Kaolin (kaolin)

Kaolin is a kind of clay or clay rock mainly composed of kaolinite clay minerals. Kaolinite clay minerals include kaolinite, halloysite, dickite and pearl clay. The ore types of kaolin can be divided into soil kaolin and massive kaolin according to its appearance. According to the main clay mineral composition, it can be divided into kaolinite massive kaolin and halloysite massive kaolin. According to its texture, plasticity and sand content, it can be divided into three types: hard kaolin: hard, not plastic, but plastic after fine grinding; Soft kaolin: soft and plastic, with sand content less than 50%; Sandy kaolin: loose, weakly plastic, with sand content greater than 50%. Kaolin is widely used in papermaking, ceramics, rubber, plastics, refractories, chemicals, pesticides, medicine, textiles, petroleum, building materials, national defense and other fields because of its many excellent technological properties.

Second, the mineral properties

The chemical formula of kaolinite is Al4 [Si4O 10] (OH) 8, and its theoretical chemical composition is: Al2O3 39.5%, SiO2 46.54%, H2O 13.96%. Monoclinic or triclinic crystal system, with fine particle size, generally between 0.2 and 5 μ m, is pure white, dull, earthy or dull, and its hardness is close to 1. It is easy to powder when wet, plastic and has a density of about 2.6g/cm3. Generally, the particle size distribution of kaolinite is between 2-0.25 microns; Halloysite is 2-0.062 micron; Montmorillonite is 2 ~ 0.25 micron, 0. 125 ~ < 0.062 micron; Hydromica is distributed in various particle sizes. Fe2O3, TiO2, MnO, organic matter and rare elements have effects on the whiteness of kaolin. Kaolin slurry has stable performance, fine particle size and good suspension performance. The higher the fineness and thickness ratio coefficient (diameter-thickness ratio), the greater the thixotropy. The ion exchange of kaolin is related to mineral types. Generally, the cation exchange capacity is 3 ~ 15 m mol, and the anion exchange capacity is 7 ~ 20 m mol. According to the plasticity index, the plasticity of kaolin and its mud can be divided into four grades: strong plasticity (> 15), medium plasticity (7 ~ 15), weak plasticity (1 ~ 7) and plasticity (< 1). The fire resistance of kaolin is generally 1700℃, which belongs to general fire-resistant clay. The fire resistance of high-quality kaolin reaches 1800℃.

Third, use.

Kaolin is widely used in many industrial sectors because of its white primary color, high dispersibility and plasticity, high resistivity and fire resistance, good adsorption, sintering, ion exchange and physical and chemical stability, and has become one of the important mineral resources in the national economy.

1) Ceramic industry: Because of the plasticity, cohesiveness, suspension and bonding ability of kaolin, ceramic clay is beneficial to turning over and grouting, and easy to form.

2) Paper industry: used as coating and filler, it can improve the covering performance and coating gloss of paper, and increase the whiteness, opacity, smoothness and printing adaptability of paper.

3) Refractory industry: it is used to produce refractories, and its products have the ability of high temperature resistance and no deformation.

4) Rubber industry: Used as filler, it can improve the mechanical strength of rubber products, enhance wear resistance and chemical stability, and delay the hardening time of rubber.

5) coating industry: mainly used as filler and pigment substitute.

6) Plastic industry: As a filler, the product surface is smooth, reducing hot cracking and shrinkage, which is beneficial to polishing, dimensional accuracy and chemical corrosion resistance.

7) Enamel industry: Kaolin is added to the enamel glaze, so that the enamel glaze layer is firmly combined with the iron blank after calcination.

8) Environment: It can be used to filter chemical and domestic water, remove heavy metal cation pollutants in water and adsorb NH3-N in wastewater. It can also be used for air pollution purification and soil self-purification.

9) Glass fiber production in tank kiln: Kaolin with low iron content is used in glass fiber production, which provides the source of aluminum and silicon and makes its luster dim.

10) other uses: kaolin can also be used to produce white cement and polyaluminum, and kaolin with low iron and sulfur can be used to produce catalysts. In addition, it is also widely used in fertilizers, pesticides, cosmetics and so on.

Four. geologic feature

Kaolin deposits are widely distributed in hydrothermal alteration, weathering and sedimentary rocks. According to the geological characteristics and mineralization of kaolin deposits, kaolin deposits are generally divided into weathering type, hydrothermal alteration type and sedimentary type.

