Quick lime or burnt lime, has the chemical name calcium oxide
(CaO). The name “lime” refers to inorganic materials containing calcium. Quick
lime is white crystalline solid at room temperature which is highly corrosive
and alkaline. It is a relative inexpensive compound and together with its
chemical derivative calcium hydroxide, they are important chemicals in the
commodity industries. Calcium oxide has melting point of 2570°C and a boiling
point of 2850°C. It dissolves in water to produce an alkaline solution calcium
hydroxide or Ca(OH)2, which is also known as hydrated lime.
Calcium oxide is usually produced by thermal decomposition of
calcium carbonate materials such as limestone in a lime kiln. The limestone is
first mined and then crushed and washed to remove impurities. The material is
heated during calcination or lime burning, releasing carbon dioxide and leaving
behind quick lime: CaCO3 (s) à CaO(s) + CO2(g). Quick lime, being unstable, can
react readily with carbon dioxide from air upon cooling as the thermal
decomposition of calcium carbonate is reversible, and completely converts back
to calcium carbonate when given sufficient time.
Quick lime is widely used in the manufacture of cement paint. It
is also used as a filler. Quick lime is also used to produce Precipitated
calcium carbonate (PCC) which is used as a coating and filling agent in paper.
Calcium oxide is used to regenerate sodium hydroxide from sodium
carbonate in the chemical recovery at Kraft pulp mills.
Mining and Oil Industry
Water detection pastes contain a mix of calcium oxide and
phenolphthalein. Should this paste come into contact with water in a fuel
storage tank, the CaO reacts with the water to form calcium hydroxide. Calcium
hydroxide has a high enough pH to turn the phenolphthalein a vivid
purplish-pink color, thus indicating the presence of water.
It is used in the construction industry to make cement and
mortar for building purposes. It is added in asphalt for building roads to
enhance its lifetime and improve cohesion. It is also used to produce other
chemicals for other purposes, such as calcium carbide. It is used to
manufacture steel and iron from ores, as quick lime combines with the silicates
in the ore to form slag that can be removed from the pure molten iron or steel.
It is also used to treat water and reduce air pollution. It is heated with
silica sand and sodium carbonate to form glass. Moreover, in the paint
industry, quick lime is widely used in the manufacture of cement paint.