Calcium oxide (CaO) commonly known as quicklime or quicklime, is a widely used compound. It is a white, corrosive, alkaline, crystalline solid at room temperature. The broadly used term "lime" denotes a calcium-containing inorganic material in which carbonates, oxides and hydroxides of calcium, silicon, magnesium, aluminum and iron predominate. In contrast, quicklime is particularly suitable for the single compound calcium oxide. Calcium oxide that survives processing without reacting in building products such as cement is known as free lime. [5]
Quicklime is relatively cheap. It and its chemical derivative calcium hydroxide (of which quicklime is an alkali anhydride) are important household chemicals.
Calcium oxide is usually produced by the thermal decomposition of materials containing calcium carbonate (CaCO3; the mineral calcite), such as limestone or shells, in lime kilns. This is accomplished by heating the material to temperatures above 825 °C (1,517 °F),[6][7] a process known as calcination or lime burning, to release a molecule of carbon dioxide (CO2), leaving quicklime. It is also one of the few known chemical reactions from prehistoric times.
Quicklime is unstable and reacts spontaneously with CO2 in the air when cooled, until sufficient time has elapsed for the quicklime to completely convert back to calcium carbonate, unless slaked with water to make lime paste or lime mortar.
The annual global production of quicklime is about 283 million tons. China is by far the world's largest producer, with a total output of about 170 million tons per year. The United States is the next largest country, with about 20 million tons per year. [9]
Calcium oxide is a key ingredient in the process of making cement.
