Where and why chalk is mined. Chalk Rock, description, properties, deposits and photos. Chalk stone. School application

Chalk is a material that is familiar to everyone from school, it is a witness to eras that ended millions of years ago. The chalk contains a large amount of calcium deposits from the shells of prehistoric microorganisms and the simplest representatives of the plant world. Mineral deposits as well as processed powders are used in a variety of areas of life - from industrial paints and food additives to cosmetics. It is important to understand how chalk is formed, what it is made of and where it is used.

As early as ninety million years ago, a large amount of silt accumulated on the territory of Northern Europe, at the depth of the sea. Many protozoa (foraminifera) lived on such clusters. Their particles are composed of fine calcite and water. The stratigraphic European Cretaceous group arose in the period of the same name.

The rock was used to create white cliffs in Kent, as well as slopes in the Dover area. It was these accumulations that became the main component of the crushed white powder. But most of all in such a rock there are remnants of algae and compounds of a finely dispersed nature. Many experts have concluded that the breed originated primarily from vegetation.

Principle of education

Many people wonder what chalk is made of. This mineral is natural breed and is mined for later use. It is based on calcium deposits that were created by the remains of ancient earth inhabitants.

When creating products with this component, as a rule, processed chalk is used. Natural deposits of this material contain a large amount of impurities - this includes sand, small stones, mineral particles of a gaseous state. It is for this reason that the chalk obtained from these deposits breaks easily and dissolves in water. A suspension is obtained from such a mixture.

In this case, heavy impurities sink mainly to the bottom of the container, and light calcium components are transferred to a special container, where, after adding adhesive components to them, they dry well, changing to the state of chalk, which is used for drawing.

Untreated chalk from quarries is used in the construction industry to create lime.

Mineral composition

Chemically, chalk is similar to the formula for potassium carbonate. But the composition of this mineral contains the following components:

A high amount of silicon within the chalk increases its density, and the presence of red colors may indicate a large amount of iron in the composition.

Where does the mining take place

The accumulation of chalk deposits began many centuries ago, back in the Cretaceous period, which covers about 80 million years. About twenty sedimentary minerals of the planet contain chalk.

The main places of origin of Cretaceous structures:

Main components

The composition of the mineral rock includes a large number of components. These include:

Basic properties

Moisture has a special effect on the quality of the rock, which violates its plasticity and strength. The resulting increase in moisture leads to a degradation process, while in dry conditions the rock can disintegrate even under the influence of minimal pressure.

The rock, which contains a large amount of moisture, quickly adheres to construction tools. It is for this reason that construction work using calcium carbonate is carried out mainly in countries with dry climates with high temperatures. The pyramid of Cheops is considered a good example of limestone buildings in ancient times.

During construction in sub-zero temperatures, such a mineral begins to disintegrate into separate parts by several millimeters.

Mineral rock price

The cost of the mineral will directly depend on the type of processing and its further use. There are several categories:

1. Colored crayons, which are used for painting on surfaces and asphalt, will cost no more than 400 rubles per pack.
2. White crayons without the addition of dyes - about 100 rubles.
3. Farming material, which is ordered in large quantities, and also taken away from factories of several tons. The price for each ton of ground limestone will range from 3 to 5 thousand.
4. The cost of edible chalk, which is used to add to products, and is also actively used in medicine, is from 40 to 300 rubles per hundred grams. The mineral belemnite is also used in medicine.

The use of lime mineral

Currently, chalk is a fairly widely used mineral that is included in many industries.

Chalk is actively used in the following areas:

Eating

The lowered level of calcium and other useful elements in the human body, as a result, leads to the desire to use the mineral in food. When carrying a baby, anemia, some women have an irresistible need to eat chalk, so it is very important to understand whether it is safe for the body.

Of course, one or several small pieces of pure chalk will not harm the human body. But it is important to remember that chalk without additional additives is not sold in the public domain and it is almost impossible to find it, except for the pharmacy, where it is sold in the form of calcium gluconate. The most common product in the store is simple school chalk; during its production, glue and other dyes are added, which are very dangerous and toxic to the body.

Acceptance of chalk in an uncontrolled dosage as a result can lead to liming of blood vessels, deposition of stones in the kidneys. All this as a result will lead to difficulties with the work of the digestive tract.

In addition to the negative effect of impurities that are included in the composition of building chalk, it begins to oxidize when interacting with gastric juice, which changes it to a harmful chemical reagent.

Why does the body require chalk

Very often, such a desire appears when there is a lack of calcium in the human body. Such a reduced indicator may occur due to too little nutrition, prolonged stress and nervousness, a weakening of the immune system after serious illnesses, as well as carrying children.

Considering that when carrying a child, it is calcium that forms the basis for the formation of the skeletal and nervous system of the body, a low amount of such a mineral is very important to replenish in time. In this case, improving the diet will not help change the situation, therefore, experts advise using vitamin complexes during pregnancy.

Due to the fact that the neural tube of the fetus develops in the early stages, in order to reduce the possibility of malformation, it is important to start taking a complex of vitamins before conception. Anemia and a low calcium ratio in the body in most cases lead to heavy and long periods.

In the presence of symptoms of calcium deficiency (convulsions, pallor of the skin, deterioration of the structure of hair and nails), you can start taking special tablets of calcium gluconate. Unlike clerical and other industrial types of chalk, they are completely safe; with prolonged use, they can lead to diarrhea.

Most often, the craving for the use of this mineral passes after improving the diet and adding a lot of dairy products, fresh herbs and vegetables, and chicken eggs to it.

