Bentonite is a clay mineral used across several industries — oil & gas, water containment, and ceramics — for a different reason in each. The breakdown below covers what it actually does in each industry.
What is it?
Bentonite is a clay composed predominantly of montmorillonite. Sodium bentonite is the form most relevant to drilling and containment applications: it swells substantially when it comes into contact with water — 15 to 17 times its dry volume in geosynthetic liner applications — forming a dense, low-permeability barrier.
Why should I use it?
- Distinct technical roles. The same swelling/hydration behavior is put to very different use depending on the industry — as a viscosity and filtration control agent in drilling fluids, as a low-permeability containment barrier, and as a plasticizer/binder in ceramics — see the breakdown below.
- Performance specified by industry standard, not just composition. Drilling-grade material is qualified against API Spec 13A; containment-grade material is qualified against a distinct set of ASTM test methods.
How its role changes by industry
- Oil & Gas: used as a viscosifier and filtration-control agent in drilling fluids. To qualify as drilling-grade under API Spec 13A, it must meet performance minimums — including a swelling requirement of at least 24 mL per 2 g of clay, a maximum fluid loss of 15 mL in a 30-minute filter-press test, and a minimum 600-rpm viscometer reading of 30 — not just natural, unprocessed sodium bentonite by itself.
- Water Treatment: the clay component in geosynthetic clay liners (GCLs) used for water and sewage pond containment and landfill leachate barriers. Bentonite’s swelling forms a barrier with hydraulic conductivity of 10⁻¹¹ cm/s or lower in qualified GCL products (ASTM D5887) — a physical containment barrier, not a chemical water treatment.
- Ceramics: a plasticizer and binder, typically added at just 1–3% — a small amount is enough to noticeably increase a clay body’s workability and keep suspensions from settling out (see Limitations for why more isn’t better here).
Limitations — when it isn’t the right choice
- In Ceramics, more isn’t better. Because it’s added at such a small percentage, overdosing it — even modestly — can cause warping and cracking in the finished body; the addition rate is a real constraint, not a target to maximize.
