calcining

Calcining is a high-temperature thermal treatment of a solid substance to drive off volatile components, decompose hydrated or other labile materials, or induce a phase change, typically at temperatures above several hundred degrees Celsius. The process is carried out in air or in a controlled atmosphere with limited oxygen, depending on the desired product. The term derives from calcinare, meaning to burn lime or to make by heating.

A classic example is the calcination of limestone (calcium carbonate) to produce quicklime (calcium oxide): CaCO3 → CaO + CO2. This reaction removes carbon dioxide and changes the material’s properties for use in cement and other sectors. Gypsum can be calcined to form plaster of Paris: CaSO4·2H2O → CaSO4·0.5H2O + 1.5 H2O. Calcination is also used to obtain anhydrous or phase-pure oxides from hydrated minerals and to modify mineral structures for ceramic, catalyst, or adsorbent applications.

Industrial relevance includes cement manufacture, lime production, dehydration of clays and gypsum, and the preparation of oxide materials for catalysts and adsorbents. Temperature ranges commonly span from several hundred to roughly 1000 °C, with duration and atmosphere influencing porosity, phase composition, and reactivity. Controlling heat exposure is important to avoid sintering or excessive grain growth, which can reduce material performance.

Calcination is distinct from roasting in pyrometallurgy: calcination emphasizes decomposition or removal of volatile constituents, often with limited oxidation, whereas roasting involves heating in air to promote oxidation of the material.