In some cases, the desire to take inedible substances may indicate a disorder with the nervous system. After consuming such products, intestinal obstruction and nutritional deficiencies very often occur.

a piece of chalk- it is a soft mountainous porous sedimentary rock of white color, is a type of limestone and consists of the mineral calcium (calcite), which is also called calcium carbonate or CaCO3. It is formed at the depths of the sea by the accumulation of small plates of calcite. The chalk contains small amounts of magnesium carbonate and metal oxides.

Chalk has a very high resistance to weathering than the clay with which it is usually associated, thus forming high steep cliffs where the chalk ridges meet the sea. Chalk hills tend to form where streaks of chalk reach the surface at an angle, thus forming a cliff. Because chalk is porous, it can hold a large amount of groundwater, providing natural bodies of water that slowly release water due to dry seasons.

1. Clusters
2. Education
3. Structure
4. Used by

Chalk accumulations

The Cretaceous group of the European stratigraphic division originated during the Cretaceous period. It forms the famous White Cliffs of Dover in Kent, England, as well as the white slopes on the other side of the Strait of Dover. In Champagne (France), chalk caves are used to store wine. Some of the tallest chalk cliffs in the world occur at Mons Klint (Denmark).

Chalk formation

Ninety million years ago in Northern Europe, silt accumulated in the lower part of the great sea. Protozoa, such as foraminifera, lived on marine debris that crumbled down from the upper layers of the ocean. Their particles were made from calcite, extracted from seawater.

Chalk composition

Chalk is mainly composed of calcium carbonate (over 98%) with small amounts of silt and clay.

Chalk used

It is used in the production of quicklime and slaked lime, as a whitewash of buildings and tree trunks. In southeastern England, Danehale is a prime example of ancient chalk quarries. In such places, silicon was mined, which was then used in the manufacture of stone tools.

They write in chalk on blackboards, mostly rough. Although natural chalk is traditionally used, modern board chalk is usually made of mineral gypsum (calcium sulfate), often supplied in compressed powder sticks about 10 cm in length.

Sidewalk chalk is similar to school chalk, although it is larger and more colored. It is used to paint on sidewalks, streets and roads. This is done mainly by both children and adult artists.

In agriculture, chalk is used to raise the pH in soils with high acidity. The most common forms are CaCO3 (calcium carbonate) and calcium oxide.

In tennis, chalk was previously used to mark the playing field. This has the advantage that if the ball hits the line, a cloud of chalk or dust pigment could be seen. Currently, chalk has been replaced by titanium dioxide.

In gymnastics, rock climbing, weightlifting, and tug-of-war, chalk - now usually magnesium - is applied to the hands to remove sweat and reduce slipping.

Tailor's chalk is tough and is used to make temporary markings on fabrics. Nowadays, it is usually made from talc (magnesium silicate).

Toothpaste also usually contains a small amount of chalk to serve as a mild abrasive.

Chalk is used for very fine polishing of metals.

Chalk is a source of quicklime by thermal decomposition or hydrated lime by water quenching.

Valuyskoye, Zaslonovskoye, Znamenskoye, Kazatskie Bugry and Korochanskoye can be classified as deposits with reserves of lower quality chalk in the Belgorod Region. The chalk of these deposits contains relatively low levels of CaCO 3 (82 - 87%) and is clogged with other impurities. It is not possible to obtain high-quality products from this chalk without deep enrichment. Without enrichment, this chalk can be used for the production of lime and used in agriculture as an ameliorant for soil deoxidation. The chalk deposits of the Voronezh region belong to the Turonian-Coniacian age. Chalk has a high content of CaCO) (up to 98.5%) and a low content of non-carbonate impurities - less than 2%, is enriched in amorphous silica, apparently brought from the Santonian deposits. Chalk occurs in close proximity to the surface and is covered by chalk eluvium or Quaternary sediments. A characteristic feature of the chalk from the deposits of the Voronezh region is its water saturation. The moisture content in chalk reaches 32%, which causes serious difficulties in its extraction and processing. The largest deposits of the Voronezh region include Kopa-nishchenskoye, Buturlinskoye, Krupnennikovskoye and Rossoshanskoye. The Cretaceous strata at the Kopanishchenskoye deposit ranges from 16.5 to 85 m (average 35 m). Overburden is represented by a soil-vegetation layer and is only 1.8 - 2.0 m. Vertically, the chalk thickness is divided into two members, of which the lower one contains up to 98% CaCO 3, and the upper one is slightly less (96 - 97.5%). The Buturlinskoe deposit with extremely homogeneous white chalk of the Turunian stage with a thickness of 19.5 to 41 m. The overburden thickness reaches 9.5 m and is represented by a vegetation layer, marls, sandstones and sandy-clay formations. The content of calcium and magnesium carbonates reaches 99.3%, with a relatively small amount of non-carbonate components.

