Calcination (also referred to as Calcining) is thermal treatment process applied to ores and other solid materials in order to bring about a thermal decomposition, phase transition, 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, in which more complex gas-solid reactions take place between the furnace atmosphere and the solids. Thermal decomposition is a chemical reaction where a chemical substance breaks up into at least two chemical substances when heated. ... In physics, a phase transition, (or phase change) is the transformation of a thermodynamic system from one phase to another. ... Roasting is a metallurgical process in which sulfide ores are converted to oxides, prior to smelting. ...

Industrial processes

The process of calcination derives its name from its most common application, the decomposition of calcium carbonate (limestone) to calcium oxide (lime). 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 furnaces or reactors (sometimes referred to as kilns) of various designs including shaft furnaces, rotary kilns, multiple hearth furnaces, and fluidized bed reactors. For other uses, see Limestone (disambiguation). ... Lime has several meanings: Look up Lime in Wiktionary, the free dictionary Lime (mineral) - a group of calcium compounds and minerals in which they predominate, including: Limestone Agricultural lime - a mineral soil additive Calcium oxide (also quicklime) - a chemical compound Calcium hydroxide (also slaked lime) - a chemical compound Lime (fruit... A furnace is a device for heating air or any other fluid. ... Charcoal Kilns, California Gold Kiln, Victoria, Australia Hop kiln. ...

Examples of calcination processes include the following:

• decomposition of hydrated minerals, as in calcination of bauxite, to remove crystalline water as water vapor;
• decomposition of carbonate minerals, as in the calcination of limestone to drive off carbon dioxide;
• volatilization of organic compounds (usually under inert or reducing atmospheres), as in petroleum coke calcination;
• heat treatment to effect phase transformations, as in conversion of anatase to rutile or devitrification of glass materials

Bauxite with penny Bauxite with core of unweathered rock Bauxite is an aluminium ore which consists largely of the Al minerals gibbsite Al(OH)3, boehmite and diaspore AlOOH, together with the iron oxides goethite and hematite, the clay mineral kaolinite and small amounts of anatase TiO2. ... Impact of a drop of water. ... For other uses, see Limestone (disambiguation). ... Carbon dioxide is a chemical compound composed of one carbon and two oxygen atoms. ... Petroleum coke (often abbreviated pet coke) is a carbonaceous solid derived from oil refinery cracking processes. ... Three crystals from Gouveia, Minas Gerais, Brazil Anatase is one of the three mineral forms of titanium dioxide (the other two being brookite and rutile). ... Rutile in trellis texture characteristic of secondary rutile. ...

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 ΔG°_r = 177,100 - 158 T (J/mol).^[1] The standard free energy of reaction is zero in this case when the temperature, T, is equal to 848°C. In thermodynamics the Gibbs free energy is a state function of any system defined as G = H − T·S where G is the Gibbs free energy, measured in joules H is the enthalpy, measured in joules T is the temperature, measured in kelvins S is the entropy, measured in joules...

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

• CaCO₃ = CaO + CO₂; 848°C

See also calcination equilibrium of calcium carbonate Calcium carbonate is a chemical compound, with chemical formula CaCO3. ...

Alchemy

In alchemy, calcination was believed to be one of the 12 vital processes required for the transformation of a substance. For other uses, see Alchemy (disambiguation). ...

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 with mercury and sal ammoniac; silver with common salt and alkali salt; copper with salt and sulfur; iron with sal ammoniac and vinegar; tin with antimony; lead with sulfure; and mercury with aqua fortis. ^[2] A reverbatory furnace is a metallurgical or process furnace which characteristically isolates the material being processed from contact with the fuel, but not from contact with the combustion gases. ... Sal ammoniac is a rare mineral composed of ammonium chloride, NH4Cl. ... The chemical compound nitric acid (HNO3), otherwise known as aqua fortis, is a colorless, corrosive liquid, a toxic acid which can cause severe burns. ...

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. ^[2]

Geological

Calcination can also occur under layers of hot volcanic ash. eg. Tungurahua volcano in Ecuador eruption in 2006. Tungurahua (Quechua tunguri=gullet, rahua=burn, spit fire) is an active stratovolcano in Ecuador. ...

References

1. ^ Gilchrist, J.D. Extraction Metallurgy, 3rd ed. Pergamon Press, Oxford, 1989, p. 145.
2. ^ ^{a b} This article incorporates content from the 1728 Cyclopaedia, a publication in the public domain.