perlite

perlite

This entry is compiled and applied by "popular science China" Science Encyclopedia

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Perlite perlite is a kind of glassy rock formed by volcanic eruption of acidic lava and rapid cooling,

It is named for its pearl fissure structure. Perlite deposits include perlite, obsidian and turpentine. The difference between the three is that perlite has arc-shaped cracks formed by condensation, which is called perlite structure, with water content of 2 ~ 6%; turpentine has unique turpentine luster, with water content of 6 ~ 10%; Obsidian has glass luster and shell fracture, with water content of less than 2%.

Genetic type

The perlite deposits in China mainly occurred in the Mesozoic with frequent continental crustal activities. This generation of volcanoes formed a volcanic belt with a length of 3000 km and a width of 300-800 km, starting from Heilongjiang in the north and reaching the South China Sea coast and Hainan Island in the south. The belt can be further divided into three sub zones. The first sub belt is also called Daxinganling and Yanshan sub belt. The main sources of perlite in this sub belt are Kuancheng, Pingquan, Zhangjiakou, Weichang and Guyuan in Hebei Province; Lingyuan, Faku, Jianping, Jinzhou, Yixian and Heishan in Liaoning Province; Lingqiu in Shanxi Province; Xinyang in Henan Province; Duolun, Taipusi, Zhenglan and Zhonghou banners in Inner Mongolia. The second sub belt is called the north northeast and Shandong sub belt. The perlite deposits in this subzone include Jiutai in Jilin Province and Muling in Heilongjiang Province. The third sub belt is called southeast coastal sub belt. The deposits in this subzone include the Ninghai songzhiyan deposit in Zhejiang Province.

Industrial types of ore deposits

There are three types of perlite in geology. The three divisions are similar or complementary to each other except for the limitation of comparative chemical composition. The specific contents of the three divisions are shown in the following three tables:

(1) The first classification: K0 refers to the expansion multiple of ore obtained from the factory roasting furnace test, which is usually about 2 times of the laboratory roasting test multiple K, as shown in Table 1.

(2) The second classification: see Table 2.

(3) The third classification: see Table 3.

The above three classification of ore grades are mainly based on the expansion performance of ore. The grade of practical application should be determined according to the needs.

The above three divisions all relate the chemical composition of rocks to their expansion ratio. We think that the expansion ratio of perlite does not necessarily depend entirely on its chemical composition. According to the data of the perlite deposit in Lingqiu County, Shanxi Province, there is perlite with expansion factor K greater than 10 and Na2O / K2O = 1 ~ 1.5.

Table 1

Ore properties

mineral composition

mineral composition

It is mainly composed of massive, porous and pumice pearlite, containing a small amount of phenocrysts and microcrystals of diorthosite and quartz, and various forms of microcrystals, cryptocrystalline minerals, hornblende and other arc-shaped cracks. The fracture surface is uneven, pearl luster, oil luster after weathering, and white streaks.

It is mainly composed of turpentine, hydrolyzed turpentine and hydrated turpentine. It contains a small amount of diorthosite and white tuff material, which is irregularly distributed. The fracture surface is shell like, with turpentine luster and white streaks.

It is mainly composed of obsidian, obsidian porphyry and hydrated obsidian. It contains a small amount of quartz and feldspar phenocrysts, and a very small amount of opaque magnetite and corundum. The fracture surface is flat or shell shaped, and some of them are uneven. It has glassy luster. After weathering, it has grease luster and white streaks.

Mineral characteristics

1) The main physical properties of perlite are shown in Table 5.

Table 2 main physical properties of perlite

2) The general chemical composition of perlite ore is shown in Table 6.

Table 3 general chemical composition of perlite ore

the distribution of mineral deposits

The raw material deposit of expanded perlite is mainly the product of acidic volcanic eruption. Since Mesozoic in China, all kinds of magma have been ejected, and expanded perlite deposits have been formed in Jurassic, Cretaceous, tertiary and Quaternary. Expanded perlite deposits have been found in Shanxi, Liaoning, Inner Mongolia, Henan, Jilin, Heilongjiang, Jiangsu, Zhejiang, Shandong, Jiangxi, Hubei, Hebei and other provinces and autonomous regions, of which Shanxi has the largest reserves. The developed ore deposits include: Shangtianti, Xinyang, Henan, Luoshan, Liaoning, Jinyun, Jilin, Jiutai, Lingqiu, Shanxi, etc.

Industrial indicators

Main industrial indexes of ore deposits

The industrial value of expanded perlite raw materials is mainly determined by their expansion ratio and product bulk density after high temperature roasting.