§1.3 Physical and chemical properties of chalk,

The study of the physicochemical properties of natural chalk was carried out by many researchers, mainly in engineering geological terms. It was found that chalk belongs to hard semi-rocky rocks. Its strength is largely dependent on humidity. The ultimate compressive strength in the air-dry state varies from 1000 to 4500 kN / m 2. chaussure adidas Dry chalk has a modulus of elasticity from 3000 MPa (for loose chalk) to 10000 MPa (for dense) and behaves like an elastic body. The angle of internal friction of the chalk is 24 - 30 °, the adhesion under conditions of all-round compression reaches 700 - 800 kN / m 2. When moistened, the strength of the chalk begins to decrease already at a moisture content of 1 - 2%, and at a moisture content of 25 - 30%, the compressive strength increases 2 - 3 times, and plastic properties appear. The manifestation of the viscous - plastic properties of natural chalk with an increase in its moisture content leads to serious complications in the technology during its processing. From this, chalk sticks to the elements of vehicles (excavator bucket, dump truck body, feeder, belt conveyor). Gear roll crushers sticking. This leads, in some cases, to the failure of chalk extraction from the lower watered horizons, although the quality of the chalk of the lower horizons belongs to high-quality chalk. Natural chalk practically does not have frost resistance, after several cycles of freezing and thawing, it breaks up into separate pieces 1-3 mm in size. In some cases, this phenomenon is a positive factor. So, for example, when using chalk as an ameliorant for soil deoxidation, it is not necessary to grind it to a size of - 0.25 mm (limestone flour), but you can add crushed chalk up to - 10 mm to the soil. When freezing and thawing with annual plowing of the soil, pieces of chalk are destroyed and its actions to neutralize the soil persist for a long time. The physical and mechanical properties of natural chalk from individual deposits are shown in Table 1.2. As already noted, chalk consists mainly of two main parts - the carbonate part, which is soluble in hydrochloric and acetic acids (calcium and magnesium carbonates) and the non-carbonate part (clays, marls, quartz sand, metal oxides, etc.), which do not dissolve in the indicated acids. The carbonate part of chalk is 98 - 99% calcium carbonate. canada goose pas cher Magnesium carbonates are present in small amounts, which form crystals of magnesian calcite, dolomite and siderite scattered in the main mass of the Cretaceous. Among the previously proposed classifications of chalk - marl rocks, the most acceptable is the classification according to the content of carbonates and brands of products from chalk (Table 1.3). Table 1.3 Classification of chalk by carbonate content and brands of products from it.

*) Letters indicate the following brands of chalk: MK - lumpy chalk; MM - ground chalk; IP - chalk for liming the soil; ZhP - chalk for feeding agricultural animals and birds; PC - for the production of animal feed; С -separated; SG - separated hydrophobized; O - enriched. In the above classification, almost pure calcium carbonate with minor impurities is called pure chalk: MgO 3 - 0.3 - 0.7%; Fe, 0, - 0.08 - 0.3%; A1 2 O 3 - 0.21 - 0.44%; SiO 2 - 0.2 - 1.3%; SiO 2 (amorphous) - 0.4; water-soluble substances 0.05 - 0.11%. The chemical characteristics of chalk from some deposits in Russia are given in table. 1.4. Initially, it was believed that chalk is a rock mass, which is the same in chemical composition and physical properties throughout the deposit. However, during the long-term operation of the deposit, and especially during the transition of the chalk enterprise to the production of higher quality chalk products, it was found that in different areas (horizons) the chalk differs both in chemical composition and in physical and mechanical properties. Air Max Noir In this regard, geological and technological mapping is carried out in some chalk deposits, in which areas of high-quality chalk are indicated. The chalk deposits of the Belgorod region are characterized by a low content of insoluble residue and a high content of carbonates. Table 1.5 shows the reserves and chemical composition of the largest deposits in the Belgorod region. Table 1.5 Chalk reserves and its chemical composition for some deposits of the Belgorod region.

In addition to the chalk deposits of the Belgorod region shown in Table 1.5, reserves have been explored and approved at 23 more deposits, the reserves of which do not exceed 3.0 million tons. Nike soldes running each. In terms of material composition and physical and mechanical properties, the chalk of these deposits is close to the deposits shown in Table 1.5. The chalk of the Lebedinsky and Stoilensky deposits is of considerable interest for industrial development, where it is mined as overburden and transported to dumps. The annual associated production is more than 15 million tons of chalk, of which no more than 5 million tons are used in the national economy (Starooskolsk cement plant and a number of other small enterprises). Most of them are lost irretrievably in dumps. The chemical composition of chalk confined to the KMA iron ore deposits is shown in Table 1.6. The table shows that chalk accompanying iron ore deposits in terms of carbonate and silica content refers to high-quality chalk from which high-quality chalk products can be obtained without deep enrichment. Table 1.6 Chemical composition of chalk accompanying iron ore deposits KM A.

The table shows that chalk accompanying iron ore deposits in terms of carbonate and silica content refers to high-quality chalk from which high-quality chalk products can be obtained without deep enrichment. It should be noted that when designing enterprises for the extraction and processing of iron ores (Chernyanskoye, Pogrometskoye, etc.), it is necessary already in the project to provide for the processing of incidentally mined chalk or its separate storage.

§1.4 Production and consumption of chalk in Russia and abroad.

Extraction and processing of chalk in Russia has been known for a long time. Chalk was mainly used in the construction industry. Lime was produced from it, paints, putty, putty, etc. were prepared on the basis of chalk powder. At the end of the 19th century, private chalk factories were organized at the Belaya Gora chalk deposit (Belgorod), which produced lime from lump chalk in shaft furnaces and chalk powder. In 1935, the Shebekinsky combine was built to produce chalk products for the needs of industry. With the development of such industries as paint and varnish, rubber, electrical, polymer, etc., the need for chalk products has increased sharply. At the same time, the requirements for the quality of chalk products also increased. The existing chalk enterprises in Russia in 1990 could no longer provide the industry with high-quality chalk products. After 1990, a "boom" began in the Belgorod region in the creation of small private enterprises for the production of chalk products. This was facilitated by the huge number of chalk deposits that come out to the surface and the seeming "simplicity" of the chalk processing technology. The primitive technology of extraction and processing of chalk at these enterprises did not provide quality products, which led to the closure of most of these enterprises. At the same time, large chalk enterprises such as Shebekinskoye, Petropavlovskoye, Belgorodskoye, having reconstructed and modernized their equipment, ensured the production of high-quality chalk products. The most important requirements for products made from chalk (except for carbonate content) is its size - the fineness of grinding, expressed by the residue on sieves of certain sizes, or the percentage of particles of a given size (for example, 90% of particles with a size of 2.0 microns) - Various grades of chalk and their destinations produced in Russia and the CIS countries are shown in table 1.7. Table 1.7 Chalk brands produced in Russia and the CIS countries and their purpose.

