Chalk application. Chalk Rock, description, properties, deposits and photos

There is no person in the whole world who has not encountered chalk in his life. In millions of classrooms on Earth, students write with chalk on the blackboard. What would a teacher do without chalk? Each of us is well aware of the usual, unremarkable school chalk. And not only represents, but also held in his hands more than once during his studies. And how many truths were discovered with the help of a piece of chalk, how many discoveries were made! And until now, a school teacher, holding an inconspicuous, but at the same time irreplaceable piece of chalk, performs miracles.

At the moment, no alternative to lime chalk has been found (wax chalk is not suitable for use on blackboards). Interactive, marker boards and other teaching aids are now appearing in schools. However, school chalk, as it existed for many hundreds of years in schools, has remained so far. The quality of school chalk is a problem for any educational institution. Our school is no exception. I decided to find out the reason why school chalk either crumbles, or leaves a slightly noticeable mark, and more often scratches the board.

Relevance work lies in the fact that the chalk used by the consumer differs in quality. Is quality always associated with safety for health?
Problem: poor quality school chalk can lead to diseases of students and teachers.
Target: The study of physical and chemical properties and the impact on the human body of school chalk.

Tasks:
1. Collect reliable information about the origin, composition, properties and use of school chalk.
2. Conduct experiments to study the qualitative and quantitative composition of various grades of school chalk, suitability for use.
3. Conduct a sociological survey to identify the effect of chalk on the human body.
4. Assess the impact of chalk on human health.

During the work, the following research methods:
- search and analysis of reliable information from reliable sources;
- chemical experiment;
- questioning of teachers and analysis of the results.

Origin, properties, application of chalk

Chalk is a white rock, soft and crumbly. Chalk does not dissolve in water.

The basis of the chemical composition of chalk is calcium carbonate with a small amount of magnesium carbonate, but there is usually a non-carbonate part, mainly metal oxides. The composition of chalk usually contains an insignificant admixture of the smallest grains of quartz and microscopic pseudomorphs of calcite after fossil marine organisms (radiolaria, etc.). Large fossils of the Cretaceous period are often found: belemnites, ammonites, etc. Its elements belong to the family alkaline earth metals, which constitute a subgroup of the periodic table of elements. The chalk with which we write on the blackboard consists mainly of shells of sea rhizomes. In the oceans and seas, the shells of dead rhizomes settle to the bottom. Over thousands and millions of years, huge strata of shells accumulate, which subsequently, during geological movements earth's crust may end up on land in the form of chalk and calcareous mountains (for example, in Ukraine). Thus, the protozoa, which are negligibly small in size and grandiose in their mass character, are part of the earth's crust.

For hundreds of years, people have been using chalk for various purposes. The chalk we use in class is mixed with binders to keep it from crumbling. best chalk for the school is 95% chalk. By adding various dyes, you can get chalk of any color. Chalk is used for writing on large boards for public viewing (such as in schools). Molded chalk is 40% chalk (calcium carbonate) and 60% gypsum (calcium sulfate).

Chalk - required component"coated paper" used in printing for printing high-quality illustrated publications. Ground chalk is widely used as a cheap material (pigment) for whitewashing, painting fences, walls, borders, and for protecting tree trunks from sunburn.

Chalk is used in the paint and varnish industry (white pigment), rubber, paper, in the sugar industry - for cleaning beet juice, for the production of binders (lime, Portland cement), in the glass industry, for the production of matches. In these cases, the so-called precipitated chalk, obtained chemically from calcium-containing minerals, is usually used.

With a lack of calcium, medical chalk can be prescribed as a food supplement.

Chalk, among other carbonate rocks in glass production, is used as one of the components of the charge in the melting of glass, introduced into the charge in powder form in an amount of up to 30% of the volume of the latter. Chalk gives glass thermal resistance, mechanical strength, resistance to chemicals and weathering.

Experimental determination of the physicochemical properties of chalk

Key quality indicators

When studying the literature on this topic, we identified the following indicators that chalk used in schools should have:

Crumbles when writing
- dirty hands
- purity (white)
- hard inclusions

These indicators of the studied samples were given in the table "Main indicators of chalk quality":

Qualitative analysis of school chalk

The main component of chalk is calcium carbonate. Natural (sawn) chalk does not contain any other components. In the manufacture of molded crayons, substances are added to the chalk powder - binders, for example, starch or gypsum.
A qualitative analysis is carried out to find out which binders were used to make the crayons available in the class.

Practical work "Qualitative analysis of chalk"

Equipment:

1) microscope
2) glass slide
3) pipette
4) laboratory stand with ring and sleeve
5) funnel
6) plug with gas outlet tube
7) mortar and pestle
8) beaker
9) test tubes
10) filter paper
11) glass rods
12) samples of school chalk
13) distilled water
14) lime water
15) hydrochloric acid (razb.)
16) porcelain spoon
17) spirit lamp
18) matches
19) tweezers
20) alcohol solution of iodine
21) sodium thiosulfate
22) potassium iodide

Recognition of carbonate - anions (CO 3 2-)

A few pieces of chalk were added to the test tube and a small amount of dilute hydrochloric acid HCl was added. The tube was quickly closed with a cork with a gas outlet tube. The end of the tube was lowered into another test tube containing 2–3 ml of lime water. For several minutes, we watched bubbles of carbon dioxide bubble through the lime water. The lime water turned cloudy. Therefore, the composition of chalk includes carbonate - anions (CO 3 2-).

