What is chalk? Properties, extraction and use
Who among us does not know what chalk is? It can be called a "witness of epochs" that passed tens of millions of years ago. This compound has a biological origin, therefore, has numerous chemical and physical properties.
Features of origin
Arguing over the fact that such chalk, we will pay attention to its appearance in nature. About 80 million years ago, when dinosaurs existed on Earth, there was a Cretaceous period. Millions of small mollusks lived in the small seas of that time and built their shells and skeletons of calcium contained in water. The remains of the creatures accumulated in multimeter layers in the bottom sediments and turned into white chalk.
As a percentage, several components of this mineral can be distinguished:
- about 10% are fragments of the skeletons of the simplest creatures, multicellular animals that can accumulate calcium in the tissues;
- up to 10% of chalk is part of the shell of small foraminifera mollusks;
- algae buildup fragments contain up to 40% calcium salts.Live microscopic suspension in the seas are coccolitophores, 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 residues), which are carried by winds and currents in the Cretaceous sediments.
Arguing over the fact that such chalk, consider its composition. In chemistry, this name has received calcium carbonate, which is a salt of carbonic acid. More detail on its composition. White chalk up to 50% contains 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% alumina, as well as minimal amounts of iron oxides. How does this affect the appearance of the mineral? In this case, the chalk for drawing becomes red or pink.
Is it possible to eat chalk for blackboard? In the case of a lack of calcium in the body, a person develops a craving for eating chalk. Doctors are ambiguous about this issue. When chalk is under the influence of gastric juice (concentrated hydrochloric acid), it significantly changes its properties.
Chalk, after going through many oxidative processes, loses its original neutrality, turns into an aggressive chemical compound, similar in properties to hydrated lime (calcium hydroxide).
That is why in contact with oxidized chalk, the mucous membrane of the digestive organs is seriously affected.
If in large quantities to eat chalk for blackboard, it provokes the liming of blood vessels. Much safer with a lack of calcium is the use of special medicines, for example, calcium gluconate.
Doctors warn patients about the inadmissibility of the use in food of agricultural feed, construction, stationery chalk.
Areas of use
In the form of masonry material, it is impractical to use chalk, since it has a slight hardness. How is the extraction of this mineral? Basically, school chalk is produced by open-pit mining. The mined lumps are crushed, then dipped in water.
With constant stirring, calcium particles float to the surface. They are dried, used for various purposes.Stones that have not undergone such processing are sent for burning, as a result of which lime is formed.
His long time used for whitewashing ceilings inside the premises. Currently, this scope of application is practically absent, since other finishing materials have appeared.
At present, chalk is introduced into the composition of cement mixtures to give them extra softness.
Also, the mineral is in demand in the manufacture of glass, rubber, plastics, paints, composite mixtures, rubber.
In large quantities, chalk is used in the linoleum and carpet industries. With it, I regulate the viscous properties of latex glue, give strength to products, improve heat-saving characteristics.
Calcium mineral is also necessary for the production of soil fertilizers and animal feed. Chalk powder is the basis for the creation of numerous cosmetic products: powder, creams, lipstick. It is difficult to imagine without the chalk and the functioning of the cardboard and paper industry.
Depending on the characteristics of the field, the natural characteristics of the chalk can be significant differences. Humidity has a significant effect on the material.Chalk is not soluble in water, it forms a suspension. Upon absorption of moisture, calcium carbonate loses its strength, while significantly increasing the ductility of the material. This introduces serious problems in the extraction and processing of the mineral; it sticks to the excavator bucket. Chalk has a low frost resistance. After thawing, the material disintegrates into many individual small particles. This quality is used in agriculture to reduce soil acidity.
Differences between lime and chalk
Despite common roots, these materials differ in properties, composition. Both are considered environmentally friendly, but the composition of chalk is 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 to a dusty form, then wash off with a small stream of water. Chalk will immediately be removed with water, but in order to get rid of lime, you will have to work hard.
There are no traces of the lime whitewash, but the chalk will remind itself for a long time even after the repair is completed.Lime has excellent antiseptic characteristics, so it is used to protect trees and shrubs from insect damage.
Chalk is a material that is familiar not only as an instrument of work for teachers in schools, but also as a historical witness to events that occurred on our planet millions of years ago.
Its main part consists of calcium deposits of shells of the simplest prehistoric plants and microorganisms.
Cretaceous sediments are currently needed in various areas of production: when creating paints, making cosmetic preparations, and developing food additives. Cretaceous natural deposits often include various undesirable impurities: sand, stones, various mineral particles.
That is why the chalk, mined in the fields, is first crushed, then mixed with water, getting a suspension. Heavy impurities settle to the bottom, light chalk particles are caught in a special container. After adding to them the adhesive composition, drying, it turns out chalk, suitable for drawing on the school blackboard.
Among the new areas of use of chalk, you can select and apply it to the playing field.The fine particles of this substance rise into the air, so the players clearly see the lines made.
For the removal of sweat and fat, chalk powder is also in demand in some sports: weightlifting, gymnastics, and 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.
The raw mineral mined by the quarry method is necessary in the construction industry for the production of lime.