The primary difference between sodium bentonite clay and calcium bentonite clay is their behavior when mixed with water, particularly concerning swelling.
While both are types of bentonite clay, their dominant exchangeable cation (sodium vs. calcium) dictates how they interact with moisture.
- Sodium bentonite is known for its significant swelling capacity. When sodium bentonites are hydrated in water, the clay particles separate considerably.
- Calcium bentonite swells much less compared to sodium bentonite.
This difference in swelling capacity is a crucial practical distinction. According to reference (2):
Practically, the difference in these types can be explained by the swelling capacity. When sodium bentonites are hydrated in water, the clay particles separate so they are on average 100 Angstroms apart. Calcium bentonites do not swell as much and remain on average 10 Angstroms apart (2).
This means that when exposed to water, sodium bentonite can expand to many times its dry volume, forming a gel-like substance. Calcium bentonite, conversely, remains relatively stable in volume when hydrated.
Comparing Swelling
Here is a breakdown of their swelling behavior:
| Characteristic | Sodium Bentonite | Calcium Bentonite |
|---|---|---|
| Primary Swelling Property | High Swelling | Low Swelling |
| Particle Separation (Hydrated) | Approx. 100 Angstroms (2) | Approx. 10 Angstroms (2) |
| Behavior in Water | Expands significantly, forms gel | Remains relatively stable |
This difference in swelling dictates their various applications across industries, from sealing ponds and drilling fluids (where high swelling is beneficial) to absorbents and certain cosmetic or health uses (where lower swelling might be preferred).
