Chemical and physical properties of chalk

Chalk is a sedimentary rock of white color. It is insoluble in water, has an organic origin. From the article we learn where the 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. On sea litter lived protozoa (foraminifera). Their particles included calcite extracted from water. The chalk group of the stratigraphic European division appeared during the eponymous period. From it are formed White rocks in the county of Kent and the slopes in the other part of the Strait of Dover. It was these remains that became the basis of chalk. However, mainly the rock consists of the formations of algae and fine-dispersed compounds. Thus, the researchers conclude that the appearance of chalk is a merit of plants.

Structure of the rock

The remains of the mollusks that accumulated in the bottom sediments turned into chalk. In the breed there are:

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

Shells of mollusks, concretions of other minerals, skeletons of coelenterates are rarely found in the breed.

Description of the physical property of chalk - strength

Studies of the substance carried out by many scientists. During the engineering-geological events it was revealed that it is a rigid semi-rock. Its strength is largely determined by humidity. In the air-dry state, the time resistance under compression varies from 1000 to 45,000 kN / m ² . Modulus of elasticity of dry rock - 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 a comprehensive compression, the grip 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 2-3 times. Along with this, other physical properties of chalk appear. The breed becomes plastic. This manifestation significantly complicates the process of processing the substance. In the course of this, the chalk begins to adhere to the elements of the machines (on the excavator bucket, conveyor belt, feeder, vehicle body). Often, the physical properties of chalk (viscosity and ductility) do not allow extraction from the lower horizons, although here it is considered qualitative.

Frost resistance

After freezing-defrosting, the chalk decomposes into particles of 1-2 mm in size. In some cases, this is a useful property of the breed. For example, when used as an ameliorant for soil deoxidation, it is not necessary to crush the substance to 0.25 mm. In the ground, crushed rock can be made up to 10 mm. When freezing-defrosting with plowing the soil, the pieces are destroyed themselves. Thus, the neutralization action remains 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 there are oxides of metals, quartz sand, marls, clays, and so on. Some of them are insoluble in these acids. In the carbonate part of 98-99% of calcium carbonate. Crystalline particles of magnesian calcite, siderite and dolomite are formed by magnesium carbonates, which are included in small amount in chalk. The composition and properties of the rock act as classification criteria.

Identification of qualitative deposits

It was initially assumed that the mechanical and chemical properties of chalk are the same throughout the deposit. However, in practice, with long-term operation of the district, especially after the transition of the extracting and processing enterprise to the production of better products, differences in these characteristics are revealed. Therefore, geological and technological mapping is carried out at some deposits. Researchers, studying the chemical properties of chalk and its mechanical characteristics in different sections of the deposit, denote areas of congestion of high-quality rock.

Industrial development

Large deposits of chalk are present in the Belgorod and Voronezh regions. Less quality substance is present in Znamenskaya, Zaslonovskaya, Valuiskaya and other deposits. These deposits show relatively low rates of CaCO ₃ (no more than 87%). In addition, various impurities are present in the rock. Therefore, it is impossible to obtain high-quality products in these deposits 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 meliorative measures for deoxidizing soils. Voronezh deposits are attributed to the Turonian-Cognac age. A better chalk is produced here. Properties and application of the rock obtained at these deposits have been studied for a long time. The product, extracted in the Voronezh region, is characterized by a high content of CaCO ₃ (up to 98.5%). The proportion of non-carbonate impurities is less than 2%. Production at the fields, however, is hampered by the physical properties of the chalk. In particular, its high water saturation. The share of moisture in the rock is about 32%.

Prospective deposits

Among the major deposits worth noting Rossoshanskoye, Krupnennikovskoe, Buturlinskoe and Kopanischenskoye. The chalk thickness of the latter is 16.5-85 m. The overburden is composed of the soil-vegetation layer. Its thickness is about 1.8-2 m. On the vertical line the Cretaceous layer is divided into two packs. In the lower part there is up to 98% calcium carbonate, in the upper part it is slightly lower - up to 96-97.5%.

In the Buturlinsky deposit an extremely uniform white chalk of the Turunian stage was discovered. The thickness of the layer is 19.5-41 m. The thickness of the overburden is 9.5 m. It is represented by margels, a vegetative layer, sandy-argillaceous formations and sandstones. The share of magnesium and calcium carbonates reaches 99.3%. In this case, non-carbonate constituents are present in a relatively small amount.

Stoilensky and Lebedinsky deposits are of great interest for industry. In these areas, the chalk is mined as an overburden and taken to the dumps. The annual production rate is more than 15 million tons. About five of them are used in the national economy. In particular, the chalk comes to the Starooskolsky cement plant and to some other small enterprises. The greater 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 is necessary to say that in the process of designing mining and processing enterprises specializing in iron ore, it is necessary to provide technological lines for the chalk extracted at the same time or a place for its separate storage.

