Calcination

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Calcination

Calcination (also referred to as calcining) is a thermal treatment process applied to ores and other solid materials in order to bring about a thermal decomposition

Thermal decomposition

Thermal decomposition, also called thermolysis, is defined as a chemical reaction when a chemical substance breaks up into at least two chemical substances when heated....
, phase transition

Phase transition

In thermodynamics, a phase transition is the transformation of a thermodynamic system from one phase to another.At phase-transition point, physical properties may undergo abrupt change- for instance, volume of the two phases may be vastly different....
, or removal of a volatile fraction. The calcination process normally takes place at temperatures below the melting point of the product materials. Calcination is to be distinguished from roasting

Roasting (metallurgy)

Roasting is a metallurgical process involving gas-solids reactions at elevated temperatures. A common example is the process in which sulfide ores are converted to oxides, prior to smelting....
, in which more complex gas-solid reactions take place between the furnace atmosphere and the solids, as calcination takes place in the absence of air.

process of calcination derives its name from its most common application, the decomposition of calcium carbonate (limestone

Limestone

File:Limestone Formation In Waitomo.jpgLimestone is a sedimentary rock composed largely of the mineral calcite . The deposition of limestone strata is often a by-product and indicator of biological activity in the geology record....
) to calcium oxide (lime

Lime (mineral)

Lime is a general term for calcium-containing inorganic materials, in which carbonates, oxides and hydroxides predominate. Strictly speaking, lime is calcium oxide or calcium hydroxide....
).

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Encyclopedia

Calcination (also referred to as calcining) is a thermal treatment process applied to ores and other solid materials in order to bring about a thermal decomposition

Thermal decomposition

Thermal decomposition, also called thermolysis, is defined as a chemical reaction when a chemical substance breaks up into at least two chemical substances when heated....
, phase transition

Phase transition

Roasting (metallurgy)

Industrial processes

The process of calcination derives its name from its most common application, the decomposition of calcium carbonate (limestone

Limestone

Lime (mineral)

Lime is a general term for calcium-containing inorganic materials, in which carbonates, oxides and hydroxides predominate. Strictly speaking, lime is calcium oxide or calcium hydroxide....
). The product of calcination is usually referred to in general as "calcine," regardless of the actual minerals undergoing thermal treatment. Calcination is carried out in furnace

Furnace

File:Piec krepa.JPGA furnace is a device used for heating. The name derives from Latin fornax, oven. The earliest furnace was excavated at Balakot, a site of the Indus Valley Civilization, dating back to its mature phase ....
s or reactors (sometimes referred to as kiln

Kiln

Kilns are thermally insulated chambers, or ovens, in which controlled temperature regimes are produced. They are used to harden, burn or dry materials....
s) of various designs including shaft furnaces, rotary kiln

Rotary kiln

A Rotary kiln is a pyroprocessing device used to raise materials to a high temperature in a continuous process. Materials produced using rotary kilns include:...
s, multiple hearth furnaces, and fluidized bed reactor

Fluidized bed reactor

A fluidized bed reactor is a type of Chemical reactor device that can be used to carry out a variety of Phase chemical reactions. In this type of reactor, a fluid is passed through a granular solid material at high enough velocity to suspend the solid and cause it to behave as though it were a fluid....
s.

Examples of calcination processes include the following:

decomposition of hydrated minerals, as in calcination of bauxite
Bauxite

Bauxite is the most important aluminium ore. It consists largely of the minerals gibbsite Al3, boehmite ?-AlO, and diaspore a-AlO, together with the iron oxides goethite and hematite, the clay mineral kaolinite and small amounts of anatase TiO2....
, to remove crystalline water
Water

Water is a common chemical substance that is essential for the survival of all known forms of life. In typical usage, water refers only to its liquid form or States of matter, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam....
as water vapor;
decomposition of carbonate minerals, as in the calcination of limestone
Limestone

File:Limestone Formation In Waitomo.jpgLimestone is a sedimentary rock composed largely of the mineral calcite . The deposition of limestone strata is often a by-product and indicator of biological activity in the geology record....
to drive off carbon dioxide
Carbon dioxide

Carbon dioxide is a chemical compound composed of two oxygen atoms covalent bond to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state....
;
decomposition of volatile matter contained in raw petroleum coke
Petroleum coke

