Bentonite swells when it comes into contact with water, a natural phenomenon primarily caused by the expansion of the mineral crystal layer intervals, allowing water molecules to enter the crystal layers. Additionally, the cation exchange action of bentonite minerals also contributes to swelling. The swelling property is greatly related to the properties of bentonite and the montmorillonite content, with sodium bentonite exhibiting a higher swelling capacity compared to calcium bentonite. Moreover, bentonite with higher purity and a higher montmorillonite content tends to swell more. Therefore, when seeking to primarily utilize the swelling property of bentonite minerals, it is crucial to first choose sodium bentonite and then consider sodium bentonite with a high montmorillonite content. In the fields of mechanical casting and iron ore pelletizing, a higher swelling capacity is required. Thus, selecting a quality bentonite product becomes particularly important.

High-quality bentonite requires careful selection and comparison. The choice of casting bentonite primarily focuses on the following criteria:

1. The reusability of bentonite; a high-quality bentonite requires minimal addition in recycled sand from repeated usage, and it can significantly enhance the overall performance of the molding sand.

2. The casting performance requirements of bentonite, including bonding strength, thermal-humidity tensile strength, etc.

3. Additional Performance: Gel Price, Swelling Ratio, etc. A high bonding strength, high thermal and wet tensile strength, and good reusability are all signs of high-quality bentonite.