Kaolin, theoretical chemical formula: Al 2 [(OH) 4 /Si 2 O 5 ] , It is a non-metallic mineral , a kind of clay and clay rock mainly composed of kaolinite clay minerals . Because it is white and delicate, it is also called dolomitic soil . It is named after Gaoling Village , Jingdezhen , Jiangxi Province. Its pure kaolin is white, delicate, soft and earthy, and has good physical and chemical properties such as plasticity and fire resistance. Its mineral composition is mainly composed of kaolinite , halloysite , hydromica , illite, montmorillonite , quartz, feldspar and other minerals. Kaolin is widely used, mainly used in papermaking, ceramics and refractory materials . Secondly, it is used in coatings, rubber fillers, enamel glazes and white cement raw materials. In small quantities, it is used in plastics, paints, pigments, grinding wheels, pencils, daily cosmetics, soaps, etc. Pesticides, medicines, textiles, petroleum, chemicals, building materials, national defense and other industrial sectors. Composition Kaolin minerals are composed of kaolinite cluster minerals such as kaolinite, dikaiite, perlite, and halloysite. The main mineral component is kaolinite. The crystal chemical formula of kaolinite is 2SiO 2 ·Al 2 O 3 ·2H 2 O, and its theoretical chemical composition is 46.54% SiO 2 , 39.5% Al 2 O 3 , and 13.96% H 2 O. Kaolin minerals are 1:1 type layered silicates. The crystals are mainly composed of silicon-oxygen tetrahedrons and aluminum-hydrogen-oxygen octahedrons. The silicon-oxygen tetrahedrons are connected along two-dimensional directions by sharing vertex angles to form a hexagonal arrangement. In the grid layer, the unshared peak oxygen of each silicon-oxygen tetrahedron faces one side; a 1:1 type unit layer is composed of the silicon-oxygen tetrahedron layer and the oxygen-absorbing octahedron layer sharing the peak oxygen of the silicon-oxygen tetrahedron layer Physical and chemical properties Properties: Mostly matte, white and delicate when pure, but may be gray, yellow, brown and other colors when containing impurities. The appearance can be loose soil lumps or dense rock lumps depending on the origin. Density: 2.54-2.60 g/cm3. Melting point: about 1785℃. It is plastic, and wet soil can be molded into various shapes without breaking, and can remain unchanged for a long time Origin of mineral deposits Kaolin is a common and very important clay mineral in nature. It is formed by the weathering of feldspar or other silicate minerals in igneous and metamorphic rocks in acidic media lacking alkali metals and alkaline earth metals . Soil classification The minerals contained in kaolin in nature 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 hydrated minerals, as well as some iron minerals such as hematite and rhosite. Iron ore , limonite , etc., titanium minerals such as rutile, etc. and organic matter such as plant fiber , etc. It is mainly clay minerals that determine the properties of kaolin . Cause classification Based on the origin of kaolin deposits and based on the differences in mineralization geology, geographical conditions, deposit scale, ore body morphology and occurrence characteristics, ore material components reflected in different mineralization processes, the “Kaolin Mine Geological Exploration Code” will China’s kaolin deposits are divided into three types and six subtypes. 1. Weathering type: It is further divided into weathering residual subtype and weathering leaching subtype; 2. Hydrothermal alteration type: It is further divided into hydrothermal alteration subtype and modern hot spring alteration subtype; 3. Sedimentary type: It is further divided into sedimentary and sedimentary-weathering subtypes and kaolinite claystone subtype in coal-bearing strata. Industrial type It is divided into three types according to its texture, plasticity and sandy quality fraction: 1. Hard kaolin: hard and non-plastic, it can become plastic after being crushed and finely ground. 2. Soft kaolin: soft, strong plasticity, sand mass fraction <50%; 3. Sandy kaolin: soft, weak plasticity , sand mass fraction >50%. Process characteristics whiteness brightness Whiteness is one of the main parameters of kaolin’s technological performance. Kaolin with high purity is white. The whiteness of kaolin clay is divided into natural whiteness and calcined whiteness. For ceramic raw materials , the whiteness after calcining is more important. The higher the calcined whiteness, the better the quality. Ceramic technology stipulates that drying at 105°C is the grading standard for natural whiteness, and calcining at 1300°C is the grading standard for calcined whiteness. Whiteness can be measured with a whiteness meter. A whiteness meter is a device that measures the reflectivity of light with a wavelength of 3800-7000Å (i.e. angstrom, 1 angstrom = 0.1 nanometer). In the whiteness meter, the reflectance of the sample to be tested is compared with that of the standard sample (such as BaSO4, MgO, etc.), which