Chemical element selenium belongs to the VI group of periodic Mendeleev's system, it is chalcogen. Natural selenium consists of six stable isotopes. Also 16 radioactive isotopes of selenium are known.
Instruction
1. Selenium is considered very rare and scattered element, in the biosphere it vigorously migrates, forming more than 50 minerals. The most known of them: bertselianit, naumannit, native selenium also halkomenit.
2. Selenium contains in volcanic sulfur, a galenite, pyrite, the vismutena and other sulfides. It is got from lead, copper, nickel and other ores in which it is in a scattered state.
3. Contains in fabrics of most of living beings from 0.001 to 1 mg/kg of selenium, some plants, marine organisms and mushrooms concentrate it. For a number of plants selenium is a necessary element. Need of the person and animals for selenium makes 50-100 mkg/kg of food, this element has antioxidant properties, influences a set of enzymatic reactions and increases susceptibility of a retina of an eye to light.
4. Selenium can exist in various allotropic modifications: amorphous (vitreous, powdery and colloidal selenium) and also crystal. At restoration of selenium from solution of selenious acid or fast cooling of its vapors receive amorphous red powdery and colloidal selenium.
5. When heating any modification of this chemical element it is above 220 °C and the subsequent cooling vitreous selenium is formed, it is fragile and has glass gloss.
6. Hexagonal gray selenium which lattice is constructed of the spiral chains of atoms located in parallel each other is steadiest thermally. It is received by means of heating of other forms of selenium to melting and slow cooling to 180-210 °C. In chains of hexagonal selenium, atoms are connected covalently.
7. Selenium is steady on air, do not affect it: oxygen, the water diluted sulfuric and hydrochloric acids, however it is well dissolved in nitric acid. Interacting with metals, selenium forms selenides. The set of complex compounds of selenium is known, all of them are poisonous.
8. Receive selenium from waste of paper or sulfate production, method of electrolytic refinement of copper. This element is present at slimes together with heavy and precious metals, sulfur and tellurium. For its extraction slimes filter, then heat with the concentrated sulfuric acid or subject to oxidizing roasting at a temperature of 700 °C.
9. Selenium is used by production of vypryamitelny semiconductor diodes and other converting equipment. In metallurgy with its help give to steel fine-grained structure and also improve its mechanical properties. In chemical industry selenium is applied as the catalyst.