CaCO 3 + 2HCl → CaCl 2 + CO 2 + H 2 O
CO 3 2- + 2H + → CO 2 + H 2 O
CO 2 + Ca (OH) 2 → CaCO 3 ↓ + H 2 O

Conclusion: The presence of calcium carbonate in the composition of the chalk is confirmed with the help of hydrochloric acid (the released carbon dioxide causes the lime water to become cloudy).

Starch recognition.

Starch is easy to detect. For example, if the chalk turns black when calcined, then we can conclude that it contains starch (carbohydrates are easily charred when heated). An iodine solution can also be used as a reagent for starch. We detected starch using an alcoholic solution of iodine. 2-3 drops of iodine solution were applied to the studied pieces of chalk. The color of the iodine solution changed from round chalk (color blue). With the rest of the chalk samples, the color of the alcohol solution of iodine did not change.

Microcrystalline reaction to gypsum.

The presence of gypsum as a binder can be proven by microcrystalloscopic reaction. Each test sample of chalk was crushed in a mortar and a mass of 1 gram was dissolved in 2 ml. distilled water. The resulting solution was thoroughly mixed with a glass rod. The resulting solution was filtered. Then a drop of the filtrate was placed on a glass slide and examined under a microscope. In the process of drying, the drops grow crystals of gypsum (if it is part of the chalk), having the shape of characteristic needles and needle-like drusen.

Small pieces of chalk for each test sample were calcined in the flame of an alcohol lamp. The flame of the spirit lamp acquired a red-orange color in each chalk sample, which confirms the presence of calcium cations (Ca 2+).

Research results:

Conclusion: Chalk samples all contain calcium ions and carbonate - anion, therefore, calcium carbonate (CaCO 3) is present in it. Of the impurities, we found gypsum and starch.

Conclusion on the experimental part:

1) All studied samples of chalk contain calcium cations.
2) The impurities in our samples were gypsum, starch and glue.
3) Lump chalk consists of calcium carbonate and a huge amount of impurities, stains hands, writes poorly.
4) Round chalk is composed of calcium carbonate, it stains hands a lot, writes softly, crumbles, because as a binder in it starch.
5) Rectangular chalk contains calcium carbonate, crumbles a little and stains hands the least, but scratches the board very much, because it contains, in addition to gypsum, glue as a binder.

The impact of school chalk on the health of students and teachers

To date, the preservation and promotion of public health is one of the most actual problems. Human health has always been the subject of close study of specialists in various professions.

According to the forecasts of the World Health Organization at the beginning of the 21st century, the most common human diseases are allergic diseases, bronchial asthma, and cardiovascular diseases.

As soon as the child goes to school, he begins to use chalk. School chalk accompanies us from the first to the eleventh grade, teachers use it all the time. Today, very serious requirements are imposed on school chalk, so school chalk is considered an environmentally friendly and safe product. However, in the process of use, school chalk begins to dust, clog up the nose, and dirty hands. Some students like to eat chalk, but school chalk is a product that contains, in addition to the main safe (as it is believed) components: limestone, gypsum, starch, and also adhesives (PVA glue, BF, casein, stationery, etc.) , dyes, which is not entirely safe for their health.

To find out the impact of chalk on human health, we interviewed our teachers, who, due to the specifics of their subjects, are forced to constantly use chalk.

Questionnaire for teachers

1. Do you think that constant work with chalk affects your body?

2. Are there any negative consequences, if so, what are they?
a) on the skin of the hands:
1.dries
2.allergic reaction
3.other
4.no consequences
b) on the respiratory system:
1.cough
2.manifestations of asthma
3.other
4.no consequences.

3. Can the blackboard and chalk be replaced at school? If yes, then what?

After analyzing the questionnaires of our school teachers, we came to the conclusion that 100% of teachers are not satisfied with the quality of the chalk coming to our school (it gets their hands dirty, scratches the board and crumbles). The students also added one bad quality - it does not wash well from the school uniform if you accidentally get dirty with it.

According to the majority of teachers surveyed, school chalk has a negative effect on the skin of the hands and can cause allergic reactions when inhaled chalk particles. Half of the respondents noted that they are forced to constantly use a moisturizing hand cream. There are teachers among those who have received serious problems with the skin of their hands: eczema, peeling and cracks on the palms.

Despite technological progress, according to teachers, it is not yet possible to completely replace chalk. Whiteboards and interactive whiteboards would be good alternatives.

1) during work, wash your hands more often with softening toilet soap: "glycerine", "lanolin", "vaseline" and "milk"
2) after each lesson, lubricate your hands with a moisturizing hand cream
3) wash the chalk from the board only with a damp cloth
4) Rinse the chalk-erasing cloth as often as possible

Conclusion

School chalk is a product that contains, in addition to the main safe (as it is believed) components: limestone, gypsum, starch, and also adhesives (PVA glue, BF, casein, stationery, etc.), dyes, which is not entirely safe for their health.

The investigated samples of chalk have a calcium carbonate content of 40 to 80% and contain gypsum. Despite their superficial similarity, the samples behave differently when added hot water and hydrochloric acid.

After studying the literature, I recommend that teachers wash the chalk cloth thoroughly and do not wipe the chalk off the board with a dry cloth. You can reduce the negative effect of chalk on the skin of your hands if you wrap the chalk with paper, and preferably with foil. Another solution to the problem of chalk flowability is to pre-treat the surface of the chalk with stationery silicate glue.

