Bentonite and cement function as a dual-action binding system designed to protect the integrity of iron ore briquettes at different stages of their lifecycle. Bentonite utilizes its swelling properties to create immediate "green strength" for initial shaping, while cement provides the long-term structural durability required for handling and storage through a chemical hardening process.
Efficient briquetting requires a two-stage approach: bentonite acts as the immediate glue holding the wet shape together, while cement acts as the structural reinforcement that creates a rock-hard solid after drying.
The Mechanics of the Dual-Binder System
To understand why both binders are necessary, you must distinguish between the needs of the fresh briquette and the finished product.
Bentonite: The Immediate Stabilizer
The primary role of bentonite is to facilitate the initial formation of the briquette.
Because of its high hygroscopicity (ability to absorb moisture), bentonite swells significantly when mixed with water.
This swelling action creates a cohesive bonding layer that wraps around individual iron ore particles.
This results in green strength, which is the ability of the briquette to hold its shape immediately after being pressed, preventing it from crumbling before it is dry.
Cement: The Long-Term Hardener
While bentonite handles the immediate formation, cement is responsible for the final durability of the product.
Cement undergoes a specific hardening process that occurs after the initial shaping.
This hardening happens during and after air or thermal drying, locking the iron ore particles into a rigid structure.
This ensures structural stability, allowing the briquettes to withstand the mechanical physical stress of transport, stacking, and long-term storage without degrading.
Understanding the Trade-offs
While using two binders optimizes strength, it introduces specific processing variables that must be managed.
Moisture Dependency
Bentonite relies heavily on water absorption to function effectively.
However, the subsequent cement hardening process requires the removal of moisture through drying.
This creates a tension where sufficient water is needed for the initial bentonite bond, but efficient drying is required to activate the cement's final strength.
Processing Time
Unlike single-binder systems that might set instantly, this dual approach requires a curing window.
The reference notes that cement strengthens through a subsequent process, meaning the briquettes are not fully durable immediately upon exiting the press.
Production timelines must account for the necessary air or thermal drying periods to ensure the cement achieves full rigidity.
Making the Right Choice for Your Goal
When optimizing your binder mix, consider which stage of production is currently suffering from quality issues.
- If your primary focus is reducing breakage immediately after the press: Increase the bentonite ratio to improve water absorption and green strength, ensuring the wet briquettes hold their shape.
- If your primary focus is durability during shipping and stockpiling: Prioritize the cement content and ensure your drying process is sufficient to fully activate the hardening phase.
By balancing the immediate cohesive power of bentonite with the lasting rigidity of cement, you ensure a briquette that is viable from the moment of compression to its final use.
Summary Table:
| Binder Component | Primary Function | Key Property | Benefit to Process |
|---|---|---|---|
| Bentonite | Immediate Stabilization | High Hygroscopicity | Provides green strength to prevent crumbling after pressing. |
| Cement | Long-term Hardening | Chemical Curing | Ensures structural stability for transport and storage. |
| Combined System | Dual-Action Binding | Synergy | Balances initial shaping with final mechanical durability. |
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References
- Rishi Sharma, D. S. Nimaje. Study of drying kinetics and moisture diffusivity in iron ore briquettes after using different drying techniques. DOI: 10.2298/jmmb240910010s
This article is also based on technical information from Kintek Furnace Knowledge Base .
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