In the periodic table of elements, it belongs to family ⅵ b, with atomic number 24 and atomic weight 5 1.99 1, and the common valence is +2, +3 and +6. The oxidation number is 6, 5, 4, 3, 2, 1, 1, ? 2, ? 4. It is the hardest metal.
In nature, ferrochrome is mainly chromite? o？ Officially exist. It is formed by reducing chromium oxide with aluminum, or electrolyzing chromite or chromic acid.
According to its content in the earth's crust, chromium is one of the widely distributed elements. More cobalt, nickel, molybdenum and tungsten than previously found. This may be because the natural compounds of chromium are very stable, insoluble in water and difficult to reduce. Some people think that the metal chromium obtained by Vauclin may be chromium carbide.
Extended data:
There are about 50 kinds of chromium-containing minerals found in nature, which belong to oxides, chromates and silicates respectively. In addition, there are a few hydroxides, iodates, nitrides and sulfides.
Among them, chromium nitride and chromium sulfide minerals only exist in meteorites. All chromium minerals with industrial value belong to chromium spinel minerals, and their chemical general formula is (Mg, Fe)(Cr, Al, Fe)? o？ Or (Mg, Fe)O(Cr, Al, Fe)? o？ , its Cr? o？ The content is 18% ~ 62%.
Chromium minerals with industrial value, its Cr? o？ The content is generally above 30%, and the common ones are:
Chromium can be used to make stainless steel. The colors of rubies and emeralds also come from chromium. As the most important metal in modern science and technology, Cr-Ni steel with different percentage of smelting is ever-changing and changeable, which is unbelievable.
The toxicity of chromium is related to its valence state. The toxicity of hexavalent chromium is 100 times that of trivalent chromium, and it is easily absorbed and accumulated in the body. Trivalent chromium and hexavalent chromium can be transformed into each other. Natural water does not contain chromium; The average concentration of chromium in seawater is 0.05 μ g/L; Drinking water is lower. The pollution source of chromium is the sewage discharged from chromium-containing ore processing, metal surface treatment, leather tanning, printing and dyeing.
Chromium is an essential trace element for human body. Trivalent chromium is an element beneficial to human body, and hexavalent chromium is toxic. The absorption and utilization rate of inorganic chromium by human body is extremely low, less than1%; The utilization rate of organic chromium by human body can reach 10-25%. The content of chromium in natural food is low and exists in trivalent form.
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