Quicklime: the formula requires detailed familiarization. Obtaining, chemical formula, types and properties of lime

Quicklime is calcium oxide. It is obtained in laboratories and industrially from natural materials. The substance is actively used in construction and industry.

Physical properties

Calcium oxide is an inorganic crystalline substance in the form of a white or gray-white powder, odorless and tasteless. The solid crystallizes into face-centered cubic crystal lattices like sodium chloride (NaCl).

Rice. 1. Cubic face-centered crystal lattices.

A general description of the substance is presented in the table.

Calcium oxide - caustic belonging to the second class of danger. It exhibits aggressive properties when interacting with water, forming slaked lime.

Rice. 2. Calcium oxide powder.

Receipt

Calcium oxide is also called burnt lime because of the way it is produced. Get quicklime by heating and decomposition of limestone - calcium carbonate (CaCO 3).

This is a natural substance found in the form of minerals - aragonite, vaterite, calcite. Included in marble, chalk, limestone.

The reaction for obtaining calcium oxide from limestone is as follows:

CaCO 3 → CaO + CO 2.

In addition, quicklime can be obtained in two ways:

• from simple substances, building up an oxide layer on the metal -

  2Ca + O 2 → 2CaO;

• during heat treatment of calcium hydroxide or salts -

  Ca(OH) 2 → CaO + H 2 O; 2Ca(NO 3) 2 → 2CaO + 4NO 2 + O 2.

The reactions proceed at high temperatures. The temperature of burning limestone is 900-1200°C. At 200-300°C, an oxide begins to form on the metal surface. The decomposition of salts and hydroxide requires a temperature of 500-600°C.

Chemical properties

Calcium oxide is the highest oxide and exhibits maximum oxidizing properties. The compounds interact with inorganic substances and free halogens. Main Chemical properties oxide are given in the table.

Application

The oxide is used in the food industry as:

• flour and bread improver;
• food additive E529;
• acidity regulator;
• nutrient medium for yeast;
• a catalyst for the hydrogenation (addition of hydrogen) of fats.

Besides, quicklime used in the chemical and construction industries for the production of various substances:

• oils;
• calcium stearate;
• grease;
• refractory materials;
• gypsum;
• high alumina cement;
• silicate brick.

Rice. 3. Cement, brick, gypsum are obtained from calcium oxide.

What have we learned?

Calcium oxide or quicklime is a crystalline substance that reacts violently with water and forms slaked lime. It is widely used in industry, in particular food and construction. Registered as a food additive E529. It has high melting and boiling points, it dissolves only in glycerin. Formed when calcium carbonate is burned. Shows oxidizing properties, forms salts with oxides and acids, interacts with carbon and aluminum.

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Lime

Lime production, lime application, lime formula, lime properties, limestone roasting, lime fertilizers, lime production technology.

