DIY chalk. Food chalk: application. What is chalk made of?

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

Education

90 million years ago in Northern Europe, silt accumulated in the lower region of the great sea. Protozoa (foraminifera) lived on marine debris. Their particles included calcite extracted from water. The Cretaceous group of the stratigraphic European unit appeared during the period of the same name. It formed the slopes in Kent and another part of the Strait of Dover. It was these remains that became the basis of the chalk. However, the rock mainly consists of formations of algae and finely dispersed compounds. Thus, the researchers conclude that the appearance of chalk is the merit of plants.

Rock structure

The remains of mollusks that accumulated in bottom sediments, turned into chalk. The breed contains:

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

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

Description of the physical property of chalk - strength

Many scientists have conducted research on the substance. During geotechnical activities it was revealed that it is a hard semi-rocky rock. Its strength is largely determined by humidity. In the air-dry state, the temporary compressive strength varies from 1000 to 45,000 kN/m2. dry rock - from 3 thousand MPa (for a loose state) to 10 thousand MPa (for a dense state). The angle of internal friction is 24-30 degrees; with all-round compression, the adhesion reaches 700-800 kN/m2.

Humidity

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

Frost resistance

After freezing and 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 using it as an ameliorant for 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 and thawing with plowing of the soil, the pieces destroy themselves. Thus, the neutralizing effect lasts for a long time.

Properties of chalk: chemistry

The rock mainly includes carbonate and non-carbonate parts. The first 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 quantities. 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 were the same throughout the deposit. However, in practice, with prolonged exploitation 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 at some fields. Researchers studying the chemical properties of chalk and its mechanical characteristics on different areas deposits indicate areas of accumulation of high-quality rock.

Industrial development

Large deposits of chalk are present in Belgorod and Voronezh regions. Less quality material is present in Znamenskaya, Zaslonovskaya, Valuyskaya and other deposits. At these deposits, relatively low levels of CaCO 3 are detected (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 production of lime, as well as in reclamation measures to deoxidize soils. The 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 quite a long time. The product mined in the Voronezh region is characterized by a high content of CaCO 3 (up to 98.5%). At the same time, the share of non-carbonate impurities is less than 2%. Production at the deposits, however, is hampered by the physical properties of chalk. In particular, its high water saturation. The proportion of moisture in the rock is about 32%.

Promising deposits

Among the large deposits, it is worth noting Rossoshanskoye, Krupnennikovskoye, Buturlinskoye and Kopanishchenskoye. The chalk thickness of the latter is 16.5-85 m. The overburden consists of a soil-vegetative layer. Its thickness is about 1.8-2 m. Along the vertical line, the chalk layer is divided into two packs. In the lower part there is up to 98% calcium carbonate, in the upper part there is slightly less - up to 96-97.5%.

Extremely homogeneous white chalk of the Turunian stage was discovered 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 margels, a plant layer, sandy-clayey formations and sandstones. The share of magnesium and calcium carbonates reaches 99.3%. At the same time, non-carbonate components are present in relatively small quantities.

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

Chalk, which is located in 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 undergoing deep enrichment. It must be said that in the process of designing mining and processing enterprises specializing in iron ore, it is necessary to provide technological lines for incidentally extracted chalk or places for its separate storage.

Production and consumption

Beneficial features chalk have been known for quite a long time. Initially, the rock was used in construction. Lime was produced from it. Chalk powder acted as a base for putty, putties, paints, and so on. At the end of the 19th century, private factories began to be organized at the White Mountain deposit. Lime and powder were produced from lump rock. In 1935, the Shebekinsky plant appeared, producing products for industrial needs. The beneficial properties of chalk were in demand in the electrical, paint and varnish, polymer, rubber and other industries.

Along with the increase in demand for products, the requirements for their quality increased. The enterprises that existed by 1990 could not provide the industry with the necessary raw materials. Private enterprises began to emerge 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 by private enterprises could not provide required quantity quality products. Accordingly, many such factories closed. Together with that large enterprises carried out modernization and reconstruction of their equipment. The production of high-quality products was ensured in the 90s by the Belgorod, Petropavlovsk, and Shebekinsky factories.

