Page 203 - Encyclopedia of Chemical Compounds 3 Vols

CALCIUM OXIDE

Calcium oxide. Red atom is
oxygen and green atom is
calcium. Gray stick shows a
double bond. PU BL I S HERS
RESOURCE GRO U P

HOW IT IS MADE

The process for making calcium oxide is believed to be
one of the first chemical reactions known to humans, dating
back to prehistoric times. When limestone (calcium carbo-
nate; CaCO 3 ) is heated, carbon dioxide (CO 2 ) is driven off,
leaving calcium oxide behind. The reaction was probably
discovered very early in human history because limestone
is a common, readily available material in the form of chalk
and sea shells, and the amount of heat needed to produce the
reaction can easily be produced in a simple wood fire. A more
efficient method for carrying out the reaction is to heat the

limestone in a kiln (oven) at temperatures of 500 C to 900 C

(900 F to 1,600 F), resulting in a more complete conversion
of calcium carbonate to calcium oxide. This method is still
used today for the commercial preparation of calcium oxide.
COMMON USES AND POTENTIAL HAZARDS
The most important single use of calcium oxide is in metal-
lurgy, particularly in the production of steel. When calcium
oxide is added to the furnace in which steel is made, it reacts
with sulfur, phosphorus, silica, and other impurities present in
the mixture from which steel is produced. The complex mixture
that results can be poured off the top of the molten steel in the
form of a slag, a nonmetallic waste formed during the produc-
tion of metals. Calcium oxide plays a comparable role in the
manufacture of other metals, such as aluminum and magne-
sium. About 40 percent of all the calcium oxide produced in the
United States goes to metallurgical applications.
The next most important use of calcium oxide is in
pollution control devices. Smoke that leaves a factory’s

152 CHEMICAL COMPOUNDS