LIME, a binder obtained by roasting and subsequent processing of limestone, chalk, and other lime-magnesian rocks. Pure lime. - colorless product, poorly soluble in water (approx. 0.1% at 20 °C); density is about 3.4 g/cm3. Depending on the chemical composition and hardening conditions, lime is divided into air, hardening in air-dry conditions, and hydraulic, which hardens in air and water. Air lime is obtained by roasting mainly limestone with a low clay content (up to 8%) at 1100-1300 ° C in shaft or rotary kilns. At the same time, the carbonates that make up the rock decompose, for example: CaCO3: CaO + CO2. Depending on the content of MgO in the rock, the following types of lime are distinguished: calcium (contains up to 5% by weight of MgO), magnesia (5-20%) and dolomite (20-40%). Depending on the method of processing the burnt product, quicklime lump (boiler), quicklime ground and slaked (hydrated) lime, or fluff, as well as lime dough are obtained. The first is a mixture of pieces of various sizes, formed after coarse grinding of the roasted product. By chemical composition it consists of CaO and MgO with a small admixture of CaCO3 that did not decompose during firing, as well as silicates, aluminates and Ca ferrates. Quicklime ground lime is a product of fine grinding of lump lime. Slaked lime is a highly dispersed dry powder obtained by reacting lumpy or ground quicklime with a small amount of water or steam (slaking); consists mainly of Ca(OH)2 and Mg(OH)2 with an admixture of CaCO3. When lime is slaked with a large amount of water, a plastic dough-like mass is formed, the so-called lime dough. The activity of air lime as a binder is determined by the total content of Ca and Mg oxides. Calcium lime containing 93-97% oxides has the highest activity. High-quality varieties of lime ("fat lime") are characterized by a high yield of lime dough (more than 3.5 liters per 1 kg of quicklime I.); the higher the dough yield, the more plastic it is and can accept large quantity sand in the preparation of mortars. Lime with a low yield of lime paste is called "lean". By the rate of quenching, quick-extinguishing (process duration is not more than 8 minutes), medium-extinguishing (not more than 25 minutes) and slow-extinguishing lime (more than 25 minutes) are distinguished. The quenching rate is taken as the time from the moment the lime powder is mixed with water until the moment it reaches maximum temperature mixtures. Hardening of air lime occurs as a result of water evaporation and Ca(OH)2 crystallization from a saturated aqueous solution, as well as interaction with air CO2 to form CaCO3 crystals. Air lime is used for the manufacture of binder mortars intended for ground laying of bricks, artificial stones and plaster, as well as in the production of lime-slag, lime-pozzolanic, and other mixed binders (see Cements). In a mixture with dyes, lime is used as a decorative material. Hydraulic lime is a finely ground powder obtained by firing at 900-1100 ° C marly limestone containing 6-20% clay and fine sand impurities. The resulting silicates (2CaO.SiO2), aluminates (CaO.Al2O3.5CaO + 3Al2O3) and calcium ferrates (2CaO.Fe2O3) give this lime the ability to maintain strength in water for a long time after preliminary hardening in air. According to the content of free Ca and Mg oxides, hydraulic lime is divided into weakly hydraulic (15-60% oxides) and strongly hydraulic (1-15%). Hydraulic lime, unlike air lime, is characterized by greater strength with less plasticity. Hydraulic lime is used for the manufacture of plaster and masonry mortars suitable for use in dry and wet environments, light and heavy concrete of low grades, foundations and structures exposed to water. All types of lime are also used in the chemical industry (for the production of bleach, soda, neutralization of acids and acid gases in industrial discharges, etc.), metallurgy (fluxes in the smelting of cast iron from iron ore), sugar production (for cleaning beet juices), agriculture (for liming soils, see Lime fertilizers), etc. In addition, lime is widely used for the production of silicate bricks and silicate autoclave products.

LIME FERTILIZERS

Lime fertilizers contain lime as the main component. They are used to eliminate excess acidity (liming) of soils, to treat non-chernozem soddy-podzolic, gray forest, and peat soils. Liming is based on the replacement of hydrogen and aluminum ions by Ca and Mg ions. As a result, the vital activity of beneficial microorganisms is enhanced; the soil is enriched with nutrients available to plants, its structure, water permeability, and other properties are improved; increases the efficiency of mineral and organic fertilizers. As lime fertilizers, hard and soft natural lime rocks, products of their processing, as well as industrial waste containing lime. Hard calcareous rocks (limestone, chalk, etc.) are crushed or burned before being introduced into the soil; soft rocks (eg tuffs, dolomite flour) do not require grinding, are more efficient and work faster than hard rocks. Limestone powder (ground limestone) is the most common lime fertilizer; the total amount of the active principle (Ca and Mg carbonates) is at least 85% (in terms of CaCO3); apply on various soils under all crops. Dolomite flour (up to 42% MgCO3) - destroyed upper layers of natural dolomite; it is expedient to apply in sandy and sandy loamy soils for legumes, potatoes, flax, root crops. Lake lime, or drywall (approx. 50% CaCO3), is mined from the bottom of dried lakes; cheap, valuable material for all cultures. Lime tuff, or key lime (up to 96% CaCO3), occurs in low places along the banks of rivers, streams, springs; used for all cultures. Marl (25-75% CaCO3) is mined from nature. deposits; suitable for liming light soils. Lime peat, or peat tuff (up to 50% CaCO3), is mined from deposits in lowland peatlands; especially valuable for the treatment of acidic, humus-poor soils. Hydrated lime, or fluff (up to 75% CaO + MgO), is a product of interaction with water of calcined hard carbonate rocks; recommended for liming (not less than 10 days before sowing) heavy clay soils. For various soils, the doses of lime fertilizers range from 1-10 t/ha. These doses are sufficient, as a rule, to maintain a slightly acidic soil reaction for 10–12 years, which provides a significant increase in yield (in c/ha) of most agricultural crops. crops, for example, cereals by 0.5-4.0, legumes by 1-3, fodder beet by 30-60, potatoes by 5-15, cabbage by 30-70, carrots by 15-45.