is the whiteness value (for example, a whiteness of 90 means that it is equivalent to 90% of the reflectance of the standard sample). Brightness is a process property similar to whiteness, equivalent to the whiteness under irradiation of 4570Å (angstrom) wavelength light. The color of kaolin is mainly related to the metal oxides or organic matter it contains . Generally, those containing Fe2O3 are rose red and brown; those containing Fe2+ are light blue and light green; those containing MnO2 are light brown; those containing organic matter are light yellow, gray, green, black and other colors. The presence of these impurities reduces the natural whiteness of kaolin. The iron and titanium minerals also affect the calcined whiteness, causing stains or melting scars on the porcelain. Particle size distribution Particle size distribution refers to the proportion (expressed in percentage) of the particles in natural kaolin within a given continuous range of different particle sizes (expressed in meshes with millimeter or micron mesh openings). The particle size distribution characteristics of kaolin are of great significance to the selection of ores and process applications. Its particle size has a great impact on its plasticity, mud viscosity, ion exchange capacity, molding performance, drying performance, and firing performance. Kaolin ore requires technical processing. Whether it is easy to process to the fineness required by the process has become one of the criteria for evaluating the quality of the ore. Various industrial sectors have specific particle size and fineness requirements for kaolin clay for different uses. For example, the United States requires 90-95% of kaolin used as coatings to have a content less than 2 μm, and 78-80% of papermaking fillers less than 2 μm. plasticity The mud formed by the combination of kaolin and water can deform under the action of external force. The property of retaining this deformation after the external force is removed is called plasticity. Plasticity is the basis of the kaolin molding process in ceramic bodies and is also the main process technology indicator. Plasticity index and plasticity index are usually used to express the degree of plasticity. The plasticity index refers to the liquid limit moisture content of kaolin clay material minus the plastic limit moisture content, expressed as a percentage, that is, W plasticity index = 100 (W liquid limit – W plastic limit). The plasticity index represents the molding performance of kaolin clay material. It can be obtained by directly measuring the load and deformation of the mud ball when it is crushed under pressure using a plasticity meter. It is expressed in kg·cm. The higher the plasticity index, the better the molding performance. The plasticity of kaolin can be divided into four levels. Plasticity strength plasticity index plasticity index Strong plasticity>153.6 Medium plasticity 7-152.5-3.6 Weak plasticity 1-7<2.5 Non-plasticity<1 associativity Combinability refers to the ability of kaolin clay to combine with non-plastic raw materials to form a plastic mud mass with a certain dry strength. The binding ability is measured by adding standard quartz sand to kaolin clay (its mass composition is 0.25-0.15 grain size accounts for 70%, and 0.15-0.09mm grain size accounts for 30%). Its level is judged by its highest sand content when it can still maintain a plastic mud mass and its flexural strength after drying. The more sand is added, the stronger the bonding ability of the kaolin. Generally, kaolin clay with strong plasticity also has strong binding ability. viscosity Viscosity refers to a characteristic of a fluid that hinders its relative flow due to internal friction. Its size is represented by viscosity (the internal friction acting on 1 unit area), and the unit is Pa·s. The viscosity is generally measured using a rotational viscometer, measured by the rotational speed in kaolin mud containing 70% solid content . In the production process, viscosity is of great significance. It is not only an important parameter in the ceramic industry, but also has a great impact on the paper industry. According to data, when kaolin is used as coating abroad, the viscosity is required to be about 0.5 Pa·s when coating at low speed, and less than 1.5Pa·s when coating at high speed. Thixotropy refers to the characteristic that mud that has thickened into a gel-like state and no longer flows becomes fluid after being stressed, and then gradually thickens back to its original state after being stationary. Its size is represented by the thickening coefficient and measured using an outflow viscometer and a capillary viscometer. The viscosity and thixotropy are related to the mineral composition , particle size and cation type in the mud . Generally, those with a large montmorillonite content, fine particles, and exchangeable cations mainly containing sodium will have high viscosity and thickening coefficient. Therefore, methods