How to Deagglomerate Aluminum Hydroxide Filter Cake

Aluminum hydroxide (ATH) filter cake is the wet solid output from filter press or vacuum filtration. It contains free moisture and forms dense, sticky agglomerated lumps. Without effective deagglomeration, these lumps will pass into downstream grinding and classification units. Hard agglomerates lead to inconsistent particle‑size distribution, incomplete surface modification, increased equipment load, and local over‑heating risk that triggers ATH crystal‑water loss. Proper deagglomeration is the critical pre‑treatment step before ultrafine grinding for ATH production.

Root Causes of ATH Filter‑Cake Agglomeration

1. Capillary force from free moisture bonds fine primary particles together to form soft and hard lumps.
2. Fine ATH particles have high surface hydroxyl activity; particles stick together during filter pressing.
3. Improper filter‑press discharging creates large compact chunks that cannot be directly fed into the grinding mill.

Important note: Deagglomeration aims to break lumps into discrete primary particles, not to reduce the fundamental primary particle size of ATH. It must operate under low‑temperature conditions to protect crystal water.

Main Industrial Deagglomeration Technologies for ATH Filter Cake

1. Flash Drying Integrated Deagglomeration (Most Widely Used for ATH Lines)

High‑speed hot‑air flash dryer combines drying and mechanical deagglomeration in one unit.

• Wet filter cake enters the crushing chamber; high‑speed rotating rotor hammers break large filter‑cake chunks.
• Hot low‑temperature airflow (< 110 °C) instantaneously removes free surface moisture. As moisture evaporates, capillary bonding force disappears, soft agglomerates collapse.
• Dispersed powder is carried by airflow out of the dryer and delivered to the closed‑circuit grinding‑classification system.

Key advantages for ATH:

• One‑step: lump breaking + free‑moisture removal + deagglomeration.
• Strict temperature control avoids crystal‑water decomposition.
• Continuous feeding, matches large‑scale industrial ATH production.

Critical risk point: Local over‑temperature inside the flash dryer will cause partial dehydration of ATH, so air inlet temperature must be strictly limited.

2. Pre‑Crushing + High‑Shear Dispersing (For small‑to‑medium production)

1. First‑stage coarse crushing: break big filter‑cake blocks into small fragments by low‑speed crusher.
2. Second‑stage high‑shear mechanical disperser: rotor‑stator high‑speed shear tears apart residual soft agglomerates.
3. Follow‑up low‑temperature drying removes free moisture.

Limitation: Poor performance for high‑moisture sticky filter cake; sticky material may stick to chamber walls. Mostly applied when filter‑cake moisture is relatively low.

3. Wet‑Route Deagglomeration (For special wet‑ground ATH)

Filter cake is re‑slurried into water. Bead milling or high‑pressure homogenizer provides shear force to separate agglomerates.

Drawbacks for most dry‑process ATH projects: Re‑introduces large amounts of water, requires complete re‑filtration and drying. Higher energy cost, extra thermal‑decomposition risk during re‑drying. Rarely adopted for LSZH cable‑grade dry ATH powder.

Key Process Control Points for ATH Filter‑Cake Deagglomeration

1. Temperature ceiling: All deagglomeration‑drying processes must keep material temperature below 110 °C. Any local hot spot will consume crystal water and reduce flame‑retardant performance.
2. Feed consistency: Stabilize filter‑cake moisture from filter press. Dramatic moisture fluctuation causes unstable deagglomeration efficiency, sticky buildup inside equipment. Typical incoming filter‑cake moisture ranges 8 ~ 15 %.
3. Mechanical shear intensity: Shear should be sufficient to break lumps, but avoid excessive high‑energy impact that generates excessive local heat.
4. Airflow matching: In flash drying systems, airflow velocity must be correctly tuned to carry away dispersed fine powder; incomplete discharge leads to material accumulation and secondary re‑agglomeration inside the chamber.
5. Anti‑wear protection: For cable‑grade high‑purity ATH, the contact parts of deagglomeration equipment should adopt ceramic lining to prevent iron contamination and preserve whiteness.

Common Problems & Troubleshooting

1. Remaining agglomerates after deagglomeration
   Root cause: Insufficient shear, too high filter‑cake moisture, or insufficient drying.
   Solution: Adjust rotor speed, stabilize filter‑press outlet moisture, optimize hot‑air volume and temperature.
2. Material sticking and wall buildup inside deagglomeration equipment
   Root cause: Over‑wet feed or uneven hot‑air distribution.
   Solution: Control filter‑cake moisture; optimize hot‑air flow field to eliminate cold zones where wet material adheres.
3. LOI drops after deagglomeration treatment
   Root cause: Over‑heating inside deagglomeration / drying chamber.
   Solution: Lower inlet air temperature; check for material dead zones with poor heat dissipation.

For dry‑process ATH ultrafine production, flash drying with integrated mechanical deagglomeration is the preferred solution for ATH filter cake. It breaks filter‑cake lumps, eliminates moisture‑driven agglomeration, removes free moisture, and feeds discrete powder into grinding‑classification system. The core principle is sufficient mechanical dispersion paired with strict low‑temperature operation to fully preserve ATH crystal water, which guarantees final flame‑retardant filler quality.