A large amount of coal gangue will be produced in the process of coal mining. When the kaolinite content in coal gangue exceeds 80%, it is called coal-measure kaolin. It is an important non-metallic mineral resource unique to China with unique characteristics and broad utilization prospects. Coal-measure kaolin is a precious natural resource and an important non-metallic mineral. It has many properties that can be used, such as fire resistance, electrical insulation, chemical stability, and dispersibility. The developed kaolin can be used in papermaking, rubber, paint, chemical industry, building materials, metallurgy, ceramics, glass, electric porcelain, petroleum and other industries, and is an indispensable mineral raw material in many industrial sectors.

Modification and Application of Coal Series Kaolin

Coal-series kaolin modification methods: According to different uses, the commonly used modification methods include calcination, intercalation/exfoliation, coating modification, acid-base modification and other methods.

Calcination modification: In order to obtain high whiteness and high quality kaolin products from coal series kaolin with black or brown appearance, calcination is one of the most critical steps. Calcined coal-based kaolin has a high whiteness and can be used in paints or white pigments. In addition, calcined coal-based kaolin has the advantages of strong scattering, good plasticity, high activity, good insulation and thermal stability, high porosity and covering rate, and small capacity, so it is used in rubber fillers, plastics, daily cosmetics, pesticides and It is widely used in pharmaceutical products, and also in textile, petroleum, national defense, chemical and other fields.

Intercalation/exfoliation modification: Intercalation/exfoliation refers to the destruction of the interlayer hydrogen bond of kaolin through mechanical physical action, chemical reaction or the combination of the two, expanding the interlayer spacing, and finally achieving the separation between layers. Obtain a method of exfoliating the structural monolayer to increase the activity and specific surface area of kaolin. There are various intercalation methods, but no matter which method is used to intercalate kaolin, it is inseparable from the use of intercalation agent, and it needs to be realized in combination with changes in external mechanical force, microwave, ultrasonic, calcination and other conditions.

Using potassium acetate as the intercalation agent, kaolin and potassium acetate solutions with a mass percent concentration of 5%, 15% and 30% were blended and stirred at a ratio of 1:4 for 2 hours, and then the stirred slurry was put into the grinding and stripping Grind and peel in the barrel for 2 hours, filter and separate, wash with water to remove excess potassium acetate, and finally dry and disperse to prepare kaolin for intercalation and exfoliation. Filling it into the styrene-butadiene rubber composite material helps to improve the mechanical properties of the styrene-butadiene rubber composite material, especially the tensile strength.

Coating modification: Coating modification is divided into two methods: metal oxide and organic coating. The method is simple and easy to operate, and can greatly increase the added value of the kaolin and expand the application field of the kaolin. For example, after surface modification and coating of titanium dioxide, coal-based calcined kaolin has similar functions to titanium dioxide, and is especially suitable for use on high-speed knife coaters due to its higher tinting and hiding power.

Acid-base modification: Acid-base modification can effectively dissolve Al2O3 and other metal oxide components in kaolin, and the leaching of Al2O3 and other components will increase the specific surface area of kaolin. Due to the existence of this characteristic, kaolin is regarded as an important mineral resource for extracting aluminum and has become a substitute for bauxite.

Calcination and Processing Technology of Coal Series Kaolin

The key technology for processing calcined kaolin with coal series kaolin lies in ultra-fine crushing and calcination. At present, the main indicators of raw materials for domestic production of calcined kaolin are: the content of kaolinite is above 97%, and the content of Fe2O3 is not more than 0.5%.

(1) Superfine grinding
Ultrafine grinding is mainly completed by equipment, and the requirements for equipment and technology mainly include: material purity, product particle size (specification, shape, particle size distribution), unit energy consumption, service life of wear-resistant parts, maintenance cost, and product quality. Whether it causes secondary pollution and the function and efficiency of ultra-fine and grading. Vibration mills, impact mills, centrifugal mills, colloid mills, jet mills and stirring mills have been developed successively at home and abroad.
At present, most of the coal-series kaolin production and processing plants that have been built use Raymond mill for dry fine grinding. The grain size of the mill is 325 mesh. Larger plant area. The latest grinding technology uses Hurricane Mill for dry fine grinding, with a particle size of 1250 mesh, which reduces the load of peeling and can also directly produce 1250 mesh dry products. The product plan can be flexibly adjusted according to the actual situation. Aiming at the phenomenon of partial particles occupying and agglomerating after calcination, special dispersing and grading equipment is equipped to ensure the whiteness and particle size of the final product.

(2) Calcination technology
Coal-series kaolin calcining technology currently includes burning first and then grinding and grinding first and then burning. There are pros and cons to both process options. The process of first grinding and then firing can obtain products with higher whiteness, because the micron particle size is more completely calcined, and iron oxide can be whitened by whitening agent in the calcining operation; another advantage is that the hardness of the raw ore is low, and the ultrafine grinding The ball consumption is low; the problem is that the grinding concentration is low and the number of equipment required is large. In addition, after calcination, the fine particles are easy to bond and even sinter, which makes the original qualified particle size coarser. In order to ensure the qualified particle size requirements, it is necessary to carry out ultra-fine grinding and drying, which complicates the process. The process of burning first and then grinding can ensure the qualified particle size, and the process is relatively simple; the disadvantage is that grinding after burning has high hardness and increased ball consumption. %~3%, requiring higher quality ore. At present, high-quality coal-based calcined kaolin mostly adopts the production process of combining dry and wet, grinding first and then firing.

The fuels that can be used for calcination mainly include natural gas, light diesel oil, heavy oil, liquefied petroleum gas, and coal gas. Light diesel oil, heavy oil, and liquefied petroleum gas have high calorific value, but the local supply price is also high; the cost of using gas is low, but the calorific value is also low, the sulfur content is high, and the one-time investment is large. If there is gas produced by coking in coking plants near the proposed project, coke oven gas can be directly used as calcination fuel, which is very clean and convenient.

Market Development Prospect of Coal Measures Kaolin Industry

At present, the application demand of kaolin processing industry generally presents the following characteristics.
(1) The field of downstream application industry and the scope of application continue to expand, and the total demand for kaolin processed products continues to grow.
(2) The coatings industry, especially high-end coatings, will gradually replace refractory materials and become the third largest kaolin consumption industry besides ceramics and papermaking industries.
(3) Refractory materials With the transformation and upgrading of the national economy and the impact of overcapacity in the overall industry, its demand for kaolin is currently in a saturated period.
(4) The demand for kaolin high-end processed products in other industries will continue to grow, mainly referring to cutting-edge material science, special industrial ceramics, national defense and military industry, pesticides, petrochemicals, cosmetics, etc.