Technical requirements for chalk products in Russia and the CIS countries are shown in Table 1.8. Table 1.8

Table 1.9

For comparison, table 1.9 shows foreign standards for fine chalk. Comparison of tables 1.8 - 1.9 shows that abroad more stringent requirements are imposed on chalk products in terms of such parameters as dispersity and whiteness. Table 1.10 shows the production of various grades of chalk in Russia and the CIS countries for 1990. This year is the last when the centralized accounting of the output in the USSR was carried out. Analyzing the state of affairs in the production of products at the Belgorod chalk enterprises, it can be noted that there was a slight increase in the production of chalk products in Russia as a whole. Table 1.10 Production of various types of chalk products in Russia and the CIS countries.

The creation of new industries for the production of paints and varnishes, polymer, rubber and other industries that consume chalk products, led to a sharp gap between the production and consumption of chalk. This was especially true during the transition of the paper industry from kaolin to chalk powder. chaussure nike max The paper industry requirements for chalk powder are fineness and whiteness. The production of high-quality brands of chalk is concentrated in Russia and primarily at chalk factories in the Belgorod region. In addition to the Shebekinsky chalk plant, which produces high quality separated chalk, new enterprises have been built. In 1995, at Lebedinsky GOK, a chalk plant CJSC Ruslaym was built according to the project of the Spanish company Reverte with a design capacity of 120 thousand tons per year. The plant produces up to 10 different grades of chalk, which in terms of quality composition are not inferior to international standards. The plant is equipped with the most modern technological equipment, all technological operations are fully mechanized and automated. At Stoilensky GOK, according to the project of Mabeteks, a chalk plant was built with a capacity of high-quality chalk products, the first stage of 300 thousand tons per year with a subsequent increase (second stage) to 1000 thousand tons. The first stage of the plant is under development ... The presence on the territory of the Belgorod region of huge reserves of high-quality chalk and the ever-increasing demand for chalk products provide a prerequisite for increasing production capacities at existing plants. The dynamics of the production of high-quality chalk in the Belgorod region is shown in Table 1.11. The annual consumption of natural calcium carbonate in lumpy, crushed and crushed form in developed countries exceeds 150 million tons per year. More than 7-7.5 million tons are produced annually in the USA and Canada, and more than 15 million tons in Europe. For comparison, it can be noted that the volume of Russian production, even taking into account the commissioning of the Stoilensky chalk plant, does not exceed 1.0 million tons. The production of ground calcium carbonate (MCC) - a product from 45 to 0.5 microns - in North America 24 companies are involved. In order to meet the demand for MCC, they are currently increasing their capacities by 1.5 times in comparison with 1994. Table 1.11 Production of high quality chalk at the factories of the Belgorod region.

The European ICC industry includes up to 50 companies. However, the market for carbonate fillers is dominated by two chalk empires: Pluess-Staufer AG with the well-known brand OMYA, headquartered in Switzerland, and ECE PLG in the UK. The firms of these companies are located throughout Europe: Germany, Austria, Sweden and other countries. After OMYA and ECE, the major independent companies operating in the leading carbonate filler markets worldwide are: Provncale S. A. - France - 400 thousand tons / year, “S. A. Reverte Productoc Minerales "- Spain - 350 thousand tons / year," Euroc and Ernstrom Mineral AB "- Switzerland - 180 thousand tons / year, Mineralia Sacilese - Italy - 300 thousand tons / year ... It should be noted that the listed countries do not have high-quality chalk reserves. Thus, in chalk deposits in France, Austria, Germany, England, etc., the content of CaCO 3 is only 50 -70%. To obtain high-quality grades of chalk, the most modern technological schemes for deep concentration were developed using the latest achievements of science and technology. Typically, for chalk processing, wet beneficiation processes are used with the use of gravity and classifying equipment. In some cases, flotation beneficiation is used. Technological processes at chalk factories are fully mechanized and automated. The technological process is controlled by industrial computers. A large number of chalk grades (up to 10-15) are typical for foreign factories. Moreover, the technological schemes are very flexible. Depending on the demand of a particular brand, the restructuring of the process takes a short time, calculated in hours. Depending on the grade of chalk, prices on the world market range from US $ 15 per tonne for ordinary chalk (45 microns) to US $ 300 or more per ton for fine chalk (1 micron or less).

Chapter 2 Methods for evaluating chalk and chalk products.

§2.1 Determination of dissolving chalk.

