Chromite reserves are of great importance in the role of mines and mining activities in the economic development of many countries today.

What is Chromite?

In today's world, the economic independence of any country is achieved when the country's income is not solely dependent on a limited economic factor, and the more diverse these income factors are, the less susceptible the country's economy will be to changes and fluctuations. For this reason, the development of non-oil exports, especially minerals, is of special importance. As we know, valuable mineral reserves are one of the factors that can have a significant impact on the economic development of any country. If the exploitation of these reserves is accompanied by technical and engineering principles and progresses based on modern technology, it will lead to the potential for employment (which is one of the current problems of the country) and increase in production, as well as an increase in per capita income. These productions, considering their application and consumption in industries, contribute to industrial development. Today, in many countries around the world such as the United States, South Africa, Turkey, Iran, Cyprus, Cuba, Canada, the Philippines, former Soviet Union, Zimbabwe, Brazil, India, Albania, and China, there are active chromite mines.

Chromium

Chromium is one of the hard, brittle metals with a silver-white color that was discovered in 1798 by V.L. Vauquelin. This element is in the sixth group of the periodic table along with molybdenum and tungsten.

Chromium is not found freely in nature. The most important mineral containing chromium in nature is chromite with the formula FeO.Cr2O3. Chromium has four natural isotopes: 50Cr, 52Cr, 53Cr, 54Cr. Pure chromium at room temperature is a potentially soft element, but it should be noted that due to its strong chemical affinity with oxygen, carbon, nitrogen, etc., obtaining pure chromium is very difficult. Chromium used for plating and polishing gives a shiny and slightly bluish-white color. The reflectivity of chromium-plated bodies is 77% silver. Also, the electrical conductivity of this element is 2.22% of copper.

The mechanical properties of chromium related to its strength and workability, including hardness, tensile strength, impact strength, rolling, etc. Chromium is considered a weak element in terms of impact strength, rolling, etc., but when this element is purified from elements such as oxygen, hydrogen, carbon, and nitrogen, it becomes somewhat softer and can be hammered or rolled. Chromium forms compounds with other elements in three groups, which can be seen in chromium oxides as follows:

Chromium with a valence of 2, CrO, chromous oxide or chromium (II)

Chromium with a valence of 3, Cr2O3, chromic oxide or chromium (III)

Chromium with a valence of 6, CrO3, chromic acid or chromium (VI)

Metallic chromium easily reacts with hydrochloric acid and chlorine to form chlorides. This metal is soluble in sulfuric acid, but not in nitric acid. Chromium and nitrogen form two types of nitrides with the formulas Cr2N and CrN. Chromium and carbon also form three known carbides with the formulas Cr23C6, Cr7C3, and Cr3C2. Chromium reacts with silicon in an electric furnace to form silicides. Chromium reacts with hydrogen to form hydride with the formula CrH2, which is a black powder.

Characteristics and Mineralogical Specifications of Chromite

The main minerals containing the element chromium are chromite, overburdenite (green garnet), kammererite (purple chlorite), fuchsites (green muscovite). Chromite minerals belong to the spinel group in terms of chemical composition, with the formula FeCr2O4 for pure chromite, (Mg,Fe)Cr2O4 for magnesiochromite, Fe(Cr,Al)2O4 for alumochromite, and (Mg,Fe)(Cr,Al)2O4 for chromopikrite. Thus, chromite group minerals are identified with the general formula (Mg,Fe)(CrAlFe)2O4.

In these minerals, the Cr2O3 content varies widely (from 18 to 62 percent). In addition to the main oxides, impurities such as CaO, NiO, ZnO, MnO, V2O3, TiO2 may also be present in these minerals.

Chromite mineral crystallizes in the cubic (hexaoctahedral) system, and its crystal structure is similar to spinel. The mineral is black, with a brownish streak, and has a semi-metallic luster. The hardness of chromite ranges from 5.5 to 5.7, and its specific weight varies from 6.3 to 7.5 grams per cubic centimeter depending on changes in chemical composition. Chromites with significant amounts of FeO and Fe2O3 exhibit magnetic properties.

Chromite is a granular mass mineral, and its commercial ores contain 35-68 percent chromite oxide. Its color ranges from dark brown to iron black with a metallic luster. Its specific weight is 6.4 grams per cubic centimeter, and its hardness is 5.5. Chromite has a melting point of 2130 degrees Celsius. The quality of the mineral is determined based on the measured ratio, which is considered inferior if the ratio is less than 2 and superior if it is more than three.

The chemical formula of chromite has been introduced as FeOCr2O3 or FeCr2O4. In some chromite samples, elements such as zinc, nickel, manganese, titanium, and vanadium have been detected in small amounts. The general formula for chromite is written as (Mg,Fe)(Cr,Al,Fe)2O4, but crystals with simpler compositions such as ferrochromite FeCr2O4, picrochromite MgCr2O4, spinel MgAl2O4, herschelite FeAl2O4, magnesioferrite MgFe2O4 have also been identified.

Geology of Chromite Deposits

Chromite deposits are always formed in ultramafic rocks despite the variety of their forms. The silica content of these rocks is less than 45 percent. Their mineralogical composition primarily consists of olivine, orthopyroxenes, and clinopyroxenes. Some of them also contain amphiboles and alkaline feldspars. These rocks include varieties such as serpentinites, gabbros, pyroxenites, peridotites, and dunites. The chromite mineral composition, namely chromite, is dependent on the surrounding rocks. The higher the percentage of olivine in the rock, the higher the percentage of Cr2O3 in the chromite composition. From a geological perspective, chromite ore is related to ultramafic intrusive rocks and is associated with oceanic crust and sea rifts that reach the Earth's surface as a result of deep gully openings and intrusion of masses into the continental crust.

Titanium, vanadium, manganese, and nickel are found in small amounts in chromite. Titanium oxide is one of the oxides

What is chromite?

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