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/ucmesabi.htm

http://web.ulib.csuohio.edu/SpecColl/glihc/articles/carrhist.html

http://www.dnr.state.mn.us/education/geology/digging/taconite.html