Hard and refractory metal chromium is very popular in many industries. Dyes, stable alloys and coatings for various surfaces, as well as refractory materials, are made from it. In nature, it exists in the form of numerous compounds in rocks and minerals. This article talks about chrome ore, its deposits and mining methods.
24th element
Chromium is an element of the sixth group of the periodic table with atomic number 24. As a simple substance, it is one of the hardest metals, but this quality strongly depends on its purity. With various impurities, its hardness increases, but in its pure form, chromium can be quite ductile.
The melting point of the metal is above 1800 degrees Celsius and also depends on the amount of impurities. Due to its refractoriness, it becomes active only when heated, and under normal room conditions it remains inert. So, it reacts with water only when it is very hot and crushed into powder. In the normal state, it is not active with air, sulfuric and nitric acids. Faced with them, he passivates, forming a thin protective film, which does not allow him to enter into a further reaction. However, in the heated state, it easily dissolves in acids, and at temperatures above 600 degrees, it burns out in oxygen.
In normal condition, chrome is a metal with a pronounced blue-white hue. Oxidizing to degrees +2, +3 and +6, it forms a huge number of compounds, which can be red, green, blue, orange and even yellow. Because of this, he was nicknamed “chrome,” which means “color” in Greek.
Chrome ore
Chromium is widely distributed on planet Earth - its content in the earth's crust is 0.012% by mass. It does not form nuggets and does not occur on its own. In nature, it exists only in compounds of various minerals, for example, in woklenite, dietzeite, boil, crocoite, melanchroite. Usually they have a dark, almost black color and have a characteristic metallic luster.
Chromium ores form minerals that belong to the group of chrome spinels. They contain the largest amount of metal, sufficient for its industrial use. They include four main types of raw materials:
- alumochromite;
- birch (magnetochromite);
- picotitis;
- lame.
Ore minerals are of magmatic origin. They vary greatly in composition, but in appearance and structure are very similar to each other. They can only be distinguished by chemical analysis.
Chrome spinels are characterized by high hardness, black, brown-black and gray color, weak magnetic properties. Along with them, often boils down, olivine, brucite, serpentine, kemmererit, bronzitis. The main source of metal is chromite.
Place of Birth
Deposits of chrome ores exist on the territory of Eurasia, Africa, as well as South and North America. South Africa has the largest reserves, accounting for more than 75% of the total explored volume of chromium. After it, Kazakhstan and Zimbabwe lead in terms of ore reserves, then the United States, India, Oman, and Turkey.
Large deposits are concentrated in Russia, where they are present mainly in the Urals. At the beginning of the 19th century, Russian chrome ores were the main source of metal in the world, but the emphasis shifted to the discovery of other deposits. Today, the country's consumption of this resource exceeds the volume of production.
Ore, as a rule, lies at considerable depths, therefore it is extracted from the bowels of the planet mainly by the mine method. In 10-15% of cases, mining occurs with the help of quarries. About 15 billion tons of ore are extracted annually.
Using
In industry, the main value of the metal is that it is very resistant to corrosion and does not collapse under the influence of air and water. These properties are used for the production of stainless steels, which are characterized by high strength and hardness. Refined chromium is also coated with aluminum, magnesium, silver, zinc, cadmium and some other metals to protect them from environmental influences.
Chrome ores containing less chromium, but rich in oxides of magnesium and aluminum, are used to produce refractory materials that can withstand high melting points.
Its color compounds are used to create dyes, pigments and colored glasses. Synthetic rubies are made from doped trivalent chromium and molten corundum mineral, which are used in jewelry.