Jet milling is an ultra-fine grinding technology used for high-grade recovered carbon black (rCB) processing. Unlike impact mills that rely on rotating hammers or pins, jet milling breaks materials using high-speed compressed gas streams. It is especially suitable for de-agglomerating pyrolysis char to produce ultra-fine, low-contamination rCB for high-end rubber, plastic and lithium-ion composite applications.
Core Working Principle
Jet milling uses compressed air (or inert nitrogen for safety) accelerated through precision nozzles to form supersonic gas jets. Pre-treated rCB feed enters the grinding chamber, where high-velocity gas accelerates the agglomerated carbon particles. Size reduction happens mainly through particle-on-particle collision, rather than impact against metal rotor surfaces.
Carbon agglomerates collide violently with each other and shatter into smaller primary particles. This mechanism minimizes metal contamination compared with mechanical mills, which is a major advantage for rCB with strict residual steel limits.
Full Jet Milling Workflow for rCB
1. Pre-Treatment (Mandatory Before Jet Milling)
Crude pyrolysis char must go through pre-processing before jet milling:
- High-intensity magnetic separation removes residual steel wire and iron fines;
- Crushing and sieving eliminate oversized lumps;
- Drying reduces moisture to prevent agglomeration and nozzle blockage.
Feed must be free of large metal fragments, because hard steel particles will abrade nozzles and wear the classifier inside the jet mill.
2. Feeding & Gas Injection
Dried, pre-cleaned rCB powder is metered into the grinding chamber by a quantitative feeder. Compressed gas is injected through multiple tangential nozzles to create a high-speed vortex inside the grinding cavity. The gas carries rCB agglomerates into the collision zone.
3. Particle Collision & De-Agglomeration
The high-speed vortex accelerates carbon clusters. Agglomerates crash into one another and break apart. Jet milling targets de-agglomeration of rCB porous clusters, instead of breaking the primary carbon black spheres. This preserves the original structure and reinforcement properties of rCB.
4. Integrated Air Classification
Most production jet mills include an internal dynamic classifier wheel. Centrifugal force separates fine qualified particles from coarse agglomerates:
- Fine particles meeting PSD requirements pass through the classifier wheel and flow to the collection system;
- Coarse agglomerates are rejected and fall back into the jet grinding zone for re-processing.
Operators adjust classifier rotational speed and gas pressure to tune D50 and D97 for different customer grades.
5. Powder Collection & Gas Treatment
The air stream carrying fine rCB enters a baghouse filter. The filter separates solid rCB powder from the carrier gas. The collected finished powder drops into the product hopper. The cleaned gas is discharged or recycled.
Key Advantages of Jet Milling for rCB
- Low metal contamination: No high-speed rotating grinding rotor; particle-to-particle collision greatly reduces metal wear and residual iron pickup.
- Ultra-fine, narrow particle size distribution: Ideal for high-spec rCB grades requiring very low D97.
- Low heat generation: Gas expansion during jetting creates cooling effect, preventing thermal degradation of rCB structure.
- Inert gas option: Nitrogen can replace air for processing rCB batches with high volatile content, lowering dust explosion risk.
Limitations
- Higher energy consumption than ACM air classifier mills;
- More sensitive to feed impurities; strict pre-milling magnetic separation is compulsory;
- Lower throughput, so it is usually selected for high-value, low-volume rCB grades instead of mass bulk production.
Jet milling processes recovered carbon black by using high-speed gas jets to accelerate carbon agglomerates and achieve particle-on-particle de-agglomeration. With internal classification and closed-loop gas flow, it delivers ultra-fine rCB with minimal metal contamination. It is a premium milling solution for high-performance rCB, used when standard ACM milling cannot meet strict purity and particle size requirements.
