Kaolin is a non-metallic mineral. It is a clay and clay rock mainly composed of kaolinite clay minerals, with good physical and chemical properties such as plasticity and refractoriness. Because it is white and fine, it is also called dolomite. Its pure kaolin is white, fine, soft and soil-like, with good physical and chemical properties such as plasticity and refractoriness. Its mineral composition is mainly composed of kaolinite, halloysite, hydromica, illite, montmorillonite, quartz, feldspar and other minerals.

Kaolin is known as the "universal stone", and this title comes from the wide application and importance of kaolin. It has a wide range of uses, mainly used in papermaking, ceramics and refractory materials, followed by coatings, rubber fillers, enamel glazes and white cement raw materials, and a small amount is used in plastics, paints, pigments, grinding wheels, pencils, daily cosmetics, soaps, pesticides, medicines, textiles, petroleum, chemicals, building materials, national defense and other industrial sectors.

Building materials

Kaolin is widely used in cement-based materials. The metakaolin obtained by calcining kaolin at an appropriate temperature and ultra-fine grinding is considered to be an admixture in the new generation of cement concrete. They have a significant effect on improving and reducing the workability, strength and durability of cement-based materials. At the same time, they also have a good inhibitory effect on the self-shrinkage and shedding phenomena commonly seen in high-performance cement-based materials.

Ceramic industry

Kaolin has been used in the ceramic industry for a long time and in large quantities, usually accounting for 20-30%. Kaolin can increase the content of Al2O3 in ceramics and make the formation process of mullite easier, thereby improving the sintering strength and stability of ceramics. When firing ceramics, kaolin decomposes mullite to form a green body framework. This process makes the ceramic green body less likely to deform and change in nature, while widening the firing temperature range and improving the whiteness of the ceramic. At the same time, the plasticity, adhesion, suspension, and bonding properties of kaolin itself improve the formability of porcelain clay and glaze, which is more conducive to the processing of turning, grouting, and ceramic forming.

Refractory materials

Industrial kaolin has good refractory properties and is often used to produce refractory materials. Its products can withstand loads at high temperatures without deformation. According to kaolin with kaolinite as the main component, as well as bentonite and bauxite, according to their high temperature resistant uses, they are collectively referred to as refractory clay. Some colored kaolin cannot be used for ceramics and papermaking, but it is a good raw material for refractory materials. There are two main types of kaolin used as refractory products: refractory bricks and silicon-aluminum fiber cotton. The former has a refractoriness of not less than 1730℃ and is made into refractory bricks of various sizes and shapes according to needs. The latter is a lightweight refractory insulation material, which is kaolin roasted at 1000-1100℃, and then the ore is melted in a 2000℃ electric arc furnace and blown into cotton under high-speed airflow.

Plastics

Kaolin is mainly used as a filler in the plastics industry. Since calcined kaolin has a large adsorption area and activity, it can be used in plastics to adsorb the conductive ions in the plastics, thereby improving the performance of the plastics, making the plastics smoother, more beautiful, and more resistant to chemical corrosion. In the plastics industry, calcined kaolin can replace titanium dioxide as a pigment. Calcined kaolin replaces more than 20% of titanium dioxide in plastics, and the optical properties of the plastics are not significantly reduced. Adding kaolin to plastic film can also reduce the impact of infrared rays. The insulation strength of plastics will be improved to a certain extent after adding calcined kaolin. Modified kaolin can also be used in PE agricultural film, which can increase the temperature in the greenhouse at night, make the light more uniform, and promote the thermal insulation effect of the agricultural film.

Paint industry

Kaolin has long been used as a filler for coatings and paints due to its white color, low price, good fluidity, stable chemical properties, and large surface cation exchange capacity. Kaolin can be used to improve the brushability of coatings, the storage stability of coating systems, the mechanical properties of coatings such as moisture absorption resistance and impact resistance, and the resistance of pigments to floating and blooming. With the development of production, the requirements for the performance and durability of coatings are becoming increasingly stringent, such as the requirement to prepare low-VOC, high-solid coatings, thinner and flawless smooth and bright coatings. At this time, kaolin is needed as an additive. Kaolin can adapt to almost all coating systems, from primer to topcoat, all solid components, coating thickness and gloss.

Rubber industry

Filling kaolin into the colloidal mixture of rubber can enhance the chemical stability, wear resistance and mechanical strength of rubber, prolong the hardening time, and improve the rheology, mixing and vulcanization of rubber, increase the viscosity of unvulcanized products, and prevent them from sinking, collapsing, sagging, deformation, flat tubes, etc. The waterproofness, permeability, fire resistance, chemical activity and other properties of kaolin rubber products have also been greatly improved. At the same time, kaolin can also be used as a filler in rubber, which can significantly reduce costs without affecting the performance of rubber.

Cable industry

The production of high-insulation cables requires the addition of excessive electrical performance modifiers. As the only product that can be made into electrical performance modifiers, kaolin has a bright future. Modified calcined kaolin needs to be added to plastic cables and insulating materials that require high electrical insulation performance. Kaolin has extremely high resistivity after calcination at an appropriate temperature. The porosity of kaolin at different calcination temperatures is different. The voids have a certain adsorption effect on some more active harmful components in cable materials, which can improve the insulation of cables; calcined kaolin is then surface modified to improve its dispersibility in polymer materials and enhance the performance of products. It can produce a good bonding interface between organic polymer materials-modifiers-calcined kaolin, so that calcined kaolin can be evenly dispersed in cables and play a better bridge role.

Environmentally friendly materials

Environmentally friendly new materials are also one of the applications of kaolin. Kaolin can be used as a synthetic molecular sieve and polyaluminum chloride. In addition, due to the high aluminum content in kaolin, it has become the main raw material for the production of polyaluminium chloride. Polyaluminium chloride is a new type of purifier with a simple process flow, good flocculation effect, low price, relatively low residual aluminum content in the water after treatment, and can generate high-density floccules, fast sedimentation rate, low corrosion to equipment, etc. It has been widely used in the treatment of drinking water and industrial wastewater. The use of kaolin to produce polyaluminium chloride can improve the quality of the corresponding products, while also reducing production costs, with little environmental pollution, and good economic and social benefits. Modified kaolin also has relatively high matrix activity, strong resistance to heavy metal pollution, good catalytic activity and selective adsorption performance. Therefore, modified kaolin has become an important filler in the preparation of various catalysts.

Papermaking industry

The amount of kaolin used in the papermaking industry far exceeds that of other industries. Kaolinite clay has a small particle size, and after peeling, it has a good scale and flake morphology, a large ratio of flake diameter to thickness, and stable chemical properties. Therefore, it is used as a paper filler and paper coating to improve the gloss of paper, fill the gaps between paper fibers, and increase opacity. As a filler, it can improve the performance of paper while reducing costs; as a coating material, it can improve the permeability and tolerance of paper to ink and the appearance of paper. The main requirements for kaolinite in papermaking are particle size and impurity content, requiring a particle size of less than 2μm and a whiteness of more than 86%.