Perlite minerals include perlite, obsidian and turpentine.

Perlite is a kind of glassy rock formed by the acid molten slurry erupted by volcano and rapidly cooled. Its composition is equivalent to rhyolite, so it is named because of its pearl crack structure. Perlite contains 2% ~ 6% water.

Pitchstone is also an acidic glassy volcanic rock with unique rosin luster, and its water content is 6% ~10% higher than that of perlite.

Obsidian is a glassy volcanic rock whose composition is equivalent to granite, and its water content is less than 2%.

Pearlite, turpentine and obsidian all have the characteristics that their volume can expand several times to more than 30 times under the condition of instantaneous high temperature (1200℃), and they are important mineral raw materials for making high-quality lightweight building materials and thermal insulation materials.

See table 3-2- 1 for the types of perlite ores.

Table 3-2- 1 perlite ore types

See Table 3-2-2 for the classification of perlite ore grades.

Table 3-2-2 Classification of perlite ore types and grades

Second, the main uses of expanded perlite

The use of perlite mainly refers to the main use of expanded perlite. Expanded perlite has excellent physical and chemical properties such as light bulk density, low thermal conductivity, strong fire resistance, good sound insulation performance, fine pores, stable chemical properties, non-toxic and tasteless, etc., which makes it widely used in various industrial sectors, especially important light building materials and heat insulation raw materials. The main uses of expanded perlite are shown in Table 3-2-3.

Table 3-2-3 Main Uses of Expanded Perlite

Tables 3-2-4 and 3-2-5 list the consumption structure of expanded perlite in Japan and the United States.

Table 3-2-4 Consumption Composition of Japanese Expanded Perlite

Table 3-2-5 Consumption Composition and Consumption of Expanded Perlite in America

Third, the quality standard of perlite

As a raw material for producing expanded perlite, the quality evaluation is mainly determined by its expansion multiple at high temperature and product bulk density. Generally, the expansion multiple is required to be greater than 7 ~10 (obsidian > 3 is enough). The expansion multiple obtained in the laboratory and the expansion multiple of industrial production are converted according to the following formula:

K0=5.2（K-0.8）

Where K0—— is the expansion multiple of industrial production; K—— expansion ratio of simple baking in laboratory.

Loose density (bulk density) ≤ 80 ~ 250kg/m3.

In addition, the content of SiO2 _ 2 in the ore should reach 70%,H2O should be 4% ~ 6%, and Fe2O3+FeO <1%should be of high quality. The ore is all-glassy, with no or only slight devitrification and no phenocrysts.

Table 3-2-6 and Table 3-2-7 list the quality requirements of perlite.

The raw perlite ore needs to be crushed and screened to obtain perlite ore suitable for furnace expansion. Generally, the crushing and screening process is as shown in Figure 3-2- 1. See fig. 3-2-2 for the beneficiation process of American Noah's melon perlite.

Table 3-2-6 Comparison between expansion coefficient K of simple baking in laboratory and expansion coefficient K0 of industrial production

Table 3-2-7 Quality Grading Standard of Perlite

Fig. 3-2- 1 process flow chart of crushing and screening principle

Fig. 3-2-2 Process Flow Chart of American Noagua Perlite Mineral Processing

The first-grade perlite ore can be used in industry, but not the third-grade ore. The standard of mineral sand for expanded perlite is in accordance with the standard issued by the State Bureau of Building Materials Industry, as shown in Table 3-2-8.

Table 3-2-8 Technical Requirements of Ore for Expanded Perlite (ZBQ25002-88)

Table 3-2-9 gives the local standards of Henan Province.

Table 3-2-9 Technical Index Requirements of Ore for Expanded Perlite (DB/410000D63001-86)

Fourth, the production process of expanded perlite

The production process of expanded perlite includes three processes: crushing, preheating and roasting. The principle process flow is shown in Figure 3-2-3, and the main production processes are shown in Table 3-2- 10.

Figure 3-2-3 Production Principle and Process Flow of Expanded Perlite

Table 3-2- 10 Main production processes of expanded perlite

The preheating heat source material is generally coal or the waste heat from other thermal operations.

The roasting heat sources include coal, gas, oil and electricity.

V. Development and utilization of Shangtianti perlite mine

Xinyang perlite mine is a key deposit of perlite resources in China, and its proven reserves account for 75% of the proven reserves of perlite in China. Its development and utilization level is a microcosm of the utilization level of similar resources in China.

