Bentonite

Bentonite handling problems are usually silo problems, and silo problems with bentonite are usually sizing problems.

Flow and discharge

The clay has a high flow function value, which means it needs a large outlet and a well-designed hopper to move at all.

• Mass flow geometry with liners selected from measured wall friction.
• Bin activators or screw dischargers rather than vibration alone.
• Level monitoring that reveals a developing rathole before discharge stops.

Swelling

Water contact produces a gel that cannot be pumped, conveyed or dug out easily.

Sealed silo tops, dried venting air and prompt attention to roof leaks are cheap compared with emptying a gelled silo.

Dust

Dry bentonite powder is fine and persistent, and some grades contain crystalline silica.

Enclosed transfer, extraction at bag and big bag emptying and monitoring at operator positions are the controls.

Dosing

Drilling mud and foundry sand preparation need a defined addition rate from a cohesive powder, which points to loss-in-weight feeding with an agitated hopper.

What to establish before buying equipment

• Flow function and wall friction on the delivered grade.
• Moisture content on receipt and the storage humidity.
• Silica content and the applicable exposure limit.
• Required dosing accuracy and turndown.

Bentonite gains strength while it sits, and it does so faster than most mineral powders.

The platelets consolidate under their own weight, and any moisture that reaches the surface of the bed starts the swelling that makes the product useful in the ground and unwelcome in a silo. A vessel that discharged on Friday can be solid on Monday.

• Size the outlet from a shear test that includes time consolidation, not from the fresh condition.
• Keep the vessel sealed against humid air; a vent filter is part of the design.
• Plan for discharge aids rather than adding them after the first blockage.

Where the silo is outdoors, the temperature swing between day and night drives moist air in and out through the vent, and the top of the bed is where the first crust forms.

Everything in a bentonite installation follows from cohesion.

The outlet is larger than the capacity suggests, the walls are steeper than they look necessary, and the discharge usually needs mechanical help: a live bottom, a vibrating discharger or an agitated outlet. A simple cone with a slide gate will work for a week and then stop.

For transfer, the powder is fine and dusty but not abrasive, so velocity is less critical than with mineral fillers. Vacuum conveying is often preferred because it keeps the dust in and tolerates a cohesive product better than a pressure line with a long run.

• Outlet dimensions from a measured flow function with time consolidation.
• A discharge aid specified with the vessel, not retrofitted.
• Closed transfer to keep a very fine dust out of the building.

Bentonite is not combustible, and the hazards are respiratory and physical.

Many bentonite grades contain crystalline silica, which makes the respirable fraction a regulated exposure rather than a nuisance. Capture at the source and the handling of collected dust are the controls that matter, and filter changes are the highest exposure moment in the plant.

• Treat the respirable fraction as a regulated exposure where silica is present.
• Capture at bag tipping, bulk bag discharge and every transfer.
• Handle collected dust in closed containers rather than by sweeping.

The second hazard is the swelling itself. Spilled bentonite plus water makes a surface that is genuinely dangerous to walk on, and a drain that is genuinely difficult to clear.