The page "LIME FERTILIZERS" was prepared based on the materials chemical encyclopedia. http://www.xumuk.ru/encyklopedia/

Quicklime production technology.

Theoretical foundations of the quicklime production process.

The production of quicklime lump consists of the following main operations: extraction and preparation of limestone, preparation of fuel and burning of limestone.

Limestone is mined in an open pit. Dense calc-magnesian rocks explode. To do this, first with the help of percussion-rotary machines (with hard rock) or rotary drilling (with rocks of medium strength) drill wells with a diameter of 105 - 150 mm and a depth of 5 - 8 m or more at a distance of 3.5 - 4.5 m from one another. They contain the right amount explosive(igdanite, ammonite) depending on the strength of the rock, the thickness of the reservoir and the required dimensions of the limestone.

The sometimes observed heterogeneity of limestone occurrence in deposits (in terms of chemical composition, strength, density, etc.) necessitates selective development useful breed. The resulting mass of limestone in the form of large and small pieces is immersed in vehicles single bucket excavator. Limestone is delivered to the plant by dump trucks.

High-quality lime can only be obtained by firing limestone in the form of pieces that differ little in size. When burning limestone in pieces different sizes unevenly burnt lime is obtained (the fines are partially or completely burnt, the core of large pieces is unburned). In addition, when shaft furnaces are loaded with limestone of different sizes, the degree of filling of the shaft furnace increases significantly, and, consequently, the gas permeability of the material decreases, which makes it difficult to burn limestone.

Therefore, prior to firing limestone is properly prepared: sorted according to the size of the pieces and, if necessary, larger oversized pieces are crushed.

In shaft kilns, it is most expedient to burn limestone separately in fractions of 40 - 80, 80 - 120 mm in diameter.

Since the dimensions of the mined limestone often reach 500 - 800 mm or more, it becomes necessary to crush it and sort the entire mass obtained after crushing into the desired fractions. This is done in a closed-loop crushing and screening plant using jaw crushers.

Firing - basic technological operation in the production of quicklime. At the same time, a number of complex physical and chemical processes occur that determine the quality of the product. The purpose of roasting is the most complete decomposition (dissociation) of CaCO3 and MgCO3 CaCO3 into CaO, MgO and CO2 and obtaining a high-quality product with an optimal microstructure of particles and their pores.

If there are clay and sandy impurities in the raw materials, then during firing between them and carbonates, reactions occur with the formation of silicates, aluminates and ferrites of calcium and magnesium.

The decomposition reaction (decarbonization) of the main component of limestone - calcium carbonate goes according to the scheme: CaCO3-CaO + CO2. Theoretically, the decarbonization of 1 mole of CaCO3 (100 g) consumes 179 kJ or 1790 kJ per 1 kg of CaCO3. In terms of 1 kg of CaO obtained in this case, the costs are 3190 kJ.

The duration of firing is also determined by the size of the pieces of the fired product. To increase the productivity of lime kilns and reduce the overburning of the surface layers of the pieces, it is desirable to reduce their size within acceptable limits. When firing pieces of various sizes, the process mode is determined based on the time required for firing pieces of medium size. The main difference in the technologies for the production of quick lime is in the method of firing.

Shaft kilns for burning lime.

Shaft furnaces are a hollow cylinder with an outer steel casing about 1 cm thick and an inner refractory masonry, vertically mounted on a foundation. These furnaces are characterized by continuity of operation and ease of operation. The construction of shaft furnaces requires a relatively small capital investment.

Depending on the type of fuel used and the method of its combustion, shaft furnaces are distinguished that operate on short-flame solid fuel, which is usually introduced into the furnace along with the material being fired; because limestone and bush fuel are loaded into the mine in alternating layers, then sometimes this method of firing is called bulk, and the furnaces themselves are bulk; on any solid fuel, gasified or burned in remote flows placed directly at the furnace; on the liquid fuel; on gas fuel, natural or artificial.