Production and consumption

Useful properties of the chalk are known for a long time. Initially, the breed was used in construction. Lime was produced from it. Cretaceous powder acted as a base for putty, fillings, paints and so on. At the end of the 19th century, private plants began to be set up at the Belaya Gora deposit. In lime kilns from lump rock, lime and powder were produced. In 1935, the Shebekinsky Combine, which manufactured products for industrial needs, appeared. 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 to its quality were raised. The enterprises existing by 1990 could not provide the industry with the necessary raw materials. Private enterprises began to appear in the Belgorod region. 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 in private enterprises, could not provide the necessary quantity of quality products. Accordingly, many such factories were closed. Along with this, large enterprises carried out modernization and reconstruction of their equipment. Production of high-quality products was provided in the 90 years by Belgorod, Petropavlovsk, Shebekinsky plants.

Production of quality brands

The key requirements for products made from chalk, in addition to the share of carbonates, are coarseness - fineness of grinding. It is expressed in the remainder on the sieves of a certain size or in the percentage of particles of a given value (for example, 90% of particles of 2 mc.).

The emergence of new production lines for the manufacture of paint and varnish, rubber, polymer and other products, for which chalk was used as raw material, provoked a sharp imbalance between its release and consumption. This was particularly evident in the paper industry. Enterprises in this industry place special demands on the chalk powder, which replaced kaolin in production.

The issue of quality brands is concentrated in the factories in the Belgorod region. In addition to the Shebekinsky enterprise, which produces the separated chalk, new combines were created. So, in 1995, a processing plant appeared at Lebedinsky GOK, ZAO Ruslaym. It was built on the Spanish project of the company "Revert" with an estimated capacity of 120 thousand tons / year. The plant produces up to 10 different brands of chalk. By their quality, they are in no way inferior to foreign analogues 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 company "Mabetex" at Stoilensky GOK, a plant was built with the productivity of chalk products of high quality of 300 thousand tons. At the same time, the plans of the company provide for a further increase in capacity.

Breeding

One of the key criteria in the process of analyzing the physical properties of the rock in a new field or a site involved in the operating processing line is the behavior of chalk during crushing. As it was said above, the substance has different mechanical characteristics on different reservoir layers. Visually, these differences are 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 the index of its spreadability in a moist environment under mechanical action. For this, special equipment is used.

Sodium bicarbonate

For its production, different materials are used, including limestone or chalk. Useful properties for the body, which has sodium bicarbonate, are known to many. Often it is used for diseases of gums and throat, heartburn, for liquefaction of sputum during coughing. In the industry, the physical properties of soda and chalk are very much in demand. Both of these substances are used in construction, finishing, 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 it was said above, this breed absorbs moisture very well, as a result of which its mechanical characteristics change. This, in turn, negatively affects the course of the technological process.

Can I eat CaCO ₃ ?

It is widely believed that doctors recommend using medical chalk. The properties of this substance are believed to contribute to the replenishment of calcium deficiency. First and foremost, it should be said that doctors disagree about this. Often, patients refer to specialists who like to eat chalk (food). Useful properties of the substance, however, are very doubtful. A craving for his eating can arise due to a lack of calcium. However, you should be aware that the characteristics of the substance undergo significant changes when ingested. Passing through several oxidative processes, it loses its original neutrality and turns into a reagent. By its action, the substance is analogous to hydrated lime. As a result, oxidized chalk begins to affect the stomach mucosa. In this case, the healing properties are not 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 to replace 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 household use

Mel acts as a necessary component of paper, which is used in printing. The high dispersity of calcium carbonate in powdered form affects the optical and printed characteristics, porosity, smoothness of the product. Due to the presence of chalk, the abrasiveness of the products decreases. The rock in the ground form is widely used for whitewashing walls, curbs, protecting trees. Chalk is used for cleaning beet juice, which, in turn, is used in the match industry. For these purposes, as a rule, the so-called besieged rock is suitable. Such chalk is obtained chemically from calcium-containing minerals. Along with other carbonate rocks, the substance is used for cooking glass as one of the components of the charge. Due to chalk, the thermal stability of the product, its mechanical strength and stability under the influence of weathering and reagents is increased. The breed is widely used in the production of fertilizers. Also, the chalk is added to the feed by agricultural animals.

Rubber technical industry

Chalk is in the first place among all fillers used in industry. This is due primarily to the fact that the use of this raw material is economically advantageous. 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 significantly simplifies the process of manufacturing rubber products. In particular, due to it, vulcanization is accelerated, the surface of the products becomes smooth. Widely used rock and in the production of spongy and porous rubber, plastic products, leatherette and so on.