Indian bentonite is exported in four main grades: drilling, foundry, cat litter and civil engineering. Smaller volumes go out as iron ore pelletising and bleaching earth grades.
Each grade is defined by tests that show how the clay performs in its use. Swelling, viscosity, bonding strength or absorption matter more than chemical purity. A grade name alone tells you little until you see those test results.
Drilling grade
Drilling grade bentonite thickens water-based drilling mud, carries cuttings to the surface and seals the borehole wall. Oil and gas buyers usually ask for material that meets API Specification 13A. Water well and horizontal drilling buyers may accept lower or local specifications.
The key tests are viscosity, filtrate loss and coarse residue. API grade bentonite for drilling explains the specification in detail. The same API standard also has a separate OCMA grade with lower requirements. Make sure your order names the exact section you need, because a supplier may offer the lower grade.
Foundry grade
Foundries mix bentonite with sand and water to form moulds for casting metal. The clay must give good green strength, so the mould holds its shape, and good dry and hot strength, so it does not crack when metal is poured.
Buyers test green compression strength, methylene blue value, which shows active clay content, and moisture. In India, foundry bentonite is covered by IS 12446. Overseas foundries usually set their own limits.
Cat litter grade
Cat litter uses granulated sodium or activated bentonite that clumps when wet. Buyers test clumping strength, water absorption, granule size, dust and sometimes bulk density.
Granule size and dust matter a great deal for retail products. Litter buyers often also ask for fragrance, colour or blends, which brings packing and labelling into the order. That is a different job from bulk clay supply.
Civil engineering grade
Civil grades support trenches and bored piles, lubricate tunnel boring and pipe jacking, and seal landfill liners and ponds. Contractors check swelling, Marsh funnel viscosity, fluid loss, density and sometimes pH. Liner makers often specify swelling index, explained in the swelling index of bentonite.
Other grades
- Pelletising grade binds fine iron ore into pellets and is usually tested for swelling and fineness.
- Bleaching earth is acid-activated calcium bentonite, used to remove colour from edible and mineral oils.
- Agricultural and feed grades are used as binders and carriers, subject to feed rules in your market.
- Paint, cosmetic and pharmaceutical grades need much higher processing and quality control.
Next step
Give suppliers the test methods and limits for your grade, not just its name. We check samples and documents, and have lots tested by an independent laboratory. To set the right grade for your use, book a free sourcing review.