Exam Master Review Sheet - Metallurgy

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EXAM MASTER REVIEW SHEET

Inorganic Chemistry: Metallurgy

Isolation of Elements, Ellingham Diagram & Refining

1. Principal Ores of Common Metals

Minerals are naturally occurring substances; Ores are minerals from which metals can be extracted profitably.

Metal	Ores (Name & Formula)
Aluminium (Al)	Bauxite: $AlO_x(OH)_{3-2x}$ \| Kaolinite: $[Al_2(OH)_4Si_2O_5]$
Iron (Fe)	Haematite: $Fe_2O_3$ \| Magnetite: $Fe_3O_4$ \| Siderite: $FeCO_3$
Copper (Cu)	Copper Pyrites: $CuFeS_2$ \| Malachite: $CuCO_3 \cdot Cu(OH)_2$
Zinc (Zn)	Zinc Blende: $ZnS$ \| Calamine: $ZnCO_3$ \| Zincite: $ZnO$

2. Concentration Methods

Froth Floatation

Specifically for Sulphide Ores. Based on differential wetting by oil and water.

• Collectors: Pine oil, Xanthates (enhance non-wettability).
• Froth Stabilizers: Cresols, Aniline.
• Depressants: $NaCN$ (to separate $ZnS$ from $PbS$).

Leaching (Chemical)

Ore is soluble in a suitable reagent while impurities remain insoluble.

• Baeyer's Process: $Al_2O_3 + NaOH \rightarrow Na[Al(OH)_4]$.
• Cyanide Process (Mac-Arthur Forrest): For $Au$ and $Ag$ using $NaCN/KCN$.

3. Ellingham Diagram & Principles

Gibbs Free Energy ($\Delta G$) vs Temperature ($T$) plots for the formation of oxides.

$$ \Delta G^\ominus = \Delta H^\ominus - T\Delta S^\ominus $$

Reaction is feasible if $\Delta G$ is negative.

Reduction Rule

A metal can reduce the oxide of any other metal which lies above it in the Ellingham diagram.

Slope Logic

Slopes are positive because $\Delta S$ is negative (gas to solid). $C \rightarrow CO$ has a negative slope ($\Delta S > 0$).

4. Industrial Extraction Processes

Iron (Blast Furnace)

• Zone of Reduction: $Fe_2O_3 + 3CO \rightarrow 2Fe + 3CO_2$.
• Slag Formation: $CaO + SiO_2 \rightarrow CaSiO_3$ (Flux + Gangue).
• Pig Iron: 4% C; Cast Iron: 3% C; Wrought Iron: Purest.

Aluminium (Hall-Heroult)

Electrolysis of fused $Al_2O_3$.
• Cryolite ($Na_3AlF_6$): Lowers M.P. and increases conductivity.
• Anode: Carbon/Graphite (consumed as $CO/CO_2$).

Self Reduction:

For $Cu$, $Pb$, $Hg$. Example: $2Cu_2O + Cu_2S \rightarrow 6Cu + SO_2$.

5. Refining of Crude Metals

Vapour Phase Refining

• Mond Process: For Nickel. Uses $Ni(CO)_4$ intermediate.

• Van Arkel: For Zr and Ti. Uses Iodide ($ZrI_4$) intermediate to remove oxygen/nitrogen.

Physical Methods

• Distillation: For low B.P. metals ($Zn, Hg, Cd$).

• Liquation: For low M.P. metals ($Sn, Pb$).

• Zone Refining: For Semiconductors ($Si, Ge, Ga$). Based on fractional crystallization.

Electrolytic Refining

Impure metal as Anode, Pure metal as Cathode. Soluble salt as electrolyte.

Anode Mud contains noble metals like $Au$, $Ag$, $Pt$.

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