how to separate fine ATH powder from coarse particles

Aluminum Trihydrate (ATH, Aluminum Hydroxide) is a widely‑used halogen‑free flame‑retardant mineral filler for cables, plastics, coatings and artificial stone. ATH processing has strict temperature constraints: its crystal water will decompose above 150 °C, which damages flame‑retardant performance. Conventional screening is ineffective for micron‑scale ultrafine ATH because of screen clogging, agglomeration risk and heat‑induced crystal‑water loss. High‑precision air classification integrated into a closed‑circuit low‑temperature grinding system becomes the reliable solution to separate fine ATH powder from coarse oversize particles.

Why conventional sieving fails for ultrafine ATH

Mechanical sieve separation works well for coarse granules but meets major limitations for fine ATH:

1. Micron‑sized ATH particles easily stick together and block sieve meshes, lowering separation efficiency.
2. Continuous mechanical vibration may generate local overheating, risking thermal decomposition of ATH crystal water and degrading its flame‑retardant property.
3. Sieving cannot achieve sharp particle‑size cut‑points required by low‑smoke zero‑halogen cable formulations, where oversize residue above target D97 must be strictly controlled.

For high‑end ATH filler production, closed‑loop air classification is the preferred industrial approach, operating under controlled low‑temperature conditions below 110 °C throughout the whole process.

Working principle of high‑precision turbine air classification for ATH

High‑efficiency turbine air classifier separates ATH fine powder and coarse particles by balancing centrifugal force from high‑speed rotating turbine and drag force from circulating airflow, without any physical screen mesh.

Milled ATH powder is carried by airflow into the classification chamber.

• Coarse particles: Larger‑size ATH particles obtain stronger centrifugal force from the spinning turbine rotor. They are thrown toward chamber walls, lose velocity, and sink down. Secondary upward airflow washes falling coarse material to strip entrapped fine powder, which rises back for re‑classification. Fully separated coarse particles drop to discharge outlet and return to the grinding chamber for re‑grinding in closed‑circuit mode.
• Fine qualified powder: Tiny ATH fine particles are dominated by air drag force. They pass through gaps of turbine blades and flow downstream with air to cyclone collectors and bag‑house filters for final finished‑product collection.

By adjusting turbine rotating speed and system air volume, manufacturers tune the cut‑point D97 value flexibly. For cable‑grade ATH, this technology keeps oversize residue above target D97 ≤ 0.1 %, satisfying ±3 μm particle‑size tolerance for low‑smoke zero‑halogen cable materials.

Complete process chain: from drying, low‑temp grinding to air classification

Effective ATH coarse‑fine separation cannot run independently. It must cooperate with preceding low‑temperature drying and closed‑circuit ultrafine grinding to avoid agglomerates and thermal deterioration.

1. Low‑temperature flash drying & deagglomeration
   Wet ATH filter cake lumps are disintegrated by turbo rotor. Tangential hot airflow stays below 110 °C to remove surface free moisture. Temperature is kept far below the 150 °C crystal‑water‑loss threshold to retain original particle morphology and flame‑retardant activity.
2. Closed‑circuit ultrafine low‑temperature grinding
   Water‑jacket‑cooled ring‑roller or air‑classifier mills limit material peak temperature ≤ 110 °C. Hard agglomerates are fully dispersed. Optional ceramic lining restricts iron impurity ≤ 10 ppm for high‑end ATH grades. Ground mixed powder directly flows into the air classifier for separation.
3. High‑precision air classification (core separation step)
   Turbine classifier disperses micro‑agglomerates and completes coarse‑fine separation. Oversize coarse particles circulate back to grinding zone; narrow‑distribution fine ATH powder goes to collection system. Stable D97 guarantees consistent filling and flame‑retardant performance for downstream polymers.
4. Optional surface activation modification
   Separated fine ATH can further undergo silane or stearic‑acid surface coating under high‑shear vortex mixing. Modifier utilization exceeds 90 %, particle coverage ≥ 95 %, improving compatibility with polymer resins and enhancing mechanical properties of end products.

Key operational notes for ATH classification

1. Strict temperature control: Keep material peak temperature ≤ 110 °C in both grinding and classification units, preventing crystal‑water decomposition and performance loss of ATH flame retardant.
2. Eliminate micro‑agglomerates: Secondary‑air‑washing function inside classifier is critical, to avoid fine‑particle entrapment inside coarse fractions.
3. Closed negative‑pressure circulation: Full closed‑circuit system prevents dust leakage and reduces fine‑powder loss.
4. Anti‑iron‑contamination configuration: Adopt ceramic‑protected rotor and liners for high‑purity ATH production targeting cables and electronic materials.

To separate fine ATH powder from coarse particles in industrial production, high‑precision turbine air classification within a full low‑temperature closed‑circuit processing line is the proven solution, instead of traditional mechanical sieving. This method delivers narrow particle‑size distribution, minimal oversize residue, preserved whiteness and stable flame‑retardant characteristics for ATH fillers used in cables, plastics, coatings and artificial‑stone industries. Coarse fractions circulate back for re‑grinding, maximizing raw‑material utilization while avoiding thermal damage to ATH crystal water.