Lime, types, production and use.
Lime – a material obtained by roasting the carbonate rocks (limestone, chalk), composed mainly of Cao and MgO.
Lime is a common cementing material, widely used in many industries. The composition is formed free oxides of calcium (CaO) and magnesium (MgO) with a predominance of the first. Get a substance during exposure to elevated temperatures on carbonate rocks, which for these purposes is fired, preventing them from melting.
Lime translated from the Greek. ἄσβεστος means “unquenchable”.
There are different types of lime.
In accordance with the scope of application of isolated technological and construction types.
The composition consists of lime silicates and alyumoferritnoy calcium, informing her hydraulic properties; depending on the level of maintenance it is subdivided into air and hydraulic. The first (air lime) allows the mortar to harden and to retain its strength properties under normal humidity level, and the second (hydraulic lime) gives them these qualities in conditions of high humidity, including water.
Aerial view of lime divided by the number of contained oxides into calcium, magnesia, and dolomite lime. In the first case (calcium lime), the proportion of calcium oxide in the product is up to 95 % and the content of magnesium oxide is less than 5 %. The second subspecies (magnesian lime) contains from 5 to 20% of magnesium oxide, the remainder being calcium oxide. The third (dolomite lime) from 20 to 40% magnesium oxide and from 60 to 80% of calcium oxide.
In addition, lime is classified according to the speed of quenching, which is slow, medium or fast. At the slow speed of the process takes at least 25 minutes, on average – no more than 25 minutes, and the quick response lasts no more than 8 minutes.
Depending on the fraction of grain lime can be divided into lumps and powder.
Classification criterion is the method of processing the end product is svezheokrashennym, hydrated quicklime.
Slaked lime is also called caustic lime is a calcium hydroxide Ca(OH)2. Has the form of a white powder, which is characterized by low solubility. Formed during quenching of calcium oxide (reaction with water).
Lime milk is called a solution formed by mixing excess of slaked lime and water. In appearance it resembles milk. When the filter is formed of a transparent liquid called lime water.
Obtaining slaked lime occurs by the reaction of calcium oxide with water. When the last allocated 16 calories in 1 mole.
Consider the substance is a strong base. The higher the temperature, the worse it is able to dissolve. Reacts with acids, as the alkali involved in the reaction of neutralization, in which are formed the corresponding salts of calcium. Because calcium hydroxide reacts with the water contained in the carbon dioxide, its solution becomes turbid when in contact with air.
Slaked lime is used in the repair work as a whitewash, based on it made of silicate concrete. In construction it is used since long time in the past was a popular component for making mortar, however today it is almost completely replaced cement, surpassing it in quality. Minus mortar based on calcium hydroxide is that it helps to maintain a high humidity in built spaces.
Slaked lime used in the manufacture of fertilizers, also based on it made bleach. As a flour or powder it is a component for asphalt mixtures.
Silicate concrete manufactured on the basis of calcium hydroxide, has a similar composition with lime mortar. However, unlike the latter, its solidification takes less time because the technology of its production involves no addition of water and steaming (for the procedure used autoclave and kept the pressure between 9 and 15 atmospheres).
Quicklime is a calcium oxide CaO and has a crystalline structure. When interacting with water it forms slaked lime. Along with the latter, it has gained popularity in construction.
Substance is produced during the thermal decomposition of calcium carbonate. Another method performs the reaction of ordinary substances, in which it is formed as a layer on the surface of the metal. In addition, it is obtained in the reaction of thermal decomposition of calcium hydroxide and calcium salts of some acids containing oxygen.
The product included in the group of basic oxides. By its interaction with water there is a vigorous reaction which generates heat and forms calcium hydroxide. A saturated solution is a strong base. The reaction is reversible, if the temperature at which it occurs, exceeds 580 OC.
Being a basic oxide, quicklime, reacts with acids and acidic oxides (with the formation of salts). When it is heated, and the simultaneous interaction with carbon to form a carbide of calcium (for this procedure use a high temperature furnace or electric arc). The resulting product can be used for the manufacture of acetylene, however, in industry it is common to use more effective methods. Despite this, the reaction still finds application, in particular, resorted to it in the production of machines for welding and laboratory practice.
Quicklime is a common component for the production of building materials. With its help are made the silicate brick, high-alumina cement, etc., which is the main sphere of its application. Till the 50-ies of the last century it was used in the construction of whitewash, helped by its quality, bright white color and good adhesion to various surfaces. After application of slaked lime is absorbed from the air carbon dioxide and the formation of a solid layer of calcium carbonate.
Modern construction almost completely moved away from the use of calcium oxide because of its disadvantage — it absorbs water and contributes to maintaining a high level of humidity in the room, creating a favourable environment for mould formation.
Chlorinated lime , also called bleaching, lime, in the home known as bleach. It is composed of calcium hydroxide and calcium hypochlorite components of the high-risk (class II), and calcium chloride. Its chemical formula Ca(Cl)OCl. Is a caustic substance that promotes the formation of corrosion. To obtain applied the chlorination of calcium hydroxide.
The substance is characterized by a slow decay. When it is exposed to air and high humidity is formed hypochlorous acid. Due to its bleaching and disinfectant properties, and the ability to remove limescale, the product is used widely; in former times it was used in the extraction of gold.
Sodium citrate was previously called naturistas lime. Has a porous structure, colour – white. Contains in its composition of slaked lime Ca(OH)2 and sodium hydroxide NaOH. Possesses water-absorbing properties – absorbs airborne moisture and carbon dioxide, this made his transition into a mixture of sodium and calcium.
The product obtained by slaking of calcium oxide, why use a concentrated solution of pure sodium hydroxide. The ratio of these substances is 2:1. Its production process includes several stages: evaporation of the educated masses, calcining, and then broken into pieces, sifting and sorting according to the grain fraction.
A substance used for removal of acid gases. Its scope includes such equipment as gas masks and equipment for divers. In the latter case, it reduces the flow of breathing gas and removes the bubbles generated during exhalation. In addition, the product is used in the medical industry, in particular, in devices for anesthesia, allowing you to spend inhalation anesthetics to a lesser extent.
Storage of the substances is carried out in a tightly closed container to prevent absorption of moisture and carbon dioxide, which degrades its properties.
Manufacturer of lime is considered a dangerous kind of production. The production process must be consistent with the requirements of GOST and the applicable technical regulations. The substance is made of carbonate rocks and mineral slags, whose parameters are regulated by normative documentation. Most commonly it is made from dense limestones.
The manufacturing process includes several stages:
– feedstock (grain size from 0 to 300 mm) in a special bunker, directing it to split,
– grinding of raw materials,
– sorting of raw material grain size and selection of the coarse fraction (from 5 mm, the smaller is used for manufacturing limestone flour),
– weighing selected fraction of its heating and burning in a furnace.
Technological lime is widely used in metallurgy, chemical industry, field of environment protection (with her help neutralize waste water, and contained in the smoke gases). In addition, it serves as a component in the production of various kinds of chemical products.
Building lime, as its name says, is used in the construction industry where it is used to bleach and the manufacture of building mixes.
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