An important point in assessing the physical and mechanical properties of chalk from a new deposit or a site involved in the current technological processing is to have information about the behavior of chalk during its grinding. It is known that even in the same chalk deposit there are areas (strata) with different physical and mechanical properties. It is almost impossible to visually assess the difference between these areas. At the same time, identifying (areas with dense varieties of chalk-marl rocks or chalk with an increased content of foreign inclusions (flint, quartz sand, etc.)) is of great practical interest. It is possible to determine the behavior of chalk during its dry grinding in the technological process by determining its dissolving in a wet environment with mechanical action. The study of the dissolving of chalk is carried out in a mechanical stirrer shown in Fig. 2.1. The stirrer consists of a removable metal glass (1) with a diameter of 060 mm. and a height of 120 mm. To prevent the pulp from rotating around the circumference of the glass, soothing ribs (2) are installed in it. A stirrer shaft (3) with an impeller (4) runs inside the bowl. The slurry is discharged through an opening closed with a rubber stopper (5). The shaft is rotated by an electric motor (9) with a power of 250 W, 1480 rpm, through a bearing (6) and a system of pulleys (7) and (8). The agitator bowl is attached to the base (11) with a screw (10). A representative sample of chalk weighing 1.5 - 2.0 kg is taken from the operating face or from the core material (during exploration). Chalk is dried to a moisture content of 1 - 0.5%, crushed in a laboratory jaw crusher to a particle size of 5 mm, and then on a laboratory roll crusher to 1.0 mm. Crushed chalk is thoroughly mixed and samples weighing 50 (80) g are taken from it in the amount of 5-6 samples. One of the samples is subjected to wet sieving with a separation of the class - 44 microns. and defining the output of this class. The subsequent sample is placed in a beaker where water is added in order to obtain a pulp density of 30% solid. It turns on only through the fitting (8) water is supplied. Rising up the casing, the water is drained through the nozzle (9) and thereby cools the mill casing. The rotation of the mill shaft is carried out through an electric motor (U). The theory of bead mills has not yet been developed and its main design dimensions and technological parameters are taken on the basis of experimental data. It has been experimentally established that the ratio between the diameter and height of the cylinder is approximately 1/4. The performance of bead mills is determined by many factors (size of grinding, physical and mechanical properties of the material being ground, etc.). Thus, the productivity of the mill for commercial enamel with a fineness of 10-15 microns is 6-8 kg / hour for 1 liter of the working volume of the cylinder with an electricity consumption of 40-50 kWh / t of the crushed product. Bead mills are manufactured with cylinder capacities from 1.5 liters (laboratory, batch) to 500 liters - industrial type. The technical characteristics of the bead mills produced by the Dmitrograd Machine-Building Plant (Ulyanovsk Region) are shown in Table 6.3. Table 6.3 Technical characteristics of bead mills.

Chapter 7 Equipment for dry and wet classification of chalk.

§7.1 Air inlet separator.

Air-pass separators are used for dry grinding and classification in a closed cycle with a grinding unit, designed to separate large particles from the air flow and return them for regrinding. The principle of operation of the separator is based on the use of centrifugal forces and own weight of larger fractions of the crushed material, which are separated from the general dust-air flow and returned to regrinding. In fig. 7.1 shows an air-pass separator. It consists of a body (1), an inner cone (2), guide vanes (4), a control mechanism for rotating blades (5), fittings (8,7,6) and an armored tip (9) to protect the fitting from wear. Fig. 7.1 Air inlet separator. 1 - separator body; 2 - inner cone; 3 - collection; 4 - guide flaps; 5 - flap control mechanism; 6 - fitting for the withdrawal of small fractions; 7 - supply connection; 8 - nozzle for the removal of large fractions; 9 - armored tip; 10 - nipple for withdrawing the middle fraction. The dust-air mixture is supplied from the mill to the separator through the choke (7). In the separator body (1), the speed decreases sharply, in this regard, large particles fall out into the collector (3). Dusty ’^. 1 current passes through the flaps (4) and enters the cone (2). Passing sshi * ki, the blades of which are set at a certain angle, pyyo? the left-handed mixture receives a rotary motion by analogy with a cyclone. Under the action of centrifugal forces, larger particles fall out of the flow, which are removed through the choke (10). The finest particles with a stream of air leave through the nozzle (6) for their further separation in cyclones or bag filters. An air-through separator can divide the crushed material into three fractions: coarse - coming out through the choke (8); middle - coming out through the fitting (10); small - coming out through the fitting (6). If necessary, coarse and medium fractions can be combined and sent for grinding or isolated as a finished product. The boundary between the fractions is separated by the angle of the rotating blades, i.e., by the magnitude of the air flow velocity. individual dimensions of the individual parts of the separator, which is shown in Fig. 7.2. Air-pass separators, easy to manufacture and operate, are widely used in the technological processing of ilmenite concentrate at paint and varnish plants, talc, gypsum and other materials. When grinding chalk in a closed cycle with air classification, an air-through separator is installed in the circuit immediately after the unit being ground. At the same time, a large fraction is released in the separator, represented by under-ground chalk particles and dense inclusions that are part of the chalk (quartz, flint, marl). Due to the presence of a high content of foreign inclusions in the coarse fraction, the quality of this product is low and it is not advisable to return it to the grinding unit. This product can be crushed separately and sold as low quality products, or without regrinding as a feed for poultry farms. Air-through type separators do not lend themselves to rigorous design. Based on the long-term practice of their operation and numerous studies have led to the establishment of the relationship between inter-Fig. 7.2 Relative dimensions of the air inlet separator. The main design dimension of the separator, which determines all the others, is its diameter. The latter depends on the performance of the separator and the particle size of the finished product. The choice of the diameter of the separator is made depending on the intensity of its volume on the gas carrier: K 0 = V / V c (7.1) Where V is the volume of gas passing through the separator; V is the volume of the separator. depending on the fractional interface, the following values ​​of the intensity of the separator volume are recommended: L50,% ………… 4-6 ………… 6-15 ………… 15-28 ………… 28-40 Ko, mChm \ ... ...-2000 ………… -2500 ………… -3500 ………… -4500. The volume of the separator is determined by the formula: Y c = V / K 0 (7.2) Knowing the volume of the separator, according to the graph (Fig. 7.3) we find its diameter, and by the diameter, using Figure 7.2, all other dimensions. Table 7.1 shows the dimensions of the separators recommended by the norms for the calculation and design of dust preparation plants. Fig. 7.3 A graph of the dependence of the diameter of the air-pass separator on its volume. Table 7.1 Recommended sizes of air-pass separators.

