The performance of adsorption and by bleaching clay has large surface area, high, from bentonite by activating (acidification) made after processing. Bleaching clay world market sales of about 860000 t/a, of which 70% ~ 80% for edible oils and fats industry. The development of bleaching clay by effects of edible oil industry development the biggest.
Clay is mainly composed of aluminous rocks, such as feldspar, pegmatite granite, porphyry, gneiss through long-term weathering, and often through the water transport and deposition, is a variety of fine mineral mixed body, its main chemical composition is SiO2, Al2O3 and crystal water. With the geological formation conditions are different, also contain a small amount of alkali metal oxide, alkaline earth metal oxide and metal oxides.
More types of main minerals in clay, kaolin clay can be divided into Tu, illite and smectite clay and clay. According to the production conditions, the clay can be divided into primary clay (Primary clay) and secondary (Secondary clay), a native of clay is feldspar weathering generated kaolin and other aqueous silicate minerals, quartz and other debris, not completely weathered residual in situ, and soluble salts are dissolved; secondary clay is composed of primary clay transfer to other places again crystalline clay in the natural dynamic conditions. According to the plasticity of the clay can be divided into soft clay (high plasticity clay), semi soft clay (plasticity clay) and hard clay (low plasticity clay), soft clay are secondary clay, because of its fine particle size, large dispersion, the plasticity; the hard clay the diagenesis, the free water is not easy to enter and the lack of leaching dispersion, poor plasticity. Use of refractory book called clay, it is divided according to the clay image, and the corresponding: ceramic clay, bleaching clay, paper clay and cement clay.
The crystal structure and crystal chemistry characteristics determine the nature of some of their. The ion exchange. Some characteristics of cation and anion adsorption and keep the exchange state. General cation is Ca2+, Mg2+, H+, K+, (NH4) +, Na+, exchangeable anion is common (SO4) 2-, Cl-, (PO4) 3-, (NO3) -. Kaolinite cation exchange capacity was lowest, 5 to 15 mEq /100 g; cation exchange capacity of montmorillonite, vermiculite, 100 to 150 mEq /100 G. The cation exchange is the cause of the broken bond and lattice isomorphous substitution caused by unsaturated charge need to have balanced by adsorption of cationic. Anion exchange is the metasomatism lattice exposed hydroxyl ions. The characteristics of the clay water system. The presence of clay minerals in the water to absorb water, interlayer water and structural water in the form of. Structure of water losing only in the destruction of high temperature structure, but the adsorbed water, interlayer water and the structure of sepiolite porous zeolite in water is low, the low temperature (100 ～ 150 ℃) after heating can emerge, at the same time as the smectite mineral water can also be water recovery, this is an important the characteristics of. The clay minerals and the role of water swelling, dispersing and condensation characteristics, viscosity, thixotropy and plasticity is widely used in the industry. The reaction characteristics of the clay minerals and organic matter. Some clay minerals and organic reaction for the formation of organic complexes, improved its performance, expanded the scope of application, and also can be used as a basis for analysis and identification of minerals. Such as montmorillonite in exchangeable calcium or sodium is organic ion replacement after the formation of organic complexes, which increases the distance between layers, from the transformation of the original hydrophilic oleophobic as dear oil hydrophobic, the complex can be prepared by grease, paint additives, anti settling agent and petrochemical products. Other such as vermiculite, kaolinite, halloysite etc. can also form complexes with organic matter. In addition, clay mineral Lattice Ion Replacement and interlayer water changes often affect the change of optical properties. Iron, magnesium ion replacement eight octahedral smectite mineral in aluminum, lose or interlayer water molecules, the refractive index increases and birefringence.