Production of quality brands

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

The emergence of new production lines for the production of paints, rubber, polymers and other products for which chalk is used as a raw material, provoked a sharp imbalance between its production and consumption. This was especially clear in paper industry. Enterprises in this industry place special demands on 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, which produces separated chalk, new plants were created. So, in 1995, a processing plant appeared at the Lebedinsky GOK - Ruslime CJSC. It was built according to Spanish project company "Reverte" with an estimated productivity of 120 thousand tons/year. The plant produces up to 10 different brands chalk. In terms of quality, they are in no way inferior to foreign analogues and correspond 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 Mabetex company, a plant with a capacity of high-quality chalk products of 300 thousand tons was built at the Stoilensky GOK. At the same time, the company’s plans provide for a subsequent increase in capacity.

Bloomability of the breed

One of key criteria in the process of analyzing the physical properties of rock at a new deposit or site involved in an existing processing line, the behavior of chalk during grinding is examined. As mentioned above, in different layers of the deposit the substance has different mechanical characteristics. Visually identifying these differences is not possible in most cases. Determination of the behavior of chalk during its dry grinding in technological process carried out by establishing the indicator of its blooming in humid environment under mechanical influence. Special equipment is used for this.

Sodium bicarbonate

For its production are used different materials, 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, and 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, production of materials, paints and other products. When it comes to the production of calcium bicarbonate, using 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 progress of the technological process.

Is it possible to eat CaCO 3?

It is a fairly common belief that doctors recommend using medical chalk. The properties of this substance are believed to help replenish calcium deficiency. First of all, it should be said that doctors have mixed opinions on this matter. Patients who like to eat chalk (food chalk) often turn to specialists. Whether they are useful, however, is highly doubtful. The craving for eating it may arise due to a lack of calcium. However, you should be aware that the characteristics of the 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 affect the gastric mucosa. Medicinal properties however, none appear. Quite the contrary. It is also worth remembering that the concentration of calcium in the substance is very high. As a result, excessive consumption 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 with this.

Industrial and domestic use

Chalk acts as a necessary component of paper, which is used in printing. The high dispersion of calcium carbonate in crushed form affects the optical and printing characteristics, porosity, and smoothness of the product. Due to the presence of chalk, the abrasiveness of products is reduced. The ground species is widely used for whitewashing walls, borders, 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, so-called sedimentary rock is suitable. This is the kind of chalk you get chemically from calcium-containing minerals. Along with other carbonate rocks, the substance is used in glass melting as one of the components of the charge. Due to chalk, the thermal resistance of products increases, its mechanical strength and resistance to weathering and reagents. The breed is widely used in the production of fertilizers. Chalk is also added to feed for farm animals.

Rubber industry

Chalk is in 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 rubber products does not cause harm. The second reason for the popularity of raw materials in the industry is technological feasibility. Chalk significantly simplifies the process of manufacturing rubber products. In particular, due to it, vulcanization is accelerated, the surface of the products becomes smooth. The rock is also widely used in the production of spongy and porous rubber, plastic products, leather substitutes, etc.

Modern lifestyle has a huge impact on human health. Increasingly, you can find people suffering from vitamin deficiency and insufficient amounts of useful substances in organism. This is why food chalk has become very popular lately.

I want chalk, what does that mean?

Many consider the need for chalk to be a very strange phenomenon, abnormal for the average human body.

In everyday life, the desire to chew chalk is usually associated with pregnant women; indeed, they often have such taste preferences. This is due to the fact that during the formation and growth of the fetus, the female body requires double portions of vitamins and microelements.

Particularly important is the adequate amount of calcium that lump chalk contains for meals. It serves as a building material for most tissues, nerve cells, skeleton, cartilage tissue, hair, nails, internal organs and skin of a small person.

However, a lack of calcium can accompany absolutely any person; it is usually characterized by the following symptoms:

Brittle and dull hair;
Caries, bone fragility (frequent fractures);
Brittle nails prone to splitting;
Dull skin tone;
Loss of skin elasticity;
Muscle cramps;

Such conditions are characterized by a pronounced disturbance of calcium metabolism, which natural chalk for food will help to cope with.

What is chalk made of?

