Chalk is a white sedimentary rock. It is insoluble in water and is of organic origin. From the article we 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 division appeared during the period of the same name. It formed the White Cliffs in Kent and the slopes in 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.
Breed structure
The remains of mollusks that accumulated in bottom sediments turned into chalk. The breed contains:
- About 10% skeletal debris. Among them are not only parts of the simplest, but alsomulticellular animals.
- About 10% of foraminifer 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 is brought into the chalk deposits by currents and winds.
Shells of mollusks, concretions of other minerals, skeletons of coelenterates are rarely found in the rock.
Description of the physical property of chalk - strength
Research of the substance was carried out by many scientists. In the course of engineering and geological measures, it was revealed that it is a rigid semi-rocky rock. Its strength is largely determined by moisture. In the air-dry state, the tensile strength during compression varies from 1000 to 45,000 kN/m2. The elasticity modulus of dry rock is from 3 thousand MPa (for a loose state) to 10 thousand MPa (for a dense state). The value of 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 is reduced. Changes occur already at 1-2% humidity. At 25-35%, the compressive strength increases by 2-3 times. Along with this, other physical properties of chalk appear. The rock becomes plastic. This ismanifestation significantly complicates the process of processing the substance. During this, chalk begins to stick to machine elements (excavator bucket, conveyor belt, feeder, vehicle body). Often the physical properties of chalk (viscosity and plasticity) do not allow mining from lower horizons, although here it is considered to be of high quality.
Frost resistance
After freezing-thawing, the chalk breaks up into particles of 1-2 mm. In some cases, this is a useful property of the breed. For example, when it is used as an ameliorant during soil deoxidation, it is not necessary to grind the substance to 0.25 mm. Crushed rock up to 10 mm can be introduced into the soil. When freezing-thawing with plowing the soil, the pieces are destroyed by themselves. Thus, the neutralization action is maintained for a long time.
Chalk properties: 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 amounts. The composition and properties of the rock act as classification criteria.
Identification of quality deposits
Initially it was believed that the mechanical and chemical properties of chalkare the same throughout the field. However, in practice, during the long-term operation of the region, 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 in different parts of the deposit, designate areas of accumulation of high-quality rock.
Industrial development
Large deposits of chalk are present in the Belgorod and Voronezh regions. Less high-quality substance is present in the Znamenskaya, Zaslonovskaya, Valuyskaya and other deposits. Comparatively low rates of CaCO3 (no more than 87%) are revealed at these deposits. In addition, various impurities are present in the rock. Therefore, high-quality products cannot be obtained at these deposits without deep enrichment. The physical properties of chalk on such deposits make it possible to use it in the manufacture of lime, as well as in land 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 a long time. The product mined in the Voronezh region has a high content of CaCO3 (up to 98.5%). The proportion of non-carbonate impurities is less than 2%. Mining at the deposits, however, is hampered by the physical properties of the chalk. In particular, hishigh 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 is the soil-vegetative layer. Its thickness is about 1.8-2 m. The chalk layer is divided into two units along the vertical line. At the bottom there is up to 98% calcium carbonate, at the top it is somewhat less - up to 96-97.5%.
Ultimately homogeneous white chalk of the Turunian stage was discovered in the Buturlinskoye deposit. The thickness of the layer is 19.5-41 m. The overburden thickness reaches 9.5 m. It is represented by margels, vegetation layer, sandy-clayey formations and sandstones. The proportion of magnesium and calcium carbonates reaches 99.3%. At the same time, non-carbonate components are present in a relatively small amount.
The Stoilenskoye and Lebedinskoye deposits are of great interest to industry. In these areas, chalk is mined as overburden and taken to dumps. The associated annual production is more than 15 million tons. About five of them are used in the national economic sectors. In particular, chalk is supplied to the Starooskol cement plant and some other small enterprises. More of the mined rock is lost in the dumps.
Chalk, which is located in the areas of iron ore deposits, is classified as high-quality in terms of silica and carbonate content. It can be used for industrial purposes without deep enrichment. It must be said that inIn the process of designing mining and processing enterprises specializing in iron ores, it is necessary to provide technological lines for incidentally extracted chalk or a place for its separate storage.
Production and consumption
Useful properties of chalk have been known for a long time. Initially, the breed was used in construction. Lime was made from it. Chalk powder acted as the basis for putty, fillers, paints and so on. At the end of the 19th century, private factories began to be organized at the White Mountain deposit. In shaft furnaces, lime and powder were produced from lumpy rock. In 1935, the Shebekinsky plant appeared, which was engaged in the production of products for industrial needs. Useful properties of chalk were in demand in the electrical, paint, polymer, rubber and other industries.
