Basic concepts of iron ore
Ore is a collection of minerals. Under modern technical and economic conditions, metals or other products can be processed and extracted from minerals on an industrial scale. Originally referred to as solid material mined from metal deposits, it has now expanded to non-metallic minerals such as sulphur, fluorite and barite deposited in the parent rock after formation.
The ratio of the weight of useful components (elements or minerals) in the ore and the weight of the ore is called the ore grade. Precious metal ores such as gold and platinum are expressed in grams per ton, and other ores are usually expressed as a percentage. The grade of ore is commonly used to measure the value of the ore, but the composition of the gangue (the useless mineral in the ore or the mineral with little useful content that cannot be utilized) and the amount of harmful impurities also affect the value of the ore.
Iron ore classification
Generally divided into lean ore, ordinary ore and rich ore. Sometimes it is only divided into lean ore and rich ore. There is no uniform standard for this division. Generally, each industrial sector and mining area has its own calculation range. According to the nature and utilization characteristics of minerals contained, it is divided into two categories: metal ore and non-metallic ore.
The main varieties of iron ore
There are many kinds of iron minerals. There are more than 300 kinds of iron minerals and iron-bearing minerals, among which there are more than 170 kinds. However, under the current technical conditions, the main ones with industrial utilization value are magnetite, hematite, maghemite, ilmenite, limonite and siderite.
1. Magnetite
Magnetite (Magnetite) is an iron oxide ore, the main component is Fe3O4, is a composite of Fe2O3 and FeO. FeO 31.03%, Fe2O3 68.97% or containing Fe 72.2%, O 27.6%, equiaxed crystal system. Single crystals are often octahedral, less diamond-shaped dodecahedron. On the surface of the rhombic dodecahedron, stripes often appear in the direction of the long diagonal. The aggregates are mostly dense and granular. The color is iron black, the streak is black, semi-metallic luster, opaque. Hardness 5.5 ～ 6.5, specific gravity 4.9 ～ 5.2, no cleavage, gangue is mainly quartz and silicate. With strong magnetism. Poor reducibility, generally contains harmful impurities such as sulfur and phosphorus. In the mineral processing (Beneficiation), the magnetic separation method can be used, and the processing is very convenient; but because of its fine structure, it is poorly reduced. It becomes hematite after long-term weathering. There is often a considerable amount of Ti4 + in magnetite that replaces Fe3 + with quasi-homomorphism, and is accompanied by corresponding substitutions of Mg2 + and V3 + for Fe2 + and Fe3 +, thus forming some mineral subspecies, namely:
(1) Titanium magnetite Fe2 + (2 + x) Fe3 + (2-2x) TixO4 (0 <x <1 =, containing 212% ～ 16% of TiO. At normal temperature, titanium is separated from it into plate-like and column-like ferro-titanium Mine and cloth-like ilmenite.
(2) Vanadium magnetite FeV2O4 or Fe2 + (Fe3 + V) O4, containing V2O5 sometimes up to 68.41% ~ 72.04%.
(3) Vanadium-titanium magnetite is a solid solution product of the above two minerals with a more complex composition.
(4) Chrome magnetite contains Cr2O3 up to a few percent. (Steel Network www.gangcai.com)
(5) Magnesium magnetite contains MgO up to 6.01%. Magnetite is the main mineral of iron ore in magmatic iron deposits, contact metasomatic-hydrothermal iron deposits, sedimentary metamorphic iron deposits, and a series of iron deposits related to volcanism. In addition, it is also common in sand deposits. It is rarely encountered in natural pure magnetite ore, and part of the magnetite is often converted into semi-fake hematite and fake hematite due to surface oxidation. The so-called false hematite is magnetite (Fe3O4) oxidized to hematite (Fe2O3), but it can still maintain its original crystal form, so it is called false hematite.
