The Most Effective Way to Increase Iron Grade in Pellets? The Broad Application Value of High-Efficiency Modified Bentonite

The steel industry is a major consumer of energy and a significant emitter of air pollutants, making it a key focus for China's energy-saving and emission-reduction efforts. The State Council's Made in China 2025 plan emphasizes green manufacturing. Faced with increasing resource and environmental constraints, green development is the only viable path for China's steel sector.

As a process-intensive manufacturing industry, steel production in China will continue to rely on blast furnace processes for the foreseeable future. Therefore, exploring process innovations—such as replacing sintering with pelletizing—to optimize blast furnace feedstock, reduce energy consumption, and lower greenhouse gas and pollutant emissions is crucial for green manufacturing.

Bentonite used in metallurgical pellets includes sodium-based, composite, and modified varieties, offering strong binding, uniform pellet formation, and high pelletization rates suitable for different ore types. Currently, the most widely used is modified pellet bentonite, which reduces binder usage while maintaining pellet quality, making it the most effective way to improve iron pellet grade.

The Role of Bentonite in Iron Ore Pellets
Pelletizing iron ore requires water and a binder, with bentonite being the most common choice globally. Bentonite's three key properties—wettability (high water absorption), expansibility (high swelling capacity), and colloidality (strong binding)—enable it to:

Enhance green, dry, and finished pellet strength – Its high surface area tightly binds iron concentrate particles during pelletizing, drying, and roasting.

Increase green pellet burst temperature – It slows water evaporation during drying and rapidly boosts dry pellet strength, significantly raising burst temperature (though effectiveness varies by bentonite and ore type).

Inhibit reduction swelling and low-temperature degradation – Bentonite reduces pellet porosity by 1–2% and increases strength, slightly lowering reducibility but mitigating swelling and degradation.

Negative Impacts of Bentonite on Pellet Quality
Bentonite's main components are SiO₂ (avg. 62.39%, 69.64% post-calcination) and Al₂O₃ (avg. 16.55%, 18.475% post-calcination). Since blast furnaces require high-grade, low-slag feed, minimizing bentonite usage is critical. Its drawbacks include:

Reducing iron grade – Adding 1% bentonite lowers iron grade by ~0.6% (e.g., 64–68% ore loses 0.62–0.66% per 1% bentonite).

Increasing SiO₂ and Al₂O₃ content – Each 1% bentonite adds ~0.7% SiO₂ and ~0.185% Al₂O₃, degrading pellet quality and metallurgical performance.

Lowering economic value – At a typical 2% dosage, 66% iron ore pellets lose 1.28% iron grade, gain 1.39% SiO₂, and 0.37% Al₂O₃.

Practical Application of Modified Bentonite
By refining high-quality bentonite through wet sodium activation, drying, modification, and grinding, new additives were developed to:

Improve pellet reducibility, green strength, and thermal stability.

Enhance pellet strength, porosity, and oxidation.

Shorten roasting time and reduce energy use.

Optimize microstructure and inhibit abnormal expansion.

Field results show modified bentonite at 1.2–1.6% achieves the same effect as 2.5–3.5% conventional bentonite, improving strength, thermal stability, and iron grade while reducing return fines. Replacing sodium bentonite (3.2%) with modified bentonite (1.8%) saves ¥10.5/ton, or ¥25.2 million annually for a 2.4-million-ton plant.

Advantages of Modified Bentonite Binder:
Enhances dispersion, thermal stability, and nucleation.

Boosts green pellet strength and burst resistance.

Cuts bentonite usage by 50–75%, raising iron grade and lowering SiO₂.

Reduces roasting time and energy consumption.

Supports high-quality pellet production aligned with green development goals.

References:
[1] Yang Xiaodong, et al. Engineering Studies, 2017.
[2] Ye Kuangwu, et al. National Ironmaking Conference, 2010.
[3] Li Yifeng. Standard Science, 2014.
[4] Xu Manxing. Steel Exchange, 2022.

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