Perlite

1. Overview

Perlite minerals include perlite, obsidian and turpentine.

Perlite is a glassy rock formed by the rapid cooling of acidic lava from volcanic eruptions. Its composition is equivalent to rhyolite and it is named because of its pearly crack structure. The water content of perlite is 2 to 6.

Pitchstone is also an acidic vitreous volcanic rock with a unique rosin luster and a higher water content than perlite, ranging from 6 to 10.

Obsidian is a glassy volcanic rock whose composition is equivalent to granite. It has a low water content, less than 2.

Perlite, rosinite and obsidian all have the characteristic that their volume can expand several times to more than 30 times under instantaneous high temperature conditions (around 1200°C). They are ideal for making high-quality lightweight building materials and An important mineral raw material for thermal insulation materials.

The types of perlite ores are shown in Table 3-2-1.

Table 3-2-1 Perlite ore types

The classification of perlite ore grades is shown in Table 3-2-2.

Table 3-2-2 Types and grades of perlite ore

2. The main uses of expanded perlite

The main uses of perlite are expanded Main uses of perlite. Because 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, it is widely used in various industrial sectors, especially important ones. of lightweight building materials and thermal insulation materials. The main uses of expanded perlite are shown in Table 3-2-3.

Table 3-2-3 Main uses of expanded perlite

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

Table 3-2-4 Consumption composition of expanded perlite in Japan

Table 3-2-5 Consumption composition and consumption volume of expanded perlite in the United States

3. Quality standards of perlite

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

K0=5.2 (K-0.8)

In the formula, K0——the expansion ratio in industrial production; K——Laboratory simple roasting expansion ratio.

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

In addition, it is required that the SiO2 content in the ore reaches 70, H2O is 4 to 6, and Fe2O3 FeO <1 is high quality. The ore is fully vitreous, with no or only slight devitrification and no phenocrysts.

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

Raw perlite ore needs to be processed through a crushing and screening process to obtain perlite ore suitable for furnace expansion. Generally, the process flow shown in Figure 3-2-1 is used for crushing and screening. The process flow of Noagua perlite beneficiation in the United States is shown in Figure 3-2-2.

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

Table 3-2-7 Quality classification standards for perlite

Figure 3-2-1 Crushing and screening principle process flow chart

Figure 3-2-2 Noagua perlite mineral processing process flow chart in the United States

Industrial application one Grade 3 perlite ore, grade 3 ore cannot be used. The standards for expanded perlite mineral sand are in accordance with the standards promulgated by the National Bureau of Building Materials Industry, see Table 3-2-8.

Table 3-2-8 Technical requirements for ore sand for expanded perlite (ZBQ25002-88)

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

Table 3-2-9 Technical index requirements for ore sand for expanded perlite (DB/410000D63001-86)

IV. 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 process is shown in Table 3-2-10.

Figure 3-2-3: The production principle and process flow of expanded perlite

Table 3-2-10: The main production process of expanded perlite

Preheating The heat source material is generally coal or waste heat from other thermal work operations.

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 my country, and its proven reserves account for 75% of my country’s proven perlite reserves. . Its development and utilization level is a microcosm of the utilization level of similar resources in my country.

1. The physical and chemical properties of Shangtianti perlite

Shangtianti perlite is relatively pure, containing a very small amount of feldspar, quartz phenocrysts, a very small amount of magnetite and biotite . Liu Chong perlite is white with a greenish tint and is commonly known as Qingite. Shizui perlite is white with a reddish tint and is commonly known as Baimine. The chemical composition is shown in Table 3-2-11.

Table 3-2-11 Chemical composition of Shangtianti perlite samples

The chemical composition of some perlite mines in my country is shown in Table 3-2-12.

The chemical composition of perlite powder in different particle sizes is shown in Table 3.2-13.

Comparing Table 3-2-11 and Table 3-2-13, it can be seen that there is no obvious change in the chemical composition of the perlite powder ore and raw ore in Shizui or Liuchong. The chemical composition of grade I products all meet the requirements of grade I products, indicating that there is no need for graded purification.

