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Concept
Calcination
Summary
Calcination refers to thermal treatment of a solid chemical compound (e.g. mixed carbonate ores) whereby the compound is raised to high temperature without melting under restricted supply of ambient oxygen (i.e. gaseous O2 fraction of air), generally for the purpose of removing impurities or volatile substances and/or to incur thermal decomposition.
The root of the word calcination refers to its most prominent use, which is to remove carbon from limestone (calcium carbonate) through combustion to yield calcium oxide (quicklime). This calcination reaction is CaCO3(s) → CaO(s) + CO2(g). Calcium oxide is a crucial ingredient in modern cement, and is also used as a chemical flux in smelting. Industrial calcination generally emits carbon dioxide (), making it a major contributor to climate change.
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.
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) to calcium oxide (lime) and carbon dioxide, in order to create cement. 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 or calciners) of various designs including shaft furnaces, rotary kilns, multiple hearth furnaces, and fluidized bed reactors.
Examples of calcination processes include the following:
decomposition of carbonate ores, as in the calcination of limestone to drive off carbon dioxide;
decomposition of hydrated minerals, as in the calcination of bauxite and gypsum, carbonate ore to remove water of crystallization as water vapor;
decomposition of volatile matter contained in raw petroleum coke;
heat treatment to effect phase transformations, as in conversion of anatase to rutile or devitrification of glass materials;
removal of ammonium ions in the synthesis of zeolites;
defluorination of uranyl fluoride to create uranium dioxide and hydrofluoric acid gas;
heat treatment of anthracite through electrically fired calcining furnace or gas calcination which results in development of graphitic structure.
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