Bentonite is used as a binding agent in the production of iron ore pellets. Through this process, iron ore fines are converted into spherical pellets, suitable as feed material in blast furnaces for pig iron production, or in the production of direct reduction iron (DRI).
Bentonite is primarily used for improving dry compressive strength of iron concentrate pellets so that they go through the processes such as smelting without much damage. Ball et al. (1973) indicated that bentonite clay has the following effects.
Bentonite absorbs moisture, allowing for higher moisture concentrate feeds to be pelletized. Moisture variations can be overcome by altering bentonite dosages.
As bentonite is mixed into the iron ore concentrate it becomes wet so that clay layers expand and disperse by the hydration of exchangeable interlayer cations, transforming into a matrix that bonds the ore particles together.
During tumbling, the pellets are formed by particles adhering to each other in layers, which are compacted by the weight of the other pellets into a spherical shape. Bentonite is well dispersed and retains an even distribution of moisture throughout the wet pellet as it grows.
During drying, bentonite increases the drying rate by providing a pathway for the moisture to be removed
Current practice for pelletizing iron ore concentrates was developed in 1950’s during which bentonite clay was practiced as a binder and since then it has remained the most acceptable binder because of its effectiveness and relatively low cost.
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