Elemental Iron (Fe) is ranked fourth in abundance in the earth's crust and is the major constituent of the Earth's core.
Metallic Iron is most commonly produced from the smelting of iron ore to produce pig iron. Iron ore is in the form of rock and vary in color from dark grey to rusty red and is usually found in the form of magnetite (Fe3O4), hematite (Fe2O3) which is also called "natural ore", limonite or siderite. Siderite is a mineral composed of Iron carbonate FeCO3. It is a valuable iron mineral, since it is 48% iron and contains no sulfur or phosphorus (two of the worst contaminants in iron ore). Pyrite (FeS) is another compound that is used for extracting Fe element
Low-grade ore is a term applied to iron-rich rocks with cut-off grades in the range of 25-30% Fe. It was the main supply of iron ore for many centuries of the World's early history of production of iron. Since the 1950's North America's main supply has been low-grade ore. Examples of low grade ore are limenite(FeTiO3 ) and Chamosite ((Mg,Fe,Al)6(Si,Al)414(OH)8).
The typical grade of iron at which a magnetite rock formation becomes economic is roughly 25% Fe, which can generally yield a 33% to 40% recovery of magnetite by weight, to produce a concentrate grading in excess of 64% Fe by weight. The typical magnetite iron ore concentrate has less than 0.1% phosphorus, 3-7% silica and less than 3% aluminum.
Inferior sources of iron ore generally require beneficiation. Beneficiation usually involves a combination of crushing and milling as well as heavy liquid separation.
Magnetite is beneficiated by crushing and then separating the magnetite from the gangue minerals with a magnet. This is usually so efficient that lower grade ore can be treated when it is magnetite than a comparable grade of hematite ore, especially when the magnetite is quite coarse
Hematite is beneficiated by passing the finely crushed ore over a bath of solution containing Bentonite or other agent which increases the density of the solution. When the density of the solution is properly calibrated, due to the high density of hematite relative to silicates, the hematite will sink and the silicate mineral fragments will float and can be removed.
| Name |
Formula |
%Fe |
| Haematite |
Fe2O3 |
69.9 |
| Magnetite |
Fe3O4 |
74.2 |
| Goethite |
HFeO2 |
63 |
| Siderite |
FeCO3 |
48.2 |
| Pyrite |
FeS |
46.6 |
| Ilmenite |
FeTiO3 |
36.81 |
| Chamosite |
(Mg,Fe,Al)6(Si,Al)414(OH)8 |
29.61 |