Physical and chemical properties of 1. Upper ladder perlite

The pearlite of Shangtianti is relatively pure, containing a small amount of feldspar and Shi Ying phenocrysts, and a small amount of magnetite and biotite. Liu Chong perlite is white and green, commonly known as green ore, and Shizui perlite is white and reddish, commonly known as white ore. See table 3-2- 1 1 for chemical constituents.

Table 3-2- 1 1 chemical composition of perlite samples from Shangtian ladder

See table 3-2- 12 for the chemical composition of some perlite ores in China.

See table 3.2- 13 for the chemical composition of perlite fines in different particle sizes.

Comparing table 3-2- 1 1 and table 3-2- 13, it can be seen that the chemical composition of perlite powder ore and raw ore in Shizui or Liu Chong has not changed obviously, and the chemical composition of each particle size has reached the requirements of Grade I, indicating that there is no need for classification and purification.

2. The quality of expanded perlite on the ladder

When roasting, perlite sand is softened due to sudden heating, and the combined water in the glass vaporizes to generate great pressure, and its volume expands rapidly, forming porous expanded perlite with cavity structure. The basic condition of perlite expansion is glassy, and the internal cause of perlite expansion is the vaporization of water when heated. The amount of water in vitreous body is usually expressed as loss on ignition. Preheating is to control the optimal water quantity (effective water quantity). If the water quantity is too large, the ore will burst into powder, and if the water quantity is insufficient, the expansion will be insufficient. The quality of expanded perlite is controlled by controlling preheating time, temperature, roasting time, temperature and ore particle size.

Table 3-2- 12 chemical composition of perlite, rosin rock and obsidian from some places in China

Table 3-2- 13 chemical composition of Tiantai perlite fine ore in different particle sizes

During the production expansion in the vertical kiln burning gas (Zhongnan Filter Aid Factory), the expansion conditions are: preheating temperature 450℃, preheating time 12min, roasting temperature 1 100℃ and roasting time 3 ~ 5 s. Expansion results: the bulk density (kg/m3) changed from 1030 before expansion to 60. 1 after expansion, and the expansion multiple (K0) was 17. 14.

See table 3-2- 14 for particle size composition and particle size capacity before and after expansion.

Table 3-2- 14 Determination of particle size composition and particle size capacity before and after production expansion

It can be seen from Table 3-2- 14 that the coarse particle size of the expanded product has increased obviously, and the+60 mesh has increased from 12.88% before expansion to 67.17%; The coarser the particle size, the smaller the bulk density.

See table 3-2- 15 for the determination results of thermal conductivity of expanded perlite.

Table 3-2- 15 Test Report on Thermal Conductivity of Tiantai Perlite Powder Ore

Testing unit: Quality Supervision and Inspection Center of Thermal Insulation and Sealing Materials of National Building Materials Bureau.

According to the national standard GB 5211.15-88 (equivalent to the international standard ISO787/5- 1980), the absorption of refined linseed oil by expanded perlite was determined, expressed as the percentage of mass/mass, and the results showed that the absorption of expanded perlite was 0 ~ 280μ m. The oil absorption of1~150μ m expanded perlite is 2 10%.

See table 3-2- 16 for the quality requirements of expanded perlite in building materials industry.

Table 3-2- 16 Building Material Industry Standard of Expanded Perlite (JC/T209-92)

According to Table 3-2- 16, the technical performance of Shangtianti expanded perlite has reached 70 grade, but the particle size composition is relatively fine, and the lower limit of particle size < 0.15 mm accounts for 12. 12%, which has exceeded the maximum allowable value (6%) of qualified products. The problem of fine particle size can be solved by collecting < 0.15 mm product at the end of expansion roasting.

3. Utilization of-60 mesh perlite powder ore

See Figure 3-2-4 for the processing flow of perlite sand in Xinyang Shangtianti.

Figure 3-2-4 Processing Process of Non-metallic Ore Perlite in Shangtianti, Xinyang

The price of perlite ore mine is 40 yuan /t, ore 80 yuan /t and expanded perlite 26 yuan /m3. In the process of ore processing,-60 mesh fine ore is discarded as tailings, and the yield is 40%, that is, 400kg of-60 mesh fine ore is discarded every time 1t perlite ore is processed, and the-60 mesh tailings lost every year reach18 ~ 200,000 t. This not only causes great waste of resources, but also causes environmental pollution. This problem has been puzzling mining enterprises. Therefore, the State Science and Technology Commission and Henan Science and Technology Commission organized the National Engineering Technology Research Center for Comprehensive Utilization of Non-metallic Mineral Resources and other units to tackle key problems in the comprehensive development and utilization of various non-metallic minerals in Shangtianti (project numbers are 96044 1034 and 97 1 14020 1 respectively). Among them, the utilization of-60 mesh perlite powder ore has achieved the following results.

