Medium-grade limestone is a carbonate sedimentary rock with moderate calcium carbonate (CaCO₃) content, typically lower than high-calcium limestone but higher than low-grade or highly impure limestone.
It is widely used where absolute chemical purity is not critical, but mechanical strength, availability, and cost-effectiveness are essential. Medium-grade limestone forms the backbone of bulk construction, infrastructure, and blended industrial applications.
Typical Chemical Range
| Component | Typical Range |
|---|---|
| Calcium Carbonate (CaCO₃) | 80 – 90% |
| Magnesium Carbonate (MgCO₃) | 0 – 5% |
| Silica (SiO₂) | 2 – 8% |
| Alumina (Al₂O₃) | Trace – 3% |
| Iron Oxide (Fe₂O₃) | Trace – 2% |
| Clay & Insolubles | 3 – 10% |
Strengthening & Metallurgical Behavior
Strengthening Behaviour:
Strength depends primarily on:
• Degree of natural cementation
• Silica and clay content
Mechanical performance can be improved through:
• Compaction
• Cement stabilization
• Blending with higher-grade limestone
Metallurgical Behaviour:
Medium-grade limestone can act as a flux, but is less efficient than high-calcium limestone.
Thermal reaction:
CaCO₃ → CaO + CO₂
Impurities:
• Increase slag volume
• Reduce lime reactivity
It is typically used only as a blended flux, not as a standalone flux in steelmaking.
Key Characteristics
✔ Balanced chemical and mechanical properties
✔ Moderate CaCO₃ content
✔ Good durability for bulk use
✔ Higher impurity tolerance
✔ Wide availability
✔ Economical pricing
Refining & Processing Properties
Quarrying:
• Open-pit quarrying
• Moderate blasting energy
• Minimal selective mining
Processing:
• Crushing and screening
• Washing (optional)
• Blending with higher-grade limestone
• Grinding (cement and filler use)
• Calcination (limited lime production)
Thermal Processing:
• Higher fuel consumption than high-grade limestone
• Produces lime with moderate reactivity
Available Forms
• Raw quarry stone
• Crushed aggregates
• Road base material
• Ground limestone powder
• Blended lime feedstock
• Construction fill
Applications
Construction & Infrastructure:
• Road base and sub-base
• Concrete aggregates
• Masonry stone
• Asphalt filler
Industrial & Manufacturing:
• Cement raw material (blended)
• Glass manufacturing (non-critical applications)
• Industrial fillers
• Flux blending
Agriculture:
• Soil conditioning
• Bulk pH correction
• Calcium supplementation
Environmental:
• Land reclamation
• Erosion control
• Basic water treatment
Advantages of Medium-Grade Limestone
✔ Cost-effective bulk material
✔ Good mechanical strength
✔ Widely available
✔ Flexible industrial usability
✔ Lower processing cost
✔ Easy blending with higher grades
Why Choose Medium-Grade Limestone?
Medium-grade limestone is ideal for large-volume, cost-sensitive projects where ultra-high CaCO₃ purity is unnecessary. Its reliability in construction, infrastructure, and blended industrial use makes it a practical choice for reducing raw material costs while maintaining dependable performance.
Quick Comparison
| Feature | Medium-Grade | High-Calcium | Low-Grade |
|---|---|---|---|
| CaCO₃ Content | 80 – 90% | 95 – 99% | <75% |
| Strength | Medium | High | Low |
| Metallurgical Suitability | Limited | Excellent | Poor |
| Cost | Low – Medium | Medium | Very Low |