Microstructure of Bentonite in Iron Ore Green Pellets

Abstract

Sodium-activated calcium bentonite is used as a binder in iron ore pellets and is known to increase strength of both wet and dry iron ore green pellets. In this article, the microstructure of bentonite in magnetite pellets is revealed for the first time using scanning electron microscopy. The microstructure of bentonite in wet and dry iron ore pellets, as well as in distilled water, was imaged by various imaging techniques (e.g., imaging at low voltage with monochromatic and decelerated beam or low loss backscattered electrons) and cryogenic methods (i.e., high pressure freezing and plunge freezing in liquid ethane). In wet iron ore green pellets, clay tactoids (stacks of parallel primary clay platelets) were very well dispersed and formed a voluminous network occupying the space available between mineral particles. When the pellet was dried, bentonite was drawn to the contact points between the particles and formed solid bridges, which impart strength to the solid compact.

Intergranular pore space evolution in MX80 bentonite during a long-term experiment

“…Apart from the development of cracks there are no other microstructural modification induced, indicating that the sublimation of free vitrified water under high vacuum does not significantly modify the bentonite in a way that renders the results of such studies to be meaningless. This finding applies to bentonite samples with high densities, however, in the case of diluted bentonite suspensions, sublimation of free water can certainly lead to significant changes in microstructure (Bhuiyan, 2013). As the ABM samples studied here have high packing densities, no artifacts caused by sublimation (freeze drying) were observed.…”

“…The main challenges in studying bentonite microstructures lie in the preparation of samples so that they can be used for FIB-nt, which occurs under high vacuum and which can be overcome by cryofixation techniques which are used to investigate the microstructures of bentonites (Vali and Hesse, 1992;Bhuiyan, 2013). The most critical aspect of these cryofixation techniques is the cooling rate.…”

Prediction of Compressive Strength of Biomass–Humic Acid Limonite Pellets Using Artificial Neural Network Model

“…Bentonite, as the main binder for pellets, cannot undergo thermal decomposition during the smelting process and mostly remains in the pellets, leading to a decrease in the iron grade of the pelletized ore [ 15 ]. Qiu et al [ 16 ] utilized organic binders to prepare pelletized ore and found that, compared to pellets prepared using bentonite, the resulting pellets had a higher iron grade and lower impurity content [ 17 ].…”