Metallurgy and the Chemistry of Metals Study Notes

Metallurgy and the Chemistry of Metals

Introduction to Metallurgy

• Mineral: A naturally occurring substance with a range of chemical compositions.
• Ore: A mineral deposit concentrated enough for economical recovery of a desired metal.
• Metallurgy: The science and technology of separating metals from their ores and compounding alloys.
• Alloy: A solid solution of two or more metals, or of a metal(s) with one or more nonmetals.

Recovery of Metals from Ores

The recovery of a metal from its ore involves three main steps:

1. Preparation of the ore
2. Production of the metal
3. Purification of the metal

Principal Types of Minerals

• Uncombined Metals: Examples include Ag, Au, Bi, Cu, Pd, Pt
• Carbonates: Examples include BaCO3 (witherite), CaCO3 (calcite, limestone), MgCO3 (magnesite), CaCO3 \cdot MgCO3 (dolomite), PbCO3 (cerussite), ZnCO_3 (smithsonite).
• Halides: Examples include CaF2 (fluorite), NaCl (halite), KCl (sylvite), Na3AlF_6 (cryolite).
• Oxides: Examples include Al2O3 \cdot 2H2O (bauxite), Al2O3 (corundum), Fe2O3 (hematite), Fe3O4 (magnetite), Cu2O (cuprite), MnO2 (pyrolusite), SnO2 (cassiterite), TiO_2 (rutile), ZnO (zincite).
• Phosphates: Examples include Ca3(PO4)2 (phosphate rock), Ca5(PO4)3OH (hydroxyapatite).
• Silicates: Examples include Be3Al2Si6O{18} (beryl), ZrSiO4 (zircon), NaAlSi3O8 (albite), Mg3(Si4O{10})(OH)_2 (talc).
• Sulfides: Examples include Ag2S (argentite), CdS (greenockite), Cu2S (chalcocite), FeS_2 (pyrite), HgS (cinnabar), PbS (galena), ZnS (sphalerite).
• Sulfates: Examples include BaSO4 (barite), CaSO4 (anhydrite), PbSO4 (anglesite), SrSO4 (celestite), MgSO4 \cdot 7H2O (epsomite).

Metals and Their Best-Known Minerals

• The periodic table highlights where different metals are found and the types of minerals (sulfides, oxides, chlorides, and uncombined) in which they are commonly found.

Production of Metals

• Roasting:
  • CaCO3(s) \rightarrow CaO(s) + CO2(g)
  • 2PbS(s) + 3O2(g) \rightarrow 2PbO(s) + 2SO2(g)
• Chemical Reduction:
  • TiCl4(g) + 2Mg(l) \rightarrow Ti(s) + 2MgCl2(l)
  • Cr2O3(s) + 2Al(s) \rightarrow 2Cr(l) + Al2O3(s)
  • WO3(s) + 3H2(g) \rightarrow W(s) + 3H_2O(g)
• Electrolytic Reduction:
  • 2MO(l) \rightarrow 2M \text{ (at cathode)} + O_2 \text{ (at anode)}
  • 2MCl(l) \rightarrow 2M \text{ (at cathode)} + Cl_2 \text{ (at anode)}

Reduction Processes for Common Metals

Blast Furnace for Producing Iron

• Process Overview:
  • A blast furnace is used to reduce iron ore to molten iron.
  • The charge (ore, limestone, coke) descends through the furnace as hot gases rise.
• Reactions at Different Temperatures:
  • 200°C: 3Fe2O3 + CO \rightarrow 2Fe3O4 + CO_2
  • 700°C: CaCO3 \rightarrow CaO + CO2
  • Fe3O4 + CO \rightarrow 3FeO + CO_2
  • C + CO_2 \rightarrow 2CO
  • 1200°C - 1500°C: FeO + CO \rightarrow Fe + CO_2
  • 2000°C: 2C + O_2 \rightarrow 2CO
• Outputs:
  • Molten iron is collected at the bottom.
  • Molten slag forms.
  • Hot air is blasted into the furnace.

