Lime Chemical
Lime is a substance usually white and powdery, obtained by thermal decomposition of limestone. It has been used since the ancient times , especially in construction.
Chemically, it is an oxide of calcium with varying oxide magnesium but the common name of lime can encompass various chemical states of this product. They are distinguished especially in the current language in relation to their use in construction:
- Quicklime is the direct product of pyrolysis of limestone, mostly of calcium oxide (CaO).
- Hydrated lime or slaked lime, is obtained by the reaction of quicklime with water. It consists mainly of calcium hydroxide (Ca (OH) 2). It is called "Air" because it reacts with CO 2 from the air.
- Hydraulic lime contains in addition to silicates and aluminates , originating from calcareous clay. It is called "hydraulic" because it hardens in the presence of water.
- Lime is also "material" having taken "after use. Although this is only the binder , there is talk of a wall with lime, but lime chemically in question is mostly returned to the limestone (calcium carbonate CaCO 3).
- There are also lime or dolomitic lime containing magnesium dolomite or magnesian limestone.
Summary |
History
The principle is to "burn" a stone calcine to extract a component cabinet that can be reconstituted then was probably first discovered with the gypsum , which, being heated (150 C) gives the plaster. This material is easier to obtain was discovered before the lime, but lime plaster and mixtures are used in support of mural painting in Egypt from 2600 BC
Lime constructions are then emerged to be used in all Roman buildings, dwellings with aqueducts through the spa. This is the lime which gave its name to the limestone, which comes from the Latin Calcarius, "which contains lime" and calcix, lime. The Romans knew a kind of hydraulic lime by adding to tiles or bricks broken.
Application of many techniques used in Roman times, crossed the Middle Ages. The use of lime is almost inevitable, however, remained in the frame until the discovery of cement in the middle of the nineteenth century. He quickly replaced the lime in all modern buildings due to greater rigidity and especially a lower cost: cement blocks, concrete ...
Lime knows at the beginning of the XXI century a renewed interest. In the cement is incompatible with the masonry of old buildings into rubble and stone. The cement is a rigid material impermeable to air, it does not fit a traditional building which requires flexibility and be breathable. The air permeability allows a dry masonry. It absorbs water from rain or rising damp, can be evacuated by its joints with lime, whereas in the case of cement mortar, the wall can not dry out and retains water it absorbs what can cause the appearance of saltpetre , mosses microscopic halos, spots and streaks. The cement should be used only in the implementation of the materials themselves in cement: A cement tile ...
Different types of lime
The quicklime
The lime is lime output of lime kiln. The main constituent of the lime is the calcium oxide , which has the formula CaO.
After adding water, a chemical reaction occurs. It becomes slaked lime Ca (OH) 2 (portlandite) used in the building for the masonry and the realization of coatings : lime or fat lime, natural hydraulic lime.
Hydration
Brought into contact with the water , there is a very exothermic reaction. This step is necessary to obtain hydrated lime, either air or hydraulics.
In the case of hydraulic lime, it is necessary to use the right amount of water, so as not to allow the taking of the material. In the case of lime obtained from pure limestone (lime), the amount of water is not limited.
When the amount of water added is just sufficient for the reaction of extinction, that is to say, hydration of lime, we obtain a white powder. If the amount of water is more important, we get a white paste which can dissolve at pH values greater: slaked lime whose formula is Ca (OH) 2.
Care and Use
Quicklime is a potentially dangerous product, mainly used in the industry and agriculture. Hydrophilic , it is used for drying, destroy organic matter-rich water. When mixed large quantities of lime and water, the heat is such that water may start to boil and throw the lime, which is corrosive. It is therefore advisable to use goggles and gloves when handling.
It is recommended to gradually pour the powder in water and not vice versa.
It is also recommended to stir the water / lime throughout its preparation, in order to limit the risks of screening.
The lime
It is the hydroxide Ca (OH) 2. Its mineralogical name is portlandite
The lime (hydrated lime, slaked lime, slaked lime) is obtained by hydration of quicklime end of a limestone very pure. It is found under different names: slaked lime, CAEB (old standards: slaked lime for the building). The name recommended by the standard NF EN 459-1 is CL (Calcic Lime resulting calcium lime) followed by a number 70, 80 or 90 indicating the proportion of calcium carbonate (CaCO3) and DL ("Dolomitic Lime" translated by dolomitic lime). More content is high, more lime is called fat.
The lime used since the ancient times to make mortar for the construction , coatings and washes on the walls. It is also used to protect fruit trees , or fight against the decaying corpses in the event of an epidemic.
Cycle
The use of lime is attested from the Bronze Age (about 2000 BC) on some archaeological sites in Switzerland. Limestone blocks are charred and walls of the inner core of certain fortified places.