2. Hematite
Hematite (Hematite) Hematite is an anhydrous iron oxide ore with a chemical formula of Fe2O3 and a theoretical iron content of 70%. This kind of ore often forms huge deposits in nature. In terms of burial and mining volume, it is the main ore for industrial production. It can be divided into many categories according to its different structural conditions, such as red hematite, specular hematite, Micaceous hematite, and red Ocher. The iron content of hematite is generally 50% to 60%, and it contains less harmful impurities such as sulfur and phosphorus, and the reduction is better than magnetite. Therefore, hematite is a relatively good ironmaking raw material. Hematite is native and wild. The regenerated hematite magnetite loses its magnetism after oxidation, but still retains the crystalline shape of the magnetite. The false hematite, which is often contained in the fake hematite Some residual magnetite. Sometimes hematite also contains some hematite weathering products, such as limonite (2Fe2O3 · 3H2O). Hematite has a semi-metallic luster, the hardness of the crystal is 5.5 to 6, the hardness of the earthy hematite is very low, no cleavage, the relative density is 4.9 to 5.3, only weak magnetic, and the gangue is silicate.
There are two kinds of homopolymorphic variants of Fe2O3 in nature, namely α-Fe2O3 and γ-Fe2O3. The former is stable under natural conditions and is called hematite; the latter is less stable than α-Fe2O3 under natural conditions and is in a meta-stable state, called maghemite. Hematite: Fe 69.94%, O 30.06%, often containing quasi-homogeneous mixtures Ti, Al, Mn, Fe2 +, Ca, Mg and a small amount of Ga and Co Trigonal crystal system, intact crystals are rare. The crystalline hematite is steel gray and cryptocrystalline; the earthy hematite is red. The streaks are cherry red or fresh pig liver. Metal to semi-metallic luster. Sometimes the gloss is dull. Hardness 5 ～ 6. The proportion is 5 ～ 5.3. Hematite aggregates have various forms, forming some mineral subspecies, namely:
(1) Mirror iron ore. It is a collection of rosette or sheet hematite with metallic luster.
(2) Mica hematite. Crystalline fine scale hematite with metallic luster.
(3) Oolitic or renal hematite. Hematite with oval or kidney shape.
Hematite is one of the widely distributed iron minerals in nature, and can be formed in various geological processes, but mainly hydrothermal, sedimentary and regional metamorphism. In the oxidation zone, hematite can be formed by dehydration of limonite or wurtzite or goethite. But it can also be turned into goethite and water hematite. Under reducing conditions, hematite can be transformed into magnetite, called false magnetite. Maghemite: γ-Fe2O3, its chemical composition often contains Mg, Ti and Mn mixed in. Isometric crystal system, pentagonal three-tetrahedral crystals, mostly granular aggregates, dense blocks, often with the illusion of magnetite. The color and streak are brown, hardness 5, specific gravity 4.88, strong magnetism. Maghemite is mainly formed by secondary changes of magnetite under oxidizing conditions. The Fe2 + in the magnetite is completely replaced by Fe3 + (3Fe2 + → 2Fe3 +), so octahedral positions occupied by 1 / 3Fe2 + generate vacancies. In addition, maghemite can be formed by the loss of water from lepidolite, and also formed by the organic action of iron oxides.
3. Limonite
Limonite is an ore containing ferric hydroxide. It is produced by weathering other ores. It is the most widely distributed in nature, but it is not uncommon for large deposits. It is the general name of two different structure ores of Goethite HFeO2 and Lepidocrocite FeO (OH). Some people also write the chemical formula of its main component as mFe2O3. nH2O, showing yellowish brown or brown, contains about 62% Fe, 27% O, and 11% H2O, and has a specific gravity of about 3.6 to 4.0. Most of them are attached to other iron ores. In fact, it is not a mineral species, but a mixture of goethite, lepidolite, water goethite, water lepidolite and hydrous silica, muddy, etc. Most of the iron-bearing minerals in limonite exist in the form of 2Fe2O3 · H2O. The chemical composition changes greatly, as does the water content. Generally, the iron content of limonite is 37% to 55%, and sometimes the phosphorus content is relatively high. Limonite is very hygroscopic and generally absorbs a large amount of water. After roasting or heating in a blast furnace, free water and crystallization water are removed, and the porosity of the ore is increased, which greatly improves the reduction of the ore. Therefore, limonite is better in reducing than hematite and magnetite. At the same time, due to the removal of water, the iron content of the ore is increased accordingly.
