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magnetite
Iron-containing raw material for pelletizing iron ore mostly, mainly magnetite, hematite and limonite ore, the second iron-containing material may be used, such as converter sludge, slag points sulfate Selected concentrate.
Magnetite is the main iron-bearing mineral in metamorphic deposits in unweathered and unoxidized metamorphic deposits or in magma areas. The iron content of this ore varies widely, from 20% to 50% of iron ore to 65% of magma deposits.
The chemical formula of magnetite is Fe 3 O 4 , often also written as FeO·Fe 2 O 3 , and its theoretical iron content is 72.4%, of which FeO is 31% and Fe 2 O 3 is 69%. Deposits in account, it can be observed its divalent iron is substituted by manganese or calcium, ferric iron and aluminum ions substituted phenomenon. In the high temperature deposits mineralization and found to contain TiO 2, it is mainly the titanium ore to separate the magnetite crystals sandwiched between. Magnetite incorporated within the crystal lattice of vanadium pentoxide, titanium and most of symbiotic mineralized gabbro rock. The spinel magnetite crystallizes into a double oxide, and its iron-containing is present in a divalent state (FeO) and a trivalent state (Fe 2 O 3 ).
The density of magnetite is 4.9~5.2g/cm 3 , the hardness is 5.5~6.5, cubic crystal shape, difficult to reduce and difficult to break. Its exterior color is steel gray, with black streaks and magnetic.
Pure magnetite ore is rarely seen in nature. Due to oxidation, some of the magnetite is oxidized to hematite ore, but it still retains the crystalline form of magnetite. Therefore, this ore is called illusory red iron and semi-artificial hematite. stone.
In order to measure the degree of oxidation of magnetite, it is usually distinguished by the ratio of total iron (TFe) to ferrous oxide (FeO). The greater the ratio, the higher the degree of oxidation of iron ore.
When w(TFe)/w(FeO)<2.7, it is a primary magnetite ore.
w(TFe)/w(FeO)=2.7~3.5, which is a mixed ore;
w(TFe)/w(FeO)>3.5, which is an oxidized ore.
It should be noted that this division is only for the simple mineral composition, and iron ore is only suitable for a single magnetite and hematite deposit. If the ore contains iron silicate, iron sulfide, iron carbonate, etc., since FeO does not have magnetism, it is imaginary to include it in the FeO in the above formula when calculating the base.
The magnet ore generally produced has an iron content of 30% to 60%. When the iron content is greater than 45% and the particle size is 5 or 8 mm, it can be directly used for iron making, and the sintering raw material is less than 5 mm or 8 mm. When the iron content is less than 45%, or the harmful impurities exceed the regulation, it cannot be directly used and must be subjected to beneficiation treatment. The most common method of beneficiation is magnetic separation, sometimes with flotation. The obtained concentrate is called a magnetic separation concentrate, and its iron content is more than 60%, and the mineral structure is basically consistent with the original ore. If the magnetic-flotation combined sorting, the grade of iron concentrate can be as high as 68%~69%, and the raw material of the pelleting is basically the concentrate after mineral processing.