Calcination
By calcining limestone at about 900 C (CaCO 3) we obtain quicklime (Calcium Oxide CaO) and a strong release of carbon dioxide (CO 2):
The reaction is accompanied by a weight loss of about 45%, corresponding to the loss of carbon dioxide by chemical formula:
- CaCO 3 CaO + CO 2
Extinction
The transformation of quicklime into hydrated lime is made by adding water (H 2 O). This operation produces the extinction of calcium hydroxide Ca (OH) 2, with high heat:
- CaO + H 2 O Ca (OH) 2 + 1155 kJ / kg CaO
After transformation, the increase in volume is nearly 30%.
Extinction can be achieved in different ways:
- surface irrigation blocks of quicklime, then terminating the reaction in air;
- Dumping blocks of quicklime in a large volume of water and then terminating the reaction in air;
- lime-water mixture in a blender with control of the exothermic reaction (in industry);
- Dumping blocks of quicklime in a large volume of water and then terminating the reaction in water.
In the first three cases we get a lime powder (flower of lime, slaked lime, CAEB, lime ...). In the latter case, the hydrated lime produced takes on the appearance of a paste (lime paste) that we will keep as long as one keeps the water surface limiting the exchange of carbon dioxide (thus carbonation ).
The lime powder corresponds to current practice of building (assay volume, mix the cement mixer ...).
Lime putty mortars can obtain more "fat", less prone to rapid drying, coatings or washes carbonating faster and therefore more stable. For cons, the dosage is more difficult, mixing with the sand more difficult unless you use the appropriate tools (planetary mixer, plane ...). The best carbonation of the lime paste as probably from the fact that extinction is being protected from the air, no carbonation anticipating partial taking occurs. Moreover, the fineness of lime is obtained, the presence of colloidal gels are all elements that should be studied.
Carbonation
The capture of the lime is by carbonation , that is to say by absorbing carbon dioxide (CO 2) in the atmosphere: hence its name "lime":
- Ca (OH) 2 + CO 2 CaCO 3 + H 2 O
Depending on the humidity of the medium, this reaction occurs over several months: the steam binds with atmospheric carbon dioxide to form the carbonic acid , lime fixes the carbon dioxide content in the acid and turns into limestone. The result of this operation is again of limestone (CaCO 3).
The mechanism adopted by carbonation occurs in the presence of water, where a master essential conditions for implementation (wetting media, climate control ...).
Usage
The uses of lime are numerous. In France , its use is as follows:
- Steel : approximately 41%
- Public works , roads: about 12%
- Agriculture: about 10%
- Water treatment: about 10%
- Construction, Building: 3%
- Absorption of carbon dioxide: anesthesia equipment and respiratory emergency.
Use in Agriculture
For agriculture , use of magnesium lime or dolomite , which amends the soil acids providing the magnesium. Is used, most often calcium lime. The lime used in agriculture are still the form of calcium oxide or calcium oxide combined with the magnesium oxide. This amendment is to use moderately on soil clay. The role of ion calcium in the clay-humus complex is already bound by the iron.
In addition to being an amendment calcium and magnesium, liming also allows the destruction of pathogenic micro-organisms contained in the manure that are acidic in nature. The base-OH associated with calcium happens suddenly in the middle causes a rapid increase in pH that kills these organisms.
In most cases, agriculture also uses limestone uncooked to amend the land. It's calcium carbonate , commonly known as "calcium carbonate". The mode of action is slower than that of calcined lime. This is because the acidity of the land must degrade the product before it becomes an oxide and associated base to develop desired. It can not guarantee a good agronomic effectiveness if it is thin enough to dissolve properly. The advantage to the use of calcium carbonate is economic, because it is cheaper to the user and the environment as it does not destroy beneficial soil organisms. In absolute terms, its neutralizing power is, in equal amounts, far below that of the quicklime.
Use in industry, water treatment, in the treatment of fumes
The lime is widely used in industry, mostly in the form of quicklime, it uses its sintering capacity of certain materials it is called "flocculation".
In steel, the addition of lime in the melt allows the extraction of some impurities.
In the treatment of wastewater sludge is stabilized.
In incinerators is used to neutralize acid fumes laden with sulfur and / or chlorine.
Use in Public Works
The lime is also used in the implementation of roads or paths, usually in the form of quicklime. As in industry, using its property of "flocculation", this is to transform the clay (plastic consistency, soft, unstable) in clotted more resistant to compression of the soil. In this action comes enlist the consumption effect of pore water. In doing so, the water content of soil is too wet lowered to reach the more often the Optimum procto st This property is also used in agriculture.
