Bulk Bentonite Supplier USA: Sodium, Calcium & API Grades

Bentonite is one of the few industrial minerals where the wrong grade fails loudly. A calcium clay in a drilling mud gives a thin, high-filtrate fluid; a foundry blend heavy in sodium clay can hold its shape so hard that the shrinking casting tears. So a bentonite quote starts with the cation, moves to the duty, and only then gets to price per ton and freight lane.

The short version: bentonite (CAS 1302-78-9) is supplied as sodium, calcium or sodium-activated grades, in bags, supersacks and bulk, for drilling, foundry, civil sealing and absorbent duties. Drilling buyers specify API Specification 13A; everyone else specifies the test that matches the job. RawSource supplies industrial bentonite in all three cation types from US stock, with a Certificate of Analysis (CoA) per lot and the grade Safety Data Sheet (SDS).

What is bentonite?

Bentonite is a natural clay made mostly of montmorillonite, a layered aluminosilicate of the smectite group (PubChem, CAS 1302-78-9; EC 215-108-5 per the product record). Cations between the layers balance the sheets’ negative charge. Mostly sodium, and water pushes the layers apart into a gel. Mostly calcium, and swelling is limited; the clay absorbs and binds instead.

One US patent puts the difference at up to about 15 times dry volume for sodium clay against 2 to 3 times for calcium (US 10081574).

The tonnage is industrial. The USGS estimates US production at about 4.1 million metric tons in 2025, with 48% going to pet-waste absorbents and 22% to drilling mud (USGS Mineral Commodity Summaries 2026). The rest goes to foundry sand bonding, iron-ore pelletizing, civil sealing and other absorbents. It enters under HTS 2508.10.0000 at a general duty rate of Free.

This page serves the industrial share only. It does not cover cosmetic, ingestion or household use, and no grade here is sold for those purposes. First time matching a grade to a job? Start with the bentonite grade and application guide. This page is where you write the purchase order.

Sodium vs calcium vs sodium-activated: how to choose

Pick the cation from the duty, then the grade from the test your process runs.

One trade-off the datasheet will not show you: an activated clay can pass API numbers on deionized water and still under-deliver in hard or brackish field water, because exchanged sodium is easier to displace than the sodium in a natural swelling clay.

API 13A carries a separate OCMA-grade clause for exactly this case. It defines a clay that “cannot meet all aspects of Clause 9” and may have been treated with soda ash or polymer (API 13A, 19th ed., Addendum 1). Cheaper per ton, and honest about it.

Recommendation: if your make-up water is anything but clean fresh water, run the API rheology test on your own water before committing to an activated grade at truckload volume.

Applications by industry

Each duty pulls a different grade and test. The spec to write on the PO closes each section.

Drilling fluids: oil and gas, water wells, HDD

Sodium bentonite is the viscosifier and filtration-control clay in water-based mud. Clause 9 of API 13A is the drilling-grade clause. The values in the public record, reproduced from API’s field-testing practice in a US patent: viscometer dial reading at 600 r/min of 30 minimum, filtrate of 15 mL maximum, and residue over 75 µm (200 mesh) of 4% maximum (US 10081574).

Clause 9 also caps the yield-point to plastic-viscosity ratio; take that limit from the API edition your operator references, not from this page.

The test suspension is 22.50 g of clay in 350 mL of deionized water, stirred 20 minutes, aged at least 16 hours, read at 25 °C. The Clause 19 OCMA grade sets the ratio at 6 maximum, filtrate at 16.0 mL maximum and residue at 2.5% maximum (Addendum 1, Table 18).

The rest of the mud is a separate line on the same order. RawSource also supplies barite as the weighting agent, guar gum as a secondary viscosifier, and polyacrylamide as a friction reducer (grade selection is on the polyacrylamide supplier page). This is an oil, gas and mining sourcing line.

