Microstructure of bentonite in iron ore green pellets

Area of Science:

• Materials Science
• Mineral Engineering
• Geochemistry

Background:

• Sodium-activated calcium bentonite is a key binder in iron ore pelletization.
• It is known to improve the mechanical strength of both wet and dry iron ore green pellets.

Purpose of the Study:

• To elucidate the microstructure of bentonite within magnetite iron ore pellets.
• To understand the role of bentonite in imparting strength to iron ore pellets.

Main Methods:

• Scanning electron microscopy (SEM) was employed to image bentonite microstructure.
• Advanced imaging techniques, including low voltage and low loss backscattered electron imaging, were utilized.
• Cryogenic methods such as high-pressure freezing and plunge freezing in liquid ethane were applied.

Main Results:

• In wet pellets, bentonite tactoids (stacks of clay platelets) dispersed to form a voluminous network between mineral particles.
• Upon drying, bentonite migrated to particle contact points, forming solid bridges.
• These microstructural changes directly correlate with enhanced pellet strength.

Conclusions:

• Bentonite's unique microstructural transformation from a dispersed network to solid bridges is crucial for iron ore pellet strength.
• This study provides the first detailed microstructural evidence of bentonite's function in iron ore pelletization.
• Understanding this mechanism can optimize binder selection and pellet processing.