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Calcination refers to heating a solid to high temperatures in absence of air or oxygen, generally for the purpose of removing impurities or volatile substances. However, calcination is also used to mean a
thermal treatment Thermal treatment is any waste treatment technology that involves high temperatures in the processing of the waste feedstock. Commonly this involves the combustion of waste materials. Systems that are generally considered to be thermal treatment i ...
process in the absence or limited supply of air or oxygen applied to
ore ore – psilomelane Psilomelane is a group name for hard black manganese oxides including hollandite and romanechite. Psilomelane consists of hydrous manganese Manganese is a chemical element Image:Simple Periodic Table Chart- ...

ore
s and other solid materials to bring about a
thermal decomposition Thermal decomposition, or thermolysis, is a chemical decompositionChemical decomposition, or chemical breakdown, is the process or effect of simplifying a single chemical entity (normal molecule, reaction intermediate, etc.) into two or more fra ...
. The root of the word calcination refers to its most prominent use, which is to remove carbon from
limestone Limestone is a common type of carbonate In chemistry, a carbonate is a salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of Salt (chemistry), salts; salt in its na ...

limestone
through
combustion Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combustion ...
to yield
calcium oxide (quicklime)
calcium oxide (quicklime)
. This calcination reaction is CaCO3(s) → CaO(s) + CO2(g). Calcium oxide is a crucial ingredient in modern
cement A cement is a binder (material), binder, a substance used for construction that solidification, sets, hardens, and adheres to other materials to bind them together. Cement is seldom used on its own, but rather to bind sand and gravel (constru ...
, and is also used as a chemical
flux Flux describes any effect that appears to pass or travel (whether it actually moves or not) through a surface or substance. Flux is a concept in applied mathematics and vector calculus which has many applications to physics. For transport ph ...
in
smelting Smelting is a process of applying heat to ore in order to extract a base metal. It is a form of extractive metallurgy. It is used to extract many metals from their ores, including Silver mining#Ore processing, silver, iron-making, iron, copper ...
. Industrial calcination generally emits
carbon dioxide Carbon dioxide (chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes also other symbols, such as pare ...

carbon dioxide
(), making it a major contributor to
climate change Contemporary climate change includes both the global warming caused by humans, and its impacts on Earth's weather patterns. There have been previous periods of climate change, but the current changes are more rapid than any known even ...
. A calciner is a steel cylinder that rotates inside a heated furnace and performs indirect high-temperature processing (550–1150 °C, or 1000–2100 °F) within a controlled atmosphere.


Industrial processes

The process of calcination derives its name from the Latin ''calcinare'' (to burn lime) due to its most common application, the decomposition of calcium carbonate (
limestone Limestone is a common type of carbonate In chemistry, a carbonate is a salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of Salt (chemistry), salts; salt in its na ...

limestone
) to
calcium oxide Calcium oxide (CaO), commonly known as quicklime or burnt lime, is a widely used chemical compound A chemical compound is a chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter ...

calcium oxide
(
lime Lime refers to: * Lime (fruit), a green citrus fruit * Lime (material), inorganic materials containing calcium, usually calcium oxide or calcium hydroxide * Lime (color), a color between yellow and green Lime may also refer to: Botany * Austra ...

lime
) and
carbon dioxide Carbon dioxide (chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes also other symbols, such as pare ...

carbon dioxide
, in order to create
cement A cement is a binder (material), binder, a substance used for construction that solidification, sets, hardens, and adheres to other materials to bind them together. Cement is seldom used on its own, but rather to bind sand and gravel (constru ...
. 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 A furnace is a structure in which heat is produced with the help of combustion. Furnace may also refer to: Appliances Buildings * Furnace (house heating): a furnace , or a heater or boiler , used to generate heat for buildings * Boiler Poland ...

furnace
s or reactors (sometimes referred to as
kiln , Wrecclesham Wrecclesham is a village on the southern outskirts of the large town of Farnham Farnham is a market town in Surrey, England, within the Borough of Waverley Borough Council, Waverley.OS Explorer map 145:Guildford and Farnham ...

kiln
s or calciners) of various designs including shaft furnaces,
rotary kiln A rotary kiln is a pyroprocessing Pyroprocessing (from Greek Πυρος = ''fire'') is a process in which materials are subjected to high temperatures (typically over 800 °C) in order to bring about a chemical or physical change. Pyroproc ...

rotary kiln
s, multiple hearth furnaces, and
fluidized bed reactor A fluidized bed reactor (FBR) is a type of reactor device that can be used to carry out a variety of multiphase chemical reactions. In this type of reactor, a fluid In physics, a fluid is a substance that continually Deformation (mechanics), ...
s. Examples of calcination processes include the following: *decomposition of carbonate ores, as in the calcination of
limestone Limestone is a common type of carbonate In chemistry, a carbonate is a salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of Salt (chemistry), salts; salt in its na ...

limestone
to drive off
carbon dioxide Carbon dioxide (chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes also other symbols, such as pare ...

carbon dioxide
; *decomposition of hydrated minerals, as in the calcination of
bauxite Bauxite is a sedimentary rock Sedimentary rocks are types of rock (geology), rock that are formed by the accumulation or deposition of mineral or organic matter, organic particles at Earth#Surface, Earth's surface, followed by cementation ( ...

bauxite
and
gypsum Gypsum is a soft sulfate mineral The sulfate minerals are a class of mineral In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with ...