Conducting research allowed me to learn how to plan and conduct chemical experiments and get reliable results. The results of the experiments were processed by the methods of mathematical statistics.

List of sources

1. Kartsova A.A. Chemistry without formulas. / A.A. Kartsova; - St. Petersburg: Avalon, 2005. S. 101-103.
2. Chalk // Natural Science: Encyclopedic Dictionary / Comp. V.D. Chollet. - M .: Great Russian Encyclopedia, 2002. - 543 p.
3. Chalk // Dal V. Explanatory dictionary of the living Great Russian language: in 4 vols. M .: Rus. lang., 1998 T 4. - 688 p.
4. Olgin O.M. Experiments without explosions. / O.M. Olgin; – M.: Chemistry, 1995. 136 p.
5. Student's handbook. Chemistry / Comp. M. Kremenchugskaya, S. Vasiliev. Moscow: Philologist, 1995. 380 p.
6. Stepin B.D. Alikberova L.Yu. Chemistry book for home reading. / B.D. Stepin, L.Yu. Alkberova. – M.: Chemistry, 1995. 270 p.
7. I know the world: Children's Encyclopedia: Chemistry / Ed. L.A. Savina. - M.: AST, 1995. - 448 p.

Internet sources

Work completed: Babueva Sayana, 8th grade
Supervisor: Garmaeva Butit-Tsybzhit Pavlovna, chemistry teacher

Russian Federation, Trans-Baikal Territory
Aginsky Buryat District
Khara-Shibir village
MOU "Khara-Shibirskaya secondary school"

White, fine-grained, weakly cemented, soft and crumbly, insoluble in water, organic (zoogenic) origin. In terms of mineral composition, chalk is close to limestone and is composed mainly of calcite (91-98.5%). The basis of the chemical composition of chalk is calcium carbonate with a small amount of magnesium carbonate, but there is usually a non-carbonate part, mainly metal oxides. In the chalk, there is usually an insignificant admixture of the smallest grains of quartz and microscopic pseudomorphs of calcite after fossil marine organisms (radiolaria, etc.). Often there are large fossils of the Cretaceous period: belemnites, ammonites, etc. Natural chalk is characterized by the absence of recrystallization and layering, a large number of passages of various worm-eating animals (ground beetles).

The mineral composition of chalk is dominated by calcite, which can be of both biogenic and autogenous origin; organic remains usually make up a significant part of the rock (up to 75%). In the main mass, they are represented by skeletal shells of planktonic algae-coccolithophores, as well as foraminifers (sometimes up to 40%). The size of skeletal remains is 5-10 microns. A variable, but sometimes significant value (10-90%) is powdered calcite with particles 0.5-2 microns in size, the content of larger particles in the form of microscopic calcite crystals is less significant. Occasionally in the Cretaceous there are shells of mollusks, skeletons of bryozoans, inocerams, remains of crinoids, sea urchins and lilies, flint sponges, and corals. In small quantities, usually up to 5, less often up to 10-12%, there are pelitomorphic non-carbonate impurities, mainly of terrigenous, less often of autogenous origin: quartz, feldspars, clay minerals (glauconite, kaolinite, hydromicas, montmorillonite), opal, chalcedony, pyrite and etc. Rarely and only in places there are concretions of flint, pyrite and phosphorite.

In the chalk strata, the development of large sustained cracks is observed - reservoir and vertical, filled with chalk flour. At the surface outcrops, the network of cracks is strongly concentrated. When chalk samples are impregnated with oil, hidden vein structures appear in them in the form of intertwining tiny cracks, as well as traces of numerous passages of worms - worms. In all Cretaceous deposits in different areas (horizons), chalk differs both in chemical composition and in physical and mechanical properties.

Density 2690-2720 kg/m3; porosity 44-50%; natural humidity 19-33%. When moistened, the strength of chalk begins to decrease already at a moisture content of 1-2%, and at a moisture content of 20-30%, the compressive strength increases by 2-3 times, while plastic properties appear. 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.

According to physical properties and structural features, three types of chalk are distinguished: white writing; marl, characterized by greater density and less whiteness, due to the presence of clay substances; chalk-like limestone is a transitional difference from chalk to limestone.

Finding

Chalk is a semi-hardened silt of warm seas, deposited at a depth of 30 to 500 m. It is widely distributed in nature and is characteristic of deposits of the upper Cretaceous system and the Lower Paleogene, which is associated with the lush development of coccolithophores. Accumulations of white writing chalk are a specific feature of the Late Cretaceous and are found in almost all stages of the Upper Cretaceous, from the Cenomanian to the Massrathian inclusive. Chalk-like limestones are common in Tertiary deposits; in the Paleozoic, Cretaceous accumulations are not preserved, being transformed into various limestones.

Place of Birth

The most significant band of chalk deposits is common in Europe, from the Emba River in Western Kazakhstan to Great Britain. Their thickness reaches several hundred meters (in the Kharkov region - 600 m). A powerful chalk belt extends across the entire European continent, including the north of France, the southern part of England, Poland, passes through Ukraine, Russia and moves to Asia - Syria and the Libyan desert. Chalk reserves are unevenly distributed over the territories: about 48-50% of high-quality chalk reserves with a high content of calcium and magnesium carbonate and a minimum content of harmful impurities are concentrated in Russia; about 32-33% in Ukraine and a little over 12% in Belarus. There are small deposits in Kazakhstan, Lithuania and Georgia. The total balance reserves of chalk in Russia are estimated at 3,300 million tons with unlimited probable reserves.

