Yuan Lei's Little Knowledge | Classification and Performance Characteristics of Kaolin

Release time:

2024-01-29 09:34

Kaolin is a non-metallic mineral, which is a kind of clay and clay rock mainly composed of kaolinite clay minerals. Because it is white and delicate, also known as white earth.


Soil classification

The minerals contained in kaolin in nature are mainly divided into clay minerals and non-clay minerals. The clay minerals mainly contain kaolinite group minerals and a small amount of montmorillonite, mica and chlorite; non clay minerals mainly contain feldspar, quartz and aluminum hydrate, there are some iron minerals such as hematite, siderite, limonite, titanium minerals such as rutile and organic matter such as plant fiber. It is mainly clay minerals that determine the properties of kaolin.



Genesis classification

Based on the formation of kaolin deposits, according to the differences in mineralization geology, geographical conditions, deposit scale, ore body morphology and occurrence characteristics, and ore material composition embodied by different mineralization processes, the Kaolin deposits in China are divided into three types and six sub-types in the Code for Geological Exploration of Kaolin Ores.

1. Weathering type: it is divided into weathering residual subtype and weathering leaching subtype;

2, hydrothermal alteration type: divided into hydrothermal alteration subtype and modern hydrothermal alteration subtype;

3. Sedimentary type: it is divided into sedimentary and sedimentary-weathered subtype and kaolinite clay rock subtype in coal-bearing strata.



Type of Industry

According to its texture, plasticity and sandy mass fraction are divided into three types:

1, hard kaolin: hard, no plasticity, after grinding with plasticity.

2. Soft kaolin: soft, strong plasticity, sandy mass fraction <50%;

3. Sandy kaolin: soft, weak plasticity, sandy mass fraction> 50%.



Performance characteristics

The wide range of uses of kaolin is inseparable from its excellent physical and chemical properties. Pure kaolin has high whiteness, soft and easy to disperse and suspend in water, good plasticity and high bonding, excellent electrical insulation properties and good acid solubility, very low cation exchange capacity, high refractoriness and other physical and chemical properties.

(1) Color. White or nearly white, with a maximum whiteness of more than 95%.

(2) Hardness. The hardness of soft kaolin is generally 1-2, and that of hard kaolin sometimes reaches 3-4.

(3) Particle size and particle morphology. The particle size distribution of kaolin is usually 0.2-5 μm, and the particle size has an effect on its plasticity, mud viscosity, ion exchange capacity, formability, drying, sintering and other properties. Generally, the finer the particle size of kaolin, the better the plasticity, the higher the drying strength, the easier it is to sinter, the lower the porosity after sintering, and the higher the mechanical strength.

(4) Plasticity. The clay formed by the combination of kaolin and water can be deformed under the action of external force. After the external force is removed, it can still maintain the nature of this deformation, that is, plasticity. Plasticity is the basis of the forming process of kaolin in ceramic bodies, and it is also the main technical index of the process.

(5) Sinterability. Sinterability refers to the properties of the solid powder kaolin body heated to close to its melting point (generally more than 1000 ℃), the material spontaneously filling the intergranular space and densification. The state where the porosity drops to the lowest value and the density reaches the maximum value is called the sintering state, and the corresponding temperature is called the sintering temperature.

(6) Dispersion. Kaolin is easily dispersed and suspended in water, and can form a suspension with good stability.

(7) Electrical insulation. Kaolin has excellent electrical insulation properties, and the resistivity is greater than 10 at 200°C.10Ω · cm, can be used for cable filler.

(8) Chemical stability. Chemical stability is one of the main performance indicators of mineral materials used as fillers. Kaolin has strong chemical stability and strong acid resistance, but its alkali resistance is poor.

(9) Cation exchange capacity (CEC). The cation exchange capacity of kaolin is generally 0.03-0.05mmol/g.

(10) Refractoriness. The refractoriness is related to the chemical composition of kaolin. The refractoriness of pure kaolin is generally about 1700 ℃. When the content of hydromica and feldspar is high, and the content of potassium, sodium and iron is high, the refractoriness is reduced, and the refractoriness of kaolin is not less than 1500 ℃. Generally, with the increase of Al2O3 content, the refractoriness increases; with the increase of the content of alkaline oxides and iron oxides, the refractoriness decreases.

(11) Interaction with organic matter. Kaolin can interact with a number of polar organic molecules, such as formamide (HCONH2), acetamide (CH3CONH2), urea (NH2CONH2), etc. to produce kaolin-polar organic molecule chimeric complexes. Organic molecules can enter the interlayer domain and bond with the two surfaces of the structural layer by hydrogen bonding. As a result, the thickness of the structural unit layer of kaolin is increased, and the surface properties of kaolin, such as hydrophilicity, are changed.

Kaolin, mineral, plasticity, properties, clay, refractoriness, general, subtype, sintering

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