Chalk is a white sedimentary rock. It is insoluble in water, has an organic origin. We learn from the article where chalk is used, the physical and chemical properties of this rock.
Education
90 million years ago, silt accumulated in northern Europe, in the lower region of the great sea. Protozoa (foraminifera) lived on marine litter. Their particles included calcite extracted from water. The chalk group of the European stratigraphic unit appeared during the eponymous period. It formed the White Cliffs in Kent and the slopes in another part of the Dover Strait. It was these remains that became the basis of the chalk. However, predominantly the rock consists of the formation of algae and finely divided compounds. Thus, the researchers conclude that the appearance of chalk is the merit of plants.
Breed structure
The remains of mollusks that accumulated in the bottom sediments turned into chalk. In the breed there are:
- About 10% of skeletal debris. Among them are not only parts of protozoa, but also multicellular animals.
- About 10% of foraminifer shells.
- Up to 40% of fragments of calcareous algae
- Up to 50% crystalline fine calcite. Its size is so small that it is practically impossible to establish the biological identity of the elements that make up it.
- Up to 3% insoluble minerals. They are mainly represented by silicates. Insoluble minerals are a kind of geological garbage (fragments of different rocks and sand), which is listed in the chalk deposits by currents and winds.
Shells of mollusks, nodules of other minerals, skeletons of intestinal cavities are rarely found in the breed.
Description of the physical property of chalk - strength
Substance studies have been carried out by many scientists. In the course of engineering and geological measures, it was revealed that it is a rigid semi-rock breed. Its strength is largely determined by humidity. In the air-dry state, the temporary compressive strength varies from 1000 to 45 000 kN / m 2 . The elastic modulus of dry rock is from 3 thousand MPa (for loose state) to 10 thousand MPa (for dense). The value of the angle of internal friction is 24-30 degrees, with full compression, the adhesion reaches 700-800 kN / m 2 .
Humidity
When exposed to water, the physical properties of the 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 a factor of 2β3. Along with this, other physical properties of the chalk appear. The breed becomes ductile. This manifestation significantly complicates the process of processing the substance. During this, chalk begins to adhere to machine elements (onto the excavator bucket, conveyor belt, feeder, vehicle body). Often the physical properties of the chalk (viscosity and ductility) do not allow production from the lower horizons, although here it is considered to be of high quality.
Frost resistance
After freezing and thawing, the chalk breaks up into particles of 1-2 mm in size. In some cases, this is a useful property of the breed. For example, when it is used as an ameliorant during deoxidation of the soil, it is not necessary to grind the substance to 0.25 mm. Crushed rock up to 10 mm can be added to the soil. When freezing-thawing with plowing the soil, the pieces are destroyed themselves. Thus, the effect of neutralization persists 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. In the non-carbonate part, metal oxides, quartz sand, marls, clays, etc. are present. Some of them are insoluble in these acids. In the carbonate portion of 98-99% calcium carbonate. The crystalline particles of magnesia calcite, siderite and dolomite are formed by magnesium carbonates, which are included in chalk in an insignificant amount. The composition and properties of the rock act as classification criteria.
Identification of quality deposits
Initially, it was believed that the mechanical and chemical properties of chalk are the same throughout the field. However, in practice, during the long-term operation of the region, especially after the transition of the mining and processing enterprises to the production of better products, differences in these characteristics are revealed. Therefore, in some fields, geological and technological mapping is performed. Researchers, studying the chemical properties of chalk and its mechanical characteristics in different parts of the reservoir, indicate areas of accumulation of high-quality rock.
Industrial development
Large deposits of chalk are present in the Belgorod and Voronezh regions. Less qualitative substance is present in Znamenskaya, Zaslonovskaya, Valuyskaya and other deposits. At these deposits, relatively low CaCO 3 values ββare detected (no more than 87%). In addition, various impurities are present in the rock. Therefore, it is impossible to obtain high-quality products at these fields without deep enrichment. The physical properties of chalk on such deposits allow it to be used in the manufacture of lime, as well as in land reclamation measures for deoxidation of soils. Voronezh deposits are attributed to the Turonian-Cognac age. It produces better chalk. The properties and application of the rock obtained in these deposits have been studied for a long time. The product, extracted in the Voronezh region, has a high content of CaCO 3 (up to 98.5%). Moreover, the proportion of non-carbonate impurities is less than 2%. Mining in the fields, however, is hampered by the physical properties of the chalk. In particular, its high water saturation. The moisture content in the rock is about 32%.
Promising deposits
Among large deposits, it is worth noting Rossoshanskoye, Krupnennikovskoye, Buturlinskoye and Kopanishchenskoye. The Cretaceous stratum of the latter is 16.5-85 m. Overburden is the soil-plant layer. Its thickness is about 1.8-2 m. The chalk line is divided into two packs along a vertical line. Up to 98% of calcium carbonate is present in the bottom, slightly less in the top - up to 96-97.5%.
