2.1 Minerals vs Ores

A mineral is any naturally occurring compound of a metal in the earth's crust. An ore is a mineral from which a metal can be extracted profitably. All ores are minerals; not all minerals are ores. Economic factors (grade, accessibility, processing cost) determine ore status.

2.2 Types of Ores

Ores are classified by the anion of the metal compound:

• Oxide: bauxite (Al), haematite (Fe), cuprite (Cu)
• Sulphide: copper pyrite (Cu), zinc blende (Zn), galena (Pb)
• Carbonate: calamine (Zn), siderite (Fe)
• Halide: cryolite (Al), rock salt (Na)

2.3 Concentration Methods

The removal of gangue from raw ore is called ore dressing or beneficiation. Four methods are tested:

1. Hydraulic washing — density-based; for heavy oxide ores
2. Magnetic separation — magnetic vs non-magnetic; for chromite, wolframite
3. Froth flotation — hydrophobicity; for sulphide ores using pine oil; NaCN depresses ZnS in a ZnS–PbS mixture
4. Leaching — chemical dissolution; NaCN for Au, NaOH (Bayer's process) for Al

2.4 Thermodynamic Principles (Ellingham Diagram)

The Ellingham diagram plots $\Delta G$° (formation of metal oxide) versus temperature. Lower line = more stable oxide. A metal reduces the oxide of another if its own oxide line lies below the other's. The 2C + $O_{2}$ → 2CO line slopes downward because $\Delta S$ > 0, making carbon an increasingly powerful reductant with rising temperature.

2.5 Extraction Processes

• Calcination: carbonates/hydrated ores + limited air → oxide + C$O_{2}$/$H_{2}O$
• Roasting: sulphide ores + excess air → oxide + S$O_{2}$
• Smelting + flux: oxide + C/CO at high T → crude metal + slag

2.6 Aluminium Extraction (Hall-Heroult)

Bayer's process (NaOH leaching) → pure $Al_{2}O_{3}$ → dissolved in molten cryolite (lowers m.p. to ~950 °C) + $CaF_{2}$ → electrolysis → Al at cathode, C$O_{2}$ at carbon anode (anodes consumed).

2.7 Copper Extraction

Froth flotation → roasting (matte: $Cu_{2}S$ + FeS) → Bessemer converter (self-reduction) → blister copper (~98%) → electrolytic refining (anode mud: Au, Ag).

2.8 Iron Extraction (Blast Furnace)

Haematite + coke + limestone → blast furnace → pig iron. CO reduces $Fe_{2}O_{3}$. CaO removes Si$O_{2}$ as $CaSiO_{3}$ slag. Reactions occur in temperature zones.

2.9 Refining Methods