Specify: “Sodium bentonite meeting API Spec 13A Clause 9” (or “Clause 19 OCMA grade” if the operator accepts it), 200 mesh, mill certificate with each lot.

Foundry green-sand and iron-ore pelletizing

Metalcasters bind silica sand with bentonite. Sodium clay gives hot strength and durability through reclaim cycles; calcium clay gives green strength and a cleaner casting skin, so most shops run a blend tuned to alloy and pour temperature. The clay is judged on the foundry’s own sand tests (green and dry compressive strength, methylene-blue clay content), not on drilling rheology.

Pelletizing plants bind iron-ore concentrate with sodium bentonite at low addition, because every point of clay in the pellet is silica the furnace carries. This is an industrial manufacturing sourcing line.

Specify: cation type or blend ratio, target green and dry compressive strength on your sand system, mesh, moisture. Ask for the blend to be held constant lot to lot; defect profiles shift when it drifts.

Civil: GCLs, slurry walls, pond and lagoon sealing

Sodium bentonite is the barrier in geosynthetic clay liners (GCLs) and the sealing medium in slurry walls and earthen ponds. The EPA’s GCL fact sheet gives the physics in two numbers: dry, unconfined bentonite runs a hydraulic conductivity of about 1 × 10⁻⁶ cm/s; hydrated, it typically drops below 1 × 10⁻⁹ cm/s, and more bentonite per unit area means lower conductivity (EPA 530-F-97-002).

The index tests are ASTM D5890 for swell index and ASTM D5891 for fluid loss. A clean-water swell index flatters a clay that will meet leachate or brine in service, so qualify on the permeant you expect. For farm and stock ponds, method and dose are on the pond sealing page; that page says how much, this one says what grade.

Specify: granular or powdered sodium bentonite, ASTM D5890 swell index and D5891 fluid loss to the project engineer’s values, moisture, pallet or supersack.

Industrial absorbents, carriers and clarification

Calcium and technical grades do the absorbing: granular calcium bentonite in oil and chemical absorbents, bentonite as a carrier and anti-caking aid in agricultural formulations, and calcium or acid-activated clay as a bleaching earth in edible-oil processing. Granule size and absorption capacity drive the first two; the third is gated by documentation, so ask for grade certification and a heavy-metals profile up front. Cat litter is the largest bentonite market by tonnage and not a duty this page serves.

Specify: calcium or activated grade, granule mesh range or powder, the absorption or decolorizing test your line uses, and any food-contact documentation your application requires.

Bulk supply, grades and quality control

RawSource supplies industrial bentonite as sodium, calcium and sodium-activated grades, powder or granule, in bags on pallets, in supersacks, and as bulk pneumatic loads, from US stock. Ask for the pallet pattern and bag count with the quote; for pneumatic loads, the bulk density in the table below drives the load calculation.

Store bagged clay dry and off the floor. Moisture as shipped runs 5 to 12%, and a bag in a damp warehouse gains weight you pay for and loses the free-flow you need at the mixer.

Typical values, not a specification. The Certificate of Analysis for the lot you buy governs.

A bentonite CoA shows the lot number, grade or cation type, moisture, grit (residue on 200 mesh), and the duty-specific numbers for that grade. If a parameter you need is missing, ask before the lot ships. Natural clay varies by seam; two lots can pass Clause 9 at different points inside it, which is why a mud plant tracks the 600 r/min reading lot by lot.

Two handling notes. Bentonite is a fine mineral powder that can contain crystalline silica as quartz; check the SDS and manage dust under OSHA’s respirable crystalline silica standards. Regulatory listings (TSCA, REACH, food-contact status) are confirmed per grade on request; never assume one from the mineral name.

How to request a quote

Send six things and we can quote the right grade the first time.