An extremely homogeneous white chalk of the Turun layer 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, a vegetative layer, sand-clay formations and sandstones. The proportion of magnesium and calcium carbonates reaches 99.3%. However, non-carbonate constituents are present in relatively small amounts.
Of great interest to industry are the Stoilenskoye and Lebedinsky deposits. In these areas, chalk is mined as overburden and dumped into dumps. The associated annual output is more than 15 million tons. About five of them are used in the national economy. In particular, chalk enters the Starooskolsky cement plant and some other small enterprises. A larger volume of mined rock is lost in dumps.
Chalk, which is located in the areas of iron ore deposits, is classified as high quality in terms of silica and carbonate content. It can be used for industrial purposes without deep enrichment. It must be said that in the design process of mining and processing enterprises specializing in iron ore, it is necessary to provide production lines for simultaneously recoverable 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 a base for putty, putties, paints and so on. At the end of the 19th century, private factories began to be organized at the Belaya Gora deposit. In shaft kilns , lime and powder were made from lumpy rock. In 1935, the Shebekinsky plant appeared, engaged in the production of products for industrial needs. Useful 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, requirements for its quality increased. The enterprises that existed by 1990 could not provide industry with the necessary raw materials. In the Belgorod region, private enterprises began to appear. A large number of them 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 at private enterprises could not provide the required amount of quality products. Accordingly, many such plants have closed. At the same time, large enterprises modernized and reconstructed their equipment. The release of quality products was provided in the 90s by Belgorod, Petropavlovsk, Shebekinsky plants.
Production of quality brands
The key requirements for products from chalk, in addition to the proportion of carbonates, include fineness - 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 2 microns in size).
The emergence of new production lines for the manufacture of paintwork, rubber, polymer and other products, for which chalk is used as raw material, provoked a sharp imbalance between its production and consumption. This is especially evident in the paper industry. Enterprises in this industry have special requirements for chalk powder, which replaced kaolin in production.
The issue of quality brands is concentrated in 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 - CJSC Ruslaym. It was built according to the Spanish project of 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 comply with 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 was built at Stoilensky GOK with a productivity of chalk products of high quality 300 thousand tons. Moreover, the plans of the enterprise provide for a subsequent increase in capacity.
Breeding rate
One of the key criteria in the process of analyzing the physical properties of the rock at a new deposit or site involved in the existing processing line is the behavior of the chalk during grinding. As mentioned above, on different layers of the reservoir, the substance has different mechanical characteristics. Visually identify these differences is not possible in most cases. Determination of the behavior of chalk in the process of its dry grinding in the technological process is carried out by establishing an indicator of its dispersal in a humid environment under mechanical stress. For this, special equipment is used.
Sodium bicarbonate
For its production, various materials are used, including limestone or chalk. The beneficial properties for the body, which possesses sodium bicarbonate, are known to many. Often it is used for diseases of the gums and throat, heartburn, to thin the sputum when coughing. In industry, the physical properties of soda and chalk are very much in demand. Both of these substances are used in construction, decoration, manufacturing of materials, paint and varnish and other products. As for 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, negatively affects the process.
Is it possible to eat CaCO 3 ?
It is widely believed that doctors recommend the use of medical chalk. The properties of this substance are believed to contribute to the replacement of calcium deficiency. First of all, it should be said that doctors have mixed opinions about this. Often, specialists who like to eat chalk (food) turn to specialists . The beneficial properties of the substance, however, are highly doubtful. Cravings for eating it may occur due to a lack of calcium. However, you should know 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. The healing properties are not manifested. Rather, the opposite. It is 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 tried to eliminate it with the help of chalk, it does not help in this.
Industrial and domestic use
Chalk acts as a necessary component of paper, which is used in printing. The high dispersion of powdered calcium carbonate affects the optical and printing characteristics, porosity, and smoothness of the product. Due to the presence of chalk, the abrasiveness of products decreases. Ground rock is widely used for whitewashing walls, borders, protecting trees. Chalk is used in the purification of beet juice, which, in turn, is used in the match industry. For these purposes, the so-called precipitated rock is generally suitable. Such chalk is obtained chemically from calcium-containing minerals. Along with other carbonate rocks, the substance is used when cooking glass as one of the components of the charge. Due to the chalk, the thermal stability of the product, its mechanical strength and stability under the influence of weathering and reagents are increased. The breed is widely used in the manufacture 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 viable. Chalk has a relatively low cost. At the same time, its introduction into rubber products does not harm. The second reason for the popularity of raw materials in the industry is technological feasibility. Chalk greatly simplifies the process of manufacturing rubber products. In particular, due to it, vulcanization is accelerated, the surface of the products becomes smooth. The breed is widely used in the production of sponge and porous rubber, plastic products, leather substitutes, etc.