About Sodium Bentonite
Sodium bentonite is the high-swelling form of bentonite clay, in which sodium is the dominant exchangeable cation on the montmorillonite platelets. On contact with fresh water the platelets separate and the clay expands to many times its dry volume. Confined in soil, inside a geosynthetic liner or in a trench, it forms a dense, low-permeability barrier that restricts the movement of water and leachate.
Our sodium grade is selected for consistent swell and low fluid loss, the two properties that govern sealing performance. It is used as the core of geosynthetic clay liners, mixed into native soil for pond and lagoon linings, and hydrated into slurries that support diaphragm walls, cut-off walls and bored piles during excavation. Granular forms suit dry placement, for example sealing the annulus around water wells, monitoring wells and geotechnical boreholes.
The clay is dried, ground and classified at our Gujarat and Rajasthan locations and tested in our NABL-accredited laboratory for swell index, fluid loss, moisture and fineness. Each lot ships with a batch Certificate of Analysis, so contractors and liner manufacturers can check it against project specifications before installation. Swell, fineness and granule size can be adjusted on request for a particular liner line, slurry plant or site design.
Typical specifications
| Parameter | Typical Value | Test Method |
|---|---|---|
| Swell index | ≥ 24 ml/2 g | ASTM D5890 |
| Fluid loss | ≤ 18 ml | ASTM D5891 |
| Moisture | 8–12 % | Internal method |
| pH (5 % suspension) | 9.0–10.5 | Internal method |
| Passing 75 µm (powder form) | ≥ 80 % | Wet sieve, internal method |
| Granule size (granular form) | 0.5–3 mm or as specified | Sieve analysis |
| Colour | Cream to grey | Visual |
Typical values for guidance. Guaranteed limits are stated on the Technical Data Sheet and batch CoA.
Key features & benefits
High free swell
A typical swell index of 24 ml/2 g or more means the clay expands quickly on hydration and fills voids in the soil or liner matrix, building a continuous barrier rather than isolated pockets of bentonite.
Low fluid loss
Low fluid loss values point to a tight, low-permeability filter cake. In liners and cut-off walls this translates into restricted seepage of water and leachate once the sodium bentonite is hydrated and confined.
Self-sealing behaviour
Hydrated sodium bentonite can swell into small punctures, cracks and settlement gaps. That helps a seal tolerate minor damage during installation and modest ground movement over the life of the works.
Powder and granular forms
Fine powder suits liner manufacture and slurry mixing, while granules suit dry placement, soil blending and borehole sealing. Particle size can be adjusted to match your equipment and installation method.
Batch-level testing
Swell index and fluid loss are measured on every batch to ASTM methods in our NABL-accredited laboratory, and the results are reported on the Certificate of Analysis that accompanies the shipment.
Applications
Geosynthetic clay liners
Powder or granular sodium bentonite encapsulated between geotextiles forms the low-permeability core of GCLs used in landfill caps and base liners, canal linings and secondary containment around tanks.
Pond, lagoon and canal lining
Blended into native soil at a controlled rate and compacted, the clay reduces seepage from farm ponds, effluent lagoons, water features and irrigation channels where a synthetic membrane is not practical.
Slurry walls and bored piling
Bentonite slurry supports trench walls and pile excavations during construction of diaphragm walls, cut-off walls and secant piles, and is later displaced by tremie concrete or backfill.
Well and borehole sealing
Granules are poured into the annulus of water wells, monitoring wells and geotechnical boreholes, where they hydrate in place and help prevent surface water from migrating down the hole.
Usage & handling
- Soil sealing: application rates depend on soil type and target permeability and often fall in the range of 5–15 kg/m²; confirm with a site permeability test.
- Slurry mixing: pre-hydrate around 4–6 % by mass in fresh water with high-shear mixing, and allow several hours of hydration before use.
- Water quality: hard, saline or contaminated water reduces swell, so test make-up water and site groundwater for compatibility first.
- Storage: keep bags dry, off the floor and under cover; absorbed moisture causes caking and reduces flowability.
Packaging & supply
- 25 kg and 50 kg HDPE or paper bags
- 1 MT and 1.2 MT jumbo (FIBC) bags for liner and slurry plants
- Custom or private-label packaging on request
- MSDS, Technical Data Sheet and batch CoA with each shipment
Frequently asked questions
What swell index does your sodium bentonite achieve?
Our sodium bentonite typically shows a swell index of 24 ml/2 g or more by ASTM D5890, together with fluid loss of 18 ml or less by ASTM D5891. These are typical values for guidance. The guaranteed limits for your order are stated on the Technical Data Sheet, and the measured result for each lot is reported on its batch Certificate of Analysis.
Is this sodium bentonite suitable for geosynthetic clay liners?
It is used as the core material in geosynthetic clay liners, where swell index and fluid loss are the key acceptance properties. Liner specifications vary by project and by manufacturer, so share your required limits and test methods. We can supply samples for qualification testing on your production line and adjust fineness or granule size to suit your needle-punching or encapsulation process.
Is your sodium bentonite natural or activated?
Depending on the deposit and the target specification, the grade is either naturally sodium-rich or calcium bentonite converted by controlled soda-ash activation. Both routes are designed to deliver the sodium-type swell and fluid loss the application needs. If your project specification requires a particular route or documentation about activation, tell us at enquiry and we will confirm what can be supplied.
How does salt water affect sodium bentonite seals?
Dissolved salts and hardness ions reduce the swelling of sodium bentonite and can raise the permeability of the seal. Where a liner or slurry will meet seawater, brine or aggressive leachate, compatibility testing with the actual site fluid is recommended. Pre-hydrating the clay in fresh water before exposure can also help it retain more of its sealing performance.
Can you supply sodium bentonite granules for borehole sealing?
Yes. Granular sodium bentonite is available for sealing the annulus of water wells, monitoring wells and geotechnical boreholes. Granules can be poured from the surface and hydrate in place to form a seal. Granule size can be matched to the annulus width and placement method, and samples are available so drillers can check sinking rate and hydration time on site.