2. The quality of expanded perlite

When roasted, the perlite sand is softened due to sudden heating, and the combined water in the glass vaporizes to produce a large pressure, volume Rapidly expands to form porous expanded perlite with a cavity structure. The basic condition for the expansion of perlite is glass, and the vaporization of water upon heating is the intrinsic cause of the expansion of perlite. The amount of water in the vitreous body is usually expressed as loss on ignition. Preheating is to control the optimal value of water volume (effective water volume). If the water volume is too large, the ore will burst into powder, and if the water volume is insufficient, the expansion will be insufficient. Control the quality of expanded perlite by controlling preheating time, temperature, roasting time, temperature, ore particle size, etc.

Table 3-2-12 Chemical composition of perlite, rosinite and obsidian from some producing areas in my country

Table 3-2-13 Shangtianti perlite powder ore in different grains Grade chemical composition

When the gas-fired vertical kiln (Zhongnan Filter Aid Factory) is used for production expansion, the expansion conditions are: preheating temperature 450℃, preheating time 12min, roasting temperature 1100℃, roasting Time 3~5s. Expansion results: Bulk density (kg/m3) changed from 1030 before expansion to 60.1 after expansion, and the expansion multiple (K0) was 17.14.

The particle size composition and particle size capacity before and after expansion are shown in Table 3-2-14.

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: the coarse particle size of the expanded product increased significantly, +60 mesh by The 12.88 before expansion increased to 67.17; the coarser the particle size, the smaller the bulk density.

The thermal conductivity measurement results of expanded perlite are shown in Table 3-2-15.

Table 3-2-15 Inspection report on thermal conductivity of Shangtianti perlite powder

Testing unit: National Building Materials Administration Thermal Insulation and Sealing Materials Product Quality Supervision and Inspection Center.

According to the national standard GB5211.15-88 (equivalent to the international standard ISO787/5-1980), the absorption of refined linseed oil by expanded perlite was measured, expressed as a percentage of mass/mass, and the measurement results : The oil absorption capacity of 0-280μm expanded perlite is 248; the oil absorption capacity of 1-150μm expanded perlite is 210.

The building materials industry’s quality requirements for expanded perlite are shown in Table 3-2-16.

Table 3-2-16 Building materials industry standard for expanded perlite (JC/T209-92)

Refer to Table 3-2-16 for the technical performance of Shangtianti expanded perlite It has reached the 70 mark, but the particle size composition is too fine. The lower limit of particle size is less than 0.15mm, accounting for 12.12, which has exceeded the maximum value allowed for qualified products (6). The problem of finer particle size can be solved by separately collecting <0.15mm particle size products at the end of expansion roasting.

3. Utilization of 60-mesh perlite powder

The processing flow of Xinyang Shangtianti perlite sand is shown in Figure 3-2-4.

Figure 3-2-4 Xinyang Shangtianti Non-metallic Mine Perlite Processing Process

The price of perlite raw ore mine is 40 yuan/t, ore sand is 80 yuan/t, and expanded pearls Rock 26 yuan/m3. During the ore processing process, -60 mesh fine ore is discarded as tailings, with a yield of 40, that is, 400kg of -60 mesh fine ore is discarded for every 1 ton of perlite raw ore processed, and the amount of -60 mesh tailings discarded every year reaches 18 ~200,000 tons. This not only causes a huge waste of resources, but also causes environmental pollution. This problem has always troubled mining companies. To this end, the National Science and Technology Commission and the Henan Provincial Science and Technology Commission organized the National Engineering Technology Research Center for Comprehensive Utilization of Non-metallic Mineral Resources and other units to conduct key research on the comprehensive development and utilization of various non-metallic minerals in Shangtianti (project numbers are 960441034 and 971140201 respectively) ). Among them, the following results have been achieved in the utilization of -60 mesh perlite powder.