The composition of food chalk is a combination of inorganic salts (carbonates). The main element of such compounds is considered to be Ca (calcium). Many are sure that natural lump chalk is nothing more than the carbonate CaCO3, known to everyone from school.

However in-depth study This question makes it possible to verify that chalk for food includes other elements of the periodic table:

Of course, calcium oxide takes up almost half of the component composition of the substance. The CaO content in the mineral reaches 55%.
The second position in the list of components is occupied by carbon dioxide or CO2. Its share in the composition of chalk sometimes reaches 43%.
The oxide of a metal such as magnesium (MgO) occupies a very small volume, which usually does not exceed 2%.
The quartz component affects the density of food chalk in direct proportion. The more SiO2 a substance contains, the higher its density. Mass fraction quartz from the total volume sometimes reaches 6%.
Al2O3 is quite slightly inferior in volumetric content to quartz inclusions. The total volume of aluminum oxide in limestone corresponds to 4%.

Sometimes you can find natural chalk with a pinkish or even reddish tint. The rock has this feature due to its high content of iron oxides. In ordinary white chalk, the Fe2O3 content does not exceed the threshold of 0.5%.

Where is chalk mined?

Those wishing to compensate for calcium deficiency should know what food chalk is and where it comes from.

In the territory Russian Federation There are more than 100 deposits of natural chalk. Among them, three zones stand out in which the concentration of carbonate reserves reaches high levels.

The Volgograd region takes a huge share of this figure; its quarries account for up to 26% of the country's reserves. Lump chalk from these deposits is of excellent quality, it contains a minimal amount of impurities. The number of foreign inclusions does not exceed 2%. However, Volgograd chalk is quite saturated with water; the water content in dry chalk exceeds the specified standards by almost 10-15%. This fact makes it difficult to obtain.

The next position is occupied by the Belgorod region, where up to 24% of chalk reserves are concentrated. The delicious chalk mined here is 99% carbonate, which is an excellent indication of its high quality.

The Saratov region owns an 11% share in the total chalk wealth of the Russian Federation.

Harm and benefits of chalk when eaten

Lump chalk for food is becoming increasingly popular; the harm and benefits of this substance are discussed by experts to this day. It is not possible to clearly evaluate the sedimentary mineral, because it has both negative and positive effects on the human body.

The benefits of natural chalk for food are as follows::

Strengthens fragile bones and serves as a preventive measure against caries;
Helps maintain healthy and beautiful hair, nails, teeth and skin;
In small quantities it helps to improve the functioning of the digestive system;
Provides joint mobility and muscle elasticity;
Promotes proper operation of cardio-vascular system;
Participates in metabolic processes at the intercellular level;
Affects blood clotting and hemoglobin levels (indirectly).

Tasty chalk for food has a negative effect only when there is an excess of it in the body.

Excessive calcium intake leads to the following side effects:

Increased blood clotting;
Reduced strength of bone tissue and tooth enamel;
The emergence of a risk of diseases of the endocrine system;
Angina;
Decreased muscle tone;
The appearance of kidney stones;
Increased acidity of gastric juices, which contributes to the development of diseases of the gastrointestinal tract (gastritis and ulcers);
Gout;
Calcinosis (deposits of Ca salts in the tissues of internal organs).

Talking about negative consequences consumption of chalk for food, we can conclude that they are caused by the quantity and quality of the mineral consumed.

Which chalk is best for food?

People with a lack of calcium in the body are often interested in where to buy chalk for food and which one is best. They are also studying the question of what is the most delicious chalk for food.

When you want to chew on block chalk, blackboard chalk usually comes to mind. However, this product not only will not bring benefits, but can also cause harm due to the presence of chemical additives in it. Such substances poison the body, the resulting toxins disrupt the functioning of internal organs and spoil health in general.

It has been proven that school crayons dry out the airways by settling on the epithelium of the larynx. They also clog blood vessels, causing liming to occur, which leads to disruptions in the functioning of the cardiovascular system.

The solid particles that this type of chalk contains can scratch the tooth enamel, which will inevitably lead to caries. They act similarly on the oral mucosa, creating microscopic wounds in it that are invisible to the human eye. These cracks are a direct path to the appearance of inflammatory processes and the penetration of infection into the body.