(1) as a functional filler in plastic and rubber products.

Perlite powder ore of-60 mesh is directly fed into a suspension roller mill or a high-speed impact mill for fine grinding, or into a jet mill for ultra-fine grinding. The obtained perlite micropowder (fine grinding100% < 40μ m, ultra-fine grinding100% < 20μ m) can be used as plastics and fatty acids after being modified by surface modifiers such as silane, titanate and fatty acid.

In the manufacturing process of rubber sheet, perlite micropowder is used to replace PNT reinforcing agent in the original formula, and the physical and mechanical properties of the obtained product are shown in Table 3-2- 17.

Table 3-2- 17 Measured Results of Physical and Mechanical Properties of Products

In the process of producing rubber pipes, the Si-Al carbon black in the original formula was replaced by perlite micropowder. The physical and mechanical properties of the products are shown in Table 3-2- 18.

Table 3-2- 18 Measured Results of Physical and Mechanical Properties of Products

In the process of cable production, perlite micropowder is used to replace the active calcined kaolin in the original formula, and the physical and mechanical properties of the product are shown in Table 3-2- 19.

Table 3-2- 19 Test Results of Physical and Mechanical Properties of Products

Using surface-modified perlite micropowder to replace PNT, Si-Al carbon black and activated calcined kaolin as filler in rubber products and cables not only meets the requirements of relevant national standards, but also has obvious price advantages.

(2) perlite polishing powder

At present, the most used perlite polishing powder is 100# perlite polishing powder. For example, the annual consumption of Anyang Glass Shell Factory is about 300 tons, and its quality requirements are as follows: ① particle size+150μ m = 0,-44μ m <15%; ② The specific gravity is 2.2 ~ 2.4; ③ The hardness (Morse hardness) is 5.5 ~ 6.

By dry screening, the yield of perlite polishing powder separated from-60 mesh perlite tailings powder is only 30%, and the dust is large. The qualified perlite polishing powder can be obtained by wet operation, rod grinding, classification, desliming, fine screen and mill forming a closed circuit, and the yield can reach 70%. The sieving results of polishing powder particle size are:+150μ m = 0,-44μ m = 8.54,-150μ m ~+44pm = 91.46. The specific gravity is 2.27g/cm3.

(3) as a filler for ordinary printing paper

Instead of talcum powder as the filler of ordinary printing paper, except for the paper with talcum powder as the filler, all the other indexes are higher than that of the paper with talcum powder as the filler.

(4) spherical glass shell expanded perlite

Expanded perlite is mainly used as lightweight building materials and thermal insulation materials. The expanded perlite produced in China is single, with only porous expanded perlite. Porous expanded perlite has large water absorption, low compressive strength and poor fluidity of mortar, which often lead to problems such as quality and performance degradation and short service life in the process of use. These weaknesses of porous expanded perlite products seriously restrict the development of perlite industry.

The products of spherical glass shell non-porous perlite avoid the above defects of porous expanded perlite. However, at present, only the United States, Japan and France have mastered this technology. Xinyang Normal University undertook the key project of Henan Science and Technology Commission-production technology of spherical closed-cell expanded perlite (project number 97 1 140204). After three years and hundreds of experiments and studies by the comrades of the research group, the first electric expansion furnace with automatic temperature control was designed and manufactured by ourselves, and spherical closed-cell expanded perlite, namely spherical glass shell expanded perlite, was successfully produced from-60 mesh perlite powder. The product performance has reached. See Table 3-2-20 for the comparison of performance indexes between expanded perlite of glass shell and porous expanded perlite.

Table 3-2-20 Properties of Closed-cell and Porous Expanded Perlite

See table 3.2.2 1 for the performance comparison with similar foreign products.

Closed-cell expanded perlite with spherical glass shell is suitable for light insulation and energy-saving fields and light fillers, especially for building energy-saving fields requiring certain strength, water absorption and mortar fluidity or used in liquid systems, such as external wall insulation materials, decorative boards, composite insulation boards and other light building plates; It is also suitable as a filter aid for processing beverages.

