The industrial production of modified kaolin is a systematic process that combines mineral purification, structural activation and targeted surface modification, which can be divided into the following core stages:
1.Raw Material Pretreatment
High-quality raw kaolin (usually coal-series or soft sedimentary kaolin) first undergoes crushing, wet grinding and delamination. The particle size is controlled to make the content of particles below 2 μm reach more than 90%, so as to fully expose the layered structure of kaolinite and create conditions for subsequent modification. This step also removes impurities such as quartz, feldspar and organic carbon through sand removal and classification, ensuring the whiteness and purity of the base material.
2.Calcination Activation
The pretreated kaolin is sent to an indirectly heated rotary kiln for controlled calcination. At 450–950 °C, the hydroxyl groups in kaolin are removed to form metakaolin; when the temperature rises to 925–1050 °C, it transforms into amorphous silicon-aluminum spinel. This process partially destroys the ordered crystal structure of kaolin, significantly increases its specific surface area and surface activity, and lays a foundation for efficient grafting of modifiers.
3.Targeted Modification Treatment
According to different application requirements, the activated kaolin is modified by corresponding processes:
Mechanochemical Modification: The modifier and kaolin are fully mixed in a high-energy ball mill. The mechanical force further reduces the particle size, destroys the agglomeration structure, and makes the modifier evenly coated on the surface of kaolin particles, realizing hydrophobic modification.
Surface Chemical Modification: In the wet slurry system, silane coupling agent, titanate or other modifiers are added. Through heating and stirring, the active groups on the modifier react with the hydroxyl groups on the kaolin surface, so that the kaolin surface is grafted with carbon-carbon double bonds, epoxy groups and other functional groups, greatly improving its compatibility with organic polymers.
Intercalation Modification: Using small molecular substances such as urea as intercalating agents, the interlayer distance of kaolin is expanded to prepare exfoliated nano-modified kaolin, which has better dispersion and reinforcement performance.
4.Post-Processing and Finishing
The modified kaolin slurry is filtered and dehydrated to obtain a filter cake, which is then dried, deagglomerated and air-classified. Finally, the finished modified kaolin products with different particle sizes, activity indexes and surface properties are obtained, which can be directly applied in rubber, coatings, 3D printing materials, environmental adsorbents and other fields.