Generally, iron ore with a grade of less than 50% needs to go through a dressing process before it can be sent to smelting for utilization. After the mined ore goes through the processes of crushing and grinding, magnetic separation, flotation and gravity separation, the high-grade concentrate is obtained. At present, the iron ore resources are decreasing day by day. The characteristics of iron ore resources are more lean ore than rich ore, and the associated ore is more and the ore composition is complex.
Iron ore classification and component
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In nature, iron mainly exist in compounds, in which oxide of iron is the most part of them. There are more than 300 kinds of iron compounds in the nature. Among them, there are some important kind of iron are following:
The main component of magnetite is Fe3O4, which is the compound of FeO and Fe2O3. The surface of magnetite is black grey. It is opacitas and with half-metal gloss. There are about 72.4% Fe and 27.6% O in the magnetite. The isometric system of a single crystal octahedron, and a small part of the diamond-shaped dodecahedron. Hardness 5.5~6.5, specific gravity 4.9~5.2, with strong magnetic.
Magnetite minerals also include titanium magnetite, vanadium magnetite, vanadium titanium magnetite, chromium magnetite, magnesium magnetite, etc. Magnetite oxidizes to hematite (pseudo hematite or limonite).
The main component is Fe2O3, and the mass fraction of Fe is about 69.9%, showing trigonal crystal system. In nature, intact crystals of heavy hematite are relatively rare, crystalline hematite is steely gray, cryptocrystalline, earthen hematite is dark red, semi-metallic luster, hardness 5-6, specific gravity 5-5.3.
Hematite is often mixed with titanium, aluminum, manganese, calcium, magnesium and a small amount of gallium and cobalt. Hematite minerals also include pyrite, mica hematite, magnetite, clay hematite, etc., of which magnetite has strong magnetism.
It is a mixture of goethite, pyrite, hydrogoethite, hydropyrite and siliceous clay containing water. Chemical composition and water content vary greatly. Goethite is an orthorhombic crystal system, which is acicular, columnar, lamellar or scaly. Limonite is rich in color, including light brown, reddish brown, black brown, tawny, dark red to black red. Goethite hardness 1~4, specific gravity 3.3~4, fibrinite hardness 4~5, specific gravity 4.01~4.1.
Refers to the ore containing ferrous carbonate, the main component is FeCO3, in which the mass fraction of Fe is about 46.6%. It is a trigonal crystal system, usually rhedral, with curved crystal surface, yellow, light brown yellow to dark brown glass luster, hardness of 3.5~4.5, specific gravity of about 3.96. Siderite often contains magnesium and manganese.
In addition to these four main iron ore, there are ilmenite, pyrite and so on in nature.