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The Influence of Bentonite on Pellet Production



Source: internal company

Introduces the application of bentonite in China's pellet production, and analyzes the reasons why the bentonite dosage is too high in most domestic pellet plants. Explained the ways and means to further reduce the bentonite dosage and improve the quality of pellet ore.

1. Effect of bentonite on pellet quality
Bentonite is used as a binder to prevent the green ball cloth from bursting when placed on the drying bed. The green balls will not agglomerate after entering the shaft furnace, which greatly improves the operation rate. Bentonite participates in pellet production and improves the compressive strength of pellets. However, the main component of bentonite is SiO2, and its content is more than 60%. According to domestic production experience, for every 1 percentage point increase in the bentonite ratio, the pellet grade decreases by 0.66%, and the corresponding SiO2 content of the finished ore also increases significantly. SiO2 is a harmful component in blast furnace smelting. Under the condition of ensuring a certain alkalinity of the slag, its entry into the furnace should be reduced as much as possible. Therefore, pellet producers should reduce the bentonite ratio and improve the pellet grade.

2. Methods to reduce the bentonite ratio
Bentonite was introduced into the pellet industry mainly to increase the bursting temperature of green pellets. However, many domestic manufacturers are currently increasing the proportion of bentonite to increase the number of drops and compressive strength of green balls to meet process requirements, resulting in a substantial increase in the amount of bentonite. According to research, when the dosage of bentonite is 5 to 15kg/t, it can meet the requirements for a burst temperature of over 800°C. Therefore, measures can be taken from the following aspects to increase the number of green ball drops and compressive strength, thereby reducing the amount of bentonite and reducing economic losses.

2.1 High-quality iron ore concentrate
Blast furnace production requires fine materials, and pellet production also requires fine materials. The pellet raw materials should have a certain particle size and suitable particle size composition, suitable moisture, and uniform and good chemical composition. These are all important guarantees for the production of pellets.

Different from sintering, the strength of pellets mainly comes from the recrystallization and solid phase consolidation of Fe2O3. Therefore, the grade of iron concentrate used for pellet production should be as high as possible, while the FeO content should be as low as possible to reduce the bentonite dosage. The iron concentrate must have a certain fineness, which is the basic condition to ensure the smooth progress of the pelletizing process. Generally speaking, the finer the particle size, the greater the specific surface area of the mineral powder, and the greater the molecular force between the particle surfaces, which is conducive to balling. Under conditions containing some fine particles, the particles are arranged very closely and the capillary action is strengthened. Therefore, the existence of ultra-fine particle sizes (especially <10 μm particle size) in iron concentrate is very important for pelletizing. Therefore, ultra-fine iron minerals should be recovered as much as possible in the mineral processing process. Foreign pellet plants generally require that the particle size smaller than 0.044 mm in raw materials account for more than 60%, and the particle size smaller than 0.074 mm must account for more than 90%; my country also requires that the particle size smaller than 0.074 mm in iron concentrates should account for more than 80%.

Since the pelletizing performance of domestic iron concentrate is poor, the quality of raw materials can be improved by adding some imported iron concentrate. The imported concentrates used for pellets in my country mainly include Brazilian concentrates, Indian concentrates, Peruvian concentrates, etc. Generally speaking, the quality of imported concentrate is better, with high grade and fine particle size. After adding some imported concentrate, the compressive strength and drop strength of green balls can be improved, and the dosage of bentonite is also reduced.

2.2 Grinding of pellet mixture
Adding a wetting and grinding process is another powerful measure to reduce the dosage of bentonite. After grinding, the particle size <0.074 mm of the mixture increases by 10 to 15 percentage points, the particle size becomes finer, the shape of the material particles changes, its surface activity is enhanced, and the pelletizing performance is greatly improved.

Mixture grinding is not ore grinding, and its effect on reducing the particle size of iron ore concentrate is not as obvious as dry grinding or wet grinding. Therefore, the appropriate time and moisture must be controlled during grinding. Generally, the grinding time is 4 to 5 minutes, and the mixture moisture is ≤7.5%.

2.3 Actively develop new bentonite and its substitutes
In view of the current situation that there are many bentonite manufacturers in China and the resource characteristics are different, how to use them together is also one of the important means to improve the ingredients and reduce the dosage of bentonite. At present, there are only a few varieties of bentonite in China, most of which are artificial sodium bentonite and some calcium-based bentonite. Domestic bentonite manufacturers should actively develop new bentonite and its substitutes.

2.4 Add steelmaking sludge
Steelmaking sludge has high grade, fine particle size and high viscosity. It can replace part of bentonite and is a good raw material for pellet production. Adding 3% to 4% steelmaking sludge can reduce the bentonite dosage by 0.7% to 0.9%. It is worth noting that due to the high viscosity of steelmaking sludge, a high concentration will easily block the pipeline, and a low concentration will weaken its bonding effect in the pelletizing process. Therefore, it is very necessary to master the appropriate dosage concentration in production.

3. Conclusion
3.1 Bentonite replaces slaked lime as the binder in iron ore pellet production, which promotes the development of my country's pellet production. However, SiO2, the main component of bentonite, is a harmful component in blast furnace ironmaking. If the dosage of bentonite is too high, it will reduce the grade of pellets and cause great losses to blast furnace ironmaking.
3.2 Bentonite is involved in pellet ingredients, mainly to increase the bursting temperature of green balls. However, due to the influence of many factors such as raw material conditions, most domestic pellet plants hope to improve the falling and compressive strength of pellets by increasing the proportion of bentonite, so the amount of bentonite added is generally high.
3.3 To reduce the proportion of bentonite, you can use high-grade, ultra-fine-grained iron concentrate; add some high-quality imported iron concentrate; use mixture grinding technology; develop new high-efficiency bentonite and binders; add steelmaking pollution Mud and other means to achieve.
3.4 It is necessary to speed up the research and development of new low-priced binders to replace bentonite, thereby further improving the grade and quality of pellets, and the status of pellets as a high-quality raw material for blast furnace smelting.

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