gypsum
, to remove
water of crystallizationIn chemistry, water(s) of crystallization or water(s) of hydration are water Water (chemical formula H2O) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's ...
as water vapor; *decomposition of volatile matter contained in raw
petroleum coke Petroleum coke, abbreviated coke or petcoke, is a final carbon Carbon (from la, carbo "coal") is a with the C and 6. It is lic and —making four s available to form s. It belongs to group 14 of the periodic table. Carbon makes up onl ...
; *heat treatment to effect phase transformations, as in conversion of
anatase Anatase is a metastable In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matter, its Motion (physics), mot ...
to
rutile Rutile is an oxide mineral The oxide mineral class includes those mineral In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the so ...

rutile
or
devitrification Devitrification is the process of crystallization in a formerly crystal-free (amorphous) glass.Werner Vogel: "Glass Chemistry"; Springer-Verlag Berlin and Heidelberg GmbH & Co. K; 2nd revised edition (November 1994), The term is derived from the La ...
of
glass Glass is a non- crystalline, often transparency and translucency, transparent amorphous solid, that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by ...

glass
materials; *removal of
ammonium The ammonium cation An ion () is an atom or molecule with a net electric charge, electrical charge. The charge of an electron is considered negative by convention and this charge is equal and opposite to charge of a proton, which is conside ...

ammonium
ions An ion () is an atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are u ...

ions
in the
synthesis Synthesis or synthesize may also refer to: Science Chemistry and biochemistry *Chemical synthesis, the execution of chemical reactions to form a more complex molecule from chemical precursors **Organic synthesis, the chemical synthesis of o ...
of
zeolites Zeolites are microporous, aluminosilicate mineral In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (g ...
; *defluorination of uranyl fluoride to create uranium dioxide and hydrofluoric acid gas.


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
Gibbs free energy In thermodynamics Thermodynamics is a branch of physics that deals with heat, Work (thermodynamics), work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these quan ...
for a particular calcination reaction is equal to zero.


Limestone calcination

In limestone calcination, a decomposition process that occurs at 900 to 1050ºC, the chemical reaction is :CaCO3(s) → CaO(s) + CO2(g) Today, this reaction largely occurs in a
cement kiln Cement kilns are used for the pyroprocessing stage of manufacture of Portland cement, portland and other types of hydraulic cement, in which calcium carbonate reacts with silicon dioxide, silica-bearing minerals to form a mixture of calcium silicat ...
. The standard Gibbs free energy of reaction is approximated as ''ΔG°r'' ≈ 177,100 − 158''T'' (J/mol). The standard free energy of reaction is 0 in this case when the temperature, ''T'', is equal to 1121K, or 848 °C.


Oxidation

In some cases, calcination of a metal results in
oxidation Redox (reduction–oxidation, pronunciation: or ) is a type of chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substance A chemical substance is a form of matter ...

oxidation
of the metal to produce a
metal oxide of rutile Rutile is a mineral composed primarily of titanium dioxide (TiO2), and is the most common natural form of TiO2. Other rarer polymorphs of TiO2 are known, including anatase, akaogiite, and brookite. Rutile has one of the highest re ...
. In the seventeenth century, Jean Rey noted that
lead Lead is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical elements ...

lead
and
tin Tin is a with the Sn (from la, ) and  50. Tin is a silvery-colored metal that characteristically has a faint yellow hue. Tin is soft enough to be cut with little force and a bar of tin can be bent by hand with little effort. When bent ...

tin
when calcinated gained weight, presumably as they were being oxidized.


Alchemy

In
alchemy Alchemy (from Arabic Arabic (, ' or , ' or ) is a Semitic language The Semitic languages are a branch of the Afroasiatic language family originating in the Middle East The Middle East is a list of transcontinental countri ...
, 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 A reverberatory furnace is a metallurgy, metallurgical or process Metallurgical furnace, furnace that isolates the material being processed from contact with the fuel, but not from contact with combustion gases. The term ''reverberation'' is used ...
with
mercury Mercury usually refers to: * Mercury (planet) Mercury is the smallest planet in the Solar System and the closest to the Sun. Its orbit around the Sun takes 87.97 Earth days, the shortest of all the Sun's planets. It is named after the Roman g ...

mercury
and
sal ammoniac Salammoniac, also sal ammoniac or salmiac, is a rare naturally occurring mineral composed of ammonium chloride, NH4Cl. It forms colorless, white, or yellow-brown crystals in the isometric-hexoctahedral class. It has very poor cleavage and is brit ...
; silver with common salt and
alkali salt Alkali salts or basic salts are salts that are the product of incomplete Neutralization (chemistry), neutralization of a Base (chemistry)#Strong bases, strong base and a Acid strength#Weak acids in water, weak acid. Rather than being neutral (as ...
;
copper Copper is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical elem ...

copper
with salt and
sulfur Sulfur (in nontechnical British English: sulphur) is a chemical element In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: th ...

sulfur
;
iron Iron () is a chemical element In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behav ...

iron
with sal ammoniac and
vinegar Vinegar is an aqueous solution of acetic acid and trace compounds that may include flavorings. Vinegar typically contains 5–8% acetic acid by volume. Usually, the acetic acid is produced by a double fermentation; converting simple sugars to eth ...

vinegar
; tin with
antimony Antimony is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science t ...

antimony
; lead with sulfur; and mercury with
aqua fortis Nitric acid (), also known as ''aqua fortis'' (Latin for "strong water") and spirit of niter, is a highly corrosive mineral acid. The pure compound is colorless, but older samples tend to acquire a yellow cast due to decomposition into nitroge ...

aqua fortis
. There was also ''philosophical calcination'', which was said to occur when horns, hooves, etc., were hung over boiling water, or other liquor, until they had lost their
mucilage Mucilage is a thick, gluey substance produced by nearly all plant Plants are mainly multicellular organisms, predominantly photosynthetic Photosynthesis is a process used by plants and other organisms to Energy transformation, convert ...
, and were easily reducible into powder.


References

{{Extractive metallurgy Chemical processes Metallurgical processes Alchemical processes