Rocks

Rock Products and Uses - Limestone.

The Manufacture and Uses of Lime.

What is Lime?

The name "lime" is used for both calcium oxide (quicklime),
and calcium hydroxide (slaked lime).


How is Quicklime (Calcium Oxide) Made?

When limestone (calcium carbonate) is heated, at about 1000 °C
it undergoes thermal decomposition.
It loses carbon dioxide and turns into quicklime (calcium oxide).

calcium carbonate  calcium oxide  + carbon dioxide.
CaCO3(s)           arrow        CaO(s)       +        CO2(g)

The reaction is carried out in specially constructed lime kilns
(a kiln is a high temperature oven). Limestone is added at the top
and quicklime is removed from the bottom in a continuous process.
The same reaction occurs in the blast furnace.


What are the Uses of Quicklime (Calcium Oxide)?

Calcium oxide is used to remove silica from the blast furnace
and to remove acidic gases from a power station chimney.

 

How is Slaked Lime (Calcium Hydroxide) Made?

Quicklime reacts with water to form slaked lime (calcium hydroxide).
The reaction is highly exothermic.

calcium oxide + water   arrow   calcium hydroxide.
CaO(s)     +  H2O(l)  arrow         Ca(OH)2(s)


What are the Uses of Slaked Lime (Calcium Hydroxide)?

Slaked lime is used to reduce the acidity of lakes and soils.
Lakes and soils can become acidic because of acid rain.
It acts faster than powdered limestone but is more expensive.
Slaked lime dissolves a little in water to form lime water.

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