Chemistry - Metallurgy

Minerals and Ores: Minerals are naturally occurring compounds of metals found in the earth's crust. Ores are those minerals from which metals can be extracted profitably and easily. For example, Bauxite ($Al_2O_3 \cdot 2H_2O$) is the primary ore of Aluminium.

Common Ores: Aluminium (Bauxite - $Al_2O_3 \cdot 2H_2O$), Iron (Haematite - $Fe_2O_3$), Zinc (Zinc Blende - $ZnS$; Calamine - $ZnCO_3$).

Concentration of Ore (Benificiation): The process of removing gangue (earthy impurities) from the ore. Methods include Magnetic Separation, Froth Floatation (for sulphide ores like $ZnS$), and Leaching (chemical separation like Baeyer's Process for $Al_2O_3$).

Calcination vs. Roasting: Calcination is heating the ore in the absence or limited supply of air to decompose carbonates ($ZnCO_3 \xrightarrow{\Delta} ZnO + CO_2$). Roasting is heating the ore in excess air to convert sulphides to oxides ($2ZnS + 3O_2 \xrightarrow{\Delta} 2ZnO + 2SO_2$).

Reduction: The process of converting metal oxides to free metals. Active metals like $Al$ are extracted by Electrolytic Reduction, while moderately active metals like $Zn$ and $Fe$ are reduced using Carbon/Coke ($ZnO + C \rightarrow Zn + CO$).

Hall-Héroult Process: The electrolytic reduction of fused Alumina. The electrolyte consists of a mixture of Alumina ($Al_2O_3$), Cryolite ($Na_3AlF_6$), and Fluorspar ($CaF_2$).

Alloys: Homogeneous mixtures of two or more metals or a metal and a non-metal. Examples: Brass ($Cu + Zn$), Bronze ($Cu + Sn$), and Stainless Steel ($Fe + Cr + Ni + C$).