Steel Manufacturing via the Oxygen Process

• Process Overview:
  • The oxygen process is used to manufacture steel from molten iron.
  • Oxygen is blown into the molten iron to oxidize impurities.
  • CaO or SiO_2 is added to form slag.

Types of Steel

• A single number indicates the maximum amount of the substance present.

Purification of Metals

• Distillation:
  • Ni(s) + 4CO(g) \rightleftharpoons Ni(CO)_4(g)
  • @70°C: Ni(s) + 4CO(g) \rightarrow Ni(CO)_4(g)
  • @200°C: Ni(CO)_4(g) \rightarrow Ni(s) + 4CO(g)
• Electrolysis:
  • Cu(s) \text{ (impure)} \rightarrow Cu^{2+}(aq) + 2e^-
  • Cu^{2+}(aq) + 2e^- \rightarrow Cu(s) \text{ (pure)}
• Zone Refining:

Zone Refining of Metals

• A heating coil is used to melt a small zone of a metal rod.
• Impurities concentrate in the molten zone, which is moved along the rod to purify the metal.

Band Theory of Conductivity

• Delocalized electrons move freely through “bands” formed by overlapping molecular orbitals.
• Example: Mg has the electronic configuration 1s^22s^22p^63s^2 or [Ne]3s^2

Energy Gaps Between Valence and Conduction Bands

• Metals: Valence and conduction bands overlap, allowing electrons to move freely.
• Semiconductors: Small energy gap between valence and conduction bands.
• Insulators: Large energy gap between valence and conduction bands.

Semiconductors

• Silicon (Si): [Ne]3s^23p^2
• n-type semiconductor:
  • Doped with donor impurities like Phosphorus (P) which has the electronic configuration [Ne]3s^23p^3
• p-type semiconductor:
  • Doped with acceptor impurities like Boron (B) which has the electronic configuration [Ne]3s^23p^1

Periodic Trends in Metallic Character

• Increasing Metallic Character: Metallic character generally increases down a group and from right to left across a period.
• The alkali metals (Li, Na, K, Rb, Cs) and alkaline earth metals (Be, Mg, Ca, Sr, Ba) are good examples of this trend.

Properties of Alkali Metals

*Refers to the cation M^+, where M denotes an alkali metal atom.
The half-reaction is M^+(aq) + e^- \rightarrow M(s).

Reactivity of Alkali Metals

• General reaction: M \rightarrow M^{+1} + 1e^-
• Reaction with water: 2M(s) + 2H2O(l) \rightarrow 2MOH(aq) + H2(g)
• Reaction with oxygen: 2M(s) + O2(g) \rightarrow M2O(s)
• Reactivity increases down the group.

Properties of Alkaline Earth Metals

*Refers to the cation M^{2+}, where M denotes an alkaline earth metal atom.
The half-reaction is M^{2+}(aq) + 2e^- \rightarrow M(s).

Reactivity of Alkaline Earth Metals

• General reaction: M \rightarrow M^{+2} + 2e^-
• Reaction with water:
  • Be(s) + 2H2O(l) → No Reaction
  • Mg(s) + H2O(g) \rightarrow MgO(s) + H2(g)
  • M(s) + 2H2O(l) \rightarrow M(OH)2(aq) + H_2(g), where M = Ca, Sr, or Ba
• Reactivity increases down the group (excluding Be).

Aluminum Production

• Purification:
  • Al2O3(s) + 2OH^-(aq) \rightarrow 2AlO2^-(aq) + H2O(l)
  • AlO2^-(s) + H3O^+(aq) \rightarrow Al(OH)_3(s)
  • 2Al(OH)3(s) \rightarrow Al2O3(s) + 3H2O(g)
• Electrolytic Process:
  • Anode: 3[2O^{2-} \rightarrow O_2(g) + 4e^-]
  • Cathode: 4[Al^{3+} + 3e^- \rightarrow Al(l)]
  • Overall: 2Al2O3 \rightarrow 4Al(l) + 3O_2(g)

Chemistry in Action: Recycling Aluminum

• Recycling aluminum is an important process.