Three types of calcium carbonate-containing rock are excavated
and used by industry. They are limestone, chalk and dolomite. Limestone and
chalk are both forms of calcium carbonate and dolomite is a mixture of calcium
and magnesium carbonates. All have impurities such as clay but some rocks
are over 97% pure. Limestone and other products derived from it are used
extensively in the construction industry and to neutralize acidic compounds in a
variety of contexts.
In the chemical industry, large quantities of limestone are heated to ca 1500 K
to form calcium oxide, known as quicklime:
Water can be added to lime to form calcium hydroxide. The process is known
as 'slaking'. Solid calcium hydroxide is known as slaked lime or hydrated lime,
and solutions and suspensions in water as milk of lime.
The term lime is often used to cover quicklime, slaked lime (hydrated lime) and
milk of lime.
For a particular use, an appropriate choice is made from the four: limestone,
quicklime, slaked lime or milk of lime. In many uses, lime reacts more quickly
than limestone but is more expensive, because a high temperature is required
to produce it from limestone.
Uses of limestone and lime
Figure 1 Principal uses of limestone and lime.
The principal uses, by far, of limestone and lime are in the construction
industry and cement making. They are also used in the chemical and
metallurgical industries and in agriculture.
On a worldwide basis, the proportions of lime used in different industries are:
60% metallurgy (mainly steel manufacture, slag formation and its use in the blast
25% construction (for example, it is used with asphalt in road paving, to
stabilize soils and in making mortar and plaster)
15% for chemical and industrial uses (for example to make bleaches used in
the manufacture of paper, to make precipitated calcium carbonate, a fine powder
used in coatings for paper and paints, and in refining sugar to remove colloidal
impurities) and for environmental uses (for example, with soda ash by both
municipal authorities and industry, to soften water (remove calcium and
magnesium ions), in the treatment of sewage to remove colloidal particles and in
flue gas desulfurization)
However, these proportions vary widely from country to country. For example,
in the US, the proportions are:
38% metallurgy (mainly steel manufacture)
31% environmental uses (for example, with soda ash, by both municiipal
authorities and industry to soften water (remove calcium and magnesium ions), in
the treatment of sewage, to remove colloidal particles and in flue gas
22% chemical and industrial uses (for example to make bleaches used in the
manufacture of paper, to make precipitated calcium carbonate, a fine powder
used in coatings for paper and paints and in refining sugar to remove colloidal
8% construction uses (for example, it is used with asphalt in road paving, to
stabilize soils and in making mortar and plaster)
Data from the US Geological Survey, 2012
The uses are described below, in more detail, in terms of different industries.
In the construction industry
Limestone has been used as a building material since the Stone Age. Indeed,
the largest use of limestone and the various forms of lime is still in the
construction industry, particularly in road building and building projects, from
vast in size, bridges and skyscrapers, to houses. Large lumps of calcium
carbonate are often used where sizeable quantities of aggregate are needed,
for example for the foundations of roads.
Lime is often used to make soil firmer. It reacts with clay minerals in the soil to
form cement-like compounds (for example calcium silicate and calcium
aluminate (calcium aluminosilicate)), Figure 2.
Figure 2(a) Clay particles are surrounded by
water, allowing them to be aligned and able to
slide easily. This results in a clay soil with a
Figure 32b) When lime is added, the amount of
water around the clay particles is reduced. The
clay particles are no longer able to slide easily
and the soil is strengthened.
The strengthening of soil enables the construction of buildings by giving a
more stable foundation. Lime is also used on building sites to allow large
vehicles to move more easily (Figure 3).
Figure 3 The wet soil has been made
harder by the addition of lime. This
earth-moving equipment is able to
move around easily.
By kind permission of Singleton
Limestone is also the main constituent of cement and concrete.
In cement making
Cement is made by heating a mixture of limestone and substances such as
clays (which contain silica, alumina and iron(III) oxide) in kilns at high
temperatures until it almost fuses. The mixture is then cooled and ground to a
fine powder and mixed with calcium sulfate (gypsum). This is cement. It is
essentially a mixture of calcium aluminosilicate and calcium sulfate. When it is
mixed with water, chemical reactions occur to form a hard solid, impervious to
About 3.6 billion tonnes of cement is produced annually, of which China
accounts for 2.1 billion tonnes. Cement powder is usually mixed with sand and
aggregate (gravel, granite) and when needed, they are mixed with water to
Figures 4 and 5 Builders and masons, prior to the use of modern cement, used a mixture of lime
(calcium hydroxide), sand and water, known as lime mortar or simply mortar. It has been used for over
6000 years, since the buildings of Ancient Greece and Rome. When these buildings are renovated, lime
mortar is used rather than cement. In these photographs of York Minster, a relatively modern building
dating back only 900 years, lime mortar has always been used in renovating the stonework that has to
be replaced because of weathering over the centuries.
By kind permission of Jessica Waddington.
In industry and the environment
Many lakes have become too acidic because of aerial pollution (acid rain), for
example in the US, Scandinavia and Scotland. The lakes are sprayed with very
finely powdered calcium carbonate (Figure 6). Another effective way to treat
this problem is to apply the powdered limestone to unplanted areas near to the
sources of the streams leading to the lakes.
Figure 6 Powdered limestone is being sprayed over a lake near Hemsjö, in Southern Sweden.
By kind permission of Rickard Gillberg.
Limestone and the various forms of lime are used in large quantities to clean
up the environment, by neutralising acids. For example, limestone and
quicklime are used to remove sulfur dioxide produced in the burning of coal in
power stations. Even 'clean' coal can contain about 1% sulfur.
The gaseous effluents, flue gases, from the burning of the coal are passed
through a spray of very finely ground limestone or quicklime suspended in
water. The sulfur dioxide, being an acid, reacts with them, for example:
The resulting calcium sulfite collects at the base of the absorber and
compressed air is blown into this residue. The calcium sulfite reacts with the air
to form calcium sulfate (gypsum), used to make, for example, plaster board
Very fine and pure calcium carbonate is used as filler in plastics and paper. A
filler is a substance that gives bulk but does not alter the properties of the
substance to which it is added and is also inert. Calcium carbonate when very
finely crushed (less than 2 microns) is used in paints to give a 'matt' finish.
Figure 7 Uses of limestone.
Calcium carbonate is also used:
to make sodium carbonate by the Solvay process
in the blast furnace to make iron
in the manufacture of glass
The uses are further summarized in Figure 7.
Crushed limestone and lime in all its forms are used to neutralize acids in the
soil and so create the optimum soil conditions for crop growth. They also help
to break down clays as described above, improving the soil structure, thus
improving drainage and reducing soil erosion. Further, they provide a source of
calcium ions that are an important