The main processes are: copper anode slime-pressure leaching of copper, tellurium-chloride leaching of selenium, gold-alkaline leaching, lead-ammonia leaching, silver-gold-silver electrolysis; the second is mainly wet method, fire method and wet method The combined semi-wet process is adopted by most domestic manufacturers. The main process is: copper anode slime-sulfuration roasting, steaming selenium, dilute acid, copper-chloride, gold-sodium sulfite, silver-gold and silver electrolysis; the third is the fire method, which is based on the fire method, and combines the wet method and the fire method. The main process is: copper anode slime-pressure leaching of copper, tellurium-fire method smelting, blowing-silver electrolysis-silver anode slime to process gold.
There are two main methods for industrial production of selenium: one is oxidizing and roasting anode slime and SeO2 distillation. The process is to capture gaseous SeO2 roasting gas in a scrubber with a solution, and then precipitate it in an acid medium or lye under the action of SO2. Selenium; the other is to add soda ash to sinter the anode slime in an oxidizing atmosphere to convert selenium into sodium selenide or sodium selenate water-soluble solution. The process is to oxidize selenium and selenide to easily soluble in water under sintering conditions. Sodium selenate or sodium selenate, and then purging to separate selenium from the solution.