1. The duty (drilling, foundry, pelletizing, civil sealing, absorbent, clarification) and the make-up water or sand system it meets. 2. Cation type if known (sodium, calcium, sodium-activated), or the test you qualify on. 3. The spec to certify against: API 13A Clause 9 or 19, ASTM D5890/D5891 values, or your own strength or absorption method. 4. Form and mesh: powder (200 mesh is the drilling default) or granule range. 5. Packaging and volume: bags per pallet, supersacks, or bulk pneumatic, with annual tonnage and reorder rhythm. 6. Delivery point and any documentation beyond CoA and SDS.

If the cation is unknown, describe the job and we start from the swell-or-absorb rule. A single-bag trial on your own water or sand is the cheapest step between a datasheet and a truckload.

Methodology and sources

Identity is anchored to the PubChem substance record; tonnage, end-use shares and tariff classification to the USGS Mineral Commodity Summaries 2026 (Clays). Drilling-grade requirements are API Specification 13A.

The OCMA table, test suspension and materials list are quoted from API’s published 19th-edition Addendum 1; the drilling-grade dial-reading, filtrate and residue values are as reproduced in US patent 10081574, which cites API’s field-testing practice rather than 13A by clause; the patent states neither the yield-point/plastic-viscosity ratio nor a moisture limit, so take those from the API edition your operator references.

Civil performance is from EPA fact sheet 530-F-97-002 and the ASTM D5890 and D5891 index methods. Typical physical properties are the RawSource product record. The CoA and SDS govern the grade and lot you handle.

Frequently asked questions

What is the difference between sodium bentonite and calcium bentonite? The exchangeable cation between the clay layers. Sodium bentonite swells many times its dry volume and gels, so it is bought for drilling mud, GCLs and sealing. Calcium bentonite swells little and is bought for absorption and binding: foundry sand, absorbent granules, carriers, clarification. Sodium-activated grades are calcium clay treated with soda ash. The sodium bentonite and calcium bentonite guides go deeper.

Where can I buy bentonite clay in bulk? From an industrial distributor that sells by grade and packaging. RawSource supplies bentonite in bags by the pallet, in supersacks, and as bulk pneumatic loads from US stock, with a CoA and SDS per lot. Send the duty, grade, form and tonnage for a quote.

What grade of bentonite is used for drilling mud? Sodium bentonite meeting API Specification 13A, Clause 9: 600 r/min reading of 30 minimum, filtrate of 15 mL maximum, residue over 75 µm of 4% maximum, plus the yield-point/plastic-viscosity cap in the current edition. Where the operator accepts it, the Clause 19 OCMA grade (ratio 6 maximum, filtrate 16.0 mL maximum) is the lower-cost tier. Write the clause on the PO and require the mill certificate.

How is bulk bentonite packaged and shipped? In bags on pallets, in supersacks, or as bulk pneumatic loads for plants with silo storage. The SDS carries the handling and dust-control detail. Keep it dry in transit and storage; the clay picks up moisture from humid air.

What does a bentonite Certificate of Analysis show? Lot number, grade or cation type, moisture, grit (residue on 200 mesh), and the duty-specific tests: API rheology and filtrate for drilling grades, swell index and fluid loss for civil grades, strength or absorption for foundry and absorbent grades. Datasheet values describe the grade; the CoA describes the lot.

Is bentonite for sale by the truckload? Yes. Truckload and multi-truckload orders are the normal unit for drilling, foundry and civil buyers, as palletized bags or bulk pneumatic. Send the annual tonnage and reorder rhythm and we quote the freight lane with the material.

Editorial note. This article is general procurement and technical reference for industrial and professional buyers, not safety, engineering or regulatory advice. Cited specification values are for the buyer to verify against the issuing body and edition their project references. Typical values are not a guaranteed specification; the Certificate of Analysis governs the material you buy.

Bentonite is sold for industrial and professional use only; nothing here is a medical, health or efficacy claim, and no grade on this page is offered for cosmetic, ingestion or household use. Consult the current SDS before handling and confirm regulatory status and suitability for your application and jurisdiction. RawSource makes no warranty, express or implied, and assumes no liability for use of this information.