CI 77004- ▸ Foundry: Binder for green-sand molds and cores
- ▸ Drilling fluids: Viscosifier and filtration-control additive in drilling muds
- ▸ Iron-ore pelletizing: Binder for taconite and iron-ore pellets
- ▸ Adsorbent: Clarifying and decolorizing agent (Fuller's earth applications)
- ▸ Suspension agent: Thickener and suspension aid in industrial slurries
A grade-specific Safety Data Sheet (SDS) — with the complete hazard classification, handling precautions, and transport information — is supplied with every shipment and available on request. Confirm all safety and regulatory details against the SDS for your specific grade.
Request SDS →Bentonite (CAS 1302-78-9) is a natural montmorillonite (smectite) clay valued for one defining behavior: it absorbs water and swells into a thixotropic, gel-forming colloid. That swelling and the clay’s high surface area make it a binder, viscosifier, sealant and adsorbent across heavy industry. Performance hinges on the dominant exchangeable cation: sodium bentonite swells many times its dry volume and forms gels and impermeable seals, while calcium bentonite swells far less but offers strong adsorption and decolorizing capacity. RawSource supplies industrial bentonite grades — sodium, calcium and sodium-activated — in bulk from domestic US stock. Mineral-commodity background is published by the USGS.
What is bentonite?
Bentonite is a clay made up mostly of montmorillonite, a layered aluminosilicate of the smectite group. Its stacked silicate sheets carry a net negative charge balanced by exchangeable cations (sodium, calcium) between the layers; when water enters that interlayer space the clay swells, disperses into platelets and builds viscosity. The result is a material that thickens and suspends in water, forms low-permeability barriers, and adsorbs ions and organics on its large internal surface. Which of those behaviors dominates depends on the clay’s source and its exchangeable cation.
Sodium bentonite vs calcium bentonite
The exchangeable cation sets the application. Many calcium bentonites are “sodium-activated” with soda ash to raise swelling toward sodium-grade performance.
| Sodium bentonite | Calcium bentonite | |
|---|---|---|
| Swelling | High — many times dry volume; forms gels and seals | Low — limited swelling |
| Dominant property | Viscosity, gel strength, low permeability | Adsorption, decolorizing capacity |
| Typical uses | Drilling muds, pond & landfill sealing, foundry sands, iron-ore pelletizing | Bleaching/decolorizing earth, adsorbents, carriers |
Regulatory & registration requirements
- TSCA (US):
- REACH (EU): Not determined from public registry
- EC number: 215-108-5
Source: EPA TSCA Inventory (July 2025 release) · ECHA CHEM — retrieved 2026-07-12
More detail in what is sodium bentonite and what is calcium bentonite.
Applications by sector
Drilling and civil/geotechnical. Sodium bentonite is the principal viscosifier and filtration-control additive in water-based drilling muds, and the sealing medium in geosynthetic clay liners, slurry walls and pond, lagoon and landfill linings — see how to seal a pond with bentonite. Foundry. It is the clay binder that gives green-sand molds and cores their green and dry strength. Iron-ore pelletizing. It binds fine ore concentrate into pellets for the blast furnace. Adsorbents and clarification. Calcium and acid-activated grades serve as bleaching earth and decolorizing adsorbents for edible oils, and as clarifiers in beverages. Agriculture and animal feed. Bentonite is used as a pelletizing binder, carrier and anti-caking/flow aid. Surface-modified grades for solvent systems are supplied as organoclay, and the high-purity smectite hectorite serves personal-care and specialty rheology.
Grades and forms
Specify the clay type (sodium, calcium or sodium-activated), the application grade (for example API drilling grade, foundry grade, pelletizing grade or technical/adsorbent grade), the physical form (powder or granule) and the mesh/particle size on your RFQ. Swelling index, viscosity yield, moisture and grit are graded to the duty; the CoA documents the lot you receive.
Handling and documentation
Bentonite is a fine mineral powder; manage dust per the Safety Data Sheet (SDS) and your site practice. Each lot ships with a Certificate of Analysis (CoA) documenting the graded properties. Physical-property, hazard and handling data are sourced from the SDS rather than reproduced here.
Bulk supply and RFQ
RawSource supplies industrial bentonite in bags, super sacks and bulk from domestic US stock for short lead times, to drilling, foundry, civil, edible-oil and agricultural buyers. Submit an RFQ with the clay type, application grade, form and target quantity for a current quote with CoA and SDS. Background reading: what is sodium bentonite, what is calcium bentonite, and how to use bentonite clay.
Typical Properties
Typical reference values, not a specification; the Certificate of Analysis (CoA) for the lot governs.
| Property | Typical Value |
|---|---|
| Mineralogy | Montmorillonite (smectite-group aluminosilicate clay) |
| CAS Number | 1302-78-9 |
| Types | Sodium, calcium, and sodium-activated bentonite |
| Appearance | Off-white to tan/grey powder or granule |
| Swelling | Grade-dependent — high for sodium bentonite, low for calcium bentonite |
| Particle size / mesh | Grade-dependent — see CoA |
| Moisture / grit | Grade-dependent — see CoA |
| Solubility | Insoluble in water; swells and disperses to form a colloidal suspension |
Reviewed and updated July 2026 by the RawSource technical team.