The main way to solve the application of-60 mesh perlite powder is to expand it into closed-cell spherical perlite with glass shell. Because this kind of expanded product has excellent performance, large market and low cost. If a closed-cell expanded perlite factory with an annual output of 5,000 t is built, the equipment investment needs 680,000 yuan, the production cost is 396 yuan /t, the ex-factory price is 1000 yuan /t, and the annual profit and tax can reach 3 million yuan.

Table 3-2-2 1 Performance comparison between this product and similar products abroad

4. Perlite filter aid

Expanded perlite is mainly used as light building materials and thermal insulation materials, accounting for about 70% of the expanded perlite output, followed by filter aid, accounting for about 20%. Perlite as a filter aid is suitable for the production of alcohol, beverage, edible oil, monosodium glutamate, medicine and chemicals. After the expanded perlite is finely crushed (-325 mesh) and classified, the product becomes perlite filter aid. After the perlite filter aid powder is piled up, it forms an uncompressed cake, that is, a filter bed is formed. 80% ~ 90% of this filter bed is air. The liquid is filtered through it, and the extremely fine solid particles in suspension are intercepted, thus achieving higher filtration speed and clarity.

The perlite filter aid produced by Xinyang Zhongnan Filter Aid Factory is mainly used in the production of monosodium glutamate, but it has not yet opened the market in the beer industry. Before 1980' s, the backward cotton cake filtration method was always used in the filtration of beer products in China. In the 1980s, China introduced diatomite filtration technology, which was widely adopted by the beer industry in China. In recent years, perlite filtration technology has appeared again, but its market share is small. Filtration plays an extremely important role in beer production. A series of solid-liquid separation processes are combined in the process of beer production, including wort filtration after saccharification, clarification filtration of beer after fermentation and refined filtration of beer before packaging. The ability to filter solid particles in beer is basically only related to the relative size of filter aid particles and pores and the shape of the structure. Table 3-2-22 lists the characteristics of common filter AIDS.

Table 3-2-22 Characteristics of Common Filter Aids

When a filter aid is used as a filter medium, a support must be selected so that the filter aid can be coated on the support to form a filter layer, that is, a filter cake. This support itself is also a filter medium. The supports mainly include filter cloth, filter paper and filter screen. Filter cloth is often used in the filtration process with diatomite as filter aid, and the main factors of filter cloth selection are shown in Table 3-2-23. Filter paper is a kind of filter similar to non-woven fabric. The characteristics of filter paper are: there is less risk of filter cake particles leaking due to the change of pressure during filtration, so some breweries use filter paper as a support in large plate-and-frame filters. However, there are some shortcomings, such as complex and fine pores, easy blockage and poor strength. The filter screen is generally made of stainless steel wire or brass wire, which is expressed by mesh number.

Table 3-2-23 Main factors of filter cloth selection

(1) acrylonitrile and vinyl chloride * * * polymer. ②S, short fiber; F, multifilament; M, monofilament.

It can be seen from Table 3-2-22 that perlite filter aid can replace diatomite filter aid in beer industry. Puyang Zhongyuan Brewery uses three kinds of filter AIDS. See Table 3-2-24 for comparison of effects.

Table 3-2-24 Comparison of Three Filtration Forms of Filter Aids

The whole wine filtering system using perlite as filter aid is exactly the same as diatomite, but the price of perlite filter aid is lower than diatomite filter aid, and the cost per ton of beer can be saved 1.5 yuan.

Filter AIDS are used in large quantities in beer industry. In order to make the perlite filter aid widely used in brewery, in addition to finely processing the raw materials of perlite filter aid, it is necessary to establish an operation procedure suitable for the use of Tiantai perlite filter aid. Every operation from pre-coating, addition, pressure difference to support replacement should have scientific and reasonable operation parameters, and appropriate supports should also be selected. Perlite filter aid is gradually popularized in beer industry.

Main references

[1] Editorial Committee of Handbook of Nonmetallic Mining Industry, Handbook of Nonmetallic Mining Industry (Volume I and Volume II), Metallurgical Industry Press, 1992.

[2] Huang Chengyan, China Diatomite and Its Application, Science Press, 1993.

[3] david lee Ming et al., Application of perlite filtration technology in beer industry, Henan Science and Technology, 1997, 1 period, p.20 ~ 22.