Magnetite (Fe₃O₄) is one of the most valuable iron ore minerals due to its high iron content and strong natural magnetic properties. It is the most magnetic of all naturally occurring minerals and typically contains about 72.4% iron.
Magnetite appears black to dark gray with a metallic to sub-metallic luster and is widely distributed in the Earth’s crust, making it a preferred raw material for iron and steel production.
Chemical Composition & Crystal Structure
| Component | Percentage (%) |
|---|---|
| Iron (Fe) | ~72.36 |
| Oxygen (O) | ~27.64 |
| Impurities (SiO₂, Al₂O₃, CaO, MgO, TiO₂, S, P) | Trace – 6% |
Crystal System: Cubic (Inverse Spinel)
Structure Type: Spinel (Fe³⁺ in tetrahedral sites, Fe²⁺ + Fe³⁺ in octahedral sites)
Bonding: Mixed ionic–electronic
This crystal structure gives magnetite its intrinsic magnetic behavior and relatively high electrical conductivity compared to other oxides.
Physical Properties
| Property | Typical Value |
|---|---|
| Color | Black to dark gray |
| Streak | Black |
| Density | 5.15 – 5.20 g/cm³ |
| Hardness (Mohs) | 5.5 – 6.5 |
| Melting Point | ~1,597 °C |
| Electrical Conductivity | Semi-conductive |
| Magnetic Behavior | Strongly ferrimagnetic |
| Thermal Stability | Excellent |
Mechanical Properties
| Property | Description |
|---|---|
| Compressive Strength | Very high |
| Tensile Strength | Low |
| Fracture Mode | Brittle |
| Abrasion Resistance | High |
| Wear Resistance | Excellent |
| Impact Resistance | Low |
Metallurgical Behavior
Magnetite undergoes reduction during ironmaking:
Fe₃O₄ → FeO (Wüstite)
FeO → Fe (Metallic Iron)
Compared to hematite, magnetite requires less energy for initial reduction, releases more exothermic heat, and improves thermal balance in blast furnaces.
Key Characteristics
✔ Strong natural magnetism
✔ High iron yield
✔ Dense, compact structure
✔ Excellent beneficiation efficiency
✔ Superior pelletizing behavior
Available Forms
| Form | Description |
|---|---|
| Lump Ore | Direct furnace feed |
| Concentrate | High-Fe beneficiated product |
| Pellets | Uniform ironmaking feed |
| Powder | Pigments, catalysts, fillers |
| Granules | Dense media separation |
| Synthetic / Nano Magnetite | High-tech & medical applications |
Applications
Iron & steel manufacturing
Pellet feed for blast furnaces and DRI plants
Heavy media separation in mining
Radiation shielding concrete
Catalysts, pigments, batteries, water treatment
Medical imaging and drug delivery (synthetic forms)
Advantages
✔ Highest iron content among natural iron oxides
✔ Easy and cost-effective beneficiation
✔ Energy-efficient reduction behavior
✔ Strong demand in global steel markets
✔ Multi-industry versatility
Magnetite vs Hematite
| Feature | Magnetite | Hematite |
|---|---|---|
| Iron Content | ~72.4% | ~69.9% |
| Magnetism | Strong | Weak |
| Beneficiation Cost | Lower | Higher |
| Reduction Efficiency | Higher | Moderate |
| Pellet Quality | Excellent | Good |
Why Choose Magnetite?
Magnetite is the preferred iron ore for modern steelmaking due to lower operational costs, higher furnace efficiency, superior pellet quality, and the advantage of magnetic separation.