(1) Weathered Kaolin deposit

There are two subtypes of weathered residual kaolin deposits and weathered residual kaolin deposits.

1. Weathered residual kaolin deposit

Weathered residual kaolin is formed by in-situ strong chemical weathering of rocks rich in aluminosilicate minerals. The ore bodies are hat-shaped, layered, trough-shaped, lenticular, cystic, wedge-shaped and vein-shaped, and occur in the upper part of the phreatic stagnant zone. The vertical zoning of the deposit is obvious, and it can be divided into fully weathered zone, semi-weathered zone, slightly weathered zone and fresh rock from top to bottom. Jiepai kaolin deposit in Hengyang, Hunan Province is a typical deposit of this type.

Jiepai Kaolin Deposit in Hengyang, Hunan Province is located at the junction of Hengyang County and Hengshan County, in the contact zone between Baishifeng mica granite, tuffaceous slate and argillaceous siltstone of Wuqiangxi Formation of Banxi Group of Pre-Sinian system. Streak natrified migmatite, sericite plagioclase gneiss, muscovite schist and albite can be seen, and pegmatite veins are interspersed among them. These rocks have undergone alteration, strong weathering and obvious vertical weathering crust. Kaolin is mainly the kaolin product of various feldspar in the parent rock, and some of it is transformed from muscovite. The mineral composition is mainly kaolinite, halloysite and illite. The ore body is layered, trending northeast and northwest, with an inclination of 30 ~ 40. The thickness of the ore body is 25 ~ 30 m, and it extends 70 ~ 150 m along the dip. Gradually reduce. The floor is sodic migmatite and the roof is quartzite. Slate, phyllite, schist and other residues are common in ore bodies. See table 2-40- 1 for the chemical composition of high-quality jiepai kaolin.

Table 2-40- 1 Chemical Composition of High Quality jiepai Kaolin (wB/%)

2. Weathered residual kaolin deposit

This kind of deposit is formed by the vertical infiltration or intrusion of groundwater between the ore-forming protolith and the underlying limestone. The ore-forming protolith is decomposed with the participation of sulfuric acid, and clay minerals are leached in the karst cavity of limestone. Ore bodies generally have obvious vertical zoning phenomenon, which can be roughly divided into: iron hat and variegated kaolin belt from top to bottom; White dense massive kaolin belt; Black and white striped kaolin belt; Inferior kaolin belt, usually very thin. Sichuan Xuyong halloysite deposit is a typical deposit of this type.

The Xuyong halloysite deposit in Sichuan Province is located in Xuyong Taiwa in the southern margin of Sichuan syncline, and the ore body is located on the unconformity surface between Longtan coal measures and Maokou limestone. The structure in the mining area is mainly a flat compound anticline. Halloysite deposits are mainly distributed in the uplift of the axis and wing of anticline, and often appear on the mountainside with higher altitude. A single ore body is nest-shaped, chicken-nest-shaped, funnel-shaped and so on, and its shape is complex. The area of a single ore body is generally several square meters or tens of square meters, and the thickness varies greatly, generally 0 ~ 3m. Kaolinite claystone containing pyrite in Longtan Formation is the main source of ore-forming materials. Halloysite is mainly distributed in the lower part of weathered residual profile, and the ore is mainly white, followed by light blue, yellowish white, yellowish brown and variegated. Yellow-brown ore is mainly distributed in the upper part of the ore body, white or light blue ore is in the lower part, often layered, and the bottom of the ore body is often black or black and white ore. The main mineral composition of the ore is halloysite. The weathering and leaching profile of the deposit can be divided into five zones from top to bottom: weak weathering and leaching zone, leaching oxidation zone, leaching deposition zone, leaching desilication zone and limestone weathering and dissolution zone.

(2) hydrothermal altered kaolin deposit

This kind of deposit is closely related to volcanic activity, and the original rocks that form the deposit are generally acidic volcanic rocks and pyroclastic rocks. Orebodies are generally distributed along bedding and occur in silicified kaolin zone, which is layered, layered and lenticular, and the occurrence is consistent with the alteration zone. Guanshan kaolin deposit in Suzhou, Jiangsu Province is a typical deposit of this type.