Along with the increase in demand for products, the requirements for its quality increased. The enterprises that existed by 1990 could not provide the industry with the necessary raw materials. Private enterprises began to appear in the Belgorod region. Their large number was due to the huge volumes of rock deposits and the apparent simplicity of processing technologies. However, the primitive methods of extraction and subsequent processing used by private enterprises could not provide the required amount of quality products. Accordingly, many such factories closed. At the same time, large enterprises carried out the modernization and reconstruction of theirequipment. The release of quality products was ensured in the 90s by the Belgorod, Petropavlovsk, Shebekinsky plants.
Production of quality stamps
The key requirements for chalk products, in addition to the proportion of carbonates, include fineness - fineness of grinding. It is expressed as a residue on sieves of a certain size or as a percentage of particles of a given size (for example, 90% of particles with a size of 2 microns).
The emergence of new production lines for the manufacture of paint, rubber, polymer and other products for which chalk is used as a raw material provoked a sharp imbalance between its production and consumption. This was especially evident in the paper industry. Enterprises in this industry have special requirements for chalk powder, which has replaced kaolin in production.
Issue of quality stamps is focused on 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 Lebedinsky GOK - ZAO Ruslime. It was built according to the Spanish project of the company "Reverte" with an estimated capacity of 120 thousand tons / year. The plant produces up to 10 different grades of chalk. In terms of quality, they are in no way inferior to foreign counterparts and meet international standards. The enterprise is equipped with the most modern technological equipment, operations on the lines are mechanized and automated.
PoA plant with a capacity of 300,000 tons of high-quality chalk products was built at the Stoilensky GOK under the Mabetex project. At the same time, the plans of the enterprise provide for a subsequent increase in capacity.
Breed bloom
One of the key criteria in the process of analyzing the physical properties of the rock at a new deposit or area involved in the existing processing line is the behavior of chalk during grinding. As mentioned above, in different reservoir layers, the substance has different mechanical characteristics. Visually identifying these differences is not possible in most cases. Determining the behavior of chalk in the process of its dry grinding in the technological process is carried out by establishing an indicator of its blooming in a humid environment under mechanical action. Special equipment is used for this.
Sodium bicarbonate
For its production, different materials are used, including limestone or chalk. The beneficial properties for the body that sodium bicarbonate possesses are known to many. Often it is used for diseases of the gums and throat, heartburn, to thin sputum when coughing. In industry, the physical properties of soda and chalk are in great demand. Both of these substances are used in construction, decoration, materials, paints and other products. With regard to the production of calcium bicarbonate, the use of chalk alone is considered an uneconomical option. As mentioned above, this breed absorbs moisture very well,as a result of which its mechanical characteristics change. This, in turn, has a negative impact on the course of the technological process.
Can I eat CaCO3?
It is widely believed 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 are ambiguous about this. Often, patients who like to eat chalk (food) turn to specialists. Useful properties of the substance, however, are very doubtful. Cravings for eating it may occur 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 original neutrality and turns into a reagent. In its action, the substance is similar to slaked lime. As a result, oxidized chalk begins to affect the gastric mucosa. In this case, no medicinal properties are manifested. Rather, on the contrary. It is worth remembering that the concentration of calcium in the substance is very high. As a result, excessive use of chalk can provoke liming of vessels. In this regard, doctors recommend replacing it with calcium gluconate or similar drugs. As for getting rid of heartburn, according to many people who have tried it with chalk, it does not help.
Industrial and residential use
Mel acts asa 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 products. Due to the presence of chalk, the abrasiveness of products decreases. The ground rock 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, the so-called precipitated rock is suitable. Such chalk is obtained chemically from calcium-containing minerals. Along with other carbonate rocks, the substance is used in glass melting as one of the charge components. Due to the chalk, the thermal stability of the product, its mechanical strength and stability when exposed to weathering and reagents are increased. The breed is widely used in the manufacture of fertilizers. Chalk is also added to animal feed.
Rubber industry
Chalk is in first place among all the fillers used in the industry. This is primarily due to the fact that the use of this raw material is economically beneficial. 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 expediency. Chalk greatly simplifies the process of manufacturing rubber products. In particular, due to it, vulcanization is accelerated, the surfaceproducts become smooth. The breed is also widely used in the production of sponge and porous rubber, plastic products, leather substitutes, etc.
