Kaolin purification and modification processing technology

The processing technology of kaolin varies depending on the nature of the raw ore, product use and product quality requirements. Generally speaking, kaolin processing technologies include: purification and whitening, ultra-fine processing, modification, etc.

1. Kaolin purification

The main minerals of kaolin are kaolinite and halloysite. In addition to kaolinite minerals, they are also often accompanied by clay minerals such as montmorillonite, illite, and pyrophyllite, quartz, feldspar, iron minerals, titanium minerals, etc. Non-clay minerals and organic matter.

In order to produce kaolin products that can meet the needs of various industrial fields, physical methods, chemical methods and high-temperature calcination methods are often used to purify and remove impurities from kaolin. Physical purification methods mainly include hand selection, water separation, flotation, and magnetic separation. Chemical purification and bleaching are mainly used to remove iron-containing minerals from kaolin. The main methods include acid leaching, chlorination, alkali treatment, reduction, oxidation and redox combined methods.

2. Kaolin ultrafine processing

The main methods for ultrafine processing of kaolin are: mechanical crushing method, classification method, intercalation-peeling method and chemical synthesis method. The mechanical crushing method mainly takes advantage of the characteristics of the layered structure of minerals. Under the action of external force, the force between layers is destroyed to achieve the purpose of ultra-fineness, but it consumes a lot of energy. The classification method mainly settles kaolin in liquid to obtain ultrafine kaolin according to Stokes' law, but the cost is high and the output rate is low. The intercalation-flaking method mainly uses the intercalation effect to expand the mineral layers in kaolin, and the bonding force is greatly weakened. After the intercalation object is removed, the original stacked flaky kaolinite will naturally decompose into small flaky kaolinite. , to achieve the purpose of natural peeling. Chemical synthesis methods generally use rock minerals or aluminum-silica gel as raw materials and use hydrothermal methods to obtain ultrafine synthetic kaolinite. It has high purity, good suspension stability, good light scattering properties, and other excellent properties.

3. Kaolin modification

Modification is one of the most important deep processing technologies for non-metallic minerals today. The modification methods of kaolin mainly include acid-base modification, surface modification and intercalation modification. Acid-base modification is mainly for calcined kaolin. According to the different chemical environments of Al and Si during the phase change process, kaolin is calcined and activated at a certain temperature, so that Al and Si can react with acid or alkali to change its acidity. , pore diameter and specific surface area. Surface modification is to use physical, chemical and mechanical methods to treat the surface of kaolin powder to change the physical and chemical properties of its surface, which can effectively improve its whiteness, brightness, surface chemical activity and compatibility with polymers. Intercalation modification mainly refers to inserting some organic molecules directly or indirectly into the layers of kaolinite without destroying the original layered structure of kaolinite.

4. Kaolin process flow

At present, there are two common beneficiation processes for kaolin in industry: dry process and wet process 

The dry process generally includes several processes such as crushing, drying (usually in a rotary dryer), fine grinding and air flotation. This process can remove most of the sand and gravel, and is suitable for processing ores with high whiteness, low sand and gravel content, and suitable particle size distribution. Dry processing has low production costs and is generally suitable for dry areas. The products are usually used as low-cost fillers in industries such as rubber, plastics and papermaking.

The wet process includes several stages such as slurry dispersion, classification, impurity sorting and product processing. The general process is: raw ore → crushing → slurry → sand removal → cyclone classification → peeling → centrifuge classification → magnetic separation (or bleaching) → concentration → filter press → drying → packaging.