According to the nature of the processes occurring in the shaft furnace, there are three zones in height: heating, firing and cooling. In the heating zone, which includes upper part ovens with a space temperature not higher than 850 o C, the material is dried and heated by rising hot flue gases. Burn out here too organic impurities. The rising gases, in turn, due to the heat exchange between them and the loaded material, are cooled and then removed to the top of the furnace.

The firing zone is located in the middle part of the kiln, where the temperature of the fired material varies from 850 o C to 1200 o C and then 900 o C; here the limestone decomposes, carbon dioxide is removed from it.

Cooling zone - Bottom part ovens. In this zone, the lime is cooled from 900 o C to 50-100 o C by the air coming from below, which then rises to the firing zone.

The movement of air and gases in shaft furnaces is ensured by the operation of fans that force air into the furnace and suck out flue gases from it. The countercurrent movement of the fired material and hot gases in the shaft furnace makes it possible to make good use of the heat of the exhaust gases for heating the raw materials, and the heat of the fired material for heating the air going into the firing zone.

Lime is a product of burning such rocks as chalk, limestone.

Quick-release lumpy (chemical formula CaO) is white or yellow-brown pieces of different fractions or powder (calcium oxide, boiling water) of an off-white color. It absorbs water well, so it is not stored for a long time.

Slaked (chemical formula Ca (OH) 2, calcium hydroxide, "fluff"), with a moisture content of not more than 5%, has White color and characteristic odour. Obtained by the interaction of quicklime with water. It is a strong basic substance (base). Hydrated lime has a wide range of applications: leather tanning, bleach production, fertilizer production, grounding points in soils with high resistance (in electrical engineering), as a food additive in food production, in dentistry for disinfection, whitewashing, to eliminate the possibility of fire and rotting wood, to soften hard water.

Lime properties

This material is characterized by astringent, plastic properties. Due to the ability of calcium particles to hold water, lime mortars do not harden as quickly as cement mortars. This is the main advantage of the lime mortar - the setting time allows you to level it over the surface with an even thin layer. It adheres well to and, when solidified, is particularly durable.

Kinds

In appearance, building lime is:

BUT. aerial, which is divided according to the content of the main component into 3 types:

• on dolomite;
• calcium;
• magnesian.

B. hydraulic- contains up to 20% of clinker minerals, is used both in air and under water.

Separate classes are chloride(chemical formula Ca(Cl)OC) and soda lime. Bleach or whitewash is best known under the name bleach. It is a technical mixture of calcium chloride, hypochlorite and chloride. Soda lime is a mixture caustic soda and slaked lime. It is used to absorb caustic gases due to its properties in gas masks, diving suits and other respiratory systems, including in medicine.

They are also distinguished according to the degree of slaking to lime of slow, medium and fast slaking.

Application area: , construction (production of concrete and mortar), chemical industry (manufacture of chemical fibers), Agriculture(liming of soils), medicine.

Limestone and what is obtained from it surrounds a person all his life. Most people do not even think about this fact, although the plaster on the wall is a derivative of this rock. The formula of limestone is very simple, it is the usual calcium carbonate CaCO₃, but much more can be said about it, and this information concerns not so much chemistry as geology and biology.

Chronicle of bygone eras

Before talking about what limestone is, it is worth talking about calcium, its basis. This element is the fifth most abundant on Earth and its share in earth's crust a little over 3%. But it was his circulation in nature that played and plays a role in the formation of limestone.

In nature, there is a so-called carbonate equilibrium, expressed by the equation:

CaCO₃+H₂O+CO₂=Ca (HCO₃) ₂+Ca² ⁺+ 2HCO₃⁻

This state has a preponderance in one direction or another, depending on the content of carbon dioxide dissolved in water. The more it is, the more the equilibrium shifts to the right, and vice versa. Living organisms play a significant role in this process, especially since the time of the oxygen catastrophe.

Cyanobacterial mats and stromatolites

Life originated on earth under anaerobic conditions. There was no free oxygen in the Earth's atmosphere; possibly, primary composition gas was a mixture of hydrogen and helium. As volcanism intensified, the primary atmosphere was replaced by a secondary one, consisting of carbon dioxide, methane and ammonia, and possibly water vapor.

