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Iron and Iron Smelting
(Metallurgy)
Iron, the Element
• Fe (from Latin ferrum)
• Stable transition metal; Period 4
• The iron atom has a nucleus surrounded
by electrons. The nucleus has a very high
mass in a small volume consisting of
protons (p+) and neutrons (n0).
• Z = 26 = atomic number = # p+
• A = 56 = mass number = # p+ + # n0
• #electrons = # e- = # p+ in neutral atom
Iron
• Soft, white, lustrous, magnetic metal that
easily rusts (combines with oxygen).
• Metals are good conductors of electricity
and heat, have luster, are malleable,
usually solid at room temperature and
pressure, tend to lose electrons to form
positive ions.
• 7 oxidation states (determined by #e-s on
iron atom; either + or 0; high capability to
form numerous chemical compounds).
Abundance of Fe
• 14 isotopes with 56Fe the most abundant
(92%) isotope.
• Meteors = main source of iron on earth.
• 6th most abundant element in universe
and most abundant metal.
• 4th most abundant element in earth’s crust
after O, Si, Al; @ 5% by weight.
• Not found as free metal, but found as
oxides (reddish color)
Uses of Iron
• Most widely used metal accounting for
95% of all metal produced worldwide.
• Key ingredient in structural materials (e.g.
steel) due to availability, low cost, high
strength.
• Essential ingredient in hemoglobin in
blood; for oxygen transport in body. Also
in numerous enzymes.
Uses of Iron
• Tools and weapons were the earliest uses.
• Later agricultural implements (plows,
hoes), cookware, machines for mills,
foundries, industrial sites were produced
(grindstones, boilers).
• As steel improved, it became and still is
the major building material. (Ironbridge
1778)
Removing Iron from Iron Ore
• Iron is found in nature not as free iron
(Fe), but as iron ore which consists of iron
oxides (Fe2O3 being the most abundant)
and impurities.
• Smelting is the process of removing or
extracting Fe from its ore; i.e. Separating
Fe and O in Fe2O3 to isolate Fe for
subsequent uses.
The Reduction of Iron
• Smelting or extractive metallurgy involves
the reduction of the iron from a positive
oxidation state to 0.
• In Fe2O3 each iron atom has an oxidation
number (Ox#) equal to +3 meaning the
iron has 26 p+ and only 23 e-.
• After smelting, each iron has gained 3
electrons so that #p+ = #e+and iron’s final
Ox# = 0.
What is Needed in the Smelting
Process
• Source of iron: Iron ore
• Source of fuel to produce high
temperatures: charcoal from wood and
later coke from coal
• Carbon to reduce iron by combining with
oxygen in iron ore to form CO.
– 2C(s) + O2(g)  2CO(g)
• Other elements to remove impurities
Chemistry of Iron Smelting
This is a multi-step process of sequential
reductions of iron to elemental iron (Fe)
1. 3Fe2O3(s) + CO(g)  2Fe3O4(s) + CO2(g)
2. 2Fe3O4(s) + 2CO(g)  6FeO(s) +
2CO2(g)
3. 6FeO(s) + 6CO(g)  6Fe(s) + 6CO2(g)
Resulting in
3Fe2O3(s)+9CO(g)6Fe(s)+9CO2(g)
• Fe2O3(s) + 3CO(g)  2Fe(s) + 3CO2(g)
Removal of Silicon Impurities
• Limestone or calcium carbonate, (CaCO3)
is added to remove Si from the iron ore.
• CaCO3(s)  CaO(s) + CO2(g)
Calcium carbonate  calcium oxide +
carbon dioxide
• CaO(s) + SiO2(s)  CaSiO3(s)
calcium oxide + silica  calcium silicate
Summary of Reaction
• This represents the smelting process to
remove oxygen from iron oxide cmps.
• We say that iron is reduced by CO. Iron
accepts electrons to go from an oxidation
state +3 in Fe2O3 to an oxidation state of 0
in Fe (via +8/3 and +2).
• Note that oxygen starts out bonded to Fe
but ends up bonded to C because the C-O
bond is stronger than the Fe-O bond.
References
• http://www.webelements.com/
• http://www.uky.edu/Projects/Chemcomics/
• http://en.wikipedia.org
Reference: Iron Ore and Mining in
Minnesota
http://geography.about.com/library/misc/ucm
esabi.htm
http://web.ulib.csuohio.edu/SpecColl/glihc/ar
ticles/carrhist.html
http://www.dnr.state.mn.us/education/geolog
y/digging/taconite.html