As a non-metallic mineral, kaolin is a kind of clay and clay rock mainly composed of Kaolinite group clay minerals. Due to its white and delicate appearance, it is also known as Baiyun soil. The pure kaolin is white, delicate and Mollisol like, with good plasticity, fire resistance and other physical and chemical properties.

In recent years, with the increasing attention paid to kaolin, many problems have also emerged that require further consideration and resolution within the industry.

Fine purification

Kaolin is mainly used as a clay mineral for ceramics, papermaking, and chemical fillers, requiring high whiteness and brightness. However, natural minerals produced in nature often contain some coloring impurities that affect their natural whiteness. Conventional beneficiation methods are often ineffective due to the extremely fine particle size of minerals and the close coexistence of minerals and impurities. Therefore, purification treatment of ores is commonly carried out both domestically and internationally.

Oxidation-reduction bleaching purification

Harmful coloring impurities in kaolin minerals are mainly organic matter (including carbon, graphite, etc.) and minerals containing iron, titanium, manganese, etc., such as Pyrite, Limonite, Hematite, Anatase, etc. Due to the easy removal of organic matter through methods such as calcination, the above-mentioned metal oxides have become the main treatment targets for improving mineral whiteness.

By using the method of strong acid dissolution, most of the above-mentioned iron and titanium compounds can be removed. However, strong acids (such as hydrochloric acid and sulfuric acid) not only dissolve iron oxide and titanium oxide, but also alumina, which may damage the lattice structure of clay minerals such as kaolin. Therefore, the oxidation-reduction bleaching method plays an important role in the bleaching and purification of clay minerals.

The commonly used bleaching methods currently include oxidation method, reduction method, and combined oxidation reduction method, among which reduction method is the most widely used.

High temperature calcination purification

In coal based kaolin, due to the presence of carbon and organic matter, it is often gray black in color. For secondary accumulation metamorphic kaolin, it is also often contaminated by other chromogenic organic substances. Using chemical oxidation method, although it can bleach, the simplest, most effective, and pollution-free method is to calcine it.

Calcination not only removes organic pollution, improves its purity and whiteness, but also serves as a specialized treatment process to improve the properties of kaolin.

Microprocessing

In order to develop deep processing and products of non-metallic minerals, many countries have vigorously studied micro crushing and ultrafine crushing technology equipment in recent years.

It mainly includes two categories: mechanical and pneumatic impact crushers. They mostly belong to micro crushing equipment, although for brittle materials with lower hardness, they can also play a role in micro crushing to some extent; Or for certain materials that exist in the form of aggregates or agglomerates, they can also have a certain degree of ultrafine grinding effect; However, the product fineness, particle size distribution, product purity, etc. produced by these equipment are often difficult to meet the requirements of industrial application departments.

As an ultra-fine grinding equipment, the air flow mill has shown excellent performance in terms of fineness, particle size distribution, purity, etc. However, there is still a significant gap in the design and manufacturing level of airflow crushers in China compared to developed countries, and mechanical crushers are still the main equipment for powder processing.

Mechanical ultrafine crushing

Mechanical ultrafine crushing equipment relies on various high-speed rotating crushing bodies, such as teeth on a rotating toothed disc, rotating crushing hammer heads, and blades on a crushing impeller, to collide with coarse ore particles dispersed on the walls of the crushing chamber due to centrifugal force, or to give these ore particles a linear velocity, causing impact collisions between particles. This type of crusher includes vibration mill, stirring mill, suspended roller mill (Raymond mill), tower mill, high-speed mill, colloid mill, centrifugal mill, extrusion mill, etc.

Airflow ultrafine crushing

Air flow mill is a widely used and efficient ultrafine grinding equipment, which uses high-pressure air flow (compressed air or Superheated steam) to make materials subject to impact (collision), friction and shearing.

In addition to the fine particle size of the product, the pneumatic comminution product also has the characteristics of narrow particle size distribution, smooth particle surface, complete shape, high purity, high activity, good dispersion, etc. Therefore, as an advanced ultra-fine crushing equipment, the airflow crusher is widely used in the ultra-fine crushing processing of non-metallic minerals and chemical raw materials.

Modification

The modification of clay minerals is an important form of deep processing of clay minerals. It is to select appropriate processing methods according to the needs of industrial applications, purposefully improve the physical and chemical properties of minerals, in order to enhance their use value or explore new application fields. The modification of bentonite is a type of modification, and the modification of clay minerals mainly includes chemical modification and heat treatment modification. For kaolin, heat treatment modification is more important.