Use as absorbing carbon dioxide
The absorption properties of carbon dioxide by lime were used in breathing apparatus called "closed circuit" to purify the gas exhaled carbon dioxide and permit its re-inhalation after a possible contribution of oxygen at very low flow. These techniques are used in medicine (anesthesia closed circuit), in breathing apparatus used in hazardous gas environments. The underwater activities (diving and underwater) also use lime as absorbing carbon dioxide. Hydrated lime is mixed with other chemicals such as sodium hydroxide (NaOH) to form lime soda or other compounds that accelerate the reaction rate of lime. The presentation porous grains of a few millimeters in suitable containers to gas flow increases the exchange surface and allows absorption with small amounts of lime easily transportable.
Use in interior decoration
Lime exists since 6000. That, with gypsum, one of the oldest materials used by man. Properties:
- Antiseptic, it disinfects, cleans the atmosphere.
- She breathable masonry thus reducing moisture and prevents condensation of water.
Rendering exceptional decorative and velvety unparalleled inside or outside a living decoration: lime breathes so the moire patterns vary with ambient water quantity. It will patina and age extremely well.
The hydraulic lime
Hydraulic lime (lime lean) is obtained from limestone containing 10 to 20% of clay during calcination gives silicates and aluminates of calcium. She is taken in a few hours, in contact with water, hence its name.
The term standard NF EN 459-1 is NHL (Natural Hydraulic Lime). The former name was XHN.
carbonation of hydraulic lime
The natural limestone is most often mixed with marl and clay -rich chemical elements mainly silica and also the iron , the aluminum. Cooking temperatures (800 C and 1500 C), the calcium combines with these elements to form silicates , and aluminates and ferro-aluminate of calcium. The higher the temperature is high and the silica content, the less it contains more free lime is hydraulic.
CaCO 3 + SiO 2 SiO 2 + 2CaO
CaCO 3 + Al 2 O 3 + Fe 2 O 3 3CaOAl 4CaOAl 2 O 3 + Fe 2 O 3 2 O 3
On contact with water during the extinction of quicklime, and especially during the implementation of mortars, these molecules form hydrates insoluble. The proportions of alumina and iron are very low: in the white binders, iron levels are below 0.1 or 0.2%. The hydraulic jack is mainly due to the reaction between CaO and silicates.
Hydraulic limes are an initial hydraulic type at the time of implementation (it is said to "fire") and taking type secondary air is where the lime and the hydrates will become carbonated in contact moist air to restore the calcium carbonate and silica original. The rate of carbonation in the secondary thickness is about 1 cm per year.
Packaging and storage
Lime is now packaged in bags of 15 kg, 25 kg. Storage should be done in a dry place.
Runoff lime
The ratio of various components associated with the clay and the share of Ca (OH) 2 defines the hydraulic index given by a number indicating the compressive strength (after taking) in MPa or kg / cm. More lime is hydraulic it is less permeable to air and water.
| Type of Lime | percentage of free lime | percentage of clay | hydraulic index | Time taken in days | Compressive strength at 28 days (kg / cm ) |
|---|---|---|---|---|---|
| CL | 50-75 | ~ 0 | 0 to 0.1 | > 30 | |
| NHL 2 | 50 | 5-8 | 0.1 to 0.16 | 10 to 25 | 20-40 |
| NHL 3.5 | 8 to 14 | 0.16 to 0.3 | 10 to 15 | 35-100 | |
| NHL 5 | 15 | 14 to 20 | 0.3 to 0.4 | 2-4 | 50-150 |
| eminently hydraulic lime, cement clinker | 20 to 30 | 0.4 to 0.5 | <2 | > 150 |
NHL 2 is used when one wants mortars very flexible eg for coatings on brittle walls, earth or soft stones. The NHL 3.5 and 5 are mainly used to climb walls, surface coatings, screeds run, put the tile. They are not recommended on fragile materials because it could cause a breakout of the support. They may also have unwanted reaction with the plaster.
Other types of lime
The standard also defines the NHL lime-Z containing up to 20% of items pozzolanic added after cooking. It is a highly hydraulic lime allowing it to harden even in water. It is waterproof and is not recommended for walls under construction for making raincoats.
Artificial hydraulic lime HL. This is not a lime itself since it does not contain Ca (OH) 2 in the free state. It is a sort of intermediary between the hydraulic lime and portland cement. It is very rich in hydraulic calcium silicates.
Magnesian lime (CaOMgO). It contains magnesium at 5% <MgO <34% dolomitic lime or even richer 34% <MgO <41.6% by calcination of magnesium limestone or dolomite. After hydration they contain MgO or Mg (OH) 2. Standardized naming DL followed by a digit.
See also
Related articles
- Lime Kiln
- Painting with lime
- Limewater
- Roman cement
- Distemper
- Concrete slab of lime
- Stucco
- Cement nomenclature
External Links
- (IMDb) Ecole d'Avignon (Avignon school)
- (En) European Association of lime (EuLA)
- (En) National Lime Association (NLA)
- (En) The natural lime
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