(1) Used as functional filler in plastic and rubber products

-60 mesh perlite powder, directly fed into suspension roller mill, high-speed impact mill for fine crushing, or Enter the jet mill for ultra-fine grinding. The obtained perlite powder (fine grinding 100＜40μm, ultra-fine grinding 100＜20μm) can be used as plastic after being modified by surface modifiers such as silane, titanate, fatty acid and so on. , Functional mineral fillers in rubber products.

In the manufacturing process of rubber sheets, perlite powder is used to replace the PNT reinforcing agent in the original formula. 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 tubes, perlite micro powder is used to replace Si-Al carbon black in the original formula, and the products The physical and mechanical properties are shown in Table 3-2-18.

Table 3-2-18 Measured results of physical and mechanical properties of products

In the process of producing cables, perlite micro powder was used to replace the active calcined kaolin in the original formula. The physical properties of the product The mechanical properties are shown in Table 3-2-19.

Table 3-2-19 Test results of physical and mechanical properties of products

Use surface-modified perlite powder to replace PNT, Si-Al carbon black, and activated calcined high soil to make rubber products , the filler in the cable, not only the physical and mechanical properties of the product meet the relevant national standard requirements, but also has obvious price advantages.

(2) Perlite polishing powder

The most commonly used perlite polishing powder is 100# perlite polishing powder. For example, Anyang Glass Shell Factory uses about 300 tons per year, among which The quality requirements are: ① Particle size + 150 μm = 0, -44 μm < 15; ② Specific gravity 2.2 ~ 2.4; ③ Hardness (Morse hardness) 5.5 ~ 6.

Using dry screening method, the yield of perlite polishing powder product separated from -60 mesh perlite tailings powder is only 30, and the dust is large. Using wet operation, using rod mill grinding, classification, desliming process, fine screen and mill to form a closed circuit, qualified perlite polishing powder can be obtained with a yield of 70%. Polishing powder particle size sieve analysis results: +150μm=0, -44μm=8.54, -150μm～+44pm=91.46. The specific gravity is 2.27g/cm3.

(3) Used as a filler for ordinary printing paper

Replace talcum powder as a filler for ordinary printing paper. Except for the whiteness of the paper, which is not as good as the paper filled with talc powder, the other indicators are All exceed the paper filled with talc powder.

(4) Spherical glass shell expanded perlite

Expanded perlite is mainly used as lightweight building materials and insulation materials. The expanded perlite products produced in my country are single, only porous expanded pearls rock. Porous expanded perlite has high water absorption, low compressive strength, and poor mortar fluidity, which often leads to problems such as reduced quality, performance, and short service life of the product during use. These weaknesses of porous expanded perlite products have seriously restricted the perlite industry. development.

The product of spherical glass shell non-porous perlite avoids the above-mentioned defects of porous expanded perlite. However, currently only three countries in the world, the United States, Japan, and France, have mastered this technology. Xinyang Normal University undertook a key research project of the Henan Provincial Science and Technology Commission - Spherical Obturator Expanded Perlite Production Technology (Project No. 971140204). After three years of hundreds of experimental studies by the research team members, they independently designed and manufactured the first automatic temperature control machine in China. The electric expansion furnace used -60 mesh perlite mineral powder to successfully produce spherical closed-cell expanded perlite, that is, spherical glass shell expanded perlite. The product performance has reached the international advanced level of similar products and has been patented (publication number CN123200A). The comparison of performance indicators between glass shell expanded perlite and porous expanded perlite is shown in Table 3-2-20.

Table 3-2-20 Performance of closed-cell and porous expanded perlite

The performance comparison with similar foreign products is shown in Table 3.2.21.

Spherical glass shell closed-cell expanded perlite is suitable for lightweight thermal insulation and energy-saving fields and lightweight fillers. It is especially suitable for building energy-saving fields that require a certain strength, water absorption and mortar flow performance or in liquid systems. It is used in various lightweight construction panels such as exterior wall insulation materials, decorative panels, composite insulation panels, etc. It is also suitable as a filter aid for processing beverages.