Bentonite is a swelling montmorillonite clay (CAS 1302-78-9) used as a drilling-mud viscosifier, foundry-sand binder, pond and landfill sealant, and adsorbent; sodium and calcium grades perform differently.
Bentonite: key figures for buyers
- 4.8 million metric tons of bentonite were sold or used by US producers in 2024, out of roughly 21 million metric tons mined worldwide, per the USGS Mineral Commodity Summaries (January 2025).
- $99 per metric ton was the 2024 average ex-works unit value of US bentonite (USGS, 2025). Use it as a mine-gate benchmark; delivered cost adds grade, form and freight.
- 48% pet waste absorbents and 23% drilling mud were the leading US end uses for bentonite in 2024 (USGS, 2025), so litter and drilling demand set baseline market pressure on every other grade.
- Free swell of at least 22 mL per ASTM D5890 is the sodium bentonite quality floor in USDA-NRCS Conservation Practice Standard 521C (2010) for pond sealing; specify it on the PO for sealing work.
- GRAS under 21 CFR 184.1155: FDA affirms bentonite (CAS 1302-78-9) as generally recognized as safe as a direct human food ingredient used as a processing aid under current good manufacturing practice (21 CFR 184.1155, 2024 ed.).
Solutions Using This Product
Process-solution guides on this site that specify this chemistry:
- Drilling Fluids & Mud Additives (Oil, Gas & Mining)
Frequently Asked Questions
What is bentonite mostly used for?
Bentonite (CAS 1302-78-9) is a natural montmorillonite clay used as a binder in foundry green-sand molds and cores, as the principal viscosifier and filtration-control additive in drilling muds, as an iron-ore pelletizing binder, as a sealant for ponds, lagoons and landfills, and as an adsorbent/clarifying agent.
What is the difference between sodium and calcium bentonite?
Sodium bentonite swells to many times its dry volume and forms gels and low-permeability seals, so it is used for drilling muds, foundry sands, pelletizing and sealing. Calcium bentonite swells far less but adsorbs and decolorizes well, so it is used as bleaching earth and an adsorbent. Calcium grades are often sodium-activated to raise swelling.
Does bentonite dissolve in water?
No. Bentonite does not dissolve; it absorbs water, swells and disperses into a colloidal, thixotropic suspension. That swelling and gel formation is the basis of its use as a viscosifier and sealant.
Which bentonite is used to seal a pond?
High-swelling sodium bentonite is used for pond and lagoon sealing because it swells to form a low-permeability barrier. Dose and method depend on the soil; see our guide on how to seal a pond with bentonite. Confirm suitability for your site.
What is the CAS number of bentonite?
Bentonite is identified by CAS 1302-78-9. It is a natural mineral (a montmorillonite clay), not a single pure compound, so it is specified by clay type and graded properties rather than a single molecular formula; the CoA documents each lot.
How is bulk bentonite supplied and quoted?
RawSource supplies bentonite in bags, super sacks and bulk from domestic US stock, with CoA and SDS per lot. Pricing is quote-based on clay type, application grade, form and volume; specify these on the RFQ for a current bulk quote.
How much bentonite to seal a 1 acre pond?
Plan on roughly 45 to 90 short tons per treated surface acre. USDA-NRCS Conservation Practice Standard 521C sets application at 0.345 to 0.700 lb of finely ground bentonite per square foot for each inch of liner thickness, graded by soil class. A minimum 6-inch liner therefore needs about 2 to 4.2 lb per square foot, and a surface acre is 43,560 square feet. Sands and gravels sit at the top of the range; a lab test on your soil fixes the final rate.
How thick does bentonite need to be to seal a pond?
At least 6 inches of finished, compacted soil-bentonite liner for water up to 8 feet deep. USDA-NRCS Standard 521C steps thickness with water depth: 12 inches for 8.1 to 16 feet, 18 inches for 16.1 to 24 feet, and 24 inches for 24.1 to 30 feet. Thicker liners are built in compacted lifts of 6 inches or less, and the finished liner needs at least 6 inches of protective soil cover.
What are the disadvantages of bentonite waterproofing?
A bentonite seal performs only while it stays hydrated and confined. USDA-NRCS Standard 521C requires protection against desiccation cracking, frost action, wave action, and traffic from animals or equipment, plus at least 6 inches of soil cover. Soil suitability is a hard limit: coarse-grained soils need 30 to 50 percent fines, so clean gravels or fractured rock may need imported soil blended in. For water deeper than 24 feet, NRCS recommends considering a flexible membrane liner instead.
Where do you get sodium bentonite?
Wyoming leads US production; its deposits hold as much as 70 percent of the world’s known bentonite supply, per the Wyoming State Geological Survey, and the clay swells up to 16 times its original size. US producers sold or used 4.8 million metric tons in 2024 (USGS). RawSource supplies sodium, calcium and sodium-activated bentonite in bags, super sacks and bulk from domestic US stock; submit an RFQ for a delivered quote.
What is the REACH and TSCA regulatory status of Bentonite (Montmorillonite Clay)?
Bentonite (Montmorillonite Clay) (CAS 1302-78-9) is listed as Active on the U.S. EPA TSCA Inventory; its REACH registration status is not determined from the public ECHA registry.