In the heat and power industry, where separators are used in the coal grinding cycle before burning them, a whole series of such modified separators has been developed.

§7.2 Centrifugal classifiers.

For the separation of fine fractions (up to 5 microns and below) from crushed chalk, centrifugal classifiers of various designs have found wide application in the dry grinding scheme, both abroad and in Russia. The main separation mechanism, in almost all centrifugal classifiers, is based on the interaction of centrifugal forces and the pressure of the air flow on solid particles of the separated material. The most widely used at chalk enterprises are trifugal classifiers of the Institute "NIIsilikatobeton" (firm "Silbet"), which are produced under the brand name ZhG. ZhG classifiers refer to units with a rotating separation zone. This zone is formed by flat rotating walls of the separator chamber. The flow in the separation zone has a shape close to a logarithmic spiral. In this flow, an equilibrium is established for particles of a certain size: large particles are thrown to the periphery, where they are separated by a "knife" and removed to the coarse product compartment, fine fractions, together with air, are sucked out through the central drain and enter the dust collector (cyclone), where fine particles which are the finished product settle. Air purified from dust can be fed back to the classifier or, after additional purification in a bag filter (electrostatic precipitator), can be released into the atmosphere. In fig. 7.4 shows a diagram of the classifier of the "ZhG" type. Fig. 7.4 Classifier "ZhG". 1 - electric drive frame; 2 - electric drive; 3 - V-belt transmission; 4 - handle for turning the rotor blades; 5 - inlet pipe; b - classifier body; 7 - classifier frame; 8 - finished fraction outlet branch pipe; 9 - auger; 10 - screw drive. adidas stan smith pas cher The classifier consists of a body (6) inside which a rotating impeller with adjustable blades is fitted with the handle (4). Rotation is carried out from the electric motor (2) through the V-belt transmission (3). The crushed chalk is fed into the fixator class through a branch pipe (5). A dust-air mixture of finely dispersed material is removed from the classifier through a system of pipes (8); precipitation cyclone. The coarse settled fraction is removed from the classifier by the screw (9) bmbqs and returned for regrinding or discharged as a finished product. ; ™ The experience of operating these classifiers shows that the fine I fraction has a residue on a sieve with a mesh size of 44 microns - 0.8 - 1.2% and to the brand MM - 1. The technical characteristics of the classifiers of the ZhG brand are given in Table 7.2. Table 7.2 Technical characteristics of classifiers of the ZhG brand.

Firm "Silbet" produces sets of grinding and classification units for grinding and classifying chalk. In fig. 7.5 shows the grinding and classification installation ZhG-70. The installation consists of a disintegrator in which chalk is crushed, a classifier (1), a cyclone (2), a fan (3) and a duct system (6). The chalk crushed in the disintegrator is fed into the classifier from where the fine fraction is sucked off by air through a cyclone. Fine-dispersed fraction, which is a finished product, settles in a cyclone, the initially purified air returns to the classifier. 4 p. Small chalk Fig. 7.5 Scheme of work of the classifier "ZhG" in a closed cycle with a cyclone. 1 - classifier "ZhG"; 2 - cyclone; 3 - fan; 4 - bunker; 5 - screw conveyor; 6 - air ducts. Table 7.3 shows the performance indicators of the classifiers "ZhG" at chalk enterprises. Table 7.3 Indicators of work of the classifier "ZhG" at factories for the production of separated chalk.

It follows from the above results that classifiers operate at relatively low efficiency.
In fig. 7.7 shows a schematic diagram of the operation of a centrifugal separator in a closed cycle with cyclones. It should be noted that a complete closed cycle separator - cyclone - fan is not feasible in practice. adidas superstar Part of the dust-air mixture is removed from the cycle and purified. Centrifugal separators with closed circulation of the flow and with high cyclones, possessing high efficiency of separation of finely dispersed material, have found wide application in various industries, including in cement and chalk production. Mel ... Encyclopedia of terms, definitions and explanations of building materials

A non-systemic unit of pitch, used mainly in musical acoustics. Zero pitch (0 chalk) is possessed by a sound with a frequency of 20 Hz at a volume level of 40 phon, and at the same volume and a frequency of 1000 Hz, 1000 chalk. Based on these data ... ... Big Encyclopedic Dictionary

a piece of chalk- CHALK, a, m. ◊ On chalk (play). On credit. ◘ Although the game was played on chalk, it was evident from the rates that many had a decrease in cash funds, only some French women were playing headlong. A.S. Afanasyev Chuzhbinsky. Petersburg players, 1872 ... 19th century card terminology and jargon

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• Reader on the study of time in psychology In three volumes, edited by A.I. Melekhin, A.I. Melekhin. The problem of studying time in psychology is rather controversial. In light of the variety of theories, time is the dominant feature in human consciousness in terms of systematization, structuring ...

Chalk is a white sedimentary rock. It is insoluble in water and is of organic origin. From the article we will find out where chalk is used, the physical and chemical properties of this rock.

Education

90 million years ago in Northern Europe, in the lower region of the Great Sea, silt accumulated. Protozoa (foraminifera) lived on marine debris. Their particles included calcite extracted from water. The Cretaceous group of the stratigraphic European subdivision appeared during the eponymous period. It formed into and slopes in the other part of the Strait of Dover. It was these remains that became the basis of the chalk. However, predominantly the rock consists of formations of algae and fine compounds. Thus, the researchers conclude that the appearance of chalk is a merit of plants.