such as adding strong plasticity clay and increasing fineness are commonly used to increase its viscosity and thixotropy, and methods such as increasing dilute electrolyte and moisture are used to reduce it. Drying performance Drying performance refers to the performance of kaolin mud during the drying process. Including drying shrinkage, drying strength and drying sensitivity. Drying shrinkage refers to the shrinkage of kaolin clay material after it loses water and dries. Kaolin mud generally dehydrates and dries at a temperature of 40-60°C and no more than 110°C. Due to the discharge of water, the distance between particles is shortened, and the length and volume of the sample will shrink. Drying shrinkage is divided into line shrinkage and volume shrinkage, expressed as the percentage change in length and volume of kaolin clay material after it is dried to constant weight. The drying line shrinkage of kaolin is generally 3-10%. The finer the particle size, the larger the specific surface area, the better the plasticity, and the greater the drying shrinkage. The same type of kaolin has different shrinkage due to different blends of water. Those with more water will shrink more. In the ceramic process, if the drying shrinkage is too large, the green body is prone to deformation or cracking. Dry strength refers to the flexural strength of mud after it is dried to constant weight. Drying sensitivity refers to the degree of difficulty with which the green body may tend to deform and crack when drying. High sensitivity, easy to deform and crack during drying process. Generally, kaolin with high drying sensitivity (drying sensitivity coefficient K>2) is easy to form defects; kaolin with low drying sensitivity (drying sensitivity coefficient K<1) is safer during drying. Sinterability Sinterability refers to the property that when the formed solid powdered kaolin body is heated to close to its melting point (generally over 1000°C), the substance spontaneously fills the gaps between the particles and becomes densified. The state in which the porosity drops to the minimum value and the density reaches the maximum value is called the sintering state, and the corresponding temperature is called the sintering temperature . As the heating continues, the liquid phase in the sample continues to increase and the sample begins to deform. The temperature at this time is called the transformation temperature. The interval between the sintering temperature and the transformation temperature is called the sintering range. Sintering temperature and sintering range are important parameters in determining the blank formula and selecting the type of kiln in the ceramic industry . The sample should have a low sintering temperature and a wide sintering range (100-150°C). In terms of technology, the sintering temperature and sintering range can be controlled by blending fluxing raw materials and blending different types of kaolin in proportion. Firing shrinkage Firing shrinkage refers to a series of physical and chemical changes that occur in the dried kaolin blank during the firing process (dehydration, decomposition, formation of mullite , melting of fusible impurities to form a glass phase that fills the gaps between particles, etc.) , and the properties that cause product shrinkage are also divided into two types: linear shrinkage and body shrinkage. Like drying shrinkage, excessive firing shrinkage can easily lead to cracking of the green body. In addition, if a large amount of quartz is mixed in the blank during roasting , it will undergo crystal transformation fire resistance Fire resistance refers to the ability of kaolin to withstand high temperatures without melting. The temperature at which it softens and begins to melt under high-temperature operations is called refractoriness. It can be measured directly using a standard thermometer cone or high-temperature microscope, or it can be measured using M. A. Calculated using Bezbelodov’s empirical formula . Refractoriness t (℃)=[360+Al2O3-R2O]/0.228 In the formula: Al2O3 is the mass percentage of Al2O3 when the sum of the analysis results of SiO2 and Al2O3 is 100; R2O is the mass percentage of other oxides when the sum of the analysis results of SiO2 and Al2O3 is 100. The error of calculating refractory degree through this formula is within 50℃. The refractory degree is related to the chemical composition of kaolin. The refractory degree of pure kaolin is generally around 1700°C. When the content of hydromica and feldspar is high, and the content of potassium, sodium and iron is high, the refractory degree is reduced. The minimum refractory degree of kaolin is not less than 1500℃. The industrial sector stipulates that the R2O content of refractory materials is less than 1.5-2%, and the Fe2O3 content is less than 3% . Suspension Suspension and dispersion refer to the performance of kaolin dispersed in water and difficult to precipitate. Also known as anti-flocculation. Generally, the