calcium
oxide + carbon
dioxide.CaCO3(s)
CaO(s)
+
CO2(g)gcsescience.com 20 gcsescience.com
Extraction of Iron.
Chemistry of the blast furnace (continued).
Limestone is calcium carbonate
(CaCO3) and it is
added to the blast furnace to remove the impurities
in the iron ore.
Calcium carbonate is decomposed by heat in
the furnace
to give calcium oxide (quicklime) and carbon
dioxide.
This is called thermal
decomposition (see examples of other
carbonates).
calcium carbonate calcium
oxide + carbon
dioxide.
CaCO3(s)
CaO(s)
+
CO2(g)
The main impurity is
silica
(sand or rock) which is silicon dioxide.
Silicon dioxide is solid at
the furnace
temperature
and the furnace would become
blocked if it was not removed.
Silicon dioxide reacts with
calcium oxide
to form calcium silicate
(called slag) which is liquid in the furnace.
Slag flows to the bottom of the furnace
where it floats on the liquid
iron and is easily
removed.
calcium oxide +
silicon dioxide calcium silicate.
CaO(s)
+
SiO2(s)
CaSiO3(l)
The slag (CaSiO3) is allowed to cool until it becomes a solid
and is used for road construction.
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