PRELIMS
Metallurgy and Ores
Metallurgy is the process of extracting pure metals from their ores.
Minerals, Ores, and Impurities
- Minerals: Naturally occurring metallic compounds.
- Ores: Minerals from which metals can be extracted economically and easily. (All ores are minerals, but not all minerals are ores).
- Gangue (Matrix): Earthy impurities (sand, rock) associated with the ore.
- Flux: Substance added to the ore to remove gangue.
- Acidic Flux ( ): Removes basic impurities (like ).
- Basic Flux ( , ): Removes acidic impurities (like ).
- Slag: The fusible material formed by the combination of flux and gangue ( ).
Systematic Extraction Processes
- Concentration: Removal of gangue.
- Methods: Gravity separation, Magnetic concentration, Froth Flotation (for sulphide ores), Chemical methods.
- Calcination: Heating ore (usually absent of air) below its melting point to expel moisture/volatile impurities. (Used for carbonates/hydrated oxides).
- Roasting: Heating ore (in presence of air) below its melting point. (Used for sulphide ores).
- Smelting: Reduction of oxide ore with Carbon at high temperatures.
Extraction Methods by Reactivity Series
The method of reduction/extraction depends on the metal's position in the reactivity series.
- Highly Reactive Metals (K, Na, Ca, Mg, Al): Extracted by electrolytic reduction of their molten (fused) salts/oxides (e.g., Al from molten via the Hall-Héroult process; Na from molten via Down's process).
- Moderately Reactive Metals (Fe, Zn, Pb, Cu, Sn): Extracted by chemical reduction of their oxides, typically with Carbon/Coke (e.g., Fe from in a blast furnace) — this class of ores is usually roasted/calcined first, then smelted.
- Least Reactive/Noble Metals (Cu, Ag, Au, Pt): Often found in native (free) state; extracted by simple physical methods (e.g., froth flotation of native ores) or by roasting sulphide ores followed by self-reduction (e.g., Cu from Copper glance).
Refining of Metals
- Electrolytic Refining: Impure metal made anode, pure metal strip as cathode, in a solution of the metal's salt; pure metal deposits at cathode. Used for Cu, Ag, Au, Al, Ni.
- Zone Refining: Used for ultra-pure metals (e.g., Germanium, Silicon for semiconductors); based on the principle that impurities are more soluble in the molten state than solid state.
- Distillation: For low-boiling metals like Zinc and Mercury.
- Liquation: Low melting-point metals (e.g., Tin) are melted and drained away from higher-melting impurities.
Comprehensive Table of Ores
- Sodium (Na): Major Ores: Chile saltpeter, Borax, Common Salt. Chemical Formula: , ,
- Aluminium (Al): Major Ores: Bauxite, Corundum, Cryolite. Chemical Formula: , ,
- Potassium (K): Major Ores: Nitre (saltpeter), Carnalite. Chemical Formula: ,
- Magnesium (Mg): Major Ores: Magnesite, Dolomite, Epsom salt. Chemical Formula: ,
- Calcium (Ca): Major Ores: Dolomite, Gypsum, Fluorspar. Chemical Formula: ,
- Copper (Cu): Major Ores: Cuprite, Copper glance, Copper pyrites. Chemical Formula: , ,
- Silver (Ag): Major Ores: Horn Silver. Chemical Formula:
- Gold (Au): Major Ores: Calaverite, Silvenites. Chemical Formula:
- Zinc (Zn): Major Ores: Zinc blende, Calamine. Chemical Formula: ,
- Mercury (Hg): Major Ores: Cinnabar. Chemical Formula:
- Tin (Sn): Major Ores: Casseterite. Chemical Formula:
- Lead (Pb): Major Ores: Galena. Chemical Formula:
- Iron (Fe): Major Ores: Haemetite, Magnetite, Siderite. Chemical Formula: , ,
- Manganese (Mn): Major Ores: Pyrolusite. Chemical Formula:
- Uranium (U): Major Ores: Pitch blende, Carnetite. Chemical Formula:
UPSC Relevance
Metallurgical concepts and the identification of ores are consistent high-yield topics for Prelims.
- Ores Identification: Recalling that Cinnabar is the ore of Mercury and Pitch blende is for Uranium is standard.
- Process Differences: Differentiating between Calcination (no air/Carbonates) and Roasting (air/Sulphides) is a common conceptual trap.
- India Context: Locations of Bauxite and Iron ore deposits (Haemetite/Magnetite) connect GS-I Geography to GS-III Science.