Guanshan kaolin deposit in Suzhou, Jiangsu Province is located at the eastern edge of Huzhou-Suzhou fault block in Taihu Uplift of Yangtze Depression, at the intersection of Mudu short syncline and the northeast extension of Tandong-Guangfu-Tongan fault. Sandstone shale of Permian Gufeng Formation-Longtan Formation, limestone of Permian Changxing Formation-Triassic Qinglong Formation, volcanic rock of Jurassic Longwangshan Formation and limestone of Qinglong Formation-Changxing Formation are exposed in the area. Faults are developed in the mining area, and igneous veins are interspersed among them. Low-temperature hydrothermal alteration activities generally exist in mining areas, which are mainly related to hydrothermal activities in the later stage of volcanic activity. In the later stage, dike intrusion has superimposed alteration, forming various altered mineral combinations: ① Marble bands are located in the lower part of ore bodies, mostly in the bottom plate of ore bodies. (2) The siderite belt is an isolated lens intermittently produced between the marble belt and the kaolin belt, and its surface is often limonite. (3) Kaolinization zone is irregular layered, lenticular or veined with an average thickness of 20m ... The main minerals are kaolinite and halloysite. (4) Alum petrified zone is often discontinuous layered or lenticular, and the main minerals are alunite, including kaolinite, halloysite, pyrite and Yingshi. ⑤ The sericite silicified zone is the roof of the ore body, and the minerals are mainly secondary, followed by sericite, accompanied by a small amount of pyrite and alunite. The sericite in the lower part of the belt is increased, and there is a small amount of kaolinite.

(3) sedimentary kaolin deposit

According to the types of sedimentary formations, it can be divided into two subtypes: clastic sedimentary formations and coal-bearing sedimentary formations.

1. Clastic sedimentary kaolin deposit

Ore types are divided into soft clay and sandy kaolin. The former has low sand content, broken wafer, poor water permeability of ore bed and difficult leaching and migration of iron. For example, kaolin mines in Qingyuan, Guangdong and Fraxinus mandshurica in Jilin belong to this category, and most of them are used as refractory clay. The latter is mostly feldspar, quartz sand layer or gravel layer containing kaolin. Good water permeability, deposited in the basin, further weathered and leached. If there is an acidic reducing environment caused by humus, flaky kaolinite with good crystallinity, low iron and titanium content and high whiteness can be generated, which is a high-quality paper coating. Kaolin mines in Maoming, Guangdong and Hepu, Guangxi belong to this category. Now, taking Maoming kaolin mine in Guangdong as an example, it is described as follows.

Guangdong Maoming Kaolin Mine is located in the northern suburb of Maoming City. Produced in Paleogene-Neogene basins. The lower part of the basin is the Paleogene Youganwo Formation, which is a set of glutenite, sandstone and oil shale deposits, with lignite and argillaceous thin layers. Above it is the Neogene Miocene Huangniuling Formation, which is a set of glutenite, sandstone and sandy clay mixed with mudstone deposits, and below it is the main kaolin ore-bearing layer. Then there is the Miocene Laohuling Formation, which is a set of glutenite, mudstone and clay deposits, and its lower part contains kaolin deposits. Kaolin seams are layered and quasi-layered. The lithology of the ore-bearing layer is gravelly feldspar timely sandstone, most of which has been transformed into kaolinite, and the ore structure is loose. The minerals are mainly timely and kaolinite, with only a small amount of illite. The content of kaolinite in raw ore is low, accounting for about 20% ~ 40%, and the timely content accounts for about 50% ~ 80%. The ore-forming materials of the deposit are gneiss, migmatite, granite and acid volcanic rocks around the basin, which were formed by strong weathering under the humid and hot climate conditions of Paleogene and Neogene.

2. Coal-bearing sedimentary kaolin deposit.

It is a kaolin deposit deposited in coal-bearing rock series. It is an important type of kaolin in China, which is widely distributed in the Taizihe River basin in Liaoning and the southern part of Liaodong Peninsula, as well as the vast coal basins in North China Plain and East China, accounting for 2/3 of the total amount of all kinds of clay in China. Kaolin is widely related in horizon, closely related to strata in various coal-forming ages in China, and often coexists with refractory clay and bauxite.

