DESCRIPTION
Calcium oxide is made by thermal decomposition of calcium carbonate in a lime kiln. This calcination process has been known for about 15,000 years. Upon heating, calcium carbonate gives off carbon dioxide gas and produces quicklime, i.e. Ca(OH)2. This calcium oxide is chemically reactive and will reform calcium carbonate if left exposed to CO2, or form calcium hydroxide if exposed to water vapor or moisture. This latter reaction is the basis for lime plaster and lime mortar.
Calcium oxide is widely used as a commodity chemical.
APPLICATIONS
Vast amounts of quicklime are used with annual production approaching 300 million tons. The basic oxygen steelmaking process (BOS) requires up to 50kg of quicklime per ton of steel made. Its function is to react with impurities and form a slag. Similarly, quicklime is used to strengthen clay-based soils by reacting with other elements such as silica and aluminium.
As mentioned earlier, calcium oxide reforms the hydroxide upon exposure to water. That reaction is highly favorable and produces a great deal of heat which must be allowed for when using it as a desiccant in plastics, coatings, and other formulations. The same reaction can be used as a portable heat source where one simply needs to add water.
Interestingly, as the calcium oxide reacts to form the hydroxide, it expands significantly because the density of the oxide starting material (3.34 gcm-3) is so much higher than that of the hydroxide formed (2.2 – 2.3 gcm-3). This effect is used in mining where the expansion on quicklime inserted into a drilled hole can be used to break apart softer rocks.
Another chemical reaction of quicklime is with sulfur dioxide gas, a reaction used commercially in scrubbers that desulfurize flue-gas.
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