Once in the stomach, school chalk causes a reaction similar to the extinguishing process. This chalk is less tasty compared to its natural counterpart.

Dry chalk has an elastic modulus from 3000 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 equal, the adhesion under conditions of all-round compression reaches 700-800.

When moistened, the strength of chalk begins to decrease already at a humidity of 1-2%, and at a humidity of 20-30%, the compressive strength increases 2-3 times, and plastic properties appear. The manifestation of visco-plastic properties of natural chalk with an increase in its humidity leads to serious complications in the technology during its processing. This causes chalk to stick to the elements. Vehicle(excavator bucket, dump truck body, feeder, belt conveyor). Sticking of roller gear crushers is observed. This leads in some cases to the failure of the extraction of chalk from the lower water-logged horizons, although the quality of the chalk of the lower horizons is of high-quality chalk.

Natural chalk has practically no frost resistance; after several cycles of freezing and thawing, it breaks up into separate pieces measuring 1-3 mm. This phenomenon is in some cases a positive factor. So, for example, when using chalk as an ameliorant to deoxidize the soil, it is not necessary to grind it to a particle size of 0.25 mm (limestone flour), but crushed chalk up to 10 mm can be added to the soil. When freezing and thawing with annual plowing of the soil, pieces of chalk are destroyed and its effects on neutralizing the soil persist for a long time.

As already noted, chalk consists mainly of two main parts - the carbonate part, soluble in salt and acetic acids(calcium and magnesium carbonates) and the non-carbonate part (clays, marls, quartz sand, metal oxides, etc.) that do not dissolve in these acids. The carbonate part of chalk is 98-99% calcium carbonate. Magnesium carbonates are present in small quantities, which form crystals of magnesian calcite, dolomite and siderite scattered in the main mass of the chalk.

The most acceptable classification is based on carbonate content and brands of chalk products.

Classification of chalk by carbonate content and brands of products made from it

The chemical characteristics of chalk from some deposits in Russia are given in Table 4. Initially, it was believed that chalk was a rock mass whose chemical composition and physical properties were the same throughout the deposit. However, during long-term exploitation 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. In this regard, at some chalk deposits, geological and technological mapping is carried out, 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 reserves and chemical composition the largest deposits in the Belgorod region.

Calcium carbonate (chalk) is a widely used material in modern global industry. The development of rubber and electrical, polymer, paint and varnish and other industries requires an increase in the production of high-quality fillers, which primarily include chalk. The annual consumption of natural chalk in lump, crushed and crushed form in developed countries exceeds 150 million tons. In the USA and Canada, more than 7.5 million tons of ground chalk are produced annually and more than 15 million tons in Europe.

Chalk, as a widely available filler, is becoming extremely important for many industries. Distinctive feature this natural material due to the fact that it is easily mined and processed at relatively low cost. The extraction and processing of chalk does not cause serious environmental disturbances. Chalk reserves are practically unlimited in many European countries, former CIS countries and Russia.

The thick Cretaceous belt extends across the entire European continent, including northern France, southern part England, Poland, passes through Ukraine, Russia and moves to Asia - Syria and the Libyan desert.

Chalk reserves are distributed unevenly across territories: about 48 - 50% of the reserves of high-quality chalk with a high content of calcium and magnesium carbonate and a minimal content of harmful impurities are concentrated in Russia; about 32 - 33% in Ukraine and a little more than 12% in Belarus. There are small deposits in Kazakhstan, Lithuania and Georgia. The total balance reserves of chalk in Russia are estimated at 3300 million tons with unlimited forecast reserves.

The Belgorod region has virtually unlimited predicted chalk resources. In total, 29 chalk deposits with total reserves of 1000 million tons have been explored in the region. The largest chalk deposits are Lebedinskoye, Stoilenskoye and Logovskoye. At the same time, the Lebedinskoye and Stoilenskoye deposits account for 75% of the explored chalk reserves of the Belgorod region. These two deposits are exploited for the extraction of iron ore, where chalk is the overburden rock.