Breed structure

The remains of mollusks, accumulating in the bottom sediments, turned into chalk. The breed contains:

1. About 10% of skeletal debris. Among them are not only parts of protozoa, but also multicellular animals.
2. About 10% of foraminifera shells.
3. Up to 40% of algae limestone fragments
4. Up to 50% crystalline finely dispersed calcite. Its size is so small that it is almost impossible to establish the biological identity of the elements that make it up.
5. Up to 3% insoluble minerals. They are mainly represented by silicates. Insoluble minerals are a kind of geological debris (debris of various rocks and sand), which is carried into the chalk deposits by currents and winds.

Shells of mollusks, nodules of other minerals, and skeletons of coelenterates are rarely found in the rock.

Description of the physical property of chalk - strength

Studies of the substance were carried out by many scientists. In the course of engineering and geological measures, it was revealed that it is a hard semi-rock. Its strength is largely determined by moisture. In the air-dry state, the ultimate compressive strength varies from 1000 to 45000 kN / m 2. dry rock - from 3 thousand MPa (for a loose state) to 10 thousand MPa (for a dense one). The value of the angle of internal friction is 24-30 degrees, with all-round compression the adhesion reaches 700-800 kN / m 2.

Humidity

When exposed to water, the physical properties of chalk begin to change. In particular, its strength decreases. Changes take place already at 1-2% humidity. At 25-35%, the compressive strength increases 2-3 times. Along with this, other physical properties of chalk are manifested. The breed becomes plastic. This manifestation significantly complicates the process of processing the substance. During this, chalk begins to adhere to the elements of the machines (excavator bucket, feeder, vehicle body). Often, the physical properties of chalk (viscosity and plasticity) do not allow mining from the lower horizons, although here it is considered to be of high quality.

Frost resistance

After freezing-thawing, the chalk breaks down into particles 1-2 mm in size. In some cases, this is a useful property of the breed. For example, when it is used as an ameliorant in soil deoxidation, it is not necessary to grind the substance to 0.25 mm. Crushed rock up to 10 mm can be added to the soil. When freezing-thawing with plowing the soil, the pieces are destroyed by themselves. Thus, the neutralizing action is maintained for a long time.

Chalk properties: chemistry

The rock mainly includes carbonate and non-carbonate parts. The first one is soluble in acetic and hydrochloric acids. The non-carbonate part contains metal oxides, quartz sand, marls, clays, etc. Some of them are insoluble in these acids. The carbonate part contains 98-99% calcium carbonate. Crystalline particles of magnesian calcite, siderite and dolomite are formed by magnesium carbonates, which are included in chalk in small amounts. The composition and properties of the rock act as classification criteria.

Identification of quality deposits

Initially, it was believed that the mechanical and chemical properties of chalk are the same throughout the deposit. However, in practice, during the long-term operation of the area, especially after the transition of the mining and processing enterprise to the production of higher quality products, differences in these characteristics are revealed. Therefore, geological and technological mapping is carried out in some fields. Researchers, studying the chemical properties of chalk and its mechanical characteristics in different parts of the deposit, designate areas of high-quality rock accumulation.

Industrial development

Large chalk deposits are present in the Belgorod and Voronezh regions. A lower quality substance is present in Znamenskaya, Zaslonovskaya, Valuiskaya and other deposits. At these deposits, relatively low indicators of CaCO 3 are revealed (no more than 87%). In addition, the rock contains various impurities. Therefore, it is impossible to obtain high-quality products at these deposits without deep enrichment. The physical properties of chalk on such deposits make it possible to use it in the manufacture of lime, as well as in reclamation measures for deoxidizing soils. Voronezh deposits are attributed to the Turonian-Coniacian age. Higher quality chalk is mined here. The properties and application of the rock obtained from these deposits have been studied for a long time. The product, mined in the Voronezh region, has a high CaCO 3 content (up to 98.5%). The share of non-carbonate impurities is less than 2%. Mining from the deposits, however, is hampered by the physical properties of the chalk. In particular, its high water saturation. The share of moisture in the rock is about 32%.

Promising deposits

Among the large deposits, it is worth noting Rossoshskoye, Krupnennikovskoye, Buturlinskoye and Kopanischenskoye. The Cretaceous thickness of the latter is 16.5-85 m. The overburden is the soil-vegetation layer. Its thickness is about 1.8-2 m. The chalk layer is divided into two members along the vertical line. The bottom contains up to 98% of calcium carbonate, the top is slightly less - up to 96-97.5%.

Extremely homogeneous white chalk of the Turunian stage was found in the Buturlinskoye deposit. The thickness of the layer is 19.5-41 m. The thickness of the overburden reaches 9.5 m. It is represented by margins, vegetation layer, sandy-clay formations and sandstones. The proportion of magnesium and calcium carbonates reaches 99.3%. In this case, non-carbonate components are present in a relatively small amount.

The Stoilenskoye and Lebedinskoye deposits are of great interest to the industry. In these areas, chalk is mined as overburden and taken to dumps. The associated annual output is more than 15 million tons. About five of them are used in the national economic sectors. In particular, chalk is supplied to the Starooskolsk cement plant and some other small enterprises. Most of the mined rock is lost in dumps.

Chalk, which is located in the areas of iron ore deposits, is classified as high quality in terms of silica and carbonate content. It can be used for industrial purposes without deep enrichment. It must be said that in the process of designing mining and processing enterprises specializing in iron ores, it is necessary to provide for technological lines for incidentally extracted chalk or a place for its separate storage.

