calcination

Calcination is a high-temperature thermal treatment of a solid material, typically carried out in the absence or limited presence of air, to bring about decomposition, phase transformation, or release of volatile components. It differs from drying in that calcination involves chemical change and the formation of a new substance, rather than simply removing moisture. The process is commonly performed in kilns, rotary furnaces, or retorts.

Common calcination reactions include the decomposition of carbonates to oxides with the release of carbon dioxide, such as calcium carbonate to calcium oxide and carbon dioxide. Hydrated minerals and salts often undergo dehydration, for example gypsum is heated to form plaster of Paris, removing part of its water of crystallization. Some compounds may undergo phase changes without complete decomposition, and others are heated to drive off volatile impurities or to activate an oxide.

Industrial uses are widespread. In cement and lime production, calcination converts limestone into lime or clinker precursors by driving off CO2 and forming reactive oxides. Calcination is also used in ore processing to prepare oxides from carbonate or hydroxide minerals, and in the production of certain refractory materials and catalysts, where removal of bound water or decomposition products is required to achieve the desired phase or porosity.

Environmental and safety considerations include energy consumption and CO2 emissions, as well as handling and dust control, since fine powders can pose inhalation and explosion risks. Process optimization often aims to balance complete conversion with minimal sintering and energy use, sometimes incorporating heat recovery and careful temperature control.