Calcines

Calcines are products of calcination, a high-temperature heat treatment designed to drive off volatile components, decompose carbonates or hydrates, and induce phase transformations. Calcination is typically performed at temperatures below melting and often in air or limited oxygen, though some applications use inert or reducing atmospheres. The resulting materials are called calcines.

Common calcination reactions include the decomposition of calcium carbonate to calcium oxide and carbon dioxide (CaCO3 → CaO + CO2) in limestone processing, which yields lime used in cement and various chemical markets. Other examples include the dehydration of gypsum to form plaster of Paris (CaSO4·2H2O → CaSO4·0.5H2O) and further to anhydrite CaSO4 at higher temperatures; dehydration of clays to produce metakaolin for pozzolanic binders; and the removal of absorbed water from hydrated alumina to produce alumina for catalysts and ceramics.

Calcines may also refer to calcined coke or other heat-treated ores that have been roasted to increase porosity or reactivity. In industry, calcination is closely controlled for reaction completeness, particle strength, and energy efficiency; overheating can cause sintering and loss of surface area. Environmental considerations include the release of carbon dioxide from carbonate calcination and the dust hazards associated with fine powders.

In summary, calcines are the end products of calcination processes and are valued for altered composition, increased oxide content, or enhanced reactivity suitable for cement, metallurgy, ceramics, and chemical applications.