Selenium is considered to be very rare and trace elements in the biosphere he vigorously migrates, forming more than 50 minerals.The most famous of them: bertselianit, Naumann, native selenium and halkomenit.
Selenium is found in volcanic sulfur, galena, pyrite and other sulfides bismuthine.It is obtained from lead, copper, nickel and other ores in which it is in the dispersed state.
In tissues of most living things contain from 0.001 to 1 mg / kg selenium, some plants, marine organisms and fungi, it is concentrated.For a number of plant selenium is an essential element.The need for human and animal selenium is 50-100 mg / kg food, this element has antioxidant properties that affects many enzymic reactions and increases the susceptibility of the retina to light.
Selenium may exist in different allotropic modifications: amorphous (glassy, powdered and colloidal selenium), as well as crystal.When recovery of selenium from a solution of selenious acid or its vapors rapidly cooling the amorphous red powder and colloidal selenium.
When heated, any modification of the chemical element above 220 ° C and subsequent cooling forms a glassy selenium, it is fragile and has a glassy luster.
most thermally stable hexagonal gray selenium, which is constructed of lattice disposed in parallel helical chains of atoms.This was prepared by heating other forms of selenium to melting and slow cooling to 180-210 ° C.Inside the chain of hexagonal selenium atoms are covalently bonded.
Selenium is stable in air, it does not apply to oxygen, water, dilute sulfuric and hydrochloric acid, but it dissolves readily in nitric acid.Working with metals, selenium forms selenides.There are many complex compounds of selenium, all of them are poisonous.
Get selenium from waste paper or sulphate production, electrolytic refining of copper.In this element is present sludge together with the heavy and noble metals, sulfur and tellurium.For removal sludge was filtered and then heated with concentrated sulfuric acid or is subjected to oxidizing calcination at 700 ° C.
Selenium is used in the manufacture of semiconductor rectifier diodes and other converters.The industry with the help of attached steel fine-grained structure and improve its mechanical properties.In the chemical industry, selenium is used as the catalyst.
- HiMiK.ru, Selenium