Every year, over 15 million tons of chalk are mined and transported to dumps at the listed deposits, where it is irretrievably lost. Only a small part of it (about 5.0 million tons) is used for the production of cement and ground chalk. In addition to traditional consumers of chalk for last years new consumers appeared, such as the pulp and paper industry, where highly dispersed chalk began to be used instead of kaolin. Chalk was also used for deoxidation acidic soils, it has been proven that its activity is 30% higher than that of lime flour.

Chalk is a carbonate rock (a type of limestone) almost entirely composed of calcite (91-98.5%). Externally, it is a white, weakly cemented, fine-grained, soilable rock called “white chalk.” In the composition of chalk, there are three main formed elements of calcite composition, both biogenic and autogenic origin. Organic remains usually make up most of the rock (up to 75%). They are mainly represented by the skeletal shells of planktonic algae-coccolithophores, as well as foraminifera (sometimes up to 40%). The size of the skeletal remains is 5-10 microns. Powdered calcite with particles 0.5-2 microns in size has a variable, but sometimes significant value (10-90%). Less development belongs to larger (5-10% microns) well-bounded calcite crystals. There are shells of inocerams (in some places up to 13-20%), remains of crinoids, sea urchins, corals. In small quantities, usually up to 5, less often up to 10-12%, pelitomorphic non-carbonate impurities are present, mainly of terrigenous, less often autogenous origin: quartz, feldspars, clay minerals (glauconite, kaolinite, hydromica, montmorillonite), opal, chalcedony, pyrite and etc. In places there are flint concretions.

In the chalk strata, the development of large sustained cracks is observed - sheet and vertical, filled with chalk flour. At surface outcrops, the network of cracks becomes very dense. 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 - silt eaters.

Who among us doesn’t know what chalk is? It can be called a “witness of eras” that passed tens of millions of years ago. This compound is of biological origin, therefore it has numerous chemical and physical properties.

Features of origin

Discussing what chalk is, let's pay attention to its appearance in nature. About 80 million years ago, when dinosaurs existed on Earth, there was the Cretaceous period. In the small seas of that time lived millions of small mollusks that built their shells and skeletons from the calcium contained in the water. The remains of the creatures accumulated in multi-meter layers in the bottom sediments and turned into white chalk.

Mineral composition

IN percentage there are several components of this mineral:

about 10% are fragments of the skeletons of protozoa, multicellular animals that can accumulate calcium in tissues;
up to 10% of chalk is included in the shells of small foraminiferal mollusks;
fragments of algae growths contain up to 40% calcium salts. Living microscopic suspension in the seas is coccolithophores, which create calcareous silt;
up to 50% is crystalline fine calcite;
lump chalk (in the form of silicates) - up to 3%. It is presented in the form of geological debris (sand, rock remains), which are carried by winds and currents into the Cretaceous deposits.

Compound

Discussing what chalk is, let's consider its composition. In chemistry, this name was given to calcium carbonate, which is a salt of carbonic acid. Let's take a closer look at its composition. White chalk contains up to 50% calcium oxide and about 2% magnesium oxide. What substances give color to this mineral? Studying what chalk is, we note that in some cases, it may even contain 3-4% aluminum oxide, as well as minimal amounts of iron oxides. How does this affect appearance mineral? In this case, the drawing chalk takes on a red or pink tint.

Is blackboard chalk safe to eat? If there is a lack of calcium in the body, a person has a craving for eating chalk. Doctors have mixed feelings about this issue. When chalk is exposed gastric juice(concentrated hydrochloric acid), it significantly changes its properties.

Chalk, having gone through many oxidative processes, loses its original neutrality and turns into an aggressive chemical compound, similar in properties to slaked lime (calcium hydroxide).

That is why, upon contact with oxidized chalk, the mucous membrane of the digestive organs is seriously damaged.

If you eat blackboard chalk in large quantities, it provokes liming of blood vessels. In case of calcium deficiency, it is much safer to use special medications, for example, calcium gluconate.

Doctors warn patients about the inadmissibility of using agricultural feed, construction, and stationery chalk for food.

Areas of use

It is not advisable to use chalk as a masonry material, since it has insignificant hardness. How is this mineral mined? School chalk is mainly obtained from open-pit mines. The extracted blocks are crushed and then lowered into water.

