Pellet binders are additives that bond finely ground ore particles into pellets and improve the properties of wet, dry, and roasted pellets. They are a type of raw material used in iron and steel metallurgy for artificial enriched ores. Pellet binders can be classified into three major categories: inorganic binders (such as bentonite, hydrated lime, etc.), organic binders (such as Peridur, modified starch, etc.), and composite binders (combinations of organic and inorganic materials). Bentonite remains a commonly used binder in pellet production both domestically and internationally. In international pellet production, the typical dosage of bentonite ranges from 0.6% to 0.8%, with a particle size requirement of less than 0.05 mm for 85% to 90% of the material. In domestic pellet production, the bentonite addition rate is generally 2% to 3%, and can be as high as 5%.
In the pelletizing process, pellet binders serve multiple functions: (1) improving the pelletizability of the material; (2) enhancing the strength of green pellets, dry pellets, and roasted pellets; (3) adjusting the chemical composition (particularly slag-forming components), mineral composition, and quality of sintered pellets. Throughout the development of pelletizing technology, various organic or inorganic binders, as well as single or mixed binders, have been tested to study their applicability.
In a moist state, bentonite particles can envelop ore powder particles, thereby increasing the wettability of the ore powder and improving the pelletizing process. Due to its high water absorption, bentonite allows particles to slide after external impact, thereby enhancing the drop strength of green pellets. After low-temperature drying, green pellets with bentonite gradually lose moisture, reducing the distance between clay mineral particles and ore powder, increasing the molecular forces between particles, and thus improving the strength of dry pellets. The role of adding bentonite is not only to increase the molecular forces between ore powder particles but, most importantly, to enhance the bonding force between ore powder particles and reduce the dehydration rate during the drying of green pellets, thereby increasing the cracking temperature during drying. Although bentonite can improve the properties of green pellets, it is relatively expensive and may introduce impurities such as SiO? and Na?O, which can lower the grade of pellets and promote pellet expansion. Therefore, the amount of bentonite added during pelletizing should be minimized. In North America, the typical dosage is 0.5% to 0.7%. In China, due to coarse concentrate particle size, fluctuating moisture content, and poor mixing conditions, the general addition rate is 2% to 3%.