In general form (slabs), limestone is massively used in finishing works, in the form of crushed stone - in the production of concrete. It is lighter than granite: the density of this rock is 2.6 t/m³. In terms of its strength, it is inferior to other materials, it barely reaches 41 MPa, and in the wet state this figure decreases to 35 MPa. On the other hand, limestone does not transmit radiation and it is possible and even necessary to use this material in residential premises: it is rare that a stone is able to maintain an optimal microclimate in a house so well.

material such as slaked lime, known to mankind since ancient times. Due to its useful properties, its use has not lost its relevance to this day. The difference only affected the expansion of the area of ​​​​use.

In order to understand how this happened, it is necessary to know what kind of slaked lime has a formula, and how this affects its interaction with other substances.

Far from always real life slaked lime is obtained under conditions where there are no additional substances. Often magnesium is added to the reaction, etc. This is necessary to enhance certain properties of the material, which will result from the interaction of all components.

Names used

In view of the rather wide distribution of slaked lime in different regions world, as well as in different fields of activity, it was called differently. Among the most popular and common names, it is worth highlighting the following:

• calcium hydroxide.
  

  This term reflects the formula of the substance, since it consists of Calcium and Hydroxide. It is used in scientific and technical literature.

  Today, this term has replaced other names in many areas.

• slaked lime. about its application. This name came about because substance is produced by redemption(i.e. adding water).

• lime milk.
  

  This is lime, which arises due to too a large number slaked lime in its ratio with aqueous solutions and directly with water.

  In appearance, it is a bit like milk in its color.

• lime water. This term denotes a translucent solution that is obtained after filtration.

• fluff lime or lump lime.
  

  Such material is obtained when long time substance is not used.

  During this period, it starts from environment absorb carbon dioxide, thereby hardening.

There are also a number of other names and terms that are commonly used in relation to slaked lime. All of them were used in one way or another over a certain period, or are currently being used.

Formula and composition of the substance

The composition of slaked lime is quite simple and understandable. This substance consists only of calcium oxides, interconnected in a certain sequence. Obtaining calcium hydroxide is also considered elementary. It has been produced for thousands of years.

To do this, you just need to add water to calcium oxide, after which these components need to be mixed well and thoroughly with each other.

The chemical formula of slaked lime is written as Ca(OH)2. The process of obtaining calcium hydroxide is as follows: CaO + H2O \u003d Ca (OH) 2.

When calcium oxide is poured with water, lime is obtained, the characteristics of which directly depend on the time of exposure of the initial components to each other.

If mixing lasted up to 8 minutes, then we can talk about quick-extinguishing lime, about 25 minutes - medium-extinguishing, and more than half an hour - long-extinguishing. Hydrated lime formula Ca (OH) 2 is compound, water solution which has alkali.

Technical properties

The formula of slaked lime in chemistry has been known for a long time. Today it is even studied in school course of this subject. Often in the classroom in the presence of a teacher, children quench calcium oxides, while noticing a violent reaction with the release of heat.

But the manufacture of calcium hydroxide in industrial scale is a slightly different process that requires certain rules and standards.

It is regulated in the Russian Federation by special normative documents entitled . It is on him that all manufacturers of this substance should be guided.

Among the requirements that must be met, it is worth noting the following:

• manufacturer must use only carbonate rocks with the possibility of using a small amount mineral additives. Each grade of lime has its own amount of additional substances that can be added to it. It is defined by GOSTs and cannot be violated.
• produced in the form of three varieties. It should not contain any additives. Powdered lime with additional inclusions can be produced in two different grades;

• slaked material is also divided into two types - with and without additives.

• calcium lime should be based predominantly on calcium. The amount of magnesium oxide (MgO) in it should not exceed 5 percent.
• according to GOSTs, dolomitic lime can contain magnesium oxide (MgO) up to 20 percent.
• Dolomitic lime is considered to be a material in which magnesium oxide (MgO) occupies up to 40 percent of the total volume.

• hydraulic lime implies the inclusion in its component composition of substances such as silica, iron oxides, and clay.