The reserves of the largest Sebryakovskoye (Volgograd region, Russia) chalk deposit for cement production are 890 million tons. Practically unlimited forecast chalk resources are concentrated in the Belgorod region (Russia), where 29 chalk deposits with total reserves of 1000 million tons have been explored, the largest of which are Lebedinskoye, Stoilenskoye and Logovskoye. At the same time, the Lebedinskoye and Stoilenskoye deposits account for 75% of the explored reserves of chalk in the Belgorod region. These two deposits are exploited for the extraction of iron ores, where chalk is the overburden. The chalk deposits of the Voronezh region belong to the Turoncognacian age. Chalk has a high content (up to 98.5%) and a low content of non-carbonate impurities (less than 2%), is enriched with amphora silica, chalk lies in close proximity to the surface and is covered with chalk eluvium or Quaternary deposits. A characteristic feature of the chalk deposit of the Voronezh region is its water saturation (moisture content reaches 32%, which causes serious difficulties in its extraction and processing).

Practical value

In industry, chalk is used for the production of lime, cement, soda, glass, school crayons. Used as a filler for rubber, plastics, paper, paints and varnishes. AT agriculture goes for liming of soils and feeding animals, in perfumery - for the preparation of toothpastes and powders. AT paper industry as a filler and bleach was used along with kaolin. Chalk is a necessary component of coated paper used in printing for printing high-quality illustrated publications. Ground chalk is widely used as a cheap material for priming, whitewashing, painting the walls of houses, and for protecting tree trunks from sunburn. The use of chalk as a filler and pigment in the production of paper and cardboard can be successful provided that the requirements for this type of raw material in terms of its optical properties and particle size distribution are met. The quality of chalk is mainly determined by its chemical composition and for many industries is regulated by state and industry standards; GOST 17498-72 "Chalk. Types of brand, basic technical requirements"; GOST 12085-73 "Natural chalk enriched (used in the rubber, cable, paint and varnish and polymer industry)"; GOST 8253-79 "Chemical precipitated chalk"; OCT 21-37-78 "Chalk and limestone for mineral nutrition of farm animals and poultry", etc.

The suitability of chalk for the production of lime and cement is determined by semi-factory tests. As of January 1, 1985, 219 chalk deposits with 1,680 million tons of chalk reserves, explored by industrial categories, were recorded in the USSR. In addition, 31 chalk deposits with reserves of 3,534 million tons were included in the balance of reserves of cement raw materials. Chalk reserves account for 12% of all reserves of carbonate cement raw materials. The reserves of the largest Sebryakovskoye (Volgograd region of the RSFSR) chalk deposit for cement production are 890 million tons. Deposits with chalk reserves of 20 million tons or more are considered large. Large reserves of chalk have France, Great Britain, East Germany, Denmark. In 1984, 75 deposits were developed in the CCCP (all open-pit) and 12.4 million tons were mined; in addition, 39.2 million tons were produced at 17 deposits of cement raw materials.

The deposits with reserves of lower quality chalk in the Belgorod region include Valuyskoye, Zaslonovskoye, Znamenskoye, Cossack hillocks and Korochanskoye. 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%, enriched with amorphous silica, brought, obviously, from the Santonian deposits. Chalk occurs in close proximity to the surface and is covered by chalk eluvium or Quaternary deposits. A characteristic feature of the chalk 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-nischenskoye, Buturlinskoye, Krupnennikovskoye and Rossoshanskoye. The chalk thickness at the Kopanischenskoye deposit ranges from 16.5 to 85 m (average 35 m). The overburden is represented by a soil-vegetative layer and is only 1.8 - 2.0 m. Vertically, the chalk thickness is divided into two packs, of which the lower one contains up to 98% CaCO 3, and the upper one is somewhat less (96 - 97.5%). Buturlinskoye deposit with extremely homogeneous white chalk of the Turunian stage with a thickness of 19.5 to 41 m. Overburden thickness reaches 9.5 m and is represented by a vegetative 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 physical and chemical properties of natural chalk were studied by many researchers, mainly in the engineering and geological plan. 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 3,000 MPa (for loose chalk) to 10,000 MPa (for dense chalk) 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 chalk begins to decrease already at a moisture content of 1–2%, and at a moisture content of 25–30%, the compressive strength increases by 2–3 times, while plastic properties appear. The manifestation of the visco-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 vehicle elements (excavator bucket, dump truck body, feeder, conveyor belt). Sticking of roller gear crushers is observed. This leads in some cases to the failure of the extraction of chalk from the lower watered horizons, although the quality of the chalk of the lower horizons refers 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 particle size of - 0.25 mm (limestone flour), but crushed chalk can be added to the soil up to - 10 mm. During freezing and thawing with annual plowing of the soil, the pieces of chalk are destroyed and its actions to neutralize the soil are preserved. long time. 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, soluble in hydrochloric and acetic acids (calcium and magnesium carbonates) and the non-carbonate part (clays, marls, quartz sand, metal oxides, etc.) which are insoluble in the indicated acids. The carbonate part of the 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 groundmass of the chalk. Among the previously proposed classifications of chalk-marl rocks, the most acceptable is the classification according to the content of carbonates and grades of products from chalk (Table 1.3). Table 1.3 Classification of chalk according to the content of carbonates and brands of products from it.

