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 (n 0 ). Z = 26 = atomic number = # p + A = 56 = mass number = # p + + # n 0 #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 56 Fe 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, 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 (Fe 2 O 3 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 Fe 2 O 3 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 Fe 2 O 3 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) + O 2 (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) 1.3Fe 2 O 3 (s) + CO(g)  2Fe 3 O 4 (s) + CO 2 (g) 2.2Fe 3 O 4 (s) + 2CO(g)  6FeO(s) + 2CO 2 (g) 3.6FeO(s) + 6CO(g)  6Fe(s) + 6CO 2 (g) Resulting in 3Fe 2 O 3 (s)+9CO(g)  6Fe(s)+9CO 2 (g) Fe 2 O 3 (s) + 3CO(g)  2Fe(s) + 3CO 2 (g)

Removal of Silicon Impurities Limestone or calcium carbonate, (CaCO 3 ) is added to remove Si from the iron ore. CaCO 3 (s)  CaO(s) + CO 2 (g) Calcium carbonate  calcium oxide + carbon dioxide CaO(s) + SiO 2 (s)  CaSiO 3 (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 Fe 2 O 3 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

Reference: Iron Ore and Mining in Minnesota esabi.htm ticles/carrhist.html y/digging/taconite.html