Using -60 mesh perlite mineral powder to expand into glass-shell closed-cell spherical perlite is the main way to solve the use of -60 mesh perlite powder. Because this kind of expansion product has excellent performance, large market and low cost. For example, to build a spherical glass closed-cell expanded perlite factory with an annual output of 5,000 tons, the equipment investment requires 680,000 yuan, the production cost is 396 yuan/t, the ex-factory price is 1,000 yuan/t, and the annual profit and tax can reach 3 million yuan.

Table 3-2-21 Comparison of performance between this product and similar foreign products

4. Perlite filter aid

The main use of expanded perlite is as Light building materials and insulation materials account for about 70% of expanded perlite production, followed by filter aids, accounting for about 20%. Perlite is used as a filter aid in the production of alcohol, beverages, edible oils, monosodium glutamate, medicines and chemicals. The expanded perlite is finely crushed (-325 mesh) and classified to become perlite filter aid. After the perlite filter aid powder is accumulated, it forms an uncompressed cake-shaped body, which forms a filter bed. 80 to 90% of this filter bed is air. The liquid is filtered through it, and the very fine solid particles in suspension are intercepted, thereby achieving a higher filtration rate and clarity.

The perlite filter aid produced by Xinyang Zhongnan Filter Aid Factory is mainly used in the production of MSG and has not yet opened up the market in the beer industry. Before the 1980s, the relatively backward cotton cake filtration method was used for the filtration of finished beer in my country. In the 1980s, my country introduced diatomaceous earth filtration technology, which has been widely used by my country's beer industry. In recent years, perlite filtration technology has appeared, but its market share is small. Filtration plays an extremely important role in beer production. The beer production process combines a series of solid-liquid separation processes, including wort filtration after saccharification, beer clarification filtration after fermentation, and refining filtration of beer before packaging. The ability to filter out solid particles in beer is basically only related to the relative size of the 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 using filter aids as filter media, a support must be selected so that the filter aids can be applied on The support forms the filter layer, that is, the filter cake. This support itself is also the filter media. The supports mainly include filter cloth, filter paper and filter screen. Filter cloth is often used in the filtration process using diatomite as a filter aid. The main factors for filter cloth selection are shown in Table 3-2-23.

Filter paper is a filter material similar to non-woven fabric. The characteristics of filter paper are: there is less risk of leakage of filter cake particles due to changes in pressure during filtration, so some breweries use filter paper as a support in large plate and frame filters. However, there are shortcomings in that the pores of cardboard are complex and small, easy to block and have poor strength. The filter screen is generally made of stainless steel wire or brass wire, expressed by mesh number.

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

①Polymer of acrylonitrile and vinyl chloride. ②S, short fiber; F, multifilament; M, monofilament.

As can be seen from Table 3-2-22, perlite filter aid can replace diatomite filter aid in the beer industry. Puyang Zhongyuan Brewery uses three types of filter aids. See Table 3-2-24 for effect comparison.

Table 3-2-24 Comparison of filtration forms of three filter aids

The entire wine filtration system using perlite as a filter aid is exactly the same as diatomite, but the perlite filter aid The agent price is lower than that of diatomite filter aid, and it can save 1.5 yuan per ton of beer.

Filter aids are widely used in the beer industry. In order for breweries to widely use perlite filter aids, in addition to fine processing of perlite filter aid raw materials, it is also necessary to establish operating procedures suitable for the use of Shangtianti perlite filter aids, from pre-coating, addition, pressure difference, to Every operation such as replacing supports should have scientific and reasonable operating parameters. In addition, appropriate supports should be selected. Perlite filter aids are gradually being promoted in the beer industry.

Main references

[1] "Non-metallic Mineral Industry Handbook" Editorial Committee, Non-metallic Mineral Industry Handbook (Volume 1, Volume 2), Metallurgical Industry Press, 1992.

[2] Huang Chengyan et al., Chinese diatomite and its applications, Science Press, 1993.

[3] Li Haoming et al., Application of perlite filtration technology in beer industry, Henan Science and Technology, 1997, Issue 1, P.20～22.