*) Letters designate the following grades 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; C - separated; SG - separated hydrophobized; Oh - 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 the chalk of some Russian deposits are given in Table. 1.4. Initially, it was believed that chalk is a rock mass, which is the same throughout the deposit in terms of chemical composition and physical properties. However, during 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) 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 at some chalk deposits, in which areas of high-quality chalk are identified. 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 fields in the Belgorod region. Table 1.5 Chalk reserves and its chemical composition for some deposits of the Belgorod region.

Place of Birth	Chalk reserves, thousand tons		Content, %
Place of Birth	Approved by TKZ and GKZ	Status as of 1.01.97.	Fe2O3	CaCO3	MgC0 3	N/0
1	2	3	4	5	6	7
Lebedinskoye, overburden chalk	A+B+C1324305	293003	0,25	97,52	1,74	1,27
Stoilenskoe, overburden chalk	A+B+C1 519521 C2- 18941 7	455712	0,07	97,87	0,41	1,27
Petropavlovsk	A+B+C122752	17133	0,33	96,67	0,43	2,15
Shebekinskoe	A+B+C1 26445	18716	0,01 — 0,043	99,67	0,42	0,4 — 6,0
Belgorodskoye (raw materials of the cement plant)	A+B+C1 142074	137620	0,28	87,14	0,43	1,73
Valuyskoye Valuyki	A+B+C1 4429	3926	-	95,5	1,25	4,32

In addition to the chalk deposits listed in Table 1.5 in the Belgorod region, reserves have been explored and approved at another 23 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. Chalk from the Lebedinsky and Stoilensky deposits is of considerable interest for industrial development, where it is mined as overburden and dumped. The annual associated production is more than 15 million tons of chalk, of which is used in national economy no more than 5 million tons (Starooskolsky cement plant and a number of other small enterprises). Most of them are lost in the dumps irretrievably. The chemical composition of chalk confined to iron ore deposits of the KMA is shown in Table 1.6. The table shows that the chalk associated with iron ore deposits, in terms of the content of the carbonate part and silica, belongs to high-quality chalk from which chalk products can be obtained without deep enrichment. High Quality. Table 1.6 Chemical composition of chalk associated with iron ore deposits KM A.

iron ore deposits	Category	Content of chemical elements, %
iron ore deposits	Category	CaCO3	MgCCh	SiO2	Re 2 Oz	ALOS
Lebedinsky	1-2	95,6-99,2	0,5- ,4	0,43-5,75	0,02-0,64	0,03-1,61
Stoilenskoye	1	98,1-99,4	0,3- ,6	0,36-0,88	0,02-0,85	0,03-1,82
Korobkovskoe	1-2	95,8-99,3	0,3- ,7	0,4-5,6	0,02-0,8	0,05-1,76
Prioskolskoe	1-2	96,2-99,1	0,5- ,8	0,35-5,4	0,03-0,55	0,032-1,54
Chernyanskoe	1-3	93,8-98,1	0,3- ,7	0,16-0,65	0,02-0,8	0,03-1,72
Pogrometskoe	1-3	94,2-99,5	0,2- ,4	0,38-3,1	0,02-0,7	0,03-0,81

The table shows that the chalk associated with iron ore deposits, in terms of the content of the carbonate part and silica, belongs 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 design to provide for the processing of incidentally mined chalk or its separate storage.

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

The extraction and processing of chalk in Russia has been known for a long time. Chalk was mainly used in the construction business. Lime was produced from it, paints, putty, putty, etc. were prepared on the basis of chalk powder. late XIX centuries, private chalk factories were organized at the Belaya Gora chalk deposit (Belgorod), which produced lime in shaft furnaces and chalk powder from lump chalk. In 1935, the Shebekinsky plant was built to produce chalk products for the needs of industry. With the development of such industries as paint and varnish, rubber, electrical, polymer, and others, the need for chalk products has increased dramatically. 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 to create small private enterprises for the production of chalk products. This was facilitated by a huge number of chalk deposits that come to the surface and the apparent "simplicity" of chalk processing technology. The primitive technology of extraction and processing of chalk at these enterprises did not provide high-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 carried out the reconstruction and modernization of equipment, ensured the production of high-quality chalk products. The most important requirements for chalk products (except for the content of carbonates) is its fineness - 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 brands of chalk and their prescriptions produced in Russia and the CIS countries are shown in Table 1.7. Table 1.7 Chalk grades produced in Russia and CIS countries and their purpose.

Designation	Chalk mark	Chalk consumption
MK-2 MK-3	Lumpy chalk-II-	For the production of lime, glass, ceramics and other industries
MD-1 MD-2 MD-3	Chalk crushed-II—II-	The same, except for the production of lime
MM-1 MM-2 MM-3	Ground chalk -II—II-	Too
MMZHP	Chalk ground animal feed	In agriculture for animal feed
MMPC	Ground chalk for mixed fodder production	In agriculture for the production of animal feed
MMOR	Chalk ground peeled	In rubber, paint, chemical and other industries
MMS-1MMS-2	Separated ground chalk -II-	In cable, paint, rubber, polymer and other industries
MMHP-1	Ground chalk for the chemical industry	Chemical industry
MTD-1 MTD-2 MTD-3 MTD-4	Fine chalk -II—II—II-	In the absence of brands MMC-1 and MMC-2 are replaced by them
MHO-1 MHO-2	Chalk ground chemically cleaned-II-	In perfumery, cosmetic, rubber, medical, food and other industries