Petroleum coke is a carbonaceous solid derived from oil refinery coker units or other cracking processes. Other Coke has traditionally been derived from coal....
;
heat treatment to effect phase transformations, as in conversion of anatase
Anatase

Anatase is one of the three mineral forms of titanium dioxide, the other two being brookite and rutile. It is always found as small, isolated and sharply developed crystals, and like rutile, a more commonly occurring modification of titanium dioxide, it crystallizes in the Tetragonal crystal system; but, although the degree of symmetry is...
to rutile
Rutile

Rutile is a mineral composed primarily of titanium dioxide, titaniumoxygen2.Rutile is the most common natural form of TiO2....
or devitrification
Devitrification

Devitrification is the opposite of vitrification, i.e., the process of crystallization in a formerly crystal-free glass. The term is derived from the Latin vitreus, meaning glassy and Transparent materials....
of glass materials

Calcination reactions

Calcination reactions usually take place at or above the thermal decomposition temperature (for decomposition and volatilization reactions) or the transition temperature (for phase transitions). This temperature is usually defined as the temperature at which the standard Gibb's free energy of reaction for a particular calcination reaction is equal to zero. For example, in limestone calcination, a decomposition process, the chemical reaction is CaCO₃ = CaO + CO₂(g). The standard Gibb's free energy of reaction is approximated as ?G°_r = 177,100 - 158 T (J/mol). The standard free energy of reaction is zero in this case when the temperature, T, is equal to 848°C.

Examples of chemical decomposition reactions common in calcination processes, and their respective thermal decomposition temperatures include:

CaCO₃ = CaO + CO₂; 848°C

Calcium carbonate

Calcium carbonate is a chemical compound with the chemical formula CalciumCarbonOxygen3. It is a common substance found as Rock in all parts of the world, and is the main component of seashells, snails, and eggshells....

Oxidation

In some cases, calcination of a metal results in oxidation of the metal. calcination is the process usually done for puriying the metals in accordance to their temperature. Jean Rey

Jean Rey (physician)

Jean Rey was a France physician and chemist.Born at Le Bugue, in the P?rigord , he studied medicine at the University of Montpellier. He practised medicine in his native town and corresponded with Ren? Descartes and Marin Mersenne....
noted that lead and tin when calcinated gained weight, presumably as they were being oxidized.

Alchemy

In alchemy

Alchemy

Alchemy , a part of the Occult Tradition, is both a philosophy and a practice with an aim of achieving ultimate wisdom as well as immortality, involving the improvement of the alchemist as well as the making of several substances described as possessing unusual properties....
, calcination was believed to be one of the 12 vital processes required for the transformation of a substance.

Alchemists distinguished two kinds of calcination, actual and potential. Actual calcination is that brought about by actual fire, from wood, coals, or other fuel, raised to a certain temperature. Potential calcination is that brought about by potential fire, such as corrosive chemicals; for example, gold was calcined in a reverberatory furnace

Reverberatory furnace

A reverberatory furnace is a metallurgy or process furnace that isolates the material being processed from contact with the fuel, but not from contact with combustion gases....
with mercury and sal ammoniac

Sal ammoniac

Sal ammoniac is a rare mineral composed of ammonium chloride, NH4Cl. It forms colorless to white to yellow-brown crystals in the Cubic class....
; silver with common salt and alkali salt; copper with salt and sulfur; iron with sal ammoniac and vinegar; tin with antimony; lead with sulfur; and mercury with aqua fortis

Aqua fortis

Aqua fortis, or "strong water," in alchemy, is a corrosive solution of nitric acid in water. It is made from Potassium nitrate. It was used in alchemy as a solvent for dissolving silver and most other metals with notable exceptions of gold and platinum that can be dissolved using aqua regia....
.

There was also philosophical calcination, which was said to occur when horns, hooves, etc, were hung over boiling water, or other liquor, till they had lost their mucilage, and were easily reducible into powder.

Geological

Calcination can also occur under layers of hot volcanic ash. For example, calcination occurred under the ash of the Tungurahua

Tungurahua

Tungurahua, , is an active stratovolcano located in the Cordillera Real of Ecuador. The volcano gives its name to the province of Tungurahua Province....
volcano in Ecuador that erupted in 2006.