With constant stirring, calcium particles float to the surface. They are dried and used for various purposes. Stones that have not undergone such processing are sent for firing, which results in the formation of lime.

Construction chalk

His for a long time used for whitewashing indoor ceilings. Currently, this scope of application is practically absent, since other finishing materials have appeared.

Currently, chalk is added to the composition cement mixtures to give them extra softness.

The mineral is also in demand in the manufacture of glass, rubber, plastics, paint and varnish materials, composite mixtures, rubber.

Chalk is used in large quantities in the linoleum and carpet industries. With its help, I regulate the viscous properties of latex glue, impart strength to products, and improve heat-saving characteristics.

The calcium mineral is also necessary for the production soil fertilizers and compound feeds. Chalk powder is the basis for creating numerous cosmetics: powder, creams, lipstick. It is difficult to imagine the functioning of the cardboard and paper industries without chalk.

Chemical and physical characteristics

Depending on the characteristics of the deposit, in natural characteristics chalk there can be significant differences. Air humidity has a significant impact on the material. Chalk does not dissolve in water, it forms a suspension. When absorbing moisture, calcium carbonate loses its strength, while the ductility of the material increases significantly. This contributes serious problems during the extraction and processing of the mineral, it sticks to the excavator bucket. Chalk has low frost resistance. After defrosting, the material breaks down into many individual small particles. This quality is used in agriculture to reduce soil acidity.

Differences between lime and chalk

Despite their common roots, these materials differ in properties and composition. Both are considered environmentally friendly, but chalk contains carbon dioxide, and lime is obtained by burning natural limestone.

In order to independently distinguish chalk and lime, you can take a small handful of each material, grind it to a dusty appearance, then rinse with a small stream of water. The chalk will immediately be removed along with the water, but in order to get rid of the lime, you will have to work hard.

Lime whitewash leaves no traces, but chalk will remain a reminder for a long time even after the renovation is completed. Lime has been shown to have excellent antiseptic characteristics, so it is used to protect trees and shrubs from insect damage.

Finally

Chalk is a material that is familiar not only as a tool of work for teachers in schools, but also as a historical witness to the events that occurred on our planet millions of years ago.

Its main part consists of calcium deposits from the shells of protozoan prehistoric plants and microorganisms.

Cretaceous deposits are currently needed in various fields production: in the creation of paints, the manufacture of cosmetics, the development of food additives. Cretaceous natural deposits often include various undesirable impurities: sand, stones, various mineral particles.

That is why chalk mined from deposits is first crushed and then mixed with water to form a suspension. Heavy impurities settle to the bottom, light chalk particles are caught in a special container. After adding adhesive to them and drying, you get chalk suitable for drawing on a blackboard.

Among the new areas of use of chalk, we can highlight its application to the playing field. Fine particles of this substance rise into the air, so players can clearly see the lines made.

To remove sweat and fat, chalk powder is also in demand in some sports: weightlifting, gymnastics, rock climbing.

The finished product is an excellent component of toothpastes and powders. It is used as a filler in the manufacture of cardboard and paper products.

Unprocessed mineral extracted by quarrying is necessary for construction industry for lime production.

Who among us doesn't know chalk? Whose pockets and fingers were not soiled as a child by a piece of light stone the color of snow? Who doesn't know happiness artistic creativity"Cretaceous" period? Who, as a teenager, did not explore the properties of chalk in “bubbling” experiments or examine a chalk smear under a microscope?

Mineral chalk is a witness to eras that passed tens of millions of years ago. Awareness of this fact changes the perception of familiar material. Having a biological origin, the chalk stone acquired its properties from organisms that lived in time immemorial.

Origin of chalk

The Cretaceous period is a period of time covering about 80 million years during the reign of dinosaurs. The warm and shallow (30-500 meters deep) seas of that time gave shelter to myriads of tiny mollusks that built their skeletons and shells from calcium extracted from the water.

