Purification of kaolins by selective dispersion and flocculation

To fulfill the increasingly higher requirements on the quality of kaolins from industries, the purification of kaolins has become more and more important. Kaolins from different mines were studied with the aim to remove the various impurities. The mineralogical studies on the kaolins indicated that kaolinite and the major gangue minerals in the ore were all very fine. Therefore, it was difficult to separate kaolinite from the gangue minerals by conventional mineral processing techniques, such as gravity concentration, magnetic separation and flotation. Techniques for fine particles processing, i. e. selective dispersion and flocculation were tried to purify the kaolins. The experiments were first carried out with pure minerals of kaolinite and the gangue minerals to study the dispersion and flocculation characteristics of the different mineral suspensions under various conditions. The key factors affecting the dispersion and flocculation of the minerals in water were the pH of the suspension, the type and dosage of the reagents, and the strength and time of agitation. These factors were adjusted to separate kaolinite from the gangue minerals. Satisfactory results were obtained with kaolin ores with different impurities from different mines. The quality of the kaolins was significantly improved with the impurities reduced to the level according with the specification set by the industries. The principles of the separation of kaolinite from the gangue minerals by selective dispersion and flocculation were discussed.