Calcium oxide, commonly known as quicklime or burnt lime, is a widely used chemical compound.
It is a white, caustic, alkaline, crystalline solid at room temperature. The broadly used
term "lime" connotes calcium-containing inorganic materials, in which carbonates, oxides and
hydroxides of calcium, silicon, magnesium, aluminium, and iron predominate. By contrast,
"quicklime" specifically applies to the single chemical compound calcium oxide. Calcium oxide
which survives processing without reacting in building products such as cement is called
free lime. Quicklime is relatively inexpensive. Both
it and a chemical derivative are important commodity chemicals.
Preparation Calcium oxide is usually made by the thermal
decomposition of materials such as limestone, or seashells, that contain calcium carbonate
in a lime kiln. This is accomplished by heating the material to above 825 °C, a process
called calcination or lime-burning, to liberate a molecule of carbon dioxide; leaving quicklime.
The quicklime is not stable and, when cooled, will spontaneously react with CO2 from the
air until, after enough time, it will be completely converted back to calcium carbonate unless
slaked with water to set as lime plaster or lime mortar.
Annual worldwide production of quicklime is around 283 million metric tons. China is by
far the world's largest producer, with a total of around 170 million tonnes per year. The
United States is the next largest, with around 20 million tonnes per year.
Usage Heat: Quicklime produces heat energy by the
formation of the hydrate, calcium hydroxide, by the following equation:
CaO + H2O Ca(OH)2
As it hydrates, an exothermic reaction results and the solid puffs up. The hydrate can be
reconverted to quicklime by removing the water by heating it to redness to reverse the hydration
reaction. One litre of water combines with approximately 3.1 kilograms of quicklime to
give calcium hydroxide plus 3.54 MJ of energy. This process can be used to provide a convenient
portable source of heat, as for on-the-spot food warming in a self-heating can.
Light: When quicklime is heated to 2,400 °C, it emits an intense glow. This form of illumination
is known as a limelight, and was used broadly in theatrical productions prior to the invention
of electric lighting. Cement: Calcium oxide is a key ingredient
for the process of making cement. As an alkali in biodiesel production
Petroleum 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.
Paper: Calcium oxide is used to regenerate sodium hydroxide from sodium carbonate in
the chemical recovery at Kraft pulp mills. Plaster: There is archeological evidence that
Pre-Pottery Neolithic B humans used limestone-based plaster for flooring and other uses. Such
Lime-ash floor remained in use until the late nineteenth century.
Chemical or power production: Solid sprays or slurries of calcium oxide can be used to
remove sulfur dioxide from exhaust streams in a process called flue-gas desulfurization.
Use as a weapon Historian and philosopher David Hume, in his
history of England, recounts that early in the reign of Henry III, the English Navy destroyed
an invading French fleet by blinding the enemy fleet with quicklime:
D’Albiney employed a stratagem against them, which is said to have contributed to the victory:
Having gained the wind of the French, he came down upon them with violence; and throwing
in their faces a great quantity of quicklime, which he purposely carried on board, he so
blinded them, that they were disabled from defending themselves.
Quicklime is also thought to have been a component of Greek fire. Upon contact with water, quicklime
would increase its temperature above 150 °C and ignite the fuel.
Health issues Because of vigorous reaction of quicklime
with water, quicklime causes severe irritation when inhaled or placed in contact with moist
skin or eyes. Inhalation may cause coughing, sneezing, labored breathing. It may then evolve
into burns with perforation of the nasal septum, abdominal pain, nausea and vomiting. Although
quicklime is not considered a fire hazard, its reaction with water can release enough
heat to ignite combustible materials. References
External links Lime Statistics & Information from the United
States Geological Survey Factors Affecting the Quality of Quicklime
American Scientist Chemical of the Week – Lime
Lime production process presentation Material Safety Data Sheet
CDC - NIOSH Pocket Guide to Chemical Hazards