Dolomitic limestone is a carbonate rock containing a significant proportion of magnesium carbonate (MgCO₃) in addition to calcium carbonate (CaCO₃). It represents an intermediate material between high-calcium limestone and pure dolomite (CaMg(CO₃)₂).
Typical MgCO₃ content ranges from 10% to 45%, providing enhanced durability, thermal stability, and metallurgical performance compared to calcitic limestone.
Dolomitic Limestone Grade Classification
Grade 1 – High-Purity Dolomitic Limestone
| Component | Typical Range |
|---|---|
| Calcium Carbonate (CaCO₃) | 70 – 85% |
| Magnesium Carbonate (MgCO₃) | 10 – 20% |
| Silica (SiO₂) | < 2% |
| Fe₂O₃ + Al₂O₃ | < 2% |
Key Characteristics:
✔ Low impurities
✔ High thermal stability
✔ Consistent composition
✔ Good reactivity when calcined
Applications:
• Steelmaking flux (controlled magnesium addition)
• Refractory-grade dolomite
• High-quality agricultural lime
• Glass and ceramics
• Chemical magnesium compounds
Grade 2 – Medium-Grade Dolomitic Limestone
| Component | Typical Range |
|---|---|
| Calcium Carbonate (CaCO₃) | 60 – 70% |
| Magnesium Carbonate (MgCO₃) | 20 – 35% |
| Silica (SiO₂) | 2 – 6% |
| Insolubles | 4 – 8% |
Key Characteristics:
✔ Balanced Ca–Mg ratio
✔ Moderate strength
✔ Good weather resistance
Applications:
• Cement manufacturing
• Road aggregates
• Soil stabilization
• Dolomitic lime production
• Construction blocks
Grade 3 – Low-Grade Dolomitic Limestone
| Component | Typical Range |
|---|---|
| Calcium Carbonate (CaCO₃) | 50 – 60% |
| Magnesium Carbonate (MgCO₃) | 30 – 45% |
| Silica (SiO₂) | 6 – 12% |
| Fe₂O₃ + Al₂O₃ | > 5% |
Key Characteristics:
✔ High magnesium content
✔ High impurity levels
✔ Lower chemical reactivity
Applications:
• Road sub-base
• Bulk fill material
• Embankments
• Low-grade cement blending
• Land reclamation
Metallurgical & Calcination Behavior
Calcination:
Produces dolomitic lime (CaO·MgO).
• MgCO₃ decomposes earlier than CaCO₃
• Requires controlled temperature to avoid dead-burning
Metallurgical Performance:
✔ Acts as a basic flux
✔ Improves slag fluidity
✔ Reduces refractory wear
✔ Supplies magnesium to steel
Available Commercial Forms
• Run-of-mine stone
• Crushed aggregate
• Powder (<200 mesh)
• Calcined dolomite
• Sintered dolomite
• Dolomitic lime
Advantages of Dolomitic Limestone
✔ Supplies both calcium and magnesium
✔ Superior durability compared to pure limestone
✔ Lower thermal expansion
✔ Reduces steel slag volume
✔ Cost-effective magnesium source
Why Choose Dolomitic Limestone?
Dolomitic limestone is selected where magnesium control, high-temperature performance, and durability are critical. It offers stronger mechanical behavior than high-calcium limestone and greater versatility across steelmaking, cement, agriculture, and construction industries.
Comparison with Other Carbonates
| Material | CaCO₃ | MgCO₃ | Primary Use |
|---|---|---|---|
| High-Calcium Limestone | 95 – 99% | < 2% | Lime, steelmaking |
| Dolomitic Limestone | 50 – 85% | 10 – 45% | Steel, cement, agriculture |
| Dolomite (Pure) | ~54% | ~46% | Refractories |