The typical deposit is Datong coal-bearing sedimentary kaolin deposit, which is a hard kaolin deposit formed by sedimentary diagenesis. The mining area is located in the southwest of Datong City, Shanxi Province, distributed in NE-SW direction, with an area of about 2000km2, and its structural position belongs to Yungang-Pinglu structural basin. The ore-bearing rock series is Taiyuan Formation of Upper Carboniferous, followed by Shanxi Formation of Lower Permian. Kaolinite beds are closely related to coal seams. There are 9 layers of coal in Taiyuan Formation, with 1 1 layer of kaolin. Among them, No.4 coal seam is the most developed in Tongjialiang and Kouquan in the north, with a single layer thickness of nearly 1 m and a maximum thickness of 2 m. The ore is coarse and fine kaolinite with stable horizon and good quality. No.5 coal seam is developed from Zhifu Mountain to Goose Maokou in the middle of the coal field, with an average thickness of 2.25m. The ore is dark gray to black colloidal kaolinite, often containing a small amount of diaspore. No.6 coal seam has good quality, stable horizon and thickness and wide distribution area. From Yin Shan, Maying, Huairen, Zhifengshan, Wujiayao to Datong Kouquan, it is the main porcelain kaolin deposit in this area. The coal seam is divided into two layers, the upper layer is fine-grained kaolinite, and the lower layer is coarse-grained kaolinite, with a single layer thickness of 0.2 ~ 0.5m；; ; No.8 coal seam is widely distributed in the whole region, and the ore is colloidal kaolinite with an average thickness of 0.34 m and good quality. The rest of the seams have no economic significance. The natural types of ores can be divided into coarse-grained kaolinite, fine-grained kaolinite, cryptocrystalline kaolinite, cryptocrystalline kaolinite containing diaspore and clastic kaolinite. The chemical composition of ore is low silicon and high aluminum.

Verb (abbreviation of verb) mineral distribution

Kaolin is widely distributed in China, covering 2/kloc-0 provinces (autonomous regions and municipalities) in six regions of the country, and 70% of the mineralization period was formed in Mesozoic and Cenozoic. Guangdong Province has the largest proven kaolin reserves, followed by Shaanxi, Fujian, Jiangxi, Guangxi, Hunan and Jiangsu. Other provinces with kaolin reserves include Hebei, Shanxi, Inner Mongolia, Liaoning, Jilin, Zhejiang, Anhui, Shandong, Henan, Hubei, Hainan, Sichuan, Guizhou and Yunnan. See figure 2-40- 1 for the distribution of main mining areas.

Figure 2-40- 1 Distribution Map of Main Kaolin Mining Areas in China

Weathered residual kaolin deposits are widely distributed in southern China. The metallogenic age is relatively new, mainly formed in Neogene Pliocene-Quaternary. Weathered residual kaolin deposit occurs between the Longtan coal measure of Leping series in Permian and the karst erosion surface of Maokou limestone of Yangxin series in early Permian. The hydrothermal altered kaolin deposits in the east are mainly related to volcanic activities in the middle and late Mesozoic. Most deposits occur in volcanic rocks of the Upper Jurassic. Clastic sedimentary kaolin deposits mostly occur in rivers, lakes and bays of Paleogene, Neogene or Quaternary, and mostly occur in fault basins, valleys and depressions or adjacent bays. Coal-bearing sedimentary kaolin deposits are distributed in Carboniferous-Permian coal measures strata.

The available resources of intransitive verbs

By the end of 2005, there were 232 kaolin mines in China, mainly distributed in Guangdong, Shaanxi, Fujian, Guangxi, Jiangxi, Hunan, Jiangsu and other provinces. The national proven resource reserves 182995× 104t, of which Guangdong Province accounts for 29.63% of the national proven resource reserves; Shaanxi's proven resource reserves account for 24.54% of the national proven resource reserves; The proven resource reserves in Fujian account for10.96% of the national proven resource reserves; Guangxi's proven resource reserves account for 7.83% of the national proven resource reserves. See Table 2-40-2 for the distribution of kaolin resources in the main kaolin mining areas in China.

Table 2-40-2 Distribution of Proven Resources and Reserves in Main Kaolin Mining Areas in China

(According to Notice of Ministry of Land and Resources on National Mineral Resources Reserves, 2005)