Kaolin Purification Technology

The minerals contained in kaolin are mainly divided into clay minerals and non-clay minerals. Among them, clay minerals mainly include kaolinite minerals and a small amount of montmorillonite, mica and chlorite; non-clay minerals mainly include feldspar, quartz and aluminum hydrate, and some iron minerals such as hematite, caltrop Iron ore, limonite, etc., titanium minerals such as rutile, etc., and organic matter such as plant fibers.

According to the different properties of kaolin, its processing technology mainly includes beneficiation and purification of kaolin, ultra-fine pulverization, chemical bleaching, and magnetization roasting.

01  Gravity separation process

Kaolin gravity beneficiation mainly uses the density difference between kaolin and gangue to remove light organic matter and high-density impurities containing iron, titanium and manganese, so as to achieve the purpose of purifying kaolin.

Kaolin gravity separation uses small cone angle cyclone group or centrifuge instead of washing and screening process, which can not only achieve the purpose of washing and grading, but also remove some impurities. However, it is difficult to obtain qualified kaolin products through the gravity separation process. After re-election, methods such as calcination, magnetic separation, and leaching must be used to obtain qualified products.

02  Magnetic separation process

Kaolin magnetic separation is mostly used to remove weak magnetic impurities such as hematite, siderite and rutile in kaolin. Magnetic separation does not use chemicals and does not pollute the environment, so it is widely used in the purification process of non-metallic minerals.

The magnetic separation process solves the problem of development and utilization of low-grade kaolin resources that have no commercial development value due to high iron content. Superconducting magnetic separator can directly process kaolin which contains many impurities. However, it is difficult to obtain high-quality kaolin products by a single magnetic separation process, and other processes such as chemical bleaching are still needed to further reduce the iron content.

03   Flotation process

The flotation process can effectively remove iron, titanium and carbon impurities in kaolin, and realize the recovery and reuse of low-grade kaolin resources such as coal series kaolinite. Kaolin particles are finer and more difficult to float than gangue minerals. Therefore, the kaolin flotation process mostly uses reverse flotation, such as reverse flotation for carbon removal, desulfurization, and iron removal.

Flotation can significantly improve the whiteness of kaolin. The disadvantage is that the added chemical substances will cause higher production costs and environmental pollution.

04  Leaching process

Leaching is a method of selectively dissolving and removing certain impurity components in kaolin by adding leaching chemicals. Such as acid leaching (using hydrochloric acid or sulfuric acid) and microbial leaching.

Compared with other purification processes, the leaching process is simple, which can significantly reduce production costs and effectively develop and utilize low-grade kaolin. However, when microbial leaching is used, strict environmental evaluation and economic benefit evaluation must be carried out.

05  Chemical bleaching process

The chemical bleaching process refers to the method of removing iron ions and their oxides by adding chemical substances. Kaolin chemical bleaching methods include oxidation, reduction and redox methods. Chemical bleaching can greatly improve the whiteness of kaolin products. However, its production cost is relatively high, and it is mostly used for further purification of kaolin concentrate.

The chemicals used in the process, such as sodium metabisulfite, will produce acid waste gas and waste water, which have a great impact on environmental pollution. Therefore, environmental protection and economic rationality should be considered when using chemical bleaching process.

06   Roasting

Roasting is also an important purification process to improve the whiteness of kaolin. Carbon impurities in kaolin can be removed by roasting process. For example, magnetic impurities can be removed by magnetic roasting and magnetic separation, and some metal impurities can be removed by chlorination roasting.

The roasting process can greatly improve the whiteness of kaolin, obtain high-quality kaolin products, realize the utilization of low-grade kaolin resources, and obtain high-quality kaolin products, but this method consumes a lot of energy in the production process and will pollute the environment.

07   Multi-process combination process

It is difficult to obtain high-quality kaolin products by a single beneficiation process, especially low-grade coal-measure kaolin and kaolin with complex components. In the actual production of kaolin, a combination of various beneficiation processes is often used.