finer the particle size, the better the suspension. Kaolin used in the enamel industry requires good suspension properties. Generally, the suspension performance of a sample dispersed in water is determined based on its sedimentation rate over a certain period of time. Optional Optionality refers to the performance of kaolin ore that has been hand-selected, mechanically processed and chemically treated to remove harmful impurities so that the quality meets industrial requirements. The selectivity of kaolin depends on the mineral composition, occurrence state, particle size, etc. of harmful impurities. Quartz, feldspar, mica, iron, titanium minerals, etc. are all harmful impurities. Kaolin mineral processing mainly includes sand removal, iron removal, sulfur removal and other projects . adsorption Kaolin has the ability to adsorb various ions and impurities from the surrounding medium, and has weak ion exchange properties in solution . The quality of these properties mainly depends on the main mineral composition of kaolin , see Table 8. Table 8 Cation exchange capacity of different types of kaolin Mineral composition characteristics Cation exchange capacity Mainly kaolinite 2-5mg/100g Mainly halloysite 13mg/100g Contains organic matter (ball soil) 10-120mg/100g chemically stable Kaolin has strong acid resistance, but its alkali resistance is poor. This property can be used to synthesize molecular sieves . electrical insulation High-quality kaolin has good electrical insulation, and this property can be used to make high-frequency porcelain and radio porcelain. The level of electrical insulation performance can be measured by its ability to resist electrical breakdown. application Industrial applications Kaolin has become a necessary mineral raw material for dozens of industries including papermaking, ceramics, rubber, chemicals, coatings, medicine and national defense . The ceramic industry is the earliest industry that uses kaolin and uses a large amount of kaolin. The general dosage is 20% to 30% of the formula. The role of kaolin in ceramics is to introduce Al2O3, which is beneficial to the formation of mullite and improves its chemical stability and sintering strength. During firing, kaolin decomposes to form mullite, which forms the main framework for the strength of the green body and prevents deterioration of the product. Deformation makes the firing temperature wider and the green body has a certain whiteness. At the same time, kaolin has certain plasticity, adhesion, suspension and bonding capabilities, which gives the porcelain mud and enamel good formability, making the ceramic mud blank conducive to turning and grouting, and facilitating forming. If used in wires, it can increase insulation and reduce dielectric loss. Ceramics not only have strict requirements on kaolin’s plasticity, bonding, drying shrinkage, drying strength, sintering shrinkage, sintering properties, refractoriness and post-fired whiteness, but also involve chemical properties, especially iron, titanium, copper, chromium, The presence of color-causing elements such as manganese reduces the whiteness after burning and causes spots. The particle size requirements for kaolin are generally finer, the better, so that the porcelain clay has good plasticity and dry strength. However, for casting processes that require fast casting, accelerated grouting speed and dehydration speed, the particle size of the ingredients needs to be increased. In addition, the difference in crystallization degree of kaolinite in kaolin will also significantly affect the process performance of the porcelain blank. If the degree of crystallization is good, the plasticity and bonding ability will be low, the drying shrinkage will be small, the sintering temperature will be high, and the impurity content will also be reduced; conversely, the It has high plasticity, large drying shrinkage, low sintering temperature, and corresponding high impurity content . edible In the old society and the Three Years of Difficulty Period, poor people often relied on eating Guanyin soil to survive during lean years or famine years. This soil can satisfy hunger, but it cannot be digested and absorbed by the human body. After eating, it will cause abdominal distension and difficulty in defecation. Eating a small amount is not fatal; Although you won’t go hungry, you will still die due to lack of nutrition. During the famine years, countless people died of suffocation due to their abdominal distension and inability to defecate after eating Guanyin soil. During Double Eleven in 2015, some merchants at Molecular Gourmet sold “kaolin clay”. After verification, it was found that there was only the name “kaolin” and there was no such term as “kaolin clay”. Kaolin (Guanyin soil) is the name of soil rich in the mineral kaolinite. The main components of kaolinite are alumina and silica . It is widely distributed in the kaolin area of ​​Jingdezhen, Jiangxi, and kaolin gets its name.