The properties of lime mainly depend on two main factors, which are the manufacturing process and the roasting of the rock. Heat treatment makes it possible to create durable pieces of quicklime material in the furnace.

The whiter it turns out, the higher quality this product can be considered. In turn, some types of lime are more gray in color.

When quicklime comes into contact with water, the gas inside is released from it. After that, the material goes into a fluid state.

Its concentration directly depends on how much water was used. The strength of the substance can turn out to be different, which is influenced by the technological features of manufacturing. It can be hard fired material, medium variant and soft fired material.

Manufacturing technique

In general, the entire lime harvesting process consists of only two stages of production:

• extraction directly from the limestone rock itself and the additives that are used. For the lumpy type, production waste is often used;
• roasting of harvested rocks in specially designed furnace devices at high temperature conditions.

Limestone, in turn, is mined in quarries. characteristics of quarry sand. For this use open method. The rock is split with explosives. If selective mining is carried out, then a raw material is obtained that is homogeneous in its chemical composition, which subsequently makes the material of higher quality.

The preparatory process of raw materials obtained in a quarry involves its crushing into small pieces. However, they must be uniform. It is connected with high temperature in kilns, which is capable of destroying too small particles, and too large ones - not completely firing to the entire volume.

Roasting is the main stage in the production of air lime. Temperature regime should directly correspond to those impurities that are in the rock.

The process itself must comply with all the requirements of the technology, since any violation can lead to the fact that a low-quality substance will be obtained as a result. For example, too burnt lime is quite poorly soluble in water.

In addition, it has a relatively higher density, which negatively affects the preparation of solutions. on the density of river sand. Various kilns are used for the roasting process. AT recent times mine and rotating tubular products are used.

The former are distinguished by the fact that the process takes place continuously in them, which makes it more economical and cost-effective. The second allows you to achieve the most High Quality, since in them the temperature effect on the rock occurs most evenly and correctly from the point of view of technology.

Also, in addition, manufacturers have developed devices that allow firing rock in a fluidized bed or in a suspended state.

They are used mainly in relation to the smallest particles of the material. The disadvantage of this production is its rather low efficiency.

Scope of application

Hydrated lime due to its properties has found a very wide scope. It is used both for personal purposes by many people and industry, both in the construction of various kinds of objects, and disinfection. It is worth highlighting the following specific ways of using this substance:

• for whitewashing trees- lime allows you to protect them from some kind of pests;

• when whitewashing interiors facilities for disinfection;

• for painting wooden products in order to extend their service life, thus protecting them from the processes of decay and fire;

• for the manufacture of used primarily for disinfection;

ChlorineA connecting solution that increases crop productivity;

In addition to the above areas, soda lime is used for many other purposes. soda lime formula. First of all, it was influenced by her very beneficial features and specifications.

In addition, the production of such material is very easy and not difficult.

For more information on the use of lime, see the video:

Maintaining the working state of the substance

The cost of lime today is not very high, which is associated with its widespread production and simplicity. technological process production. But, despite this, having bought this material, it is necessary to understand how to extend the period of its working condition.

• if the density of the material changes due to the fact that moisture evaporates from it, you can just add a little water to it;
• in the process of using slaked lime, it must be stirred all the time;
• it is worth adding water until the material stops absorbing it;
• to store lime, it is necessary to cover it from above with a layer 20 centimeters high;
• if a large amount of material is stored in the winter on open ground, should be protected from frost. To do this, the top needs to be covered with sand, on top of which add a layer of soil. heat capacity of sand;
• it is not worth using material in which there are sawdust, inclusions or lumps. This can significantly affect the integrity of the surface being treated;
• if lime is to be used for the preparation of a mortar, then it must be aged for at least two weeks. For plaster work should be extended up to 4 weeks.

If all the above requirements are met, slaked lime will be used quite well for various purposes without any problems. If they occur, then this may indicate a poor quality of the material, and not about the conditions of storage and use.

Conclusion

The formula of hydrated and quicklime has been known for a long period of time, while the use of these materials has a long history. For this period they have not lost their relevance and usefulness, both for the individual and for society as a whole.

The industrial production of this material contributes industrial development and improvement of many technologies. That is why it is very important that the production process is carried out clearly in accordance with GOSTs and in accordance with certain rules. In this case, the use of lime will be beneficial and beneficial.