Material
Talc
Answer in brief
Talc is the material that makes engineers respect particle shape.
The platelets interlock, so the powder arches over large openings, and the same platelets trap air, so it floods through a valve minutes later.
- Size outlets generously and add a mechanical discharge aid from the start.
- Deaerate before feeding, or accept that dosing accuracy will drift.
- Enclose transfers, because the dust travels everywhere.
Reviewed October 21, 2026 · Updated November 10, 2026
Handling challenges
Talc looks harmless and behaves like one of the most difficult powders in industrial use.
Why the shape matters
Platy particles pack together with a high contact area, which gives strong interparticle friction and a flow function well into the cohesive range.
The same shape holds air between plates, so freshly conveyed talc has a bulk density far below the settled value and flows uncontrollably.
Silo discharge
- Large outlets sized from measured flow properties, not from experience with other minerals.
- Mass flow geometry with low wall friction liners.
- Mechanical discharge aids such as bin activators or screw dischargers.
Aeration pads should be used sparingly, since over-aeration converts an arching problem into a flooding problem.
Feeding
Loss-in-weight feeding with an agitated hopper, a deaeration volume and vibration isolation delivers a usable rate.
Volumetric feeding of talc is unreliable because the bulk density is not a constant.
Dust and exposure
Talc dust is respirable and persistent, and cosmetic grades carry additional purity scrutiny.
Closed transfer, contained bag emptying and well-maintained extraction are the practical controls.
What to establish before buying equipment
- Flow function and wall friction on the delivered grade.
- Aerated and settled bulk density, which differ widely.
- Deaeration time available before the feeder.
- Exposure limit applicable to the grade and the plant.
Storage and conditioning
Talc is one of the most difficult powders to store well.
The particles are platy and ultrafine, so the material aerates to almost a liquid and then consolidates to almost a solid. Both states appear in the same silo on the same day.
- Design for the fluid state with a deaeration volume and for the consolidated state with a generous outlet.
- Expect strong time consolidation; a weekend changes the required outlet size.
- Keep it sealed; talc dust travels and settles on everything.
What this means for equipment
Flooding and cohesion together rule out the simple arrangements.
A plain cone with a slide gate will not work reliably. A live bottom or agitated discharge, a deaeration volume and gravimetric feeding are the normal answer where the rate matters.
- Agitated or fluidised discharge, specified with the vessel.
- Isolation that can close against a flowing column.
- Closed, low-velocity transfer; talc is not abrasive but it is extremely fine.
Safety and regulatory
Talc is not combustible, and the controls are respiratory.
The respirable fraction is a regulated exposure, and some deposits have historically carried asbestiform contamination, which makes the supplier declaration and its verification part of the specification rather than paperwork.
- Capture at the source at every transfer.
- Closed handling of collected dust.
- Verified supplier declaration on contamination, grade by grade.
Material behavior
- Flowability
- Very poor, with flooding after aeration
- Abrasiveness
- Low
- Cohesiveness
- Very high
- Moisture behavior
- Low moisture uptake, but moisture worsens bridging
- Contamination risk
- Respirable dust exposure and strict purity requirements in cosmetic grades
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Frequently asked questions
Why is talc both flooding and bridging?
Because the platy ultrafine particles hold air for a long time and then consolidate hard. The two states are hours apart in the same silo.
Can a plain cone discharge talc?
Not reliably. A live bottom or agitated discharge plus a deaeration volume is the normal arrangement, and it belongs in the original design.
What should be checked with the supplier?
The contamination declaration for the specific deposit and grade, verified rather than filed. Talc deposits have historically differed in this respect.
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