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

Technical requirements for chalk products.
The name of indicators	Chalk ground according to OST 24-10-74			Chalk technical dispersed according to TU 21 RSFSR - 783 - 79				Natural chalk enriched according to GOST 12085-88
The name of indicators	MM-1	MM-2	MM-3	MTD-1	MTD-2	MTD-3	MTD-4	MMOR	MMS-1	MMS-2
Content:
CaCOi+MgCOj, not less than, %	98,0	95,0	90,0	98,0	96,0	90,0	85,0	98,5	98,2	98,2
KES, no more than, %				0,6	0,7	0,8	1,0	0,4	0,4	0,6
But not more, %	1.0	2,0	3,0	1,5	2,0	4,5	6,0	1,3	1,3	1,5
Mo, no more, %				0,01	0,02			0,01	0,015	0.02
Si, not more than, %				0,001	0,001			0,001	0,00!	0,001
Fe2Oj, no more, %	0,1	0,2		0,25	0,25	0,4		0,15	0,15	0,25
Free alkali in terms of
for CaO, no more than, %								0,01	0,02	0,04
Water-soluble substances, not more than, %				0,25	0,25	0,3		0,10	0,10	0,25
SO4″ and SU ions in water
exhaust, no more than, %								0,05	0,04	0,04
Iron extractable
magnet, no more than, %				0,02	0,03	0,04		0,020	0,020	0,020
Sand, no more than, %								0,015	0,020	0,030
Humidity, no more than, %	2,0	2,0	2,0	0,15	0,15	0,2	0,2	0,15	0,2	0,2
				90,0	85,0			90,0	90,0	85,0
Remaining on the sieve:
0.2 no more, %	1,0	3,0	6,0
0.14 no more. %				0,4	0,8	1,5	2,0			0,4
0.045 no more, %								0,5	1,0

Table 1.9

Foreign standards for fine chalk.
Indicators	No. p / p	USA	Poland	Bulgaria BDS - 694 - 78
		K79.170	-84070-73
		1C PS \| III C	A B \| D \| BUT
Mass fraction of CaCO3 + MCO3, %	1	95,0	92,5 — 98,0	92,0
Insoluble residue, no more than, %	2	2,5	1,0-6,5	3,0
Mass fraction of iron oxide, no more than, %	3		0,1-0,3	1,0
Mass fraction of copper, no more than, %	4		0,005-0,01
Mass fraction of manganese, no more than, %	5		0,01-0,04	0,03
Mass fraction of SCh, no more than, %	6			0,5
Mass fraction of moisture, no more than, %	7	0,2	0,5 — 0,8	0,5
Reflection coefficient, not less than, %	8		55-70
Remaining on Grid No.:
01 50 no more than, %	9		0.0l	1,0
0063 no more, %	10		0.2 0.5 4.0°)
0045 no more, %	11	0,05 0,5 25

For comparison, Table 1.9 shows foreign standards for fine chalk. From a comparison of tables 1.8 - 1.9, it can be seen that abroad, more stringent requirements are imposed on chalk products in terms of such parameters as dispersion and whiteness. Table 1.10 shows the production of various grades of chalk in Russia and the CIS countries in 1990. This year is the last when a centralized accounting of manufactured products was carried out in the USSR. 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 CIS countries.

Chalk marks	Chalk output, thousand tons	Specific weight, %
1	2	3
MMOR	8,8	0,4
MMS-1	2,6	0,1
MMS-2	0,4	…
MMHP	6,5	0,3
MM - hydrophobic	38,1	1,6
Fine chalk	17,1	0,7
MTL-1	15,5	0,7
MTD-2	201,4	8,5
MTD-3	42,0	1,8
MTD-4	45,3	1,9
MHO-1	24,2	1,0
MHO-2	32,2	1,4
MM-1	145,0	6,1
MM-2	178,5	7,5
MM-3	129,4	5,4
Ground B/m	15,7	0,7
MMHP	368,2	15,5
MMPC	178,8	7,5
MD-2	165,4	7,0
MD-3	365,0	15,3
MK-1	262,0	11,1
MK-2	74,6	3,1
MK-3	0,6	-
Volume of production:
the Russian Federation	1455,9	-
Ukraine	715,0	_
Kazakhstan	83,0	_
Belarus	123,5	_
Total:	2377,0	100,0

The creation of new industries for the production of paint and varnish products, polymer, rubber and other industries consuming 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's requirements for chalk powder are fineness and whiteness. The production of high-quality chalk grades is concentrated in Russia and, first of all, at chalk plants in the Belgorod region. In addition to the Shebekinsky chalk plant, which produces high quality separated chalk, new enterprises have been built. In 1995, a chalk plant of CJSC Ruslime was built at Lebedinsky GOK 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 are not inferior to international standards in terms of quality composition. 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 Mabetex, 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 provides a prerequisite for increasing production capacity 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 lump, 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 volumes of Russian production, even taking into account the commissioning of the Stoilensky chalk plant, do 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 capacity by 1.5 times compared to 1994. Table 1.11 Production of high-quality chalk at factories in the Belgorod region.