(1) Goethite α-FeO (OH), containing 62.9% Fe. Those with non-quantitative adsorbed water are called water goethite HFeO2 · NH2O. The orthorhombic crystal system has needle-like, columnar, thin-plate or scale-like shapes. Usually bean-like, kidney-like or stalactite-like. Cut masks are parallel or radiating fibrous structures. Sometimes it is dense, soil, or ooliform. The color is reddish brown, dark brown to dark brown. The weathered powdery and ocher-like limonite is yellowish brown. The goethite streaks are reddish brown, with a hardness of 5 to 5.5 and a specific gravity of 4 to 4.3. The limonite streaks are generally light brown or yellowish brown, with a hardness of 1 to 4 and a specific gravity of 3.3 to 4.
(2) Wurtenite γ-FeO (OH), containing 62.9% Fe. Those with a certain amount of adsorbed water are called water fiber iron ore FeO (OH) · NH2O. Orthorhombic system. Common scaly or fibrous aggregates. The color is dark red to black red. The streaks are orange-red or brick-red. Hardness 4 ～ 5, specific gravity 4.01 ～ 4.1.
4. Siderite
Siderite (Siderite) is an ore containing iron carbonate. The main component is FeCO3, which is bluish gray, the theoretical iron content is 48.2%, and the specific gravity is about 3.8. FeCO3, FeO 62.01%, CO2 37.99%, often contains Mg and Mn. Trigonal crystal system. Common rhombohedral, the crystal plane is often curved. The aggregate is coarse-grained to fine-grained. There are also nodules, grapes, and soil. Yellow, light brownish yellow (dark brown after weathering), glass luster. The hardness is 3.5 ～ 4.5, and the specific gravity is about 3.96. It varies with the content of Mg and Mn. In nature, there are fewer siderites with industrial mining value than the other three ores. Siderite is easily decomposed and oxidized to limonite. Generally, the iron content is not high, but after decomposing CO2 by heating, the iron content is not only significantly increased but also becomes porous, and the reducibility is very good. Most of this ore contains a considerable amount of calcium and magnesium salts. Since the carbonate will absorb a lot of heat and emit carbon dioxide at a high temperature of about 800 ~ 960 ℃, we mostly roast this type of ore before adding it to the blast furnace.
5. Other
Ilmenite (Ilmenite) its chemical formula is FeTiO3, Fe 36.8%, Ti 36.6%, O 31.6%. Trigonal crystal system. Rhombohedral crystals. It is often irregular grain, scale or thick plate. Above 950 ° C, ilmenite and hematite form a completely homogenous homology. When the temperature is lowered, melting occurs, so ilmenite often contains fine scale-like hematite inclusions. The color of ilmenite is iron black or steel gray. The streaks are steel gray or black. The hematite-containing inclusions are brown or brownish red streaks. Metallic-semi-metallic gloss. Not transparent, no cleavage. Hardness 5 ～ 6.5, specific gravity 4 ～ 5. Weak magnetic. Ilmenite mainly occurs in ultrabasic rocks, basic rocks, alkaline rocks, acid rocks and metamorphic rocks. In the Panzhihua vanadium-titanium magnetite deposit in China, ilmenite is distributed in granular or flake form between titanomagnetite and other mineral particles, or oriented lamellae along the split surface of titanomagnetite. Iron silicate ore (Silicate Iron) This kind of ore is a compound salt. There is no certain chemical formula. The composition varies greatly. It generally shows a dark green color with a specific gravity of about 3.8. The iron content is very low. Poor iron ore. Sulphide iron (Sulphide iron) This kind of ore contains FeS2, containing only 46.6% Fe and S content of 53.4%. Appears gray-yellow, with a specific gravity of about 4.95 ~ 5.10. Because this kind of ore often contains many other precious metals such as Copper, Nickel, Zinc, Gold, Silver, etc., it is often used in other metal smelting industries Raw materials; because it contains a large amount of sulfur, it is often used to extract sulfur, but iron has become a by-product, so it can no longer be called iron ore