Production and consumption

The beneficial properties of chalk have been known for a long time. Initially, the breed was used in construction. Lime was produced from it. Chalk powder served as a base for putties, putties, paints and so on. At the end of the 19th century, private factories began to be organized at the Belaya Gora deposit. Lime and powder were released from the lump rock. In 1935, the Shebekinsky plant appeared, which was engaged in the production of products for industrial needs. The useful properties of chalk were in demand in the electrical, paint and varnish, polymer, rubber and other industries.

Along with the increase in the demand for products, the requirements for its quality increased. The enterprises that existed by 1990 could not provide the industry with the necessary raw materials. Private enterprises began to appear in the Belgorod region. Their large number was due to the huge volumes of rock deposits and the apparent simplicity of processing technologies. However, the primitive methods of extraction and subsequent processing used in private enterprises could not provide the required amount of quality products. Accordingly, many of these factories have closed. At the same time, large enterprises have modernized and reconstructed their equipment. The release of high-quality products was ensured in the 90s by the Belgorod, Petropavlovsk, Shebekinsky plants.

Production of quality brands

The key requirements for chalk products, in addition to the proportion of carbonates, include coarseness - fineness of grinding. It is expressed as a residue on sieves of a certain size or as a percentage of particles of a given size (for example, 90% of particles with a size of 2 microns).

The emergence of new production lines for the manufacture of paint and varnish, rubber, polymer and other products, for which chalk is used as raw material, provoked a sharp imbalance between its production and consumption. This is especially evident in the paper industry. Enterprises in this industry have special requirements for chalk powder, which has replaced kaolin in production.

The production of quality brands is concentrated at factories in the Belgorod region. In addition to the Shebekinsky enterprise producing separated chalk, new plants were created. Thus, in 1995, a processing plant, CJSC Ruslaym, appeared at Lebedinsky GOK. It was built according to the Spanish project of the Reverte company with an estimated capacity of 120 thousand tons / year. The plant produces up to 10 different brands of chalk. In terms of their quality, they are in no way inferior to foreign counterparts and meet international standards. The enterprise is equipped with the most modern technological equipment, operations on the lines are mechanized and automated.

According to the project of the company "Mabeteks" at Stoilensky GOK, a plant with a capacity of high quality chalk products of 300 thousand tons was built. At the same time, the company's plans provide for a subsequent increase in capacity.

Breeding of the breed

One of the key criteria in the process of analyzing the physical properties of rock in a new deposit or an area involved in an existing processing line is the behavior of chalk during grinding. As it was said above, in different layers of the reservoir, the substance has different mechanical characteristics. It is not possible to visually identify these differences in most cases. Determination of the behavior of chalk in the process of its dry grinding in the technological process is carried out by establishing the indicator of its dissolving in a humid environment under mechanical action. For this, special equipment is used.

Sodium bicarbonate

Various materials are used for its production, including limestone or chalk. The beneficial properties of sodium bicarbonate for the body are known to many. It is often used for diseases of the gums and throat, heartburn, to thin phlegm when coughing. In industry, the physical properties of soda and chalk are in great demand. Both of these substances are used in construction, decoration, manufacturing of materials, paints and varnishes and other products. With regard to the production of calcium bicarbonate, the use of chalk alone is considered an uneconomical option. As mentioned above, this rock absorbs moisture very well, as a result of which its mechanical characteristics change. This, in turn, negatively affects the course of the technological process.

Is it possible to eat CaCO 3?

It is widely believed that doctors recommend the use of medical chalk. The properties of this substance are believed to contribute to the replenishment of calcium deficiency. First of all, it should be said that doctors are ambiguous about this. Often, patients who like to eat turn to specialists. However, they are highly questionable. The craving for eating it can occur due to a lack of calcium. However, you should be aware that the characteristics of a substance undergo significant changes when it enters the stomach. Passing through several oxidative processes, it loses its initial neutrality and turns into a reagent. The substance is similar in its action. As a result, oxidized chalk begins to influence the gastric mucosa. In this case, no medicinal properties are manifested. Rather, the opposite is true. It is also worth remembering that the concentration of calcium in the substance is very high. As a result, excessive use of chalk can provoke liming of blood vessels. In this regard, doctors recommend replacing it with calcium gluconate or similar drugs. As for getting rid of heartburn, then, according to many people who have tried to eliminate it with chalk, it does not help in this.

Industrial and domestic use

Chalk acts as an essential component of paper used in printing. The high dispersion of calcium carbonate in crushed form affects the optical and print characteristics, porosity, smoothness of the product. Due to the presence of chalk, the abrasiveness of the products is reduced. The ground rock is widely used for whitewashing walls, curbs, and protecting trees. Chalk is used in the purification of beet juice, which, in turn, is used in the match industry. For these purposes, as a rule, the so-called precipitated rock is suitable. Such chalk is produced chemically from calcium-containing minerals. Along with other carbonate rocks, the substance is used in glass melting as one of the charge components. Chalk increases the thermal stability of the product, its mechanical strength and stability when exposed to weathering and reagents. The breed is widely used in the manufacture of fertilizers. Also, chalk is added to compound feed for farm animals.

Rubber industry

Chalk is in the first place among all fillers used in industry. This is primarily due to the fact that the use of this raw material is economically profitable. Chalk has a relatively low cost. At the same time, its introduction into industrial rubber products does not harm. The second reason for the popularity of raw materials in the industry is technological expediency. Chalk greatly simplifies the process of manufacturing rubber products. In particular, due to it, vulcanization is accelerated, the surface of the products becomes smooth. The breed is also widely used in the production of spongy and porous rubber, plastic products, leather substitutes, etc.