	Years, thousand tons
	1997	1998	1999	2000		2005
JSC "Shebekinsky chalk plant"	129,4	132,0	150,0	250,0		350,0
CJSC Ruslime (Lebedinsky GOK)	70,9	70,9	100,0	110,0			200,0
JSC Stoilensky Chalk Plant	-	-	-	300,0			1000,0
JSC "Melstrom"	62,0	65,0	75,0		80,0			90,0
JSC Belgorod Combine
building materials"	50,0	58,0	60,0		60,0			60,0
Total:	312,3	325,9	341,0		750,0			1680,0

The European IWC industry includes up to 50 companies. However, the carbonate filler market is dominated by two chalk empires: Pluess-Staufer AG with the well-known trademark OMYA (OMYA) headquartered in Switzerland and ECE PLG in the UK. Firms of these companies are located throughout Europe: Germany, Austria, Sweden and other countries. After OMYA and ECE, the major independent companies that operate 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 A B" - Switzerland - 180 thousand tons / year, "Mineralia Sacilese" - Italy - 300 thousand tons / year . It should be noted that the listed countries do not have stocks of high-quality chalk. So in the chalk deposits in France, Austria, Germany, England, etc., the content of CaCO 3 is only 50 -70%. To obtain high-quality chalk grades, the most modern technological schemes for deep enrichment were developed using the latest achievements of science and technology. As a rule, wet enrichment processes are used for chalk processing using gravity and classifying equipment. In some cases, flotation enrichment is used. Technological processes at chalk plants are fully mechanized and automated. The technological process is controlled by industrial computers. A characteristic of foreign factories is a large number of chalk grades (up to 10-15) intended for production. And 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 $15 per ton for ordinary chalk (45 microns) to $300 or more per ton for fine chalk (1 micron or less).

Chapter 2 Methods for assessing chalk and chalk products.

§2.1 Determination of chalk blooming.

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 (layers) with different physical and mechanical properties. It is almost impossible to visually assess the difference between these areas. At the same time, to distinguish (areas with dense differences of chalk-marl rocks or chalk with a high content of foreign inclusions (flint, quartz sand, etc.)) is of great practical interest. To determine the behavior of chalk during its dry grinding in the technological process, it is possible by determining its disintegration in a wet environment with mechanical action. The study of the melting of chalk is carried out in a mechanical mixer, shown in fig. 2.1. The stirrer consists of a removable metal cup (1) with a diameter of 060 mm. and 120 mm high. To prevent the rotation of the pulp around the circumference of the glass, damping ribs (2) are installed in it. Inside the glass there is a stirrer shaft (3) with an impeller (4). The pulp is released through the hole closed with a rubber stopper (5). The rotation of the shaft is carried out by an electric motor (9), with a power of 250 watts, 1480 rpm, through a bearing (6) and a system of pulleys (7) and (8). The stirrer bowl is attached to the frame (11) with a screw (10). In the active face or from the core material (during exploration), a representative sample of chalk is taken, weighing 1.5 - 2.0 kg. The 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 roller crusher to 1.0 mm. Crushed chalk is thoroughly mixed and samples are taken from it weighing 50 (80) g in the amount of 5-6 samples. One of the samples is subjected to wet sieving with the separation of the class - 44 microns. and defining the output of this class. The subsequent sample is placed in a glass where water is added to obtain a pulp density of 30% solid. Me which water is supplied through the fitting (8) is turned on. Rising up the casing, the water drains through the fitting (9) and thereby cools the mill body. The rotation of the mill shaft is carried out through an electric motor (Yu). 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 (grinding size, physical and mechanical properties of the material being ground, etc.). So the productivity of the mill for commercial enamel with a dispersion of 10-15 microns is 6-8 kg / h la 1 liter of the working volume of the cylinder at an electricity consumption of 40 - 50 kWh / t of the crushed product. Bead mills are manufactured with a cylinder capacity from 1.5 liters (laboratory, periodic) to 500 liters - industrial type. The technical characteristics of bead mills manufactured by the Dmitrograd Machine-Building Plant (Ulyanovsk region) are shown in Table 6.3. Table 6.3 Technical characteristics of bead mills.

Parameter	ate meas.	B1-0.005	B1-0.050	B1-0.125	B1-0.250
Slurry Capacity: CST Pigments	kg/h	20 3,5	230 34	50075	1600-2000
Particle diameter: Crushed, no more Crushed, no more	mm µm	0,2 0,5-5	0,2 0,5-5	0,2 0,5-5	0 — 0,15 — 60% 0,15-0,2-40% 1-1,5-98%1,5-2-2%
Heat exchange surface area	sq.m	0,15	0,8	1,5	2,3
Grinding media diameter	mm	1,7	1,7	1,7	1,7.
Mass of grinding media	kg	5	50	125	200
Installed capacity total	.kW	4,55	15,6	30,6	61,2
Rotor speed	rpm	1770	1160	930	620
Weight	kg	366	900	1510	3340
	mm	900 890 820	1290 1000 1365	1280 1090 1840	3345 2160 2940

Chapter 7 Equipment for dry and wet chalk classification.

§7.1 Air passage separator.

