Kaolin is a soft, white clay mineral primarily composed of kaolinite, widely used in industries like ceramics, paper, paint, rubber, and cosmetics. To process kaolin into a fine powder suitable for these applications, it undergoes crushing and grinding stages. Here’s an overview of the process:
1. Crushing Kaolin
– Primary Crushing: Raw kaolin ore (often mined in lumps) is first crushed using a jaw crusher or hammer crusher to reduce the particle size to around 5–20 mm.
– Secondary Crushing: Further size reduction may be done with a cone crusher or impact crusher to achieve smaller particles (~1–5 mm).
2. Grinding Kaolin
After crushing, kaolin is ground into fine powder (typically <45 µm or even sub-micron for high-value applications). Common grinding methods include:
# (a) Dry Grinding
– Ball Mill: A rotating drum with steel balls crushes and grinds kaolin into fine powder.
– Raymond Mill (Roller Mill): Uses rollers to grind dried kaolin; suitable for medium-fine powders (80–400 mesh).
– Jet Mill (Air Classifier Mill): Uses high-speed air streams for ultrafine grinding (D97 < 10 µm), ideal for high-purity applications.
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# (b) Wet Grinding
– Used when ultra-fine particles (<2 µm) are needed (e.g., for paper coating).
– Involves mixing kaolin with water and dispersants before grinding in:
– Attrition Mills (for delamination and refining).
– Bead Mills (for nanoparticles).
– Followed by dewatering (filter pressing) and drying (spray drying).
3. Classification & Purification
– After grinding, classifiers (air classifiers or hydrocyclones) separate particles by size.
– Impurities like quartz or iron are removed via magnetic separation or flotation.
4. Surface Modification (Optional)
– For specialty applications, kaolin may undergo surface treatment (e.g., silane coupling agents for polymer composites).
Key Considerations
– Moisture Control: Dry grinding requires pre-drying to <1% moisture.
– Energy Efficiency: Wet grinding consumes less energy for ultrafine particles but requires drying.
– Contamination Prevention: Use ceramic or lined mills to avoid iron contamination.