Chromium, chemical symbol Cr, simple substance is steel gray metal. The element name comes from Greek, meaning "color" because chromium compounds have color. In 1797, French chemist L.N. Vauquelin discovered a new mineral in the Siberian red lead (chromite), which was obtained by carbon reduction the following year.

Chromium, chemical symbol Cr, simple substance is steel gray metal. The element name comes from Greek, meaning "color" because chromium compounds have color. In 1797, French chemist L.N. Vauquelin discovered a new mineral in the Siberian red lead (chromite), which was obtained by carbon reduction the following year. The content of chromium in the earth's crust is 0.01%, ranking 17th. Free chromium is extremely rare and is mainly found in chromite. It belongs to Group VIB in the Periodic Table of Elements, chromium has an atomic number of 24, an atomic weight of 51.9961, and a body-centered cubic crystal. The oxidation number is 6, 5, 4, 3, 2, 1, −1, −2, −4, which is the hardest metal.

Discover history

Chromium was discovered in 1797 by French chemist Walkerland from what was then called red Siberian ore.

As early as 1766, German Lehmann, a professor of chemistry in St. Petersburg, Russia, analyzed it and determined that it contained lead. In 1798 Walkerland named the gray needle-shaped metal he found, chrom, from the Greek chroma (color). This gives the Latin name chromium for chromium and the element symbol Cr. Almost in the same period, Klaprot also independently found chromium from chromite.

Ｄistributed

The natural reserves of chromite in the crust are more than 1.8 billion tons, and the recoverable reserves are more than 810 million tons. In 2004, the world's chromite mining volume was 17.5 million tons, of which 7.63 million tons were mined in South Africa, 3.27 million tons in Kazakhstan, 2.95 million tons in India, 670,000 tons in Zimbabwe and 580,000 tons in Finland. China's chrome ore resources are relatively scarce. According to the extent that it can meet demand, it is a shortage of resources. Total reserves of 10.78 million tons of ore, of which 53.6% are rich ore. There are 56 places of chromium ore, distributed in 13 provinces (regions) such as Tibet, Xinjiang, Inner Mongolia, and Gansu. Tibet is the most important, and its reserves are about half of the country. Chromium deposits in China are typical magmatic deposits related to ultrabasic rocks, most of which are of ophiolite type, and the deposits occur in ophiolite belts. The Luobusa chrome mine in Tibet and the Saltohai chrome mine in Xinjiang belong to this category. From the perspective of metallogenic age, the formation period of China's chromium ore was mainly Mesozoic and Cenozoic.

In the metallurgical industry, chromite is mainly used to produce ferrochrome and metallic chromium. Ferrochrome as a steel additive produces a variety of high-strength, corrosion-resistant, wear-resistant, high-temperature, oxidation-resistant special steels, such as stainless steel, acid-resistant steel, heat-resistant steel, ball bearing steel, spring steel, tool steel, etc. Metal chromium is mainly used for smelting special alloys with cobalt, nickel, tungsten and other elements. These special steels and special alloys are indispensable materials for the production of guns, missiles, rockets, and ships in the aerospace, aerospace, automotive, shipbuilding, and defense industries. In refractories, chromite is used to make chrome bricks, chrome-magnesia bricks and other special refractory materials.

Chromite is mainly used in the chemical industry to produce sodium dichromate, and then to produce other chromium compounds, used in pigments, textiles, electroplating, tanning and other industries.

Chromite is a scarce mineral species in China, with small reserves and low output, and imports more than 80% of its annual consumption. Chromium has oxyphilicity and ironophilicity, and is strongly oxyphilic, and exhibits thiophilicity only in the case of reduction and sulfur fugacity. Chromium is generally trivalent under endogenous conditions. The ionic radii of Cr3 +, Al3 + and Fe3 + are close to each other at the sixth acid position, so they can present a wide range of isomorphisms. In addition, the elements that can be replaced with chromium-like substances are Mn, Mg, Ni, Co, Zn, etc., so there is a wide distribution of chromium in the magnesium iron silicate minerals and secondary minerals. Under the strong oxidizing conditions of the epigenetic zone (alkaline medium), Cr3 + is oxidized to chromate ions in the form of Cr6 +, so that inactive chromium ions become soluble chrome anions and migrate. When it encounters highly polar ions (such as Cu, Pb, etc.), it forms an insoluble chromium acid mineral.

About 50 kinds of chromium-containing minerals have been found in nature, which belong to oxides, chromates and silicates. There are also a few hydroxides, iodates, nitrides and sulfides. Among them, chromium nitride and chromium sulfide minerals are only found in meteorite. The chromium minerals with industrial value belong to chromium spinel minerals, and their chemical formula is (Mg, Fe2 +) (Cr, Al, Fe3 +) 2O4 or (Mg, Fe2 +) O (Cr, Al, Fe3 +) 2O3, Its Cr2O3 content is 18% to 62%.

The chromium minerals of industrial value generally have a Cr2O3 content of more than 30%. The common ones are：

1.chromite

The chemical composition is (Mg, Fe) Cr2O4, between ferrous chromite (FeCr2O4, containing FeO32.09%, Cr2O3 67.91) and magnesite (MgCr2O4, containing MgO20.96%, Cr2O3 79.04%), Ferrous chromite and magnesite are also commonly referred to as chromite. Chromite is an equiaxed crystal system. The crystals are fine octahedrons, usually granular and dense aggregates, black in color, brown in stripes, semi-metallic luster, hardness 5.5, specific gravity 4.2-4.8, and weak magnetism. Chromite is a magma-forming mineral and is produced in ultrabasic rocks. When ore-bearing rocks are weathered and damaged, chromite is often transferred to sand ore. Chromite is the most important mineral raw material for smelting chromium. Inferior ore rich in iron can be used as high-grade refractory materials.

2.Cr-rich spar

Also called chromite spinel or aluminite. The chemical composition is Fe (Cr, Al) 2O4, containing 32% to 38% of Cr2O3. Its morphology, physical properties, genesis, occurrence and use are the same as chromite.

3.Hard chrome spinel

The chemical composition is (Mg, Fe) (Cr, Al) 2O4, containing 32% to 50% of Cr2O3. Its morphology, physical properties, genesis, occurrence and use are also the same as chromite.