At present, the preparation methods of ultrafine kaolin include mechanical pulverization method, intercalation method, chemical synthesis method, etc. Among them, mechanical pulverization method is the most extensive.
1. Mechanical crushing method
The process of preparing ultrafine kaolin by mechanical pulverization method is simple and high in efficiency. It is one of the more commonly used methods. The prepared ultrafine kaolin has been applied in many industries, and it can be divided into dry method and wet method according to the processing method.
(1) Kaolin dry superfine crushing
The dry method is mostly used for ultrafine crushing of hard kaolin or kaolinite, especially for directly processing kaolinite into ultrafine powder that meets user requirements. At present, the fineness of products that can be achieved by domestic dry production is generally d90≤10μm, that is, the final product is about 1250 mesh.
Dry ultra-fine crushing equipment mostly adopts jet mill, cyclone self-mill, high-speed mechanical impact type ultra-fine powder mill, vibration mill and vertical mill. Multi-stage ultra-fine crushing can be carried out by using an impact crusher and a jet mill (jet mill) in series to prepare ultra-fine kaolin.
In order to control the particle size distribution of products, especially the content of the largest particles, it is often necessary to configure fine classification equipment. Currently, turbine-type air centrifugal classifiers, such as LHB type, ATP type, MS and MSS dry centrifugal classifiers, are generally configured.
(2) Wet superfine crushing of kaolin
Wet superfine crushing is mostly used for soft and sandy kaolin clay after sand and impurity removal, especially for processing paint grade kaolin products with d80≤2μm or d90≤2μm, and it is also industrial hard kaolin Or the ultra-fine crushing method that must be used for processing kaolin products with d80≤2μm or d90≤2μm.
Wet grinding is based on the relative motion of the grinding media to produce shear, impact and abrasive effects on the kaolin particles, so that they are peeled into thin flaky particles along the layers. Commonly used equipment is grinding and peeling machine, stirring ball mill, sand mill and so on.
2. Intercalation-stripping method
Intercalation method is currently the most promising and most effective method for preparing nano-level kaolin. The main chemical component of kaolin is the structural unit of kaolinite, which is formed by the hydrogen bond between the hydroxyl group of a layer of aluminum oxide octahedron and the oxygen atom of a layer of silicon oxytetrahedron. key. It is inserted between its layers to increase its layer spacing to make it peel off. This method is also called interlayer-stripping method.
The chemical additives commonly used in the intercalation method include potassium acetate, dimethyl sulfoxide, urea, formamide, hydrazine hydrate and its extensions. The intercalation compound is heated, ultrasonically treated, washed with water or microwave combined with the action of chemical additives, and a strong physicochemical reaction occurs, resulting in the destruction of the kaolin interlayer force or a certain degree of weakening, and finally through grinding , Washing, drying and other technologies to obtain nano-kaolin products.
3. Chemical synthesis
The chemical synthesis method is to obtain the ultra-fine synthetic kaolin by using a series of methods by using the alkali dissolution product of sodium bauxite and sodium metaaluminate and acidified sodium silicate sol as the raw material. Its high purity, suspension stability, light scattering, and other properties are all excellent, but its synthesis cost is higher.