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Fine processing technology of kaolin

Fine processing technology of kaolin

  • August 26,2020.

Fine processing technology of kaolin

Kaolin, also called china clay, soft white clay that is an essential ingredient in the manufacture of china and porcelain and is widely used in the making of paper, rubber, paint, and many other products. Kaolin is named after the hill in China (Kao-ling) from which it was mined for centuries.

Approximately 40 percent of the kaolin produced is used in the filling and coating of paper. Kaolin is used extensively in the ceramic industry, where its high fusion temperature and white burning characteristics makes it particularly suitable for the manufacture of whiteware (china), porcelain, and refractories. Substantial tonnages of kaolin are used for filling rubber to improve its mechanical strength and resistance to abrasion. Kaolin is also used as an extender and flattening agent in paints. It is frequently used in adhesives for paper to control the penetration into the paper. Kaolin is an important ingredient in ink, organic plastics, some cosmetics, and many other products where its very fine particle size, whiteness, chemical inertness, and absorption properties give it particular value.

The processing technology of kaolin varies with the nature of raw ore, product use and product quality requirements. In general, the processing technology of kaolin includes purification and whitening, ultra-fine processing, modification and so on.

1. Kaolin purification and whitening
In its natural state kaolin is a white, soft powder consisting principally of the mineral kaolinite. The main minerals of kaolin are kaolinite and hydrous kaolinite. In addition to kaolinite minerals, clay minerals such as montmorillonite, illite and pyrophyllite are often associated with kaolinite, as well as non-clay minerals such as quartz, feldspar, iron ore and titanium minerals and organic matters. In order to produce kaolin products that can meet the needs of various industrial fields, physical method, chemical method and high temperature calcining method are often used to purify kaolin impurities.

2. Ultra-fine processing of kaolin

The main methods of ultra-fine processing of kaolin are: mechanical comminution method, classification method, intercalation-stripping method and chemical synthesis method.

2.1 Mechanical comminution method mainly takes advantage of the characteristics of mineral layered structure. Under the action of external forces, the force between layers is destroyed, so as to achieve the purpose of ultra-fineness, but the energy consumption is relatively large.

2.2 The classification method is mainly based on Stokes' Rule to settle kaolin in liquid to obtain ultra-fine kaolin, but the cost is high and output is low.

2.3 The intercalation-stripping method mainly uses intercalation to make the mineral layers in kaolin expand and the bonding force is greatly weakened. After removing the intercalation object, the original laminated kaolin will naturally decompose into small flake kaolinite to achieve the purpose of natural stripping.

2.4 Chemical synthesis method generally uses rock minerals or silica-alumina gel as raw materials to obtain ultra-fine synthetic kaolinite by hydrothermal method. It has high purity, good suspension stability, good light scattering, and other excellent properties.

The particle size is one of the important indexes to measure the quality of kaolin products, and the particle size and distribution of kaolin are also important factors to influence its viscosity. At present, the research on ultra-fine kaolin mainly focuses on the intercalation -stripping method, use the high-purity soft kaolin as raw material and adopt the intercalation -stripping method to prepare the nanometer kaolinite wafers with an average diameter of 300 ~ 500nm, and an average thickness of 20 ~ 50nm, which are suitable for making various rubber products as reinforcer.

Although the particle size of kaolin can reach the nanoscale through processing, the immaturity of viscosity reduction technology is still the main reason for the lack of kaolin for coating of papermaking in China. Liu Pan et al. found that relatively concentrated particle size distribution can effectively reduce the viscosity of slurry.

Kaolin mineral nanomaterials can not only reduce the viscosity of slurry, but also have good surface effect and small-scale effect, which is an important research direction to expand the application scope of kaolin.

3. Modification of kaolin
Modification is one of the most important deep processing technologies for nonmetallic ore today. Due to the difference of mineral forming conditions and mining and processing methods of kaolin, the physical and chemical properties are very different, which limits its application range. Therefore, the research and development of different modification methods is an important means to expand the application range and effect of kaolin. The modification methods of kaolin mainly include acid-base modification, surface modification and intercalation modification.

4. Process flow of kaolin
At present, there are two common processing techniques of kaolin in industry: dry process and wet process.

4.1 Dry process generally include 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 those ores with high whiteness, low content of sand and gravel, and suitable particle size distribution. Dry process production cost is low, generally suitable for dry areas, the products are usually used as the low cost fillers in rubber, plastic and paper industry.

4.2 The wet process includes several stages such as slurry dispersion, classification, impurity sorting and product treatment.

The general process is as follows:

4.3 Coal series (hard) kaolin is a unique kaolin resource in China. Currently, it is basically processed by ultra-fine before calcination or ultra-fine after calcination.

The general process of superfine first and then calcination is as follows:

The general process of calcinationg first and then superfine is as follows:

Taking China Kaolin Company as an example, kaolin production process can be divided into two parts: mining and ore dressing.

Mining process:

Ore dressing process:

If it wants to produce powder kaolin with low moisture content and high grade, it has to go through grinding and drying process. China is rich in kaolin resources, but there are not many natural flaky kaolin resources that are really suitable for paper pigments, so it is particularly important to strengthen the processing technology of raw ore. Although the deep processing technology and products of kaolin industry in China have developed rapidly in recent years, the overall technical level of kaolin industry still lags far behind that of foreign developed countries, mainly reflected in backward mining and ore dressing methods and low mechanization degree, backward processing technology and low added value of products, the physical and chemical properties of kaolin are not well studied, etc. Therefore, our country will strengthen the research and development of new mining, beneficiation technology and technical skills, improve the quality of kaolin concentrate, improve the market competitiveness, strengthen basic research of application, develop new products with high added value, broaden the application range in high-tech fields, etc.

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