Air-through 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 with their return to regrinding. The principle of operation of the separator is based on the use of centrifugal forces and its own weight of larger fractions of the crushed material, which are separated from the general dusty air flow and returned for regrinding. On fig. 7.1 shows an air-through separator. It consists of a body (1), an inner cone (2), guide vanes (4), a rotary vane control mechanism (5), fittings (8,7,6) and an armored tip (9) to protect the fitting from wear. Rice. 7.1 Air passage separator. 1 - separator body; 2 - inner cone; 3 - collection; 4 - guide flaps; 5 - sash control mechanism; 6 - fitting for the withdrawal of small fractions; 7 - power fitting; 8 - fitting for removal of large fractions; 9 - armor tip; 10 - fitting for the removal of the middle fraction. The dust-air mixture comes from the mill to the separator through the fitting (7). In the separator housing (1), the speed decreases sharply, in this regard, large particles fall into the collector (3). Dusty'^. 1 the current passes through the flaps (4) and enters the cone (2). Passing through the * ki, the blades of which are set at a certain angle, pYo? the left-air mixture receives a rotational movement by analogy with a cyclone. Under the action of centrifugal forces, larger particles fall out of the flow, which are removed through the fitting (10). The finest particles with the air flow exit through the fitting (6) for further separation in cyclones or bag filters. The air-through separator can be used to separate the crushed material into three fractions: coarse - coming out through the fitting (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 fractional interface is separated by the angle of the rotary blades, i.e., by the magnitude of the air flow velocity. individual dimensions of individual parts of the separator, which is shown in fig. 7.2. Air-through 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 crushed unit. At the same time, a large fraction is released in the separator, represented by undersized 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 top dressing for poultry farms. Air-through type separators are not amenable to strict calculation. On the basis of many years of practice of their operation and numerous studies have led to the establishment of the relationship between 7.2 Relative dimensions of the air separator. The main constructive size 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 separator diameter is made depending on the tension of its volume with respect to 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 interface, fractions are recommended the following values separator volume intensity: 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 \u003d V / K 0 (7.2) Knowing the volume of the separator, according to the graph (Fig. 7.3) we find its diameter, and according to the diameter, using Figure 7.2, all other dimensions. Table 7.1 shows the sizes of separators recommended by the norms for the calculation and design of dust preparation plants. Rice. 7.3 Graph of the dependence of the diameter of the air-through separator on its volume. Table 7.1 Recommended dimensions for air separators.

Separator No.	Diameter, mm				Separator volume
Separator No.	Separator	Branch pipes			Separator volume
1	1900	350	400	-	2,4
2	2250	500	600	-	4,2
3	2500	600	750	-	5,5
4	2850	700	850	1000	8,4
5	3000	800	950	1150	10,0
6	3420	800	950	1150	14,3
7	4000	950	1100	1140	22,0

In the thermal power industry, where separators are used in the coal grinding cycle before their combustion, a whole series of such modified separators has been developed.

§7.2 Centrifugal classifiers.

To isolate 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 air flow pressure on solid particles of the material being separated. The most widely used at chalk enterprises are the troubling classifiers of the institute "NIIsilikatobeton" (fir - "Silbet"), which are produced under the ZhG brand. ZhG classifiers refer to units with a rotating separation zone. This zone is formed by the 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 precipitator (cyclone), where fine particles , which are the finished product, settle. The dust-free air can be fed back into the classifier or, after additional cleaning in a bag filter (electrostatic precipitator), it can be released into the atmosphere. On fig. 7.4 shows the scheme of the classifier type "ZhG". Rice. 7.4 Classifier "ZhG". 1 - frame of the electric drive; 2 - electric drive; 3 - V-belt transmission; 4 - handle for turning the rotor blades; 5 - inlet pipe; b - classifier body; 7 - classifier frame; 8 - branch pipe for the exit of the finished fraction; 9 - auger; 10 - screw drive. adidas stan smith pas cher The classifier consists of a body (6) inside of which there is a rotating impeller with adjustable blades with a handle (4). The rotation is carried out from the electric motor (2) through the V-belt drive (3). Crushed chalk is fed into the fikator class through the branch pipe (5). The dusty mixture of finely dispersed material is removed from the classifier through a system of nozzles (8); precipitation cyclone. The coarse settled fraction is removed by the screw (9) bmbqs from the classifier and returned for regrinding or is issued as a finished product. ; ™ The operating experience of 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 MM brand - 1. The technical characteristics of classifiers of the ZhG brand are given in table 7.2. Table 7.2 Technical characteristics of classifiers of the ZhG brand.

Options	Units	Type (brand) of classifier
Options	Units	ZhG-60	ZhG-72	ZhG-27	ZhG-67
Productivity according to the source material, up to	t/h	0,7	3,0	6,0	10,0
Separation border	micron	3-40	3-40	10-60	10-60
Installed capacity	kW	16,0	23,0	76,0	113,0
Separation chamber diameter	mm	310	490	930	900
air performance	m 3 / hour	1000	4000	10000	20000
Overall dimensions: length width height	mm mmmm	2000 1050 1300	1700 1180 1095	2685 1835 1525	1570 GO50 1300
Weight	t	0,8	0,76	1,5	3,16 ‘

Firm "Silbet" produces sets of grinding and classification plants for grinding and classifying chalk. On fig. 7.5 shows the grinding and classification plant ZhG-70. The installation consists of a disintegrator in which chalk is crushed, a classifier (1), a cyclone (2), a fan (3) and an air 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. The fine-dispersed fraction, which is the finished product, settles in the cyclone, the primary purified air returns to the classifier. 4 p. little chalk Rice. 7.5 Scheme of operation 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 of classifiers "ZhG" at chalk enterprises. Table 7.3 Performance indicators of the classifier "ZhG" in factories for the production of separated chalk.

Size classes, mm	Petropavlovsk Chalk Plant		Shebekinsky Chalk Plant
Size classes, mm	Before classification	After classification	Before classification	After classification
+ 0,1	0,96	0,06	1,7	0,5
— 0,1 + 0,071	0,80	0,08	1,2	0,7
— 0,071 + 0,056	0,56	0,06	0,6	0,6
— 0,056 + 0,044	1,08	0,28	1,9	1,1
-0,044	96,6	99,52	94,6	97,1
Total:	100,0	100,0	100,0	100,0

It follows from the above results that the classifiers operate at a relatively low efficiency.
On 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 cleaned.