1. Expansion ratio K05 ~ 15 times

2. Bulk density ≤ 80kg / m3 ~ 200kg / m3

Quality requirements:

1. Pure glass, good transparency, light color is high quality.

2. There is no or slight devitrification, and the serious one is inferior.

3. There is no or little crystalline substance, and the one with more is inferior.

4. Chemical composition: SiO2 70% ±, H2O 4 ~ 6%, Fe2O3 < 1% is high quality, 1% is medium and poor quality.

Process characteristics

When acidic lava erupts from the earth's surface, it has a great viscosity due to the sudden cooling of the magma, so that a large amount of water vapor can not escape from the magma and exist in the vitreous. When baking, due to the sudden heating to soften, the combined water in the glass vaporizes to produce a great pressure, and the volume expands rapidly. When the glass is cooled to below the softening temperature, it condenses into a cavity structure and forms porous expanded perlite. Therefore, vitreous is the basic condition of ore expansion, water is the internal cause of ore expansion, and iron is one of the unfavorable factors.

The oxidation and melting temperatures of perlite are as follows: the initial shrinkage temperature is 1025 ℃, the softening temperature is 1175 ℃, the melting temperature is more than 1500 ℃, the softening temperature range is 150 ℃, and the melting temperature range is 325 ℃. The shrinkage temperature of perlite is 120 ℃ lower than that of feldspar, the softening temperature is 75 ℃ lower and the softening range is 95 ℃ wider. Because of these characteristics, perlite can greatly reduce the sintering temperature and improve the sintering quality. Through further study, there is another characteristic of perlite, that is, mullite crystal forms earlier in the ceramic body containing perlite, which is conducive to the sintering process. In this way, the pearlite bearing body not only has the same technological characteristics as the feldspar quartz clay (Kaolin mineral) ternary system body formula, but also can reduce the sintering temperature (from 1280 ℃ to 1180 ℃ - 1160 ℃), and has good thermal stability.

The types and grades of perlite ores are shown in Table 8.

Table 3 Classification of perlite ore types and grades

Appearance

Morphology is one of the most striking appearance features of perlite. Different characteristic forms of perlite, the same kind of perlite, because of different formation conditions, internal structure, composition and so on, often have other characteristics and may appear in different forms, which is not only a sign to identify perlite, but also a basis to analyze the genesis of perlite.

The morphology of crystalline perlite is mainly composed of monomer and aggregate. Therefore, the morphology of perlite is not only complex. For solid-state amorphous quasi (or quasi) perlite, there is only the monomer form of aggregate perlite, that is, the single crystal of perlite. The monomer morphology of perlite mainly includes crystal habit (embodied in crystal shape) and crystal pattern

Crystallization habit

When the growth conditions are fixed, the same kind of crystal can always develop into a certain shape. This property is called crystal habit, or crystal habit for short. According to the development characteristics of perlite crystals in three-dimensional space, the crystallization habits are generally divided into three types, i.e. always elongated type: crystals develop along one direction in columnar, acicular and fibrous forms, such as columnar quartz, acicular hornblende, fibrous gypsum and asbestos; Two direction elongated type: the crystal is developed along two directions, showing scaly, flaky, plate-like morphology, such as flaky mica, plate-like gypsum, etc.; three direction isometric type: the crystal is nearly equiaxed or granular in three-dimensional space, such as cubic halite, pyrite, etc.

In addition to the three basic types mentioned above, there are some transitional types of crystallization habit of perlite. For example, the plate columnar shape is between the one-way extension and the two-way length type, the thick plate shape is between the two-way extension and the three-way isometric type, and the short columnar shape is between the three-way isometric type and the one-way extension type.

The shape of perlite monomer is first related to its structure, composition and other internal factors. For example, the pearlite with chain complex anion group in amphibole structure often develops into columnar, acicular and fibrous along the direction of chain. In addition, the shape of perlite monomer is also controlled by the external environment of crystal growth. For example, due to the different growth temperature, the section of the axis is rhombic. For another example, calcite crystals can be in more than 800 shapes due to different growth temperatures.

Main uses

Perlite raw sand can be used as filling material in rubber and plastic products, pigments, paints, inks, synthetic glass, thermal insulation bakelite and some mechanical components and equipment.

Perlite is a new kind of lightweight and multifunctional material after expansion. It has the advantages of light apparent density, low thermal conductivity, high thermal conductivity and high thermal stability

Chinese PinYin : Zhen Zhu Yan