The iron content of kaolin ore produced in China is generally high and the particle size is relatively coarse. There are only a few high-quality kaolin mining areas with certain reserves. Driven by the continuous development of high-grade kaolin market demand and the gradual depletion of high-quality kaolin resources in China, China’s kaolin processing technology has developed rapidly in recent years.
1. Iron removal technology
Whiteness is the most important indicator of kaolin products. The higher the iron content of mineral products, the lower the firing whiteness. The development of iron removal technology to improve the whiteness of kaolin products has become an inevitable development trend in the industry. Iron removal technologies include magnetic separation, chemical bleaching, flotation, oxidation, and microorganisms. Among them, the magnetic separation method is the main development direction of iron removal technology. Iron exists in various forms in kaolin. The forms of iron in kaolin ore in different mining areas are quite different. In the actual iron removal process, it is necessary to focus on different situations. Only by formulating a targeted iron removal program can the iron removal effect be improved. Magnetic separation and iron removal have developed technologies such as high gradient magnetic separation and superconducting magnetic separation.
Main iron removal and purification technologies
2. Grinding and peeling technology
Particle size is one of the important performance indicators of kaolin products, which directly affects the application performance of products. Grinding and stripping technology is a commonly used technology in ultra-fine grinding of non-metallic minerals. The principle of kaolin grinding and stripping method is to use the relative movement of grinding media in the pulp to produce shearing, extrusion, impact and grinding and stripping. The stack of kaolins peeled off and tended to separate the sheets individually. The particle size of kaolin in my country is generally coarse, and as an additive for ceramic glazes, paper coatings, and chemical coatings, the particle size requirements are relatively high. The development of kaolin grinding and stripping technology is an important means to improve the value of kaolin products, and the use of grinding and stripping technology in kaolin processing has become more and more extensive.
3. Mineral blending technology
The stability of kaolin product indicators is one of the key indicators to measure product quality. Due to various natural factors, the quality of kaolin mines in my country varies greatly in different mining areas or in different layers of the same mining area. The indicators of kaolin products fluctuate greatly, while the downstream industries High requirements for the quality and stability of kaolin products, so mastering ore blending technology has become a necessary condition for the development of kaolin enterprises. On the one hand, ore blending technology can ensure the stability of kaolin product quality, on the other hand, it can increase the added value of products and improve the economic benefits of enterprises . Ore blending is widely used in kaolin enterprises with a certain production scale in my country.
4. Calcination technology
There are few large and high-quality deposits in China’s kaolin resources. The northern coal measure kaolin has the largest reserves, but it cannot be directly used for downstream use and needs to be calcined to improve its purity. The so-called calcination refers to a thermal processing process in which the target component minerals of the mineral raw materials undergo physical and chemical changes, which are carried out in a suitable atmosphere and at a temperature lower than the melting point of the mineral raw materials. The changes that often occur in this process are the removal of carbon (in whole or in part), the removal of colloidal water and the crystal water and compound water in the mineral crystal lattice, so that the minerals are pyrolyzed into one or several minerals with simpler compositions. Finally, the properties such as product whiteness, porosity and activity are improved and optimized.
During the heating process, kaolin will undergo physical and chemical changes such as dehydration, decomposition, and precipitation of new substances, which is relatively complicated. It is generally believed that the heating process of kaolin mainly includes two stages: the dehydration stage and the transformation stage of the dehydrated product.
Kaolin calcination mechanism
Different calcination conditions have great influence on the quality of calcined kaolin products, especially for paper coating grade kaolin. The key influencing factors are calcination temperature, constant temperature time, heating rate, raw material particle size, calcination process, calcination aids and calcination equipment. According to the shape of kaolin material in the calcination process, its calcination process is divided into: forming calcination, powder static calcination, powder dynamic calcination and other methods.
Summary
With the continuous deepening of kaolin research and the development of the demand structure of downstream industries to the mid-to-high end, the market demand for high-quality kaolin is growing faster than the overall market growth, which intensifies the structural contradiction between supply and demand in China’s kaolin market. In order to adapt to the development trend of the kaolin industry and combine the characteristics of China’s kaolin resource endowment, China’s dominant kaolin enterprises need to continuously carry out research and industrial application of deep processing technologies such as iron removal, grinding and stripping, and ore blending, so as to improve the whiteness, fineness, Plasticity and other physical and chemical indicators to improve product quality stability.