The remains of these creatures, accumulated in multi-meter layers in bottom sediments, turned into the familiar chalk. In percentage terms, the chalk mineral is divided into the following parts:

fragments of skeletons – about 10%. It's about not only about the simplest creatures, but also about multicellular animals endowed with the ability to extract and concentrate calcium salts in tissues.

shells of microscopic foraminiferal mollusks – about 10%. However, not all rhizomes (the Russian name for animals) had a calcareous shell. Some constructed their protective layer from a chitin-like substance. This is largely why no more than 98% (and no less than 91%) of calcium carbonate itself is found in the Cretaceous deposits.

fragments of calcareous growths of algae – up to 40%. Coccolithophores - plant plankton of the oceans - feel great in our time. Up to 98% of microscopic live suspension in upper layers seas accounted and accounted for this type of algae. Therefore, the calcareous mineral is, in fact, a product of mostly plant rather than animal origin. The origin of chalk is the merit of plants!

finely dispersed crystalline calcite – up to 50%. We are talking about “fragments of debris”, and so miniature in size that it is not possible to determine their biological identity.

insoluble minerals (mainly silicates) – up to 3%. This is mainly geological debris (sand and fragments of various rocks), carried into the Cretaceous deposits by winds and currents. Although, in addition, biogenic calcium formations are enriched with phosphorus and silicon compounds during metabolic processes during the life of the animal.

Shells of more or less large mollusks, skeletons of coelenterates, and concretions of foreign minerals in the Cretaceous strata are relatively rare. Only a few photographs of chalk show the observer massifs dotted with cavities of voluminous shells.

Chalk composition

It is conventionally considered that chemical formula chalk corresponds to the formula of calcium carbonate CaCO3. However, the actual composition of chalk differs from the composition of the calcium salt of carbonic acid.

Actually, calcium oxide in the mineral is about half: the concentration of CaO ranges from 47% to 55%. A lot in chalk and carbon dioxide, which is in a bound state. CO2 – up to 43%!

Magnesium oxide MgO can reach up to 2% of the total mass of chalk. Inclusions of quartz SiO2 are usually not very significant, but are generally obligatory, and can reach a concentration of 6%. The density of chalk with a high silicon content is greater than usual.

There is slightly less aluminum oxide Al2O3 in the chalk composition - no more than 4%. Various iron oxides rarely exceed the half-percent concentration threshold, but they are the ones that color the chalk red quite often.

Application of chalk

As an independent construction material chalk is used only as a raw material for the production of chalk paints. Having fallen out of widespread use half a century ago, whitewashing premises with a colloidal solution of pure or colored chalk is almost never done today.

As a masonry stone, chalk is untenable - although rooms excavated in chalk massifs remain suitable for life for centuries. The low hardness of chalk makes it possible to gradually remove the stone without large-scale destruction of the massif.

In the construction industry, the use of chalk is growing and expanding. The production of cement and glass without chalk is almost impossible! Chalk is required by paper-making enterprises, light industry, and organic chemistry. Paints and rubber, hygiene products and soil fertilizers, animal feed and perfume compositions are produced using chalk.

Is it possible to eat chalk?

It is known that with a lack of calcium in the body, a craving for eating chalk may develop. The experience of generations who grew up in conditions of organic calcium deficiency says: chalk is edible! However, doctors, answering the question of whether chalk can be eaten, are not so clear-cut.

The properties of chalk change dramatically under the influence of gastric juice. Chalk, having passed through the crucible of oxidative processes, loses its original neutrality and becomes a chemically active reagent. In terms of effectiveness, it is similar to slaked lime. The mucous membrane of the digestive tract suffers from contact with oxidized chalk.

In addition, the concentration of calcium in chalk is excessively high. Eating chalk can cause liming of blood vessels. In case of calcium deficiency, it is much safer to pay attention to medications for this metal. A calcium gluconate tablet has a much more positive effect on the body than a piece of chalk eaten.

Stationery, construction and even agricultural feed chalk are not suitable for consumption! A person does not have the opportunity to safely (and even more so for his own benefit) process and assimilate this mineral!

The Cretaceous deposits of Eurasia stretch in a wide strip from the Kazakh River Emba to the western tip of Britain. The deposits reach their greatest thickness south of Kharkov: here there are real chalk mountains with a massif thickness of up to 600 meters. The ongoing development of the white mineral promises scientists many new discoveries.