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Influence of calcined kaolin What is the key to processing technology?

Release time:

2024-02-23 10:16

The main purposes of kaolin calcination are: (1) to remove organic carbon and other impurity minerals to improve the whiteness; (2) Remove the water and hydroxyl contained in kaolin to improve the void volume and chemical reaction activity of calcined products, improve physical and chemical properties, meet a variety of application needs, and lay the foundation for further development of new application fields.

The main factors affecting the calcination of kaolin are: feed size, calcination temperature, atmosphere, time and process equipment.

 

 

1. Feed particle size

The granularity of kaolin into kiln has been debated for a long time, mainly related to the process of calcining before stripping or stripping before calcining.

If no wet stripping is done before calcination, the minimum particle size of kaolin dry grinding is -10μm≥90%. If the particle size is larger, the specific surface area of the particles is small, and the contact area with oxygen is small, which is not conducive to the rapid combustion of carbon, and the constant temperature calcination time is longer, and the carbon inside the particles can not be fully in contact with oxygen, it is difficult to oxidize and remove, and the product will appear black heart phenomenon. After calcination and then peeling, due to the existence of sandwich, the whiteness of the product is greatly affected.

If the first strip (-10μm≥90%) after calcination, because the powder particles are prone to agglomeration during high temperature calcination.

Many scholars have done a lot of experiments in this regard, and finally reached a consensus that the first strip and then into the kiln, after calcining, and then the second depolymerization strip. At present, the high quality coal measure burning kaolin mostly adopts the production technology of dry and wet combination, grinding first and then burning.

2. Calcination temperature

Due to the different calcination temperature, chemical reaction, crystal structure transformation, the physical and chemical properties and application fields of calcined kaolin are also different.

Many scholars have done a lot of work on the influence of calcination temperature on the physical and chemical properties of products, and it is concluded that the best calcination temperature of calcined kaolin applied to paper coating grade is roughly in the range of 950-1000℃, and the activity and whiteness of products meet the ideal requirements.

Preparation of molecular sieve, active soil, used in plastics, rubber industry as functional fillers of kaolin, calcination temperature is controlled in the range of about 850-950℃.

Kaolin calcined at high temperature can be used as clinker and ceramic materials for refractory materials.

It is worth mentioning that for kaolin raw materials from different places, the optimal calcination temperature will be different.

 

 

3. Calcination atmosphere

The calcination atmosphere mainly refers to the oxidation or reduction atmosphere maintained in the furnace.

Although the oxidation atmosphere is conducive to the oxidation of organic matter, it is not conducive to the effect of calcination on staining impurities such as Fe2O3 and TiO2. The reducing atmosphere in the kiln can be maintained by adding reducing agents, controlling the amount of O2 or the appropriate amount of CO2.

4. Calcination time

Calcination time has great influence on the activity and whiteness of kaolin. In general, the longer the calcination time, the more adequate the reaction, the higher the whiteness of the product.

In actual production, the best combination of calcination time and production efficiency as well as product performance should be sought. Due to the removal of hydroxyl and carbon, the loss of calcined kaolin in coal measures is related to raw materials, which is generally about 15%. The relative content of the main chemical components SiO2 and Al2O3 has increased, and the content of other components has not changed much.

5, calcining equipment

Calcination equipment is also critical to the production of kaolin. In the United States and the United Kingdom and other kaolin production countries, the general use of large dynamic shaft kiln and flame-proof rotary kiln production of calcined kaolin, the raw material is generally selected after soft kaolin, product whiteness 85%-95%.

There are few high-quality soft kaolin resources in China, but there is a large amount of high-quality kaolin associated with coal measures. Therefore, most calcined kaolin in China uses coal measure kaolin as raw material.

The main production equipment is flame-proof rotary kiln (with diesel, gas or natural gas or electric heating), shaft kiln, tunnel kiln and shuttle kiln. Among them, the flame-proof rotary kiln can conveniently adjust the atmosphere, good temperature control, uniform heating of the material, high whiteness of the product and stable quality, simple operation, and has become the main equipment for calcination of coal measures kaolin in China.

kaolin,calcined kaolin,processing technology,Feed particle size,Calcination temperature,Calcination atmosphere

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